Mineral Deposit Models for Northeast
Asia
By Alexander A. Obolenskiy1,
Sergei M. Rodionov2, Sodov Ariunbileg3,
Gunchin Dejidmaa4,
Elimir G. Distanov1, Dangindorjiin Dorjgotov5,
Ochir Gerel6,
Duk Hwan Hwang7, Fengyue Sun8, Ayurzana
Gotovsuren9,
Sergei N. Letunov10,
Xujun Li8, Warren J Nokleberg11,
Masatsugu Ogasawara12,
Zhan V. Seminsky13, Akexander P. Smelov14,
Vitaly I. Sotnikov1,
Alexander A. Spiridonov10, Lydia V. Zorina10,
and Hongquan Yan8
1 Russian Academy
of Sciences, Novosibirsk
2 Russian Academy
of Sciences, Khabarovsk
3
Mongolian Academy of Sciences, Ulaanbaatar
4
Mineral Resources Authority of Mongolia, Ulaanbaatar
5
Mongolian National University, Ulaanbaatar
6
Mongolian University of Science and Technology, Ulaanbaatar
7
Korea Institute of Geology, Mining, and Materials, Taejon
8
Jilin University, Changchun, China
9
Mongolia Ministry of Industry and Commerce, Ulaanbaatar
10 Russian Academy
of Sciences, Irkutsk
11
U.S. Geological Survey, Menlo Park
12 Geological Survey
of Japan/AIST, Tsukuba
13 Irkutsk State
Technical University, Irkutsk
14 Russian Academy
of Sciences, Yakutsk
Introduction and Companion
Studies
Metalliferous
and selected non-metalliferous lode and placer deposits for Northeast
Asia are classified into various models or types described below. The
mineral deposit types used in this report are based on both descriptive
and genetic information that is systematically arranged to describe
the essential properties of a class of mineral deposits. Some types
are descriptive (empirical), in which instance the various attributes
are recognized as essential, even though their relationships are unknown.
An example of a descriptive mineral deposit type is the basaltic Cu
type in which the empirical datum of a geologic association of Cu sulfide
minerals with relatively Cu-rich metabasalt or greenstone is the essential
attribute. Other types are genetic (theoretical), in which case the
attributes are related through some fundamental concept. An example
is the W skarn deposit type in which case the genetic process of contact
metasomatism is the genetic attribute. For additional information on
the methodology of mineral deposit types, the reader is referred to
discussions by Eckstrand (1984) and Cox and Singer (1986). For each
deposit type, the principal references are listed in parentheses.
This
article is prepared by a large group of Russian, Chinese, Mongolian,
South Korean, Japanese,
and USA geologists
who are members of the joint international project on Major Mineral
Deposits, Metallogenesis, and Tectonics of the Northeast Asia. This
project is being conducted by the Russian Academy of Sciences, the Mongolian
Academy of Sciences, Mongolian National University, Mongolian Technical
University, the Mineral Resources Authority of Mongolia, Geological
Research Institute, Jilin University, China Geological Survey, Korea
Institute of Geoscience and Mineral Resources, the Geological Survey
of Japan, and the U.S. Geological Survey. Information about major goals
and pubications for this project is available at the USGS Internet/Web
site at http://minerals.usgs.gov
/west/projects/minres.html
Several
companion studies, that are part of the study of NE Asia, are closely
related to this paper. These companion studies are: a detailed geodynamics
map of Northeast Asia (Parfenov and others, in press); a database of
significant lode mineral deposits and placer districts (Ariunbileg and
others, in press); a series of metallogenic belt maps (Obolenskiy and
others, 2001).
Classification of Mineral
Deposits
The
following three main principles are the basis for the following classification
of mineral deposits for this study. (1) Ore forming processes are close
related to rock forming processes (Obruchev, 1928) and mineral deposits
originate as the result of mineral mass differentiation under their
constant circulation in sedimentary, magmatic, and metamorphic cycles
of formation of rocks and geological structures (Smirnov, 1969). (2)
The classification must be as more comfortable and understandable for
appropriate user as possible. And (3) the classification must be open
so that new types of the deposits can be added in the future (Cox and
Singer, 1986).
The
below classification is constructed as further development of mineral
deposit classification of Smirnov (1969), and on the mineral deposit
types of Eckstrand (1984), Cox and Singer (1986), Nokleberg and others
(1997), cited references for specific models, and available data on
the problem. In the classification of Smirnov (1969), the mineral deposits
are grouped into six hierarchic levels of metallogenic taxons according
to such their stable features as: (a) environment of formation of host
and genetically-related rocks, (b) genetic features of the deposit,
and (c) mineral and (or) elemental composition of the ore. The six hierarchial
levels are as follows.
Group of deposits
Class
of deposits
Clan of deposits
Deposit types (models)
Table
1 provides a hierarchial ranking of mineral deposit models according
to these levels. For simplicity, the classification in this table does
not employ the family and genus levels.
The
deposit models are subdivided into the following four large groups according
to major geological rock-forming processes: (1) deposits related to
magmatic processes; (2) deposits related to hydrothermal-sedimentary
processes; (3) deposits related to metamorphic processes; and (4) deposits
related to surficial processes. A separate group of exotic ore-forming
processes is also defined. Each group includes several classes. For
example, the group of deposits related to magmatic processes includes
two classes: (1) those related to intrusive rocks; and (2) those related
to extrusive rocks. Each class includes several clans, and so on. The
most detailed subdivisions are for magmatic-related deposits because
they are the most abundant in the project area. In the below classification,
lode deposit types models that share a similar origin, such as magnesian
and (or) calcic skarns, or porphyry deposits, are grouped together under
a single genus with several types (or species) within the genus.
Some
of the below deposit models differ from cited descriptions. For example,
the Bayan Obo type was described previously as a carbonatite-related
deposit. However, modern isotopic, mineralogical, and geological data
recently obtained by Chinese geologists have resulted in a new interpretation
of the deposit origin. These new data indicate that the deposit consists
of deposit minerals that formed during Mesoproterozoic sedimentary-exhalative
process, and along with coeval metasomatic activity, sedimentary diagenesis
of dolomite, and alteration. The sedimentary-exhalative process consisted
of both sedimentation and metasomatism. Later deformation, especially
during the Caledonian orogeny, further enriched the ore. Consequently,
the Bayan Obo deposit type is herein described as related to sedimentary-exhalative
processes, not to magmatic processes. However, magmatic processes also
played an important role in deposit formation. Consequently, this deposit
model is part of the family of polygenetic carbonate-hosted deposits.
Similar revisions are made for carbonate-hosted Hg-Sb and other deposit
models.
Deposits Related to Intrusive
Magmatic Rocks
I. Deposits Related to
Mafic and Ultramafic Intrusions.
A. Deposits Associated
with Rift-related Differentiated Mafic-Ultramafic Complexes
Mafic-Ultramafic-Related
Cu-Ni-PGE (Eckstrand, 1984; Page, 1986c; Dyuzhikov, and
others, 1988)
This
deposit type consists of magmatic sulfide Cu-Ni deposits in differentiated
layered mafic-ultramafic intrusions. Layered intrusions generally occur
in a cratonic setting, in many cases associated with intracontinental
rifts and flood basalts. Mafic and ultramafic phases of layered intrusive
complexes include peridotite, pyroxenite, gabbro, norite, picrite, troctolite
and gabbro-diabase. The deposits may occur either in the footwall below
the main intrusion, or near the bottom of the intrusion. Conformable
layers or lenses commonly occur in a local depression or embayment,
at or near the base of the host intrusion. Deposit minerals consist
of massive sulfide minerals, sulfide-matrix breccias, interstitial sulfide
networks, and disseminated sulfide minerals. In well-preserved deposits,
the rich areas of deposit minerals occur close to the base, and are
overlain by sparse disseminated sulfide minerals. Sulfide veins and
dissemination commonly penetrate footwall rocks. The deposit minerals
are complex and contain Ni and Cu along with PGE, Co, Se, Te, and Au.
Deposit minerals include pentlandite, chalcopyrite, cubanite, millerite,
pyrrhotite, various PGE minerals, pyrite, sphalerite, and marcasite.
They are associated with plagioclase, hypersthene, augite, olivine,
hornblende, biotite, quartz and a variety of alteration minerals. The
main deposit minerals are syngenetic with the host intrusions. The depositional
environment is emplacement of multiple ore-bearing mafic magmas (probably
mantle-derived) in upper crustal levels in tensional environments associated
with rifting. Contamination of the magma was an important factor for
sulfur saturation and formation of a sulfide phase. Examples of the
deposit type are at Hongqiling, Jilin Province, China, Kalatongke, Xinjiang,
China, Norilsk I and II, Russia, and Talnakh, Russia.
Mafic-Ultramafic Related
Ti-Fe (+V) (Lee and others, 1965; G.A. Gross and E.R. Rose, in Eckstrand,
1984; Page, 1986a; Sinyakov, 1988; S.M. Rodionov, this study)
This
deposit type consists of layers and lenses, and disseminated titanomagnetite
or vanadium-magnetite, with minor amount of ilmenite and chromite, in
differentiated gabbroic intrusions. The host rocks are mainly norite,
gabbro-norite, dunite, harzburgite, peridotite, pyroxenite, troctolite,
anorthosite, gabbro, and diabase. Deposit minerals occur near tops of
intrusions as stratiform or irregular bodies consisting of disseminated
and interstitial Fe-Ti-V oxide minerals. Pipes and ilmenite-rich veins
may cut layers. Massive ore is generally more important economically
than disseminated ore. The principal ore mineral is titanomagnetite
and (or) V-magnetite. Associated minerals are ilmenite, hematite, spinel,
and sulfide minerals (pyrite, pyrrhotite, chalcopyrite). Rock-forming
minerals are plagioclase, olivine, pyroxene, apatite, and sphene. Also
occurring are Fe and Ti-oxide phases that formed during by crystal settling
or filter pressing during crystallization of anorthosite or gabbro magmas,
thereby forming syngenetic layers and segregations, as well as massive
oxide autointrusions in partly solidified gabbro and genetically related
host rocks. The depositional environment consists of intrusions of gabbro-anorthosite,
dunite-pyroxenite-gabbroic and gabbro-diabasic magmatic associations
with magmatic layering of host intrusions. Mafic-ultramafic rocks often
intrude into granitic gneiss or into volcanic-sedimentary units. An
association exists between the ore-bearing layered plutons and deep-fault
zones. Age of the deposits is generally Precambrian, but may be as young
as Tertiary. Locally, Precambrian deposits may be highly metamorphosed
with occurrence of deposits in hornblende schist as at the Soyonpyong
deposit on the Korean Peninsula. The depositional environment consists
of stratiform to irregular mafic to ultramafic plutons in continental
margins or island arcs. Examples of the deposit type are at Damiao,
Hebei Province, China, Kavakta, Russia, and Lysanskoye, Russia.
Zoned Mafic-Ultramafic
Cr-PGE (Page and Gray, 1986; Kosygin and Prikhod’ko, 1994; Malich,
1999)
This
deposit type consists of zoned ultramafic to mafic plutons with Cr and
PGE minerals. The central part of the pluton is generally composed of
dunite and the peripheral part consists of pyroxenite, koswite, and
rare gabbro. The zoned plutons are often intruded by sills and dikes
of gabbro, diorite, monzonite, and various alkaline rocks. The mafic
and ultramafic rocks comprising the pluton, as well as host metamorphosed
sedimentary-calcareous rocks may be locally altered into feldspar-pyroxene
metasomatite and skarn. Deposit minerals in the zoned plutons are chromite,
native PGE, various PGE minerals and alloys, and Ti-V magnetite, and
accessory local pentlandite, pyrrhotite, bornite, and chalcopyrite.
Deposit minerals generally occur in dunite in the top-central part of
the pluton. Large (up to 3 kg and more) to small nuggets of platinum
may occur in peripheral placer deposits. The depositional environment
consists of zoned mafic to ultramafic plutons that form the lower parts
of island-arc or continental margin arc systems.
I. Deposits Related to
Mafic and Ultramafic Intrusions.
B. Deposits Associated
with Ophiolitic Complexes
Podiform Chromite (J.M.
Duke in Eckstrand, 1984; Albers, 1986)
This
deposit type consists of pods or lenses of chromite in the ultramafic
parts of ophiolite complexes (alpine peridotites) that may be locally
intensely faulted and dismembered. Host rocks are mainly dunite and
harzburgite that are commonly serpentinized, and local troctolite in
some few areas. The principal ore mineral is chromite. Associated minerals
are olivine, pyroxene, serpentine, magnetite, clinopyroxene, and plagioclase.
Deposits generally consists of lenticular bodies of massive to heavily
disseminated chromite. Tabular, rod-shaped and irregular bodies may
also occur. Nodular textures, and foliation and banding are common.
A specific deposit may consist of a number of individual pods that tend
to occur in linear zones, in some cases, in an echelon fashion. The
depositional environment consists of magmatic cumulates in elongate
magma pockets along oceanic ridges or the basal parts of island arcs.
Associated minerals are magnetite and PGE-minerals and alloys. Examples
of the deposit type are at Ganbi, Japan, Hegenshan 3756, Inner Mongolia,
China, Khalzan uul, Mongolia, and Sulinheer group, Mongolia.
Serpentinite-Hosted Asbestos
(Cho and others, 1970; Zolojev, 1975;
J.M. Duke in Eckstrand, 1984; Page, 1986b)
This
deposit type consists of chrysotile asbestos developed in stockworks
in serpentinized olivine-rich ultramafic rocks that consist mainly of
harzburgite, dunite, wehrlite, and pyroxenite. Serpentinized ultramafic
rock may be locally intruded by pegmatite dikes (as in the central Korean
Peninsula). Associated minerals are magnetite, brucite, talc, and tremolite.
The major deposits occur in allochtonous bodies of serpentinized ophiolitic
or alpine ultramafic rocks in Phanerozoic orogenic belts. The depositional
environment consists of ultramafic rocks that form the basal part of
ophiolite sequences that are obducted onto a continental margin, or
form part of an accretionary wedge or subduction zone complex. Examples
of the deposit type are at Ikh nart, Mongolia, Molodezhnoye, Russia,
and Sayanskoye, Russia.
I. Deposits Related to
Mafic and Ultramafic Intrusions.
C. Deposits Associated
with Anorthosite Complexes
Anorthosite Apatite-Ti-P
(Sang and Shin, 1981; Kosygin and Kulish, 1984; Force, 1986a; Jeong
and others, 1998)
This
deposit type occurs in anorthosite plutons composed of andesine and
andesine-labradorite. The anorthosite plutons are highly alkalic and
are associated with gabbro, ferrodiorite, syenite, alkalic granite,
and sometimes mangerite. The plutons generally intrude granulite-facies
country rocks. Principal deposit minerals are apatite, titanomagnetite,
and ilmenite that occur either as: (1) disseminations near melanocratic
gabbro, pyroxenite, and dunite along the margins of the anorthosite
plutons; or (2) rich apatite (nelsonite) veins that occur in tectonically
weak zones. Associated minerals are lesser ilmenite and magnetite. The
depositional environment is intrusion into the basal part of continental
crust or craton under hot, dry conditions. Examples of the deposit type
are at Gayumskoe, Maimakanskoe, and Dzhaninskoe, Russia.
I. Deposits Related to
Mafic and Ultramafic Intrusions.
D. Deposits Associated
with Kimberlite.
Diamond-Bearing Kimberlite
(Khar’kiv and others, 1997; Zhang and Xu, 1995)
This
deposit type consists of pipes and dikes made of kimberlite breccia.
The deposits occur mostly near secondary branches of giant, deep, long,
extension faults in stable craton (e.g., the Tanlu Fault Belt in eastern
North China Platform). The pipes have rounded or elongated shapes with
diameters of few hundred meters. In the North Asian Craton in the study
area, kimberlite pipes range in age from Devonian through early Tertiary.
Within a few hundred meters of the surface, the pipe is usually funnel-shaped,
at deeper depths (down to about 1,500 m), is cylindrical, and at greater
depths may have the shape of a feeder dike. The kimberlite dikes generally
range from 0.3 to 0.7 m to 20 m wide, are 100 to 800 m long and several
hundred meters long down dip. Kimberlites usually are concentrated in
kimberlite fields generally less than 1 hectare in area, and from several
kilometers to 20 kilometers apart. The kimberlite breccia consists of
fragments of sedimentary cover rocks, including limestone, sandstone,
shale, schist, granulite, and gneiss that from parts of Precambrian
cratonal basement, as well as dunite, garnet lherzolite, garnet saxonite,
picotite lherzolite, phlogopite, diamond‐bearing ultramafic rocks
eclogite, spinel and spinel‐free ultramafic rock, and pyroxenite.
The ultramafic and associated rocks are interpreted as mantle-derived.
Inclusions of Phanerozoic sedimentary cover and craton basement rocks
are abundant at margins of kimberlite pipes and dikes. Pipes and dikes
usually also contain inclusions of mantle-derived minerals that range
from 1 to 10 cm, including Cr pyrope and picotite. The breccia is cemented
by tuff with xenocrysts of altered olivine (group I), pyrope, picroilmenite,
Cr spinel, Cr diopside, and rare large (up to 2 cm) grains of gem-quality
zircon. The minerals are embedded in a carbonate-serpentine matrix including
olivine II, picroilmenite II, Cr spinel II, phlogopite, and perovskite.
Secondary minerals, such as serpentine, carbonate, and chlorite, comprise
the bulk of the kimberlite in both the upper and deeper parts of the
pipe. Rare minerals are Cr diopside, picrotanite, morssanite, rutile,
oysanite, and zircon. Kimberlite is intruded in hypabyssal conditions
as indicated by typical massive structures and pseudomorph of coarse
olivine crystals that are scattered in fine-grained matrix of phlogopite,
serpentine, calcite, and perovskite. Only part of kimberlite pipes and
dikes contain industrial diamond. Indicator minerals for diamond in
kimberlite are Cr diopside and picotite, and associated diamond placer
deposits. The depositional environment consists of kimberlite magma
as forming during deep-level subduction of oceanic crust and mantle
metasomatism in cratonal regions. The kimberlite magmas are erupted
along various shear-fault systems to near-surface levels during uplift
of craton. Subsequent younger uplift resulted in the erosion of the
kimberlite and exposure of root systems, including pipes and dikes.
Examples of the deposit type are at Ingashinskoye, Mir, and Yubileinaya,
Russia.
II. Deposits Related to
Intermediate and Felsic Intrusions. A. Pegmatite.
Muscovite Pegmatite (Sokolov,
1970; Chesnokov, 1975; Vasil’eva, 1983; Hongquan Yan, this study)
This
deposit type consists of pegmatite veins, containing high-quality foliated
muscovite that occurs in schist that is metamorphosed to amphibolite
facies. Pegmatite veins are generally concentrated in apical parts of
large granite-migmatite domes and are mainly confined to horizons of
aluminum silicate rocks (e.g., biotite-muscovite granite gneiss, two-mica
schist). Groups or fields of pegmatite veins may be hosted in hinge
areas of anticlines and flexures in schist that are multiply deformed.
The shape of deposits is diverse, and cross-cutting dikes with numerous
tongues are dominant. The pegmatite minerals are plagioclase (oligoclase,
oligoclase-andesine), microcline-perthite, quartz, biotite, muscovite,
tourmaline, and rare beryl and almandine garnet. Veins with plagioclase,
plagioclase-microcline, and microcline mineral types are dominant. High-grade
muscovite is typical in quartz masses that contain corroded feldspar
crystals. The depositional environment consists of pegmatite fields
in regional metamorphic and granitic belts that occur along the periphery
of ancient cratons. A large number of muscovite pegmatite fields, some
with REE, occur in some pegmatite belts and may extend for several hundred
kilometers. Examples of the deposit type are at Chuyskoye, Lugovka,
and Vitimskoye, Russia.
REE-Li Pegmatite (Lee,
1959; Kovalenko and Koval, 1984; Rundqvist, 1986; Kim, and Park, 1986;
Zagorskiy and others, 1997; Lin and others, 1994a; S.M. Rodionov, this
study; Ochir Gerel, this study; Hongquan Yan, this study)
This
deposit type consists of two subtypes.
(1)
The first subtype consists of REE spodumene granite pegmatite that is
associated mainly with two-mica granite. Pegmatite deposits generally
occur exocontact zones of granite intrusions, generally within 1 to
3 km of contacts and intrude metamorphosed carbonaceous and clastic
rocks. Pegmatite bodies often clustered in elongated belts that occur
along regional faults. Pegmatite veins often occur along feather joints.
Two morphological types of pegmatite bodies are distinguished: (a) elongated
and persistent veins and vein systems that occur at depth; and (b) single
and small vein-shaped bodies. Major minerals are albite, oligoclase,
spodumene, quartz, microcline, muscovite, beryl, helvite, columbite-tantalite,
fluorite, tourmaline, cassiterite, and zircon. Lesser minerals are various
sulfide minerals, including pyrite, molybdenite, galena, and others.
The principal ore element is Li along with associated Ta, Nb, Sn, Be,
Mo, and W. Mineral zonation is typical in large pegmatite bodies. The
Keketuohai pegmatite No. 3 (Xinjiang, China) consists of a large cupola-like
body that is about 250 m long, 150 m thick, and 250 m high. From an
outer graphic pegmatite to a central massive microcline-quartz pegmatite,
the temperature of formation gradually decreased.
(2)
The second subtype consists of REE pegmatite that is associated mainly
with calc-alkaline, Li-F leucocratic granite. Three varieties of REE
pegmatite are defined: (a) Li-mica pegmatite; (b) muscovite (muscovite-albite)
pegmatite; and (c) muscovite-microcline pegmatite. The first two varieties
are Ta-bearing, and the last contains cassiterite and wolframite. Li-mica
pegmatite contains Ta-Nb minerals, cassiterite, Li-mica, quartz, albite,
microcline, apatite, tourmaline, topaz, beryl, and other minerals. Muscovite-albite
pegmatite contains columbite, tantalite, quartz, albite, microcline,
and muscovite. Muscovite-microcline pegmatite includes cassiterite,
wolframite, quartz, microcline, and muscovite. REE pegmatite deposits
form dike-like or lenticular bodies that range from few meters to hundreds
of meters long, and from 1 to 10 meters wide. Associated Li-Sn-Be pegmatite
contains Li-mica, Ta and Sn-W minerals. The depositional environment
is REE-Li pegmatite and associated granitic intrusions in post-accretionary
intrusions that postdate the peak of batholith emplacement. Associated
granite is mainly calc-alkaline and Li-F leucogranite and related, coeval
volcanic and subvolcanic units. Examples of the deposit type are at
Kelumute, Xinjiang, China, Keketuohai, Xinjiang, China, and Vishnyakovskoye,
Russia.
II. Deposits Related to
Intermediate and Felsic Intrusions. B. Greisen and Quartz Vein.
Fluorite Greisen (Govorov,
1977)
This
deposit type consists of fine-grained, dark-violet rock composed of
fluorite (from 63 to 66%) and micaceous minerals, mainly muscovite (25
to 35%), along with lesser ephesite and phlogopite. Subordinate minerals
are (in decreasing order) tourmaline, sellaite, cassiterite, topaz,
sulfide minerals, and quartz. Deposits generally occur in veins in gneiss
(as on the Korean Peninsular) or in limestone or marble (as in the Khanka
area, Russian Southeast). In the latter case, veins occur concordant
to limestone layers, and form lenticular and flame-shaped bodies of
apocarbonate greisen that occurs in limestone intruded by Li-F, S-type
granite. Metasomatic rock replacing limestone occurs at, and above contacts
with granitic intrusions. Muscovite-quartz pegmatite veins with molybdenite-cassiterite-diopside,
vesuvianite- diopside -andradite, and scapolite skarn also occur near
intrusive contacts, and are interpreted as having formed prior to formation
of fluorite-mica greisen. Boron isotopic composition of tourmaline indicate
a primary evaporite source (V.V. Ratkin, written commun., 1994), suggesting
that deep-seated evaporites in zones of granitic magma generation were
the source of fluorine. Alternatively, some fluorine may be derived
from the volatile phase of granitic magma. Scarce quartz and absence
of paragenetic calcite suggest an extremely high activity of fluorine
in silica-poor solutions. The depositional environment is thick clastic
limestone sequences or carbonate gneiss in cratonal or continental margin
terranes that are intruded by continental margin arc plutonic rocks.
Examples of the deposit type are at Preobrazhenovskoye and Voznesenka-II,
Russia.
Sn-W Greisen, Stockwork,
and Quartz Vein (Rodionov and others, 1984; Reed, 1986b)
This
deposit type consists of disseminated cassiterite, cassiterite- and
wolframite-bearing veinlets in stockworks, lenses, pipes, and breccia
in granite that is altered to greisen. The granite is mainly biotite
and (or) muscovite leucogranite emplaced in mesozonal to epizonal environments.
Deposits usually associated with cupolas and domes of silicic and ultra-silicic,
F-enriched rocks of late-stage, fractionated granitic magmas. Deposits
usually consist of simple to complex quartz-cassiterite±wolframite and rare sulfide minerals
fissure fillings or replacement lodes that occur in, or near felsic
plutonic rocks. The veins are associated with mineralized greisen zones.
Main deposit minerals are cassiterite, wolframite, arsenopyrite, sheelite,
rare molybdenite, beryl, and pyrite. Associated minerals are chalcopyrite,
various Bi-minerals, and rare galena, stannite, and sphalerite. Mineralogical
and metal zonation may occur on a small scale (within single veins or
vein systems) and (or) on a larger scale (within the ore districts).
An inner zone of cassiterite±wolframite is usually bordered by Pb,
Zn, Cu, and Ag sulfide minerals. The depositional environment generally
consists of mesozonal to epizonal (hypabyssal) silicic plutons that
contain felsic dike swarms. Typical tectonic environment consists of
zones of accreted terranes that are intruded late- to post-orogenic
granitoids that ascended from deep-seated magmatic chambers. Examples
of the deposit type are at Deputatskoye, Russia, and Mungon-Ondur and
Tugalgatain nuruu, Mongolia.
W-Mo-Be Greisen, Stockwork,
and Quartz Vein (Kim and Koh, 1963; Malinovskiy, 1965; Kuznetsov and
others, 1966; Sotnikov and Nikitina, 1971; Park and others, 1980; Cox
and Bagby, 1986; Kolonin, 1992)
This
deposit type consists of veins and stockworks of W, Mo-W and Be-Mo-W
deposit minerals that occur within endo- and exocontact zones of multistage
granitoid intrusions. Deposits generally occur in cupolas and domes
of silicic and ultra-silicic granitic rocks. Deposits consist of elongated
quartz veins and vein systems, stockworks, and greisen cupolas. Quartz-sheelite
stockworks are common in exocontact zones. Disseminated wolframite and
molybdenite occur in greisen, quartz veins, and veinlets. Other deposit
minerals are bismuthinite, pyrite, pyrrhotite, arsenopyrite, bornite,
chalcopyrite, scheelite, cassiterite, beryl, galena, sphalerite, and
various Bi-minerals. Gangue minerals are quartz, muscovite, K-feldspar,
fluorite, lepidolite, and rare tourmaline. Veins occur at the upper
level apices of granitic plutons, including alaskite, and in peripheral
zones of contact-metamorphosed sandstone and shale. Associated hydrothermal
alteration includes greisen with albite, and rare chlorite and tourmaline
with Li, Nb, and Ta minerals. The deposit type is sometimes associated
with Sn-W vein and Sn greisen deposits. The depositional environment
consists of tensional fractures in epizonal granitoid plutons that intrude
sedimentary or metasedimentary rocks. Typical tectonic setting consists
of anatectic granitic plutonic belts related to collisional zones and
(or) interplate strike-slip-fault zones. Examples of the deposit type
are at Lednikovy-Sarmaka, Ondortsagan, Mongolia, and Okunevskoye, Russia,
and Tsunkheg, Mongolia.
II. Deposits related to
intermediate and felsic intrusions. C. Alkaline metasomatite.
Ta-Nb-REE Alkaline Metasomatite
(Solodov and others, 1987)
This
deposit type consists of Ta-, Nb-, and REE-bearing alkaline metasomatite
that replaces multistage alkali REE granites and host-rocks that are
generally composed of marble, gneiss, or amphibolite. Deposits are composed
of fine- and medium-grained quartz-albite-microcline rock. Ta-Ni minerals
(e.g., columbite and pyrochlore), zircon, and thorite are widespread
along with REE minerals. Columbite and zircon are of practical significance.
REE minerals include gagarinite, yttrofluorite, monazite, bastnasite,
and xenotime and are important as accessories. Mineral zonation of metasomatic
bodies is characteristic. Complex multistage metasomatic processes,
that occur in the apical part of the granite massive and rocks within
shear zones, consist of microcline, albite, muscovite, and silica alterations.
Relatively rich deposits occur in columns and lens-shaped planar bodies
that extend to depths of hundreds of meters. This deposit type is a
unique resource containing Ta, Ni, Zr, Hf, and Th along with Li, REE,
and U. The depositional environment consists of deposit-hosting intrusions
and metasomatic deposits that occur along major shear zones connected
with intraplate and continental-marginal rift and strike-slip faults.
Examples of the deposit type are at Katuginskoye, Russia, Khalzanburegtei,
Mongolia, and Zashikhinskoe, Russia.
II. Deposits Related to
Intermediate and felsic Intrusions. D. Skarn (Contact Metasomatic).
Au Skarn (Hwang and Kim,
1963; Vachrushev, 1972; Theodore and Hammarstrom, 1991)
This
deposit type consists of veinlet-disseminated and bunches of gold-sulfide
deposit minerals that are superimposed on hydrothermally-altered calc-silicate
and magnesium-silicate skarn. The various skarns replace carbonate rocks
and coeval volcanic rocks along intrusive contacts with andesite stocks,
diorite, granodiorite, granite, and granite porphyry. Deposits are usually
small and irregular, but may persist at the depth. Deposit minerals
are garnet, pyroxene, wollastonite, vesuvianite, magnetite, epidote,
actinolite, quartz, pyrite, chalcopyrite, bornite, sphalerite, and native
gold. Gold forms simultaneously or after deposition of sulfide minerals,
sometimes in association with hydrothermal alteration that consists
of epidote, chlorite, and silica. The depositional environment consists
of contacts of calcareous-volcanic sequences intruded by gabbro-diorite-granitic
complexes in continental margin or island-arc systems. Examples of the
deposit type are at Boltoro, Mongolia, and Andryushkinskoe and Sinyukhinskoye,
Russia.
Boron (Datolite) Skarn
(Nosenko and others, 1990; Ratkin and others, 1992; Ratkin and Watson,
1993)
This
deposit type consists of danburite and datolite skarn associated with
garnet-hedenbergite-wollastonite skarn. The B skarn is interpreted as
having formed during successive metasomatic replacement of limestone
by wollastonite, grossularite-andradite, and hedenbergite, and by danburite,
datolite, axinite, quartz, and calcite. The deposit is characterized
by thin-banded wollastonite that forms kidney-shaped aggregates of pyroxene
and datolite in walls of paleohydrothermal cavities in marble. The hydrothermal
cavities occur to depths of 500 m from the paleosurface, above a metasomatic
zone of wollastonite and grossularite. The central part of these cavities
(0.5 to 50 m across) is filled with danburite druse. Danburite formed
after a second, boron metasomatism, and boron was redeposited at higher
paleogypsometric levels in datolite associated with garnet-hedenbergite
skarn. Genesis of neighboring Pb-Zn deposits is associated with formation
of the later skarn. B isotopic data suggest that the source of B solutions
was a deep-seated granitoid intrusion. The depositional environment
consists of early formation of grossular-wollastonite skarn, followed
by formation of thin-banded wollastonite aggregates with datolite, and
danburite that occurred simultaneously with eruption of a postaccretionary
ignimbrite sequence that overlies an accretionary wedge complex. The
complex contains large limestone xenoliths with lateral dimensions of
0.5 by 2.0 km and a highly-deformed siltstone and sandstone matrix.
The one example of this deposit type is the large Dalnegorsk boron mine
in the Russia Southeast that constitutes the main source of boron in
Russia.
Carbonate-Hosted Asbestos
(Wrucke and Shride, 1986; Xujun Li, this study)
This
deposit type occurs along contacts between mafic dikes and sills that
intrude silicified carbonate rocks. The major rock types are serpentinite,
diabase, gabbro, chert-bearing dolomite, and marl. The deposits are
usually stratiform, lensoid, or irregular in shape and are concordant
to host carbonate rocks. The industrial minerals are serpentine asbestos,
massive serpentine, calcite, and dolomite. Varied and distinct metasomatic
structures occur. Major alteration minerals are serpentinite, talc,
tremolite, diopside, and carbonate. Alteration zoning is not apparent.
The deposition environment is metasomatism associated with intrusion
of mafic intrusions into impure carbonate rocks. The deposits may be
of any age, but in the study area, the main deposit age is Mesoproterozoic.
The tectonic environment is mafic plutons that form part of continental-margin
arcs. The best example of the deposit type is at Chaoyang, Liaoning
Province, China.
Co Skarn (Nekrasov and
Gamyanin, 1962; Bakharev and others, 1988; Lebedev, 1986)
This
deposit type forms along the contacts between siltstone and limestone
during contact metamorphism associated with intrusion of granodiorite,
syenite-diorite, and granite plutons, and small intrusions (stocks and
dikes) of alkali gabbro. The skarn typically consists of pyroxene and
grossularite-andradite garnet, and lesser axinite and scapolite. The
deposits consist of small masses of Co-pyrite, sulfoarsenides, and arsenides
along with gersdorffite, arsenopyrite, lollingite, and cobaltite. Native
gold occurs in association with Bi- and Te-minerals, including native
bismuth, joseite, hedlyite, and bismuthine. Examples of the deposit
type are at Karagem and Vladimirovskoye, Russia.
Cu (±Fe, Au, Ag, Mo) Skarn
(Cox and Theodore 1986; Nokleberg, W.J. and others, 1997)
This
deposit type consists of chalcopyrite, magnetite and pyrrhotite in calc-silicate
skarn that replace carbonate rocks along intrusive contacts with plutons
ranging in composition from quartz diorite to granite, and from diorite
to syenite. Zn-Pb-rich skarn tends to occur farther from the intrusion
whereas Cu- and Au-rich skarn tends to occur closer to the intrusion.
Major minerals are pyrite, hematite, galena, molybdenite, sphalerite,
and scheelite. Mineralization is multistage. The deposit type is commonly
associated with porphyry Cu-Mo deposits. The depositional environment
is mainly calcareous sedimentary sequences intruded by felsic to intermediate
granitic plutons that form part of continental-margin arcs. Examples
of the deposit type are at Boltoro, Russia, Kamaishi, Japan, Khokhbulgiin
khondii, Mongolia, Kuma, Russia, and Muromets, Russia.
Fe Skarn (Mazurov, 1985;
Cox, 1986d; Sinyakov, 1988)
This
deposit type consists of dispersed magnetite in calc-silicate or magnesium-silicate
skarn that replaces carbonate, tuffaceous-carbonate, or calcareous clastic
rock near the contact of intrusive rocks that vary from gabbro and diorite
to granodiorite and granite. Coeval volcanic rocks occur locally. Associated
minerals are relatively rare chalcopyrite, pyrite, and pyrrhotite. Metasomatic
replacements consist of a wide variety of calc-silicate and related
minerals. The main skarn minerals are magnesium-silicates, calc-silicates,
albite, scapolite, chlorite, and amphibole. The depositional environment
is metavolcanic and metasedimentary rock sequences including dolomite,
dolostone, and rare limestone that are intruded by gabbro to granite
in island arcs, continental marginal arcs, or rifted continental margins.
Examples of the deposit type are at Abakanskoye, Beloretskoye, Inskoye,
Lavrenovskoye, Tabratskoye, and Timofeevskoe, Russia, and Tomortei,
Mongolia.
Fe-Zn Skarn (Bakhteev and
Chizhova 1984; Podlessky and others, 1984, 1988)
This
deposit type consists of sphalerite and associated minerals in calcic
skarn that typically occurs along the pre-intrusive tectonic-lithologic
contacts between uplifted blocks of metamorphosed calcareous sedimentary
rocks that are intruded by granitoids. The intrusive rocks are mainly
K-subalkaline granite and leucogranite. The skarn occurs in lenses or
in layers, and range from tens to hundreds of meters in thickness and
several hundreds meters along strike. The intrusives display little
or no alteration. Major deposit minerals are sphalerite and magnetite
with lesser chalcopyrite, hematite, bismuthinite, molybdenite, pyrite,
and galena. Gangue minerals are andradite-grossularite garnet, hedenbergite,
magnetite, epidote, and feldspar. Typical and frequently-developed zonation
consists of epidote-feldspar, epidote-andradite, andradite-magnetite,
andradite-pyroxene-magnetite, and pyroxene-magnetite. Typical retrograde
minerals are actinolite, quartz, calcite, and chlorite. Fe- and Zn-mineral
distribution is irregular, and occurs mostly in garnet and garnet-pyroxene
skarn. Pb/Zn/Cu ratios are about 0.2/4.5/0.1. Deposit typically exhibits
four stages of mineralization: garnet- pyroxene skarn, andradite-magnetite
aposkarn, sulfide, and quartz-carbonate. The depositional environment
consists of metamorphosed calcareous rock sequences including dolomite,
dolostone, and rare limestone that are intruded by granitoids in island
or continental marginal arcs. Examples of the deposit type are at Khol
khudag, Mongolia, Jinling, Shandong Province, China, Tumurte, Mongolia,
and Tumurtiin-Ovoo, Mongolia.
Sn Skarn (Reed, 1986c;
Nokleberg, and others, 1997)
This
deposit type consists of Sn-, W-, and Be-minerals in skarn, vein, stockwork,
and greisen near intrusive contacts between generally epizonal(?) granitic
plutons and limestone. Deposit minerals include cassiterite, and local
scheelite, sphalerite, chalcopyrite, pyrrhotite, magnetite, and fluorite.
Alteration consists of greisen near granite margins, and metasomatic
andradite, idocrase, amphibole, chlorite, chrysoberyl, and mica in skarn.
The depositional environment consists of epizonal granitoid plutons
that intrude calcareous sedimentary or metasedimentary rocks. Typical
tectonic setting is back-arc granitoids forming in continental-margin
arcs, or anatectic granitoids forming in collisional zones and (or)
interplate strike-slip-fault zones. Examples of the deposit type are
at Haobugao and Huanggan, Inner Mongolia, China.
Sn-B (Fe) Skarn (Ludwigite
Type) (Lisitsin, 1984; V.I. Shpikerman in Nokleberg and others, 1997)
This
deposit type consists of metasomatic replacement of dolomite by mainly
ludwigite and magnetite adjacent to granitoids. Ludwigite forms up to
80 percent of the deposit, and Sn occurs as an isomorphic admixture
in ludwigite. Other minerals are magnetite, suanite (Mg2B5O),
ascharite, kotoite, datolite, harkerite, monticellite, fluroborite,
clinohumite, calcite, periclase, forsterite, diopside, vesuvianite,
brucite, garnet, axinite, phlogopite, serpentine, spinel, and talc.
The deposit consists of limestone that is metasomatically replaced by
pyroxene-garnet-calcite skarn that is commonly altered to greisen to
form Sn skarn. Magnesium and associated calcic skarn generally form
near highly-irregular (convoluted) contacts of granite plutons, and
in large xenoliths of carbonate rocks. The depositional environment
consists of epizonal granitoid plutons that intrude calcareous sedimentary
or metasedimentary rocks. Typical tectonic setting consists of back-arc
granitoids forming in continental-margin arcs, or anatectic granitoids
forming in collisional zones and (or) interplate strike-slip-fault zones.
No noteable examples of this deposit type occur in the region.
W±Mo±Be Skarn (Beus,
1960; Kuznetsov and others, 1966; Cox, 1986j; S.M. Rodionov, this study)
This
deposit type consists of scheelite and (or) sheelite-helvite in pure
or altered (greisen or silica alteration) calc-silicate skarn that replaces
carbonate rocks or calcareous sedimentary rocks, along or near intrusive
contacts with quartz diorite to granite plutons. Skarn forms irregular
and vein-shaped bodies and layers. Associated minerals are molybdenite,
pyrrhotite, sphalerite, bornite, pyrite, and magnetite. Two mineralogical
varieties of skarn exist: (1) sheelite skarn containing disseminated
W minerals; (2) sheelite-helvite skarn with disseminated W and Be minerals.
Skarn typically contains garnet, vesuvianite, pyroxene, epidote, actinolite
fluorite, helvite, sheelite, beryl, quartz, muscovite, and rare sulfide
minerals. Replacement of wall rocks consists of a wide variety of calc-silicate
and related metasomatic minerals. Scheelite also occurs in quartz-topaz
and quartz-mica greisen that is formed by replacement of skarn. The
depositional environment is contact zones along the margins of granitic
intrusions in continental-margin or island arcs, or adjacent to anatectic
granitoids intruding into collisional zones. Examples of the deposit
type are at Lermontovsky, Russia, Sangdong, South Kora, and Vostok-2,
Russia.
Zn-Pb (±Ag, Cu, W) Skarn
(Cox, 1986k; K.M. Dawson and D.F. Sangster in
Eckstrand, 1984; Nokleberg, and others, 1997)
This
deposit type consists of sphalerite and galena in calc-silicate skarn
that replaces carbonate rock or impure calcareous sedimentary rock along
intrusive contacts with plutons varying in composition from quartz diorite
to granite, and from diorite to syenite. Zn-Pb-rich skarns tend to occur
farther from the intrusion relative to Cu-, and Au-rich skarns. Deposit
may occur at considerable distance from source granitic intrusion. Associated
minerals are pyrite, chalcopyrite, hematite, magnetite, bornite, arsenopyrite,
and pyrrhotite. Deposits vary from stratiform skarn that occurs parallel
to limestone bedding near plutonic contacts to discordant bodies that
commonly occur at lithologic and structural contacts at some distance
from pluton and dike contacts. Deposits are rather narrow, but may extend
downdip to 1 km depth. They may be controlled by ring faults around
volcanic-tectonic depressions. The depositional environment is mainly
calcareous sedimentary sequences intruded by felsic to intermediate
granitic plutons in continental margin arcs. Examples of the deposit
type are at Baiyinnuoer, Inner Mongolia, China, Huanren, Liaonig Province,
China, Kamioka Tochibora, Japan, and Xiaoyingzi, Inner Mongolia, China.
II. Deposits Related to
Intermediate and Felsic Intrusions. E. Porphyry and Granite Pluton-Hosted
Deposits.
Cassiterite-Sulfide-Silicate
Vein and Stockwork (Kim and Shin, 1966;
Ontoyev, 1974; Lugov and others, 1972;
Seminsky, 1980; Togashi, 1986; S.M. Rodionov, this study)
This
deposit type consists of linear zones, veins, and stockworks with cassiterite,
wolframite, sheelite, and various sulfide minerals in a gangue of quartz
with siderophyllite, tourmaline, sericite, and chlorite. Deposit occurs
in, or adjacent to hypabyssal multistage intrusive massifs (stocks and
laccoliths), subvolcanic bodies that intrude sedimentary, volcanic or
metamorphic rocks. Composition of associated intrusive rock varies from
gabbro to diorite to granodiorite to granite. Deposit typically contains
abundant simple and complicated veins and zones that are controlled
by large crosscutting faults, or occur in various elements of concentric
or radial faults surrounding volcanic-plutonic complexes. Stock with
greisen is relatively older and scarce. Deposit often contains stockwork
minerals with the same composition as veins and zones. Deposit minerals
are cassiterite, arsenopyrite, chalcopyrite, galena, sphalerite, pyrite,
pyrrhotite, sheelite, wolframite, fluorite, native bismuth, argentite,
native gold, bismuthine, and complex sulfosalt. Gangue minerals are
quartz, tourmaline, sericite, and chlorite, and rare muscovite and feldspar.
Typical alteration assemblages are quartz-tourmaline, quartz-siderophillite,
quartz-sericite, and quartz-chlorite. High-sulfide deposits (cassiterite-sulfide)
and low-sulfide (cassiterite-silicate) deposits may occur. Several stages
of mineralization may occur along with horizontal zonation. The depositional
environment consists of back-arc zones of continental-margin arcs. Examples
of the deposit type are at Sherlovogorskoye and Ulakhan-Egelyakh, Russia.
Felsic Plutonic U-REE (Nokleberg
and others, 1997)
This
deposit type consists of disseminated uranium minerals, thorium minerals,
and REE-minerals in fissure veins and alkalic granite dikes in or along
the margins of alkalic and peralkalic granitic plutons, or in granitic
plutons, including granite, alkalic granite, granodiorite, syenite,
and monzonite. Deposit minerals include allanite, thorite, uraninite,
bastnaesite, monazite, uranothorianite, and xenotime, sometimes with
galena and fluorite. The depositional environment is mainly the margins
of epizonal to mesozonal granitic plutons in back-arc zones of continental-margin
arcs. Examples of the deposit type are at Chergilen, Diturskoe, and
Neozhidannoye, Russia.
Granitoid-Related Au Vein
(R.I. Thorpe, and J.M. Franklin in Eckstrand, 1984; Firsov, 1985; Cherezov
and others, 1992)
This
deposit type consists of fissure veins and veinlet-stockwork zones with
disseminated gold and and sometimes sulfide minerals that occur generally
in small, complex, granitic intrusions. Plutonic rocks consist mainly
of calc-alkalic and sub-alkalic diorite, granodiorite, and granite.
Deposits may consist of dissemination gold that occurs at apices of
plutons, or in contact metamorphic aureoles. Deposit minerals are native
gold, Au-bearing telluride and sulfide minerals, and associated quartz,
tourmaline, muscovite, sericite, chlorite, feldspar, carbonate minerals,
and fluorite. Disseminated sulfide minerals in wall rocks, especially
arsenopyrite, are commonly enriched in Au and Ag. Alteration to berizite-listvenite
is common with formation of quartz, sericite, tourmaline, and chlorite.
The depositional environment is interpreted as epizonal plutons that
intrude miogeoclinal sedimentary rocks that in some cases were regionally
metamorphosed and deformed before intrusion. The plutons commonly occur
in the back arc of a continental-margin arc. Deposits display a similar
mineralogy and chemical environment and are often associated with polymetallic
vein deposits containing disseminated Au-bearing sulfide minerals. Examples
of the deposit type are at Boroo, Mongolia, Linglong, Shandong Province,
China, Sanshandao, Shandong Province, China, Xincheng, Shandong Province,
China, Tuanjiegou, and Heilongjiang Province, China.
Polymetallic Pb-Zn ±
Cu (±Ag,
Au) Vein and Stockwork (Hwang and Kim, 1962; Moon, 1966; Cox, 1986e;
Wang, 1989; Mironov and others, 1989; Tian and Shao, 1991)
This
deposit type consists of quartz-carbonate veins with base metal sulfide
minerals and associated Ag-minerals and gold. Deposits are related to
hypabyssal bodies that intrude volcanic, sedimentary, and metamorphic
rock, including interbedded calcic siltstone, siliceous marble, and
rhyolite. Intrusions range in composition from calc-alkaline to alkaline
diorite to granodiorite, and monzonite to monzogranite, and occur in
small plutons and dike swarms. Some deposits are controlled by faults
along contacts between host rocks and felsic intrusions, and vary in
form from stratiform or vein to lensoid. Deposits are locally very large
and are concordant to the bedding of host rocks (e.g., Au-Ag polymetallic
vein deposits in Jilin Province, China). Gold vein deposits are usually
sulphide-poor (total sulphide content less than 5%), and generally occur
in masses, disseminations, or veinlets. Deposit minerals are native
silver, galena, sphalerite, pyrite, chalcopyrite, tetrahedrite, arsenopyrite,
argentite, Ag-sulfosalt minerals, native gold, and Cu- and Sn- sulfide
minerals. Vein minerals are quartz, carbonate, barite, and fluorite.
Metallic zoning is very common and consists of Pb, Zn (Au and Ag) at
depth, Au, Ag (Pb and Zn) at middle horizons, and Ag (Au) at upper levels.
Similar metallic zoning patterns also occur horizontally. Alteration
consists of wide propylitic zones, and narrow sericite and argillite
zones. For Au vein deposits, the most intense host rock alterations
are silica and beresite (pyrite+sericite+carbonate) alterations. Silica
alteration usually occurs adjacent to deposit minerals, and successive
outward are are sericite and propylite alterations. Width of alteration
zones ranges up to several tens to 100 meters. The depositional environment
consists of zones of local domal uplift in continental margin arc and
island-arc volcanic-plutonic belts. Examples of the deposit type are
at Khartolgoi, Mongolia, Kuolanda, Russia, Lianhuashan, Inner Mongolia,
China, Meng'entaolegai, Inner Mongolia, China, and Prognoz, Russia.
Porphyry Au (Fogelman,
1964, 1965; R.I. Thorpe and J.M. Franklin in Eckstrand,
1984; Gamyanin and Goryachev, 1990, 1991; Sillitoe, 1993b; Dejidmaa,
1996)
This
deposit type consists of stockwork zones and disseminated gold and with
local sulfide minerals that generally occur in simple to complex granitic
intrusions, or in breccia pipes that are associated with volcanic-plutonic
complexes. Related intrusive rocks are calc-alkalic and sub-alkalic
granodiorite or granite. Breccia, if present, contains fragments of
host rocks (flows, tuffs, granitoids, and sedimentary rocks), igneous
breccias, and other hypabyssal and subvolcanic rocks. Deposit minerals
are native gold, Au-bearing tellurides, and sulfide minerals. Accessory
minerals are quartz, tourmaline, muscovite, sericite, chlorite, feldspar,
carbonate minerals, and fluorite. Two mineralogical subtypes exist:
(1) a low-sulfide subtype with chalcedony veins; and (2) a high-sulfide
subtype with abundant disseminated sulfide minerals. Within breccia
pipes, gold generally occurs in the cement (matrix) as disseminations
or stringer-disseminations, along with disseminated sulfide minerals
(pyrite, sphalerite, galena, arsenopyrite, and chalcopyrite). Disseminated
sulfide minerals in wall rocks, especially arsenopyrite, are commonly
enriched in Au and Ag. Host rocks exhibit chlorite, argillite, and quartz
alteration. Advanced argillic alteration is widespread in shallow parts
of deposits. Sericite alteration is typically minor. Stock and associated
volcanic rock range in composition from low-K calc-alkalic through high-K
calc-alkalic to K-alkalic. The deposit type is often associated with
polymetallic vein Au, Au-Ag epithermal vein, and porphyry Cu deposits.
The depositional environment consists of subduction-related continental
margin or island arc with composite epizonal porphyry stocks that intrude
coeval volcanic piles and adjacent passive continental-margin sedimentary
rocks that in some cases were regionally metamorphosed and deformed
before intrusion. Examples of the deposit type are at Ara-Ilinskoe,
Russia, Delmachik, Russia, and Naozhi, Jilin Province, China.
Porphyry Cu (±
Au) (Cox, 1986g; Sukhov and Rodionov, 1986; Evstrakhin, 1988; S.M. Rodionov,
this study)
This
deposit type consists of stockwork veinlets and rare veins of chalcopyrite,
bornite, and magnetite in porphyry intrusions and coeval volcanic rocks.
The host intrusive rocks vary in composition from tonalite and monzogranite
to syenite and monzonite. Coeval volcanic rocks consist of dacite and
andesite flows and tuffs. High-K, low-Ti volcanic rocks (shoshonite)
may also be common. Chalcopyrite and bornite are the main deposit minerals,
and associated minerals are magnetite, pyrite, rare native gold, electrum,
sylvanite, and hessite. Rare PGE minerals may also occur. Gangue minerals
are quartz, K-feldspar, biotite, sericite, and chlorite, and rare actinolite,
anhydrite, calcite, and clay minerals. A general, systematic alteration
consists of: (1) an inner zone of quartz, biotite, rare K-feldspar,
chlorite, actinolite, and anhydrite; (2) an outer alteration zone of
propylitic minerals; and (3) late-stage quartz-pyrite-white mica-clay
minerals that overprint early feldspar alteration. Deposit mineral veinlets
and mineralized fractures are closely spaced. Deposit generally exhibits
a cylindrical or bell-shape that is centered on the volcanic-intrusive
center. Highest-grade ore commonly occurs at the level where stock divides
into branches. The depositional environment consists of subduction-related
continental margin or island arc with porphyry stocks, dikes, and large-scale
breccia intruding coeval volcanic rocks nearby volcanic center and adjacent
passive continental-margin sedimentary rocks. Granitoids hosting deposit
type tend to intrude in waning stage of volcanic cycle. Examples of
the deposit type are at Khongoot, Mongolia, Oyu Tolgoi, Mongolia, and
Xiaoxinancha, Jilin Province, China.
Porphyry Cu-Mo (±
Au, Ag) (Sotnikov and others, 1977, 1985; Cox, 1986h; Sukhov, and Rodionov,
1986; Nokleberg and others, 1997; S.M. Rodionov, this study)
This
deposit type consists of stockwork veinlets and veins of quartz, chalcopyrite,
and molybdenite in, or near porphyritic intrusions. The host igneous
rocks are felsic and calc-alkalic, predominantly tonalite to monzogranite
plutons occurring mainly in stocks that intrude granitic, volcanic,
or sedimentary rocks. Breccia pipes (including pebble breccia) and dikes
are common. Veinlets and veins contain mainly quartz and carbonate minerals.
The deposit minerals are chalcopyrite, molybdenite, pyrite, sphalerite,
Ag-rich galena, and gold. Alteration minerals are quartz, K-feldspar,
sericite, and biotite or chlorite. Anhydrite occurs on deep levels of
deposits. Most deposits exhibit varying amounts of hypogene alteration,
including sodic, potassic, and phyllic alteration. Alteration zones,
from inner to outward, are sodic-calcic, potassic, phyllic, and argillic
to propylitic. Widespread, episodic development of abundant joints in
intrusions and wall rocks is typical. The depositional environment is
shallow, porphyry intrusions that are contemporaneous with abundant
dikes, faults, and breccia pipes associated with andesite stratovolcanoes
in back-arc regions of subduction-related continental-margin or island
arcs. The granitoids are mainly moderately to strongly alkalic plutons.
Examples of the deposit type are at Duobaoshan, Heilongjiang Province,
China, Erdenetiin Ovoo, Mongolia, Tsagaan Suvarga, Mongolia, and Wunugetushan,
Inner Mongolia, China.
Porphyry Mo (±
W, Sn, Bi) (Sotnikov and others, 1977, 1985; Theodore, 1986; Pokalov,
1992; Ludington, 1986; Nokleberg, and others, 1997; S.M. Rodionov, this
study)
This
deposit type consists of quartz-molybdenite stockwork in felsic porphyries
and adjacent country rock. The porphyries range in composition from
granite-rhyolite, with >75% SiO2, to tonalite, granodiorite,
and monzogranite. Radial silicic dikes and small breccia pipes are common.
Associated deposit minerals are pyrite, scheelite, and chalcopyrite,
and rare cassiterite, wolframite, and tetrahedrite. Gangue minerals
are quartz, K-feldspar, biotite, calcite, and white mica. Some deposits
are high-F and have larger tonnages and higher average grades than the
low-F deposits hosted in quartz monzonite. Alteration consists of potassic
grading outward to propylitic, sometimes with phyllic and argillic overprints.
Intense quartz and quartz-feldspar veins are typical for F-rich deposits.
Minor greisen veins may occur below the ore body. Accordingly deposit
mineralogy and tectonic setting, the deposit type is subdivided into
two subtypes: (1) high-grade, rift-related deposits with multistage
F-rich, highly evolved granite to rhyolite stocks that constitute a
high-silica, alkalic, rhyolite suite; and (2) low-grade, continental-margin
arc-related deposits hosted in F-poor, calc-alkalic stocks or plutons
that form a differentiated monzogranite suite. High-grade, F-rich deposits
are also associated with intraplate alkaline igneous rocks. The depositional
environment is shallow, epizonal porphyry intrusions in the back-arc
regions of subduction-related, continental-margin arcs that are built
on a thick continental crust. Examples of the deposit type are at Birandzha,
Russia, Daheishan 2, Jilin Province, china, Melginskoye, Russia, Metrekskoye,
Russia, Lanjiagou, Liaoning Province, China, and Zhirekenskoye, Russia.
Porphyry Sn (Reed, 1986a;
Rodionov, 1990; Nokleberg and others, 1997)
This
deposit type consists of mainly cassiterite and associated minerals
in stockworks, veinlets, and disseminations that occur in complex, subvolcanic,
multiphase granitic plutons, granitic porphyry or quartz porphyry stocks,
subvolcanic and volcanic rhyolite breccias, and also in coeval volcanic
rocks and surrounding clastic rocks. The composition of the subvolcanic
host rocks varies from intermediate to silicic (quartz-latite, dacite,
rhyodacite). Cogenetic volcanic rocks consist of calc-alkaline pyroclastic
rock and lava (quartz-latite to rhyodacite). Closely-related intrusions
are mainly strongly-altered and brecciated quartz porphyry. Magmatic-hydrothermal
breccia, and extensive metasomatic propylitic and phyllic alterations
are typical. The alterations are accompanied by quartz, tourmaline,
sulfide minerals, and sericite. Deposit minerals are cassiterite, quartz,
pyrrhotite, pyrite, arsenopyrite, chalcopyrite, sphalerite, galena,
stannite, wolframite, muscovite, sericite, chlorite, albite, adularia,
siderite, rhodochrosite, calcite, topaz, fluorite, and sulfostannates,
and Ag- and Bi-minerals. Alteration zones, from interior to periphery,
are tourmaline (±adularia), phyllic, propylitic, and argillic. Some
deposits exhibit a quartz-tourmaline core with a peripheral zone of
sericite. Deposit type is often associated with Sn- and Ag-bearing polymetallic
veins. The depositional environment is mainly shallow, subvolcanic stocks
emplaced from 1 to 3 km beneath, or within vents of stratovolcanoes
in the back-arc region of subduction-related continental-margin arcs.
Examples of the deposit type are at Mokhovoye, Mopau, Surkho, Yantarnoe,
and Zvezdnoe, Russia.
III. Deposits Related
to Alkaline Intrusions. A. Carbonatite-Related Deposits.
Apatite Carbonatite (Smirnov,
1982; Entin and others, 1991)
This
deposit type consists of apatite-carbonate, apatite-quartz-carbonate,
martite-apatite-quartz-carbo-nate assemblages, martite-apatite-carbonate,
and apatite-carbonate-quartz assemblages in asymmetric, early- and late-stage
stocks. Early-stage carbonatites form veins, vein zones, and stockworks
in a mafic complex intruded into crystalline basement. Thickness of
the veins varies from a few centimeters to 30-40 m, and the length varies
from a few meters to 500 m, rarely up to 1.5 km. Early-stage, apatite
carbonatite contains apatite, car