Marion Twin Mine, Willow Creek Mining District, Matanuska-Susitna Borough, Alaska, USAi

Regional Level Types
Marion Twin Mine	Mine
Willow Creek Mining District	Mining District
Matanuska-Susitna Borough	Borough
Alaska	State
USA	Country

Location: 2,000 ft east-northeast of the end of the unimproved road that parallels to Craigie Creek. Marked with quarry symbol and labeled 'Marion Twin Mine' on the Anchorage D-7 1:63,360-scale topographic map. Accurate within 400 ft. Locality 15 of Cobb (1972) and locality 12 of MacKevett and Holloway (1977).
Geology: Quartz vein, 2 to 10 inches thick, cuts quartz diorite of the Late Cretaceous Willow Creek Pluton. The thin, gently NW dipping quartz vein is in a shear zone and contains free gold, pyrite, galena, and chalcopyrite. The vein has been broken by post-mineralization faulting. The ore plays out where vein rolls upward into a shear zone, south of the mine (Ray, 1954). The Willow Creek Pluton is a zoned pluton: the outer part consists of hornblende quartz diorite and lesser hornblende tonalite; the core consists of hornblende-biotite granodiorite, and lesser hornblende-biotite quartz monzodiorite and biotite quartz monzonite. Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).
Workings: The extent of the mine was an open cut about 50 ft x 30 ft.
Age: Late Cretaceous or younger; vein cuts the Late Cretaceous Willow Creek Pluton.
Alteration: Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).
Production: Capps and Tuck (1935) reported that in 1929 and 1930 a few tons of rich ore was mined; some ore was sent to a smelter and some ore was sent to the company's mill on the Little Susitna River (at Lonesome Mine ARDF number AN063). Last production was reported in 1935.

Commodities (Major) - Au; (Minor) - Cu, Pb
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	AN026

Other Regions, Features and Areas containing this locality

References