Double Glacier

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au; Cu; Zn
Ore minerals gold; pyrite; sphalerite
Gangue minerals barite; calcite; gypsum; quartz

Geographic location

Quadrangle map, 1:250,000-scale KN
Quadrangle map, 1:63,360-scale A-8
Latitude 60.093
Longitude -152.976
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is located near the mouth of Double Glacier in section 13, T. 1 S., R. 22 W., of the Seward Meridian. The occurrence is at an elevation of about 1,000 feet.

Geologic setting

Geologic description

The Double Glacier occurrence is within the lower Jurassic Talkeetna Formation, an approximately 2,575 meter thick sequence of volcanic and volcaniclastic rocks (Determan and Hartsock, 1966). The volcanic section near the prospect is structurally bounded on the west by the Bruin Bay Fault, a major fault system traceable for over 500 kilometers. On the east, the volcanics are unconformably overlain by upper Jurassic marine sediments (Determan and Hartsock, 1965). The Talkeetna Formation is intruded by rocks of the Aleutian range -Talkeetna Mountain plutonic belt approximately 23 km. southwest of the prospect. These intrusives which consist dominantly of coarse-grained quartz diorites and quartz monzonites have been dated between 175 and 145 m.y. (Steefel, 1987).
At the Double Glacier occurrence, the Talkeetna Formation has been divided into three major groups (Steefel, 1987). The lowest group consist of purple and green andesite flows and breccia which locally show well-developed pillows. The middle group that host the mineralization, consists of coarse-grain felsic breccias, reworked volcaniclastic rocks, crystal tuff, and dacite flows. The upper group consist of polymictic andesitic breccias and conglomerates with andesitic flows. Informally, the middle group has been named the Johnson unit (Steefel, 1987). Numerous structures within the unit including turbidites and reverse graded bedding indicate a subaqueous origin.
The mineralization consists of stratiform massive sulfide layers and lens which contain pyrite, chalcopyrite, and sphalerite. There are no published assay results for this occurrence William Ellis (personal communication, 1999) speculates that this occurrence is an upper portion of a Kuroko type massive sulfide deposit.
Geologic map unit (-152.978231303337, 60.0923886256861)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization Jurassic massive sulfide.
Alteration of deposit The Double Glacier occurrence has alteration characteristics of a Kuroko type massive sulfide deposit that include sulfate alteration and silicification.

Production and reserves

Workings or exploration The occurrence was discovered by Anaconda Minerals in 1982 as part of an exploration program at the Johnson River prospect. To date there has been detailed mapping, stream and soil geochemical surveys, and surface trenching and sampling. No assay results are available.
Indication of production None

Additional comments

This occurrence is owned by Cook Region Native Association.

References

MRDS Number 10307711
Reporters Jeff A. Huber (Anchorage)
Last report date