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).
Fe-Zn exchange reaction between tetrahedrite and sphalerite in natural environments
Microprobe and fluid inclusion analyses of hydrothermal ore deposits containing the subassemblage sphalerite+ tetrahedrite-tennantite ∼[(Cu, Ag)10(Fe, Zn)2(As,Sb)4S13] reveal that the Gibbs energies of the reciprocal reaction Cu10Zn2Sb4S13 + Cu10Fe2As4S13 = Cu10Fe2Sb4S13 + Cu10Zn2As4S13 and the Fe-Zn exchange reaction 1/2Cu10Fe2Sb4S13 + ZnS = 1/2Cu10Zn2Sb4S13 + FeS are within the uncertainties of the values established by Sack and Loucks (1985) and Raabe and Sack (1984), 2.59±0.14 and 2.07±0.07 kcal/gfw. However, this study suggests that the Fe-Zn exchange reaction between sphalerite and Sb and Ag-rich tetrahedrites does not obey the simple systematics suggested by Sack and Loucks (1985) wherein tetrahedrite is assumed to behave as an “ideal” reciprocal solution. Instead these studies show that the configurational Gibbs energy of this exchange reaction,RTln[(XFe/XZn)TET(XZnS/XFeS)SPH], corrected for sphalerite nonideality exhibits both a local maximum and minimum as a function of Ag/(Cu+Ag) ratio at a givenXFeSSPHand temperature. The local maximum forXFeSSPH∼0.10 corresponds to the position of the cell edge maximum established for natural tetrahedrites by Riley (1974), Ag/(Ag+Cu)∼0.4. These studies and the results of structural refinements of Ag-bearing tetrahedrites suggest that in low silver tetrahedrites Ag is preferentially incorporated in trigonal-planar sites but that in tetrahedrites with intermediate and greater Ag/(Ag+Cu) ratio, Ag is preferentially incorporated in tetrahedral sites. A nonconvergent site ordering model for tetrahedrite is developed to quantify and extrapolate these predictions.
Do leptites represent precambrian island arc rocks
Abstract Comparison of 172 analyses of Recent to Mesozoic volcanic rocks from New Zealand and 122 analyses of Svecofennian volcanic rocks (leptites) from the Swedish Precambrian (1,700–2,200 my), reveal strong similarities between these rock types. This suggests that the leptites form an island are suite of calc-alkaline rocks, ranging from basalt to rhyolite in composition and that they represent a well-defined rock type containing little or no sedimentary material. Probably they originated at a Precambrian subduction zone.