ILVAITE FROM THE CAVNIC DEPOSIT, ROMANIA
HÎRTOPANU P.1, ANDERSEN J.C. 2, HÂRTOPANU I. 1, UDUBAŞA S.S. 1
University of Bucharest, Faculty of Geology and Geophysics, RO, paulinahirtopanu@hotmail.com
2
University of Exeter, Camborne School of Mine, Cornwall, UK,
1
The Cavnic deposit is located in the East Baia Mare metallogenetic district which belongs to
the Neogene volcanic belt from East Carpathians, Romania. The Neogene volcanic belt is
characterized by presence of many precious/base-metal hydrothermal ore deposits of low
sulphidation type, like Ilba, Nistru, Sasar, Suior, Dealul Crucii, Baia Sprie, Cavnic and Herja. The
hydrothermal activity was related to the presence of an underlying magmatic pluton of 65 Km length
and 15Km wide, established by geophysical data. This is considered as the source of ore metals
(Borcos, 1994). The Cavnic deposit was considered a typically carbonate base metal gold system,
with rare Au-Ag concentrations and mined in the past. The mineralization is principally of vein type
and is developed on the fractures oriented NE-SW. Fourteen veins 400-1500m long, 1-8m thick and
900m vertical development are known, hosted by Neogene volcanics. In the deeper and the midle
part of the deposit the host rocks are Paleocene-Miocene sedimentary and Pannonian age dioritic
bodies. At the deposit scale, four main mineralisation stages were distinguished at Cavnic (Piantone
et al., 1999):
(1) Fe-+W (hematite-pyrite-quartz-magnetite-sheelite), T=3200C; (2) Cu-Fe,
(chalcopyrite-pyrite), T=3000C; (3) Zn-Pb-Fe-Cu (sphalerite-galena-pyrite-chalcopyrite), T=2600C;
(4)Mn silicates and carbonates (rhodonite-rhodochrosite-kutnahorite-bournonite–tetrahedrite,
T=
2000C. The earlier stage (1) was a higher temperature mineralization, the stages (2) and (3) are rich
in chalcopyrite and the late stage is rich in carbonates. Our samples, collected on the mine dump are
rich in Fe and W belonging, most probably to early stage (1). Until now, the Fe richness of stage (1)
was linked with magnetite, hematite and ferberite. Now, we determined in the Cavnic deposit for the
first time the ilvaite, the mixed valence iron and calcium silicate and that it is frequently recognized
as a type mineral of the skarn deposit. The name “ilvaite”of mineral comes from the old name of
Elba Island, on which the type locality is situated. The type locality is Torre de Rio-Santa Filomena
area (Monte della Torre) Rio Marina, Elba Island, Livorno Province, Tuscany, Italy (Lelievre,
1807).First occurrence of ilvaite in Romania has been mentioned in Ferdinand Mine, Dognecea
(Dogneczka), Banat (Scheerer, 1893). llvaite has been identified in the polymetamorphic iron ores
from Ruschita as a recrystallisation product of the banatitic contact metamorphism with increase in
Si content. Ilvaite occurs in magnetite hedenbergite skarnes formed from regional metamorphic
volcanic-sedimentary iron carbonate ores (Krautner and Medesan, 1969). Ilvaite occurs in the
62
banatite skarns from Baisoara (Popescu, 1973). The ilvaite was identified in Ghezuri deposit of the
Oas neogene metallogenetic district, in the high temperature paragenesis with magnetite, pyrrhotite,
chalcopyrite, cubanite, pyrite, and native gold (Jude, 1986). Ilvaite was determined in calcic skarn
deposits at Dognecea – Ocna de Fier related to Upper Cretaceous – Paleocene banatitic intrusions
developed in the Banat Mountains (Vlad, 1997) and in the Herja epithermal ore deposit related to
neogene magmatism (Damian, 1996). Also, Clain and Haake (2006) mentioned the ilvaite in Turt
Mine, Maramures. First occurrence of manganilvaite, a new mineral, was identified in the skarn
deposit at Dognecea, southwestern Banat (Ilinca et al., 2006) in association with Mn-hedenbergite
and magnetite. Its chemical composition, crystal structure and cation ordering have been presented.
Although the ilvaite is a rare mineral, in the last years were mentioned many occurrences in the
world. Between them we mention some recent occurrences. In the USA, ilvaite occurs in the
Fortitude Au skarn deposit, Nevada, the first reported occurrence in an Au skarn deposit. At
Fortitude, ilvaite is present as resinous, black grains with quartz, ferroactinolite, and sulfides
(pyrrhotite-arsenopyrite-bismuthinite). Ilvaite occurs as a late-phase replacing prograde pyroxene
(Hd 91–96 Jo 3–5 ) in magnetite-rich exoskarn near the skarn-marble contact and replacing calcite grains
at the marble front (Franchini et al., 2002). An occurrence of ilvaite layers in the Cinco Villas
metasomatic rocks, Western Pyrenees, Spain (Pesquera and Velasco, 1986), in the Artikutza area,
near the contact with the southern Aya granite, skarns containing hedenbergite, grandite, epidote,
quartz, calcite, actinolite, idocrase and magnetite occurs. This is the second reported occurrence of
ilvaite in Spain, where the monomineralic ilvaite lens intercalation developed by hydrothermal
alteration of hedenbergite in a second stage of skarn formation. Ilvaite occurs in Permian veins
transecting Proterozoic granitic gneisses on the southwestern flank of the Late Paleozoic Oslo
Graben, Norway. The mineral occurs in hydrothermal quartz-magnetite veins in association with
hedenbergite, andradite, fluorite and calcite. Ilvaite as an accessory mineral in hydrothermal veins is
a very unusual mode of occurrence (Larsen and Dahlgren, 2002). Also, ilvaite occurs in some
typical contact deposits within the region. These ilvaites are generally much richer in Mn (varying
from 8.60 % MnO to 15.03 % MnO) than the ilvaites from the hydrothermal veins. This is a new
mineral, manganilvaite, that was determined for the first time in Pb-Zn skarn deposits in the
Rhodope Mountains, Bulgaria as a product of retrograde alteration of the early skarn pyroxenes
(Bonev et al., 2005).
The Cavnic ilvaite is associated with sphalerite, galena, magnetite, hematite, pyrite, chalcopyrite,
ferberite, native gold and native Bi. The sphalerite has a yellow color in transmitted light (low Fe
content) and frequently is zoned; also, it could be red in the same thin section having a high Fecontent proving a high chemical variability. The native gold grains have an isometric shape of
63
micronic to mm dimensions and it can see easy on optical microscope. On the microprobe image one
can see many grains of native gold forming a little “veins” on the fine crack in the ilvaite (Fig 1).
Also, the native gold surroundins the pyrite grains. This location of native gold could be explain the
forming of gold after ilvaite and pyrite. The composition of native gold determined by microprobe
shows a some silver, ca 1% (Fig 1). The gangue minerals are: quartz, siderite, phillosilicate with Zn
(?), chlorite, rhodochrosite, rhodonite. The quartz presents a hexagonal idiomorphic shape on which
grow radiary others fibrous quartz grains. The carbonate directly associated with ilvaite has a
mixture composition, with Fe, Mn, Ca and little Ba, Mg (determined by microprobe). The yellow
phyllosilicate (with Zn) is intimately associated with sphalerite and was probably formed from it by
hydrothermal alteration. The chlorite(?) don’t looks like a phyllosilicate; it has not any cleavages, has
isometric, round shape and very light green color. Because of the Mn richness mentioned before (the
occurrences of rhodonite and rhodochrosite as gangue minerals) and because of the ilvaite and the
manganilvaite form a continuous solid-solution series and gradations between them can be observed
even in a single crystal (Bonev et al., 2005), it is very probably for manganilvaite to occurs in the
Cavnic deposit. To prove this supposition will need to continue this study, especially need
microprobe analyses. The chemical composition of ilvaite determined by microprobe (mass%):
SiO 2 =31.313; MnO=4.917; FeO=49.956; CaO=14.064; 2.9118; TiO 2 =0.047. Electron microprobe
analyses show that the Cavnic ilvaite is similar in composition to ilvaite from skarn Fe-deposit, both
having high iron and relative low manganese. The high Fe content in ilvaite from Cavnic deposit is
consistent with the high Fe activities and low F O2 conditions that characterize both skarn types and
their associated intrusions. The X-ray diffraction powder data for the Cavnic ilvaite: 3.856(40),
3.246(40), 3.102(90), 2.859(60), 2.823(100), 2.699(100),
2.660(60), 2,250(25), 2.350(25),
2.450(30), 2.230(30), 1.807(25), 1.621(60), 1.445(30).The Cavnic ilvaite presents a large prisms of
few mm until 1cm long, forming a compact texture. It is translucent, with iron black, dark grayish to
black colour, brittle and present a submetallic luster. The cleavage is distinct on (001) and (010). In
thin sections the ilvaite has a intense pleochroism: X=dark green; Y=yellow red brown to dark
brown; Z=dark brown. In reflected light, the pleochroism is from light gray to bluish gray, pinkish
red to violet, being strongly anisotropic. The ilvaite is associated with sphalerite, hematite,
magnetite, pyrite, chalcopyrite, galena, ferberite, native Au and Bi and also with quartz, Fe-Mn-Ca
carbonates, rhodochrosite, rhodonite, chlorite and apatite as gangue minerals. By isotopic study
Piantone et al. (1999) calculated the crystallization of sphalerite/galena assemblages from Cavnic
between 234-2900C, this being thus a epithermal deposit. According with the mineral association of
relative high temperature, including magnetite, chalcopyrite, cubanite, pyrite, ferberite,
the
mineralisation has a pneumatolitic character. The native gold of Cavnic is included in ilvaite, similar
64
to Turt Ghezuri deposit, where the crystallisation of ilvaite took place at ca 4000C (Jude, 1986). The
presence of rhodonite as mineral gangue, is according to a T higher than 4000C. The forming and
stability of rhodonite in the hydrothermal experimental conditions are situated at ca 7000C (Momoi,
1974), but in natural conditions the T could be lower. The rhodonite Cavnic could be rather a result
of manganiferous skarns and the formation of ilvaite is associated with it later retrogression.
Fig 1. The association gold (white)-ilvaite (grey)-pyrite (cream)-quartz (black) from Cavnic deposit (left); the chemical
profile of the ilvaite (up) and the chemical profile of the gold (bottom) (right).
References
Bonev I.K. et al., 2005, Canadian Mineralogist, v.43, p.10027-1042.
Borcos M., 1975, Revue Roumaine de Geologie, v.19, p.23-35.
Clain E. and Haake R., 2006, Mineralien-Welt, 17(5), p.52-64 (in German).
Damian G. et al., 1996, Studia Universitatis Babes-Bolyai, Geologia 1-2, p.201-214.
Editura Academiei Romane, p.132.
Franchini Marta B. et al., Economic Geology, 2002, v.97, no.5, p.1119-1126.
Ilinca Gh. et al., 2006, Mineralogica-Petrographica, Abstract Series 5, p.47, Szeghed.
Jude R., 1986, Metalogeneza asociata vulcanismului Neogen din NV Muntilor Oas,
Krautner H.G. and Medesan A., 1969, Miner. and Petrol., v.13, no2, p.157-164.
Larsen A.O. and Dahlgren S., 2002, Neues Jahrb Mineral-Monatshefte, v.4, p.169-181.
Lelievre M., 1907, Journal des Mines, v.21, p.65-74.
Momoi H., 1974, Min.Journ., v.7, p.359-373.
Pesquera A. and Velasco F., 1986, Mineral. Mag., v. 50, no.358, p. 653-656.
Piantone P. et al., 1999, Mineral Deposits: Processes to Processing, Stanley et al.(eds), v.1, p.79-82.
Popescu M., 1973, Stud.Cerc.Geologie, v.18, nr.1, p.101-107.
Scherer Fr., 1893, Studien am Arsenkiese, Z.K., v. 21.
Serban V., 1997, Mineralium Deposita, v.32, no.5, p. 446-451.
65