Copper-bearing minerals are not only numerous, but widely though irregularly distributed. More than this, copper is found associated with many different metals and under varied conditions. Nevertheless but few copper-bearing minerals are important in the ores of this metal, and the number of important producing districts is comparatively small. Most of the copper ores now worked are of low grade, but can be profitably treated because of the extent of the operations and possibility of concentration. Occasionally low-grade ores are found which are self-fluxing, as those of the Boundary District of western Canada. The introduction of pyritic smelting has permitted the profitable treatment of low-grade pyritic-copper ores, even if they carry no gold or silver.

Complex ores of copper, lead, and zinc sulfides are more costly to treat, but this expense may be more than made up for by their gold and silver contents. Sulfide ores of copper are almost invariably leached near the surface, except where the former surface material has been removed by rapid erosion or glaciation. Many copper ores, however, contain other metals that are not so easily leached as copper. As a result, many valuable deposits of copper sulfide ore have been discovered by downward exploitation of oxidized gold and silver ores. In regions where copper ores abound areas richly stained with iron are generally considered worthy of exploration in a search for copper. On the other hand, deposits of copper have been found below outcrops that show very little iron oxide. These outcrops, however, are generally silicified and kaolinized.

Most of the large copper sulfide deposits in the United States show three zones a leached zone near the surface, an enriched zone below the leached zone, and a zone of lower-grade primary ore below the enriched zone. In the unaltered primary portion of the ore body the copper compounds are mainly sulfides, but arsenides and antimonides are also known. In the leached goethite gossan zone the copper occurs as carbonates, sulfates, silicates, oxides, native, and more rarely as phosphates, arsenates, antimonates and vanadates.e highest safety procedures involving attentive gas monitoring, good ventilation and vigilant site management.

SOURCE: Nevada Outback Gems