Acta Musei Moraviae

Mineralogy of molybdenite-bearing quartz vein from Pohled quarry, Havlíčkův Brod Ore District (Czech Republic)

A mineralogical study of a poorly mineralized quartz vein with macroscopic molybdenite, cutting biotite paragneisses in the Pohled quarry (Moldanubicum), revealed a very rich mineral assemblage involving 24 species. In addition to quartz (belonging probably to several populations) and molybdenite, we proved the presence of pyrrhotite, pyrite, marcasite, chalcopyrite, cobaltite, arsenopyrite, galena, gustavite, native bismuth, joséite-A, Te-rich zipserite, anatase, brookite, uraninite, coffinite, hydroxylsynchysite-(Ce), baryte, muscovite, chamosite, clinochlore, fluorapatite, K-feldspar, and calcite. Apart from calcite, which fills youngest veinlets cutting the quartz vein, all remaining minerals form small disseminations in a quartz gangue; in some cases, these minerals probably represent components of older quartz-rich veinlets. The textural development and chemical compositions of minerals indicate that temperature decreased significantly during evolution of the vein – from 350–370 °C in early stage to up to 160 °C in the late stage. The Eh and pH of the fluid also experienced significant changes during evolution of the vein. The presence of hardly remobilizable elements in the given mineralization, including W, Sn, Zr, Nb, Th, Ti, Sc, Y, and REEs, suggests that specific complexing ligands (likely fluoride and/or sulphate anions) were present in the fluids. Broad similarities are found when texture and compositions of a number of silicate and sulphide minerals are compared with those from other types of mineralization in the quarry Pohled. This implies for cogenetic nature of various types of hydrothermal mineralizations and continuous evolution of the hydrothermal system, with variable local representation of individual mineralizing stages. The differences in chemical compositions of some minerals can be at least in some cases explained by topomineral influence of host rocks (the local source of Co and Ni in small bodies of amphibolites and serpentinites, source of W and Mo in granitoids).