Bulletin Volume 906 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: ...in the product of the Quartette mine was about two-thirds that of copper, but the Duplex mine produced over three times as much lead as copper. Lead was more abundant than copper in the product of the Good Hope and Big Casino mines. To what extent these variations were due to differences in the processes of mining and milling used is not known. With the exception of an unknown proportion of the ore of the Big Casino mine, the entire production of the district has come from oxidized or weathered ores. Weathering and leaching of vein materials has extended to the greatest depths attained in mining in all the veins of the main part of the district (pl. 41). WTeathered vein material was found in the Quartette mine in the lowest levels, more than 800 feet vertically below the present surface and more than 600 feet below water level when the mine was first developed. No zone of secondary sulphides is known to have been found in any of the mines. Galena is the only primary sulphide remaining to any extent in the weathered veins, where it occurs as scattered lumps surrounded by its weathering products from a position within a few feet of the surface to the greatest depths of the ore shoots. Jaggar and Palache in a private report on the Quartette mine report traces of chalcopyrite and chalcocite in that mine. Unweathered vein material probably representative of that in many of the weathered veins was found on the dump at the Big Casino mine. It consists of a breccia of country rock cemented with quartz. Most of the quartz shows comb structure, and vugs are numerous. Sphalerite, galena, and chalcopyrite occur in the quartz, the first two in about equal proportions and the chalcopyrite mostly subordinate. Some of the country rock is silicified, contains scattered areas of ...