Alaska's mineral industry 1990

Abstract

The report is designed to provide current, accurate, and technically reliable information about Alaska's mineral industry. The report depends on the cooperation of individuals, private industry, and government agencies to provide information on their mining projects and activities.In 1990 the sum of expenditures for exploration and development, and the estimated value of production totaled $61 0.6 million. Exploration expenditures rose to $63.3 million, with most of the effort concentrated on hardrock gold projects, some of them in advanced stages. Development expenditures were $14.3 million, considerably less than the $134.3 million in 1989, mainly due to completion of development at the Red Dog1 and Greens Creek mines.Value of mineral production in 1990 was $533 million, doubling the 1989 production value of $277 million.In 1990, with 55 percent of the nation's supply, Alaska led the United States in zinc production. Consequently, U.S. net import reliance for this crucial commodity decreased from 61 to 48 percent.Alaskan silver production accounted for about 18 percent of the domestic mine production. Only Idaho and Nevada produced more.Alaska continues to have the nation's largest placer gold mining industry, which provides jobs to many rural Alaskans.Significant progress in land reclamation and water quality at placer mines indicate that Alaska's mining industry is capable of providing economic diversity and environmentally sound operations in the 1990s.'Names of significant mines and deposits appear in boldface type throughout this report.. . I ICONTENTS m m n n w n t~t t~~m t t n m t n t ! t~~n t t t n n m n n~m t n n m m m m m m~m n m~m m m m

Greenschist Facies Metamorphic Zircon Overgrowths as a Constraint on Exhumation of the Brooks Range Metamorphic Core, Alaska

“…Metamorphic devolatilization reactions in pelitic sedimentary rocks, such as might have generated the fluids that enabled zircon growth, have been invoked to explain important gold deposits of similar age in northern Alaska (Goldfarb et al, ; Rose et al, ). In the Chandalar‐Koyukuk gold district (e.g., Swainbank et al, ), auriferous veins are associated with high‐angle shear zones that cut early Cretaceous upper greenschist facies fabrics (Goldfarb et al, ) and may represent metal remobilization by Albian age fluids (Dillon et al, ). East of Fairbanks, Alaska, the significant Pogo gold deposit has been interpreted as having formed during a regional extensional event yielding Molybdenite Re‐Os ages of 104 ± 1 Ma as mineralizing hydrothermal fluids derived from an inferred magmatic source at depth followed brittle extensional structures upward (Rhys et al, ; Selby et al, ).…”

Orogenesis, high-T thermal events, and gold vein formation within metamorphic rocks of the Alaskan Cordillera

“…Orogenic belts throughout the world (Fig. 3) yielded at least 330 000 oz of gold from placer mines (Swainbank et al, 1991) and is the only significant gold district in the Brooks Range; none of the other rare and scattered placer occurrences reported across the southern Brooks Range yielded more than a few tens of thousands ounces of gold. Small gold-and stibnite-bearing quartz veins are scattered throughout the Chandalar-Koyukuk region.…”

“…Placer deposits of the Yukon-Tanana upland in east-central Alaska have yielded about 11 million ounces of gold, with approximately 75% of past production coming from the Fairbanks district (Swainbank et al, 1991). In addition, approximately 10 million ounces of placer gold have been recovered from the Klondike area immediately to the east in the Yukon Territory of Canada (Rushton, 1991).…”

“…Unlike most of Alaska, rocks of west-central Alaska and of the Alaska Peninsula to the south are largely unmetarnorphosed (Dusel-Bacon, 1991). Approximately three million ounces of placer gold, with about half of that amount coming from the Flat-Iditarod district, have been recovered from the Kuskokwim basin of westcentral Alaska (Koschmann and Bergendahl, 1968;Swainbank et al, 1991). Productive areas are underlain predominantly by Late Cretaceous flysch, with the placers and hypothesised lode sources being spatially associated with 70-60 Ma andesitic and monzonitic volcanic-plutonic complexes (Bundtzen and Miller, 1992).…”

“…A TOTAL of 32 million ounces of gold has been recovered from placer and lode occurrences throughout Alaska (Cobb, 1984a,b;Swainbank et al, 1991). Just over 25% of this production has come from Tertiary mesothermal vein deposits along the Pacific rim ( Fig.…”