in
mineralization
Precam
brianmetallic
NewMexico
cies. Two episodesof isoclinal folding were
followedby two periodsof opento tight foldrng.
In the area of Truchas Peak in the central
part of the Sangrede Cristo uplift a thick semostly pure metaquenceof metasediments,
NM
Albuquerque,
Department
University
of NewMexico,
of Geology,
by Michael
S. FulpandLeeA. Woodward,
quartziteand metapeliticrocks, is overlainby
But onlyGod plutons. Barker (1958) describeda strati- interbedded metavolcanic and metasedimenmaywriteextravaganzasr
"Geologists
(J.E. Spurr,1927).
graphic sequencein the Tusas-Brazosuplift tary rock (Grambling,1979).The metavolcancanmakebonanzas."
consistingof 14,000-20,000ft of metaquartz- ics form a bimodal suite with amphibolitesof
The purposesof this report are to describe ite overlain by severalthousand feet of mafic basaltic parentageand felsic schistsderived
ser- from rhyolitic tuffs. Thesemetamorphicrocks
metavolcanic
rocks(Moppin metavolcanic
briefly the known metallicmineraldepositsof
probable Precambrianagein New Mexico, to
ies) that are overlain in turn by quartzose in the Truchas area are correlatedwith the
with minor interbeddedmafic metamorphicsin the Picuris Range,although
suggest a genetic classification for these metasediments
Metarhyolitesare interbedded the two terranesare separatedby a major
deposits,to placethem in a regionallithologic metavolcanics.
and the mafic strike-slip fault (Miller and others, 1963).
framework, and to note the implicationsfor with both the metasediments
that the rocks in
Pegmatitesand granitic rocks Grambling(1979)suggested
metavolcanics.
mineral exploration.Becauseof the lack of
part
Truchas
area were
The
rocks.
of
the
intrusive
into
the
metamorphic
northern
geologic
are
the
and
lithologic
descripdetailed
maps
tions for much of the Precambrianterranein metarhyolitehasbeenradiometricallydatedat depositedin a stable-shelfenvironment,but
m.y.; the granodioriteintrusive correlativerocks to the south were deposited
New Mexico, along with the scarcityof reli- 1,750-1,800
able radiometricdates,this synthesisis some- into the mafic metavolcanicshas an age of in a deep-waterbasin.The gradeof metamorwhat speculative.However, in view of the 1,700-1,750m.y.; trondhjemiteis dated at phism reachedthe middle amphibolitefacies.
1,724 + 34 m.y. (Barker and Friedman, Oldest folds are tight to isoclinal, and later
current interest in mineral exploration in
Precambrianrocks in New Mexico, this syn- 1974).Gresensand Stensrud(1974)suggested foldsareopen.
The deep basin proposed by Grambling
that the stratigraphic sequenceconsists of
thesismay providenew ideasfor exploration.
the (1979)appearsto be the site of a thick seoverlainby metasediments,
Precise correlations of metasedimentary metavolcanics
basalt
metamorphosed
and metavolcanicunits from one major Pre- inverse order of that describedby Barker quenceof subaqueous
cambrianterraneto another in New Mexico (1958). Grade of metamorphismis upper and locally important felsic metavolcanics
includingiron forto middleamphibolitefacies.Two along with metasediments,
are difficult becauseof discontinuityof out- greenschist
crops and paucity of reliable radiometric episodesof isoclinal folding have been fol- mation, that has beencalledthe Pecosgreenstone belt (Robertsonand Moench, 1979).
dates.Accordingly,we havegroupedthe Pre- lowedby openfolding.
Condie (1979) suggestedthat a metasedi- Metavolcanicsare dominant in the southern
cambrianoutcropsinto severalmajor regions
(fig. 1) having broad similarities.Numerous mentary sequencein the Taos Rangein the and westernpartsof the belt, but interbedded
increasein abundanceto the
unresolvedproblemsexist within eachmajor northern part of the Sangrede Cristo uplift metasediments
region concerning stratigraphic relations consisting of locally graphitic gneiss and northeast.The greenstonesequenceis interquartzitethat totals at least4,900ft thick, is preted by Robertsonand Moench (1979)to
becauseof lack of data on directions of
but J. A.
younging and complicationsresulting from
overlainby metavolcanicrocksat least16,000 overliean older quartzitesequence,
folding and faulting. Therefore,the general- ft thick. Felsicmetavolcanicsare dominant, Crambling (personalcommunication, 1980)
are with interbeddedminor mafic metavolcanics. reports that in the Rio Mora area primary
ized stratigraphicand lithologicsequences
structuresindicatethat the quartsubjectto revision as more detailedwork is Tonalite-trondhjemiteand granite are intru- sedimentary
done. Many of the mineral depositsare not siveinto the metamorphicrocks and are inter- zite stratigraphicallyoverliesthe metavolcanprecisely dated; although we interpret the pretedby Condie(1979)to be mostly syntec- ics in an inverted section. Robertson and
mineralizationto be Precambrian.some de- tonic. Pegmatites,quartz veins, and diabase Moench (1979,p. l7l) suggestthat the felsic
posits could be younger. Mineral deposits dikesalsoarepresent.Metamorphismreached metavolcanicsmay be approximately1,110describedin the text are shown as numbered the amphibolitefacies;two periodsof folding 1,720m.y. old basedon modelleadagesfrom
associatedore deposits.Two suites of inlocalitieson fig. l. An annotatedbibliography arerecognized.
Montgomery (1953)describeda metasedi- trusive rocks are present: a coeval, suband mapping index of the Precambrianof
New Mexico is availableas Bull. 103 of the mentary sequence(Ortega formation) in the volcanic complex of amphibolite, quartz
New Mexico Bureauof Mines and Mineral Re- Picuris Range,approximately6,600 ft thick,
(Robertson,1976).
that he thought was overlain by a partly
sources
ALSOIN TH]SISSUE:
metavolcanic sequence(Vadito Formation)
Lithologicframework
A mosasaurf rom the Lewis Shale
that is approximately4,500 ft thick and con(UpperCretaceous),northwestern
Precisecorrelationsof Precambrianrocks tains rhyolitic and basalticprotoliths. J. F.
P.37
New Mexico
throughout New Mexico have not been Callender(personalcommunication,1980)innomenclature
P.47
Stratigraphic
achieved;however,severalmajor regionshave terprets the stratigraphic successionto be
P.43
Service/News
(fig. l).
reversed; that is, the metasedimentsare
distinctlithologicassemblages
The
RegionA (fig. l) includesthe Tusas-Brazos thought to overlie the metavolcanics.
SOON
COMING
areintruded
and metasediments
and Sangrede Cristo uplifts wherea thick se- metavolcanics
N U R Ep r o g r a mi n N e w M e x i c o
quenceof metasediments
has beeninterpreted by the EmbudoGranitethat Long (1974)conCaias Gypsum Memberof Yeso
to be overlainby a dominantlymetavolcanic sideredto be composedof severalintrusions
Formation
sequence(Montgomery, 1953).All of these rangingin agefrom 1,700to 1,400m.y. MetaOliver Lee State Park
supracrustalrocks are intruded by granitic morphismreachedthe upper amphibolitefa-
Mountains (Reiche, 1949; Woodward and
others, 1979),where the basal unit consists
of approximately1,900ft of metasediments,
mostly phyllite with subordinatemetaquartzite. Thesemetasediments
are overlainby approximately4,500 ft of mafic metavolcanics
(Tijeras-HellCanyongreenstone)
with minor
chertyiron formation and silicicmetavolcanics. Above the greenstoneEuemore metasediments (maximum thicknessof 9,500 ft) that
are mostly phyllites and metaquartzites.
Locally, a rhyodacitecrystal-richtuff2,000 ft
thick, containing abundant lithic fragments,
unconformablyoverliesthe greenstone.The
uppermostunit is metarhyolitewith subordinate metabasaltic sills with maximum
thicknessof about 5,000 ft in the Manzano
Mountains (Stark, 1956). At least two
episodesof folding occurredhere. Grade of
metamorphismreachedthe greenschistfacies.
In the southernManzano and Los Pinos
Mountainsonly the upper sequence
of metasedimentsand the overlyingmetarhyoliteare
exposed.Metamorphismreachedlower amphibolite faciesand the rocks are isoclinally
folded.Metasediments
and overlyingmetavolcanics in the Ladron Mountains (Condie,
1976) may be broadly equivalentto those
supracrustalunits exposedin the southern
Manzano Mountains. In the Ladron Mountains metamorphismwas of greenschistto
loweramphibolitefacies.
Granitic rocks are intrusive into the
metasediments and metavolcanics noted
above. The Sandia Mountain Granite is
reportedto be approximately1,500m.y. old
by Brookins (1974).The Ojito quartz monzonite and Priest Granite in the Manzano
Mountains and the Los Pinos pluton in that
"
r V o l c o n o g e npi co l y m e t o l l i cs u l f i d ed e p o s i l s
o G r e e n s l o n e x h o l o t i v e - f u m o r o l igco l d - ( c o p p e r ) d e p o s i l s
1 l r o n - b e o r i n gc h e m i c o l s e d i m e n l o r yd e p o s i t s
I D e p o s i t so f u n c e r l o i no r i q i n
B o u n d o r yb e t w e e nl i l h o l o g i c _ l e c t o n i cr e g i o n s
'
B
o u n d o r yb e l w e e nr o d i o m e f r i co g e p r o v i n c e sw
, i f h o g e s i n m i l l i o n s o f y e o r s ( m . y)
"'
FIGURE I -PnecnvgnlnN ourcRoPs ANDRADIoMETRIC
AGEpRovrNCEs
rN NEw Mexrco. Numbered localities
and lettered lithologic-tectonic regions are discussedrn text.
diorite, trondhjemite,quartz porphyry, and
minor metamorphosedultramafics, and a
youngerplutoniccomplexof tonalite,granodiorite, and granite.euartz diorite westof the
open.
Region B (fig. l) consisrsof precambrian
outcrops in the Nacimientouplift. Descriptions are mainly from the summaries by
Woodwardand others(1974, lg77l. The oldest rocks are metasediments
and metavolcanics that occurprincipallyas inclusionsor roof
pendantsin granitic intrusions.In the northern Nacimiento uplift, these rocks are intruded by variably foliated tonalite, quartz
diorite, and granite plutons. Minor ultramafic, gabbroic,and dioritic bodieshavebeen
Augustl98l
New Mexico Ceology
partially assimilatedby the granitic rocks.
Pegmatiticand mafic dikes cut the granitic
bodies.In the southernpart of the Nacimiento
uplift, the plutonic rocks include foliated
quartz diorite, quartz monzonite,and granodiorite that are cut by nonfoliatedgraniteand
quartzmonzonite.Dikes of aplite, pegmatite,
and granite cut the other rocks. Silicic
metavolcanicsin the northern part of the
region have been radiometrically dated at
1,800 + 50 m.y. (Brookins, 1974).A large
quartzmonzonitepluton, also in the northern
part of the region,has an ageof 1,720 + 30
m.y.(L. T. Silver,personalcommunication,
1972). The grade of metamorphismin the
Nacimientoarea probably reachedthe upper
greenschist
facies.
RegionC (fig. t) includesthe Sandia,Manzano,Los Piflos,and Ladron Mountains.The
most completesequenceof surface-accumulatedrocks is found in the northernManzano
New A4exfico
GEOLOGV
. Scionce
andSeruics
Volumo
3, No. 3, August
1 981
publishedquanerly by
Ncw MexicoBureauof Minesand Mineral Rercurces
a divisionofNew Mexico lnstitutc of Mining & Technology
BOARD OF RBGENTS
Ex Ofhcio
Bt\ce King, Govenor oJ NewMexko
Leonard Del-ayo, Srp€rintendeil of Public Instruction
Appointcd
WilliamG. Abbott, Pres, 196l-1985,
Ilortr
Judy Floyd, 1977-1987,
Lqs Cruces
OwenLopez, 1977-1983,
SantaFe
Dave Rice, 1972-1983,Carlsbad
SteveTones, Sety/Treas., I 957-1985,Strorro
New Mexico InstituteofMining & Technology
Prcsident
, KennethW. Ford
New Mexico Bureauof Mina& Mineral Resources
D i r e c t o r, . , , . .
... FrankE Kottlowski
DeputtDirector., -Ceorges.Austin
Editor-ceologist
-... ... RobenW.Kelley
Sub&riptiorc: lssued quanerly, February, May, August,
Novmber; sub$ription price$4 00/yr.
Editorial moilet: Contributions of possible material for
considcrarionin future issuesof NMC are welcome
Address inquiries ro Marla D. Adkins, editor of New
Mexico Aeobpl, New Mexico Bureau of Mines &
Mineral Resources,
Socorro,NM 87801
Circulotion: 1,2@
Printer: Universityof New MexicoPrinting ptant
rangeintrude the supracrustalrocks. Condie
(1976)reportedthat graniteand quartz monzonite plutons occur in the Ladron Mountains.
RegionD (fig. l) consistsof the Zuni Mountains where little detailed information is
available.The most usefulwork is a map and
report by Goddard(1966)that is the basisfor
the following interpretation. Pelitic metasediments and quartzite appear to be the
oldestrocks. Plutonic igneousrocks ranging
from quartz monzonite to granite were emplacedand are now strongly gneissic.Metavolcanic rocks, mostly rhyolitic, are next
youngest and are slightly gneissicto well
foliated. Biotite granite was emplacednext,
followed by basalticdikes that are now amphibolites. Monzonite and diorite dikes seem
to be the youngestPrecambrianrocks there.
The oldest plutonic rocks (quartz monzonite
and granite)have beenradiometricallydated
at 1,490 t 90 m.y.; the silicicmetavolcanics
weredatedat 1,380t 30 m.y. (Brookinsand
others,1978).Metamorphismappearsto have
reachedthe upper greenschistor lower amphibolite facies. At least one episode of
isoclinalfoldingprobablytook place.
Region E (fig. l) consistsof Precambrian
rocks of the PedernalHills, divided by Gonzalez and.Woodward (1972)into five major
rock units: l) metaquartzite;2) a heterogeneousunit containing micaceousphyllite
and schistoserocks along with subordinate
augen gneiss, metaquartzite, epidiorite,
greenstone, and arnphibolite; 3) granitic
gneiss;4) intrusivegranite;and 5) cataclastic
rocks.Detailedstratigraphicrelationsbetween
rocks, and
the metaquartzite,heterogeneous
graniticgneisshavenot beendetermined.The
metaquartzite contains quartz-specularite
schist that may have been derived from
chemically precipitatediron formation (ironrich metachert).Although Conzalez(1968)reported the heterogeneous
unit to be mostly
metasedimentary,unpublished mapping in
1979by Fulp revealeda highly differentiated
metavolcanic-metasedimentary
terrane consisting of protoliths of mafic, intermediate,
and felsicvolcanics,epiclasticsediments,and
intermediate conglomerates,agglomerates,
and breccias.Metavolcanicrocks have been
datedat 1,493+ 30 m.y. and graniteat 1,416
+ 100 m.y. by Rb-Sr whole-rockmethods
(D. G. Armstrong, personalcommunication,
1980).The grade of metamorphismreached
the middle greenschistfacies.Early isoclinal
folding wasfollowedby openfolding.
RegionF (fig. l) consistsmostlyof Precambr.ian granite and granite gneiss in southcentralNew Mexico. Minor schist,quartzite,
and phyllite are presentin the San Andres
Mountainsand includea talc deposit(Fitzsimmons and Kelley, 1980).The granitic rocks
rangein agefrom I ,300to I,570m.y. (Muehlberger and others, 1967). Metamorphism
reached the lower amphibolite facies and
isoclinalfoldsmay be present.
RegionG (fig. l) in southwestern
NewMexico is underlainmostlyby the compositeBurro
Mountainsbatholithof Precambrianagethat
is intrusive into metasediments.Accordine
to Hewitt (1959), two metasedimentary sequences that consist of clastics and carbonaterich clastics are found here. The older sequence, atleast 2,300ftthick, was intruded by
leucogranite and regionally metamorphosed to
quartz-feldspar gneiss and hornblende gneiss
prior to deposition of the younger metasediments. The younger sequence,approximately
5,900 ft thick, was metamorphosed to serpentine-carbonate rocks, hornfels, quartzite,
phyllite, and schist. Anorthosite and diabase
were injected into the metamorphic rocks
prior to emplacement of the batholith. K-Ar
and Rb-Sr dating of granitic gneiss of the
presumably older metasedimentary sequence
gives agesof 1,550 and 1,270m.y. (Hedlund,
1978a, b) that probably represent the time of
metamorphism. Hedlund also reported a K-Ar
date on a biotite granite from the Burro
Mountains batholith that gives a model age of
950 m.y.
Sutvlveny-Greenstone terranes characterized by subaqueous metavolcanics with intercalated, dominantly pelitic metasediments occur in the Tusas Range (Moppin metavolcanic
series),Pecos area, Tijeras Canyon-Hell Canyon arca, Pedernal Hills, Picuris Range
(Vadito Formation), and the Taos Range.
Also, a remnant of a greenstonesequencemay
occur in the northern Nacimiento Mountains
where intrusive rocks have mostly engulfed the
older metasediments and metavolcanics. In
southern New Mexico, mainly in the Burro
and San Andres Mountains, a thin sequenceof
shelf sediments including clastics, carbonaterich clastics, and carbonates is present. Intrusive granitic rocks are present throughout
the Precambrian of New Mexico, but are especially widespread in regions F and G. Radiometric dates indicate these rocks are increasinglyyounger toward the south (fig. l).
Mineralization
Metallic mineralization of probable Precambrian age is subdivided into four categories: 1) volcanogenic polymetallic sulfide
deposits; 2) greenstoneexhalative gold with or
without copper deposits; 3) iron-bearing
chemical deposits; and 4) deposits of uncertain
genesis and minor occurrences of various
origins. Each category is describedwith regard
to geologic characteristics and followed by a
compilation of known deposits and prospects.
Volcanogenic polymetallic sulfide deposits
Volcanogenic zinc-lead-copperdepositsthat
commonly contain economic values of precious metals are of great exploration interest
in New Mexico. They occur within the greenstone terranes, and host rocks are generally
felsic metavolcanics (proximal ores) or epiclastic metasediments (distal ores) with
associatediron-bearing metacherts. Ore mineralogy is generally simple, consisting of
pyrite and/or pyrrhotite, with subordinate but
variable amounts of sphalerite, galena, chalcopyrite, and magnetite. Distinguishing characteristics of these deposits are their occurrence in highly differentiated, complex,
metavolcanic-metasedimentarypiles and their
stratiform or stratabound confieuration that
reflects syngenetic, hydrothermal deposition
(Sangster, 1972\. Ev ery recognized greenstone
sequencein New Mexico contains prospectsof
this type, although only one such deposit has
been productive.
The Pecos greenstone of the southern Sangre de Cristo Mountains is a recently recognized volcanogenic massive-sulfide province
(Giles, 1974; Riesmeyerand Robertson, 1979).
The Pecosmine (locality I, fig. l) near Terrero
produced 2.3 million tons of ore, averaging
12.9 percent zinc, 4.0 percent lead, 0.78 percent copper, 3.4 oz/ton silver and 0.ll ozlton
gold during 1927-1939. Up to 1963 this remarkable orebody accounted for nearly 20
percent of the state's total zinc and lead production and 8 percent of its gold and silver
(U.S. Geological Survey, 1965). At today's
prices, the value would be at least $600
million. Riesmeyer (1978) interpreted the host
rocks to be chloritized metarhyolite tuffs
associatedwith a proximal breccia dome.
The Jones Hill deposit (locality 2, fig. l) is
a recent discovery by Conoco, Inc. in the
Macho-Indian Creek area 4 mi southwest of
the Pecos mine. Host rocks and mineralization
appear to be time-stratigraphic equivalents of
the Pecos deposit with both proximal and distal ore lenses; the deposit resembles the Flin
Flon deposit of east-central Manitoba (P. J.
Sterling, personal communication, 1980). Several other prospects are known in the region
including the Rociada district (locality 3, fig.
l), where small copper-lead-zinc occurrences
are found in amphibolites, felsic schists, and
marble lenses;the Doctor Creek area (locality
4, fig. l), where a differentiated, metamorphosed volcano-sedimentary sequence contains abundant cherty iron formation and
minor copper; the Dalton Canyon area (locality 5, fig. l), where intense, stratiform copper
mineralization occurs in metagraywackes and
metapelites, with indications of a buried zinclead deposit in metarhyolite and felsic metatuffs (Fulp, l98l); and Wild Horse Canyon
(locality 6, fig. l), where minor chalcopyritepyrite mineralization is noted in quartzites and
metafelsitesintercalated with metabasalt.
In addition to the aforementioned areas of
obvious economic potential, other occurrences
of base and precious metals include: Mikado
prospects along the Santa Fe River, Penacho
Peak southeast of Santa Fe, Aspen Mountain,
Ruiz Canyon area in the Glorieta district,
Gallinas-Hollinger Canyon area, Tecolote
district, and the western slope of the Rincon
Range (Harley, 1940; Anderson, 1957).Grambling (1979) reported zinc-bearing staurolite
and gahnite in metasediments intercalated
with metavolcanics in the Truchas Range.
Anomalous tungsten and bismuth occur in
stream sediments in the Pecos belt. and
anomalous tin occurs in streams draining
areas underlain by two-mica granite west of
the Glorieta Baldy area (Moench and Erickson, 1980).The Barillas Ridge area has a small
cobalt-nickel-chromium-copper prospect in an
ultramafic xenolith in granite, and a substantial ultramafic terrane is present at Cow Creek
(Wyman, 1980).
I3
New Mexico Geology
Augustl98l
35
The Moppin greenstone terrane of the
Tusas-Brazos Mountains of north-central
New Mexico also hosts polymetallic sulfide
deposits. The Hopewell district (locality 7, fig.
l) consists of numerous patented claims,
mostly placer gold operations, worked sporadically from the late 1870'sto the 1960's.Lode
prospects include narrow stratabound copperlead-zinc lenses and quartz-sulfide veins in
sheared greenschist and metarhyolite. Mineralized lenses, consisting of concentrated
sulfide cores decreasing outward to disseminated pyrite zones and then unmineralized
country rock suggesta syngeneticorigin. Prospects in the Bromide district (locality 8, fig. l)
resemble those of the Hopewell district to the
north. Host rocks, mineralogy, and mode of
occurrence are generally the same except for
the presence of argentiferous tetrahedrite in
the Bromide mines, molybdenite in the Tampa
mine, and lower gold values. Mining activity
commenced in the 1880's with 35 patented
claims, but by 1910, activity had ceased. The
Bromide mine reopened and operated during
1956-57 (Bingler, 1968), and renewed interest
in both these districts occurred in the 1970's
with much exploration and drilling but no announced discoveries.
The Tijeras-Hell Canyon greenstone complex of the Manzanita and northern Manzano
Mountains contains one known volcanogenic,
polymetallic sulfide deposit at the York mine
(locality 9, fig. 1). The deposit is a small,
stratiform copper-lead-zinc body occurring in
a cherty-iron-marble lens. Host rocks are tuffaceous metasedimentswithin a terrane dominated by greenstoneand mafic metasediments.
Numerous copper occurrencesare reported in
the greenstone between Tijeras Canyon and
Hell Canyon (Reiche,1949;Elston, 1967).
The Pedernal schist belt of east-central New
Mexico (locality 10, fig. l) also is a greenstone
terrane. Although there are only sparsesecondary copper occurrences in the complex, the
lithologic sequence(including felsic pyroclastics) is indicative of an environment of deposition favorable for volcanogenic massive sulfides. A similar lithologic sequenceoccurs ro
the northwest in the Lobo Hill horst (locality
I I, fig. l). Although outcrops of Precambrian
rock are rare. rocks similar to the Pedernal
terrane including metagraywacke, felsic
gneiss, chlorite schist, and meta-agglomerate
are exposedin severalprospect pits with minor
chalcopyrite and malachite. A large quartzite
body (metachert?) crops out southeast of the
sequencedescribedabove.
The Twining (Rio Hondo) district (locality
12, fie. l) of the Taos Range includes a200-ftwide shear zone that can be traced for at least
2.5 mi in a northeasterly direction and is conformable with the metamorphic foliation. Several mines and prospects have been developed
along the shear zone including the Frazer,
Bull-of-the-Woods (Highline), and Comstock.
The country rock is amphibolite, but talc,
sericite, and chlorite schists are present in the
shear zone. Mineralization consists of pyrite,
copper sulfides, secondary copper minerals,
and gangue along fractures and as disseminations in the sheared schist. Precious-metal
values have been reported. To the north
36
A u g u s tl 9 8 l
New Mexico Geology
several prospects are found in other parallel
shears including the Silver Star lead-zinc, the
Iron Dyke specularite schist, and the Commodore copper occurrences. The mineralization is interesting because it is associated
with amphibolite, chlorite-talc-sericite-quartz
schist (shearedand altered metarhyolite?), and
specularite schist (sheared iron formation?)
that may be a differentiated metavolcanic sequence. Restrepo (1972), in a detailed study of
the area, favored a volcanogenic massive sulfide origin for the deposits with remobilization and redistribution during subsequent
events.
Greenstoneexhalative gold with or without
copper deposits
Also of major exploration interest in the
greenstone terranes are the exhalative gold
with or without copper deposits. These orebodies are generally found in metamorphosed
mafic volcanic sequences with interlayered
cherty-iron or iron-carbonate-facies chemical
precipitates. The orebodies are believed to be
syngenetic, hot-spring deposits in submarine
environments, with the metals leached from
underlying flows and pyroclastics and redeposited by late-stagehydrothermal activity.
Remobilization by later metamorphic processes may concentrate and redistribute the
ore, and the deposits thus may occur in concordanI stratabound horizons, in vein systems, in shear zones, or in saddle reefs.
The most common assemblageincludes goldquartz-pyrrhotite-arsenopyrite and may include ankerite, siderite, pyrite, chalcopyrite,
graphite, and scheelite. Cuinmingtonite schist
is commonly the host rock in medium-grade
metamorphic rocks. Alteration of host rocks
to talc and chlorite schist or serpentineis common (Sawkins and Rye, 19'14;D. L. Giles, personal communication, 1979).
Three deposits of this type are known in
New Mexico. In Tijeras Canyon, the Great
Combination and Mary M mines (locality 14,
fig. 1) consist of a few small pits and adits in
shearedgreenstonewith abundant quartz veinlets. Mineralization consists of malachite.
chalcopyrite, pyrite, magnetite, and gold;
small shipments of ore have been reported
(Kelley and Northrop, 1975).In the Hell Canyon area to the south, the Milagros mine and
adjacent Star shaft (locality 15, fig. l) are
deposits that occur in sintery quartz veins and
metachert in shearedgreenstoneand metasediments. The deposits are within the zone of oxidation and consist of copper carbonates, iron
oxides, minor native copper, gold, and silver.
The mines produced gold and copper in the
1880's and early 1900's; in 1975-76 the
Milagros mine was operated as an open pit
and produced over $300,000of gold and silver
(Woodward and others, 1978). The Moppin
greenstone of the Hopewell district (locality
16, fig. l) hosts numerous quartz-sideritepyrite-gold veins in greenschist. The presence
of abundant siderite and pyrite in the remobilized veins suggestsa precursor of chertyiron exhalite. They are the probable source of
the placer gold found in the area (Bingler,
1968). A small amount of gold is reported to
occur in an iron formation at Iron Mountain
(locality 17, fig. l) (Lindgren and others,
l9l0).
Iron-bearingchemicaldePosits
There are two principal types of banded
iron formations: the Lake Superior type,
which is strictly sedimentaryand forms by
chemical precipitation in tectonically stable
basins with restricted circulation; and the
Algoma type, which is volcanogenicand
forms by exhalativeprocessesduring quiescent periodsin volcanic cycles(Sims, 1976).
The vast majority of the world's iron-ore
reservesare of the Lake Superior type. However, the Algoma-typedepositsmay contain
gold that may be concentrated by silica
leaching, metamorphic differentiation, and
structuraldeformation.
Two small Algoma-typedepositsoccur in
the Moppin greenstonecomplex. The Iron
Mountain area (locality 17, fie. l) north of
Hopewell Lake consistsof two layers of
schistaveraging40
magnetite-quartz-chlorite
percent iron. The depositsare 10-20 ft thick
with a strike length of severalhundred feet
(Bingler, 1974).ln the Cleveland Gulch area
(locality 18, fig. 1) of the Bromide district a
similar body occursand is traceableby magnetometerfor 3,000ft along strike.Two ironrich samplesran 29.7 and 37.7 percentiron
(Harrer and Kelly, 1963). In the Cabresto
Creek area (locality 19, fig. 1) of the
Taos Range,magnetite-hematite-ilmenite-rich
bands of uncertain origin are common in
quartzite,gneiss,and schist.Richer concentrationsrangeup to 25 percentiron and are up to
50 ft thick (Schilling, 1960). In addition,
numeroussmall lensesand bodies of metamorphosed cherty iron formation occur
throughout the greenstoneterranesof New
Mexico. They are of economicinterest,however, becauseof their common association
with volcanogenicmineralization.
and minor
Depositsof uncertaingenesis
of variousorigins
occurrences
In the Copper Hill-Copper Mountain district (locality20, t\g. 1) in the Picuris Range,
mineralizationconsistsof secondarycopper
carbonates,silicates,and oxides and minor
secondaryuranium minerals along fracture
planes in massive Ortega Quartzite and
shearedschists.Gold and silvervaluesarealso
reported(Lindgrenand others,l9l0). The depositsweredevelopedin the early 1900'sand
extensivelydrilled in the Iate 1960'sand early
low-gradecopperde1970's.A medium-size,
posit is presentat Copper Hill but is subeconomic. The secondary,remobilized copper
mineralsare of interestbecauseof proximity
to the Vadito Formation,thought to be corwhich hosts
relativewith the Pecosgreenstone
massivesulfidedeposits.
In the Copperton, Diener Canyon, and
Montezumaareasof the Zuni Mountains(locality 21, fig. l), copper sulfides, pyrite,
secondarycopper minerals,gold, and silver
occur in shearzonesand as disseminationsin
metarhyolitesand hypabyssalgranitic rocks.
Someof theseprospectsoccur with potassic
(continuedon p. 41)
Precambrian
metallic mineralization
and phyllic alteration and may represent
Precambrian porphyry-type copper deposits
(M. Seay, personal communication, 1980). In
the Hagen Creek-Glorieta Canyon area of the
southern Santa Fe Range, chalcopyrite-pyrite
disseminations occur in Precambrian granite
(D. G. Armstrong, personal communication,
1980).
In the central San Andres Mountains (locality 13, fig. l) two small prospects have been
describedthat may be of syngeneticorigin. In
Sulphur Canyon, high-grade copper-iron ore
consisting of chrysocolla, malachite, and
specularite is associated with a massive
chlorite lens that shows a very sharp contact
with enclosing sericite schist. To the south in
Grandview Canyon, sheared greenstone, altered to chlorite and calcite but showing original igneous texture, contains pods and veinlets
of chalcopyrite, malachite, and calcite near a
contact with quartzite (Lasky, 1932). Condie
and Budding (1979) included the shearedrock
in a schist and phyllite unit with thick, conformable m etadiabasesills.
Base and/or precious metal prospects in
Precambrian host rocks are reported from
nearly every county with Precambrian rock exposuresand are listed below:
Bernalillo County-Tijeras Canyon, goldquartz veins (Elston, 1967);
Colfax County-Hematite
Creek and West
Moreno areas in the ElizabethtownBaldy district, gold-quartz veins (Clark
and Read, 1972);
Dofla Ana County-Gold Camp (gold-copper-quartz veins) and Mineral Hill (goldquartz veins) in the Organ Mountains
(Dunham, 1935);
Grant County-Gold
Hill district in the
Burro Mountains, gold-silver-lead-zincquartz veins (Lindgren and others, l9l0;
Gillerman, 1964);
Hidalgo County-Little
Hatchet Mountains, copper (Zeller, 1970);
Luna County-Stenson mine in the Florida
Mountains, copper-quartz veins and disseminatedcopper (Griswold, l96l);
Mora County-Rio de la Casa, Lujan Creek
prospects, gold-quartz veins (tIarley,
1940);
Sandoval County-Nacimiento
district
prospects, disseminated copper in schist,
diabase dikes with gold, base and precious metals in shear zone (Lindgren and
others, l9l0; Woodward and others,
1972);
Sierra County-Shandon (Pittsburg) district, gold-quartz veins (Harley, 1934);
Socorro County-Ladron Mountains, copper-quartz veins (Condie, 1976); Corkscrew Canyon prospect, zinc-copper in
shear zone (Lasky, 1932); and
Taos County-Cabresto Creek (base metals), Columbine Creek (lead-zinc-copper
disseminations), San Cristobal Creek
(copper in shear zone), Enderman prospect (gold in shear zone), Golden Goose
prospect (gold-quartz in shear zone) in
the Questa-Red River areas (Schilling,
(continuedf rom p.36)
1960; Clark and Read, 1972); Picuris
Range, copper-quartz in veins and shears
(Montgomery, 1953).
Several molybdenum- or tin-bearing
pegmatites of minor importance are known
from the northern part of the state (U.S.
Geological Survey, 1965). Minor tungsten
with or without bismuth prospects occur in
severalscatteredlocalities. Most of theseprospects are pegmatite or quartz vein occurrences
containing scheelite and minor wolframite.
Some appear to be skarnlike deposits of
scheelite-quartz-hornblende-epidote assemblages in schist and amphibolite that are probably derived from marly sediments. Tungsten
prospects(Dale and McKinney, 1959)include:
Peak, Gold Hill,
Grant County-Bullard
Rice-Graves area in the Burro Mountains;
San Miguel County-El Porvenir district in
the Las VegasRange;
Sierra County-Grandview prospect in the
San Andres Mountains: and
Taos County-Tungsten (Wichita) mine in
the Picuris Range.
Moench and Erickson (1980) proposed a
stratabound volcanogenic origin for scheelite
in the Pecos greenstone terrane although the
scheelite-quartz-hornblende-epidote association with amphibolites is analogous to skarn
prospects described by Hewitt (1959) in the
Burro Mountains.
Implications f or exploration
Greenstonebasins are volcano-sedimentary
terranes characterized by subaqueous differentiated metavolcanics with intercalated, predominantly pelitic metasediments. The association of polymetallic massive sulfides and
exhalative gold with or without copper deposits with greenstone terranes makes the
following areas prime targets for mineral exploration: Pecos greenstone,Moppin metavolcanics, Tijeras-Hell Canyon greenstone, and
the Pedernal schist belt. Of lesser importance
are the Vadito Formation of the Picuris area
and the relatively unknown Taos Range metamorphics.
Becauseof the tendency for massive sulfide
deposits to occur in clusters and the fact that
the Pecos area contains two discovereddeposits, additional occurrencesare likely. Of particular interest are the central and southwest
parts of the belt where there are major felsic
metavolcanic centers,including Willow Creek,
Macho Canyon-Jones Hill, Doctor Creek,
and Dalton Canyon and surrounding areas.
The other greenstoneterranes contain stratiform base-metal prospects, but none has produced significant tonnages. However, the
most important criteria in massive sulfide
evaluation are the lithologic associations and
environments of deposition, not the grade or
tonnage of outcropping prospects. Because
outcropping major ore deposits will probably
not be found, exploration must focus on
minor prospects and buried, even blind,
targets. The most effective prospecting
method is reconnaissancemapping followed
by an airborne electromagnetic and magnetometer survey. Panned heavy minerals and
bulk sediment stream sampling are often
employed with good success. After broad
targets are delineated, the successfulexploration program will employ thorough geologic
mapping, coupled with ground geophysicsand
geochemicalprospecting.
The potential for economic exhalative gold
with or without copper deposits is also deemed
very high in New Mexico. Because of their
known gold occurrences, the Tijeras-Hell
Canyon and Moppin terranes are assignedthe
greatest potential. The exploration program
should involve recognition of suitable rock
types (iron-bearing metachert within metavolcanic sequences) coupled with geophysical
surveys and extensive geochemical sampling
using pathfinder elements such as arsenic,
mercury, and tungsten. Recognition of fold
styles and geometry is important as these ore
bodies tend to be concentrated in dilatant
zones and nosesof folds.
Iron formations in New Mexico probably
will not be of economic interest in the near
future for their iron content because of low
reserves and/or grade combined with distance
from a market. The Algoma-type iron formations, however, can be useful in prospecting
for gold deposits as they are in some cases
related to exhalative deposits containing gold.
Magnetic geophysical methods and geochemical investigation for pathfinder elementsin the
iron formations could lead to definition of
targets.
Of undetermined economic importance are
the numerous minor prospects scattered
throughout the Precambrian rocks of New
Mexico. Most are small and low grade; however, any of the gold-bearing veins and shears
could have potential for a large disseminated
deposit. Metamorphic and structural processesand geologic history are important in
that differentiation, remobilization, and concentration of slightly anomalous or even background values of gold in country rocks could
produce an orebody in suitable host rocks.
The occurrence of Precambrian porphyrytype copper prospects merits further exploration in the granitic stocks and plutons
throughout the state. Also, some potential
must be assigned to the tin and tungsten
anomalies reported in the southern Santa Fe
Range, primarily because their existence has
been reported only recently and they have not
been evaluated. More investigation of the twomica granites in that area is warranted, as
these kinds of rocks are hosts for most of the
world's tin. The possibility of volcanogenic or
skarn-type scheelitebodies in metabasalts also
deservesfurther investigation.
Considerable economic mineral potential
exists in the Precambrian rocks of New Mexico. Discovery of major deposits, however,
will require long-range exploration programs
with field geologists experienced in structurally complex metamorphic terranes, sophisticated geophysical and Beochemical
New Mexico Geology
Augustl98l
techniques,and a perseveringand dedicated
management.
AcKNowLEDGprBNrs-We
thank Philip J.
Sterling,DaleG. Armstrong,and JonathanF.
Callenderfor critically reviewingthe manuscript.
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New Mexico Bureau of Mines and Mineral Resources,
B u l l 9 6 , 2 3p
l
MineHealth,Safety,
and TrainingInstitute
scheduled
The SeventhInstitute of Mine
Health, Safety,and Training will
be held at the ColoradoSchoolof
Minesin Golden,CO, on November 4-6, 1981.The institute,establishedto provide a forum for
the mining community to focus
upon mine healthand safetyconcerns,is sponsoredby the Colorado School of Mines, Mine
Safety and Health Administration, U.S.Bureauof Mines,Colorado Mining Association, and
ColoradoSafetyAssociation.For
information on registrationand
fees, contact Robert T. Reeder,
Program Institute Chairman,
Associate Professor, Mining
EngineeringDepartment, Colorado School of Mines, Golden,
co 80401.