|Quadrangle map, 1:250,000-scale||KC|
|Quadrangle map, 1:63,360-scale||A-6|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The approximate location of the Grenadier prospect is at an elevation of about 200 feet at the south foot of Punch Hill. The prospect is in section 19, T. 77 S., R. 91 E., of the Copper River Meridian. It is about 0.7 mile from Dall Bay, and is in, or adjacent to, the valley of an unnamed, southeast-flowing creek that reaches Dall Bay at its north entrance. The site corresponds to loc. 121 in Elliott and others (1978). The location probably is accurate within about 0.2 mile.|
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. 73) describes the Grenadier prospect as a mineralized shear or breccia zone at the contact of pegmatite with schist and greenstone.Maas and others' (1995, p. 227) description of the mineral deposits in the area north of Dall Bay probably applies in general to the Grenadier deposit. They report that chalcopyrite is associated with sheared, silicified zones, chiefly in trondhjemite. Small barite veins are also found in the area. About 0.6 mile north of Dall Bay, chalcopyrite occurs as clasts or pods in a siderite-hematite matrix in altered trondhjemite. The Grenadier prospect is near the intersection of high-angle, NE- and NW-striking faults that juxtapose trondhjemite and metavolcanic rocks (Maas and others, 1995, fig. 58). The characteristics and setting of the deposits suggest that they mainly are polymetallic veins of Late Triassic or younger age.
|Geologic map unit||(-131.750677912558, 55.1726532099455)|
|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||Probably local silicification, carbonatization, pyritization, and introduction of hydrothermal hematite.|
|Indication of production||Undetermined|
Berg, H.C., 1982, The Alaska Mineral Resource Assessment Program; guide to information about the geology and mineral resources of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Circular 855, 24 p.
Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map I-1807, 27 p., scale 1:250,000.
Brooks, A.H., 1902, Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska: U.S. Geological Survey Professional Paper 1, 120 p.
Elliott, R.L., Berg, H.C., and Karl, S.M.,1978, Map and table describing metalliferous and selected non-metalliferous mineral deposits in the Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73B, 17 p., 1 sheet, scale 1:250,000.
|Reporters||H.C. Berg, USGS|
|Last report date||7/5/1999|