Technical paper . country rock contains a considerableproportion of clay or shale. In regard to the vertical distribution of the ores mined, above andnear the level of the ground waters are found galena and the oxidizedores of zinc and other minerals; below that level the sulphides of zincand iron become dominant and little galena is present. The sul-phide of iron is usually associated in such quantities with zinc blendethat even a fairly clean blende concentrate is obtained with diffi-culty through wet methods of milling, the specific gravity of the twominerals being so near alike. Marcasite,
Technical paper . country rock contains a considerableproportion of clay or shale. In regard to the vertical distribution of the ores mined, above andnear the level of the ground waters are found galena and the oxidizedores of zinc and other minerals; below that level the sulphides of zincand iron become dominant and little galena is present. The sul-phide of iron is usually associated in such quantities with zinc blendethat even a fairly clean blende concentrate is obtained with diffi-culty through wet methods of milling, the specific gravity of the twominerals being so near alike. Marcasite, with minor proportions ofblende, is so abundant in places that it is being mined and sent toplants that manufacture sulphuric acid. MINERAL CONSTITUENTS. The most important minerals of commercial value occurring in theWisconsin district are galena, sphalerite, smithsonite, and , as in other districts, these minerals are known by local terms, a From Grant, U. S., and Burchard, E. F., op. cit., p. MIXING AXD MILLING OF LEAD AND ZINC ORES. 13 such as lead for galena, jack for sphalerite, carbonate orefor smithsonite, and sulphur for the iron sulphides—marcasiteand pyrite. Closely associated with these ores, including the gangueminerals, are chalcopyrite, calcite, dolomite, and barite, and in placessmall quantities of other minerals. The ores are relatively simple in composition, practically nonebeing complex. The country rock is mainly the dolomite of theGalena formation, which has a gray to blue color, turning brown whenoxidized. The other constituents of the country rock are shale, oilrock, glass rock, and some flint in the upper parts of the ore-bearing formation. PROSPECTING METHODS. Prospecting is commonly done with a churn drill, the ore bodiesnot lying deep enough to hinder its being used to good holes are drilled, and from the cuttings a fairly representa-tive sample of the rock and ore penetrated can be obtained. Theholes are space
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectminesandmineralresou
