Mineralogy of the Near-Surface Expression of Au-As-Cu Mineralization in an Arid Environment

R. Bogoch, M. Shirav, A. Gilat and L. Halicz
Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem 95501, Israel

Abstract: In the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.

Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.

The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.

Keywords: secondary Au-As-Cu minerals • conichalcite • gold • arid environment

Mineralogical Magazine; June 1994 v. 58; no. 391; p. 315-323; DOI: 10.1180/minmag.1994.058.391.14
© 1994, The Mineralogical Society
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