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.). |
