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).
Tennahedrite Thermochemistry and Metal Zoning
Provisional activity-composition relations are developed for tennahedrites approximating the chemical formula (Ag,Cu)10(Fe,Zn)2−(Sb,As)4S13. These relations are based on a “Temkin” type model for the configurational entropy combined with an expression for the vibrational Gibbs energy based on a second-degree Taylor series expansion in terms of the composition variables X2≡Zn/(Zn+Fe), X3≡As/(As+Sb), and X4≡Ag/(Ag+Cu) and an ordering variable s≡\( {\rm{(X}}_{{\rm{Ag}}}^{{\rm{TRG}}}\,{\rm{ - }}\,{\rm{3/2}}\,\,{\rm{X}}_{{\rm{Ag}}}^{{\rm{TET}}}{\rm{)}} \) which describes the distribution of Ag and Cu between trigonal-planar and tetrahedral metal sites. Calibration of the parameters in the resulting expression for the Gibbs energy is based on considerations of the Ag-Cu and Fe-Zn exchange reactions between tennahedrites and other crystalline phases. This calibration gives an expression for the distribution of Ag and Cu between trigonal-planar and tetrahedral metal sites that predicts changes from trigonal-planar to tetrahedral site preference for Ag with increasing Ag/(Ag+Cu) in accord with the local maxima in cell edge observed in natural (Ag,Cu)10(Fe,Zn)2Sb4S13 tennahedrites. The resulting activity-composition relations predict extensive miscibility gaps for (Ag,Cu)10Fe2(Sb,As)4S13 and (Ag,Cu)10Zn2(Sb,As)4S13 tennahedrites consistent with the chemical variations observed in nature. They support the hypothesis that crystal energetics and As-Sb fractionation between tennahedrite and hydrothermal fluids determine the distribution of silver in many zoned Pb-Zn-Cu-Ag sulfide ore deposits.
Die wisselwerking tussen ekonomiese en konstitusionele hervormings in Suid‐Afrika
Abstract This article deals with the interplay between economic and constitutional reforms in South Africa. Historical and contemporary forces which obtain in these spheres are taken into consideration after which a number of conclusions are drawn.