New occurrences of willemite-franklinite assemblages in Bergslagen, central Sweden

摘要

Two new occurrences of willemite coexisting with franklinite are described from the Bergslagen region. At the Garpenberg Norra Pb-Zn mine (Hedemora, Dalarna) willemite and franklinite occur in silicate skarn rocks in association with clino-amphibole, phlogopite, quartz, galena, sphalerite, fluorite and barite. At the Hasselhojden metacarbonate quarry (Hallefors, Orebro) the two minerals appear with mainly sphalerite in talc-bearing dolomite marble. Based on electron-microprobe (EMP) analyses, willemite from Garpenberg Norra contains 0.4-2.1 MnO, 0.2-1.5 MgO and 0.1-1.2 Fe_2O_3, whereas at Hasselhojden the mineral has 0.4 Fe_2O_3 as the main impurity (all in wt.%) Mossbauer spectroscopy and EMP data show that Fe is dominantly trivalent and to some extent substitutes for Si in these willemite samples. Franklinite from Hasselhojden contains up to 7.6 wt.% V_2O_5, incorporated according to the substitution 2 (Zn, Fe)~(2+) + V~(5+) = 3 Fe~(3+).