Aspects of germanium mineralogy and geochemistry (renierite, arsenorenierite, germanite, Ruby Creek, Alaska, Apex Mine, Utah)
Stanford University, Palo Alto, CA
177 p., Illus.
Rasmuson Library: ALASKA QE375.5 A4 B47 1985a
Germanium is a geologically intriguing element, commonly substituting for silicon in amounts of a few parts per million in silicates, while being concentrated in such diverse environments as coal, iron meteorites, and sulfide ore deposits. It is generally lithophile in sili- cate melts, but chalcophile in sulfur-bearing hydrothermal solutions. The element tends to concentrate in sphalerite (up to 3000 ppm) in low- to moderate-sulfur environments, while forming its own sulfide minerals with copper or silver (or substituting for As or Sn in sulfo- salts) in high sulfur environments, generally in carbonate host rocks. Germanium can be highly concentrated in goethite, hematite, and limonite (up to 5300 ppm) in oxidized germanium-bearing sulfide deposits, such as the recently re-opened Apex Mine in Washington County, Utah. This mine is in a steeply dipping dolomitized, brecci- ated fault zone within the Pennsylvanian Callville Limestone. Copper ore consisting mainly of azurite, malachite, and conichalcite has been largely mined out, leaving large quantities of limonite, goethite, hematite, and plumbian jarosite, which contain the germanium and gallium now being mined. Similar high concentrations of germanium may occur in gossans and other oxidized zones of copper- and arsenic-rich sulfide deposits. The most abundant and widespread germanium mineral, renierite (often overlooked as "orange bornite"), is found to have the composition Cu(,10)ZnGe(,2)Fe(,4)S(,16), with consider- able solid solution existing to the new mineral arsenorenierite, Cu(,11)- GeAsFe(,4)S(,16) through the coupled substitution Zn(II) + Ge(IV) (<--->) Cu(I) + As(V). This is the first reported example of extensive coupled solid solution in sulfide minerals. The minerals are tetra- gonal, pseudoisometric derivatives of the sphalerite structure type, with space group P(')42m determined for renierite through powder X-ray diffraction and single crystal electron diffraction. Mossbauer spectroscopy and magnetic susceptibility data indicate that renierite (which has bulk magnetism) contains Fe(III) in three distinct sites, with slightly uncompensated antiferromagnetic ordering (weak ferri- magnetism). Type localities for arsenorenierite are Jamestown, Colorado and Ruby Creek, Alaska, where renierite also occurs. At Ruby Creek, the largest orebody contains early-formed fine-grained pyrite and later copper-bearing sulfide minerals concentrated in the matrix of a dolomite breccia body, which is enclosed by phyllite and marble. The ore is mineralogically zoned, with the most copper-rich sulfides occurring in the core of the orebody. The germanium minerals renierite, arsenorenierite, and vanadian germanite occur as grains up to 75 (mu)m across embedded in bornite and chalcocite in the core zone, with vanadian germanite always being rimmed by renierite.
Minerals Data and Information Rescue in Alaska (MDIRA)