Mary T.

Prospect, Undetermined

Commodities and mineralogy

Main commodities Au
Other commodities Cu
Ore minerals chalcopyrite; gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale C-6
Latitude 55.599
Longitude -131.971
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Mary T. prospect is at an elevation of about 250 feet, 0.3 mile northeast of the head of the falls at the mouth of Falls Creek. The site is in section 30, T. 72 S., R. 88 E., of the Copper River Meridian. It corresponds to loc. 257 in Maas and others (1995, fig. 46), and to loc. 36 in Elliott and others (1978). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rocks near this site include gray and green phyllite and semischist derived from intertonguing flysch and andesitic and basaltic volcanic rocks (Berg and others, 1988, p. 17-20); and gray felsic schist possibly derived from silicic tuff (Maas and others, 1995, p. 183 and fig. 46). Near Smugglers Cove, the bedded rocks are intruded by diorite that may be transitional to the andesitic and basaltic volcanic rocks. The bedded and intrusive rocks were regionally metamorphosed to greenschist grade in Late Cretaceous time (Brew, 1996, p. 27). Their premetamorphic age is uncertain. Berg and others (1988, p. 17) note that the intertonguing flysch and volcanic rocks closely resemble Upper Jurassic to mid-Cretaceous marine strata nearby on Gravina Island.
The deposit consists of sericite or chlorite schist containing quartz blebs and abundant disseminated cubes of pyrite, minor chalcopyrite, and small amounts of gold (Wright and Wright, 1908, p. 157). The chalcopyrite locally is oxidized to malachite and azurite. Maas and others (1995, p. 184 and tables 45 and 46) suggest that the Mary T. prospect may be part of a belt of exhalative volcanogenic gold deposits (KC035) that extends along the northeast shore of Smugglers Cove and also includes the U.S. (KC037) and Blue Bucket (KC039) deposits. The average metal contents of their samples of the Mary T. deposit are: 0.95 ppm Au, 2.89 ppm Ag, 2698 ppm Cu, 7.0 ppm Pb, and 117 ppm Zn. Workings dating to the early 1900s include a flooded, 9-foot-deep shaft, a trench, and two pits. The owners at that time reported assays of up to 15% Cu and $11 in gold/ton (Au at $20.67/oz.).
Geologic map unit (-131.972682866113, 55.5986373512895)
Mineral deposit model Distal disseminated Ag-Au? (Bliss, 1992; model 19c)
Mineral deposit model number 19c?
Alteration of deposit The hostrocks are pyritized, and the chalcopyrite locally is oxidized to malachite and azurite.

Production and reserves

Workings or exploration Workings dating to the early 1900s include a flooded, 9-foot-deep shaft, a trench, and two pits. The owners at that time reported assays of up to 15% Cu and $11 in gold/ton (Au at $20.67/oz.). The average metal contents of U.S. Bureau of Mines (Maas, 1995) samples of the Mary T. deposit are: 0.95 ppm Au, 2.89 ppm Ag, 2698 ppm Cu, 7.0 ppm Pb, and 117 ppm Zn.
Indication of production None

References