USGS Professional Paper 1697 - Alaska Resources Library

content decreases with depth, as does topaz and pyrophyllite;
quartz content increases with depth. The deposit occurs in a
district that extends north-northwest along a zone of intensely
fractured Early Cretaceous clastic sedimentary rocks. The
zone has surface dimensions of 180 by 350 m. The clastic
sedimentary rocks are replaced by quartz, tourmaline, pyrophyllite,
kaolinite, and locally by dumortierite and topaz. The
ore bodies coincide with the most altered rocks, are pipe-like,
and extend along strike for hundreds of meters. The mine at
the deposit is of small to medium size and is mostly exhausted.
Mechta Ag-Polymetallic Vein Deposit
The Mechta Ag-polymetallic vein deposit (V.I.
Tkachenko and others, written commun., 1976-1979; Plyashkevich,
1986; V.I. Kopytin, written commun., 1987) consists
of a set of en-echelon, generally north-south-trending,
arcuate fracture zones that range from 3.5 to 4 km wide and
10 km long. The zones contain quartz-chlorite-sulfide veins
and veinlets. The ore bodies form a fan-like structure that
branch at the upper levels and are hosted by Late Cretaceous
ignimbrites with propylitic and argillic alteration. The main
vein minerals are Ag-bearing galena, sphalerite, chalcopyrite,
Early Late Cretaceous Metallogenic Belts (100 to 84 Ma; figs. 79, 80) 205
pyrite, arsenopyrite, freibergite, pyrargyrite, stephanite, famatinite,
tennantite, argentite, quartz, chlorite, and hydromica.
Subordinate minerals are pyrrhotite, stannite, native gold and
silver, feldspar, kaolinite, and carbonate. Ores are dominated
by galena-sphalerite and chalcopyrite-freibergite associations.
The deposit is of medium size with average grades of about
1 percent Pb, and 0.74 percent Zn, and as much as 310 g/t Ag
and 0.3 g/t Au.
Dukat Ag Epithermal Vein Deposit
The major Ag epithermal vein deposit at Dukat (fig. 96)
(Brostovskay and others, 1974; Savva and Raevskaya, 1974;
Kalinin, 1975a, 1986; Raevskaya, Kalinin, and Natalenko,
1977; Sidorov, 1978; Natalenko and others, 1980; Sakharova
and Bryzgalov, 1981; Sidorov and Rozenblum, 1989; Shergina
and others, 1990; Goncharov, 1995) consists of numerous,
extensive disseminated replacement zones and quartz-adulariarhodochrosite-rhodonite
veins with diverse Ag- and base-metal
sulfide minerals. The estimated reserves are 15,000 tonnes
silver (Natalenko and others, 1980; Konstantinov and others,
1998). The deposit occurs in ultra-potassic rhyolite, part of the
Early Cretaceous Askoldin igneous complex that occurs over
Undifferentiated volcanic and
sedimentary rocks (Late Mesozoic
and Cenozoic)
Nevadite dikes (Late Cretaceous)
Subvolcanic rhyolite (Early and Late
Cretaceous)
Rhyolite flows (Cretaceous)
Terrigenous rocks (Triassic and Jurassic)
Ore body
Fault
Contact
0 3 km
Figure 96. Dukat Au-Ag epithermal vein deposit, Omsukchan zone, eastern Asia-Arctic metallogenic belt, Russian Northeast.
Schematic geologic map of deposit and surrounding area. Adapted from Goncharov (1995a). See figure 79 and table 4
for location.