Unnamed (on southeast coast of Nagai Island)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities As
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SN
Quadrangle map, 1:63,360-scale D-4
Latitude 54.975
Longitude -160.115
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is on the southeast coast of Nagai Island approximately 2 miles northeast of Saddler Peak and includes mineral showings at sea level and in the adjacent sea-cliffs. Location is accurate to within a few hundred feet.

Geologic setting

Geologic description

At this mineral occurrence two Tertiary quartz diorite sills intrude siltstone and sandstone of the Cretaceous Shumagin Formation (Ellis and Apel, 1989). The strata strike northwest and dip 20-50 degrees to the southwest. They are silicified and pyritic adjacent to the contact. The sills crop out along the sea cliffs and beach for approximately 1600 feet.
Gold is present in the sills in quartz-arsenopyrite veins and stockworks thought to be associated with northwest-trending faults and shear zones. Gold also occurs in the altered rocks adjacent to the sills and in a 100-foot wide hydrothermal breccia zone.
In 1989 Battle Mountain Exploration Company collected 61 rock-chip samples, 22 of which contained >100 ppb gold (Ellis and Apel, 1989). Fifteen samples contained 100 to 499 ppb gold, 5 contained 500 to 999 ppb gold, and 2 had >1ppm ppm gold (up to 6.55 ppm). Elsewhere on the island they also obtained scattered pan concentrate and rock samples anomalous in arsenic, gold, and mercury. Free gold was also noted on the beach at Saddlers Mistake and in several streams draining the area. Anomalous gold was also found over a 1/2 mile area associated with a color anomaly located in steep cliffs approximately 3 miles north of this site. Numerous gold anomalies were detected on the north part of the island by the U.S. Geological Survey (Frisken and Kelly, 1992).
Geologic map unit (-160.117075329355, 54.9741784939125)
Age of mineralization Tertiary.
Alteration of deposit Sedimentary country rocks are silicified and pyritic adjacent to the sills. Hydrothermal breccia zone in sills. Color anomaly about 3 miles north of site.

Production and reserves

Workings or exploration
In 1989 Battle Mountain Exploration mapped and sampled this mineral occurrence. Of 61 rock-chip samples collected 22 contained >100 ppb gold. The highest value obtained was 6.55 ppm gold (Ellis and Apel, 1989).
The U.S. Geological Survey mapped and geochemically sampled in the Simeonof Island quadrangle in the late 1980s (Wilson and others, 1991; Frisken, 1992).
Indication of production None

Additional comments

This site is located on land selected by the Aleut Native Corporation.

References