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Bernstein, L.R., 1985

Aspects of germanium mineralogy and geochemistry (renierite, arsenorenierite, germanite), Ruby Creek, Alaska, Apex Mine, Utah

Bibliographic Reference

Bernstein, L.R., 1985, Aspects of germanium mineralogy and geochemistry (renierite, arsenorenierite, germanite), Ruby Creek, Alaska, Apex Mine, Utah: Palo Alto, California, Stanford University, Ph.D. dissertation, 177 p., illust.


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 silicate melts, but chalcophile in sulfur-bearing hydrothermal solutions. The element tends to concentrate in sphalerite (up to 3,000 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 5,300 ppm) in oxidized germanium-bearing sulfide deposits, such as the recently reopened Apex Mine in Washington County, Utah. This mine is in a steeply dipping dolomitized, brecciated fault zone in 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 Cu10ZnGe2Fe4S16, with considerable solid solution existing to the new mineral arsenorenierite, Cu11GeAsFe4S16 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 tetragonal, pseudoisometric derivatives of the sphalerite structure type, with space group P42m 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, 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 µm across embedded in bornite and chalcocite in the core zone, with vanadian germanite always being rimmed by renierite.

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