USGS Professional Paper 1697 - Alaska Resources Library

Karalveem Au Quartz Vein Deposit
The only commercial Au quartz vein deposit at Karalveem
(fig. 98) (Olshevsky, 1974, 1976, 1984; Davidenko, 1975, 1980;
Skalatsky and Yakovlev, 1983) consists of numerous longitudinal,
transverse, and diagonal, steeply dipping ladder quartz veins as
much as several meters thick that occur in Triassic gabbro-diabase
sills, especially near contacts with Triassic sandstone and
shale. The sedimentary rocks and sills are strongly deformed into
narrow, steep, northwest-trending folds. The ore bodies are controlled
by strike-slip faults associated with the folding. Host rocks
exhibit greenschist facies metamorphism. The Au quartz veins
consist of 95 to 97 percent quartz with segregations of arsenopyrite
and lenses of scheelite, albite, ankerite, and muscovite. Also
widespread are calcite, dolomite, white mica, galena, native gold,
aquamarine, sphalerite, pyrite, and pyrrhotite. Gold occurs mainly
in bluish-gray quartz veinlets in a matrix of coarse-grain quartz
and arsenopyrite in the upper horizons of the deposit. Silica-carbonate
and sulfide alteration occur adjacent to ore zones. Near the
surface, quartz veins often host druse-like intergrowths of large,
well-crystallized quartz and isometric gold crystals. Coarsegrained
masses of gold, and less common dendritic gold, as much
as 1 cm diameter, are characteristic of the deposit. At depth, the
gold occurs mainly as fine, dispersed masses in arsenopyrite. The
deposit is of medium size and has been prospected and developed
preparatory to mining.
Origin of and Tectonic Controls for Chukotka
Metallogenic Belt
The Au quartz vein and Au shear zone deposits of the
Chukotka metallogenic belt are herein interpreted as forming
in the Late Cretaceous during regional deformation and
900 m
800
700
Map
Cross Section
Early Late Cretaceous Metallogenic Belts (100 to 84 Ma; figs. 79, 80) 209
associated metamorphism and anatectic granite magmatism
(Goryachev, 1998, 2003) that occurred during a major period of
collision and accretion of the Chukotka terrane (Nokleberg and
others, 2000). Preceding the accretion was (1) Early Cretaceous
opening of the Canada (Arctic Ocean) Basin, (2) migration of
the Chukotka superterrane to the southwest, and (3) closure of
the late Paleozoic(?) and early Mesozoic South Anyui ocean.
After closure, the Chukotka superterrane was accreted against
the South Anyui and Velmay subduction-zone terranes and
the Nutesyn island-arc terrane, which in turn collided with the
Kolyma-Omolon superterrane farther southwest (present-day
coordinates). The Au quartz vein deposits are interpreted as
forming during the early stage of the accretion. Similar origin
and coeval Au quartz vein deposits occur to the east in the
Southern Brooks Range metallogenic belt of Au quartz vein
deposits (fig. 80). Anatexis or partial melting is interpreted as
occurring during the final stage of accretion and associated
crustal thickening. The Sn polymetallic vein deposits are interpreted
as forming during the final stage of accretion.
Metallogenic Belts Formed in Late Mesozoic
Collision and Accretion of Wrangellia
Superterrane, Southern Alaska
East-Central Alaska Metallogenic Belt of Granitic
Magmatism Deposits (Older, Mid-Cretaceous
Part; Belt ECA), East-Central Alaska
The East-Central Alaska metallogenic belt of granitic magmatism
deposits (older, mid-Cretaceous part) fig. 80; tables 3,
4) (Nokleberg and others, 1995a, 1996, 1997a) consists of two
0 80 160 M
Gabbro and diabase
(Triassic)
Siltstone (Triassic)
Au quartz vein
Fault
Adit
Contact
Borehole on surface
Borehole on cross
section
Figure 98. Karalveem Au quartz vein deposit, Chukotka metallogenic belt, Russian Northeast. Schematic geologic
map and cross section. Adapted from Goryachev and others (1996) and Eremin and Sidorov (1995). See figure 79 and
table 4 for location.