lead–zinc deposits

lead–zinc deposits Lead and zinc are commonly found together in many types of ore deposit. They may constitute the metals of primary interest or may be produced as by-products of the mining of other metals, in particular, copper, silver, and gold. The sulphides of lead and zinc (galena and sphalerite) are important ore minerals that are found in volcanogenic massive sulphide deposits, where they occur with those of copper. Galena and sphalerite are also commonly found in skarn (contact-metamorphic) and epithermal (shallow vein) deposits, where they are co-deposited with ore minerals of copper, gold, silver, tungsten, and tin. Although these types of deposit contain high concentrations of the two metals, there are types of deposit that are mined almost exclusively for their lead and zinc contents. Carbonate-hosted lead–zinc deposits occur in ancient reef deposits that have undergone partial dissolution by hydrothermal solutions. The open spaces thus created become filled with high concentrations of lead and zinc sulphides, together with minor amounts of copper and cadmium. The metals are transported by heated aqueous fluids derived from adjacent sedimentary deposits, which migrate into the porous reef horizons. The name ‘Mississippi-Valley type’ has been applied to these deposits because of important occurrences in that area of the United States. Sedimentary exhalative deposits also host lead and zinc as their primary ore metals. These deposits are comprised of fine layers of galena and sphalerite, together with pyrite, pyrrhotite, barite, and minor chalcopyrite interbedded with deep-water sedimentary rocks. Important examples are found at Mt Isa and McArthur River, Australia, and Sullivan, Canada.

Bruce W. Mountain