Mineral Investigations in the Koyukuk Mining District, Northern Alaska, Progress Report

The Bureau of Land Management Anchorage Mineral Resource Team (AMRT) is conducting a five-year mineral resource assessment of the 11. 6 million acre Koyukuk mining district in northern Alaska. The district comprises the upper portion of the Koyukuk River drainage basin, the headwaters of which lie on the southern flank of the Brooks Range. The federal government manages 72% of the land within the district. District production totals approximately 286,000 ounces of placer gold and six tons of antimony ore. In 1998 there were 13 active placer mines in the district.

There are 407 documented mines, prospects, and mineral occurrences within the district. These include gold placers; gold- and antimony-bearing quartz veins; copper- and zinc-bearing massive sulfides; copper-bearing porphyries; tungsten-, copper-, and tin-bearing skarns; tin bearing greisens; chromite; and coal. A total of 175 sites have been examined to date and 960 rock, soil, stream sediment, pan concentrate, and placer samples collected.

A portion of the study, consisting of an airborne geophysical survey, was done in cooperation with the Alaska Division of Geological and Geophysical Surveys (ADGGS). Ground magnetic and electromagnetic conductivity surveys were done by AMRT as a follow up to the airborne survey. In addition ground penetrating radar surveys were conducted over known placer deposits to identify channel locations and bedrock depth.

Significant results from the first two years of this assessment include the delineation of anomalous gold . values within volcanic rocks on the upper Indian River, anomalous placer gold. in bench gravels above the Hammond River, gold-bearing quartz veinlets on nearby Vermont and Smith Creeks, and gold anomalies associated with skarn and massive sulfide occurrences in the Chandalar copper belt north of Bettles River.