PARAGENESES AND COMPOSITIONAL VARIATIONS OF SB OXYMINERALS FROM LANGBAN-TYPE DEPOSITS IN VARMLAND, SWEDEN

The L (a) over circle ngban, Nordmark and Jakobsberg Mn-Fe deposits co ntain the only known occurrences of filipstadite and manganostibite (i deal formulae (Mn, Mg)(2)(Sb0.55+Fe0.53+)O-4 and Mn72+SbAsO12, respect ively). Filipstadite from Nordmark is newly recognized, and occurs in assemblages with svabite-johnbaumite, calcite, tephroite-forsterite, p hlogopite-kinoshitalite, tilasite, +/-jacobsite, +/-plumbian romeite, +/-adelite, +/-hedyphane. Manganostibite from L (a) over circle ngban and Jakobsberg is reported for the first time, and the mineral is gene rally associated with katoptrite, tephroite, humite-group minerals, ca lcite, svabite, allactite, manganosite, hausmannite, jacobsite, spinel s.s., etc. Whereas filipstadite is clearly secondary relative to the major part of the matrix components, manganostibite is believed to hav e formed coevally with the principal ore and skarn minerals at these d eposits. The previously known compositional ranges are extended. Based on electron-microprobe analyses, Nordmark filipstadite contains 4.1-7 .3 MgO, 0.0-0.5 Al2O3, 30.5-45.3 MnO, 17.0-40.1 Fe2O3, 0.2-0.9 ZnO, 19 .9-29.9 Sb2O5 (all in wt.%), corresponding to 58-100 mol.% of a pure f ilipstadite component. Associated jacobsites show Sb2O5 contents of up to c. 5 wt.%. Manganostibites (all three deposits considered) contain 1.0-2.9 MgO, 2.8-3.8 SiO2, 57.4-60.3 MnO, 0.2-3.5 Mn2O3, 0.3-2.0 Fe2O 3, 0.0-2.4 ZnO, 21.5-23.0 Sb2O5, 7.7-10.0 As2O5 (all in wt.%). Si and trivalent cations are incorporated via a (Mn3+,Fe3+) + Si4+ = Mn2+ + A s5+ exchange mechanism, which improves the local charge-balance at tet rahedral structural sites dominated by As.