After a galena ore is mined it is customarily crushed and the galena removed from the gangue by a gravity-separation process which takes advantage of the difference in “heaviness” (specific gravity) between galena (7.5) and limestone (calcite) or chert (2.7-2.6), or by a froth flotation process in which the galena is preferentially wetted and carried off by an oily froth or foam. The galena concentrate is roasted to burn out the sulphur, reduced by carbon, and smelted to metallic lead. The origin of some Missouri lead deposits is debatable, but the writer believes the most reasonable explanation to be that warm, chemically active waters arose from an igneous body below and carried to the place of deposition the lead which they held in solution.
Missouri is one of the leading producers of lead in the world from its Flat River, Fredericktown, Joplin, and central Missouri districts, from which in 1941 lead concentrates having a value of over $15,000,000 were produced.
Sphalerite (locally called Jack, Rosin Jack, Black Jack, Ruby Jack, Zinc, Rosin Spar) is a tan-brown, resinous, brown or brownish black mineral having a very high luster on its broken (cleavage) surfaces. Much of it so strongly resembles lump rosin that the term “Rosin Jack” is truly descriptive. Less commonly, a ruby red variety occurs as crystals perched on other sphalerite or on waste rock. Sphalerite is readily scratched with steel. Its chemical composition is zinc sulphide, ZnS—zinc 67 per cent, sulphur 33 per cent—and it is an important ore of zinc.
Sphalerite occurs abundantly in the mining district of southwest Missouri, but small, non-commercial amounts of it have been found through an area extending even north of the Missouri River. At the mines, after the ore and rock are taken out, they are crushed and separated, the ore going to the smelter and the rock to tailings piles. Under the old milling process employed in south_western_ Missouri, thousands of tons of coarse tailings, largely chert, were poured onto huge “chat” piles, many of which remain as a low-priced by-product for some one to put to use. This chat differs mineralogically from the south_eastern_ Missouri chat, which is largely dolomite.