Marble Copper

Prospect, Undetermined

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Au; Pb; Zn
Ore minerals chalcopyrite; malachite
Gangue minerals calcite; calc-silicate minerals

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale C-3
Latitude 55.724
Longitude -130.868
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Marble Copper prospect is on the north shore of Walker Cove about 1.4 miles from its mouth. The site is in section 9, T. 71 S., R. 95 E., of the Copper River Meridian. It corresponds to loc. P-19 in Berg and others (1977, p. 120-121), and to loc. 24 in Elliott and others (1978). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rocks in the area of the Marble Copper prospect are Tertiary or Cretaceous foliated granodiorite and quartz diorite of the Coast Range batholith, and paragneiss and minor marble that form metamorphic roof pendants, screens, and inclusions in the batholith (Berg and others, 1977, p. 120-121; Berg and others, 1988). The metamorphic rocks represent marine strata that underwent high-grade regional metamorphism in Cretaceous or Tertiary time. The premetamorphic age of the strata is uncertain, but they probably are mainly Paleozoic and may be as old as Precambrian (Berg and others, 1988, p. 26; Gehrels and others, 1990; Crawford and others, 2000).
The deposit consists of chalcopyrite and malachite in a marble-skarn zone in a paragneiss roof pendant in gneissic diorite and quartz diorite (Berg and others, 1977, p. 120-121 and fig. 33). The marble-skarn zone is about 20 feet wide, and it adjoins a zone of paragneiss and subordinate marble and skarn about 60 feet wide. The calc-silicate minerals in the skarn are not described, but their green color (fig. 33, spl. no. 2K008) suggests that they include diopside. A 22-inch-long channel sample of the most heavily copper-stained part of the marble-skarn zone assayed up to 0.7% Cu, 150 ppm Pb, 300 ppm Zn, 30 ppm Ag, and 3.5 ppm Au (Berg and others, 1977, fig. 33, spl. no. 2K009). Adjacent channel samples showed much lower assay values, and a chip sample of a second band of marble northeast of the marble-skarn zone showed only traces of copper. The prospect was explored sometime before 1972 by a shallow opencut, but there was no evidence in 1973 that any claims had been staked.
Geologic map unit (-130.869705134295, 55.7236548264792)
Mineral deposit model Cu skarn (Cox and Singer, 1986; model 18b)
Mineral deposit model number 18b
Age of mineralization Probably Cretaceous or younger.
Alteration of deposit Local oxidation of copper minerals.

Production and reserves

Workings or exploration The prospect was privately explored sometime before 1972 by a shallow opencut, but there was no evidence in 1973 that any claims had been staked. A 22-inch-long channel sample of the most heavily copper-stained part of the marble-skarn zone assayed up to 0.7% Cu, 150 ppm Pb, 300 ppm Zn, 30 ppm Ag, and 3.5 ppm Au (Berg and others, 1977, fig. 33, spl. no. 2K009). Adjacent channel samples showed much lower assay values, and a chip sample of a second band of marble northeast of the marble-skarn zone showed only traces of copper.
Indication of production None

Additional comments

Prospect is in Misty Fiords National Monument Wilderness.

References