1:30 Prospect, Yentna Mining District, Matanuska-Susitna Borough, Alaska, USAi

Regional Level Types
1:30 Prospect	Prospect
Yentna Mining District	Mining District
Matanuska-Susitna Borough	Borough
Alaska	State
USA	Country

Location: Alaska Department of Natural Resources claim records show this prospect area two miles up a southern tributary to Portage Creek in the southeast quarter of Section 28, T. 22 N., R. 19 W. Exposed on mountain slopes on the northwest side of the creek. Approximately 7 miles west-southwest of the confluence of Portage Creek and the Skwentna River.
Geology: Fine- to medium-grained, equigranular biotite-hornblende diorite intrudes and hornfels Mesozoic marine sedimentary rocks (KJs) of the Kahlitna terrane (Reed and Elliott, 1970). The hornfels is pyritic and locally sheared. Float from inaccessible portions of the diorite have thin (less than 1 inch) veins of quartz-arsenopyrite-pyrite and quartz-molybdenite-sphalerite. Samples of vein material from the diorite contained up to 4400 ppb gold and 1380 ppm silver. A 15 foot chip samples across pyritic, sheared hornfels ran 3800 ppb gold. (Cominco American Incorporated, unpublished reports, 1987-1988). The diorite is probably part of the Late Cretaceous/Early Tertiary Mount Estelle plutonic suite (Tme) (Reed and Elliott, 1970; Reed and Nelson, 1980); veins may be genetically related to the host rocks.
Workings: Exploration work included silt and rock chip geochemical sampling and mapping. (Cominco American Incorporated, unpublished report, 1987).
Age: Host rocks are late Cretaceous or Early Tertiary (?) (by Reed and Elliott, 1970 and Reed and Nelson, 1980); the veins may be genetically related to the host rocks.
Alteration: Limonite, quartz

Commodities (Major) - Ag, Au, Cu, Mo, Zn ; (Minor) - As, Sb
Development Status: No
Deposit Model: Polymetallic vein(s); copper-moly porphyry?

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Link to USGS - Alaska:	TY021

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References