Island Mountain Prospects, Yentna Mining District, Matanuska-Susitna Borough, Alaska, USAi

Regional Level Types
Island Mountain Prospects	Group of Prospects
Yentna Mining District	Mining District
Matanuska-Susitna Borough	Borough
Alaska	State
USA	Country

Location: Alaska Department of Natural Resources unpublished claim records locate these prospects on the west side of the Skwentna River, one to one-and-one half miles south of the confluence of Emerald Creek and the Skewntna River. The site covers an area of about eight square miles in Sections 28, 29, 31,32, and 33, T. 20 N., R. 19 W. Location given is in the northeast corner of the area.
Geology: Reed and Elliott (1970) show this locality to be underlain by Mesozoic sediments (KJs) of the Kahlitna terrane that are intruded by a small body of granite and quartz monzonite (TKig). Detailed mapping in the late 1980's by Cominco American Incorporated identified veins and disseminations of pyrite-chalcopyrite and arsenopyrite-gold and stockwork quartz veins with magnetite and trace amounts of molybdenite cutting fine- to medium- grained plagioclase-hornblende porphyritic andesite and medium-grained monzonitic plutonic rocks at this site. Carbonate-rich beds in the sedimentary country rocks are locally replaced with pyrrhotite, pyrite, and sphalerite. Numerous occurrences are reported over an 8 square mile area. (Cominco American Incorporated, unpublished reports, 1987and 1988.) Host rocks are most likely Late Cretaceous or Early Tertiary(?) based on nearby K-Ar ages published by Reed and Lanphere (1972). Mineralization is probably related to these intrusions.
Workings: Exploration included silt sampling, mapping, rock and contour soil sampling, soil grid geochemical surveys, magnetic and VLF geophysical surveys and diamond drilling by Cominco America in mid-1980's.
Age: Host rocks are late Cretaceous or Early Tertiary(?) based on K-Ar ages published by Reed and Elliott (1970). The deposit is probably related to these intrusions.
Alteration: Propylitic (chlorite-epidote-carbonate +/- magnetite); argillic/sericitic; silicic.

Commodities (Major) - Au, Cu, Mo, Zn; (Minor) - As, Fe
Development Status: None
Deposit Model: Porphyry copper(?); porphyry copper-gold(?); polymetallic vein; replacement

Other Databases

Link to USGS - Alaska:	TY018

Other Regions, Features and Areas containing this locality

References