THE ARSENIDES, SULFARSENIDES, AND TELLURIDES ASSOCIATED WITH THE RĂZOARE Fe-Mn DEPOSIT, PRELUCA MOUNTAINS, ROMANIA

n the Răzoare deposit the Fe:Mn ratio seems to characterize both the lower part, with Mn > Fe, and the upper part, with Mn < Fe, of the ore-bearing sequence. The lower part is dominated by an assemblage composed of tephroite, manganese humites, jacobsite, and rhodochrosite and the upper part is amphibole-dominated, typically containing clino-suenoite (formerly "manganocummingtonite"), clino-ferro-suenoite (formerly “manganogrünerite”), spessartine, magnetite, pyrrhotite, and pyrite. The middle part is dominated by manganoan fayalite, manganoan ferrosilite, and spessartine. The Răzoare tephroite - manganese humites - jacobsite assemblage has a highly restrictive mineralogical and chemical composition. The presence of Ni, Co, Sb, Mn, and Fe arsenides/antimonides and sulfarsenides/sulfantimonides is one of the striking features of this assemblage. The Ni-monoarsenides and Ni-monoantimonides, Ni-, Ni-Co, Co-, Fe and Mn diarsenides, triarsenides, and sulfarsenides were identified by light microscopy, X-ray, and SEM analyses. These minerals exhibit a wide range of isomorphic substitutions among Ni, Co, Mn, and Fe. Notably, the Mn content is higher than that of Fe, and some of these minerals contain chlorine. Their zoning reflects sudden changes in the composition of hydrothermal fluids and depict a polyphase evolution. Later minerals overgrow and replace earlier ones. The trend of mineralogical evolution was gradual, from initially Ni-Co monoarsenides with low As to higher content of As and Co (diarsenides and triarsenides) and finally, the enrichment in S allowed the deposition of the sulfoarsenides and sulfides. The Ni, Co, Mn, Fe arsenides/antimonides and sulfarsenides/sulfantimonides are genetically associated with the local hydrothermal activity that accompanied later lower-grade metamorphism. In the upper and middle parts of the deposit occur arsenides rich in Fe and sulfarsenides, bismuthinides, native Bi, and tellurides. Gold occurs associated with jacobsite in the Mn-rich assemblage, and with magnetite and pyrrhotite in Fe-rich assemblage. The mineralogical changes continued with the appearance of a large variety of manganese arsenates at the expense of arsenides.