Geologic descriptionA quartz vein crops out on the beach at the southeast end of the south arm of Port San Antonio (Roehm (1936 [PE 119-3]). It can be traced S65E for about 4,000 feet and averages about 2 to 3 feet thick. The veins cuts both the Cretaceous granite south of Port San Antonio and the Silurian or Ordovician argillite and graywacke of the Descon Formation peripheral to the granite (Eberlein and others, 1983; Brew, 1996). The most intense mineralization is 200 to 300 feet from the granite contact. The vein contains pyrite, sphalerite, and galena, with minor chalcopyrite and bornite. Several channel samples contained a trace of gold and up to 2 ounces of silver per ton. In 1916, the prospector who discovered the vein said that it averaged about $3 per ton in gold (at $20.67 per ounce?) and 4 ounces of silver per ton over a distance of 3,000 feet. The vein has been prospected by several trenches and open cuts. This may be the prospect described by Wright and Wright (1908) as quartz veinlets with galena, sphalerite, and pyrite that cut argillite, but they locate it on the north side of Port San Antonio. |
