USGS Professional Paper 1697 - Alaska Resources Library

Yur Au Quartz Vein Deposit
The small Yur Au quartz vein deposit (Strona, 1960; N.D.
Kobtseva, written commun., 1988) consists of four interbedded
quartz veins that occur in a zone of meridional faults in
middle Carboniferous sandstone-shale. The veins range from
0.3 to 0.4 m thick and are 100 to 500 m long. The main ore
A
C
0
Map
L
2 km
Cross sections
A
C
L
Dikes (Early
Cretaceous)
L L
Gabbrodiorite stocks
(Early Cretaceous)
Siltstone and sandstone
(Late Permian and Triassic)
Sandstone (Late Permian)
B
Siltstone
(Late Permian)
Shale
(Early Permian)
Siltstone
(Early Permian)
Fault
Contact
Figure 66. Nezhdaninka Au-Ag-quartz vein deposit, South Verkhoyansk
metallogenic belt, Russia, east-central Yakutia (Verkhoyansk
area). Schematic geologic map and cross sections. Adapted
from Shour (1985). See figure 61 and table 4 for location.
Early Cretaceous Metallogenic Belts (144 to 120 Ma; figs. 61, 62) 147
B
D
D
minerals are gold, arsenopyrite, galena, pyrite, and sphalerite.
The ore minerals are as much as 2 percent of veins. The
gangue minerals are quartz, ankerite, and albite. Wallrock
alteration is insignificant, but includes sericite, silica, and arsenopyrite
alteration. The deposit is small with an average grade
of 3.5 to 5.7 g/t Au.
Levo-Dybin Granitioid-Related Au Deposit
The Levo-Dybin granitioid-related Au deposit (A.V.
Kokin, written commun., 1978; Zubkov, 1984; Goryachev,
1998, 2003) consist of abundant quartz stringers, from 0.2 to
0.3 m thick, which form peculiar sheet stockworks in contact
metamorphosed, Late Permian sandstone beds, which range
from 5 to 20 m thick. The stringers consists of quartz (90 to 95
percent), muscovite, potassium feldspar, scheelite, molybdenite,
arsenopyrite, niccolite, löllingite, pyrrhotite, bismuth, gold, bismuthine,
bismuth tellurides and sulfotellurides, and maldonite.
The deposit occurs for 800 to 1,000 m along the strike of the
bedding; and also occurs above an Early Cretaceous granitoid
body and in adjacent country rocks. The deposit contains as
much as 3 percent As, 7-13 g/t Au, as much as 2.5 percent WO3, as much as 1 percent Bi, and as much as 0.6 percent Te.
Origin of and Tectonic Controls for Allakh-Yun
Metallogenic Belt
The vein deposits of the Allakh-Yun metallogenic belt
are interpreted as forming during two major tectonic events
(Goryachev, 1998, 2003). The relatively older, metamorphicrelated
Au quartz vein deposits are interpreted as forming during
the early stages of thrusting and associated metamorphism
of the southern part of the North Asian Craton Margin (unit
NSV, Verkhoyansk fold belt) during accretion of the Okhotsk
terrane and Kolyma-Omolon superterrane onto the North
Asian Craton Margin. Accretion of the Okhotsk terrane may
have been accentuated by the coeval accretion of the outboard
Kony-Murgal island-arc terrane. The relatively younger, crosscutting,
Au-quartz vein deposit, and granitioid-related Au and
W-Sn quartz vein deposits of the Allakh-Yun metallogenic belt
are interpreted as forming during intrusion of the Early Cretaceous
anatectic granitoid rocks of the Verkhoyansk collisional
granite belt (unit vk; Nokleberg and others, 1994c, 1997c).
This Late Jurassic and Early Cretaceous granite belt consists
of two main belts, the Main granite belt of Late Jurassic to
early Neocomian age, and the Northern granite belt of Neocomian
age. The Main granite belt, which hosts the Allakh-Yun
metallogenic belt, extends for about 110 km along southwest
border of the Kolyma-Omolon superterrane and stitches the
superterrane to North Asian Craton margin. The granites occur
as inclined, sheet-like plutons, as much as 200 km long, which
are generally conformable with major folds. Ar-Ar ages of
granitoid rocks range from 134 to 144 Ma (Parfneov, 1995).
These granitoid rocks are interpreted as forming immediately
after the Late Jurassic accretion of the Kolyma-Omolon
superterrane to the North Asian Craton Margin (Nokleberg and
others, 1994c, 1997c, 2000).