Per Nysten

Phosphate mineralogy of the Hålsjöberg and Hökensås kyanite deposits

Abstract Phosphates present at Halsjoberg, Varmland, and at Hokensas, Vastergotland, Sweden, represent at least two different stages of rock formation, as shown by their spatial relationships. At Halsjoberg a chemical separation into an early F-rich and a later Al-rich assemblage is indicated. The former comprise wagnerite, F-apatite and wyllieite and the latter is represented by lazulite-scorzalite, trolleite, augelite, gatumbaite, berlinite, burangaite, a ‘wicksite-like’ phase and ferro-wyllieite. At Hokensas Mn-apatite, lazulite-scorzalite, trolleite, augelite, woodhouseite, crandallite and florencite-Ce occur. For the ‘wicksite-like’ phase and wyllieite Mossbauer spectroscopy data are presented. At Halsjoberg, peak metamorphic conditions are estimated at P>2kb and 520°C<T<575°C. The intimate association of banded kyanite and early phosphates at Halsjoberg suggests a simultaneous formation due to a common mechanism. A genetic model, proposed by Wise & Loh is adopted, whereby kyanite and early phosphate...

The gold mineralization at Enåsen, central Sweden

Abstract The sillimanite bearing quartzite occurring at Enasen has been found to carry high amounts of gold together with Bi, Sb, Tc and Se. Cation distribution between Fe-Mg silicates in the regionally metamorphosed country rocks (gneisses) yields temperatures of 600–700°C and pressures of 4–6 kb with an estimated XH2O = 0.5. The temperatures indicated by the arsenopyrite geothermometer, 385–435°C, are assumed to show retrograde equilibrium conditions. The present study shows the gold to occur in two different modes, as elementary gold associated with sulphides and as elementary gold and gold-antimony tellurides together with complex graphic intergrowths of tellurides and sulphides. The presence of Te, Bi, Sb, Se and abundant rutile and topaz suggests that hydrothermal activities provided for the original deposition of ore minerals.

Beryllium phosphates from the Proterozoic granitic pegmatite at Norrö, southern Stockholm archipelago, Sweden

Abstract The early Proterozoic Svecofennian granitic pegmatites at Norro, and Rano, situated 40 km south of Stockholm, carry primary FeMn-phosphates (e.g. triphylite, triplite, wolfeite, sarcopside, graftonite) which have been partly altered to secondary phosphates of the Hagendorf type. The dykes, which both are emplaced in garnet-cordierite bearing veined gneisses, are moderately fractionated as shown by the presence of beryl, columbite, and ruby mica. Beryl from Norro shows progressive alteration into mixtures of hurlbutite/hydroxyl-herderite and hydroxyl-herderite/vayrynenite. Beryllonite was observed in one sample only, intergrown with hurlbutite. Hydroxyl-herderite/hurlbutite occurs partly rimming beryl at Rano. Microprobe analysis shows that beryllonite, hydroxyl-herderite and hurlbutite are close to stoichiometric and vayrynenite from Norro gave: (Mn0.80Fe0.16Mg0.04)0.96Be0.97(PO4)(OH)0.97. Cell dimensions of vayrynenite obtained from Si calibrated XRD are: a = 5. 410(1) A, b = 14.528(3) A, c = 4....

Mechanism of formation of wittichenite rims around native bismuth in chalcocite and bornite from Längban, Sweden

Abstract Veins of sulfide ore comprising chalcopyrite, bornite and chalcocite are confined to skarn and oxide ore in a dolomitic host rock at Langban, Sweden. “Reaction rims” of wittichenite around grains of native bismuth occur in bornite/chalcocite ore. This texture may be explained by localized, postmetamorphic, supergene enrichment of copper. Rapid formation of bornite and chalcocite through replacement of metamorphosed sulfides is indicated, while simultaneous formation of wittichenite took place at a slower rate.

A willemite-bearing paragenesis from Långban

Abstract A Zn-rich mineral association from Langban, consisting of willemite, franklinite, baryte, calcitc, and pyrobelonite is described. Chemical investigation shows the willemite to contain up to 5 wt-% MnO and the franklinite to be rich in manganese and ferric iron. Awaruite is found as inclusions in franklinite indicating a low sulphur fugacity.

Textural relations of betechtinite and cobalt pentlandite from Långban, Sweden

Abstract Betechtinite and cobalt pentlandite, two minerals new for Langban, were observed coexisting with chalcocite, bornite, sphalerite, galena, and magnetite in a serpentinized skarn. Magnetite occurs in two generations, as euhedral crystals and as fracture fillings. This feature plus the textural relations of sulfides suggest an oxidation at very low temperature. The presence of chalcocite, bornite and minor amounts of native bismuth, and the absence of pyrite indicate a low sulfur activity during crystallization of these sulfides.