Mineralogy and geochemistry of Cu-Ni±Co±Ag±Bi polymetallic ores from the Hintermühlergang vein in the Chełmiec deposit, Sudetes Mountains, Poland

Chełmiec is a hydrothermal vein-type carbonate-sulphide deposit in the Kaczawa Mountains, where polymetallic Cu-Ni±Co±Ag±Bi mineralization occurs. Samples, collected from an old dump of the Hintermühlergang vein, were studied by reflected light microscopy and electron microprobe. Two mineral parageneses, Ni-Co±Bi and Cu-Zn-Pb±Sb±Ag, associated with two stages of precipitation, were discovered in samples from the Chełmiec deposit. The first stage is associated with quartz, and is represented by pyrite, arsenopyrite, gersdorffite, cobaltite, bismuth minerals (native Bi, bismuthinite, and matildite), pyrrhotite, marcasite and chalcopyrite. The second stage associated with siderite and quartz is represented by sulphides (sphalerite, chalcopyrite, galena, pyrite), tetrahedrite group minerals [tetrahedrite-(Fe), tetrahedrite-(Zn), tennantite-(Zn), and argentotetrahedrite-(Fe)], gersdorffite and bournonite. Two generations of sulpharsenides were discovered in the samples studied. The first is represented by massive gersdorffite-cobaltite aggregates, the second generation occurs as tiny zoned gersdorffite crystals. Sulpharsenides are characterized locally by presence of high amounts of As (up to 1.55 apfu). Silver in the Chełmiec ores is hosted mainly in tetrahedrite group minerals [from 0.07 to 2.07 apfu in tetrahedrite – (Zn) and -(Fe), and from 4.37 to 4.90 apfu in argentotetrahedrite-(Fe)], less in matildite. In the Sudetes, the presence of massive sulpharsenides is rare, whereas freibergite is much more common.