Dutton Prospect (Dutton; Goodro and Thomas), Bristol Bay Mining District, Lake and Peninsula Borough, Alaska, USAi

Regional Level Types
Dutton Prospect (Dutton; Goodro and Thomas)	Prospect
Bristol Bay Mining District	Mining District
Lake and Peninsula Borough	Borough
Alaska	State
USA	Country

Location: This prospect is at an elevation of about 2,000 feet 2.5 miles northeast of Meadow Lake. It is at the head of an unnamed south-flowing tributary to Silver Creek, in the SE1/4 SE1/4, sec. 1, T. 6 S., R. 28 W., Seward Meridian. The location is probably accurate within 0.5 mile for the approximate center of a group of claims that extends as much as 2.5 miles. The Dutton prospect is locality 5 of Detterman and Cobb (1972).
Geology: The Dutton prospect is a skarn deposit along the contact of the Triassic Cottonwood Bay Greenstone and Kamishak Formation limestone. The deposit is on the north flank of a Jurassic quartz diorite batholith whose north contact can be traced for at least 12 miles (Detterman and Reed, 1980). The deposit consists of 'garnet rock,' magnetite- and garnet-magnetite rock, and, at the greenstone-limestone contact, epidotized rocks enriched in chalcopyrite, pyrite, calcite, quartz, and amphibole. Martin and Katz (1912) suggested that most of the mineralization was in the limestone. Butherus and others (1981) proposed that the greenstone was more highly mineralized. Butherus and others (1981) described rocks exposed in the Dutton adit, which was open at the time of their investigation. The rocks exposed along the southeast-trending adit, commencing at a fault, consisted of buff to light gray limestone about 105 feet thick, followed by 60 feet of massive garnet-magnetite rock containing some unreplaced limestone. The garnet-magnetite rock grades into a 90-foot-thick zone of epidotized rock containing fracture fillings of magnetite, quartz, and calcite. Farther southeast is 200 feet of propylitically-altered diorite in sharp contact with 200 feet of light-gray limestone. In general, pyrite and subordinate chalcopyrite, pyrrhotite, and magnetite occur in fracture-fillings in skarn; molybdenite has also been reported (Martin and Katz, 1912). The sulfide minerals are locally oxidized to malachite, azurite, chrysocolla, and limonite. Metal contents in samples collected in 1981 were relatively low (Butherus and others, 1981). A selected sample from a pit northeast of the adit contained 0.80 percent copper and 9.6 parts per million silver; the rock contained visible pyrite, arsenopyrite, chalcopyrite, and chrysocolla. A selected sample of manganiferous limonite gossan collected southeast of the adit assayed 0.5 percent lead and 36 parts per million silver. A representative sample of a 60-foot-thick garnet-magnetite layer contained about 225 parts per million copper. Substantially higher assays were reported by Martin and Katz (1910, 1912), who sampled when the prospect was active. Their assays ranged from 4 to 6 percent copper, 6 to 13.5 percent lead, up to 2 ounces of silver per ton, and less than 0.5 ounce of gold per ton. Studies by both Martin and Katz (1910, 1912) and Butherus and others (1981) indicated substantial widths of altered and mineralized rock. Martin and Katz (1912) reported an average mineralized width of about 200 feet and a maximum of 400 feet. They also reported that mineralization along the claims is best in two zones: one 3,000 feet long and one 1,000 feet long. Within these zones, the mineralization is discontinuous. Butherus and others (1981) recognized sufficient mineralization and alteration to propose prospecting the 12-mile-long contact zone of the nearby Jurassic batholith.
Workings: The Dutton prospect was discovered in 1901 and explored intensively until about 1910. Some claims (as the 12-claim Karen group) were patented. One adit was still open in 1981.
Age: Probably Jurassic.
Alteration: Propylitic alteration of diorite; development of skarn in both limestone and greenstone. Oxidation of iron and copper minerals.

Commodities (Major) - Cu; (Minor) - Ag, Au, Fe, Mo
Development Status: None
Deposit Model: Cu skarn, Fe skarn? (Cox and Singer, 1986; model 18b, 18d).

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Link to USGS - Alaska:	IL023

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References