Jewel; Jumbo Prospect, Ketchikan Gateway Borough, Alaska, USAi

Regional Level Types
Jewel; Jumbo Prospect	Prospect
Ketchikan Gateway Borough	Borough
Alaska	State
USA	Country

Early reports refer to the Jewel prospect as the Jumbo claim (Cobb and Elliott, 1980, p. 59).
Location: The approximate location of the Jewel prospect is at an elevation of about 150-200 feet, about 0.5 mile north-northwest of the west head of Seal Cove. The site is in section 17, T. 77 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 116 in Elliott and others (1978). The location is probably accurate within about 0.5 mile. Also see Additional comments.
Geology: 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). The rocks are complexly folded and are cut by high-angle faults and by low-angle thrust faults. 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). Brooks (1902, p. 71) and Wright and Wright (1908, p. 139) describe the Jewel deposit only as a pyrite- and chalcopyrite-bearing quartz [fissure] vein 5-10 feet wide, that strikes N-S. Maas and others' (1995, p. 227) description of the mineral deposits in the Seal Cove area probably applies in general to the Jewel prospect. They report that chalcopyrite occurs as vein fillings, disseminations, and in fault breccias west and northwest of Seal Cove. The mineralized breccias have a siliceous matrix. Small quartz-barite veins with galena and sphalerite have been found west of Seal Cove, and on the northeast slopes of Punch Hill. In addition to the N-S fault that probably localizes the Jewel vein, the rocks near the prospect also are cut by a high-angle fault that strikes NW (Maas and others, 1995, fig. 58). Maas and others (1995, p. 227) report that copper mineralization on southern Gravina Island generally is associated with faulting. The deposits are mainly in meta-andesite (greenschist) and trondhjemite, but also in the overlying Triassic strata. The deposits are chiefly chalcopyrite- and pyrite-bearing quartz fissure veins, but the sulfide minerals also occur as disseminations in the metavolcanic rocks, in silicified zones in the trondhjemite, and as clasts or pods in silicified or carbonatized breccia. The character and setting of the deposits suggest that they mainly are polymetallic veins of Late Triassic or younger age.
Workings: The deposit was explored in the early 1900s by a small crosscut (Brooks, 1902, p. 71).
Age: Late Triassic or younger.
Alteration: Probably local silicification, carbonatization, pyritization, and introduction of hydrothermal hematite.

Commodities (Major) - Cu
Development Status: Undetermined.
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c)

Other Databases

Link to USGS - Alaska:	KC119

Other Regions, Features and Areas containing this locality

References