USGS Professional Paper 1697 - Alaska Resources Library

224 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
Palyanskoe Clastic Sediment-Hosted Hg or Hot-Spring
Hg(?) Deposit
The Palyanskoe clastic sediment-hosted Hg or hot-spring
Hg(?) deposit (Syromyatnikov, 1972; Babkin, 1975; Syromyatnikov,
Dubinin, 1978) consists of stockworks, veinlets,
and disseminations, podiform occurrences that are hosted in
Late Cretaceous sandstone and shale. The sedimentary rocks
overly a deeply-eroded volcanic dome now exposed as a block
of volcaniclastic rocks with an intrusive core. The Hg deposit
formed in several stages. Most parts of the deposit occur at
the intersections of major north-south- and east-west-trending
faults. The ore bodies tend to occur along extensive layering in
the volcanic rocks and along zones of tectonic disruption and
explosive brecciation. More than 30 minerals are recognized,
including quartz, dickite, dolomite, siderite, calcite, cinnabar,
marcasite, pyrite, galena, sphalerite, native arsenic, and realgar,
and nickel minerals. Wall-rock alteration is not identified.
The deposit contains an estimated 10,117 tonnes Hg in ore
grading 0.53 percent Hg.
Seward Peninsula Metallogenic Belt of Granitic
Magmatism Deposits (Belt SP), Northwestern
Alaska
The Seward Peninsula metallogenic belt of granitic magmatism
deposits (fig. 103; tables 3, 4) occurs on the western part
of the Seward Peninsula and St. Lawrence Island (not shown
on fig. 103) in northern Alaska (Nokleberg and others, 1995a;
Hudson and Reed, 1997). The metallogenic belt is hosted in the
part of the region intruded by Late Cretaceous silicic granitoid
plutons (Hudson and Arth, 1983). The deposit types are
mainly Sn granite, porphyry Mo, polymetallic vein, and felsic
plutonic U deposits. The significant deposits in the belt are
(table 4) (Nokleberg and others 1997a,b, 1998) (1) Sn quartz
vein deposits at Cape Mountain and Potatoe Mountain, (2) a Sn
skarn deposit at Ear Mountain (Winfield), (3) a complex Sn-W
skarn, Sn greisen, carbonate-replacement Sn(?) deposit at Lost
River, (4) a Sn greisen deposit at Kougarok; polymetallic vein
deposits at Independence, Omilak, Quartz Creek, and Serpentine
Hot Springs, (5) a porphyry Mo deposit at Windy Creek,
(6) a sediment-hosted U deposit at Death Valley, and (7) a felsic
plutonic U deposit at Eagle Creek. The deposits and host granite
plutons are interpreted as the extreme northeastern end of the
Cretaceous and early Tertiary Okhotsk-Chukotka volcanic-plutonic
belt that extends for several thousand kilometers to the
west across the Bering Straits and southwest into the Russian
Far East (Nokleberg and others, 1994c, 1997c). The various
Sn deposits are commonly referred to as the Cretaceous tin
province of the Seward Peninsula. The origins of many of the
polymetallic vein deposits are somewhat enigmatic.
Lost River Sn-W Skarn and Sn Greisen Deposit
The classic Lost River Sn-W skarn and Sn greisen
deposit (fig. 107) (Dobson, 1982; Hudson and Arth, 1983;
Reed, Menzie, and others, 1989; Newberry and others, 1997)
consists of several prospects and one mine in veins, skarns,
greisens, and intrusion breccia formed above a shallow Late
Cretaceous granite stock that intruded thick sequence of Early
Ordovician limestone and argillaceous limestone. Early-stage
andradite-idocrase skarn and later fluorite-magnetite-idocrase
vein skarns are altered to chlorite-carbonate assemblages that
are contemporaneous with formation of cassiterite-bearing Sn
greisen. The major ore minerals in skarn and greisen are cassiterite
and wolframite and lesser stannite, galena, sphalerite,
pyrite, chalcopyrite, arsenopyrite, and molybdenite, plus a wide
variety of other contact metasomatic and alteration minerals.
The K-Ar isotopoic age of the granite is 80.2 Ma. Production
of 320 tonnes Sn occurred mostly from 1951 to 1956 from
underground workings a few hundred meters deep along the
Cassiterite dike, a near-vertical rhyolite dike that is extensively
altered to greisen over the buried granite. Similar smaller
deposits nearby include Sn greisen and veins near the Tin
Creek Granite and various polymetallic veins and skarns near
the Brooks Mountain Granite. A large beryllium deposit occurs
peripheral to the skarns and consists of limestone replaced by
fluorite-white mica veins that contain diaspore, chrysoberyl,
and tourmaline. The Be deposit is probably associated with
early stages of granite intrusion. Some placer Sn was recovered
from creek below Lost River mine. A major exploration program
in early 1970’s drilled several large Sn-W-fluorite-Be ore
bodies. The deposit contains estimated reserves of 25 million
tonnes grading 0.15 percent Sn, 0.03 percent WO 3, 16.3 percent
CaF 2 (WGM, Inc., written commun., 1975).
Felsic Plutonic U and Sandstone U deposits
A complex, multiphase felsic plutonic U deposit occurs
at Eagle Creek and a sandstone U deposit occurs at Death
Valley, both in the eastern part of the Seward Peninsula. The
felsic plutonic deposit consists of disseminated U-, Th-, and
REE-minerals, which occur along the margins of alkaline
dikes intruded into a Cretaceous granite pluton and adjacent
wall rocks (Miller, 1976; Miller and Bunker, 1976). The Death
Valley sandstone U deposit consists mainly of metaautunite in
Paleocene sandstone along the margin of a Tertiary sedimentary
basin (Dickinson and Cunningham, 1984; Dickinson and
others, 1987). The U in the sandstone probably was transported
by groundwater from Cretaceous granitoid plutons to
the west (Dickinson and Cunningham, 1984).
Origin of and Tectonic Controls for Seward Peninsula
Metallogenic Belt
The felsic-magmatism-related deposits of Seward Peninsula
metallogenic belt generally occur in or adjacent to moderate
or highly silicic granites of latest Cretaceous age (Hudson
and Arth, 1983; Nokleberg and others, 1995a). The porphyry
Mo, felsic plutonic U, and polymetallic vein deposits occur in
slightly older and slightly less siliceous granites, whereas the
Sn granite and associated deposits occur in slightly younger
and more silicic deposits. The granites associated with both