Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

Pokrovskoe Au-Ag Epithermal Vein Deposit
The Pokrovskoe Au-Ag epithermal vein deposit (Khomich and others, 1978; Mel'nikov, 1984; V.D. Mel'nikov, written
commun., 1993; Khomich, 1990) occurs in Late Cretaceous andeeite, dacite andesite, and related tuff. This volcanic sequence
overlies a Jurassic coal-bearing sequence of sandstone, siltstox, and argillite. The ore bodies consist of gently-dipping quartz
veins and zones of hydrothermal alteration. Main alteration types are propylitization (albite, micite, calcite, chlorite, and pyrite),
berezitization (quartz, seric~te, and hydromica), and argillization (kaobte, montmorillonite, hydromica, carbonates, quartz, and
pyrite). The largest ore bodies ax gently-dippingzm of altered rock, located near the lower contact of andesitic sequema with a
granodiorite porphyry sill. Hyd~othtrmally altered rocks consist of quartz (25-85%), carbonate (2-5%). hydromica (5-12%).
adularia (up to 5%), kaol~nite (5-7%), and sutfides (less than 1% and mostly pyrite). Gold is fme-pined (0.0005 to 0.032 mm), is
associated with quartz, and is virtually not associated with sulfides. Silver grains (0.002 to 0.016 mm) were observed in Fehydroxide
alteration. The deposit is medium size with reserves of: 15 million tomes grading 4.4 g/t Au and 15 glt Ag. The deposit
is interpreted as forming in the Late Cretaceous.
Pioneer Granitoid-Related Au Deposil
The Pioneer granitoid-rehted Au deposit V.E. Mdyarnis and V.E. Boc-4 dtten txunmm., 1990; V.N. Akatkin.
written commun., 199 1) occun XEK the margin of an Early C~tateous granodiorite intrusion, bofh with the intrusion, md in
adjacent country rock of contact-metamorphosed Jurassic m&tone and siltstone. The ore bodies consist of quartz, quartzfeldspar,
quartz-tourmal~w, and quartz-carbonate veins and zoacs of dttred qmlz-potassium felbpar-wicitaalbite rocks. The
ore bodies vary from 1 to 50 m thick, and in plan branch with variable trends. The are bodies m large, have low Au content, and
have no visible boundaries. The extent of mioemhakion is dctemhed by geochemical samplwag. BMtr gold and Au-sulfide bodit%
are recognized. The gold ore type cansists dqW-aduluia-carbonate veins, and the Au-aulfide type consists of quartz veh
with pyrite, galena, stibnite, and A@t-dfosalts. The dapasit ie d l , with estimated rema? of 17.1 tonne Ay 20.1 tonne Ag, d
average grades of grade 2.7 g/I Au, md 5.2 g/t Ag.
Origin of and Tectonic Controls for
North Bureya Metallogenk Belt
The Umlekan-Ogodzhin volcanic-plutonic belt (Volsdry, 1983; Kozlovsky, 1988) whkh hosts tbe North Bureya
metal logenic be1 t consists chiefly of: (1) Exrly Cretaceous sandstone, conglomemte, and mudstone with aparse flora 4
freshwater fauna; (2) Early Cretww calc-alkalic andmite, dacitz, and tuff which yield K-Ar isotopic qes of 112-135 Ua; and
(3) Late Cretaceous alkalic basalt and rhyolite. The belt is isW By coeval Wly Ctetaww Zganite, g~an*rite, &orb, d
monzodiorite. Some granltoid plutcm are probably Late J ~ i c w , older because derired detrihs occurs in the Early Cretaceous
part of section of the Umlekaa-Ogodzhin igneous belt. This belt was depasited on Gonzba tenrane, and an hbnyn d T m
terranes of Bureya superterrane after collision of these ter~8a89 with the Tulmhgm-Dzhagdinsk ternme (Nakl.&rg aad otbemp,
1994c, 1997~).
The Umlekan-Ogodzhin volcanic-plutonic belt belt wnstitwes part of the Udekan conaatal-m arc wbb is
interpreted as forming from subduction of part of the ancestral Pacific Ocean plate which is now preserved as kctoniedly
interwoven fragments of the Badzhal (BD), older Jurassic, part part of the Khabmovsk (KB), and Smarka (SMA) ~~. This
tectonic pairing is based on: (I) occufience of the accretionary-wedge terranes outboard (oeeanwd) of tbi! Umleleaa arc (fig. 48);
(2) formation of milange structures during the Jurassic and Early Gretaceous (NoIdeberg and otks, 1994s: binchuk and others,
1 996); and (3) where not disrupted by extensive Cretacsous and early Cenozoic movement aloag, the GentPal Siho-Aline strikeslip
fault, the melange structures and bo'lmding fa& dip toward and beneath the igneous units of the arc. Sub8uctbn is generally
interpreted as ending in the Early Cretaceous when extensive skWal faulting occurred along the subductim zone (Khanchuk and
others, 1996).
Chersky-Argatass Ranges Inferred
Metallogenic Belt of Kuroko Massive
Sulfide Deposits (Belt CAR)
West-Central Part of Russian Northeast
An infed metallogenic belt of kuroko d v e sulfide &posits (Q. 48; tables 3,4) occuts in the ~ t ~ t rpart a of l
the Russian Northeasl The me&ganic bk is hosted in Me Jwassic volcanic rocks in the Cbersky and kga@s Ranges in the
Indigirka-Oloy sedimentary-volcanic assemblqt (unit io. fig .48) (NWeberg md otbers, 19&, 199%). The belt extends
northwest for nearly 700 km and oocm in f m arws which re up to 35 to 30 km wide each @aailuv ancf orhem, 1990). The
significant deposit is at Khotoidokh in the northwest part ofthe bell ( ale 4) (Noklekg and o h 1997% b, 1998).