Damon Prospect, Ketchikan District, Ketchikan Gateway Borough, Alaska, USA

Location: The Damon prospect is at an elevation of about 700 feet in, or adjacent to, the valley of an unnamed creek that follows the northwest flank of Punch Hill. The site is on the boundary of sections 17 and 18, T. 77 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 111 in Elliott and others (1978). The location is accurate within 0.1 mile.
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). Wright and Wright (1908, p. 140) describes the Damon deposit only as a quartz vein heavily mineralized with pyrite. The vein is in banded chlorite country rock and strikes N20W. The Wrights' description suggests that the Damon and the Plutyas (KC117) prospects are on different parts of the same, NW-striking, vein. Their map (Wright and Wright, 1908, fig. 10), however, shows that the prospects align E-W, not NW-SE, which suggests instead that the veins are on separate, parallel, NW-striking faults. Maas and others' (1995, p. 227) description of the mineral deposits in the Seal Cove area probably applies in general to the Damon 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. The rocks at or near the Damon prospect are cut by a high-angle fault that strikes north-northeast (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.
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)

Mineral List

3 entries listed. 3 valid minerals.

References