Session 11
Metallogeny of the
Tethys-Himalayan Orogen
Close
Close
Chapter 11-1
11-1
Epithermal Au-Ag-Cu, porphyry Cu-(Au-Mo) and
Cu-Au-Ag-Zn-Pb skarn deposits of the Gangdese Arc, Tibet
G. Beaudoin, R. Hébert
Université Laval, Québec, Québec, G1K 7P4, Canada
C.S. Wang, J. Tang
Chengdu University of Technology, Chengdu, Sichuan 610059, P.R. China
Abstract. The Gangdese Arc is a plutonic-volcanic complex that
formed during the late Jurassic-early Cretaceous and the late Cretaceous-Tertiary in response to subduction of Tethyan oceanic lithosphere beneath the Lhasa block. The Gangdese Arc contains a series of porphyry Cu- (Mo-Au), skarn Cu-Au-Ag-Zn-Pb and epithermal
Au-Ag-Cu deposits defining a metallogenic belt in the Tethys-Himalayan Orogen. Epithermal mineralization is associated with Tertiary calc-alkaline magmatism whereas the porphyry and skarn mineralization is associated with younger Miocene adakitic magmatism.
Keywords. Porphyry, skarn, epithermal, copper, gold, silver, mineral
deposit, continental arc, Tibet
1
Introduction
The Tibetan plateau is a product of collision of the Asian
plate with the Indian plate. In southern Tibet, the YarlungTsangpo suture zone formed from subduction of Tethyan
oceanic lithosphere beneath the Lhasa crustal block
(Hébert et al. 2003), a fragment of continental crust
accreted to the Asian plate. Subduction of Tethys resulted
in the construction of the Gangdese volcano-plutonic Arc
at the southern margin of the Lhasa block. This tectonic
setting has similarities with several continental volcanoplutonic arcs, such as those of the American Cordilleras.
The Gangdese Arc contains several porphyry Cu-Mo- (Au),
skarn Cu, and epithermal Au-Ag deposits that define a poorly
known metallogenic province (Beaudoin et al. 1999). This
paper presents the geology of representative examples.
2
Regional geology
The Gangdese Arc (Fig. 1) is a volcano-plutonic belt
formed by northward subduction of the Tethys oceanic
plate beneath the Lhasa continental block (Allègre et al.
1984). Plutonic and volcanic rocks formed in series of
magmatic events from about 120 to about 40 Ma when
obduction thrusted the Yarlung-Tsangpo ophiolite belt and
fore-arc sediments (Fig. 1, Schärer et al. 1984; Allègre et
al. 1984; Coulon et al. 1986). The core of the Gangdese
Arc is comprised of intermediate to felsic plutonic rocks
overlain by Permian to Cretaceous volcanic and sedimentary sequences (Fig. 1). N-S ultra-potassic dikes and calkalkaline porphyric dikes and plugs of adakitic affinity
intruded the Gangdese during late Himalayan extension,
between 26 and 10 Ma, and are associated with porphyrystyle Cu-Mo (Au) mineralization (Chung et al. 2003; Qu
et al. 2004; Williams et al. 2001).
3
Mineral deposits
3.1 Jiama skarn and porphyry deposit
The Jiama deposit is located 80 km east of Lhasa, and it
is accessible from the Lhasa River valley road. The Jiama
deposit is sited within a shallow intra-arc basin assemblage (Fig. 1). Cu-Zn-Pb-Au-Ag mineralization occurs in
a skarn at the contact between limestones of the Jurassic
Duodigou Formation and pelites of the Cretaceous
Linbuzong Formation (Fig. 2). The mineralized skarn has
a thickness of up to 35 m and is followed on surface and
at shallow depth for about 4.2 km by 4 adits (400 m) and
numerous exploration trenches (13 400 m). The central
part of the deposit has been drilled (30 holes for ~5000
m) using an irregular orthogonal grid with a spacing of
60 to 200 m that delineate a near surface resource estimated at 0.5 Mt with an average grade of 1.14% Cu, 3.49%
Pb, 1.66% Zn, 9.9 g/t Ag, 0.32 g/t Au and 0.07% Mo. Representative skarn samples confirm high gold grades (up
to 7.9 ppm Au) associated with high silver values (up to
178 ppm Ag). The metal signature is characterized by high
values of Bi, As, and Sb (Table 1) but low Mo (< 11 ppm),
whereas S/Se are < 1400 and skarn δ34S values are between -1 and -5‰ (Du et al. 1998; Qu et al. 2004). The
metal signature, S/Se and δ34S values suggest a magmatic
source for sulphur.
Du et al. (1998) suggested an exhalative origin for the
skarn but our investigations provide no evidence in support of this interpretation. The skarn is composed of andradite, wollastonite and diopside with compositions typical of those minerals in Cu-skarn (Meinert 1992).
Duodigou limestones are metamorphosed to marble at
the contact with the skarn (Fig. 2) The skarn is cut by
younger, unaltered, quartz-feldspar porphyries (Fig. 2).
The skarn contains lenses and disseminations of chalcopyrite, bornite, low-Fe (2-3 wt.%) 1sphalerite, Ag-Bi
bearing galena (0.16 ± 0.05 wt.% Ag; 0.97 ± 0.22 wt.%
Bi), hessite and argentiferous (0.07 to 0.16 wt% Ag)
tennantite.
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G. Beaudoin · R. Hébert · C.S. Wang · J. Tang
Linbuzong pelites are metamorphosed into a 3 x 2 km
hornfels in which porpyroblasts are retrograded to chlorite (Fig. 2). The hornfels comprises a broad pale-coloured
sericite alteration zone (insert, Fig. 2) which contains zones
of local clay or biotite-pyrite-chalcopyrite alteration. Dense
stockwerks of quartz-adularia veins with disseminated
pyrite, bornite and chalcopyrite are found in drill cores.
These observations suggest that the Jiama deposit contains buried porphyry Cu-(Au-Mo) mineralization associated with an outcropping Cu-Zn-Pb-Au-Ag skarn.
Close
Chapter 11-1 · Epithermal Au-Ag-Cu, porphyry Cu-(Au-Mo) and Cu-Au-Ag-Zn-Pb skarn deposits of the Gangdese Arc, Tibet
3.2 Neymo Area
3.3 Zedang Area
Several porphyry-Cu deposits are located about 35 km
north-west of Nyemo (Fig. 1). At the time of visit (1999),
one of the deposits was being developed by the Tibet Mining Co., however, no resource estimate could be provided.
Table 1 shows that representative samples from the bench
have metal signature characterized by Cu (< 0.47%), Au
(< 19 ppb), Ag (< 4 ppm), no detectable Bi, As (< 66 ppm),
Sb (<13 ppm) and Mo (< 33 ppm). This metal signature
is different from that of the Jiama deposit (Table 1).
The deposit is hosted by the Nyemo coarse-grained granite pluton. The granite is intruded by feldspar porphyry dykes
and cut by magmatic breccias. Granite and porphyry Sr/Y
(26-65) vs Y (8-9 ppm) and La/Yb (42-56) vs Yb (0.7-0.9 ppm)
plot in the adakite field as other 18-14 Ma intrusions in the
Nyemo and Jiama areas (Qu et al. 2004; Chung et al. 2003).
Feldspars in granite are strongly sericitized whereas a biotite alteration retrograded into chlorite characterizes the
porphyries. Mineralization is associated with stockwerk of
quartz veins with chalcopyrite and pyrite weathered to malachite and azurite. Historic mining was focussed on m-thick,
shallow-dipping, quartz-chalcopyrite-pyrite veins. Mineralization is cut by fresh quartz-feldspar porphyry dykes.
A series of small Cu deposits have been explored east of
Zedang (Fig. 1) near the main road on the south shore of
the Yarlung-Tsangpo river. Of these, the Chongmuda deposit was the subject of small scale mining in the past.
The Chongmuda deposit is a reaction skarn developed
at the interface between pelites and marble of the upper
Cretaceous Bima Formation near the contact with a
coarse-grained, feldspar porphyric hornblende granodiorite. In contrast to Jiama, the reaction skarn is characterized by Fe-rich grossular. Barren reaction skarn is cut by
porphyry-style, E-W quartz-chalcopyrite veins (up to 30
cm) surrounded by inner albitic and outer argilic alteration, or develop an intense biotite alteration, where they
cut a medium-grained diorite.
1221
3.4 Xaitongmoin Area
The Dongga Au-Ag-Cu deposit near Xaitongmoin is located about 6 km north of the village of Louma, on the
north shore of the Yarlung-Tsangpo (Fig. 1). The Cretaceous-Tertiary host rocks comprise volcanic agglomerate and andesitic breccias and tuffs interbedded with clas-
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G. Beaudoin · R. Hébert · C.S. Wang · J. Tang
tic sedimentary rocks that are intruded by a diorite porphyry. Andesite and diorite are cut by intermediate
porphyric dykes. Tertiary andesite breccia Sr/Y (9) vs Y
(7 ppm) and La/Yb (3) vs Yb (1.3) are similar to those of
the diorite porphyry (Qu et al. 2004), plotting outside the
adakite field and into the field of calc-alkaline arc lavas
(Chung et al. 2003; Qu et al. 2004). This suggests that the
diorite and volcanic rocks are cogenetic and most likely
older than the adakites associated with porphyry-Cu-Au
and skarn from Nyemo to Zedang (Fig. 1).
Pyrite and chalcopyrite occur in metre-thick WNWESE quartz veins, stockwerk and dissemination cutting
the andesitic breccia and tuff. The metal signature shows
high Au and Ag values, moderate As, Sb and low content
in Mo, Bi (Table 1). The andesitic rocks are pervasively
sericitized and chloritized with zones of strong argilic
alteration. The different chemical signature of the volcanic and intrusive rocks and the different metal signature and alteration of the Au-Ag-Cu polymetallic mineralization suggests that Dongga represent a lowsulphidation epithermal deposit.
4
Conclusions
The Gangdese Arc contains low-sulphidation epithermal
Au-Ag-Cu and Cu-(Au-Mo) porphyry associated with CuAu-Ag-Pb-Zn skarn forming a metallogenic belt more than
200 km long in the Tethys-Himalayan Orogen.
The Dongga low-sulphidation epithermal mineralization formed during calc-alkaline magmatism, probably
late during the build-up of the Gangdese Arc. The porphyry and skarn Cu-Au mineralization formed later during Miocene (18-14 Ma) adakitic magmatism.
References
Allègre CJ (1984) Structure and evolution of the Himalaya-Tibet orogenic belt. Nature 307: 17-22
Beaudoin G, Hébert R, Wang C, Tang J (1999) The Gandise Arc, Tibet, China: A porphyry- and skarn-Cu metallogenic province
Annual Meeting. Geological Society of America
Chung SL, Liu DY, Ji JQ, Chu MF, Lee HY, Wen DJ, Lo CH, Lee TY, Qian
Q, Zhang Q (2003) Adakites from continental collision zones:
Melting of thickened lower crust beneath southern Tibet. Geology 31: 1021 - 1024
Coulon C, Maluski H, Bollinger C, Wang S (1986) Mesozoic and Cenozoic volcanic rocks from central and southern Tibet; 39Ar-40Ar
dating, petrological characteristics and geodynamical significance. Earth and Planetary Science Letters 79: 281-302
Du GS, Yao P, Su DK (1998) Mineralization of exhalation skarn – an
example from the Jiama polymetallic ore deposit. Chengdu
Sichuan Press of Science and Technology, 268 p
Hébert R, Huot F, Wang C, Liu Z (2003) Yarlung Zangbo ophiolites
(Southern Tibet) revisited: geodynamic implications from the
mineral record. In Dilek Y, Robinson PT, eds. Ophiolites in Earth
history. Geol. Soc. London, Sp. Pub. 218: 165-190
Meinert LD (1992) Skarns and skarn deposits. Geoscience Canada
19: 145-162
Qu X, Hou Z, Li Y (2004) Melt components derived from a subducted
slab in late orogenic ore-bearing porphyries in the Gangdese
copper belt, southern Tibetan plateau. Lithos 74: 131-148
Schärer U, Xu R-H, Allègre CJ (1984) U-Pb geochronology of
Gangdese (Transhimalaya) plutonism in the Lhasa-Xigaze region,
Tibet. Earth and Planetary Science Letters 69: 311-320
Close
Chapter 11-2
11-2
Origin of phenocrysts in mineralized porphyries of
porphyry copper deposits
Chen Wenming, Sheng Jifu
Institute of Mineral Resources, Chinese Academy of Geological Sciences, 26 Baiwanzhuang R, Beijing 100037, China
Abstract. The genetic mechanism of phenocrysts in mineralized porphyries of the Yulong porphyry copper deposit, Tibet, China, has been
studied in the context of fluid inclusions in quartz and K-feldspar
phenocrysts, phenocryst textures and mineral crystal textures. Phenocrysts in mineralized porphyries are not the product of direct crystallization of magmas derived from the mantle or lower crust but are
very likely to originate mainly from metasomatism, recrystallization
and secondary enlargement of copper-bearing rocks in the upper
crust by deep-seated, alkali-rich, siliceous hydrothermal fluids.
Keywords. Phenocrysts, copper, porphyry, fluid inclusion, texture,
metasomatism, siliceous hydrothermal fluid
1
Introduction
It is generally considered that phenocrysts in mineralized porphyries of porphyry copper deposits are of magmatic origin, but our study shows that phenocrysts in
many mineralized porphyries are not the product of magmatic crystallization but mainly result from the processes
(including metasomatism, recrystallization and secondary enlargement) by deep-seated, alkali-rich, siliceous
hydrothermal fluids. Below we mainly deal with the genetic mechanism of phenocrysts in the contexts of fluid
inclusions in quartz and K-feldspar phenocrysts, phenocryst textures and mineral crystal textures.
2
Fluid inclusions
Much work has been done on fluid inclusions in the Yulong
mineralized porphyry, Tibet (e.g. Rui et al. 1984; Tang et
al. 1995). However, in previous studies, “homogeneous”
trapping and “heterogeneous” trapping of fluid inclusions
were not distinguished, nor were the features of fluid inclusions in different minerals or fluid inclusions of different phases and different modes of occurrence of the
same mineral species. Therefore, it is very difficult to obtain accurate temperature and pressure conditions during trapping of fluid inclusions, i.e. during rock and ore
formation. Based on the above analysis, combined with
previous work, we have focused our fluid inclusion study
on the best developed quartz phenocrysts for fluid inclusions in mineralized porphyries and selected 14 quartz
phenocrysts in five core samples from the central part
and edges of a high-salinity fluid inclusion-containing
monzogranite porphyry in mineralized porphyries of the
Yulong porphyry copper deposit, Tibet, for measurements.
A total of 205 fluid inclusions were analyzed. Owing to
the limitation of space, here we only present the analytic
data of two phenocrysts (Table 1).
The fluid inclusions in quartz phenocrysts of the Yulong
monzogranite-porphyry have the distinct features of saturated and supersaturated saline-vapor boiling fluid inclusion assemblage. Among the inclusions, supersaturated
saline inclusions account for 29%, saturated saline inclusions 2%, unsaturated inclusions 45% and vapor inclusions 24%. In the inclusions, the percentage of the gas
phase varies widely from 5 to 95% and the main volatiles
H2O and CO2 percentages also vary widely (Tables 1). Thus
we may determine that this type of fluid inclusion is
trapped in a “heterogeneous” phase state.
The homogenization temperatures of saturated saline
inclusions (4) in the saturated and unsaturated saline-vapor boiling fluid inclusion assemblage range from 311 to
407°C and the vapor-liquid homogenization temperatures
of supersaturated saline inclusions (59) from 190 to 397°C.
According to these data we determine that the trapping temperatures of fluid inclusions in quartz phenocrysts of this
porphyry body is mainly in therange of 190 to 407°C and
chiefly cluster at 220 to 340°C (accounting for 85%). The
inclusions tend to occur as negative crystals, showing the
features of primary inclusions. According to the composition of fluid inclusions, the dominant components of the
fluid inclusions in quartz phenocrysts are H2O, CO2, Na+,
K+ and Cl– with subordinate Ca, Mg, SO42- and F.
3
Crystal textures
By X-ray diffraction analysis and infrared spectrum analysis of K-feldspar phenocrysts in the Yulong mineralized
porphyries, it has been confirmed that: the degree of order of K-feldspar is 0.457–0.597 (X-ray diffraction) and
0.64–0.72 (infrared spectrometry), the triclinity is 0.675–
0.775 (X-ray diffraction) and 0.17–0.44 (infrared spectrometry) and the texture index n is 0.278–0.813 (Table 2)
- all the three parameters prove that these K-feldspar phenocrysts are andesine-microcline. Its formation temperatures are < 500°C and generally range from 360 to 430°C.
The temperatures are close to the formation temperatures
of quartz phenocrysts and also markedly lower than the
solidus of intermediate-acid magmas. These data provide
reliable and strong evidence that K-feldspar phenocrysts
are not the product of direct crystallization of magmas.
Close
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Chen Wenming · Sheng Jifu
Close
Chapter 11-2 · Origin of phenocrysts in mineralized porphyries of porphyry copper deposits
4
Phenocryst textures
Microscopic observations of phenocrysts show that these
phenocrysts have distinct crystalloblastic textures, which
mainly include the following kinds.
Mosaic texture: This results from ‘mosaicking’ of
metacrysts of the same species of mineral, and sometimes matrix relics are present at mosaicking boundaries of different metacrysts (Augustithis 1985; Dong
et al. 1987).
Poikiloblastic (sieve) texture: The phenocrysts contain
inclusions and matrix relics of various kinds of minerals (including metallic minerals). In some phenocrysts inclusions are oriented with their direction parallel to the growth line of the minerals. Most inclusions show a sieve texture.
Cumulophyric texture: This texture results from clustering of metacrysts of grains of the same kind or the
different kinds of minerals. There are many matrix
relics between metacrysts. The metacrysts are mostly
anhedral or subhedral.
Secondary overgrowths: The phenocrysts form by secondary overgrowth of grains (fragments) of primary
minerals. The outline of the primary mineral grains is
usually retained inside the phenocrysts.
Blastocrystalloclastic (blastoclastic) texture: Phenocrysts
are formed by mosaicking and grouping of secondary
overgrowths of several adjacent grains (crystals or clasts)
of the same mineral. They have highly variable shapes
and often show embayed and crystallocalstic shape.
5
Discussion and conclusions
The above-mentioned data suggest that the quartz phenocrysts in mineralized porphyries of the Yulong porphyry copper deposit contain abundant fluid inclusions,
while melt inclusions are lacking or rare. The fluid inclusions are mainly represented by assemblages of saturated
and supersaturated saline-vapor boiling fluid inclusions,
with their trapping temperatures, i.e. the formation temperatures of the quartz phenocrysts, mainly ranging from
190 to 407 C. Then where and when did these high-salin-
1225
ity boiling fluids come from? In what way did they coexist with the quartz phenocrysts? From the view of magmatic crystallization, phenocrysts in porphyries formed
in a relatively closed deep environment with relatively
stable temperature and pressure conditions and a relatively slow cooling rate at depths. However, saturated and
supersaturated saline-vapor boiling fluids cannot be produced in such an environment because such boiling fluids are formed in an open or semi-open environment in
which temperatures and pressures fall suddenly. Furthermore, according to a wealth of experimental data, at pressures of 100 to 500 MPa and in the presence of excess
water the solidus of intermediate-acid magmas is 600 to
925°C and the crystallization temperature of quartz (phenocrysts) is higher than or equal to the solidus (Piwinskil
1968; Cao et al. 1980). Therefore, if quartz phenocrysts
and fluid inclusions hosted in them had formed in the
magmatic stage, then their formation temperatures should
have been higher than the solidus temperature. However,
the temperatures obtained by us are noticeably lower than
these values. So it is evident that quartz phenocrysts and
fluid inclusions captured by them during their crystallization did not form in the magmatic stage.
Then is it possible that the hydrothermal fluids removed
by secondary boiling during the late stage of magmatic
crystallization entered the quartz phenocrysts crystallized
during the magmatic stage through fractures after cooling? If so, all these fluid inclusions should be secondary,
but what we have observed are all primary inclusions. In
addition, the formation temperatures of the quartz phenocrysts obtained by us are also just the principal temperatures of crystallization of quartz from hydrothermal
fluids (Kennedy 1950; Zeng 1987). Therefore, the quartz
phenocrysts mainly did not crystallize from magmas but
are the product of hydrothermal processes.
K-feldspar phenocrysts were determined by X-ray diffraction analysis and infrared spectrum analysis to be
andesine-microcline. Its formation temperatures range
from 360 to 430°C, which are also notably lower than the
solidus of intermediate-acid magmatic rocks. Evidently
K-feldspar phenocrysts are also not the product of magmatic activity but the product of hydrothermal processes.
Until now, microcline has neither experimentally nor theo-
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Chen Wenming · Sheng Jifu
retically been proved to form by transformation of
sanidine through cooling at high temperatures (during
the magmatic stage), and on the contrary, it can be synthesized by alkali-metasomatic reactions under hydrothermal conditions (Hong 1980). Moreover, according to
the crystalloblastic textures of various kinds of phenocrysts, and of the fluid inclusion composition features, we
have reason to infer that the phenocrysts of the Yulong
mineralized porphyries are not the product of direct crystallization of magmas derived from the mantle or lower
crust but are more likely to originate from metasomatism (including recrystallization and secondary enlargement) of copper-bearing rocks in the upper crust by deepseated, alkali-rich, siliceous hydrothermal fluids (which
were mixed with fissure water and groundwater in crustal
rock). (Chen 2001, 2002).
References
Augustithis SS (1985) Atlas of the textural patterns of Metamorphoseal
(transformed and deformed ) rocks and their genetic significance.
Theophrastus pulictions S. A. Athens
Baskin Y (1956) Observations on heat-treated authigenic microcline
and albite crystals. Geology 64: 219-224
Cao RL, Zhao B, Zeng Y, Ai R, Wang SY, Liu YS, Wang J, Wang HS
(1980) Experiments on diagenesis and mineralization. Beijing:
Geological Publishing House (in Chinese)
Chen W (2001) Genetic relation between deep-seated alkali-rich
hydrothermal fluids and ore-bearing porphyries of porphyry
copper deposits—evidence from field inclusions and phenocryst
textures. Earth Science Frontiers 8: 409-420 (in Chinese with
English abstract)
Dong S, He G (1987) The classification of metasomatic replacement
fabrics of granitic rocks and its genetic signicance.Bulletin of
the Chinese academy of geological sciences, 16:71-82
Hong D (1980) Order-disorder of K-feldspars and their geological
significance. Collection of Mineralogy and Petrology (1): 193210 (in Chinese with English abstract)
Kennedy GC (1950) A portion of the system silica-water. Econ Geol
45: 629-653
Piwinskil AJ (1968) Experimental studies of igneous rock series in
the Central Serra Nevada Batholith, California. J Geol 76: 548570
Rui Z, Huang C, Qi G, Xu J, Zhang H (1984) Porphyry copper (molybdenum) deposits of China. Beijing: Geological Publishing
House(in Chinese)
Tang R, Luo HS, Li Y (1995) The geology of Yulong porphyry copper
ore belt, Xizang (Tibet). Beijing: Geological Publishing House,
(in Chinese)
Zeng Y (1987) Experimental geochemistry. Beijing: Geological
Publishing House (in Chinese)
Close
Chapter 11-3
11-3
Magma mixing and Cu-Au mineralization in the Gangdese
magmatic belt in response to India-Asia collision
Guochen Dong1,2, Xuanxue Mo1,2, Zhidan Zhao1,2, Tao Chen1
Key Laboratory of Lithospheric Tectonics and Lithoprobing Techniques of China University of Geosciences, Ministry of
Education of China, Beijing, 100083, China
1
2
School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China
Abstract. The Quxu pluton in the northern Yalu tsangpu suture of
southern Gandese, Tibet, consists petrologically of gabbro, diorite,
granodiorite and granite. Mafic macro-granular enclaves (MME) are
widespread in the granitic intrusions. There are many Cu-Au deposits and mineralized occurrences in the pluton. Detailed geological
investigations, systemic research, and petrological and geochemical studies, have been conducted. Results suggest the three types
of rocks are likely to have formed during the same magmatic event;
that is, magma mixing in the Eocene. The host granitoid is an acidic
end member, gabbros are akin to basic end members and mafic
microgranular enclaves represent incompletely mixed basic magma
clots trapped in acidic magma involved in magma mixing. Zircon
SHRIMP ? U-Pb dating gave a mixing age of 50 Ma. The isotopic
dating also suggests that the magma mixing took place soon after
the initiation of India-Eurasia continental collision related to
underplating of collision-induced basic magma under continental
crust. Underplating and magma mixing likely played an important
role in Cu-Mo mineralization, forming skarn type Cu-Au (Fe) deposits and porphyry Cu-Au mineralization in southern Gangdese north
to the collision zone. This paper describes the magma mixing event
and the related mineralization, aims at the understanding of the
petrogenesis of MME-bearing granitoids, the tectonic settings and
related mineralization. Evidence from petrology and elemental
geochemistry show that the Cu-Au mineralization is closely related
to the magma mixing for chalcopyrite and malachite occurrences
around the MME. Therefore, it is argued that the mineralization
formed during Eocene (ca. 50 Ma). Magma mixing was likely the
main process of mass-energy interaction between mantle and crust
and of related Cu-Au mineralization due to crustal partial melting
by mafic magma underplating during the continental collision.
Keywords. Magma mixing, underplating, Cu-Au mineralization,
Gangdese
1
Introduction
It is widely accepted that the collision of India with Eurasia
occurredbetween c. 65-70 Ma and c. 45 Ma (Yin and
Harrison 2000; Flower et al. 2001; Dong 2002; Mo et al.
2003; Zhou et al. 2004, and refs therein). Obviously, it is
important to understand what kind of process took place
beneath the Tibetan plateau and related ore-forming processes responding to India-Eurasia continental collision.
There are abundant granitoid bodies and many CuAu deposits and mineralization in southern Gangdese.
The granitoid belt extends west to east parallel to the
Yarlung Tsangpo suture for 2000 km by 100 km and covers an area of 110,000 km2 which comrpises mainly di-
orite, quartz diorite, granodiorite, granite, syenogranite
and two-mica granite (Jin and Zhou 1978; Jin and Xu 1982).
These are accompanied by a mafic-ultramafic belt, consisting of intermittently distributed small bodies of gabbro with subordinate pyroxenite, olivine pyroxenite and
pegmatitic pyroxenite, along the southern margin of the
Gangdese belt. It directly contacts with granitoids and
corresponds to an airborne magnetic anomaly belt. The
skarn type Cu-Au deposits occur along the contact between Jurassic-Cretaceous volcanic rocks and the granitoid intrusions, and the Cu-Au mineralization are all
hosted by the granitoid in Quxu batholith.
2
Magmatism and mixing event
Abundant mafic microgranular enclaves (MMEs) are
widespread in granitoids of the Gangdese giant magmatic
belt, within which the Quxu batholith is the most typical
MME-bearing pluton and they tend to become less and
smaller away from the mafic-ultramafic belt. Systematic
research on the granodioritic host rock, mafic microgranular enclaves and gabbro nearby in Quxu batholith
indicate that they formed during a magma-mixing event
at about 50 Ma as determined by Zircon SHRIMP II
U-Pb dating. The MMEs have igneous texture, rapidly
quenched minerals and flow structure, quenched-rims
and light color halos showing mass exchange at the contacts between MMEs and the host rocks. Compositionally, MMEs, granitoid host rocks and gabbros show a linear correlation in Harker variation diagrams and a mixing array in diagrams of correlation between Nd and Sr
isotopes. All those characteristics are likely the result of
processes of underplating and magma mixing between
mantle-derived basic magma and crust-derived felsic
magma (Didier 1973; Didier and Barbarin1991; Wang et
al. 1992; Zhou 1994; Mo et al. 2002). It thus rules out the
possibilities of mafic microgranular enclaves being refractory residues after partial melting of source region,
or xenoliths of country rocks or later intrusions. Both
underplating and magma mixing are important mechanism of mass-energy exchange between the mantle and
the crust and in turn important for accretion of the continental crust and evolution of the lithosphere (Jin and
Gao 1996).
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Guochen Dong · Xuanxue Mo · Zhidan Zhao · Tao Chen
3
Granitoid and Cu-Au mineralization
There are many Cu-Au (Fe) deposits in the southern
Gangdese, such as the Chumuda Cu-Au, Luebu Cu and
Shenbujialai Cu deposits. Most of them formed in volcanic rocks along the boundary with the granitoid with
metal minerals of pyrite, chalcopyrite, molybdenite and
bornite. We have discovered 17 mineralized occurrences
in total by field investigation in the last two years. All of
them occur in the Quxu pluton, one of several typical granites located in the centre of the southern Gangdese, extending west-east parallel to the Yarlung Tsangpo suture
with 50 km long by 30 km wide and 1,500 km2 in area.
The main metal minerals are chalcopyrite and pyrite. It
is common that malachite halos with green color occur
around the MMEs in the pluton, varying in both size and
shape on outcrop.
Recent studies have confirmed that porphyry Cu-MoAu deposits formed in association with magmatism in
Gangdese belt (Xing et al. 1998; Hou et al 2001; Qu et al.
2001, 2002). It is obvious that the mineralization is closely
related to the granitoids. The granites in Chushu pluton
as calk-alkaline with plagioclase (An > 30) and alkaline
feldspar (Or ~55) are potential copper-bearing intrusions
(Xing et al. 1998). Content of SiO2 shows a negative linear
relation with those of Al2O3, CaO, MgO and FeO in the
pluton, reflecting magma mixing, which is potential for
copper deposit formation (Wang et al. 2001). Regarding
the age of the mineralization, no isotopic data has been
obtained from the metal or alteration minerals and many
dating results were about the host granite. Besides the 50
Ma SHIRMP U-Pb age of Quxu pluton mentioned above,
Wan Jiang et al. (1997) obtained an Ar-Ar age of about
43.6 Ma for host granodiorite. Gui Xuntang et al. (1982)
reported an 47 ± 16 Ma Rb-Sr isochron age and the Xizang
Geological Survey (1993) obtained a zircon U-Pb age of
47.7 Ma and 50 Ma for hornblende diorite and quartz diorite, respectively. Petrological microscope studies indicate that
the primary ore minerals such as chalcopyrite and pyrite
are highly concentrated in the MME; secondary ore minerals like malachite occur along the fracture near the contact
between the MMEs and granite host rocks. Evidence from
petrology and elemental geochemistry shows that the CuAu mineralization is closely related to magma mixing for
the chalcopyrite and malachite occurrence around the MME
and linear pattern of major elements. Therefore, it is argued that the mineralization likely formed during the process of magma mixing in the Eocene (ca.50 Ma).
The chemical composition shows linear correlation
between granitoids and the MMEs (Jiang et al. 1999) and
2-3 times higher Cu content in gabbro and MMEs. Research indicates that the Cu-Au mineralization is different from porphyry type Cu-Mo deposits hosted by high
K content (K2O=2.97-8.56%) and close related to the calk-
alkaline granitoid in the Gangdese granitoid belt. It is
possible that Cu-Au elements are mainly occurring as
water-soluble phases, immigrating and precipitating locally when physical conditions changed (Wang et al. 2001).
4
Discussion
The Gangdese giant granitoid belt formed during subduction and collision and contains abundant geodynamic
information to understand the deep processes beneath
the Tibetan plateau (Mo et al. 2005).
Therefore, it is concluded that the granitoid host rocks,
MME and gabbro in the gangdese belt are likely the result of magma mixing related to underplating of basic
rocks in the Eocene (50 Ma). Compositionally, the granitoid host rocks represent acidic end members involved
in magma mixing, gabbros are akin to basic end members and the mafic microgranular enclaves are the result
of incompletely mixed basic magma clots trapped in acidic
magma. Magma mixing likely promoted the related CuAu mineralization due to crustal partial melting by mefic
magma underplating during the continental collision. The
mixing event was the main process of mass-energy exchange between the mantle and the crust and played a
key role in Cu-Au mineralization.
Acknowledgements
We sincerely thank Mr. Wei Baojun, Mr. Li Guo- liang, Mr.
Li Guobiao and Mr. Ba Dengzhu for assistance with field
work and provision of sample material. We are also grateful to Professors Liu Dunyi and Jian Ping for carrying out
SHIRMP II U-Pb dating and interpretation and Professors
Ma Yuguang and Mao Qian for helping cathodoluminescence study of zircon. This work is financed by the grants
of National Key Project for Basic Research of China
(No.2002CB412600), of National Natural Science Foundation of China (Nos. 40172025, 40103003, 49802005, 49772107
and 40473020).
References
Anderson AT (1976) Magma mixing: petrlogical process and volcanological tool. J. Volcanol. Geotherm. Res 1: 3-33
Didier J (1973) Granites and Their Enclaves: The Bearing of Enclaves
on the Origin of Granites. Development in Petrology. Amsterdam:
Elsevier, 393
Didier J, Barbarin B (1991) Enclaves and Granite Petrology. Amsterdam: Elsevier
Dong GC (2002) Linzizong volcanic Rocks in Linzhou Basin, Tibet
and implications for India-Asia Continental Collision. Ph. D. dissertation, China University of Geosciences, Beijing
Flower M, Russo RM, Tamaki K, Nguyen H (2001) Mantle contamination and the Izu-Bonin-Mariana (IBM) ‘high-tide mark’: evidence for mantle extrusion caused by Tethyan closure, Tectonophysics 333: 9-34
Close
Chapter 11-3 · Magma mixing and Cu-Au mineralization in the Gangdese magmatic belt in response to India-Asia collision
Gui XT, Cheng ZL, Wang JW(1982) Studies on Rb-Sr isotope of intermediate – acidic rocks in The Gangdese magmatic belt, Tibet.
Geochemistry 3: 217-225
Jiang W, Zhang SQ, Mo XX Petrological studies on the Gangdese granites and mafic microgranular enclaves in Tibetan Plateau. Tethyan
Geology 22: 90-96
Jiang W, Mo XX, Zhao ChH, Guo TY, Zhang SQ (1999) Geochemical
characteristics of granitoids and mafic microgranular enclaves
in middle Gangdese of Tibetan Plateau. Acta Petrologica Sinica
15 (1): 89-97
Jin ZM, Gao S (1996) Underplating and its significance for
geodynamics in the evolution of the crust-mantle. Information
of Science and Technology in Geology 15 (2): 1-7
Mo XX, Zhao ZD, Deng JF, Dong GC, Zhou S, Guo TY, Zhang SQ,
Wang LL (2003) Response of volcanism to the India-Asia collision. Earth Science Frontiers 10:135-148
Mo XX, Luo ZH, Xiao QH, Yu XH, Liu CD, Zhao ZD, Zhou S (2002)
Research approaches to magma mixing in granites. In Xiao
Qinghui, The ways of Investigation on Granitoids. Beijing: Geological Publishing House, 53-70
Mo XX, Dong GC, Zhao ZD, (2005) Timing of magma mixing in
Gangdese magmatic belt responded to the India-Asia collision:
zircon SHIRMP U-Pb dating. Acta geologica Sinica (in press)
1229
Qu XM, Hou ZQ, Huang W (2001) Is Gangdese porphyry copper belt
the second “Yulong” copper belt?. Mineral Deposits 20 (4): 354-366
Qu XM, Hou ZQ, Li YG (2002) Implications of S and Pb isotopic compositions of the Gangdese porphyry copper belt for the ore forming material source and material recycling within the orogenic
belt. Geological Bulletin of China 21(11): 768-776
Wang DZ, Zhou XM, Xu XS (1992) Genesis of microenclaves in
granitoids. Jour. of Guilin Institute of Nonferrous Geology 12 (8):
235-241
Wang JZ, Li CY, Hu RZ (2001) Reasearch progress in porphyry copper deposit. Advance in Earth Sciences 16(4): 514-519
Xing WC, Yu GF, Ji SX (1998) Discrimination of ore bearing granite
body in Tibet. Volcanology and Mineral Resources 19(3): 197204
Yin A, Harrison TM (2000) Geologic evolution of the HimalayanTibetan orogen. Annual Review of Earth and Planetary Sciences
28: 211-280
Zhou S, Mo XX, Dong GC, Zhao ZD, Qiu RZ, Guo TY, Wang LL (2004)
40
Ar-39Ar geochronology of Cenozoic Linzizong volcanic rocks
from Linzhou Basin, Tibet, China, and their geological implications. Chinese Science Bulletin 49 (18): 1970-1979
Zhou XR (1994) Hybridization in granites. Earth Science Frontiers
1(1-2): 87-97
Close
Close
Chapter 11-4
11-4
Metallogenesis in the Tibetan collisional orogenic Belt
Zengqian Hou, Qingtian Lu,, Xiaoming Qu, Fengjun Nie, Xiangjin Meng, Zhenqing Li, Zhusen Yang
Institute of Mineral Resource, CAGS, Beijing 100037
Xuanxue Mo
ChinaUniversity of Geosciences, Beijing, 100081, China
Anjian Wang
Chinese Academy of Geological Sciences, Beijing 100037, China
Xiaobo Li
Information Center of Land and Mineral Resource, Beijin, China
Wang Zongqi
Institute of Geology, CAGS, Beijing 100037, China
Wang Erche
Institute of Geology and Geophyscis, Beijing, China
Abstract. The Tibetan collision orogen, characterized by the occurrence of large-scale, intense, recent mineralization, various kinds of
large-scale deposits and weak reworking on these deposits, is regarded to be a significant metallogenic domain for the understanding of ore-forming processes in collisional orogens. Although this
metallogenic domain was initiated in the Palaeozoic-Mesozoic periods, extensive metallogenesis occurred in the Himalayan epoch, during which the Indian -Asian continent collision (since 65Ma) resulted
in the Himalayan-Tibetan orogen. This continent-continent collision
had produced three significant tectonic units in the domain. They
are: (1) a main collisional deformation zone, (2) a south Tibet detachment (STD) zone, and (3) a tectonic transformation zone in east Tibet,
in which important gold, copper, base metals, and tin ore belts, incorporating a large number of giant deposits, were developed. In the
main collisional zone, the Gangdese porphyry Cu and associated skarn
Ag-Pb-Zn belt, and recent hot-spring Cs-Au mineralization were developed since the Paleocene. An epithermal Sb-Au belt, controlled
by the detachment system and NS normal fault, appears in the STD
zone. In tectonic transformation zone, a series of large-scale strikeslip faulting system, thrusting system, and shearing system controlled
on development of the Yulong porphyry Cu belt, Lanping Ag-Pb-ZnCu districts and Ailaoshan Au belt, respectively. Three giant mineralized system were divided in the Tibetan orogen, i.e., systems related
to (1) continental collision since the Paleocene, (2) strike-slip and shearing associated with Indo-Asian collision, and (3) post-collisional extension at mid-Miocene. On the basis of above analysis, we proposed
a preliminary working model for the tectonic constrains on the formation of ore deposits in the Tibetan orogen.
Keywords. Continental collision, metallogeny in orogen, deposit type,
Tibetan plateau
1
Introduction
The metallogeny in collisional orogens is of great interest to economic geologists. The Himalayan-Tibetan orogen
consists of several continental fragments (terranes), which
were accreted to the southern margin of Asia during the
Paleozoic and Mesozoic eras, and formed via Indian-Asian
continent collision since 65Ma (Yin and Harrison, 2000).
This collisional orogen forms a significant part of the
Tethyan metallogenic belt and is characterized by its
unique collisional setting, a variety of mineralization
styles, and complicated deposit types with significant
potential. This paper describes the geological features and
temporal-spatial distribution of significant ore deposits
in the Tibetan orogen, then discusses geodynamic settings, mineralization environments, and key geological
processes constraining the formation of these deposits,
and finally proposed possible working models for the
metallogeny in the Tibetan orogen, on the basis of the
previous data and our preliminary study results.
2
Major tectonic units
The Indo-Asian continent collision since 60 Ma has resulted in three significant tectonic units controlling the
development of ore deposits in the Tibetan orogen.
Main collisional deformation zone: This zone is
bounded by the Yarlung Zangbu suture (IYS) and Bangong
suture (BNS), and tectonically developed in the Lahsa terrane with crustal thickness of 74–80km. Within the zone,
the Gangdese belt is the most important unit, underwent
long-term evolution from collisional granitic-plutonismvolcanism (65–34Ma; Schärer, et al., 1984) and grantic
batholith uplift (21–19Ma; Copeland et al. 1995) to the
Miocene post-collisional extension, with associated NS
normal faulting and potassic magmatism (18–12 Ma;
Terner et al. 1993; Blisniuk et al. 2001; Williams et al. 2001).
South Tibet detachment zone (STD): This zone developed in the Tethyan Himalayan region, south to IYS, and is
characterized by a series of EW-striking detachment faults,
i.e., north-dipped gently normal faults (17–21Ma) and associated south-dipped thrust faults (Burg and Chen 1984).
This zone was cut by NS-trending normal fault system (18–
13 Ma). Along the zone, more than four felsic intrusions
appear to have formed a series of thermal domes.
Close
1232
Z. Hou · Q. Lu · X. Qu · F. Nie · X. Meng · Z. Li · Z. Yang · X. Mo · A. Wang · X. Li · W. Zongqi · W. Erche
East Tibetan tectonic transformation zone: This zone,
located on the eastern margin of the Tibetan Plateau, is a
tectonic belt to accommodate and regulate the stressstrains produced by the Indo-Asian collision. It underwent a complex tectonic evolution from the Paleo-Tethys
orogeny in the Paleozoic-Meozoic to Himalayan largescale intracontinental deformation during the Cenozoic.
Cenozoic deformation was chiefly manifested by Eocene–
Oligocene (40–24Ma) transpressional deformation (4024Ma), early-middle Miocene (24–17Ma) transtensional
deformation (24–17Ma) and E-W extension (16–0Ma)
(Wang et al. 2001). This zone is characterized by a number of strike-slip fault systems, thrusting structure groups,
and large-scale shearing belt.
3
Major metallogenic belts
In the main collisional deformation zone, the Gangdese
porphyry copper belt is the most significant metallogenic
belt. This 350-km long, 80-km wide belt extends in EWdirection along the Gangdese batholiths, but mineralized
stocks were locally controlled by NS-striking normal faults,
i.e., orogen-transverse faults. Dating define a duration of
11.2–17.6Ma, peaking at ~16Ma, for these porphyry stocks
(Hou et al. 2004a), and a limited range of molybdenite
Re-Os ages from 13.8 to 16.0 Ma for mineralization (Hou
et al. 2004b), which is consistent with that (10–18Ma) of
the east-west extension (~18Ma) and subsequent NS-striking normal fault systems (=13.5Ma) in the Tibetan orogen.
These Cu-bearing felsic intrusives are shoshonitic and
high-K calc-alkaline, showing geochemical affinity with
adakite, which are regarded to be formed by partial melting of thickened, newly-formed basaltic lower-crust (Hou
et al. 2004c). Principal characteristics of deposits in the
collisional zone is similar to those in arc settings in many
aspects, but large accounts of magnetite in K-silicate zone,
advanced argillic alteration, and overprinting of
epithermal Au-Cu mineralization have not been observed.
Three significant metallogenic belts have been recognized in the eastern Tibet tectonic transformation zone.
Lanping zinc-lead-silver-copper belt: This belt is tectonically located in the Lanping basin, a large composite
basin developed on the Changdu-Simao continental block.
One giant Pb-Zn deposit (Jinding), two large Ag deposits
and three medium-sized Cu-Ag metallic deposits, as well
as several smaller deposits occur in this basin. Major genetic type is hydrothermal vein-type; the generation of
most deposits is related to the Himalayan events, such as
thrusting structures, large-scale fluid flows, mixing of twoendmember fluids and input of metal from felsic magmas (cf. Hou et al. 2005). Available dating data yielded an
age range of 65–45Ma for mineralization, suggesting an
earliest mineralization event associated with the IndoAsian collision.
Yulong porphyry copper belt: This belt is over 200km
long and 15−30km wide, and composed of more than 20
monzonitic granite-porphyry bodies, which was mainly distributed around the Cenozoic uplift between the Gonjo and
the Nanqen strike-slip pull-apart basins. The felsic magmatism was strictly controlled by a large-scale strike-slip fault
system, and has three peaks at 52, 41 and 33Ma, respectively (Hou et al. 2003). The ore-bearing porphyries are characterized by high-K content, rich in LILE and depleted in
HFSE, but showing affinity with adakite. Molybdenite ReOs dating yielded an ore-forming age range of 40-36 Ma for
these porphyry deposits. Although they developed in an intra-continental environment, their mineralization style and
alteration zoning are similar to those in island-arc setting.
The Ailaoshan gold belt: It is 120km long and 500–5000m
wide, and composed of four large, eight medium and numerous small gold deposits, with cumulative reserves >
150tons. This Au belt is largely distributed along the Jinshajiang (Ailaoshan) suture and is controlled by a complicated
thrusting-shearing zone formed by the Indian-Asian continent collision. Tectonically, both the NW-trending AF and
JMF constrain the distribution of the Ailaoshan gold belt,
whereas the intersections of NW-striking brittle shear zones
and nearly E-W-striking thrust faults control the spatial-temporal localization of the gold fields and gold deposits (Hu
et al. 1995). Individual deposits or orebodies normally occur
in lithologically different brittle-ductile shear zones. Dating
of the ore-bearing host rocks and altered wall rocks indicate that most of the gold deposits in the belt were formed
mainly in the Himalayan epoch with peaking at 30Ma.
In the STD zone, an epithermal Sb-Au metallogenic
belt was developed. This belt extends for 250km in eastwest direction, and is controlled by STD and associated
felsic domes. Generally, Au mineralization mainly developed around the felsic domes, vein-type Au orebodies
associated with felsic stock or dikes is the main type. Sb
mineralization is related to ancient hot-spring activity,
and occurs in hydrothermal breccia pipe and overlying
silica sinters. The intersection of EW-striking detachment
fault and NS-trending normal faults usually constrains
on spatial localization of these Sb-Au deposits.
4
Giant mineralized systems
Three giant mineralized systems can be recognised within
the Tibetan orogen, i.e., systems related to (1) continental collision since the Paleocene, (2) thrusting, strike-slip
and shearing associated with Indian-Asian collision, and
(3) post-collisional extension at mid-Miocene. The deposits in the system related to the syn-collision was partly
eroded due to uplift of the Tibetan plateau since MidMiocene, though a few of deposits, such as recently-discovered orogen-type Au and skarn-type Cu-Pb-Zn deposits in the main collisional deformation zone (Gangdese
Close
Chapter 11-4 · Metallogenesis in the Tibetan collisional orogenic Belt
belt), greisen-type tin and rare-metallic deposits related
to collision granites in the east Tibetan tectonic transformation zone (western Yunnan), were preserved. A REE
belt, associated with the Himalayan carbonatite-alkic complex in the western Sichun, probably occurs in the second
system (Yuan et al. 1995), except for Yulong Cu and Ailaoshan
Au belts. It was controlled by NS-trending faults that have
been reactivated during the last collisional period. Mineralization in systems related to post-collisional extension has
occurred since the Mid-Miocene. Some new types, such as
large-sized sinter-type Cs deposits, lake-type B, Li, Rb deposits in this system, have also been discovered.
Acknowledgements
This study is supported by a National Basic Program 973
project (2002CB4126) from Ministry of Science and Technology of China.
References
Blinsiuk, PM, Hacker B, Glodny J, Ratschbacher L, Bill S, Wu ZH,
McWilliams MO, Calvert A (2001) Normal faulting in central Tibet since at least 13.5 Myr ago. Nature 412: 628-632
Burg JP, Chen GM (1984) Tectonic and structural formation of southern Tibet. Nature 311: 219-223
Copeland P, Harrison YM, Yun P (1995) Thermal evolution of the
Gangdes batholith, Southern Tibet: A history of episodic unroofing. Tectonics 14: 223-236
Hou ZQ, Pan GT, Mo XX, Xu Q, Hu YZ, Li XZ. The Sanjiang Tethyan
metallogenesis in S.W. China: tectonic setting, metallogenic epoch and deposit type. Ore Geology Reviews (in press)
1233
Hou ZQ, Meng XJ, Qu XM, Gao YF (2004a) The Gangdese porphyry
copper belt in Tibet: petrogensis of adakitic host rocks and tectonic constraints. Acta Petrologica Sinica 21: 239-248 (in Chinese
with English abstract)
Hou ZQ, Wang SX, Qu, XM, Gao YF (2004b) Re-Os Age for Molybdenites from the Gangdese porphyry copper belt on Tibetan plateau: Implication for geodynamic setting and duration of the Cu
mineralization. Science in China 47: 221-231
Hou ZQ, Gao YF, Qu XM, Rui ZY, Mo XX (2004c) Origin of adakitic
intrusives generated during mid-Miocene east-west extension in
South Tibet. Earth Planet. Sci. Lett. 220: 139-155
Hou ZQ, Ma HW, Zaw K, Zhang, YQ, Wang MJ, Wang Z, Pan GT, Tang
RL (2003) The Himalayan Yulong porphyry copper belt: Product
of large- scale strike- slip faulting in Eastern Tibet. Economic
Geology 98: 125-145
Hu YZ, Tang SC, Wang HP, Yang YQ, Deng J (1995) Geology of the
Ailaoshan gold deposits. Beijing: Geological Publishing House,
278 (in Chinese)
Schärer E, Xu RH, Allegere CJ (1984) U-Pb geochronology of the
Gangdese (Transhimalaya) plutonism in the Lhasa-Xizang region,
Tibet. Earth Planet. Sci. Lett.v. 69: 311-320
Turner S, Hawkesworth G, Liu J, Rogers N, Kelley S, Calsteren PV
(1993) Timing of Tibetan uplift constrained by analysis of volcanic rocks. Nature 364: 50-54
Wang JH, Yin A, Harrison TM (2001) A tectonic model for Cenozoic
igneous activities in the eastern Indo-Asian collison zone. Earth
Planet. Sci. Lett. 88: 123–133
Williams H, Turner S, Kelley S, Harris N (2001) Age and composition of dikes in Southern Tibet: new constraints on the timing of
east-west extension and its relationship to post-collisional volcanism. Geology 29: 339-342
Yin A, Harrison TM (2000) Geologic evolution of the HimalayanTibetan orogen. Annu. Rev. Earth Planet. Sci, 28: 211-280
Yuan ZX, Shi ZM, Bai G, Wu CY, Chi R, Li XY (1995) The Maoniuping
rare earth ore deposit, Mianning County, Sichuan Province. Seismological Press 1-121 (in Chinese with English abstract)
Close
Close
Chapter 11-5
11-5
Geochronological and geochemical study on the Yulong
porphyry copper ore belt in eastern Tibet, China
Huaying Liang, Yuqiang Zhang, Yingwen Xie, Wu Lin
Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510640, China
Ian H. Campbell
Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
Hengxiang Yu
Guilin Institute of Technology, Guilin 541004, China
Abstract. The Yulong copper belt, along part of the Red River-Ailao
Shan fault system and its northwestern extension in eastern Tibet,
consists of five porphyry pipes that contain a total copper resource
of over 8 million tons. The porphyries are characterized by high alkali
content (K2O+Na2O>6%), K2O/Na2O>1, and marked negative Ti, Ta
and Nb anomalies on mantle-normalized incompatible element diagrams. U-Th-Pb laser ICP-MS dating of zircons from the Yulong porphyries showed that they were emplaced over a 4.3 Ma period and
that they young systematically from northwest to southeast as follows: Yulong, 41.2±0.2Ma; Zalaga, 38.5±0.2Ma; Mangzong, 37.6±0.2
Ma; Duoxiasongduo, 37.5±0.2Ma; and Malasongduo, 36.9±0.4 Ma. We
suggest that the source of the shoshonites was lower crust that was
pushed into the mantle by the compressive component of
transpressional movement on the adjacent Tuoba-Mangkang fault
and that the compositional variation in the porphyries is due to mixing between magmas of different composition, generated by different degrees of partial melting of a heterogeneous source region.
Keywords. Igneous petrology, porphyry copper deposits, geochronology
1
2
Methods and results
Representative weakly altered or unaltered samples were
collected from drill cores for analysis of major and trace
elements. Major chemical composition was analyzed by
wet chemical methods at the Guangzhou Institute of
Geochemistry, Chinese Academy of Sciences, and some
samples were analyzed using XRF method at the Australian National University (ANU). Zircon ages, rare earth
and trace elements concentrations were measured by ELAICP-MS at the ANU.
The ore-bearing porphyries are entirely felsic (SiO2:
63.11%–77.60%), characterized by relatively low
TiO 2(<0.5%), P 2O 5(<0.6%) and high alkali content
(K2O+Na2O>6%, most >8%) with K2O/Na2O>1. The five
ore-bearing porphyries are similar in major composition.
On a diagram of K2O vs. SiO2 (not shown), most of the
samples are plotted within the shoshonitic field as defined by Morrison (1980).
Introduction and geological setting
The Yulong porphyry copper ore belt is located in the
Qiangtang terrane of the Himalayan-Tibetan orogen
(Fig. 1) (Sengor et al. 1996; Yin et al. 2000). The Yulong
porphyry copper ore belt is bounded by a series of strikeslip fault zones: to the west by Tuobao-Mankang fault and
to the east by the Gonjo Tertiary basin and the Ziga fault
(Fig. 1) (Rui et al. 1984; Ma 1990; Tang et al., 1995). All the
important copper deposits varying from medium- to giant-sized are located in a much smaller domain of about
50 km in length and 10 km in width. The focus of our
work is this copper-rich domain. The Yulong ore-bearing
porphyries intruded Trassic sandstone and limestone. The
Yulong ore-bearing porphyries, from north to south are
the Yulong, the Zalaga, the Mangzong, the Duoxiasongduo,
and the Malasongduo (Fig. 1). They occur as rock pipes
and small stocks and individually have a surface area ranging from 0.1 to 0.7 km2. The five ore-bearing porphyries
host one giant-, two large- and two medium-sized copper deposits (Tang et al. 1995).
Close
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Huaying Liang · Yuqiang Zhang · Yingwen Xie · Wu Lin · Ian H. Campbell · Hengxiang Yu
The five ore-bearing porphyries are similar in trace
element composition. The REE chondrite- normalized
patterns are characterized by weak negative Eu anomalies and are LREE-enriched (Fig. 2). The mantle-normalized trace element patterns are characterized by highly
enriched large-ion lithophile elements (LILE), with pronounced Nb, Ta and Ti, positive Sr anomalies. All of which
are typical of convergent plate margin magmas (Fig. 2).
The zircon age data of the Yulong, the Zalag, the
Mangzone, the Duoxiasongduo, and the Malasongduo are
41.2 ± 0.2 Ma with MSWD = 1.06, 38.5 ± 0.2 Ma with
MSWD = 1.04, 37.6 ± 0.2 Ma with MSWD = 1.40, 37.5 ±
0.2 Ma with MSWD = 1.49, 36.9±0.4 Ma with MSWD =
1.25, respectively.
3
Discussion
3.1 Lifespan of magmatic activities and multihydrothermal events associated with the Yulong giant
copper deposit
The emplacement age of the Yulong ore-bearing porphyries vary from 41.2 to 36.9 Ma and the lifespan of the
magmatic activities associated with the Yulong giant porphyry copper deposit is 4.3 Ma, which is similar to that
(5.5 Ma) of the Los Picos-Fortuna/Pajonal-El Abra complex associated with super-giant porphyry copper ore in
Chile (Ballard et al. 2002).
The lifetime of a hydrothermal system driven by a shallow-level intrusion will be ~0.1 Ma (Ballard et al. 2001,
Cathles et al. 1997). The Yulong ore belt underwent four
pulses of magmatic activity and related superposition of
magmatic-hydrothermal event. The long lifespan of magmatic activities and the superposition of multi-hydrothermal events may have favored the formation of the supergiant Yulong porphyry copper deposit.
3.2 Tectonic model for the Yulong copper ore belt
The trace element and REE patterns of the Yulong orebearing porphyries, which are highly enriched in largeion lithophphile elements (LILE) and in light rare earth
elements (LREE), with pronounced negative Nb, Ta and
Ti anomalies, weak negative Eu anomalies and weak positive Sr anomalies, are typical of convergent plate margin
magmas. The zircon age of the Yulong ore-bearing porphyries become more and more young from north (the
Yulong) to south (the Duoxiasongduo) (Fig. 1), varying
from 41.2 to 36.9 Ma.
Average values of Ba/Th and Cs/Th ratios increase progressively with the increasing age, whereas those of Th/
U, U/Zr, K2O/Na2O and K2O/(K2O+Na2O) ratios decrease
with the decreasing age. The element ratio variations of
the Yulong ore-bearing porphyries with their emplace-
ment ages are similar to those of the Kurile volcanic crossarc (Morris et al. 2004), suggesting that the Yulong orebearing porphyries bear a genetic relation to subduction
from north to south.
Eastern Tibet underwent contraction and transpression
caused by the collision of India with Asia during the
Eocene-Oligocene. The movement within this region was
sinistral during the Tertiary and was coeval with
transpressive thrusting and folding in the red basin of
the Yunnan, which has started prior to 42 Ma (Ratchbacher
et al. 1996, Pan et al. 1990, Wang et al. 1997). The total
movement on the Red River-Ailao fault is 700 ± 200 km,
which is greater than the displacement along major plate
boundary faults, such as the San Andreas and Alpine faults
(Tapponnier et al. 2001).
Based on the above discussion, we proposed that the
Yulong ore-bearing porphyries derived from the local
continental subduction from north to south. This subduction is associated with large scale sinistral Red RiverAilao Shan Fault and its northward stretching fault system. The local continental subduction was caused by the
contraction and transcompression along the Red RiverAilao Shan Fault and its northward stretching fault system. This proposal is similar to the model proposed by
Wang et al. (2001) for the Cenozoic high potassic igneous
activities along the Red River-Ailao Shear fault. The
Nangqian thrust and the Paleocene to early Miocene basins in eastern Tibet may represent the foreland basins
formed by transpression (Wang et al. 2001).
4
Conclusion
The ore-bearing porphyries show shoshonitic affinity. The
trace element patterns of the Yulong ore-bearing porphyries are characterized by pronounced negative Nb, Ta, and
Ti anomalies, weak Eu anomalies and are LREE-enriched.
The Yulong- the Zalaga-, the Mangzong-, the
Duoxiasongduo-, and the Malasongduo- ore-bearing porphyries emplaced at 41.2 ± 0.2 Ma, 38.5 ± 0.2, 37.6 ± 0.2
Close
Chapter 11-5 · Geochronological and geochemical study on the Yulong porphyry copper ore belt in eastern Tibet, China
1237
References
Ma, 37.5 ± 0.2 Ma, 36.9 ± 0.4 Ma, respectively. The lifespan
of the magmatic activities associated with the Yuong giant porphyry copper deposit is 4.3 Ma. The Yulong orebelt underwent four pulses of magmatic activities and
related magmatic-hydrothermal events.
The Yulong ore-bearing porphyries derived from the
local continental subduction from north to south. This
local continental subduction bears a genetic relation to
large scale sinistral strike-slip fault system in eastern Tibet. The local continental subduction associated with
large-scale sinistral strike-slip fault system in eastern Tibet was caused by the contraction and transpression along
the Red River-Ailao Shan fault zone and its northward
stretching fault system due to the Indian-Asian continental
collision.
Acknowledgements
This work was co-supported by Chinese NSF (40472049,
48972035), Chinese National Key Project for Basic Research
(G1999043200) and CAS Key Project (kzcx2-sw-117 and
GIGCX-03-04).
Ballard JR, Palin JM, Williams IS, Campbell IH (2001) Two age of
porphyry intrusion resolved for the super-giant Chuquicamata
copper deposit of northern Chile by ELA-ICP-MS and SHRIMP.
Geology 29(5): 383-386
Ballard JR (2002) A comparatives study between the geochemistry
of ore-bearing and barren calc-alkaline intrusions: Unpub. PhD
thesis, Australian National University
Cathles LM, Erendi AHJ, Barrie T (1997) How long can a hydrothermal system be sustained by a single intrusive event?, Economic
Geology 92: 766-771
Hou ZQ, Ma HW, Zaw K, Zhang YQ, Wang MJ, Wang Z, Pan GT, Tang
RL (2003) The Himalayan Yulong porphyry copper belt: Product
of Large-scale strike-slip faulting in eastern Tibet, Economic
Geology 98: 125-145
Ma HW (1990) Granitoid and mineralization of the Yulong of the
Yulong porphyry copper belt in eastern Tibet. Beijing: Press of
China University of Geosciences, 158
Morrision GW (1980) Characteristics and tectonic setting of the
shoshonite rock association. Lithos 13: 79-108
Morris JD, Ryan JG (2004) Subduction zone processes and implications for changing composition of the upper and lower mantle:
in: Holland HD, Turekian KK, Carlson RW (eds) Treatise on
Geochemistry 2: 451-469
Pan GT, Wang PS, Xu YR, Jiao SP, Xiang TX (1990) Cenozoic tectonic
evolution of Qinghai-Xizang Plateau. Beijing: Geological Publishing House, 190
Ratschbacher L, Frisch W, Chen C, Pan G. (1996) Cenozoic deformation, rotation, and stress patterns in eastern Tibet and western
Sichuan, China, in: Yin A., Harrision TM. (eds) The Tectonic evolution of Asia. New York: Cambridge University Press, 227-249
Rui ZY, Huang CK, Qi GM, Xu J, Zhang MT (1984) The porphyry copper deposits in China. Beijing: Geological Publishing House, 350
Sengor AMC, Natalin BC (1996) Paleotectonics of Asia: Fragments
of a synthesis. in: Yin A and Harrison TM (eds) The tectonics of
Asia. New York: Cambridge University Press, 486-640
Tang RL, Luo HS (1995) The Geology of Yulong Porphyry Copper
(Molybdenum) Ore Belt, Xizang (Tibet). Beijing:Geological Publishing House, 320
Tapponnier P, Xu Z, Roger F, Meyer B, Arnaud N, Wittlinger G, Yang
JS (2001) Oblique stepwise rise and growth of the Tibet Plateau.
Science 294: 1671-1677
Wang E, Burchfiel (1997) Interpretation of Cenozoic tectoincs in the
right-lateral accommodation zone between the Ailao Shan shear zone
and the eastern Himalayan xyntaxis. Int. Geol. Rev 39: 191-219
Wang JH, Yin A, Harrison TM, Grove M, Zhang, YQ, Xie GH (2001) A
tectonic model for Cenozoic igneous activities in the eastern
Indo-Asian collision Zone, Earth and Planetary Science Letters
188: 123-133
Yin A, Harrison T M (2000) Geological evolution of the HimalayanTibetan orogen. Annual Review of Earth and Planetary Sciences
28: 211-280
Close
Close
Chapter 11-6
11-6
Cenozoic skarn Cu-Au deposits in SE Gangdese:
Features, ages, mineral asssemblages and exploration
significance
Guangming Li1, Kezhang Qin1, Kuishou Ding1, Xingchun Zhang2
1
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,
China
2
Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, Guizhou, China
Abstract. Kelu, Liebu, Chongmuda and Chengba are medium to large
skarn and vein-type Cu-Au deposits in Shannan area in the southeastern part of the Gangdese Cu-Au belt. These deposits, hosted in
carbonate and other calcareous rocks, formed between 21.35 to 23
Ma and are older than the mid-Miocene porphyry Cu mineralization in central Gangdese belt. The skarn mineral assemblage and
their fluid inclusions indicate that they are similar to deposits found
in the upper parts of zoned porphyry-skarn-vein systems. The recognition of this spatial association suggests potential for additional
targets at depth.
Keywords. Skarn Cu-Au, contact skarn, porphyry, K-Ar age, SEGangdese
1
Introduction
The Gangdese copper province consists of north and south
belts. The north belt contains, from east to west (over a
length of 350 km and width of 30-50 km), the Jiama,
Lakang’e, Qulong, Dabu, Chongjiang, Tinggong and
Bairong large to giant porphyry Cu (Mo) deposits. The
south belt contains (over a length of 60 km and width of
10-20 km), the Kelu, Liebu, Chongmuda and Chengba
medium to large skarn and vein type Cu-Au deposits. The
south belt, the so called Kelu-Liubu-Chongmuda Cu-AuAg belt, lies between the Zhalang County, Naidong County
and Sangri County of Shannan area. Several tens of complex geochemical anomalies (Cu-Au ± Pb-Zn-Ag-Cr-NiCo-W-Mo-Bi-Sb) (Cheng et al. 2001) of high intensity and
excellent overlap of individual elements and copper, gold
and polymetallic occurrences are scattered along the 60km-long belt (Cheng et al. 2001). The major deposits types
recognized to date are hydrothermal veins and contact
metasomatic bodies, including Duojizha, Kelu, Pulong and
Sangyesi deposits in the west, the Liebu, Shuangbujiere,
Mingze, Chemen and Niangguchu deposits in the center,
and the Bieji, Chongmuda, Chengba and Jizhong deposits in the east. Among them, Liebu Cu-Ag, Chongmuda
Cu-Au, Kelu Cu-Au and Chengba Cu-Au deposits appear
to be medium-sized, whereas the Liebu deposit may reach
large size with Cu reserve more than 0.5 Mt. Cheng et al.
(2001) proposed that the deposits are skarns, whereas
Wang and Chen (2003) and Yao et al. (2004) inferred a submarine-sedimentary massive sulfide origin (VMS-type).
This paper describes the recent studies of the skarn
and porphyry, hydrothermal alteration, K-Ar dating, and
fluid inclusion data on Liubu, Shuangbujiere, Chongmuda
and Kelu deposits. We propose that the deposits are parts
of zoned porphyry-skarn systems, but that the present
level of outcrop represents the upper part of those deposits.
2
Regional geology of the Cu-Au belt
Located in the southeast segment of Gangdese magmatic
arc, the Kelu-Liebu- Chongmuda Cu-Au belt lay in the
Xigaze-Sangri fore-arc during the Mesozoic, and in the
Yarlung-Zangbo arc-continental collision zone in Cenozoic. Outcropping strata include Triassic clastic and carbonate rocks, Jurassic calc-alkalic arc volcanic and clastic rocks of Mamuxia Formation with a thickness of more
than 1740 m, Cretaceous coal-bearing clastic, carbonate
and calc-alkalic volcanic rocks of Biema Formation with
a thickness of more than 4155 m (Wang and Chen 2003).
These rocks outcrop in an east-trending belt.
Magmatic activity in this belt was from late Yanshanian
to Himalayan. Two intrusive types are known. One is the
intermediate to felsic composition facies of Gangdese
batholith. The second consist of isolated porphyry stocks.
Gabbro, gabbro-diorite and granodiorite dominated in
late Yanshanian; granodiorite, quartz-monzonite,
monzodiorite, monzonite and granodiorite dominated in
early Cenozoic. Both suites commonly constitute the wall
rock of late hydrothermal veins, and some of the intrusive rocks have been considered to be genetically related
to the vein systems.
Diorite, quartz diorite and granodiorite porphyry
stocks and dikes form the youngest suite, which was intruded in the late Cenozoic. The porphyries intruded carbonate strata or interlayered carbonate and clastic rocks.
The contact between intrusions and calcareous strata are
typically skarns and have been silicified with associated
chalcopyrite, bornite, chalcocite and tetrahedrite.
Close
1240
Guangming Li · Kezhang Qin · Kuishou Ding · Xingchun Zhang
3
Features of typical Cu-Au deposits
The Liubu district is underlain by the lower Cretaceous
Biema Formation, which consists of mainly carbonate
rocks and siltstone with minor volcaniclastic rocks. Eocene
quartz diorite, granodiorite and quartz diorite intruded
the Biema Formation. Hydrothermal metasomatism and
alteration occurred along the contact between the intrusion and wall rocks. Copper mineralization formed in
banded skarn, with the carbonate rocks also being silicified and converted to hornfels. Skarn formation was controlled by an older north-northeast-striking and southsoutheast dipping fracture system. This fracture system
also controlled the regional distribution of the mineralization along the belt.
At Liubu, a dioritic porphyry body separates mineralized rock, referred to as mineralization I and II. Mineralization I, the larger of the two, is 4500 m in length and
varies in width from 50 m to 230 m and 200 m in depth
stretch. The mineralized units dip 40°–60° to NW, parallel to the dip of the enclosing stratigraphic units. The host
rocks are epidotized felsic hornfels, skarn and limestone,
as well as quartz diorite porphyry. The contact between
the orebody and wall rocks is not distinctive.
Eleven zones of sulfides are found in the Zk4101 drill
hole at Liubu with a total thickness of 32.87 m and Cu
grade of 0.92%. At 192.8-195.6 m depth near the end of
this drill hole disseminated copper mineralization 2.89
m thick and 1.16-1.18% Cu sulfides are also in the quartz
diorite porphyry. The disseminated mineralization is accompanied by intense silicification and sericitization.
Copper sulfides are found in three types, large veins hosted
in a fracture zone at elevation of 3800-4100 m, massive
and semi-massive Cu skarn at elevation of 3750-3950 m,
and porphyry Cu mineralization within and above diorite porphyry at elevations of 3600-3800 m or deeper.
4
Mineral assemblage
The Kelu, Shuangbujiere, Liebu, Chenba and Chongmuda
deposits are skarn-type. Ore textures include irregular
blebs, disseminated, veinlet, and minor massive, banded
and breccia texture. The ore minerals consist of bornite,
chalcopyrite, and minor secondary chalcocite, cuprite,
malachite, galena, native gold and other Au-Ag-Te minerals. Gangue minerals include garnet, epidote diopside,
tremolite, quartz, calcite, vesuvianite and wollastonite.
Microscopic observation and EPMA analysis show that
the mineral assemblages both rock-forming minerals and
ore minerals are simpler than skarn-type Cu or Cu-PbZn deposits in eastern China (Wang et al. 1994; Zhao et
al. 1996). The major silicate mineral is andradite, and locally forms a monomineralic rock hosting sulfide. Bornite
is the dominant ore mineral with minor chalcopyrite and
pyrite. This appears to be the salient feature of upper contact skarns in this region.
We have also identified special ore minerals such as
wittichenite. Wittichenite (Cu3BiS3) which is a very rare
sulfide in nature. It is very fine grained and irregular in
shape.
Bornite (Cu5FeS4) has a chemical composition of Cu
63.33,Fe 11.12,S 25.55 and has a very high content of Ag
(200 to 20620 g/t) much higher than found in bornite in
Yunnan Province where the highest Ag content measured
was 389 g/t. Bismutite (Bi2CO3O2) also has been identified by EPMA.
5
K-Ar age of skarn Cu-Au mineralization at
Shannan
We determined K-Ar ages on biotite and hornblende from
ore-bearing intermediate porphyries. For Liubu quartz
diorite porphyry, a biotite K-Ar age of 22.92 Ma ± 0.34 Ma
is reported. For the Chongmuda granodiorite porphyry,
a hornblende K-Ar age of 21.35 Ma ± 1.99 Ma is reported.
Both ages are older than biotite and hornblende K-Ar
ages from Tinggong and Bairong porphyry Cu deposits
(12.28 Ma, 13.54 Ma, 13.79 Ma, Qin and Li 2005 unpublished) as well as U-Pb and Re-Os ages of 18-12 Ma for porphyry Cu(-Mo) deposits in the middle segment of the
Gangdese porphyry belt. (Hou et al. 2003; Qu et al. 2003; Li
and Rui 2004). Based on the age distrintions, it appears that
the skarn Cu-Au mineralization in Shannan area is older
than known porphyry Cu(-Mo) mineralization in Gangdese,
and likely represents another metallogenic event.
6
Fluid inclusion microthermometry
Fluid inclusions were analyzed from different ore deposits to resolve differences in fluid temperature and salinity. Results of microthermometry study of fluid inclusions
show intermediate temperature and low to intermediatesalinity features for all samples. The dominant inclusion
type is composed of two phases, being about 4% to 15%
vapor and 85% to 96% liquid at room temperature. Homogenization temperatures vary from 232°C to 335°C.
Salinities are between 4.2 and 15.5 wt.% NaCl equivalent.
In Tinggong porphyry Cu deposit of Gangdese arc, the
homogenization temperatures vary from 298°C to 460°C,
and salinities have been recorded between 31.4 and 48.5
wt.% NaCl equivalent. In Yulong porphyry Cu deposit of
eastern Tibet, the homogenization temperatures vary from
275°C to 520°C, and salinities have been recorded between
13.5 and 52.8 wt.% NaCl equivalent. This skarn mineralization formed at lower temperature than known porphyry
Cu deposits in Tibet, which suggest these skarns are likely
distal skarns or formed at a shallower depth than the porphyry Cu deposits.
Close
Chapter 11-6 · Cenozoic skarn Cu-Au deposits in SE Gangdese: Features, ages, mineral asssemblages and exploration significance
7
Conclusion and significance
Generally, skarn deposits can be divided into three types
according to their depth of formation (Qin and Ishihara
1998). These include (a) mineralization associated with
recrystallized limestone lying distal to a subvolcanic porphyry; (b) contact skarns in along porphyry stocks or
dikes, such as at the Kamioka Pb-Zn-Cu mine and the
Nakatatsu Pb-Zn-Cu mine, both of which are related genetically to aplite and quartz porphyries (Shimazaki 1980),
and the skarn-type mineralization at Bingham Cu-Mo
mine (Einaudi 1982); and (c) contact-metasomatic skarns
in an equigranular or porphyritic granitoid stock or even
a batholith, such as the Kamaishi Cu-Fe mine in Japan
(Ishihara 1981) as well as the Dayi Fe-Cu and Gejiu SnCu skarn ore fields in China (Wang et al. 1994).Based on
the mineral assemblages and fluid inclusion results, the
Cu-Au skarn deposits in the Kelu-Liubu-Chongmuda belt
are interpreted as the upper part of a porphyry-skarn
mineralized systems. Presumably there should be potential for deeper porphyry–type Cu-Au targets.
Acknowledgements
This study was supported by the Major State Basic Research Program of China (No. 2002CB412605). We wish
to thank Shaohuai Wang, Shanyuan Jiang, Jindeng Lin,
Huazhai Jiang and Shuyuan Fang of No.2 Institute of CEEB
1241
for their help in field work, and Dr. R M Tosdal kindly
checked and improved the manuscript.
References
Cheng LJ, Li Z, Liu HF, Du GW, Guo JC (2001) Basic features of the east
Gangdese polymetallic metallogenic belt. Tibet Geology 19(1):43-53
Ishiahara S (1981) The granitoid series and mineralization. Economic
Geology 75: 458-484
Li GM, Rui ZY (2004) Petrogenetic and metallogenetic ages for the
porphyry copper deposits in the Gangdese metallogenic belt in
southern Tibet. Geotectonica et Metallogenia 28(2): 165-170
Qin KZ, Ishihara S (1998) On the possibility of porphyry copper mineralization in Japanese Islands. International Geology Review 40(6):
539-551
Qu X, Hou Z, Li Z (2003) The 40Ar/39Ar ages of the ore-bearing porphyries in Gangdese copper belt and their geological significance.
Acta Geologica Sinica 77(2): 245-252
Shimazaki H (1980) Characteristics of skarn deposits and related acid
magmatism in Japan. Economic Geology 75: 173-183
Titley SR (1993) Characteristics of high- temperature, carbonatehosted massive sulfide ores in the United States, Mexico and Peru.
In Kirkham R (eds) Mineral Deposit Modeling: Geological Association of Canada, 585-614
Wang SH, Chen ZK (2003) Geological characters and metallogenic
regulation of Kelu-Chongmuda copper and gold belt in Tibet. Geology and Prospecting 39(2): 21-25
Wang ZT, Qin KZ, Zhang SL (1994) Geology and Exploration of Large
Copper Deposits. Beijing: Metallurgical Industry Press, 165
Yao P, Zhen MH, Peng YM (2002) Ore source and origin of Jiama Cupolymatallic deposit in Gangdise arc, Tibet. Geological Review,
48(5): 468-479
Close
Close
Chapter 11-7
11-7
Partial melting in the upper crust in southern Tibet:
Evidence from active geothermal fluid system
Zhenqing Li, Zengqian Hou
Institute of Mineral Resources, CAGS, Beijing, 100037, China
Abstract. During the process of carrying out a series of geophysical
probes, a suite of seismic bright spots were observed along the
Yadong-Gulou rift valley zone. Concerning the nature of these bright
spots, two interpretations have been advanced: 1) saliferous supercritical fluid and 2) magma bodies on the top of partially melted
layer in the upper crust. Due to lack of direct means and methods
of investigation, their characteristics and distribution remain speculative. Based on research of violent hydrothermal activity of the south
Tibet, this paper makes an attempt to discuss the characteristics of
these bright spots from another perspective. Helium isotope composition of geothermal gas, geochemistry of geothermal water and
modelling of temperature field suggest that these bright spots consist of silicate magma, providing new evidence for the existence of
partial melting in southern Tibet.
Keywords. Partial melting, geothermal, geochemical, helium isotope,
southern Tibet
1
Introduction
One of the important discoveries of a series of geophysical
probes along the Yadong-Gulou rift valley zone is a suite of
seismic bright spots at a depth of 15 to 18 km (Brown et al
1996; Wenbo Wei 2001). Although these bright spots are
usually considered as evidence for a fluid phase, there are
divergent interpretations regarding their nature (supercritical fluid or silicate magma) and crustal distribution.
Makovsky and Klemperer (1999) considered the seismic
bright spots as dissociative saline supercritical fluid in the
mid-upper crust. By contrast, Nelson et al (1996) and Brown
et al (1996) explained them as magma bodies above the top
of partial melting in the mid-upper crust.
Constraints on property, origin and distribution of these
bright spots are very important to determine the thermal
condition of the crust in the Tibet plateau and to develop
models for crustal evolution and deformation. However,
there is hitherto no proper characterisation of the bright
spots. We thus selected some hot springs in four typical N–
S-trending rift valley zones to do some research. Results
from hydrochemistry of geothermal water, helium isotope
composition of spring gases, sulphide isotope composition
of sinters and hydrothermal dynamic analysis are presented
here to elucidate these seismic bright spots.
2
Tectonic background and distribution of hot springs
Regional uplifting of the Tibet plateau started in the Miocene, with subsequent development of E–W extension (ca.
18 Ma; Willams et al. 2001) and N–S normal fault systems
that transect the IYS (the Indus-Yarlung Tsangpo suture
zone) and BNS (the Bangongcu-Nujiang suture zone). In
some regions, the N–S normal fault systems culminated in
rift valleys or fault trough basins (Bllsnluk et al. 2001), and
intense modern hydrothermal activity represented by the
famous Himalaya geothermal belt. Geophysical prospecting data have already indicated that the N–S active tectonic
belts are possibly situated at a crustal upwarp and that they
are analogous to a rift valley. According to the Wilson’s model
of continental rift valley, rift-fault depressions represent the
beginning of one plate motion. Hence the crustal upwarp
should reflect the upwellling of deep magma.
The violent modern geothermal activity system, mainly
distributed to the south of the BNS, was controlled by the
N–S tectonic belts, resulting in a series of N–S-trending
belts of hydrothermal activity. There are several hydrothermal belts in the hinterland of the plateau, known as
(1) Damre Yumco-Guco, (2) Xainza-Xaitongmoin, (3)
Yadong-Gulou and (4) Sangri-Cona. Numerous high-temperature geothermal fields are located in these four hydrothermal belts. In the Yadong-Gulou rift valley belt, the
high-temperature geothermal fields are coincident with
the surface projections of bright spots of the seismic section (Fig. 1; Hou and Li 2004).
3
Geochemical character of geothermal springs
3.1 Hydrochemistry types of geothermal water
According to data from Tongwei et al (2000), geothermal
water can be grouped into four types: (1) HCO3––Na+, (2)
HCO3––Cl––Na+, (3) Cl––Na+ and (4) SO42–. Types 2 and 3,
which are often considered to be related to magmatic activities, are main types of geothermal water. Three-quarter
geothermal water in southern Tibet belongs to the two types.
3.2 Ion composition of geothermal water
Compared with other geothermal areas and crustal abundances, the Tibet geothermal waters have higher Li, Rb,
Cs, As and HBO2 (Zhang 1982). The concentration of Li is
50×10-6, Rb is 0.0n-n×10-6, Cs is 0.0n-n×10-6, As is even as
high as 125.6×10-6, and the highest content of HBO2 is
1917×10-6 (Tong Wei 2000). Usually, Rb and Cl are regarded
as elements related to magmatic activity. Moreover, the
Close
1244
Zhenqing Li · Zengqian Hou
Hoke et al (2000) divided the He isotope composition
of Tibet into two domains with the borderline of R/Ra
=0.10 (R is the 3He/4He value of samples and Ra is that
of air). Helium isotope data from our study also reflect
the existence of two domains, but the values and distributions have some variance. The R/Ra values of the crustal
He domain vary from 0.017 to 0.08, being distributed in
the Ngamring geothermal regions in the hinterland of
the plateau, including the high-temperature hot springs
in Xaitongmoin, Ngamring, Samig and Tagejia. The
R/Ra values of the mantle He domain vary from 0.11 to
5.38 and are distributed in at least three hydrothermal
zones, known as Lhasa, Shiquanhe and Tengchong (Hou
and Li 2004).
4
Discussion
As mentioned above, the nature of the seismic bright is
unclear. Based on the correspondence between these bright
spots and surface hydrothermal activity, this paper attempts to understand these bright spots by investigating
geothermal fluids.
4.1 Is there partial melting in the upper crust in southern
Tibet?
areas where Rb is enriched often show high concentrations of F, Cl, As, HBO2, Cs and Li (Zhao Ping 1998).
3.3 Sulphur isotope composition of geyserite and native sulphur
Sediments of high-temperature geothermal springs usually contain geyserite and nature sulphur in southern Tibet. δ34S values of geyserite have a very narrow range in
various regions. They range from -5.2 to +4.2‰, and centre between -2 and +2‰. δ34S values of native sulphur range
from -10.1 to +7.6‰ and, like geyserite, show normal distribution centred from -2 to +2‰ (Li et al 2005). The geyserite and native sulphur from hot springs have δ34S values
comparable to that of magmatic sulphur, which is 0‰.
3.4 Helium isotope composition of geothermal gas
There are different 3He/4He values: the 3He/4He value of
air is 1.4×10-6, that of crustal gas is n×10-8, and the value
of mantle gas is above 10-5 (Kimmelmann 1996).
Hydrochemistry of geothermal springs shows that Cl–
Na+-bearing waters occur broadly in southern Tibet. High
contents of Li, Rb, Cs, As and Cl and their positive correlation in geothermal waters, as well as sulphur isotope
composition of geyserite and sulphur, suggest a magmatic
signature. However, there is no modern volcanic activity in southern Tibet. On the other hand, geothermal fluid
chemistry reflects some magmatic input. It thus seems
reasonable to interpret the seismic bright spots as magma
bodies at the top of a partially melted layer.
Furthermore, the regular composition and distribution of helium isotopes of geothermal gas also provide
some evidence for partial melting. There are three possible origins for mantle helium: (1) He release from fluid
inclusions in minerals from mantle mafic rocks; (2) direct degasification from active upper mantle; and (3)
degasification of small volumes of mantle melts. For the
first possibility, a 50 × 100-km geothermal region with
R/Ra>0.1 requires a mafic substratum with thickness of
several kilometres below all the geothermal regions. It is
obvious that is not accordant with geological observation. For the second possibility, because crustal hinterland of the Tibet has a thickness of about 70km, there is
no evidence to prove that the N–S normal faults have
penetrated so deep into the crust to account for removal
small quantities of mantle gas to the surface. Hence, the
explanation for mantle helium seems to be degasification
of mantle melts emplaced in the crust.
Close
Chapter 11-7 · Partial melting in the upper crust in southern Tibet: Evidence from active geothermal fluid system
4.2 Possibility of the existence of partial melting
References
Ut supra, there is some evidence for partial melting in
the upper crust of southern Tibet. Nevertheless, is it indeed possible that partial melting of upper crust exists in
southern Tibet?
In southern Tibet, explosive hot springs with temperature of 80–90°C are common. Geothermal waters with temperatures as high as 329°C and 306°C were found in geothermal wells at Yangbajing and Yangyi geothermal fields,
respectively. It is thus possible that temperatures at depths
of 15–25 km are higher than 600°C.
Moreover, heat reservoir and temperature modelling
also suggests the possibility of melting. The calculated
temperature of heat reservoir according to formula of
thermometric scale (Zhu et al 1992) is from 114°C to 277°C
(Li et al 2005). Supposing that the temperature is 200°C at
the depth of 2.5 km, the temperature at 15 km should be
as high as 700°C. This temperature is compatible with the
melting temperature of wet granite (≈ 650°C). Furthermore, temperature modelling of by Shi Yaolin et al. (1992)
showed that only the frictional heating of underthrusting could generate high-temperature conditions capable
of melting wet granite in the interior crust of subducted
zone. Yuan Xuecheng et al deduced the distribution of
temperature fields using magnetotelluric methods, and
concluded that the temperature of low resistivity layers
at depths of 17–41km was 600–800°C (Zhao 2001).
Bllsnluk P M, Hacker B, Glodny J (2001) Normal faulting in central
Tibet since at least 13.5 Myr ago. Nature 412: 628-632
Brown L D, Zhao W J, Nelson K D (1996) Bright spots, structure, and
magmatism in southern Tibet from INDEPTH serimic reflection
profiling. Science 274: 1688-1690
Hoke L, Lamb S, Hilton D, Poreda R J (2000) Southern limit of mantlederived geothermal helium emissions in Tibet: implications for
lithoshperic structure. Earth Planet Sci Lett 180: 297-308
Hou ZQ, Li ZQ, Qu XM (2001) The uplifting processes of the tibetan
plateau since 0.5Ma B.P.: evidences from hydrothermal activity
in the Gangdise belt. Science in China (Series D) 44 (sup): 35-44
Hou ZQ, Li ZQ (2004) Possible location for underthrusting front of
the Indus continent: constrains from helium isotope of the geothermal gas in southern Tibet and eastern Tibet. Acta geologica
sinica 78(4): 482-493
Li ZQ, Hou ZQ, Nei FJ (2005) Characteristic and distribution of the
partial melting layers in the upper crust: evidence from active
hydrothermal fluid in the south Tibet. Acta geologica sinica 79(1):
68-77
Kimmelmann ES (1996) Use of Helium isotopes in groundwater studies of the Parana Basin,Brasil. In: 30th international geological
congress abstracts 3(3): 238
Kind R, Ni J, Zhao W (1996) Evidence from earthquake data for a
partially molten crustal layer in southern Tibet. Science 274: 16921694
Makovsky Y, Klemperer SL (1999) Measuring the seismic properties
of Tibetan bright spots: evidence for free aqueous fluids in the
Tibetan middle crust. J Geophys Res 104: 10795-10825
Nelson KD, Zhao WJ, Brown LD (1996) Parially molten middle crust
beneath Southern Tibet: synthesis of project INDEPTH results.
Science 274: 1684-1688
Shen XJ, Zhang WR, Yang SZ (1990) Heat flow and heat evolvement
of terrain tectonic in Qinghai-Xizang plateau. Beijing: Geological Press, 1-90
Tong W, Liao ZJ, Liu SB (2000) Thermal springs in Tibet. Beijing:
Science Press
Wei WB, Martyn U, Alan J (2001) Detection of widespread fluids in
the Tibetan crust by magnetotelluric studies. Science 292: 716718
Williams H, Turner S, Kelley S (2001) Age and composition of dikes
in Southern Tibet: new constraints on the timing of east-west
extension and lt’s relationship to post-collisional volcanism. Geology 29: 339-342
Yokoyama T, Nakai S, Waikita H (1999) Helium and carbon isotopic
compositions of hot spring gases in the Tibetan plateau. J Volcan
Geotherm Res 88: 99-107
Zhang LG (1985) Application of stable isotope in geological science.
Xi’an: Shanxi Science And Technology Press
Zhao P, Jin J, Zhang HZ (1998) Chemical composition of thermal
water in the Yangbajing geothermal field, Tibet. Chinese Science
Bulletin 33(1): 61-72
Zhao WJ, Nelson KD, Poject INDEPTH Team (1996) Deep seismic
reflection evidence for continental underthrusting beneath the
south Tibet. Nature 366: 557-559
Zhu BQ, Zhu LX, Shi CY (1992) Geochemical exploration of geothermal fields. Beijing: Geological Press
5
Conclusions
Geothermal water and sinter geochemistry and He isotope composition of geothermal gases point to a magmatic contribution, suggesting that magma bodies exist
in the upper crust in southern Tibet. Moreover, both heat
reservoir and temperature modelling of geothermal fields
suggest the possibility of partial melting. Therefore, we
conclude that the seismic bright spots should be magma
bodies formed by melting of crust.
Acknowledgements
Dr. Bie Fenglei, Prof. Li Shengrong and Prof. Li Youguo
are thanked for assistance with fieldwork and provision
of sample material; we are grateful to Dr. Qu Xiaoming,
Prof. Gao Yongfeng and Dr. Zhaoping for advice and help.
This study acknowledges support via National Basic Research Project (973) Fund 2002CB412606 and National
Nature Science Fund 40302028.
1245
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Close
Chapter 11-8
11-8
Copper and gold metallogeny in the Tethyan domain
in China
X-X. Mo
Beijing 100083, China
K-H. Yang
Department of Geology, University of Toronto, Toronto, Ontario M5S 3B1, Canada
L-L. Wang, G-C. Dong
School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
Abstract. The Paleo-Tethyan Ocean in China formed in the early Carboniferous and closed at the end of the Triassic. Then the NeoTethyan Ocean opened no later than the end of Triassic and began
to close about 65 Ma, followed by the uplift of Tibetan Plateau driven
mainly by India-Eurasia collision. Each stage or substage possesses
its characteristic mineralization and ore deposits. However, in places,
mineralization and ore deposits formed during Paleo-Tethyan and
Neo-Tethyan stages overlap spatially.
Copper deposits in the Tethyan metallogenic belt are mainly
porphyry deposits with some skarns and VMS deposits. Three porphyry copper metallogenic belts are known so far in the Tethyan
domain. The Gangdese and the Yulong copper belts formed in NeoTethyan period mainly in post-collisional environments; and the
subduction-related Zhongdian copper belt formed in middle-late
Triassic, Paleo-Tethyan period. In addition to the Derni copper deposit located in Xiugou-Maqin (XMSZ) ophiolite, VMS-type copper
deposits in the Tethyan domain in China mainly formed in late Triassic post-collisional rift volcanic basins. The copper deposit at Yangla
is probably a composite deposit, that is, the late Triassic ~208-227
Ma porphyry with skarn style mineralization overprinted on the
Permian VMS-style mineralization in an oceanic arc environment.
Alternatively, the Yangla could be the late Triassic porphyry with
skarn style mineralization combined with high-temperature mantos.
Multi-mineralization seems to be an important characteristic for
the Tethyan metallogenic belt responding to multiple tectonic
events.
Gold deposits in the Tethyan metallogenic belt are concentrated
in the following three regions, the joint of Guizhou, Yunnan and
Guangxi provinces (known as Carlin-type “Gold Triangle” of SW
China), Sanjiang region (including Songpan-Garze area) and north
Tibet-south Qinghai. The main types of gold deposits are large fault
/ suture zone-controlled gold deposits (orogenic gold deposits),
Carlin-type gold deposits, alkaline-rich hypabyssal intrusion-related
gold deposits and epithermal gold deposits. Most of gold deposits
formed in Tertiary post-collisional settings.
Xizang (Tibet) Provinces, as well as parts of Guizhou,
Guangxi and Gansu provinces. Tectonically it is neighbored by Indian Craton (I) to the south, Yangtze Platform
(YZ) to the east and the Altaides to the north, respectively. The Tethyan domain is composed of the following
tectonic units (Fig. 1) from south (west) to north (east):
the Himalayas (II), the Gangdese/Lhasa (III ), the Qiangtang
(?), the Hohxil-Baryan Har-Sanjiang (?), and the KunlunQaidam-Qilian (VI) terranes, bounded by the following fault
zone and suture zones, i.e., the main boundary fault zone
(MBT), the Yarlung-Tsangpo (YZSZ), the BangongcoNujiang (BNSZ), the Lancangjiang- Changning-Menglian
(LSZ), and the Xiugou-Maqin (XMSZ), respectively. Among
Keywords. Tethyan metallogenic belt, copper and gold deposits, Tibetan Plateau, Sanjiang
1
Tectonic outline of the Tethys in China
The Tethyan domain in China geographically covers the
Qinghai-Xizang (Tibet) Plateau and ‘Sanjiang Region’ (abbreviation of the valleys of three rivers – Jinshajiang,
Lancangjiang and Nujiang in SW China), i.e., western
Yunnan, western Sichuan and southern Qinghai and
Close
1248
X-X. Mo · K-H. Yang · L-L. Wang · G-C. Dong
them, the Gangdese and the Sanjiang tectonomagmatic belts
and the above-mentioned ophiolite suture zones are the
most favorable for gold and copper. Temporally, the Tethys
in China underwent two stages of evolution, Paleo-Tethys
and Neo-Tethys. It is commonly believed that the opening of Paleo-Tethyan Ocean, which mainly consisted of
Lancangjiang-Changning-Menglian and JinshajiangAilaoshan oceanic basins, started in early Carboniferous
and reached its maximum width in early Permian. Subsequently, two other oceanic basins, the Garze-Litang and
Xiugou- Maqin oceanic basins, opened in late Permian.
All Tethyan oceanic basins were closed at the end of Triassic by collision events between continent and continent,
arc and continent, and arc and arc. Then the Neo-Tethyan
Ocean, composed of two major branches, BangongcoNujiang and Yarlung Zangpo oceanic basins, opened no
later than the end of Triassic and closed in 65 Ma to 45
Ma or so, followed by post-collisional tectonomagmatism
and the uplift of Tibetan Plateau driven mainly by IndiaEurasia collision.
Each stage or substage possesses its characteristic mineralization and ore deposits. However, mineralization and
ore deposits formed in Paleo-Tethyan and Neo-Tethyan
stages typically overlap spatially. (Mo et al. 1994; Wang
anf Mo 1995; Xiao and Li 1995; Zhong 1998; Yin and
Harrison 2000)
2
Copper deposits in the Tethyan metallogenic
belt in China
Copper deposits in the Tethyan metallogenic belt are
mainly porphyry deposits with some skarns and VMS
deposits.
Three porphyry copper metallogenic belts have been
identified so far, whose formation ages of both ores and
ore-bearing porphyries increase from south to north.
The Gangdese copper metallogenic belt in southern
Tibet extends more than 450 km in length and 30 to 50
km in width, within which several large Cu-Mo, Cu-Au
and Cu-Fe deposits (more than one million tons of metallic copper for each) occur such as Qulong (QL in Fig. 1),
Jiama, Chongjiang (CJ), and Xiongcun-Dongga (XD) deposits and tens of medium- to small-sized deposits. They
were controlled by both E-W striking faults and ~ N-S
striking faults. Ore-bearing porphyries are mainly
monzogranitic, quartz-monzonitic and syenogranitic
porphyries, 18–12 Ma in age with a peak at 15 ± 1 Ma,
intruding into the older granitoids and volcanic rocks in
the Gangdese. Re-Os isotopic dating of associated molybdenite from Qulong, Chongjiang, Tinggong and
Lakange copper deposits gave ages ranging from 14.5 to
16.8 Ma of ore-forming processes, showing a short interval of mineralization, less than 3 Ma. Porphyry-type
stringer and stockwork ores have grades of Cu 0.16–1.47
wt.% and Mo 0.024–1.37 wt.%, and skarn-type ores have
higher grades of metals, Cu 0.23–2.27 wt%, Pb 1.1–3.48
wt% and Zn 0.24–1.04 wt%. (Zheng et al. 2002; Hou et al.
2003; Rui et al. 2003).
The Yulong porphyry copper metallogenic belt in eastern Tibet extends over 200 km and 15-30 km width,
within which more than twenty mineralized porphyries
and three large copper deposits occur (YL in Fig. 1; 6.22
Mt of contained Cu), Malasongduo (1.0 Mt Cu) and
Duoxiasongduo deposits (0.5 Mt Cu) with a total of more
than 7.72 million tonnes contained copper. Ore-bearing
porphyries are mainly monzogranitic porphyries of ages
ranging from 55.0 to 33.7 Ma, having three peaks at 52 ±
2.8, 40 ± 2.3 and 33 ± 3.3 Ma, respectively. Porphyries
intruded into upper Triassic slate and sandstone and were
controlled by the Gongjue-Mangkang strike-slip fault. ReOs isotopic dating of associated molybdenite gave ages
of 35-36 Ma of ore-formation. (Du et al. 1994; Tang and
Luo, 1995; Hou et al. 2003).
Both the Gangdese and Yulong porphyry copper belts
formed in Neo-Tethyan period and post-collisional environments. These copper deposits are quite similar in characteristics to those in Andean-type porphyry copper deposits in South America. Ore-bearing porphyries have
high-K calc-alkaline, shoshonitic and adakitic geochemistry. However, post-collisional tectonic environments for
both Gangdese and Yulong copper belts were obviously
different from subduction-related Andean copper belt. It
seems that ore-bearing porphyries in both Gangdese and
Yulong copper belts were genetically related to the previously subducted Tethyan oceanic slabs, which re-melted
to produce porphyries when the geotherm reached their
solidus triggered by decompression of post-collisional N–
S rifts c.15 Ma for the Gangdese belt and strike-slip faults
c.50-30 Ma for the Yulong belt.
The third porphyry copper belt Zhongdian (ZD in
Fig. 1) formed in middle to late Triassic, Paleo-Tethyan
period and was subduction-related. It is located southeast of the Yulong belt in Yunnan Province at the southern end of Yidun magmatic arc formed by the westward
subduction of Garze-Litang plate under the Zhongzan
block in the Triassic. The large copper deposit at Pulang
is one of the examples, having Cu–Au–Pb–Zn metal association and being genetically related to Triassic porphyries. It is currently being explored and, in two drill
holes, has announced ore intersections 300 m thick grading 0.7 wt% Cu on the average (Li, personal comm. 2005).
In addition to the Derni copper deposit located in
Xiugou-Maqin (XMSZ) ophiolite, VMS-type copper deposits in the Tethyan domain in China mainly formed in
late Triassic post-collisional rifting volcanic basins, which
developed on a base of the late Permian-Triassic JiangdaWeixi volcanic arc. Radiolarian cherts and basalt-dominated bimodal volcanic suite developed in this N-S elongating zone of basins, which extends for hundreds kilometers from western Yunnan to eastern Tibet. A large
Close
Chapter 11-8 · Copper and gold metallogeny in the Tethyan domain in China
deposit (Luchun, with Cu-Zn-Pb, in Yunnan Province),
and tens of medium- to small-sized deposits have been
found within the basins (Pan et al. 2003). Post-collisional
extension extensively took place in the Sanjiang region
from the end of the Triassic right after the closure of the
Paleo-Tethys, providing a favorable environment for VMSstyle mineralization.
The copper deposit Yangla with a reserve of 130 Mt of
metallic copper ore grading 1.05 wt% on average is a composite deposit, that is, late Triassic ~208-227Ma porphyry
with skarn style mineralization overprinted on the Permian
VMS-style mineralization in an oceanic arc environment.
Alternatively, the Yangla could be the late Triassic porphyry
with skarn style mineralization combined with high-temperature mantos. Multi-mineralization seems to be an important characteristic for the Tethyan metallogenic belt in
response to the multiple tectonic events.
3
Gold deposits in the Tethyan metallogenic belt
in China
Gold deposits in the Tethyan metallogenic belt are concentrated in the following three regions, the joint of
Guizhou, Yunnan and Guangxi Provinces (known as
Carlin-type “Gold Triangle” of SW China), Sanjiang region (including Songpan-Garze area) and north Tibetsouth Qinghai.
The main types of gold deposits are large fault / suture zone-controlled gold deposits (orogenic gold deposits), Carlin-type gold deposits, alkaline-rich hypabyssal
intrusion-related gold deposits and epithermal gold deposits. Most of gold deposits formed in Tertiary post-collisional settings, although many of them are hosted in
pre-Tertiary rocks. However, Zhu (2005, this volume) recently reported that Au-mineralized clues were found in
the porphyry bodies at 58.7 Ma with the contents of gold
up to 1-3g/t in the Linzhou Basin in the Gangdese. Placer
gold deposits occur widely in the regions of bedrock gold.
Laterite-type (oxidized) gold deposits developed in some
parts of southern Yunnan because of a semi-tropic climate. In addition, gold occurs as a by-product in silver
and base metal deposits.
Suture zones in the Tethyan domain are considered
potentially idea targets for gold deposits. Among them,
many economic gold deposits have been found in
Jinshajiang-Ailaoshan (JSZ) and Garze-Litang (GLSZ)
suture zones with gold occurrences in other sutures as
well. The large Laowangzhai gold belt (LWZ in Fig. 1) in
Yunnan was controlled by the Ailaoshan-Jinshajiang
ophiolite suture zone, which contains several large gold
deposits, such as Laowangzhai, Donggualin, Jinchang,
Chang’an and Daping deposits with more than 150 tonnes
of Au reserves (Hu et al. 1995, Shen et al. 1997, Li and Li
2000). The main factors contributing to the formation of
the deposits were probably ophiolitic mafic-ultramafic
1249
rocks (possibly one of the main sources of gold), largescale shear zones and related fault systems (might have
played roles as feeders of ore solutions and places for precipitation of metals) and later (mainly Cenozoic) small felsic
intrusions and lamprophyres (possible one of the major
sources of heat and fluids). Ores are hosted in volcanic tuffaceous rocks, low-grade metamorphic sandstone and slate,
silicified ultramafic rocks and cross-cutting fracture zones.
Gold deposits in the Garze-Litang suture zone have similar
ore-controlling factors to those of Laowangzhai gold deposit belt. The Gala deposit (GL in Fig. 1) in the Sichuan
Province in mylonitized basaltic rocks is the largest. The
Xianshuihe fault zone to the east of Garze-Litang suture
zone is also a promising gold metallogenic belt.
Alkaline hypabyssal intrusion-related gold deposits
occur on both sides of Jinshajiang-Ailaoshan suture, especially to the south of 25o20’ N. This belt also has good
potential for exploration. Beiya is a typical of this belt,
with Cenozoic porphyry-skarn-epithermal and Tertiary
-Quaternary sediment-hosted stratabound styles of mineralization. Only an area of 0.9 km2 within one deposit
has been drilled with an estimated resource of >1 million ounces of gold grading 5-6 g/t in the skarn, 8-10 g/t
in oxides and 1-3 g/t in the Quaternary and Tertiary sediments. Gold mineralization was likely genetically related
to Cenozoic post-collisional potassic hypabyssal intrusions (40–24 Ma), which are believed to be a result of decompression melting of the previously enriched lithospheric mantle (Guo et al. 2005).
Acknowledgements
This work is financed by the grants of National Key Project
for Basic Research of China (2002CB412600), of National
Natural Science Foundation of China (Projects 40172025,
40103003, 49802005 and 49772107) and of the key project
on Tibetan Plateau of the Ministry of Land and Resources
of China (Grant No.2003009).
References
Du A, He H, Yin W (1994) Method for Re-Os isotopic dating of molybdenite. Acta Geologica Sinica 68: 339–346
Guo ZF, Hertogen J, Liu JQ, Pasteels P, Boven A, Punzalan L, He HY, Luo
XJ Zhang WH (2005) Potassic magmatism in western Sichuan and
Yunnan provinces, SE Tibet, China: Petrological and Geochemical
Constraints on Petrogenesis. J Petrology 46 (1): 33–78
Hou Z, Lu Q, Wang A, Li X, Wang Z, Wang E (2003) Continental collision and related metallogeny: a case study of mineralization in
Tibetan Orogen. Mineral Deposits 22(4): 319–333 (in Chinese)
Hou Z, Ma H, Zaw K, Zhang Y (2003) The Himalayan Yulong porphyry copper belt: Product of large-scale strike-slip faulting in
eastern Tibet. Economic Geology 98: 125–145
Hou Z, Qu X, Wang S, Gao Y, Du A, Huang W (2003) Re-Os molybdenite ages for Gangdese porphyry copper Metallogenic belt, Tibet: Timing of mineralization and geodynamic settings. Science
in China (D Series) 33(7): 609–618
Close
1250
X-X. Mo · K-H. Yang · L-L. Wang · G-C. Dong
Hu Y, Wang H, Tang S (1995) Geology of Ailaoshan Gold Deposit.
Geological Publishing House, Beijing (in Chinese) 218
Li D, Li B (2000) Conditions of mineralization of Ailaoshan gold deposit, Yunnan Province. Sedimentary and Tethyan Geology.20 (1):
60–77 (in Chinese)
Mo X, Deng J, Lu F (1994) Volcanism and the evolution of Tethys in Sanjiang area. Journal of Southeast Asian Earth Sciences 9(4): 325–333
Pan G, Xu Q, Hou Z, Wang L, Du D, Mo X, Li D, Wang M, Li X, Jiang X,
Hu Y (2003) Archipelagic Orogenesis, Metallogenic Systems and
Assessment of the Mineral Resources Along the NujiangLancangjiang-Jinshajiang Area in Southwestern China. Geological Publishing House, Beijing (in Chinese) 420
Rui Z, Hou Z, Qu X, Zhang L, Wang L, Liu Y (2003) Timing of oreformation of Gangdese porphyry deposits and the uplift of Tibetan Plateau. Mineral Deposits 22: 217–225 (in Chinese)
Shen S, Wei Q, Cheng H, Mo X (1997) Metallogenic types of Ailaoshan
gold belt, Yunnan Province. Tethyan Geology 21: 73–84 (in Chinese)
Tang R, Luo H (1995) Geology of Yulong Copper Porphyry (-Molybdenum) Metallogenic Belt, Tibet. Geological Publishing House,
Beijing (in Chinese) 213
Wang H, Mo X (1995) An outline of tectonic evolution of China: Episodes 18 (1–2): 6–16
Xiao X, Li T (1995) Tectonic evolution and uplift of the QinghaiTibet Plateau. Episodes 18 (1-2): 31-35
Yin A, Harrison TM (2000) Geologic evolution of the HimalayanTibetan orogen. Annual Review of Earth and Planetary Sciences
28: 211–280
Zheng Y, Wang B, Fan Z, Zhang H (2002) Tectonic evolution
of the Gangdese Mountains in Tibet and the metallogenic
potentialities of copper, gold and poly metals. Geological
Science and Technology Information 21(2): 55–59 (in
Chinese)
Zhong DL (1998) Paleo-Tethyan Orogenic Belt in West Sichuan and
West Yunnan. Science Press, Beijing (in Chinese), 231
Close
Chapter 11-9
11-9
Constraints on the formation of Carlin-type gold
deposits in Sichuan and Gansu provinces, China
F. Neubauer
Department Geography, Geology and Mineralogy, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria
S. Borojevic-Sostaric
Dept. of Mineralogy and Petrography, University of Zagreb, Zvonimirova 8, CRO-10 000 Zagreb, Croatia
A. von Quadt, I. Peytcheva
Inst. of Isotope Geology and Mineral Resources, ETH Zürich, Sonneggstr. 5, CH-8092 Zürich, Switzerland
G. Friedl, J. Genser
Department Geography, Geology and Mineralogy, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria
Z. Zeng
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Abstract. Carlin-type gold deposits exposed within and along borders of the Triassic Songpan-Garze Flysch and adjacent areas of
northwestern Sichuan and southern Gansu Provinces, Western China,
have been investigated. Field data suggest that formation of these
Carlin-type gold deposits is related to late-orogenic, calcalkaline
magmatism. Results from two preliminary U-Pb single-zircon analyses suggest an age of ca. 220 Ma for magmatism at A’gyi and Dashui
deposits. Magma emplacement was likely related to regional deformation. Calcite associated with ores precipitated from low-salinity fluids containing Na+, Mg2+, Na+ > Mg2+, +K + and Ca2+ at temperatures of up to 300 °C, plausibly under boiling conditions.
Keywords. Calcalkaline magmatism, fluid composition, ion chromatography, U-Pb zircon
1
Introduction
2
Regional tectonic setting
Host rock of these Carlin-type gold deposits are siltstones/
shales and graded sandstones of the Middle-Late Triassic Songpan-Garze turbidite basin. The deposits are also
associated with regional structures interpreted to have
formed during late Indosinian or Yangshanian and early
Himalayan deformation events (Zeng et al. 2001a; Liu et al.
2003). These structures include: (1) decollement faults along
the contact zone between Triassic and Pre-Triassic; (2) the
N-trending Minjiang fault, a thrust zone of E–W shortening; (3) NW-trending thrust and strike-slip faults paralleling the trend of the northerly adjacent Qinling belt, particularly the Maqu-Lueyang fault zone, along which Dashui,
Manaoke and further ore deposits are located (Gu et al.
2003; Liu et al. 2003; Zeng et al. 2001a, b) (Fig. 1).
During the last decade, many Carlin-type ore and other
gold deposits were discovered in north-western Sichuan
and southern Gansu Provinces (Hu et al. 2002; Mao et al.
2002a, b; Zhou et al. 2002; Liu et al. 2003). Most of these
deposits are located within the Middle-Upper Triassic
Songpan-Garze turbidite basin (Fig. 1). Fine-grained gold
occurs in arsenical pyrite, which is commonly associated with cinnabar, stibnite, realgar, and orpiment. These
hydrothermal ore deposits display features of silicification, carbonatization, and pyritization. Previous studies
show the structural control of these deposits along major regional fault zones. In some deposits, dacite porphyry dykes have been described (e.g. Hu et al. 2002; Liu
et al. 2003).
Here, we report petrographic and geochemical composition as well as preliminary U-Pb zircon ages of some
dykes and stocks, which seemingly controlled mineralization. Furthermore, we report compositional data of oreforming fluids.
Close
1252
F. Neubauer · S. Borojevic-Sostaric · A. von Quadt · I. Peytcheva · G. Friedl · J. Genser · Z. Zeng
Granodiorite and subordinate diorite stocks/ dykes are
closely associated with regional faults and ore deposits.
Some of these have been dated making use of the K-Ar
method. Ages range from 190 Ma to 82 Ma (Mao et al.
2002b; Liu et al. 2003 and references therein).
3
Mafic dykes and granodiorite stocks
Similar types of granodiorite and rare diorite stocks have
been found in nearly all deposits visited. These are unaltered in some localities and commonly grade into strongly
altered rocks, which are affected by hydrothermal, oreforming solutions along upper terminations of these
stocks. There is thus an intimate relationship of magma
emplacement to ore forming processes. These stocks and
veins are in part subparallel to regional faults.
Fifteen samples of unaltered mafic (A’gyi) and granodioritic (Hulugou, Dashui, Zaozigou) dykes and stocks
from four deposits have been selected for geochemical
analysis of major, minor, and trace elements (Table 1).
These rocks can be divided into Group 1 (found only at
A’gyi), with 50 to 54.2 wt% SiO2, and Group 2 (Hulugou,
Dashui, Zaozigou), with 61 to 74 wt% SiO2. High contents
of K2O and low contents of Nb and Fe2O3* (Table 1) indicate that these rocks are calcalkaline, of subduction-related magmatism (e.g. Tarney and Jones 1994). Rare earth
elements show pronounced La/Yb ratios and moderate
negative Eu anomalies that are typical of calcalkaline
magmatism (e.g. Tarney and Jones 1994; Fig. 2). Unaltered
Group 1 and some Group 2 rocks have elevated metal contents (e.g. As, Cr, V, and Pb; Table 1) underling a possible
relationship with ore deposit formation.
Two samples were selected for preliminary U-Pb singlegrain zircon analysis. Sample LM34 is a diorite from A’gyi
deposit. A single zircon grain yielded a concordant data
point with an age of ca. 219 Ma. Two further grains are
slightly discordant at ca. 210 and 214 Ma. Calculation of a
preliminary discordia yields an age of ca. 220 Ma, which
is suggested to represent a geologically significant age of
zircon crystallization and magma emplacement, respectively. Two zircons of sample LM39 from the Dashui deposit are also slightly discordant and yield a similar intercept age of ca. 220 Ma.
Close
Chapter 11-9 · Constraints on the formation of Carlin-type gold deposits in Sichuan and Gansu provinces, China
4
1253
Fluid composition
Phase transition in fluid inclusions was measured
using a Linkam THM-600 heating/freezing stage according to the procedure described in Shephard et al. (1985)
and Roedder (1988). Salinities were recalculated using
the computer program FLINCALC (Cavaretta and Tecce
1995).
Calcite-hosted fluid inclusions irregularly distributed
within mineral have negative crystals or irregular, treedimensional shapes. All measured inclusions are composed of an aqueous liquid and 5–15 vol.% vapour, and
may reach up to 100 µm in diameter.
Temperatures of initial melting between -44 and -37
°C indicate the presence of bivalent cations Mg2+ or Ca2+
in addition to Na (Davis et al., 1990). Hydrohalite melts
range from -25 to -21°C and correspond to NaCl/
(NaCl+CaCl2) ratio of 0.75 to 1. Recalculated salinities,
using final ice melting temperatures in the range from 2.3 to -0.8°C, are generally uniform and low, from 1.4 to
3.9 wt.% NaCl-equivalent. Homogenization temperatures
range from 134 to 211°C. There is a homogenization vs.
salinity trend that could indicate boiling conditions under pressure not higher than 20 bars (Fig. 3), but further
measurements are needed to support this suggestion.
The chemical composition of solutes (Table 2) was determined using a Dionex DX-500 system by the technique
modified after Bottrel et al. (1988). Geothermometers were
calculated using equations according to Can (2002),
Fournier and Truesdell (1973) and Giggenbach (1988).
Increased concentration of NaCl along with MgCl2, KCl
and CaCl2 are consistent with lowering of eutectic temperatures. However, much of the CaCl2 is due to dissolution of calcite during the crushing procedure, and should
be neglected. Na/K and K2/Mg geothermometers gave temperatures from 177 to 280 °C, which are compatible with
the homogenization temperatures.
Calcite precipitated from boiling(?), low-salinity fluids of up to 300 °C, consisting of Na+, Mg2+, K+ and Ca2+.
5
Discussion
Our new field data suggest that formation of these Carlintype deposits is related to late-orogenic, calc-alkaline
magmatism, including rare mafic and dioritic dykes and
widespread granodiorites. The latter type is common in
other Carlin-type deposits of the region (Hu et al. 2002;
own observations). Results from two preliminary U-Pb
single-zircon analyses disagree with previous work (although seemingly no rocks from A’gyi and Dashui deposits were dated yet) and suggest an age of ca. 220 Ma
for magmatism at A’gyi and Dashui deposits. Magma
emplacement was likely related to regional deformation
on the southern margin of the Qinling orogenic belt (e.g.
Yin and Harrison 2000; Tapponnier et al. 2001) as well as
with ore deposit formation. Calcite associated with ores
precipitated from low salinity-high/temperature fluids
of uniform composition, dominated by Na+ over Mg2+,
K + and Ca2+, plausibly under boiling conditions.
Close
1254
F. Neubauer · S. Borojevic-Sostaric · A. von Quadt · I. Peytcheva · G. Friedl · J. Genser · Z. Zeng
Acknowledgements
We appreciate review by A. R. Cabral and suggestions by
G. Beaudoin. We acknowledge support by the National
Natural Science Foundation of China and the Ministry of
Land and Resources of China, which allowed field work
during 2001. We also acknowledge Sichuan Bureau of
Geology and Resources and Gansu Institute of Geological Survey, which helped us during the field trip.
References
Bottrel SH, Yardley B, Buckley F (1988) A modified crush–leach
method for the analysis of fluid inclusion electrolytes. Bulletin
de Mineralogie 111: 279–290
Can I (2002) A new improved Na/K geothermometer by artificial
neural networks. Geothermics 31: 751–760
Cavarretta G, Tecce F (1995) FLINCS and FLINCALC: PC programs
for fluid inclusion calculations. Computers and Geosciences 21:
715–717
Davis DW, Lowenstein TK, Spencer RJ (1990) Melting behavior of
fluid inclusions in laboratory-grown halite crystals in the systems NaCl-H2O, NaCl-KCl-H2O, NaCl-MgCl2-H2O, and NaClCaCl2-H2O. Geochimica et Cosmochimica Acta 54: 591–601
Fournier RO, Truesdell AH (1973) An empirical Na-K-Ca geothermometer for natural waters. Geochimica et Cosmochimica Acta 37:
1255–1275
Giggenbach WF (1988) Geothermal solute equilibria. Derivation of
Na-K-Mg-Ca geoindicators. Geochimica et Cosmochimica Acta
52: 2749–2765
Gu XX, Liu JM, Schulz O, Vavtar F, Zheng MH (2003) Syngenetic origin
for the sediment-hosted disseminated gold deposits in NW Sichuan,
China: ore fabric evidence. Ore Geology Reviews 22: 91–116
Hu RZ, Su WC, Bi XW, Tu GZ, Hofstra AH (2002) Geology and
geochemistry of Carlin-type gold deposits in China. Mineralium
Deposita 37: 378–392
Liu J, Zheng M, Liu J, Gu X. Zhou Y, Feng C (2003) Mechanical transport of metallogenic materials in endogenic hydrothermal solutions: evidence from the microspherules in micro-disseminated gold deposits, northwestern Sichuan, China. Ore Geology Reviews 22: 1–16
Mao J, Goldfarb RJ, Zhang Z, Xu W, Qiu Y, Deng J (2002) Gold deposits in the Xiaoqinling-Xiong´ershan region, Qinling Mountains,
central China. Mineralium Deposita 37: 306–325
Mao J, Qiu Y, Goldfarb RJ, Zhang Z, Garwin S, Fengshou R (2002)
Geology, distribution, and classification of gold deposits in the
western Qinling belt, central China. Mineralium Deposita 37:
352–377
Roedder E (1984) Fluid inclusions. Mineralogical Society of America
Reviews in Mineralogy 12: 644
Shepherd T, Rankin AH, Alderton DHM (1985) A practical guide to
fluid inclusion studies. Blackie, 239 p
Tapponnier P, Xu Z, Roger F, Meyer B, Arnaud N, Wittlinger G, Yang J
(2001) Oblique stepwise rise and growth of the Tibet Plateau.
Science 294: 1671–1677
Tarney J, Jones CE (1994) Trace element geochemistry of orogenic
igneous rocks and crustal growth models. Journal of the Geological Society 151: 313–345
Yin A, Harrison TM (2000) Geologic Evolution of the HimalayanTibetan Orogen. Annual Reviews of Earth and Planetary Sciences
28: 211–280
Zeng Z, Hu Y, Zhou J, Liu L, Fan C, Yang W (2001a) Relationship between decollement-extrusion tectonics and gold deposits in adjoining area of Sichuan, Gansu and Shaanxi provinces. Earth Sciences–Journal of China University of Geosciences 26: 631–637
(in Chinese with an English abstract)
Zeng Z, Zhou J, Liu L, Hu Y, Fan C, Yang W (2001b) Prediction of
perspective districts of gold mineralization using MAPGIS in the
adjacent area of Sichuan, Gansu and Shaanxi Provinces. Earth
Sciences Frontiers 8: 415–420 (in Chinese with an English abstract)
Zhou T, Goldfarb RJ, Phillips GN (2002) Tectonics and distribution
of gold deposits in China – an overview. Mineralium Deposita
37: 249–282
Close
Chapter 11-10
11-10
The Xiongcun Cu-Zn-Au deposit in the western segment
of the Gangdese, Tibet: A Mesozoic VHMS-type deposit
cut by late veins
Kezhang Qin, Guangming Li, Jinxiang Li, Kuishou Ding, Yihan Xie
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,
China
Abstract. The Xiongcun Cu-Zn-Au deposit lies in the western segment of the Gangdese porphyry copper belt and in the forearc basin of the Southern Gangdese volcanic arc. The deposit is hosted
by Cretaceous marine intermediate and basic volcanic clastic rocks
that filled a supra-subduction forearc basin. The mineralized alteration zone is 2 km in length and varies in width from 100 m to
400 m with an average of about 200 m. The mineralized horizon is
divided into a lower stringer mineralization and upper massive, submassive and banded mineralization. Laminated and banded mineralization lies in the hanging wall. Weak sulfidation is documented
in the footwall. In addition, some late veins and lenticular sulfide bodies
cut the early formed sulfide horizons. The most prospective ore bodies are developed in the upper mineralization horizon. Alteration is
zoned with distal propylitization and proximal silicification,
sericitization ± chrolitization in the ore body. Fluid inclusion analysis,
sulphur isotopes, and trace elements of sulfides reveal that the deposit has the similar features compared with ancient volcanic-hosted
massive sulfide deposits (VHMS) and modern active chimney. Based
on these characteristics, we propose the deposit is a deformed VHMStype deposit that formed in the forearc of the Gangdese volcanomagmatic arc during Mesozoic subduction. Second stage veins, inferred to form during collision between the India subcontinent and
Eurasia cut the VHMS deposit prior to or simultaneous with intrusion
of a post-mineral Himalayan-age diorite porphyries.
Key words. Tibet, Xiongcun, Cu-Zn-Au deposit, Cretaceous, VHMStype
1
mesothermal Cu-Au deposit has also been proposed (J. Lang
2005, oral communication). We propose that the salient characteristics of the deposit (summarized below) are dominantly those of a VHMS type Cu-Zn-Au deposits. These
features are of the metallogenetical and geological setting,
lithology on ore-hosting rocks, mineralization styles and
zonation, structure and texture of ores, fluid inclusions, trace
elements of sulfides and sulphur isotope. It was locally overlapped by second-stage auriferous quartz-veins.
2
Geological setting
The Xiongcun Cu-Zn-Au deposit lies in the western segment of the Gangdese porphyry copper belt and in the
forearc basin of the Southern Gangdese volcanic arc.The
ore bodies are hosted by Cretaceous marine intermediate
and mafic pyroclastic rocks, which are intruded by biotite
granite (42Ma, K-Ar age of biotite), a dioritic porphyry stock
of presumed Himalayan age, and late dykes such as lamprophyre, felsic porphyry and diabase. In the district, NNWstriking faults and folds dominate and controlled the distribution of intrusions and mineralized zones. Late NE-striking faults cutting the mineralized zone are filled by lamprophyre dykes.
Introduction
3
Xiongcun Cu-Zn-Au deposit, located in 60 km west of
Xigaze City (Tibet) and 3 km north of the Yarlung Zangbo
River, was found by No. 6 Geological Team of the Tibetan
Geological Bureau. Preliminary prospecting suggested 3 Mt
of copper extractable from ores averaging 1.05% Cu in exploration adit and 0.51% in drill core. A resource of 100 t of
gold is inferred in ores averaging 0.49 ppm in the exploration adit and 0.57 ppm in drill core. Limited exploration of
the Cu-Zn-Au orebody has hindered the assignment of the
sulfide accumulations to a genetic class. Four genetic models have been proposed. A spatial relationship between distal dioritic _orphyries and the mineralization has led to a
model that the deposit belongs to porphyry-epithermal CuAu deposit (Qu 2004, oral communication). In contrast, the
silicification and sericitzation has formed the basis for a
model that the prospect is a high-sulfidation epithermal
Cu-Au deposit (Hou, 2004, oral communication). A
Mineralization and alteration
The Xiongcun Cu-Zn-Au deposit is about 2 km long and
100 to 400m wide with an average width of about 200m.
The mineralized zone strikes 310° and dips 40° to the NE.
Our observation shows that the mineralized horizon consists of a lower stringer mineralization and an upper massive, sub-massive and banded mineralization. Laminated
and banded mineralization lie in the hanging wall. Weak
sulfidiation and strong silicification lies in the foot wall.
The most economic ore bodies are developed in the upper
mineralization horizon.
3.1 Foot wall
Weak sulfidiation and strong silicification form the footwall. Up to now, the vertical extension of this part is not
controlled completely.
Close
1256
Kezhang Qin · Guangming Li · Jinxiang Li · Kuishou Ding · Yihan Xie
3.2 Lower mineralization horizon
Host volcanic breccia tuff and crystal-lithic tuff are cut
by stringer with lesser stockwork and disseminated
sulfide. Ore minerals are pyrite, chalcopyrite, minor
sphalerite and galena. Sulfide contents ranges from 10%
to 20%. Alteration of wall rocks is characterized by strong
silicification and weak alteration by chlorite and sericite.
Crystal fragments of biotite and hornblende are replaced
by chlorite and magnetite. In this horizon, copper mineralization is dominant over 100m in thickness. Average
grade of copper, gold and silver are 0.39 wt%, 1.15 ppm,
8.25 ppm (ZK701, Honglu Limit Co. 2004, unpubl.), respectively.
4
Fluid inclusion, trace elements of sulphides and
sulphur isotope of the deposit
Laminated and banded mineralization lie in tuffaceous siltstone in the hanging wall. The sulfide horizon is over 100m in thickness. Lamina and band in the
ores are composed of pyrite, pyrrhotite, minor sphalerite, chalcopyrite, magnetite and marcasite. Magnetite
and pyrrhotite are enriched in the hanging wall compared to other zones in the prospect. Wall rocks are mainly
silicified.
Of the 72 samples collected from the different mineralization styles 18 samples were selected for studies of fluid
inclusions, sulphur isotope and trace elements of sulphides.
Fluid inclusions were analyzed from different samples to
resolve differences in fluid temperature and salinity. Micro-thermometry shows intermediate to low temperature
and low-salinity features for all samples. The dominant
inclusion type in the massive ores is composed of two
phases, being about 5% to 10% vapor and 90% to 95%
liquid at room temperature. Homogenization temperatures vary from 135°C to 196°C with average at 168°C.
Salinities have been recorded between 1.5 and 13.5 wt.%
NaCl equivalent. Minor halite-bearing inclusions with
variable sized halite crystals were found in the stringer
and disseminated ores, and their homogenization temperatures and salinities range from 150 to 290°C and from
21 to 36.5 wt.% NaCl equivalent, respectively. Pyrite,
sphalerite and chalcopyrite from different mineralization
styles have δ34S values between 0 and 1.4‰. Locally however, a pyrite from stringer mineralization had a δ34S (CDT)
of -5.9‰, which likely reflects influence of reduced sulphur derived from seawater sulfate. Analyses show that
cobalt and nickel have lower abundance in pyrite from
massive ore (Co - 10.4-50.5 ppm, Ni - 6.4-21.4 ppm) than
in pyrite from stringer and disseminated ores (Co: 29337 ppm, Ni: 8.69 ppm). The content of Co and Ni in pyrite from this deposit is much less than that from typical
porphyry copper deposits (Rui et al. 1984; Wang et al. 1994).
Co/Ni ratio from different ores ranges from 0.25 to 7.89
with average 3 and Se/Te ratio shows increasing trend
downwards. In pyrite from massive ore, Se has lower abundance than in pyrite from stringer ore, which is similar
to that of Kidd Creek VHMS deposit and modern massive sulfide deposits (Cabri et al. 1985; Auclair et al. 1987).
Gold and silver in sphalerite are 1.33 ppm and 20.5 to
67.5 ppm respectively, implying that they were concentrated in initial mineralization process.
3.5 Crosscutting younger veins
5
In the ores, sulfides are mostly intermediate to coarse
grains, and have been recrystallized. Early massive ores
are brecciated, and cut by large quartz-sulfide veins from
several meters to several tens of meters in length and several tens of centimeters in width. The late en-echelon lodes
are lenticular in plan view or are veins. The veins mineral
assemblage is pyrite, sphalerite, pyrrhotite, chalcopyrite
and quartz. Sulfides in veins are coarsre grained, but their
content is less than 5%. These veins indicate a second generation of sulfide deposition due to late metamorphism
or intrusion of diorite.
5.1 Tectonic setting
3.3 Upper mineralization horizon
Crystal-lithic tuff and tuffaceous siltstone. host massive,
sub-massive, disseminated and banded sulfide minerals.
Ore minerals consist of pyrite, chalcopyrite, sphalerite and
subordinate pyrrhotite, magnetite, native copper and galena. The horizon is estimated to be 150-200 m in thickness. Alteration of wall rocks is characterized by pervasive silicification, chloritization and minor sericitization.
Chlorite is intergrown with pyrite. Hydrothermal actinolite and tremolite are locally present. Copper, gold, silver
and zinc grades in the sulfide horizons in exploration adits
and ZK701 drill hole average 1.82 wt.%, 2.37 ppm, 28.4
ppm, 2.3 wt.%, respectively.
3.4 Hanging wall
Discussion and conclusion
Tethys was subducted northward during early and middle
Cretaceous at southern margin of the Tibetan Gangdese
magmatic arc (Yin and Harrison 2000), resulting in the
development of a forearc basin in the Xigaze region (Durr
1996; Hao et al. 1999). Accompanying Cretaceous subduction, volcanic beds hosting sulfide ore bodies filled
the basin. Although extensional tectonics, felsic and bimodal volcanism, and back-arc mineralization are inferred for many massive sulfide deposits (Sawkins, 1990;
Close
Chapter 11-10 · The Xiongcun Cu-Zn-Au deposit in the western segment of the Gangdese, Tibet: A Mesozoic VHMS-type deposit cut by late veins
Gemmell, 1995), gold-rich Cu-Zn VHMS deposits are typical in forearc and oceanic arc settings (Wang et al, 1994;
Qin et al., 2002). Several examples have been discovered
recently at modern ocean floor (Izasa 1999; Petersen et
al. 2002).
5.2 Characteristics of ore-forming fluids and mineralizated
metals source
Results of microthermometry study of fluid inclusions
show relatively wider range of temperatures and salinities, and indicate that ore-forming fluids were generated
by heated seawater. Magmatic fluids from the late diorite
porphyry likely contributed to the ore-forming fluids, but
these were only involved in reworking of the sulfide minerals. Sulphur isotope analyses suggest that sulphur is
mostly igneous in origin, and partly from reduced sulphur derived from seawater sulfate. Variation of S isotope values in the deposit is greater than that in the
Gangdese porphyry copper belt (+0.4 to +1.4‰ for
Tinggong and Bairong porphyry copper deposits, unpublished data from this study). Furthermore, S isotope values of the deposit differ from typical skarn copper deposit in Eastern segment of the Gangdese (+1.3~ -3.8‰;
unpublished data from this study) (Li et al. 2005, this volume). In the same sample from massive ore, pyrite,
sphalerite, and chalcopyrite are in S isotope equilibrium
with FeS2>ZnS>CuFeS2, In contrast, the same sulfide minerals from stringer ore are not in S isotopic equilibrium,
reflecting a different S isotope fractionation in the lower
feeder zone than in the upper volcanic and mineralized
zone. The S isotope signature is similar to gold-rich VHMStype Cu-Zn deposits (Prokin and Buslaev, 1999).
5.3 Comparison to deposit types
The Xiongcun deposit has several features that distinguish
it from typical porphyry copper deposits as well as typical high-sulfidation epithermal Cu-Au deposits. These are:
(1) dioritic porphyrite intrusion in volcanic beds is not
mineralized, but display propylitic alterationy; (2) typical K-feldspar-biotite alteration zone of porphyry copper deposits is not recognized; and (3) the main ore body
is stratiform and lenticular in form with a thickness of
200m, and is composed of massive, banded, disseminated,
siliceous stringer, veins type ores. Contents of sulfides
range from 10 to 50 wt%.
The geological setting of the deposit, mineralization
style, alteration, S isotope analyses, trace elements of sulfide, element assemblage and characteristics of fluid inclusions, are most consistent with the deposit being a
VHMS- type deposits, having some similarity to the Jurassic Eskay Creek Au-Ag-Cu-Zn VHMS deposit in western Canada (Mortensen et al. 2004).
1257
The two different mineralization styles at Xiongcun are
spatially related with the massive ore in the upper part of
the ore horizon and the stringer ore is in the lower horizon.
Texture and structure of primary ores reveal that there is
no clear replacement relation among sulfides, and pyrite,
chalcopyrite and sphalerite occur in both massive ore and
stringer ore. Electrum forms inclusion in idiomorphic cubic pyrite, indicating that initial deposition of sulfide was
gold-rich. Wall rock alteration is zoned from distal propylitization to proximal weak silicification, sericitization± chrolitization and strong silicification, chrolitization ±sericitization
within ore body. It is similar to the zoning of gold-rich CuZn VHMS deposits (Large et al. 2001). Quartz-sulfide veins
(about tens meters wide and several meters to tens of meters
long) cut the massive ores and disseminated ores and suggest a second mineralizing event due to the late regional
metamorphism or intrusion of diorite.
It is proposed that the deposit belongs to VHMS-type
deposit, located in the forearc basin of the Gangdese volcano-magmatic arc associated with Mesozoic subduction.
We further proposed that a second sulfide deposition event
formed during the Himalayan collision between India and
Eurasia. These features are similar to Mt Morgan Au–Cu,
Australia and Eskay Creek, Canada (Ulrich et al. 2002;
Mortensen et al. 2004).
Acknowledgements
This study was supported by the Major State Basic Research Program of China (No.2002CB412605). We would
like to thank No. 6 Geological Team of Tibetan Geological Bureau and Honglu Limited Co. for providing access
to the field area. We would like to express our gratitude
to Drs. R.M. Tosdal and G. Beaudoin for their through
review to improve this contribution.
References
Auclair G, Fouquet YBohn M (1987) Distribution of selenium in hightemperature hydrothermal sulfide deposits at 13°C north, East
Pacific Rise. Canadian Mineralogist 25: 577-587
Cabri LJ, Campbell JL, Laflamme J HG. Leigh RG Maxwell J A and
Scott J D (1985) Proton-microprobe analysis of trace elements in
sulfides from some massive-sulfide deposits. Canadian Mineralogist 23:133-148.
Davison J (2001) The spectrum of Ore Deposit types, volcanic environments, alteration halos, and related exploration vectors in
Submarine volcanic successions: some examples from Australia,
Econ. Geol. 96: 913-938
Durr S B (1996) Provenance of Xigaze fore-arc basin clastic rocks
(Cretaceous, south Tibet). Geol. Soc. Am. Bull. 108:669–84
Gemmell, J B (1995) Comparison of volcanic-hosted massive sulphide
deposits in modern and ancient back-arc basins; examples from
the Southwest Pacific and Australia. In: Mauk, L., George, J.D.S.
(Eds.), Proceedings of the 1995 PACRIM Congress; Exploring the
Rim. Australasian Institute of Mining and Metallurgy,Parkville,
Victoria, Australia, 227– 232
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Kezhang Qin · Guangming Li · Jinxiang Li · Kuishou Ding · Yihan Xie
Hao J, Chai YC, Li JL (1999) Original tectonical setting of the Tsangpo
ophiolite and sedimentary evolution of the Xigaze forearc basin.
Scientia Geologica Sinica 34(1): 1-9
Izasa K, Yuasa M, Yokota S (1992) A Kuroko-type polymetallic sulfide deposits in a submarine silica caldera. Science 283: 975-977
Large Ross R, McPhie Jocelyn, Gemmell J Bruce, Herrmann Walter,
and Sawkins FJ (1990) Integrated tectonic– genetic model for volcanic-hosted massive sulfide deposits. Geology 18 (11), 1061–1064.
Mortensen, J.K, Gordee, S.M., Mahoney, J.B. and Tosdal, RM (2004) Regional studies of Eskay creek-type and other volcanogenic massive sulfide mineralization in the upper Hazelton group in Stikinia: preliminary results. B.C. Ministry of Engergy, Mines, and Petroleum
Resources, Geological Fieldwork 2003, Paper 2004-24, 249-262.
Petersen Sven, Herzig Peter M, Hannington Mark D, Jonasson Ian R,
and Arribas Antonio, Jr (2002) Submarine Gold Mineralization
near Lihir Island, New Ireland Fore-Arc, Papua New Guinea. Economic Geology 97: 1795-1813
Prokin V A , Buslaev F.P (1999) Massive copper–zinc sulphide deposits in the Urals. Ore Geology Reviews 14: 1–69
Qin KZ, Sun S, Li JL, Xiao WJ, Hao J (2002) Division of six tectonic
stages for Paleozoic ore deposit association in Northern Xinjiang
and its significance. Mineral deposits 21(Supp): 203-206
Rui ZY, Huang CK, Qi GM, Xu Y, Zhang HT (1984) Porphyry Copper
(Molybendum) Deposits in China. Geological Publishing House,
Beijing, 300
Ulrich T, Goldinga S D, Kamberb B S , Khin Zawc, Taube A (2002)
Different mineralization styles in a volcanic-hosted ore deposit:
the fluid and isotopic signatures of the Mt Morgan Au–Cu deposit, Australia. Ore Geology Reviews 22: 61–90
Wang Zihitian, Qin kezhang, Zhang Shulin (1994) Geology and Exploration for Large Copper Deposits. Meatllurgical Industry Press,
Beijing, 162. (in Chinese with English abstract)
Yin A, Harrison T Mark (2000) Geologic evolution of the Himalayan
Tibetan orogen. Annu. Rev. Earth Planet. Sci. 28:211–280
Close
Chapter 11-11
11-11
Geodynamic relationships between large-scale
copper mineralization and rapid crustal uplifting in
the Gangdese collisional orogen, southern Tibet
Qu Xiaoming, Hou Zengqian, Xu Wenyi
Institute of Mineral Resources, Chinese Academy of Geosciencs Beijing 100037, China
Abstract. The latest zircon U-Pb SHRIMP dating of two ore-bearing
porphyry samples from the Chongjiang and Nanmu Co-Mo deposits in the Gangdese porphyry copper belt yields ages of 14.0 Ma
and 15.36 Ma. These ages are consistent with molybdenite Re-Os
ore-forming ages of 13.99 Ma and 14.67 Ma. These geochronological results also reveal that ore-forming process of the Gangdese
copper belt occurred simultaneously with rapid crustal uplifting of
the Gangdese orogen inferred by previous researchers. Studies have
demonstrated that these ore-bearing porphyries have geochemical characteristics of adakite. Nd, Sr, and Pb isotopic data in this study
further indicate that these porphyries formed from partial melting
of subducted ocean-crust slabs under eclogite-facies metamorphic
conditions and contain minor amount of subducted sediments
mixed in the magma source. The temporal overlapping of ore-forming process and rapid crustal uplifting in the Gangdese orogen was
not accidental and instead reflects a geodynamically linked relationship. Generation and extraction of the ore-bearing adakitic
magma caused further increase in density of the residual eclogitic
slabs, which, in turn, forced them to delaminate and asthenospheric
upwelling at higher velocities. Conversely, extentional tectonic environment brought about by asthenospheric upwelling provided
necessary conditions for up-intrusion of the ore-bearing magma
and concentration of ore-forming metals.
Key words. Geodynamic relationship, copper mineralization, crustal
uplifting, Gangdese orogen, southern Tibet plateau
1
Introduction
Studies and investigations undertaken by Chinese geologists in the past several years have confirmed that a prospective porphyry copper belt occurs along the Gangdese
magmatic arc on the south margin of Lhasa Terrane inside
the Tibetan plateau (Fig. 1; Qu et al. 2001, 2005). The
Gangdese magmatic arc mainly consists of late Palaeoceneearly Eocene volcanic rocks and Cretaceous-Tertiary granite batholiths (Allegre et al., 1984). The ore-bearing porphyries were emplaced in a post-collisional environment
of Miocene and display temporal overlapping with rapid
crustal uplifting of the Gangdese orogen inferred by some
researchers (Harrison et al.,1995; Coleman et al., 1995; Williams et al. 2001). Based on the latest zircon U-Pb SHRIMP
dating results and Nd, Pb isotopic data of the ore-bearing
porphyries, this paper assesses interaction mechanism between ore-forming process and rapid crustal uplifting of
the Gangdese orogen and gives some insight into the deep
geodynamic processes.
2
Zircon U-Pb SHRIMP dating
Samples for zircon U-Pb dating were collected from orebearing porphyries in the Chongjiang and Nanmu deposits. Zircon crystals commonly display euhedral to subhedral
forms with size of tens to hundreds µm. Magmatic, broad,
oscillatory and sector zoning is prevalent in most crystals.
Some crystals contain residual cores with bright or cloudy
zoned domains. U-Th-Pb analyses were performed using a
sensitive high-resolution ion microprobe (SHRIMP II). The
measured 206Pb/238U ratio was corrected using reference
zircon TEM (417Ma). Age calculations were done using the
software Ludwig SQUID1.0 and ISOPLOT. Results reveal
formation ages of 14.0 ± 0.6 Ma (MSWD=2.43) for the
Chongjiang deposit and 15.36 ± 0.56 Ma (MSWD=0.76) for
the Nanmu deposit (Fig. 2). These ages are highly consistent with their molybdenite Re-Os ages of 13.99 Ma and
14.76 Ma (Qu et al. 2005).
3
Pb, Nd, Sr isotope compositions
Nd, Sr, and Pb isotopic analyses of the Gangdese porphyry
copper belt were obtained for 6 deposits: Jiama, Lakang’e,
Nanmu, Tinggong, Chongjiang, and Dongga (Fig. 1). Pb
isotope compositions become more radiogenic along the
copper belt from west to east and constitutes a mixing
line between Indian Ocean MORB and Indian Ocean sediment end members (see Qu et al. 2005).
Nd and Sr isotopic analysis was carried out using MAT261 solid isotopic mass spectrometer at the Isotope Unit
of Institute of Geology, CAGS. Nd isotopic ratios were
corrected for mass bias using 146Nd/144Nd=0.7219. Sr isotopic ratios were corrected for mass bias using 88Sr/86Sr
=8.37521. Nd and Sr isotopic compositions of the orebearing porphyries in the Gangdese copper belt are plotted in Figure 3. Their Sr isotopic compositions have a very
small range (87Sr/86Sr = 0.704636 ~ 0.707920). Furthermore, a spatially regular variation exists, in which Jiama
and Dongga deposits at the east and west ends of the copper belt display the highest (0.707358~0.707920, average
is 0.707625) and lowest (0.704635~0.705517, average is
0.705076) 87Sr/86Sr ratios, respectively. The deposits located in the middle portion of the copper belt also have
87Sr/86Sr ratios inside the above range. Compared with Sr
Close
1260
Qu Xiaoming · Hou Zengqian · Xu Wenyi
isotopic compositions, Nd isotopic compositions display
much larger variation with 143Nd/144Nd ratios ranging from
0.502313 ~ 0.512931. Conversely, the Jiama and Dongga
deposits have the lowest (0.512313~0.512559, average is
0.512461) and highest (0.512897~0.412931, average is
0.512914) 143Nd/144Nd values. Thus, they constitute a
marked negative covariation array in the 143Nd/144Nd ~
143
Nd/144Nd diagram (Fig. 3). In Fig. 4 these adakitic orebearing porphyries display notable difference with the
adakite formed completely from subducted oceanic slab
melting, and also plot much above the Archean and Proterozoic crustal evolution lines. Like Pb isotope, Nd and
Sr isotopic compositions also suggest a source mixing signature (Fig. 3), whose two mixing end members are Indian Ocean MORB and Indian Ocean sediments.
4
Geodynamic relationship of copper
mineralization with crustal uplifting
Geochemical study shows that the ore-bearing porphyries of the Gangdese copper belt share enrichment of
the LILE Rb, K, Th, U, Sr and Pb and depletion of the
HFSE Nb, Ta and Ti and the HREE Yb (Qu et al. 2004)
and possess the essential characteristics of adakite summarized by Defant and Drummond (1990). Pb, Nd and
Sr isotopic compositions demonstrate that they were
derived from partial melting of subducted oceanic crust
and adhered sediment after being transformed to eclogite
in the deep subduction zone and accompanied by a con-
siderable amount of residual garnet left in the magma
sources. The zircon U-Pb SHRIMP dating yields formation ages of about 16~14 Ma, which is almostly identical
to the copper mineralization age (14 Ma ± 1). Since the
large-scale continent-continent collision of the
Yaluzangbu River suture took place in early Eocene
(55~45 Ma), these porphyry and mineralization ages of
the Gangdese copper belt are equivalent to the post-collisional extensional stage of the Gangdese orogenic evolution. In the same time, according to Harrison et al.
(1992) and Coleman et al. (1995), the mineralization age
of the Gangdese copper belt also overlapped with rapid
crustal uplifting and/or the highest altitude reached in
the southern Tibet plateau. We consider that the overlapping relationship of the copper mineralization and
the rapid crustal uplifting in the Gangdese collisional
orogen were controlled by an inherent geodynamical
mechanism of collisional orogen evolution. Generation
and extraction of the adakitic ore-bearing magma from
the eclogitic oceanic slabs would cause a further increase
in density of the residual eclogitic slabs after the first
density increase resulted from eclogite facies metamorphism and force them to rapidly sink into the asthenosphere, which in turn resulted in more rapid upwelling of
asthenospheric material therefore causing rapid crustal
uplift. In return, the extensional environment brought
out by rapid crustal uplifting provided conditions for
intrusion of the ore-bearing magma and differentiation
and concentration of the ore-forming metals.
Close
Chapter 11-11 · Geodynamic relationships between large-scale copper mineralization and rapid crustal uplifting in the Gangdese collisional orogen, southern Tibet
1261
2. Zircon U-Pb SHRIMP dating yields formation age of
16~14 Ma for the ore-bearing porphyries, which are
consistent with Re-Os mineralization age (14 Ma ±) of
molybdenite from the Gangdese porphyry coppermolybdenium deposits. These dating results constraint
the ore-forming process in a post-collisional extensional stage of the Gangdese orogen evolution.
3. The temporal overlapping of the copper ore-forming
process and the rapid crustal uplifting in the Gangdese
collisional orogen reflects a mutual relationship inherent of a collisional orogenic belt. Generation of the
adakitic ore-bearing magma caused the residual eclogitic
slabs to rapidly sink into asthenosphere, which in turn
resulted in rapid upwelling of asthenospheric material
and the rapid crustal uplifting. In return, the extensional
environment brought out by rapid crustal uplifting provided conditions for intrusion of the ore-bearing
magma and differentiation and concentration of the
ore-forming metals.
References
Allegre C.J. and 34 others (1984) Nature 307: 17-22
5
Conclusions
1. The ore-bearing porphyries of the Gangdese copper
belt possess the essential characteristics of adakite. Nd,
Sr, and Pb isotopic compositions reveal that they originated mainly from partial melting of subducted Indian Ocean crustal slabs under eclogite-facies metamorphic condition and were mixed with minor amount
of subducted sediment in the magma source.
Coleman M., Hodges K. (1995) Nature 374: 49-52
Defant MJ, Drummond M.S. (1990) 347: 662–665
Harrison T.M., Copeland P., Kidd W.S.F., Yin A. (1992) Science
255: 1663-1670
Qu XM, Hou ZQ, Huang W (2001) Mineral Deposits 20: 355-366
(in Chinese)
Qu XM, Hou ZQ, Li YG, (2004) Lithos 74: 131-148
Qu XM, Hou ZQ, Khin Z, Li YG( 2005) Ore Geology Review. (in
press)
Williams H, Turner S, Kelley S, Harris N. (20001) Geology 29:
339–342
Close
Close
Chapter 11-12
11-12
Porphyry copper belts in Tibet
Z.-Y. Rui, L.-S. Wang
Institute of Mineral Resources, CAGS, 26, Baiwanzhuang Rd, Bejing 100037, China
L.-S. Zhang
Chengdu Institute of Geology and Mineral Resources, CGS, New 82, North Section 3, Yihuan Rd, Chengdu 610082, China
Abstract. 3 prospective porphyry copper belts - Yulong, Gangdese,
and Bangon Co-Nujiang Belts - have been identified in Tibet. This
paper outlines the distribution, scale, prospectivity, ore-forming age
and genesis for these porphyry copper belts.
Keywords. Porphyry copper belt, Yulong, Gandese, Bangon CoNujiang, A-type subduction
1
Introduction
Three prospective porphyry copper belts - Yulong,
Gangdese, and Bangon Co-Nujiang Belts - have been discovered in Tibet. These porphyry copper belts formed by
porphyritic magmatism and metasomatism during the
Andean-type subduction of Indian continental crust with
Neotethyan oceanic crust beneath Eurasian continental
crust after closure of the Neotethys 65 Ma ago. The porphyries formed from mantle-derived deep subduction
granitic magma which originated from dehydration and
partial melting of eclogite. As a result of mixture (assimilation) of small amounts of crust-derived material,
this granitic magma was characterized by high fO2 (fO2
= 10-13~10-8 for the magmatic system, and fO2 = 10-22~10-12
for the hydrothermal system), high volatile component,
initial Sr isotopic ratios less than 0.708, depletion in high
field strength elements and enrichment in large ion incompatible elements.
2
Yulong porphyry copper belt
The Yulong porphyry copper belt was discovered and assessed from 1966 to 1977. It lies in east Tibet to the west
of the Jinsha River and extends northwestwards for more
than 800 km into Qinghai Province (Narigongma porphyry copper deposit) in northwest and into Yunnan Province (Xuejiping, Pulang, Machangqing, Jinping porphyry
copper deposits) to the southeast (Fig. 1).
The porphyry copper belt formed during the Himalayan (40~35 Ma) (Rui et al. 1984; Linag 2002) and IndoChinese epochs (213~235 Ma) (Zheng et al. 2004; Huang
et al. 2001). Several pull-apart basins associated with
emplacement of abyssal granitic magma formed in east
Tibet during the Paleogene where the Yulong, Zhalaga,
Mangzong, Duoxiasongduo and Malasongduo deposits
were formed (Fig. 1). In the Yidun region, accretion of
the Zongza block on the western margin resulted in the
formation of the Xuejiping (224.6 Ma) (Huang et al. 2001)
and Pulang (235.4~213 Ma) (Zheng et al. 2004) porphyry
copper deposits in the Middle and Late Triassic.
Alkanlinity of porphyry rock series which were formed
in the southeastern sector of the Yulong porphyry copper belt i.e. in northwest Yunnan in the Himalayan epoch
increases gradually. The porphyry Cu (Mo) mineralization became porphyry Cu (Au, Pb-Zn) mineralization with
increase in alkalinity.
Ore reserves of the Yulong porphyry Cu deposit are
estimated at about 107 t.
3
Gangdese porphyry copper belt
The Gangdese porphyry copper belt can be divided into
3 sectors from east (Nyingchi-Rinbung), central (RinbungSaga) to west (Saga-China-Nepal border; Fig. 1).
The east sector lies on both sides of Lhasa and has a
well-developed infrastructure.
The eastern sector extends for 800 km from east to
west and 120~200 km from south to north, where porphyry deposits are associated with skarn deposits and
epithermal deposits. The eastern sector is divided into 3
zones from south to north: south zone, central zone and
north zone.
Kelu and Chongmuda stratiform skarn Cu (Au) deposits occur in the south zone. The deposits are controlled
by a contact zone between hornblende granitite and volcanic-sedimentary rock of the Bima Formation of the
Upper Jurassic-Lower Cretaceous Sangri Group. Chuibaizi,
Qulong, Lakang’e, Dabu, Tinggong, Chongjiang and
Bairong porphyry Cu (Mo) deposits occur in the central
zone. The deposits are controlled by monzonite porphyry
and quartz monzonite porphyries. Locally, porphyry Cu
(Mo) mineralization, for example, in the Jiama and outside the Qulong Cu deposits, is superimposed on skarn
Cu-polymetallic mineralization. The Lawu, Leqingla and
Dongzhongsong skarn Pb-Zn-Ag deposits occur in the
north zone. The deposits are controlled by abyssal intermediate and acid granitoids. Metallic mineralization in
the eastern sector of the Gangdese porphyry copper belt
is characterized by a clear horizontal zonation with Cu
(Au) mineralization in the south zone -> Cu (Mo) mineralization in the central zone -> Pb-Zn-Ag mineralization
in the north zone. SHRIMP ages for ore-bearing porphyry
in the central zone range from 18 Ma to 13 Ma (Rui et al.
Close
1264
Z.-Y. Rui · L.-S. Wang · L.-S. Zhang
2003; Qu et al. 2001), Re-Os isochron ages for molybdenite in the central zone range from 20 Ma to 12 Ma (Rui et
al., 2003; Meng et al. 2003), and Ar-Ar ages and K-Ar ages
for skarn and epithermal Pb-Zn-Ag ores in the north zone
range from 64 Ma to 12 Ma. These ages correspond with
ages (60~42 Ma) of the Indian plate-Eurasian plate collision orogeny (65 Ma; Lee et al. 1995), age of the first phase
of the Himalayan orogeny (40~35 Ma) (Li 1995) and age
of the second phase of the Himalayan orogeny (20~12
Ma) (Li 1995), respectively.
Cu-polymetallic resource potentiality in the east sector of the Gandese porphyry copper belt is estimated at
more than 15x106 t by Wang and Wang (2002).
The middle (Central) sector which is 360 km long from
east to west and 80~220 km wide from south to north
contains porphyry (skarn)-epithermal (skarn) mineralization. Geological setting analysis shows higher level of
emplacement of granitic magmatic rock in closer relationship with volcanic rock, slighter acid-intermediate
porphyry and more perspective porphyry-epithermal Cu(Au) mineralization. Xiongcun-Dongkar-Puqinmu Cu(Au) orefield has been discovered in the middle sector.
The epithermal Cu-(Au) mineralization is confined to NWtrending fractured zones, extending for up to 6 km with
a width of 100~400 m. The mineralization resulted from
interaction of two ore fluids with a temperature of
110~360°C and a salinity of 5~23 and 27~38 wt% eq NaCl.
The Xiongcun granite yields K-Ar ages ranging from
56 ± 7 to 63.3 ± 2.5 Ma and Ar-Ar ages of 38.68 ± 0.76 for
hydro-muscovite. Obtained metal reserves in the Xiongcun
deposit are estimated at 3.12x106 t Cu (with ore grades of
0.65~1.39% Cu) and 253 t Au (with ore grades of
0.7~1.12 g/t Au). The Zhunuo porphyry copper deposit
with high grade ore at the surface has been discovered in
the middle sector. It is hosted in a granodiorite porphyry.
The underexplored west sector extends northwestwards
for about 600 km. The geological setting is similar to that
in the east sector with association of abyssal high-level
granitoids with abyssal medium-high-level granitoids favor of ore-formation of skarn-porphyry-epithermal deposits.
4
Bangong Co-Nujiang porphyry copper belt
The Duobzha porphyry copper deposits have been discovered in the northwest of Gêrzê in this porphyry copper belt (Fig. 1). According to reports by the China Land
and Resources Newspaper, the Duobzha porphyry copper deposit is a giant copper deposit with reserves of
about 15x106 t Cu. This belt joins up with the Tethyan
porphyry copper belt hosting the Sar Cheshmeh porphyry
copper deposit in Iran and the Saindak porphyry copper deposit in Pakistan. These occurrences are controlled
by granodiorite porphyries with mineralization ages of
50~20 Ma. Thus, it should be considered that the Bangong
Co-Nujiang porphyry copper belt has significant prospecting potential.
References
Lee TY, Lawver L.A. (1995) Cenozoic plate reconstruction of Southeast Asia. Tectonophysics 251 (1–4): 85–138
Li TD (1995) The uplifting process and mechanism of the QinghaiTibet plateau. Acta Geoscientica 34(1): 1–9
Liang HY (2002) New advances in the research on diagenetic mineralization of porphyry copper deposits in eastsouth margin of the
Qinghai-Xizang plateau. Mineral Deposits 21(4): 365
Close
Chapter 11-12 · Porphyry copper belts in Tibet
Huang CK, Bai Z, Zhu YS (2001) The copper deposits in China. Beijing.
Geol. Pub. House. 705
Meng Xj, Hou ZQ, Gao YF (2003) Re-Os dating for molybdenite from Qulong porphyry copper deposit in Gangdese metallogenic belt, Xizang
and its metallogenic significance. Geol. Review 49(6):660–666
Qu XM, Hou ZQ, Huang W (2001) Is Gangdese porphyry copper belt
the second “Yulong copper belt? Mineral Deposits 20(4): 355–366
Rui ZY, Huang CK, Qi GM (1984) Porphyry copper (molybdenum)
deposits of China. Beijing: Geol. Pub House. 350
1265
Rui Z, Hou ZQ, Q XM, et al. 2003. Metallogenetic epoch of Gangdese
porphyry copper belt and uplife of Qinghai-Tibet plateau. Mineral Deposits, 22(3): 217–225
Wang QH, Wang BS, Li JQ (2002) Basic features and ore prospect
evaluation of Gangdese island arc, Tibet, and its copper
polymetallic ore belt. Geol. Bulletin of China 21(1): 35–40
Zheng PS, Hou ZQ, Li LH (2004) Age of the Pulang porphyry copper
deposit in NW Yunnan and its geological significance. Geol. Bulletin of China 23(11): 1127–1131
Close
Close
Chapter 11-13
11-13
The evolution of epicontinental marginal
sedimentary basins of the Tethys Ocean in Asia
Vitaly I. Troitsky, Leyla P. Sharafutdinova
National University of Uzbekistan,700174, Vuzgorodok, Tashkent, Republic of Uzbekistan
Abstract. Two epochs of development stand out in the evolution of
epicontinental margin sedimentary basins of the Tethys in Asia. The
basic stages of sedimentation were accomplished through the influence of the Tethys Ocean and Alpine-Himalayan folding belts.
These processes developed simultaneously and confirm the correlation of eustatic sea transgression and regression, and climate
change. The study places particular emphasis on the sedimentary
basins of the Turan platform and Tien Shan orogen.
Keywords. Tethys, Pery-Tethys, Paratethys, epicontinental sedimentary basins, eustatic change of sea level, paleoclimate, sedimentary
deposits
1
Introduction
Study of geodynamic and paleogeographic connections
of the Tethys Ocean and the Alpine - Himalaya fold belt
with the epicontinental basins of Peritethys and Paratethys
and the Central Asian intercontinental orogenic basins
have important implications in addressing a number of
problems related to the geodynamics and evolution of
the Asian lithosphere plate. A geodynamic zonation reflects global processes of Gondwana and Eurasia convergence and the origin of microplates and blocks along their
boundaries.
Geodynamic and paleogeographic reconstructions
include the study of the geodynamic regime, paleomagnetic co-ordinates, eustatic and regional transgressions,
climatic change, and magmatism. Analysis of composition, absolute masses of sedimentary formations and speed
of sedimentation (m / Ma) of terrigenous, authigenetic
and biogenetic parts of sedimentary series make it possible to reconstruct mechanical differentiation, changes
in the geochemical situation, and the biological productivity of different types of sedimentary basins. They are
represented by the basins of the Tethys Ocean (spreading
zone), the Tethys continental margins (continental slope,
microcontinent, volcanic arc, rift and suboceanic basin),
the Peritethys and Paratethys epicontinental seas with terrigenous, carbonate, evaporite, silicilite rocks, the plain
alluvium and deltas of the Turan platform and the Central Asia orogenic belt piedmond and inter montane depressions (eluvium, proluvium, river fans and lakes).
Mezozoic and Cenozoic sedimentary basins of Central Asia had steady geodynamic and paleogeographic
connections with the Tethys Ocean and the Alpine - Himalayan fold belt. In the West, deformation associated
with the closure of the Tethys Ocean was realized inside
the belt and did not spread into the Turan platform. In
the East, the compression stipulated collision of the Tethys
continental margins and the Cenozoic orogeny in Central Asia. Therefore, relations between the Indian plate,
the Pamir - Karakoram and the Tien Shan are key to many
problems related to the development of Central Asian intercontinental sedimentary basins.
Zonel ammonites, foraminifers and nannofossils from
supporting sections (Pamir, Elburs, Kopetdag, Big Balkan,
Hissar) and dating assemblages of ecostratigraphic complexes (marine and fresh-water mollusks and ostracods,
fossilplants and others) compose a reliable biostratigraphic basis for a regional stratigraphic scale of Mezozoic
and Paleogene sedimentary basins of Central and Southern Asia. The Neogene and Quaternary stratigraphy is
based on assemblages of the Parathetys and paleomagnetic data.
The sections have are cyclic and reflect both development stages and basins zonation and manifestation of
geological events - geodynamic regime, climate change
of the alternation and transgressions and regressions of
the Peritethys and Paratethys epicontinental basins in
Central Asia.
Epicontinental seas of the Tethys Ocean covered Central Asia about 14 times in Mezozoic and Paleogene. Every such cycle included 3-4 smaller cycles. Mezozoic and
Paleogene transgressions and regressions are correlated
with eustatic oscillation of the World Ocean level both in
general and in detail. Neogene and Quaternary cycling
was stipulated by changes in the Paratethys sea level.
The alteration of climatic conditions of sedimentation
(temperature, regime-tropic, subtropic, moderate, nival and
moisture - humid, semihumid, semiarid, arid and extra arid)
is also expressed in these cycles. Climate indication includes
the study of biofossils, authigenetic minerals, ogranic substance, Eh, pH, clay minerals, degree of rock polimiction,
rock’s colour, formation compositions and mineralization.
Climate evolution is represented by Rhetian - Bajocian, Late
Aptian-Early Albian humid, Late Bajocian-Bathonian,
Barremian-Early Aptian, Middle Albian-Cenomanian, Oligocene semihumid - semiarid, Callovian, ValanginianHauterivian, Turonian-Maastrichtian, Thanetian - Priabonian, Early Miocene, Late Miocene arid and OxfordianBerriassian, Hauterivian, Danian, Middle Miocene extraarid sedimentation conditions. Climate was colder at the
Close
1268
Vitaly I. Troitsky · Leyla P. Sharafutdinova
beginning of the Oligocene and acquired increased zonation in Neogene and Quternary.Formation of continental crust and lithosphere was completed in the beginning
of the Mezozoic. The lower part of lithosphere caused
gravitational balance between heterogeneous blocks of
consolidated continental crust and origin of the peneplain relief. Peneplain deformation marked the beginning
of the appearance of a new generation of Central Asia
sedimentary basins that were formed in conditions of
autonomic geodynamics. Thus, we have to pinpoint the
two main tectonic epochs.
The first epoch (Mezozoic - Paleogene) began with
drawing in riftogene microplates and blocks of the Asian
lithosphere. Asian deyteroorogens (intercontinental basins) and Turan platforms (region of general sinking)
formed in the Jurassic. During the Cretaceous the main
events in Central Asia included Neocomian repeating orogeny and alkali-basaltic volcanism, Late Cretaceous planation of rises and final formation of Turan platform and
Central Asian peneplain. The Paleogene was the beginning of the final closure of the Thethys Ocean. Meridi-
onal stress was transmitted into Central Asia. This stipulated the rebuilding of the Tadjik depression structure,
the orogen of Hissar and other virgations, basaltic volcanism and abundant pyroclastic material in the Tien Shan.
The second epoch (Late Cenozoic) was a period of complete rebuilding of the geodynamic regime. The modern
kinematic model reflects convergence of Alpine - Himalayn
belt with the Asian lithosphere. Neotectonic destruction
along faulting boundaries stipulated formation of Afghan Tadjik, Amu Darya, Karakum, Syr Darya, Northern Usturt
and other microplates. Microplates located to the East of
the Talas - Fergana strike-slip fault were formed in frontal
conditions. Geodynamics in the West of the fault was more
complicated (frequent change of strain vectors, different
combinations of folds, slips, upcasts, thrusts, underthrusts
and rotational deformations). All microplates were displaced
forming systems of diagonal slipping structures. The change
of paleopole vectors and altitudes of base - leveling flats,
composition and thickness of sedimentary formations, gradient of basement deformation, morphology of structures
and others bear witness to the cyclic character of
Close
Chapter 11-13 · The evolution of epicontinental marginal sedimentary basins of the Tethys Ocean in Asia
geodynamic evolution of sedimentary basins. Geodynamic
activity increased from cycle to cycle and the boundary
between the Central Asian orogen and the Turan platform
did not remain constant.
The evolution of sedimentary basins was reflected by
lateral and vertical sedimentary formation series.
Main events in the Central Asia included the formation of continental lithosphere and the peneplation of the
relief, followed by riftogenesis with basaltic magmatism
in Triassic-Early Jurassic, repeating orogenes and the general sinking of the Turan platform and the elevation of
the Tien Shan deyteroorogen in Middle Jurassic, stratigraphic break and folding on the boundary JurassicCretaceus, repeating orogenesis with basaltic magmatism
in Hauterevian - Barremian, regional stratigraphic break
on Maastrichtian-Danian boundary, riftogenesis with
basaltic magmatism in Eocene, beginning of rebuilding
of mantle regime and the origin collisional structures with
continental olistostromes along depression boards, first
manifestation of thrust faults in Miocene-Early Pliocene,
intercontinental collision, closing of intermountains depressions and general orogenesis before front of the PamirKarakoram arc in Pliocene-Quartenary.
Simultaneous influence of geodynamic regime, climate
and eustatic variation stipulated formation of numerous
paleolandscapes with different combination of mechanical, chemical and biological differentiation. Every development stage is represented by unrepeating formation
series. Each of them reflects basins of paleogeografic zoning and mineral deposits specialisation. For example,
Rhetien-Bathonian-bauxites, coal, siderite, CallovianOxfordian - oil-gas deposits in barrier reefs, upper
Oxfordian-Lover Kimmeridgian-bituminiferous marlstones (stagnation), Kimmeridgian-Tithonian evaporites,
1269
Barremian - cupriferrous sandstones, Aptian-Turonianglauconitic sandstones, Danian-gypsum, Thanetian-combustible schist (stagnation), Lutetian - phosphatic rocks,
Middle Miocene - evaporates.
Oil and gas generation process was controlled by cyclic development of landscapes and geodynamic movement. Every such cycle (sedimentary series) is characterized by the combination of genetic rock groups of marine, intermediate and continental facies with different
biological productivity of landscapes. The main hydrocarbon reserves are concentrated in large fields arranged
for terrigenous plain alluvial, deltas and shelf, limestones
and barrier reef formations of the Turan province. The
oil and gas deposits of Central and Middle Asia piedmont
and intermountaine depressions is situated in the terrigenous formations of the interior basins. Moreover stratigraphic serie was specialised in determinate mineral deposits - coal, combustible schist, bauxite, phosphate, evaporate, uranium and others.
Study of geological events can bring about essential
changes in traditional views on regional Mezozoic and
Cenozoic stratigraphy, formation and metallogeny in Central Asia.
References
Atlas of the lithology-paleogeographical, structural, palinspastic and
geoenvironmental maps of Central Eurasia. (2002) Daukaev S.J.
and other. Kazakhstan
Geology and mineral of Uzbekistan, ed. T.N.Dolimov (2001) 750
Troitsky V.I. (1996) Evolution of Jurassic Sedimentary Basins of
Central and Southern Asia. Museum of Nothern Arizona Bulletin 60: 413-419
Webby B.D., Laurie J.R (1992) Global Perspectives on Ordovician
Geology. Proceedings of the sixth international symposium on
the ordovician systems. Rotterdam/ Brookfield. 261-276
Close
Close
Chapter 11-14
11-14
Geological characteristics of gold deposits in the
Ailaoshan gold belt, western Yunnan Province, China
Wang Haiping, Hu Yunzhong, Yang Yueqing
Institute of Mineral Resources, CA GS, 26 Baiwanzhuang Road Beijing 100037, China
Abstract. Through detailed research of regional alteration types and
stages of the gold deposition in the Ailaoshan gold belt, combined
with analysis of regional geochemistry, mineral chemistry, stable
isotopes and fluid inclusions microthermometry in gold deposits,
four genetic types of gold deposits in the Ailaoshan belt have been
established for the first time in this paper.
The distribution of gold deposits in Ailaoshan is controlled by
NW-trending deep fracture zones. The intersection of the NW-trending deep fractures, and EW- and NS-trending thrusts control the
distribution and localization of goldfields, and their secondary faults
and the interlayered decollement structure control the local distribution of gold orebodies.
Fluid inclusions in quartz of gold deposits, indicate that pressure
and temperature increased gradually from the north to the south of
the belt. Sulfur isotopes indicate that the sulfur source of the gold
deposits is mainly characterized by mantle source in the northern
part of the belt, whereas mainly by a mixture of stratum and mantle
sulfur in the southern part of the belt. H and O isotope composition
of the gold deposits suggests that the ore-forming fluid is a mixture
dominated by metamorphic or magmatic hydrothermal fluids and a
meteoric fluid component. Lead isotopes indicate that the ore lead
comprise a mixture of crustal and mantle leads.
The ore-forming process in the belt lasted for a prolonged period from Late Yanshannian period to Himalayan period.
Keywords. Ailaoshan tectonic belt, Laowangzhai gold orefield, Geology characteristic, China
1
Introduction
Geotectonically, the Ailaoshan gold belt lies in the eastern part of Tethyan-Himalayan tectonic domain, and at
the junction between Gondwana and the Eurasian continent. Since the 1980s, three large gold deposits, two medium-sized deposits and a number of small gold deposits have been discovered, and Ailaoshan has constituted
one of the important gold-mineralizing belts of China.
Since the Ailaoshan gold belt was discovered in 1980s,
studies on the belt focussed on one or two gold deposits.
There are also many other types of gold deposits and these
deposits appear to have complex mineralization history
and long span of metallogenic epoch. However, little was
known about metallotectonic environment of the gold belt,
and geochemical characteristic and genetic relation of
the gold deposits.
In this paper we discuss gold-mineralizing mechanisms, the geochemical and depositional environments,
and the epoch of the gold mineralization in order to help
understand the overall history of the gold mineralization
in the Ailaoshan belt.
2
Regional geologic setting
The Ailaoshan belt lies at the junction of the Yangtze continental block and the Tanggular- Changdu-LanpingSimao fold system, and displays a broom-like geometry
converging northwestward and spreading southeastward
(Fig. 1).
The structural framework of Ailaoshan area is mainly
made up of three thrust faults striking NW, which are the
principal fracture zones controlling the regional geological
metamorphism and magmatic activities of the Ailaoshan
area. The three faults from east to west are the Honghe
(F1), Ailaoshan (F2) and Jiujia-Mojiang faults (F3). These
faults strike N20-300W, dip N60-800E, and are over 100km
long and about 1-3 km wide. They are characterized by
multiperiodic activities, large-scale mylonitization zones
and the conspicuous ductile shear nature. Gold deposits
commonly occurred at the intersection of NW-, NS- and
EW-trending structures. The individual gold deposits are
mainly controlled by NW-striking ductile shear zones and
tectonic emplacement of mafic-ultramafic rocks. Three
NW thrust faults divide the Ailaoshan region into eastern hypometamorphic zone that is made up of Proterozoic Ailaoshan Group, and western epimetamorphic zone,
which is composed of Paleozoic strata.
The Proterozoic Ailaoshan Group occurs widely in the
area between the Honghe (F1) and Ailaoshan faults (F2),
which are mainly composed of migmatite, gneiss, granulite, hornblendite and marble.
The Paleozoic strata are also distributed in the area
between the Ailaoshan fault (F2) and Jiujia-Mojiang fault
(F3).
A large amount of intrusive rocks of different ages are
widespread in the Ailaoshan area. There are two maficultramafic belts in the area, i.e. Ailaoshan belt between
the Jiujia-Mojiang (F3) and Ailaoshan faults (F2), and the
Dali-Jinping belt located in the central part of the
epimetamorphic rocks. There are many large- to mediumsized, felsic and alkalic intrusive bodies in the Ailaoshan
area. Especially, the intrusive rocks of Yanshanian-Himalayan period are the largest in scale, and were closely accompanied by gold mineralization in the area. Many gold
deposits, which were related to tectonic movements, magmatic activities and metamorphism, were formed in the
Ailaoshan area during the Yanshanian-Himalayan period
(Luo et al. 1994; Hu et al. 1995; Wang et al. 1997).
Close
1272
Wang Haiping · Hu Yunzhong · Yang Yueqing
3
Geochemistry
The fluid inclusions in quartz from five mineralizing stages
are circular, elliptical and or irregular in shape, and generally 2.5–17.5 microns in size. The homogenization temperature of fluid inclusions of quartz was measured using heating/freezing stage. The pressure and the depth
were calculated on basis of the homogenization temperature, the CO2—H2O graphics. The homogenization temperature of the gold deposits is about 110—3400C, and
the calculated pressure and the depth are 300—720 bar
and 1.0—2.5 km, respectively.
The δ34S of pyrite at Laowangzhai is between –3.23‰
and 3.60‰, with ranges of up to 6.83‰, and a peak value
of zero. The δ34S of pyrites in the Jinchang is from –8.30‰
to –1.10‰, the range 7.20‰, and the peak value is about
-5‰. Pyrite δ34S values of the Daping range from –4.9‰
to 9.5‰, the average is 14.4‰, and the peak value is 4‰.
H and O isotopes of the gold deposits are different in
each mineralization stage. In Stage 1, the δ18OH2O of
quartz is -3.81 - 0.73‰, and δDH2O values are -96.90 84.40‰. During Stage 2, δ18OH2O of auriferous quartz
veins formed in the stage are 7.88 - 11.76‰, δDH2O =
-94.10 - 68.10‰. In Stage 3, δ18OH2O of quartz veins is
1.60‰, δDH2O -95.80‰. In Stage 4, δ18OH2O of quartz is
from 2.42‰ to 6.31‰, δDH2O -87.40 - 49.00‰. In the
Stage 5, δ18OH2O of quartz veins is from 4.95‰ to 6.91‰,
and δDH2O -77.30‰ to -41.10‰.
The 206Pb/204Pb value of pyrites of gold deposits is 18.33–
18.58, the average 18.47; the 207Pb/204Pb is 15.55–15.66, the
average 15.61; the 208Pb/204Pb is 38.60–38.75, the average
38.69. The lead isotope composition of pyrites indicates that
the ore lead is the mixture of crustal and mantle lead.
4
Gold deposits
The Ailaoshan gold belt is over 100km long, and 0.5 to 5km
wide. Since the 1980s, three large gold deposits (in every
deposit the average of the grade is about 5-7g/t, and the
tonnage of Au is over 50t), two medium deposits (in every
deposit the grade is 3-8g/t, and the tonnage is over 10t) and
a number of small gold occurrences have been discovered.
Gold deposits of the belt can be divided into four genetic
types: a) metamorphic hydrothermal gold deposits (such
as the Kudumu, Daqiaoqin and Donggualin deposit), b)
volcanic-subvolcanic hydrothermal gold deposits (such as
the Laowangzhai deposit), c) gold deposits in ultramafic
rocks (such as Jinchang deposit), and d) polymetallic sulfide-quartz vein type gold deposits (such as the Daping
deposit).
Close
Chapter 11-14 · Geological characteristics of gold deposits in the Ailaoshan gold belt, western Yunnan Province, China
The distribution of gold deposits in the belt is strictly
controlled by NW trending fracture zones. The belt occurs in the hanging side of the Jiujia-Mojiang fault, and
the intersection of NW-trending ductile shear zones, NSand EW-trending thrust zones controls the gold ore field
distribution of the belt, and interlayer decollement structure and secondary fault are the important structures
which control the ore body distribution.
The host horizons of the gold deposits are Late Paleozoic volcanic-sedimentary rocks. Ore-bearing horizons
are composed of mafic volcanic tuff, meta-tuff,
metaclastics, limestone and radiolarian-bearing siliceous
rocks. Among the ore-bearing horizons, it is noted that
the higher the contents of the volcanic material and carbon, the better the gold mineralization.
The gold-bearing mineral in four deposit types is predominantly euhedral pyrite. As the evolution of the mineralization stages, pyrite gradually increased in gold content in the coarser grains than in the finer grains, and the
contents of As, Te, Co and Ni show a positive correlation
to that of gold in pyrite. The grains of gold-carrying pyrites tended to have gradually become finer from the south
to the north of the gold belt.
Regionally, the gold mineralization in the Ailaoshan belt
can be divided into five stages: Stage 1 is metasomatic
quartzification alteration with very minor gold mineralization. Stage 2 is an early silicification stage. Auriferous
quartz veins formed in this stage and consist of quartz,
chrome-hydromica and pyrite filling microfractures. Pyrite-sericite Stage 3 is the most important mineralization
stage. Pyrite-carbonate stage IV is another important mineralization stage in the belt. Stage V is the late silicification
stage, gold mineralization in the stage is characterized
mainly by quartz veins.
According to a fluid inclusion study of gold deposits,
in the northern part of the belt the homogenization temperature range from 1100°C to 2800°C, the average about
2000°C, and the calculated pressure for the ore-forming
depth is 1.0–2.0 km; in the southern part of the belt the
homogenization temperature range from 1600°C to
3400°C, and the calculated pressure shows that the oreforming depth is about 2.2–2.5 km. These characteristics indicate that the pressure and the temperature of the
formation of gold deposits increased from the north to
the south during the formation of the gold belt.
On the basis of the stable isotope study of gold deposits, the average δ34S of the Laowangzhai orefield is 0.3‰,
the Jinchang orefield –5‰ and the Daping orefield 4‰,
suggesting that the sulfur source of gold deposits in the
north of the belt is characterized mainly by mantle source,
and that of the south in the belt mainly by mixed sulfur
source. H, O isotope compositions of the gold deposits
show a remarkable variation, implying that the ore-forming hydrothermal solution is a mixed hydrothermal fluids dominated by metamorphic or magmatic hydrother-
1273
mal solution with meteoric water. The ore lead, by the
lead isotope study, mainly belongs to the orogenic belt
lead mixed with the minor mantle lead.
5
Conclusions
Distribution and mineralization of gold deposits in
Ailaoshan gold belt have the following characteristics:
The distribution of gold deposits in the belt is strictly
controlled by NW-trending thrust fracture zones and the
relevant stratigraphic-structural unit. The Ailaoshan fracture and Jiujia-Mojiang fracture acted as an important
passageway for ore-forming fluid. The intersections of the
NW-trending fractures, the EW- and NS-trending thrusts
control the distribution of gold fields, and their secondary faults and the interlayered decollement structure control the distribution of individual gold orebodies. The
Upper Paleozoic epimetamorphic rocks of the belt are
the main host unit for the gold deposits.
During gold mineralization, there were five mineralization stages, among them Stage III (i.e. pyritization-sericitization stage) and Stage IV (i.e. pyritization-carbonatization
stage) are more important mineralization stages in which
many gold deposits of the gold belt have formed.
The gold-carrying mineral in the deposits was mostly
pyrite with the pyritohedral shape. As the evolution of
the mineralization stages, the pyrites gradually increased
gold content in the coarser grain than the finer grain, and
the contents of As, Te, Co and Ni in the pyrites showed a
positive correlation to that of gold in the pyrite. The grains
of gold-carrying pyrites tended to have gradually become
finer from the south to the north of the gold belt.
The ore-forming process in the belt lasted for a prolonged period. During the napping, shearing and
decollement caused by multiple tectonic movements, gold
was repeatedly introduced and concentrated, and the
major ore-forming period was from late Yanshannian to
Himalayan periods. The gold ore-forming process is characterized by multicyclic tectonic movements, and multistage mineralization from a variety of sources for oreforming fluids and metals.
References
Chang XY, Zhu BQ (1997) Topological projection of Pb isotopes in
Tri-dimension space and their application to geochmical exploration and evaluation. Acta Geoscientia Sinca 18:182–1184 (in
Chinese)
Chen BW, Li YS, Qu JC Wang KY, Zhu ZZ (1991) The main geotectonic problems in Sanjiang region and their relations to metallization. Geological Publishing House, Beijing, 67-80 (in Chinese)
Doe BR, Stacey JS (1974) The application of lead isotopes to the problems of ore genesis and ore prospect evaluation, A review. Econ.
Geol 69:757–776
Hu, Y.Z., Tang, S. C., Wang, H. P., Yang, Y. Q., Deng, J., Li, J. D. (1995)
Geology of gold deposits in Ailaoshan. Geology Publishing House.
Beijing, 58–158 (in Chinese)
Close
1274
Wang Haiping · Hu Yunzhong · Yang Yueqing
Luo JL, Yang YH, Zhao Z, Chen J C, Yang JZ (1994) Evolution of the
Tethys in western Yunnan and mineralization for main metal
deposits. Geology Publishing House. Beijin, 69–116 (in Chinese)
Wang HP, Hu HZ (1997) Ground spectrum property of gold deposits in Northern Ailaoshan and stydy of correlative model between
the property and TM brightness. Acta Geoscientia Sinca 18: 162–
170 (in Chinese)
Wang HP, Hu YZ (2002) Principal component analyses for mineralization alteration information of Xiasai deposit. Mineral Deposits 2: 1190–1193 (in Chinese)
Ye QT, Shi GH, Ye JH, Yang ZQ (1991) Geological characteristics and
metallogenic series of lead-zinc deposits in Nujiang-Lanchangjiang-Jinshajiang region. Beijing Scientific and Technical Publishing House. Beijing, 4-57 (in Chinese)
Zartman R.E. (1971) Lead isotopes and mineralization ages in Belt
supergroup rocks, northwestern Montana and northern Idaho.
Econ. Geol. 66: 849–860
Zhang LG (1985) The application of the stable isotope to geology.
Science and Technology Publishing House, Shanxi Provence,
China. 9-36 (in Chinese)
Close
Chapter 11-15
11-15
Possible causes for large-scale mineralization in the
Lanping area, western Yunnan: New evidence from
Cenozoic igneous rocks and mantle xenoliths
Yu Xuehui, Mo Xuanxue, Zhao Xin, Zhou Su
Institute of Geoscience and Resources, The China University of Geosciences (Beijing), Xueyuanlu 29#, Beijing, 100083, China
Zeng Pushing
Department of Resources and Environment, Yunnan University of Finance and Economics, Kunming, 650221, Yunnan
Province, China
Abstract. The injection of magma from the upper mantle into a continent may be a direct driving force for continental mineralization
(Li et al. 1993; Deng 1999b). Therefore, to understand the dynamic
mechanisms, processes and sources of metals in large-scale mineralizing systems derived from subcontinental mantle and/or the lower
crust has become an important aspect of research in the formation
of ore deposits. Western Yunnan, and especially the Lanping area, is
an important component of the Tethyan-Himalayan metallogenic
domain and is an area of research interest because of the large
Jinding zinc (-lead) deposit and significant concentrations of Ag
and polymetallic mineralization in the adjacent Baiyangping area.
A key question concerns why such a large concentration of mineral
deposits occurs in this specific area. This paper aims to provide some
evidence from Cenozoic magmatism and lithosperic characteristics and evolution.
Keywords. Western Yunnan, Cenozoic magmatism, Deep-seated xenoliths, Crust-mantle transition zone, Lanping, Baiyangping, largescale mineralization
A 3700 km-long Cenozoic potassic igneous belt occurs
along the Jinshanjiang (Red-River)- Ailaoshan Mountain
belt in western Yunnan. Some of the alkaline porphyry
alkaline basalt and basanite bodies contain abundant xenoliths derived from both crust and mantle sources. Mineralogical, petrological, trace element, REE and Pb, Sr, Nd
isotopic studies of the alkaline igneous rocks and deepseated xenoliths not only provide information on source
areas and deep Cenozoic alkaline magmatism, but also
provide some constraints on conditions during large-scale
mineralizing events.
Studies on the alkaline porphyry, alkaline basalt and
xenoliths show that all of the Cenozoic igneous suites in
Western Yunnan belong to shoshonitic rock series, and
are enriched in LREE and LILE, but depleted in HFSE.
The Cenozoic igneous rocks have nopronoucned Eu
anomaly. Pb, Sr and Nd isotopic geochemistry of the alkaline igneous rocks indicate that the source of the alkaline magmas has characteristics of EM11. However, 87Sr/
86Sr (0.705906-0.70774) and 206Pb/204Pb (18.464-18.791)
of the Cenozoic igneous of Western Yunnan, have lower
87
Sr/86Sr but higher 206Pb/204Pb than that of typical end
member of EM11 and are very close to the 87Sr/86Sr ratio
of the lower crust. The Tethyan domain belongs to the
mantle geochemical domain of India Ocean and general
has higher 87Sr/86Sr and lower 206Pb/204Pb and ∈Nd. However, geochemical characteristics of Western Yunnan mentioned above are different from common Tethyan mantle
(Xu et al., 2002; Zhang et al., 2005), which may be the
result of subduction or mixing of the abyssal sediments
or ancient lithosphere or lower crust (>1 Ga) with lower
U/Pb ratios in the magma source. For this reason, the EM11
end member of Cenozoic igneous of Western Yunnan may
be not only related to subducted lower crust, but also related to mixing and recirculation of sediments of ancient
Tethyan oceanic crust.
The depth of the source of the alkaline magmas, according to equilibrium P and T calculations on the crustal
and mantle xenoliths is about 50-95km, consistent with
the crust-mantle transition zone in Western Yunnan as
determined by geophysics (Gao et al. 1991; Kan 1992),
Why does such a wide zone of transitional crust-mantle
exist in the Western Yunan?
Geophysical studies on Cenozoic volcanic rocks and
the tectonic evolution of Western Yunnan indicate that,
most of “Sanjiang” (Jinshanjiang River, Lancangjiang River
and Nujiang River) belongs to the ancient Tethyan orogenic belt. Strong intracontinental deformation and strikeslip faults with different displacements formed since about
65 Ma because of subduction and collision between Indian and Euroasian continents. Especially, large-scale
Cenozoic shear-strike-slip faults trending NNW-and SN
of Jinshanjiang River-Ailaoshan Mountain-Hohe River
faults and Lancangjiang River faults as a result of subblocks cut by the many faults since late Cretaceous epoch. Therefore, it can be inferred that the pre-Cenozoic
(ancient Tethyan) tectonic elements of the “Sanjiang area”
may have trended NWW and EW. The Tectonic features
of ‘Sanjiang area” at present might comprise superimposed
Cenozoic structures over older Tethyan structures (Zhong
et al., 2000). Superimposed slabs have been demonstrated
by seismic tomography from reflective zones at different
depths in the Western Yunnan lithospheric mantle.
Morever, the asthenosphere apparently rises from about
400 km to 120 km depth and might be stored at the
Close
1276
Yu Xuehui · Mo Xuanxue · Zhao Xin · Zhou Su · Zeng Pushing
boundary between Yangtze block and Indo-ChinaMyanmar block under the Lanping-Siamo Basin (Zhong
et al. 2000; Liu et al. 2004). This rise in the asthenosphere
could be related to large scale (700+/-200 km) east-southeastward lateral mantle flow extrusion of the IndoChina
block to accommodate the indentation of India into Asia
(Tapponnier et al. 1982; Leloup et al. 1995).
Recently, studies on Cenozoic post-collision potassic
and ultra-potassic volcanic rocks in Tibetan Plateau and
adjacent area (Mo et al. 2003a, b; 2004; 2005) indicate that
Cenozoic post-collisional potassic and ultra-potassic volcanism is widely distributed in various terranes in the
Tibetan Plateau and adjacent area. Three stages of volcanism have been recognized, i.e, ca. 45-25Ma; 25-5Ma; 5Mapresent time. The composition of the volcanic rocks plots
in shoshonitic (SHO) and highly potassic calc-alkaline
(HKCA) fields of K2O vs. SiO2 diagrams and in shoshonitic/
potassic (SHO) and ultrapotassic (UP) fields of a K2O vs.
Na2O diagram. All of the rocks are enriched in LREE and
depleted in Yb with (La/Yb)N 4.3-699, mainly 40-50, and
have higher ΣREE abundance (50-2560ppm, mainly 300500ppm). Most of them, especially the more basic, have
no or very weak Eu negative anomalies. Spidergrams for
most post-collisional rocks are characterized both by
strongly negative Nb, Ta, Hf and/or Zr spikes and by strong
enrichment in Rb, Ba, Th, U and La but depletion in Yb
and Y. However, those for kamafugite and carbonatite are
OIB-like pattern with no negative or even slightly positive HFSE anomalies. A ∈Nd vs. 87Sr/86Sr diagram for Tibetan post-collisional volcanic rocks shows a mixing array between Neo-Tethyan MORB and High Himalaya crust,
giving a wide range of the values of ∈Nd (+5.7 to –14.86)
and 87Sr/86Sr (0.703831-0.736451). While Nd and Sr isotope compositions in the volcanic rocks from northern
parts of the Plateau, the “Sanjiang” and the Western
Qinling define a relatively small range. those from the
Gangdese spread across a large rang with extreme variations in 87Sr/86Sr (0.705778- 0.736451) and 143Nd/144Nd
(0.511075- 0.511814) ratios. Pb isotopes show less variation than Sr and Nd isotopes, varying in a range of 206Pb/
204Pb 18.461- 19.354, 207Pb/204Pb (15.476- 15.803), 208Pb/
204Pb (37.613- 40.168). In general, Pb isotopes show regional DUPAL anomaly and mixing characters between
MORB and EM11. Major elements, trace and isotopic
geochemistry and mineralogy of both mantle-derived xenoliths and the most primitive volcanic rocks give constrains
on the nature of magma sources and demonstrate the
sources for the magma are likely potassium and incompatible elements-rich but HFSE-depleted metasomatized phlogopite/amphibole-bearing mantle by fluids or small
amounts of H2O-CO2-containing melts, presumable subduction related. The range in geochemistry and petrology among post-collisional volcanic rocks from various
terranes suggest different magma sources and mechanism
for magma generation. All of the characters mentioned
above show that Cenozoic post-collision volcanism in Tibetan and adjacent area clearly migrated with time. The
path of migration of volcanism seems to trace out channels for laterally asthenospheric mantle flows presumably
induced by the India-Asia collision. As the laterally
asthenospheric mantle flows not only kept asthenospheric
uplift-convectional systems beneath Tibetan plateau and
adjacent area, but also resulted Cenozoic potassic and
ultrapotassic volcanism in Tibetan plateau and adjacent area.
In summary, such processes can explain the large transition zone between the crust and mantle. These peculiar
tectonic features could also be responsible for the large metal
endowment in this part of Western Yunnan. Fluid inclusion studies of Pb, Zn, Cu and Au deposits in Western Yunnan
also support the involvement of deep asthenosphere-derived fluids in ore formation (Xue et al. 1999; Yang et al.
1999). These asthenospheric fluids in the Lanping area mixed
with basinal fluids. The combination of fluids in an area of
high heat flow where probably key factors in concentrating
so much metal in the Lanping area.
References
Deng JF (2004) Igneous rocks and mineralization, In Deng JF, Luo
ZH, Su SG, Mo XX, Yu BS, Lai XY Shen HW (eds): Petrogenesis,
tectonic setting and mineralization, Geological Publication press,
Beijing, 150-155
Deng JF, Mo XX, Zhao HL (1999b) The catastrophe of the lithospheric and asthenospheric systems and large scale ore concentration area, In Pei RF, Zhai YS and Zhang BR (eds): The deep
tectonics and mineralization, Geological Publication Press,
Beijing, 36-43
Deng JF, Mo XX, Zhao HL (1999c) lithospheric and asthenospheric
systems and Mineralization setting in China, Mineral Deposits
18(4): 309-315
Deng WM, Zhong DL (1998) The crust-mantle transitional zone and its
significance in the evolution of lithospheric tectonics, Chinese Science Bulletin 42(23): Kan rongju (1992) The geophysic collection of
Yunnan province, Yunnan University Publication Press, 2474-2482
Gao MX, Kan RG (1991) The lithospheric structure and Himalayan
orogenic movement of West Sichuan and Yunnan, China, In: The
Year book of lithosphere and tectonics evolution opening laboratory, Geological Institute, CAS (1989-1990) China Science and
technology publication Press, Beijing, 49-53
Kan R (1992) The geophysic collection of Yunnan province, Yunnan
University Publication Press
Li XB, Xiao QH (1993) A national project for the continental dynamics study in America, China Institute of Geological and Minerals
Information, 1-73;
Leloup PH, Lassassin R, Taponnier P (1995) The Ailaoshan-RedRiver
shear zone (Yunnan China), Tertiary trasform boundary of
Indochina, Tectonophysics 251:3-84
Liu M, Cui XJ, Liu F (2000) Cenozoic rifting and volcanism in eastern
China: A mantle dynamics link to the Indo-Asian collision, In
M.F.J.Flower, C.T.Chi, N.T.Yem and V Mocanu (eds) Tectonophysics,
Special issue: “Mantle and Lithosphere Responses to Tethyan Closure” (in Press)
Mo XX, Zhao ZD, Deng JF, Yu XH, Luo ZH, Zhou S, Dong GC (2003a)
Diachronous Cenozoic volcanism in Tibet and implications for
outward growth of the Plateau and inhomogeneity in source region of magma, The 18th HKTW, Ascona: 81-82
Close
Chapter 11-15 · Possible causes for large-scale mineralization in the Lanping area, western Yunnan: New evidence from Cenozoic igneous rocks and mantle xenoliths
Mo XX Deng JF, Zhao ZD, Martin Flower, Luo ZH, Yu XH, Zhou S
(2003b) Volcanism records of India-Asia collision and post collision processes, EGS-AGU-EUG joint Assembly, Nice, Geophysical Research Abstracts vol5, 04194
Mo XX, Zhao ZD, Deng JF, Luo ZH, Yu XH, Guo TY, Zhou S, and Dong
GC (2004) Deep probe of Mesozoic and Cenozoic igneous rocks
in Tibetan Plateau: some new accomplishments and cognitions,
In Chen Yuntai (eds): “The advances of Continental seismology
and plutology physics in China” 449-461, Seism Publication Press,
Beijing
Mo XX, Zhao ZD, Deng JF, Martin Flower, Yu XH, Luo ZH, Li YG and
Zhou S (2005) Post-collisional volcanic rocks and implications
for heterogeneity of the lithosphere and collision-deduced mantle
flow in Tibetan Plateau, GSA Special Volume (in Press)
Tapponnie P., Peltzer G., Le Dain A.Y, R. Armijo and Cobbold P. (1982)
Propagating extrusion tectonics in Asia: new insights from simple
plasticine experiments, Geology 10(7): 611-616
Xue CJ, Wang DH, Chen YC (1999) He has been found from the
metallogenic fluids of Jinding-Baiyangping, Lanping basin: a
evidence of crust-mantle metalogenic fluids, J.Earth 20(supp):
385-389
1277
Xu JF, Castillo P.R., Li XH (2002) MORB-type rocks from the PaleoTethyan Mian-Lueyang northern ophiolite in the Qinling Mountain, central China: implications for the source of the low 206Pb/
204
Pb,and high 143Nd/144Nd mantle component in the Indian
ocean, Earth and Planetary Science Letters 198:323-337
Yang WG, Yu XH, Li WC, Su Qi (2003) The characteristics of
metallogenic fluids and metallogenic mechanism of Baiyangping
Ag and polymetallic minerallization concentration area in
Yunnan Province, Geoscience 17(1): 25-33
Yu XH, Mo XX, Zhao X (2005) Cenozoic magmatism and deep seated
xenoliths in Western Yunnan, In: Mo XX, Zhao ZD, Deng JF, Yu
XH and Dong GC (eds): The Mesozoic and Cenozoic magmatism
in Tibetan Plateau and adjacent area, The Science and technology publication press of Guangdong Province. (in press)
Zhong D, Ding L (2000) Multi ways and layers structure of the orogenic lithosphere and a constraints for Cenozoic magmatism,
Science in China (series D) 30(supp): 1-8
Zhang SQ, Mahoney J.J, Mo XX, Ghazi, A.M., Milani L., Crawford A.J.,
Guo Taiyu and Zhao Zhidan, Evidence for a widespread tethyan
upper mantle with Indian-Ocean-Type isotopic characteristics,
Jour. Petrology (in press)
Close
Close
Chapter 11-16
11-16
Relationship of the Cenozoic Beiya Cu–Au mineralization
to alkali-rich porphyries in western Yunnan, China
Zeng Pusheng1, 2, Hou Zengqian2, Mo Xuanxue3, Yang Weiguang4, Li Wenchang5, Yu Xuehui3
1Department of Resources and Environment, Yunnan University of Finance & Economics, Kunming, 650221,P. R. China
2Institute
of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China
3
China University of Geosciences, Beijing, 100083, China
4Yunnan Geology & Mineral Resources Co. Ltd, Kunming, 650000, China
5Yunnan
Geological Survey, Kunming, 650011, China
Abstract. The Beiya gold-copper mine is situated within the famous
Jinsha River-Red River Cenozoic alkali-rich porphyry belt. It is one
of the most important porphyry gold-copper ore deposits with a
gold reserve over 40 tonnes. Gold and copper are hosted by oxides,
such as magnetite and hematite. The oxides were generated by the
early skarn formation; whereas the gold-copper mineralization was
superimposed over the iron oxide zone.
Keywords. Cenozoic alkali-rich porphyry, Au-Cu mineralization, Beiya,
Western Yunnan, China
1
Introduction
In the eastern part of the Tibetan Plateau, most Au-Cu
deposits occur within close proximity of Cenozoic alkalirich porphyries. These deposits mainly occur along the
Jinsha River-Red River fault zone and form an important
porphyry gold-copper-molybdenum belt (Tu 1982, 1989).
The porphyries include monzogranite porphyry, granite
porphyry, and quartz syenite porphyry. The copper mineralization is mainly related to monzogranite porphyry,
whereas the gold mineralization is mainly related to quartz
syenite porphyry (Zeng et al. 1999, 2002; Hou et al. 2003).
Representative deposits include the Yulong Cu (-Mo), the
Beiya Au-Cu(-Pb-Zn-Fe), the Machangqing Cu-Mo-Au, the
Chang’an Au-Cu along the Jinsha River-Red River belt,
and the Xifanping Cu-Au and the Yao’an Au in the Yangtze
Craton (Fig. 1a). These ore deposits formed between
~40.1-35.8 Ma, as constrained by Re-Os molybdenite dates
from the Yulong Cu deposit and the Machangqing CuMo-Au deposit (Hou et al. 2004). The Beiya porphyry AuCu deposit formed bat ~38.36-35.98 Ma, as determined
by K/Ar dating of altered quartz syenite porphyries in
the mine district (Yang et al. 2001); however, it is noteworthy that there exists a younger stage of mineralization with
an age of 24.56 Ma, as constrained by Ar/Ar plagioclase
plateau ages from the Block Hongnitang of the Beiya district (Wang et al. 2001). A close spatial relationship exists
between Au-Cu mineralization, lamprophyres and quartz
syenite porphyry, quartz monzonite porphyry or
monzogranite porphyry at Beiya, Chang’an, and Yao’an,
implying that the mineralization is attributed to a deep
interaction of the crust and mantle in a strike-slip fault
regime east of the Tibetan Plateau.
2
Geology of the Beiya gold-copper deposit
The Beiya Au-Cu deposit is located in the west margin of
Yangtze Craton in the southern part of the Lijiang marginal depression belt (Fig. 1a). The mine district is on the
east limb of the Ma’anshan Composite Anticline, locally
occurring in a small syncline, called the Beiya Syncline.
Topographically, the mine district is a basin, the Beiya
Basin. The strata that outcrop in the mine district (Fig. 1b),
from lower to upper, include Permian Emeishan basalts
(Pβ) in the eastern part of the basin, the Early Triassic
clastic sedimentary rocks (T1) and the Middle Triassic
(T2) carbonate rocks, the Paleocene Lijiang Formation
(E2l) sedimentary clastics and conglomerate, intercalated
with trachytic volcanic rock, and Quaternary regolith with
laterite-type gold in topographic depressions. The strata
were intruded by Cenozoic alkali-rich porphyries of quartz
syenite porphyry, quartz monzonite porphyry and
lamprophyre with an age range of ~25-45Ma, a peak of
35Ma (Wang et al. 2001; Yang et al. 2001). These porphyries are closely related to gold-copper-iron mineralization, and belong to the Jinsha River-Red River Porphyry
Belt (Fig. 1a). The Beiya gold deposit is superlarge in size
with over 40 tonnes of gold reserves; copper, lead, zinc,
and iron in the deposit are also of economic significance.
In the Beiya district, gold is hosted in magnetite and
lesser hematite (rarely in the form of specularite). The
magnetite occurs in the contact zone of skarn between
Cenozoic intrusions and Triassic carbonate rocks. From
drillhole data, the oxides mainly occur above the 1710 m
level, generally 300-400 m below surface. Below this level,
the host mineral of gold gradually changes to pyrite in
the altered intrusions; also, the copper content increases
from 0.3 to 1.5%. Orebodies occur along the porphyry
Close
1280
Zeng Pusheng · Hou Zengqian · Mo Xuanxue · Yang Weiguang · Li Wenchang · Yu Xuehui
contact in Block Wandongshan, or within a hydrothermal breccia in Block Hongnitang, and along fracture zones
in Blocks Bijiashan and Weiganpo. Laterite-type gold
mineralization is also widely developed in the basin. Ore
minerals include magnetite, hematite, limonite, pyrite,
galena, sphalerite, marcasite and chalcopyrite. They occur in the altered porphyry as disseminations and veinlets. Gangue minerals are calcite and quartz, and chlorite
in Block Hongnitang. Secondary minerals are malachite,
covellitie, chalcocite, and tenorite.
Alteration includes K-felspathization, silicification,
sericitization, chloritization, skarn, and hornfels. Most of
the carbonate rocks (e.g. limestone and dolostone) of the
wall rocks have suffered contact metamorphism, and, in
places, are recrystallized. The iron minerals occur mainly
in early skarn, whereas copper and gold mineralization
is mainly associated with later potassic silicates, silicification and sericitization, and locally fluorite (e.g. in the
Block Wandongshan).
3
Characteristics of the various blocks
The Beiya mine district is divided into six blocks, namely, the Blocks Wandongshan, Hongnitang, and Jingouba in the west of the basin; and the Blocks of
Weiganpo, Bijiashan, and Guogaishan in the east of the
basin (Fig. 1b). Among them, the Block Wandongshan
is the largest block with a gold reserve over 20 t. The
type of mineralization is mainly skarn, superimposed
by the late gold, copper-bearing quartz-calcite(-flourite)
vein or veinlet related to porphyries, such as quartz
syenite porphyry, quartz monzogranite porphyry, and
lamprophyre.
In Block Hongnitang, a cryptobreccia pipe is exposed and is associated with porphyry-type mineralization. From porphyry to country rocks, quartz syenite
porphyry, explosion breccia, shattering breccia and then
carbonate host rocks occur. The cryptobreccia is generally filled by the gold-bearing chlorite-magnetite-
Close
Chapter 11-16 · Relationship of the Cenozoic Beiya Cu–Au mineralization to alkali-rich porphyries in western Yunnan, China
marcasite veins, thus the appearance of the brecciated
rocks are greenish, called “the green zone”, implying that
the alteration zone of the intrusions is less eroded. If the
mineralization mechanism is similar to the situation of
the Grasberg, Indonesia (Lu et al. 2000), “the red zone”
resulted from the K-felspathization will occur below the
green zone, meanwhile the content of copper in the red
zone will be increased, and finally “the white zone”, from
the strong silicification, will occur at even greater depth.
In other words, the gold and copper mineralization of
the Block Hongnitang is of a typical porphyry gold-copper type.
In Block Wandongshan, skarn-type gold mineralization well developed and covered by the late laterite-type
gold ore bed. Quartz syenite porphyry was strongly
weathered and is difficult to sample the fresh rock.
4
Summary
The Beiya gold-copper mine, within the famous Jinsha
River-Red River Cenozoic alkali-rich porphyry belt, is one
of the most important porphyry gold-copper ore deposits. Gold and copper are hosted by iron oxides, such as
magnetite and hematite. The oxides were generated by
early skarn formation; whereas the gold-copper mineralization is superimposed over the iron oxide zone.
Acknowledgement
We give our thanks to Mr. Su Gangsheng and Mr. Zhang
Wenhong for help during the field work.
1281
References
Hou ZQ, Zeng PS, Gao YF, Du AD (2005) Himalayan Cu-Mo-Au Mineralization in the eastern Indo-Asian Collision Zone: Constraints
from Re-Os Dating of molybdenite.Mineralium Deposita (in press)
Hou ZQ, Ma HW, Zaw K, Zhang YQ, Wang MJ, Wang Z, Pan GT, Tang RL
(2003) The Himalayan Yulong porphyry copper belt: product of largescale strike-slip faulting in Eastern Tibet. Econ Geol 98:125-145
Liang HY (2002) The zircon SHRIMP ages of the Yulong porphyry
Cu belt. Report of National Foundation of Natural Science in
China (in Chinese)
Tu GC (1982) Preliminary study on the two alkali porphyry belts in
the South of China. In: Annual Report of Guiyang Institute of
Geochemistry, China Academy of Science, 127-129. Guiyang:
People’s Publishing House of Guizhou. (In Chinese with English
abstract)
Tu GC (1989) On alkali intrusive rocks. Mineral Resources and Geology 3 (3): 1-4. (In Chinese with English abstract)
Wang DH, Yang JM, Xue CJ, et al. (2001) Isotope geochronology constrain on gold mineralization of Himalayan in the Sanjiang
(Lancangjiang- Nujiang- Jinshajiagn)- Daduhe River region,
Southwestern China. In: Chen Yuchuan, et al. (eds), Study on Himalayan endogenic mineralization, 88-95. Beijing: Seismic Publishing House. (In Chinese with English abstract)
Yang JM, Xue CJ, Xu J et al. (2001) Geological features and mineralization of the Himalayan alkalic porphyry in Western Yunnan. In: Chen
YC et al (ed.), Study on Himalayan endogenic mineralization, 5768.Beijing: Seismic Publishing House. (In Chinese with English abstract)
Zeng PS, Mo XX, Yu XH (2002) Strike-slip and Compression: Tectonic Background of the Alkaline-rich Porphyries in West Yunnan,
China. Acta Petrologica et Mineralogica 21(3): 231-241. (In Chinese with English abstract)
Zeng PS, Yang WG, Yu XH (1999) Alkalic porphyry belt in Western
Yunnan and its relation to gold mineralization. Acta Geoscientia
Sinica 20(sup.): 367-372. (In Chinese with English abstract)
Close
Close
Chapter 11-17
11-17
Deposit geology, geochemical characteristics and ore
formation of the Jiayashan sector of the Jinding zinc
(-lead) deposit, Yunnan, China
H.-B. Zhao
School of Earth Sciences and Mineral Resources, China University of Geosciences, Beijing 100083;
2 Qiqihar Branch, Heilongjing Institute of Geological Survey and Research, Qiqihar 161005, China
X.-X. Mo
School of Earth Sciences and Mineral Resource, China University of Geosciences, Beijing 100083, China
P.-S. Zheng
Yunnan University of Finance and Economics, Kunming 650221, China
Y. Wang
East China Institute of Technology, Fuzhou 344000, Jiangxi, China
Abstract. Recent research has demonstrated that thermal waters in
sea-floor environments can be important for ore formation. Thermal waters can be important in ore formation in continental settings. Sanjiang is one of the areas that has the most intense current
geothermal activit in China. The world-class Jinding zinc(-lead) deposit occurs in the Sanjiang area. This study focuses on the Jiayashan
sector of the Jinding deposit and discusses continental thermal
water sedimentation and mineralization. We agrue that our research
has far-reaching significance on regional ore-deposit theory and
exploration.
Keywords. Jiayashan, Jinding, Yunnan Province, continent, thermal
water, sedimentation, Bijiang fault zone, Himalaya
1
Introduction
The Jinding deposit is located in the center of the northern
part of the Mesozoic-Cenozoic Lanping-Siamo basin. The
basin lies to the west of the Jinshajiang (Red River)-
Ailaoshan fault system and shear zone, respectively, with
the Yangzi Block to the east and the Zangdian plate, between the Lancangjiang and Nujiang faults, to the west. A
central fault in the basin was an important control on sedimentation and ore formation. Alkaline igneous bodies (6823Ma) from mantle and crust-mantle sources and an exhumed thermal metamorphic belt (31-24Ma) formed during Himalayan epoch along the shear zone. The N-S-trending Bijiang fault was the main structure that controlled the
ore deposit. The Cenozoic Yunlong Formation ore host is
composed of variegated red sandstone, sandy shale and
mudstone. Ore minerals in the Jiayashan sector of the deposit are mainly supergene zinc and lead minerals with few
remaining primary sulfides. The ore body contains many
extraneous gypsum block in the Sandonghe Formation
(T3s). Alteration includes silicification, carbonation, and
supergene limonite. The ore is brecciated and cancallated
tufa with encrustations (Fig. 1, 2, 3, 4), which is very similar
Close
1284
H.-B. Zhao · X.-X. Mo · P.-S. Zheng · Y. Wang
with the characteristics of the modern sediments of in adjacent northern Dalongcun hot spring (Fig. 5, 6). Multiple
periods of ejecta can be documented in outcrop. Every stage
of ejecta has different composition which can be distinguished by different colors. Ore body contacts with wall
rocks are disconformable (Fig.7).
δ34S, δ18O, δD, δHe, Ne, Xe and Pb isotope and fluid
inclusion studies show that ore-forming metals are derived mainly from deep levels and mixed with wall rock
sources. Thermal brines are the main ore fluid which is
resulted from the interaction between meteoric precipitation and wall rocks, as well as participation of deep origin fluid.
There are three δ34S peak value of sulfides in Jinding
deposit: -45%, -13.5 and-19.0% (Xue et al. 2002),which is
characteristic of δ34Siron pyrites >δ34S pseudogalena
>δ34S galena. This fact shows that sulfide in the ore fluid
was in equilibrium, and rich in 34S showing the sulphur is
close related to the sulphate and sulphide under reduction condition. Plotted point from Pb isotope formation
in deposit is closely packed, with three sources: mantle
Pb, sialic crust and upper crustal Pb, which show that
source of Pb is consecutive and have surface-deep complexity (Luo et al. 2001). Isotope studies of fluid inclusions show that He, 3He/4He=0.19-1.97Ra have 2%–32%
mantle-He, 50.1% mantle-Ne (20Ne/22Ne=10.45-10.83,
21Ne/22Ne=0.03) and significant Xe, 129Xe/130Xe= 5.84-6.86,
134Xe/130Xe=2.26-2.71 ( Xue et al. 2003). Thermometric
Close
Chapter 11-17 · Deposit geology, geochemical characteristics and ore formation of the Jiayashan sector of the Jinding zinc(-lead) deposit, Yunnan, China
1285
to SO4–Cl–Na–Ca in chemical type of water. Variation of
H-O isotopes [DH2O (-40.5‰—14‰), δ18OH2O (–7.94‰+6.07‰)] of ore fluid is similar with those δD and δ18O
(D=+20‰-150‰, δ18O= +10‰—20‰) obtained from
sedimentary basins (Pirajna 1992),which shows that the
deposit has characteristic of thermal fluids related to
meteoric precipitation (Li et al. 1995).
According to Xue et al. (2003) and Li et al. (2000), the
age of mineralization of Jinding lead-zinc deposit is 2562 Ma, which corresponds with age of intrusion and metamorphism. This fact shows that mineralizing process was
lengthy. It is only in lengthy geological history that can
formed such a super-large deposit.
On the basis of field evidences and geochemical information, we believe that ore genesis of Jiayashan ore section in Jinding zinc(-lead) deposit was related to continental thermal water sedimentation which was formed
by the long period of activity of the deep Bijiang fault
during the Himalayan period. Lead-zinc precipitation in
the Dalongcun hot spring is good evidence that Bijiang
fault is still active today. Sources of ore-forming elements
was mainly from depth, and mixed with near-surface
sources. The ore fluid was meteoric and probably had
participation of deep fluids. We can infer that Bijiang fault
zone is a prospective region for hot spring-type lead-zinc
deposits.
References
measurement of fluid inclusions indicate that the ore fluid
was thermal brine of medium to low temperature (260o150o), medium to low salinity (eq. Wt.% NaCl 11.4-6.70)
and high density (average 0.97 g/cm3). The fluid belongs
Luo J, Li Z (2001) The new advance in study on Himalayan
magmatism and metallogenesis in central western. J. Yunnan
Geology 20(3): 229-242 (in Chinese with English abstract).
Li X, Tan K, Gong G (2000) Preliminary studies of tectonic evolution
and metallogenic processes in Lanping basin with fission track
analysis. J. Mineral petrol 20(2): 40-42
Pirajna F (1992) Hydrothermal mineral deposits. Springer-Verlag
Xue CJ, Chen YC, Yan E, Jian M (2002) Jindiing Pb, Zn Deposit: Geology and Geochemistry. J. Mineral Deposits 21(3):270-245
Xue J., Chen YC, Wang DH (2003) Geology, He-Ne-Xe isotopes and
ages deposits in Jinding and Baiyangping, north western
Yunnan.J. Science in China 33(4): 315-322
Wen C, Chai J, Lu W (1995) Geochemical characteristics of fluid inclusions in the Jinding lead-zinc deposit, Yunnan, China. J. Mineral Petrol 5(4): 78
Close
Close
Chapter 11-18
11-18
Geochronology, geochemistry and implications of
Au-mineralized porphyries in the Linzhou basin,
Gangdese belt, Tibet
Zhu Dicheng, Pan Guitang, Wang Liquan, Li Guangming, Liao Zhongli, Geng Quanru
Chengdu Institute of Geology and Mineral Resources, Chengdu, China
Abstract. The Linzhou porphyry bodies are distributed within or along
the edge of Linzhou basin, which is located to the south of NamlingLuobadui-Milashan fault in the central Gangdese magmatic arc. The
porphyry bodies can be divided into two groups including the early
intruded the Sexing Formation, the Dianzhong Formation and the
late intruded the upper Linzizong volcanic successions. The single
zircon from the early porphyry body (Hutouya) yielded a restrictedly concordant weighted mean 206Pb/238U age of 58.7±1.1 Ma (2σ)
and is ascribed to the collisional stage porphyries when India collided with Asia. The early porphyries are geochemically similar to
Linzizong volcanic rocks, and are interpreted to the predominately
remelting of crustal components, and to a lesser extent, the contributions from subducted oceanic crust were also involved in their
generation. The early porphyries with Au mineralization at collisional
stage indicate that the collisional stage intrusives (60-50 Ma) in the
Gangdese have potential for gold.
Keywords. Geochronology, geochemistry, Linzhou porphyry,
Gangdese belt, Tibet
1
Introduction
The Miocene ore-bearing porphyries (25-10 Ma) that are
generally ascribed to the partial melting of mafic materials in a thickened lower crust with input of enriched
mantle and/or upper crust components in southern Tibetan Plateau have been widely studied in recent years
(Qu et al. 2001; Gao et al. 2003; Hou et al. 2004). Recently,
porphyry occurrences related to India-Asia collision have
also been recognized in the Gangdese belt in Tibet.
This paper reports SHRIMP U-Pb zircon ages, the
geochemical characteristics and implications for the porphyries intruded during the collisional stage in the
Linzhou basin of the Gangdese Belt.
2
Geological setting
The subduction of the Neo-Tethyan oceanic crust and the
collision of India with the Lhasa terrane resulted in the
Himalayan-Tibetan orogen. Although the Lhasa terrane
was shortened by about 180km as a result of the
Qiangtang-Lhasa terrane collision during the JurassicCretaceous (Murphy et al. 1997), several tectonic units,
i.e., the Bangong-Nujiang suture, the Gangdese batholiths,
the Xigaze forearc basin, and the Indus-Yarlung-Zangbo
suture, are well preserved in the Lhasa terrane (Fig. 1a).
The northward subduction of the Neo-Tethyan oceanic
crust gave rise to an Andean-type Gangdese magmatic
arc, which is generally thought to manifest by the voluminous Gangdese batholith with typically calc-alkaline
compositions emplaced from Cretaceous to Eocene (ca.
120- 40 Ma) time (Tapponnier et al. 2001) and Linzizong
volcanic successions (~64.47- 40.84 Ma) recorded the transitional process from the end of subduction of NeoTethyan oceanic crust to India-Lhasa terrane collision (Mo
et al. 2003), now exposed in the Lhasa terrane of southern Tibetan Plateau. Subsequently magmatisms are generally represented by Miocene magmatic rocks in
Gangdese, and their geochemical signatures indicate a
dominant source originated from the enriched sub-continental lithospheric mantle or thickened Tibetan lower
crust (Miller et al. 1999; Chung et al. 2003; Hou et al. 2004).
The Linzhou basin, which is very famous for its wellexposed Linzizong volcanic rocks (including Dianzhong,
Nianbo, and Pa’na Formation from bottom to top), is located to the south of Namling-Luobadui-Milashan fault
in the central Gangdese magmatic arc. The Linzhou porphyry bodies mostly intruded the Sexing Formation and
the Dianzhong Formation; only two porphyry bodies
(Nianbo) intruded the upper Linzizong volcanic successions. All the porphyry bodies generally occur as apophyses within or along the edge of Linzhou basin (Fig. 1b).
3
Geochronology
The Linzizong volcanic rocks have been well dated by 40Ar/
39Ar method (Mo et al. 2003; Zhou et al. 2004). In order to
constrain the genetic relationship between the porphyry
bodies and the Linzizong volcanic rocks, two samples from
Hutouya (porphyry) and Tuomu (associated rhyolite, Fig. 1b)
were dated using single zircon U-Pb dating by the SHRIMP
II at the Chinese Academy of Geological Science (Beijing).
Details of the procedure for the analysis of zircons using
SHRIMP have been given by Song et al.(2002).
The single zircon from the Hutouya porphyry yielded
a concordant weighted mean 206Pb/238U age of 58.7±1.1
Ma (2σ) (Fig. 2a). Rhyolite from Tuomu has relatively wide
range of single zircon SHRIMP ages from 57.6±1.9 Ma to
68.9±1.7 Ma (Fig. 2b), indicating that the emplacement
of porphyry slightly lag behind the eruption of rhyolite,
Close
1288
Zhu Dicheng · Pan Guitang · Wang Liquan · Li Guangming · Liao Zhongli · Geng Quanru
corresponding to the field relationship between porphyry
and rhyolite. The age of porphyry is close to that of the
Dianzhong Formation (~64.43—60 Ma, Mo et al. 2003)
and is generally consistent with the age range of collisional stage (Mo et al. 2003; Zhu et al. 2004). Therefore,
the porphyries were emplaced at the collisional stage when
India collided with Asia.
4
Geochemistry
Based on their SiO2 concentrations (from 65.96% to
83.8%), the porphyries are acid intrusives in compositions. All the analyzed samples have relatively high K2O/
Na 2O ratios ( > 0.5), which are consistent with the
Dianzhong data.
The early porphyries are variably fractionated between
LREE and HREE (Fig. 3a) with (La/Yb)N from 4.22 to 13.72
and slightly - moderately negative Eu anomalies (Eu/
Eu*=0.51 – 0.84). The N-MORB-normalized trace element
spidergrams show that all the analyzed samples have HFSE
negative anomalies, typical of orogenic magmas. That is,
all the analyzed samples show significantly negative Nb,
Ta, Ti and P anomalies (Fig. 3b). Although the absolute
abundances within the early porphyries vary slightly for
the trace element, the general pattern is subparallel
(Fig. 3a, b), suggesting a similar origin of these samples.
Note that the late porphyries (Nianbo intrusives) have
higher absolute abundances of trace element (Fig. 3a, b)
and more fractionated between LREE and HREE ((La/
Yb)N= 14.08 - 18.52) than those of the early porphyries,
indicating a different origin, which is consistent with the
result of Pa’na volcanic rocks (Mo et al. 2003).
By contrast, although the early porphyries have relatively
low absolute REE abundances, their trace element
spidergrams are widely similar to those of Linzizong volcanic rocks (Fig. 3a, b). Obviously, all the analyzed samples
clearly differ from Miocene intrusives in Gangdese for their
higher HREE (Dy, Er, Yb) and Y abundances (Fig. 3a, b),
Close
Chapter 11-18 · Geochronology, geochemistry and implications of Au-mineralized porphyries in the Linzhou basin, Gangdese belt, Tibet
1289
indicating that the porphyries are unlikely related to the
partial melting of thickened Tibetan lower crust.
5
Discussion
5.1 Petrogenesis
A key problem for the origin of porphyries is that these
acid magmas are whether derived from basic magma by
fractional crystallization or from remelting of crustal components? Although the fractional crystallization may affect the evolution of acid magmas for their negative Eu
anomalies, the remelting of crustal components and the
addition of subducted oceanic crust-derived melts probably played a significant role in controlling the origin of
porphyries for several reasons. The La/Sm vs. La diagram
(Fig. 4) clearly exhibit a trend of partial melting rather
than fractional crystallization except for three samples,
suggesting that partial melting predominately controlled
the magmatic process. The scatter of sample BLZ10-4 and
BLZ11-1 (Nianbo intrusives) could be ascribed to a different origin (not discussed here), while the sample BLZ083 can be resulted from extensively alteration (LOI=8.17%).
Additionally, all the analyzed samples of early porphyry
bodies have fairly similar spidergrams, indicating that
crustal components were extremely involved in the generation of the porphyries. This is also supported by the
enormous volume of acid volcanic rocks in Linzizong
volcanic successions (Mo et al. 2003).
Close
1290
Zhu Dicheng · Pan Guitang · Wang Liquan · Li Guangming · Liao Zhongli · Geng Quanru
It is important to note that all the analyzed porphyry
samples have N-MORB-normalized HREE ratios around
1 (Fig. 3b), suggesting that the contributions of subducted
oceanic crust cannot be entirely ruled out, corresponding to the results of Sr, Nd and Pb isotopic study for the
Linzizong volcanic rocks (Mo et al. 2003). In summary,
the Linzhou porphyries can be interpreted as the predominately remelting of crustal components, and to a lesser
extent, the contributions from subducted oceanic crust
were also involved in their generation.
5.2 Implications
Previous works show that the early porphyries from
Huangya Lake and Baxue have Au mineralization with
contents range from 0.1 to 1.3 g/t and from 0.46 to 0.58 g/t,
respectively (Li et al. unpublished data). Recently, Au mineralization was also recognized from Qushui pluton
at ~50 Ma (Mo et al. personal communication). These studies suggest that the collisional stage (60-50 Ma) in the
Gangdese has potential for gold.
6
Conclusions
1. The single zircon weighted mean 206Pb/238U age of
58.7±1.1 Ma of Linzhou porphyries in central Tibet is
the first precise report of collisional stage porphyries
with Au mineralization.
2. The Linzhou porphyries can be interpreted as the
predominately remelting of crustal components, and
to a lesser extent, the contributions from subducted
oceanic crust were also involved in their generation.
3. The collisional stage intrusives (60-50 Ma) in the
Gangdese have potential for gold.
Acknowledgements
This study was financially supported by the National Keystone Basic Research Program of China (Grant No.
2002CB412609), the Integrated Study of Basic Geology in
the Blank Area of Southern Tibetan Plateau (Grant No.
200313000025).
References
Chung SL, Liu D, Ji J, Chu MF, Lee HY, Wen DJ, Lo CH, Lee TY, Qian Q,
Zhang Q (2003) Adakites from continental collision zones: Melting of thickened lower crust beneath southern Tibet. Geology
31(11): 1021-1024
Gao YF, Hou ZQ, Wei RH (2003) Post-collisional adakitic porphyries
in Tibet: geochemical and Sr-Nd-Pb isotopic constraints on partial melting of oceanic lithosphere and crust-mantle interaction.
Sinica Geologica Acta 77: 123-135
Hou ZQ, Gao YF, Qu XM, Rui ZY, Mo XX (2004). Origin of adakitic
intrusives generated during mid-Miocene east-west extension in
South Tibet. Earth Planet. Sci. Lett. 220: 139-155
Miller C, Schuster R, Klötzli US, Frank W, Purtscheller F (1999).
Post-collisional potassic and ultrapotassic magmatism in SW
Tibet: Geochemical and Sr-Nd-Pb-O isotopic constrains for
mantle source characteristics and petrogenesis. Journal of Petrology 40(9): 1399-1424
Mo XX, Zhao ZD. Deng JF, Dong GC, Zhou S, Guo TY, Zhang SQ, Wang
LL (2003) Response of volcanism to the India-Asia collision. Earth
Science Frontiers 10(3): 135-148 (in Chinese with English abstract)
Murphy MA, Harrison TM, Durr SB, Chen Z, Ryerson FJ, Kidd WSF,
Wang X, Zhou X (1997) Significant crustal shortening in south-central Tibet prior to the Indo-Asian collision. Geology 25: 719-722
Pan GT, Ding J, Yao DS, Wang LQ, Luo JN, Yan YJ, Yong YY, Zheng JK,
Liang XZ, Qin DH, Jiang XS, Wang QH, Li RS, Geng QR, Liao ZL,
Zhu DC, Yu RL (2004) Geological map of Qinghai-Xizang (Tibetan) Plateau and adjacent areas (1:1500000) Chengdu: Chengdu
Cartographic Publishing House
Qu XM, Hou ZQ, Huang W (2001). Is Gangdese porphyry copper
belt the second “Yulong” copper belt? Miner. Depos 20(4): 355366 (in Chinese with English abstract)
Song B, Zhang YH, Wan YS. Jian P (2002) Mount making and procedure of the SHRIMP dating, Geological Review 48(Supp.): 26-30
(in Chinese with English abstract)
Sun SS, McDough WF (1989) Chemical and isotope systematics of
oceanic basalts: implications for mantle composition and processes. In: Saunders AD (eds.), Magmatism in ocean Basins. Geological Society Publication, 42: 313-345
Tapponnier P, Xu ZQ, Roger F, Meyer B, Arnaud N, Wittlinger G, Yang
JS (2001) Oblique stepwise rise and growth of the Tibet Plateau.
Science 232, 94: 1671-1677
Zhou S, Mo XX, Dong GC, Zhao ZD, Qiu RZ, Guo TY and Wang LL
(2004) 40Ar/39Ar geochronology of Cenozoic Linzizong volcanic
rocks from Linzhou Basin, Tibet, China, and their geological implications. Chinese Science Bulletin 49(18): 1970-1979
Zhu DC, Pan GT, Mo XX, Duan LP, Liao ZL (2004). The age of collision between India and Eurasia. Advances in Earth Science 19(4):
564-571 (in Chinese with English abstract)
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