Unnamed (headwaters of West Fork Maclaren River)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Mo; W
Ore minerals gold; molybdenite; pyrite; scheelite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-6
Latitude 63.3734
Longitude -146.6791
Nearby scientific data Find additional scientific data near this location
Location and accuracy
This placer occurrence is in the headwaters of the West Fork Maclaren River at elevations between about 3,700 and 4,600 feet. The occurrence is shown as the approximate midpoint of the placer at the common south corner of section 1, T. 18 S., R. 5 E., and section 6, T. 18 S., R. 6 E., Fairbanks Meridian. The occurrence corresponds to locality A4 of Kurtak and others (1992).
The topographic map of the area (Mount Hayes B-6, edition of 1951) shows the location as glacier and medial moraine. Since 1951, the glacier has receded at least one mile, and the site now is alluvial in character.

Geologic setting

Geologic description

This placer occurrence is underlain by schist, amphibolite, slate, and schistose quartz probably of Cretaceous metamorphic age (Nokleberg and others, 1982). The metamorphic rocks are cut by quartz veinlets, some of which contain pyrite and trace amounts of molybdenite (to 22 parts per million molybdenum). Anomalous concentrations of tungsten in placer concentrate samples suggest the probable existence of scheelite at or near the site.
Placer gold occurs both in glacial moraine and in active stream gravel. The maximum concentration in a panned concentrate was 10,000 parts per billion (ppb) gold in active stream alluvium; the moraine material contained as much as 1,800 ppb gold (Kurtak and others, 1992, locality A4). The concentrates also contained tungsten; four of five pan-concentrate samples contained from 120 to 310 parts per million (ppm) tungsten. In addition, sample 3005 contained 0.15 percent arsenic, and sample 2662 (concentrates from glacial moraine) contained 740 ppm arsenic. The bedrock sources of the gold, arsenic, and tungsten are unknown.
Geologic map unit (-146.681373059825, 63.3729680639759)
Mineral deposit model Placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Holocene.

Production and reserves

Workings or exploration The area was sampled at a reconnaissance level by the U.S. Bureau of Mines (Kurtak and others, 1992).
Indication of production None

Additional comments

The U.S. Bureau of Mines recommended additional prospecting along the margins of the glaciers for the bedrock sources of gold and tungsten (Kurtak and others, 1992).

References