Unnamed Occurrence (ARDF - SK019; on the west side of Tarr Inlet), Glacier Bay Mining District, Juneau Mining District, Alaska, USAi

Regional Level Types
Unnamed Occurrence (ARDF - SK019; on the west side of Tarr Inlet)	- not defined -
Glacier Bay Mining District	- not defined -
Juneau Mining District	Mining District
Alaska	State
USA	Country

The deposit is within Glacier Bay National Park and Preserve where exploration and development is restricted.
Location: This occurrence is in the Glacier Bay National Park and Preserve on the west side of Tarr Inlet about 4.5 miles southeast of the Canadian border. It is on a knob, informally known as 'Tarr Inlet Knob', that reaches a height of about 600 feet. It is shown as number 6 on figure C-2 and in figure C-39 of Brew and others (1978) and as location 17 on Plate 1 of MacKevett and others (1971). A less accurate location of this occurrence, which places it about 3/4 mile farther to the northwest, is shown as number 2 by Cobb (1972 [MF-424]).
Geology: The following description is summarized from Brew and others, 1978. Mineralization is found along altered fault and shear zones in quartz monzodiorite that makes up the Tarr Inlet Knob. The quartz monzodiorite contains large xenoliths of shale and volcanics. Porphyritic granite, probably in the form of small plugs, occurs at two sites on the knob. The altered and mineralized fault and shear zones are up to 200 feet thick and are often brightly iron-stained. Most of the mineralization occurs along altered fault zones that are oriented N20-30W and N10-30E. The deposit consists of pyrite, chalcopyrite, sphalerite, arsenopyrite, and quartz. The prospect is generally similar to the Margerie (SK020) prospect located about 2.5 miles to the west and both may have been mineralized by the same process. Most of the more significant mineralization has been found on the east side of the Tarr Inlet Knob below the 500-foot elevation. Samples of the richer portions of the mineralized zone that vary from 3 feet to 16 feet wide contain up to 3,300 ppm copper, 5,000 ppm zinc, 3,100 ppm lead, 50 ppm silver, and 0.15 ppm gold. A 1/2-foot sample contained 0.48% copper, 4.3% zinc, 100 ppm silver, 1,500 ppm lead, and 0.15 ppm gold. The Tarr Inlet Knob is in the Geikie province of Brew and others (1978) near its western margin. It is along the Brady Glacier fault zone, the eastern edge of the Tarr Inlet suture zone, which forms the western boundary of the Geike province. Movement along these structures is probably responsible for the fault and shear zones which localize the mineralization at this site. The faulting and mineralization must be younger than the Cretaceous intrusive rocks at Tarr Inlet Knob.
Age: The mineralization must be younger than the Cretaceous age of the host intrusive rocks (Brew and others, 1978).
Alteration: Alteration is mentioned but not described in Brew and others (1978).
Reserves: Brew and others (1978) judged the mineralized zones to be too small and too low-grade to be economic.

Commodities (Major) - Ag, Cu, Pb, Zn ; (Minor) - Au
Development Status: None
Deposit Model: Mineralized veins and shear zones in a quartz monzodiorite, possibly a porphyry

Other Databases

Link to USGS - Alaska:	SK019

Other Regions, Features and Areas containing this locality

References