The Bering Sea region
includes St. Lawrence, St. Matthew, and the Pribilof Islands and nearby
smaller islands and offshore rocks. It is considered as one district.
The islands of the Bering Sea are mainly rolling uplands and emerged
marine platforms, generally within a few hundred feet of sea level.
Isolated mountain masses rise to altitudes between 800 and 900 feet,
or about 2,000 feet above the shallow Bering Sea. (See Hopkins (1967).)
The Pribilof Islands and St. Matthew are composed mainly of Cenozoic
volcanic rocks and surficial deposits; peridotite older than the volcanic
rocks underlies a small area on St. George Island in the Pribilofs
(Barth, 1956; Cobb and others, 1968, p. K3—K5). St. Lawrence
Island is made up of a thick section of Paleozoic and Mesozoic carbonate
and clastic rocks generally similar to coeval rocks exposed in the
Brooks Range of northern Alaska and in the Chukotsk Peninsula of ~Siberia
(Patton and Dutro, 1969; Patton and Csejtey, 1970, 1971). The western
part of the island contains small areas of coal-bearing Tertiary continental
deposits and Cre¬- taceous and Tertiary volcanic rocks. Tertiary(?)
and Quaternary basaltic rocks cover the older rocks in central St.
Lawrence Island. Permian gabbro and diabase, hypabyssal phases related
to some of the volcanic rocks, and Cretaceous monzonitic plutons invaded
the older rocks in both the eastern and western parts of the Island.
All of the known lodes in the region are on St. Lawrence Island; they
include disseminated molybdenite in one of the plutons, a small low-grade
porphyry copper deposit with minor molybdenite in a small satellitic
stock, and several small sulfide deposits con¬- taining lead,
zinc, and silver. None of these occurrences has been thoroughly explored.
Anderson (1947, p. 41—42) mentioned a re¬- port of cassiterite
near the southwestern end of the island but did not specify whether
it was a bedrock or placer occurrence. Recent stream-sediment sampling
and reconnaissance geologic mapping in the area failed to find any
indication of tin mineraliza¬- tion (oral commun., Bela Csejtey,
Jr., Sept., 1970). With the possible exception of the rumored cassiterite,
no placer deposits have been reported from the land area of the Bering
Sea region. There has been very little prospecting in the region,
however, owing in part to its remoteness and in part to governmental
restrictions. Recent investigations in the Bering Sea (Nelson and
Hopkins, 1969; Nelson and others, 1969) disclosed local concentrations
of gold in bottom sediments, in particular between St.. Lawrence Island
and the Seward Peninsula. A little native copper of no probable economic
interest was found in bottom samples collected near the northwest
corner of St. Lawrence Island.