Palladian gold and palladium arsenious antimonides from Gongo Soco iron ore mine, Quadrilatero Ferrifero, Minas Gerais, Brazil

摘要

Gongo Soco was the first major underground gold mine in Brazil and produced 12.9 t of gold between 1826 and 1856. Palladium extracted from this gold was used to make the Wollaston Medal presented in 1845 by the Geological Society of London.~1 At the present time, some tens of kilograms of gold are recovered annually by gravity methods as a by-product of iron mining.The gold mineralization, known as jacutinga, occurs in crosscutting ore shoots rich in specular hematite within Palaeoproterozoic banded iron formation (itabirite) and associated high-grade hematite ore. The gold is characteristically Pd-rich, with up to 7 wt percent Pd. The palladium arsenious antimonide minerals mertieite-II (Pd_8(Sb,As)_3) and isomertieite (Pd_(11)Sb_2As_2) occur as 0.1-0.5 mm, sub- to anhedral crystals attached to the surface of, or as inclusions in, millimetre- to centimetre-size palladian gold.