Mineralogy and origin of the distal volcanosedimentary deposit at the Haellefors silver mine, Bergslagen, central Sweden
In the Zn-Pb-Ag deposit of Hiillefors silver mine, four types of sulfide ores are recognized: l) stratabound ore associated with manganiferous iton ores, 2) arsenopyritebearing stratiform (stratabound ?) ore, 3) galena-rich fissures, 4) galena-arsenopyrite veins. Type 3 and 4 are thought to originate by remobilization from types I and 2, respectively. The antipathetic behavior of arsenopyrite with magnetite in the stratabound ores probably reflects environmental conditions during the deposition and early diagenesis. Metamorphic, hydrothermal remobilization led to the formation of many Ag, Pb and Sb minerals. Results of electron-microprobe analyses indicate that the principal sources of silver are argentian galena, freibergite and pyrargyrite. The silver content of galena (up to 0.17 wt.9o) has a linear relation with its antimony content. Tetrahedritegroup minerals contain ll.3 to 31.6 fi.qo Ag. An extremely silver-rich freibergite (48,2 wt.9o Ag) exceeds the previously reported maximum (42,5 wt.Vo).
Solid solution in synthetic zinkenite, robinsonite and meneghinite in the system Cu 2 S-PbS-Sb 2 S 3
The extent of solid solution in zinkenite, robinsonite and meneghinite has been deternined from electron-microprobeestablished compositions of their synthetic analogs in pertinent assemblages in the course of a phase-equilibrium study of the system CurS-PbS-Sb2S3. All three solid-solution fields are elongate more or less parallel to the PbS-SbrS3 binary join, and are relatively broader at their PbS-rich ends. The positions of the PbS-rich ends are practically insensifive to variations in temperature. Robinsonite and meneghinilg are not stable at 300"C. Plots of molar propoftions of Sb2S3 yersus PbS suggest a cofirmon scheme of substitution, 3Pb2+=2Sb3+. In PbS-rich compositions of the solid solutions, the proportion of Cu is substantial, and Cu must be incorporated on the left-hand side of the substitution scheme. Natural compositions of meneghinite cluster at one point in the CurS-PbS-Sb2S3 temary system, but zinkenite and robinsonite have variable compositions. The most appropriate formula for zinkenite appears to be 6PbS.7SbrS3. Likewise,4PbS.3Sb2S3 is the preferred formula for robinsonite.
Strukturverfeinerung des Freibergits
Aus 3-dimensionalen Filmdaten wurde die Kristallstruktur eines Freibergits mit 13 Gew% Ag fur 130F hkl aufR=0,035 verfeinert. Es wird abgeleitet, das das Silber von den beiden zur Verfugung stehenden Punktlagen die 3-koordinierte bevorzugt; somit ergibt sich die kristallchemische Formel (Cu3,8Ag2,2)[3S]Cu6[4S][SbS3]4Sk. Eine Aufspaltung der partiell von Ag besetzten Punktlage ist wahrscheinlich.