Prince William Sound Region Gold Production

  
Posted July 16, 2009 in Gold Mining

By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968

Click here for the Principle Gold Producing Districts of the United States Index

The Prince William Sound region is along the southern coast of Alaska, immediately east of the Kenai Peninsula. It is a constricted area between the rugged Chugach Mountains on the north and that part of the Gulf of Alaska known as Prince William Sound. In this region copper and gold are the chief mineral commodities, and the notable mining districts are Port Wells, Port Valdez, and Ellamar. Only Port Valdez is shown on the index map (fig. 5) because it is the only district that has produced any significant quantities of gold.

The earliest record of gold production in the Prince William Sound region was in 1894, when some placers were worked on a small scale near Port Valdez (Brooks, A. H., in Grant and Higgins, 1910, p. 72). A few years later other small placers were found in the Port Wells district. Auriferous veins were found here in 1907, and in the following 6 years numerous properties were developed and small shipments were made (Johnson, 1914, p. 214-215). The Cliff mine, staked in 1906 in the Port Valdez district, became the largest gold producer in the district in the early years (Moffit, 1954, p. 228,304).

The copper ores at Ellamar and La Touche Island carry variable amounts of gold (Grant and Higgins, 1910, p. 71), but the amount produced from this source could not be determined.

Gold production from this region reached its zenith before 1920. Thereafter, except for a slight revival in the late 1930's, output has dwindled. No production was reported for 1957-59. Total recorded gold production was 137,600 ounces, all from lode mines or as a byproduct from copper mines. Production data for individual districts have not been found. It is fairly certain that the Port Valdez district has produced most of the lode gold from this region; however, it is not known how much of the total gold production was a byproduct from copper ores of Ellamar, La Touche, or elsewhere.

Numerous fiords along the irregular coastline and glaciated islands that dot Prince William Sound give evidence of a once extensive ice covering in this region (Grant and Higgins, 1910, p. 18-19). In the northern part of the region, especially in the Port Wells district, several ice tongues still travel far enough down the valleys to meet the sea.

The rocks of this region consist of two loosely denned groups of low-rank metasedimentary rocks of Mesozoic age, distinguished from one another by minor differences in gross lithologic characteristics and by differences in metamorphism (Moffit, 1954, p. 234-250). These rocks have been complexly folded, faulted, and intruded by basaltic and granitic igneous rocks.

The Valdez Group is composed predominantly of graywacke, slate, and argillite, with subordinate siliceous and carbonaceous slate, feldspathic quartzite, and a few beds of conglomerate and impure limestone. The rocks are metamorphosed locally to schist and phyllite. The Orca Group consists dominantly of slate and graywacke, and in places greenstone and conglomerate are major components. Though the rocks of the Orca Group are intensely folded and faulted, their metamorphism seems to be related to igneous intrusions rather than regional tectonism. The distinction and separation of the Valdez and Orca Groups cannot be consistently made everywhere in the region (Moffit, 1954, p. 234-273). The ages and stratigraphic relations of these two groups have not been clearly established; however, the meager paleontological evidence suggests a Late Cretaceous age for both groups (Moffit, 1954, p. 273-275).

The gold-bearing quartz veins of the Port Valdez district are found in slates and graywackes of both the Valdez and Orca Groups. At Pdrt Wells, gold occurs in quartz veins and stringers that occupy fissures in slate, graywacke, and conglomerate. Mineralization probably is late Mesozoic or Tertiary in age, closely associated with granitic intrusions (Moffit, 1954, p. 295). Vein minerals are pyrite, galena, sphalerite, pyrrhotite, arsenopyrite, stibnite, chalcopyrite, gold, and silver in a gangue of quartz. The copper deposits of Prince William Sound, which have yielded moderate amounts of gold, occur as impregnations or replacement bodies usually along zones of shearing in the country rock. Chalcopyrite and pyrrhotite are ubiquitous, pyrite is common, and galena, sphalerite, bornite, chalcocite, native copper, cuprite, and malachite are present in small amounts. The nonmetallic minerals in these deposits are quartz, calcite, epidote, and chlorite (Grant and Higgins, 1910, p. 53-54).


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