Willow Creek mining district

Willow Creek mining district
Alaska Mining District
Willow Creek mining district
Coordinates: 61°47′N 149°15′W / 61.783°N 149.250°W / 61.783; -149.250

The Willow Creek mining district, also known as the Independence Mine/Hatcher Pass district, is a gold-mining area in the U.S. state of Alaska. Underground hard-rock mining of gold from quartz veins accounts for most of the mineral wealth extracted from the Hatcher Pass area. The first mining efforts were placer mining of stream gravels, and placer mining in the area has continued sporadically to this day. Robert Hatcher discovered gold and staked the first claim in the Willow Creek valley in September 1906. The first lode mill in the area started operating in 1908. Underground mining continued at a variety of locations around the pass until 1951. In the 1980s one of the area's hard-rock mines was briefly re-opened. At least one mining company is actively exploring for gold in the area now.^[1] Through 2006 the district produced 667-thousand ounces of hard rock gold and 60-thousand ounces of placer gold.^[2]

The Willow Creek district at Hatcher Pass is historically the third-largest lode-gold producing district in Alaska, having produced 624,000 oz of gold.^[3] At Hatcher Pass proper the southwestern margin of the Cretaceous to Tertiary age Talkeetna Mountains batholith is in fault contact with a pelitic schist. The Talkeetna Mountains batholith in this area consists of a pervasively altered zoned 74 Ma (million years old) tonalite body underlying Hatcher Pass and the headwaters of Willow Creek, and a 67 Ma quartz monzonite pluton farther west. The schist to the south consists mainly of metamorphosed and deformed sedimentary rocks, of Late Cretaceous to Paleocene age. The schist may represent subducted Valdez Group that was exhumed in the forearc region from beneath the Peninsular terrane.^[4] Both deformed and undeformed small felsic dikes occur in the schist. Several bodies of serpentinite are contained within the schist. Unmetamorphosed Late Cretaceous or Tertiary terrestrial sedimentary rocks of the Arkose Ridge Formations lie to the south of the schist and intrusives, across a low-angle detachment fault. Those bedded rocks are derived from the schists and intrusive rocks to the north. A rock unit variously mapped as intricately intermixed amphibolite and quartz diorite; or as a migmatite, occurs in contact with the Arkose Ridge formation on Government Peak and in contact with the Arkose Ridge Formation and quartz monzonite east of the Little Susitna River. It is not clear if the migmatite is a higher-metamorphic-grade equivalent of the schist.^[5][6]

Gold-bearing (+/- Ag, W, Sb, As, Cu, Mo, Pb, Te, Zn, Hg) veins occur in the tonalite, in small amounts in the schist, and in the Jurassic? migmatite, but not in the western quartz monzonite or in the Tertiary sediments. Most of the mineral deposits are close to the tonalite-schist contact.^{[citation needed]}