Supergene Minerals

Supergene Minerals

 

minerals that form in a supergene zone—that is, in the uppermost part of the earth’s crust—at low temperatures and pressures. They are characterized by hydration (the entry of molecular water or hydroxyl into the crystal lattice) and a high degree of oxidation of the elements (iron, manganese, sulfur, and others). The weathering of silicate rocks yields clay minerals, which are among the most widespread supergene minerals.

The supergene minerals include many compounds of several types: oxides, hydroxides, salts of oxy acids (carbonates, sulfates, nitrates, phosphates, and so on), and chlorides. Supergene minerals in oxidation zones of ore deposits —compounds of iron, copper, lead, and zinc (malachite, cerussite, anglesite, and so on)—are of great practical significance. The composition of supergene minerals from the same initial rock or ore depends on the climatic conditions under which the supergene processes take place. For example, the weathering of silicate rocks under mild climatic conditions leads to the formation of clay minerals, primarily of the hydromica type; weathering of the same rocks in the tropics yields kaolin clays and aluminum-oxide hydrates (bauxites).

References in periodicals archive ?
Goodchild, of the Scottish Geological Survey, found wulfenite there in 1875 but the locality only really became of interest to collectors in the 1950s following the reporting of a suite of rare supergene minerals including bayldonite, duftite, beudantite, carminite, lindgrenite and stolzite (the first authenticated British occurrence).
The north-south tungsten-bearing veins, a well-known source of fine scheelite, apatite, rare crystallized bismuth, arsenopyrite and other minerals, are cut by east-west lead veins; interaction between the two mineralizations has resulted in the formation of some interesting supergene minerals. Vanadinite specimens attributed (probably incorrectly) to the Carrock mine in the Kingsbury collection at the Natural History Museum, London, show small short-prismatic crystals, zoned pale brown and cream.
(2005) Supergene minerals from the oxidized zone of the Elura (Endeavor) lead-zinc-silver deposit.
Each is placed into at least one of five categories: rock-forming minerals (R); ore minerals (O); gangue minerals (G); alteration minerals (A); and supergene minerals (S).
Autunite has been reported as a very minor supergene mineral produced by weathering of alteration products of early-stage veins at the Globe Hill mine, and associated with other secondary uranium minerals in Tertiary volcanics (Thompson et al., 1985; Young and Mickle, 1976; Nelson-Moore et al., 1978).
Covellite has been reported as a supergene mineral formed by alteration of chalcopyrite and as distinct, minute grains associated with other copper sulfides (Lane, 1976; Thompson et al., 1985).
Goethite is a supergene mineral, formed by weathering of alteration products and vein minerals by oxidizing water at the Globe Hill mine (Thompson et al., 1985) and elsewhere.
Supergene minerals on the surface of the jasperoid breccia include a uniformly thin, colorless, botryoidal opal crust and a later coating (and local microcrystals) of pale yellow, impure carbonate-fluorapatite.
Goldquarryite is a latestage supergene mineral associated with opal, carbonate-fluorapatite and hewettite, on a host rock composed principally of brecciated and hydrothermally rounded jasperoid fragments which have been lightly cemented by late-stage silicification.
Metastibnite, schafarzikite, stibiconite and very minor senarmontite appear late in the paragenetic sequence, and may be either very late hypogene or supergene minerals.