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

magmatic bodies (with approximate K-Ar ages of 70 Ma). The first stage consists of grossular-wollastonite skam and
concentrically zoned, findy banded aggregates with numerous finely crystalline datolite and &use-like accmlations of danburite
crystals in palmhydrothermal cavities. The second stage skam consis~s predominantly of long, radiated hedenbergite and andradite
with coarsely-crystallii datolite, danburite, quartz, axinite, and calcite. The arcuate nature of metasomtic mineral zonation in the
skim is interpreted by Shkolnik and others (2003) as replacement of stromatolite build-ups in the host Triassic Limestone. The
complm layering are relict biogcnic features of the stomatolite-bearing limestone. An Ar-Ar age for orthoclase indicates an age
for the late-stage skarn assdlage of 57 Ma. The silicate mineralogy of the early-stage skam is similar to which in Pb-Zn skam
deposits in this same region. B isotopic studies indicate a magmatic source for boron (Ratkin and Watson, 1993). The deposit is
E A
Quaternary alluvial deposits
Rhyolitic tuff
[::I
. ., Aplite dike
Andesite and diabase dike
Granite
Limestone
B &-met, garnetmagnetite skam
rn
Garnet. garnet-pyroxene, garnet-pyroxenevesuv~,
and wet-magnetite-aspidine skam
Figure 84. Belogorskoe Fo skm deposit, Taukha metallogenic belt, Russian Southeast. Adapted frm Valuy and RDS~OW~~ (I*&).
*Very large and had been mhed from 1970's to present. The deposit produces over 90% of all borate in Russia. The Dalnegorsk
@% flnbpen-Pit mioc at the &posit is prospected to the depth of I km. '-• 1
Nfkdasvskee Pb-Zn Skarn Deposlt kr(
-- . II
The Nikolaevskpe Pb-Zn skarn deposit (fig. 86) (Garbuzov and others, 1987; V.V. Ratkin, this study; Vasilenko and
Valuy, 1998) ~ ~sists of large, layered ore bodies formed in a giant olistolith of Triassic limestone which is psrt of Early
Cretaceous accrrfionary-fold complex The skam occurs at the contacts of limestone with hosting siltstone and sandstone, and
with overlying fekic volcanic rocks ofa Late Cretaceous to Paleogene post accretionary sequence. Small ore bodies also occur iti
limestone blocks in the vdcanic rocks which were tom off the underlying basement. The ore minerals are dominantly 4- and
sphaletite which replace an earlier hedenbergite skarn near the surface, and, at depth, replace a garnel-hedenbergite skam.
Suhrcbareure minerals cue ckalcopyrite, arsenopyrite, pyrite, pyrrhotite, fluonte, and Ag-sulfosalts. K-Ar isotopic studies
indicate which as age of mineralization between 60 and 80 Ma. A 60 K-Ar Ma isotopic age is obtained for an umnhdized
basalt dike which cuts the deposit, and a K-Ar age of 70-80 Ma is obtained for a mineralized ignimbrite whicb overlies the