Page 55 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

54 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
small size of the individual ore bodies in this region and their scattered distribution within the veins and beds, it appears doubtful if an operating company of large capitalization, bur- dened as it would be with overhead and administrative expense and probably oversupplied with plant and equipment for the con- ditions locally existing, could make an ultimate success of an ex- tensive search for deeper lying ore bodies. On the other hand, prospectors, small groups of individuals, or organized companies with modest capitalization and minimum overhead expense, who confine their efforts largely to surface outcrops, the extension of known ore in place, or to the handling of stope fill and low grade dump ore, have a fair chance for profitable operations in many of these old camps.
Except in the blanket type of replacement deposits in lime- stone, there has been little mineralization of the wall rock adja- cent to veins in the region. At water level in places the second- ary sulfides extend beyond the strict limits of the opening, but this has been of minor economic importance. In the primary zone below water level, it is believed that with added depth the fissures will tend to tighten and the quantity of ore will thus decrease with each unit of depth gained, although minable ore may persist in the vein for a considerable distance below the zone of enrichment. Probably there will be a shifting of the pro- portions of the different metals in the veins as depth increases, copper becoming more important compared to gold and silver.
In general the best ores produced in the county have been from the oxidized zones of the silver-lead and the gold deposits, where silver chloride, native silver, lead carbonate and sulfide, and native gold have predominated. Much oxidized manganese and manganiferous iron ore has also come from this horizon.- At and near the ground-water level secondary sulfide deposits of copper have been characteristic, and deposits of zinc carbonate have been found. These secondary sulfide deposits include important quantities of lead sulfide, native and ruby silver and argentite. Below water level occur the primary ores of the dif- ferent metals. So far as known, all of these have been of much lower grade than were the ores from the same shoots at higher levels, although in places, if a sufficient tonnage could be devel- oped, the grade is such that these ores could be concentrated profitably. The water level is from 50 to 400 feet below the sur- face, and primary sulfides may begin to make their appearance anywhere from the surface down, due to incomplete oxidation and secondary enrichment.
A careful survey of current costs in the mining districts of Sierra County was made by the writer while in the field. Later it was decided to increase the scope of the survey, making the figures applicable to operations throughout the State, and to compile them in greater detail for Bulletin 7 of the State Bureau of Mines and Mineral Resources, "The Metal Resources of New