Stromeyerite and mckinstryite from the Godejord polymetallic sulphide deposit,central Norweigan Caledonides

The Cu-Ag-S minerals, stromeyerite and mckinstryite, have been found for the first time in a stratabound polymetallic pyritic deposit in the Caledonides of central Norway. The surface specimens examined contained approximately 0.5% Ag, 1.8% Cu, 15.0% Zn and over 10 g/t Au and showed the mineral association pyrite, sphalerite, chalcopyrite, galena, tennantite, bornite, Cu-Ag sulphides, covelline, native Au, a Cu-Sn sulphide, and a new mineral of composition Ag₅CuTeS₂. The Cu-Ag sulphides appear to be replacing preexisting sulphides, with the exception of pyrite and sphalerite. The nature of this replacement is discussed. Analyses, by microprobe, of the Cu-Ag-S phases are reported and compared with published data. The stromeyerite shows an average composition Cu_1.01Ag S, the mckinstryite Cu_0.77Ag_1.19S. Values are reported of the reflectance at 542 nm for both minerals. The data indicate that stromeyerite is optically positive with Rg: 30.7%, Rm: 27.3%, Rp: 25.8% while mckinstryite is negative with Rg: 32.5%, Rm: 31.9%, Rp: 27.6%.