Carita

Prospects, Undetermined

Alternative names

Erhart
Starlight

Commodities and mineralogy

Main commodities Cu
Other commodities Barite
Ore minerals barite; chalcopyrite; galena; pyrite; sphalerite
Gangue minerals quartz; siderite

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-6
Latitude 55.167
Longitude -131.781
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Carita group of prospects is in section 25, T. 77 S., R. 90 E., of the Copper River Meridian, at or near the east corner of Nehenta Bay. The prospects are in an estimated half-mile-square area that trends roughly eastward from the shoreline of the bay to an elevation of about 200 feet. The map site is at the approximate center of the group of prospects and is accurate within a few hundred feet. The site corresponds to loc. 124 in Elliott and others (1978), and to loc. 316 (1-5) in Maas and others (1995).
Also see Additional comments.

Geologic setting

Geologic description

Southern Gravina Island is underlain by an assemblage of undivided Silurian or Ordovician metamorphosed bedded and intrusive rocks; a stock and associated dikes of Silurian trondhjemite that cuts the metamorphic assemblage; and a sequence of Upper Triassic carbonate, clastic, rhyolitic, and basaltic strata that unconformably overlies the older rocks (Berg, 1973, 1982; Berg and others, 1988). In many places, the Triassic rhyolite and the rocks beneath it are permeated by microscopic particles of hydrothermal hematite, giving them a pink, purple, or red hue (Berg, 1973, p. 14). The country rocks in the area of the Carita prospects are cut by a complex system of high-angle faults that strike NE and NW, and by at least one thrust fault that dips gently northward (Berg, 1973, pl. 1).
Brooks (1902, p. 73) described the Erhart and Starlight claims. The Erhart prospect is a mineralized shear zone in porphyritic rock. The mineralization, chiefly chalcopyrite, extends over a width of 4-5 feet, but the richer parts are less than 2 feet thick. On the Starlight claim, the deposit is a quartz-chalcopyrite-pyrite breccia zone about 3 feet thick, apparently hosted by the same country rocks as the deposit at the Erhart prospect.
Wright and Wright (1908, p. 140) describe the Carita deposit only as a chalcopyrite-bearing quartz vein in calcic conglomerate.
Maas and others (1995, p. 227) report that exploration of the Carita group by private interests in 1973-74 identified a zone of mineralized, siliceous breccia hosted by limestone, metavolcanic rocks (greenschist), and altered trondhjemite. The breccia includes quartz, barite, siderite, pyrite, galena, sphalerite, and chalcopyrite. The zone was defined by geochemical anomalies in soil samples, and by an induced polarization survey. Four holes, totalling about 200 feet, drilled to test the anomaly, indicated only minor copper mineralization. The richest 10-foot section assayed 0.28% Cu. Maas and others (1995, p. 229) were able to locate a 50-foot adit and a few small pits and trenches, but not the other adit and shafts reported in the area.
The characteristics and setting of the Carita deposits indicate that they are polymetallic veins of Late Triassic or younger age.
Geologic map unit (-131.782677439397, 55.1666534317294)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Late Triassic or younger.
Alteration of deposit Locally conspicuous iron staining. Probably local silicification, carbonatization, pyritization, and introduction of hydrothermal hematite.

Production and reserves

Workings or exploration Development work in the early 1900s included an opencut and a 50-foot tunnel (Brooks, 1902, p. 73). Maas and others (1995, p. 227) report that exploration of the Carita group by private interests in 1973-74 identified a zone of mineralized, siliceous breccia hosted by limestone, metavolcanic rocks (greenschist), and altered trondhjemite. The breccia includes quartz, barite, siderite, pyrite, galena, sphalerite, and chalcopyrite. The zone was defined by geochemical anomalies in soil samples, and by an induced polarization survey. Four holes, totalling about 200 feet, drilled to test the anomaly, indicated only minor copper mineralization. The richest 10-foot section assayed 0.28% Cu. Maas and others (1995, p. 229) were able to locate a 50-foot adit and a few small pits and trenches, but not the other adit and shafts reported in the area.
Indication of production Undetermined

Additional comments

Early descriptions of the Carita group of prospects also refer to the Erhart and Starlight claims (Cobb and Elliott, 1980, p. 24).

References

MRDS Number A012368

References

Reporters H.C. Berg, USGS
Last report date 7/5/1999