Parageneses and Compositional Variations of Sb Oxyminerals from Långban-type Deposits in Värmland, Sweden

Dan Holtstam, Per Nysten and Kjell Gatedal
Department of Mineralogy, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
Institute of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden
Xenos Mineral, Rågvägen 7, SE-713 34 Nora, Sweden

Abstract: The Långban, Nordmark and Jakobsberg Mn-Fe deposits contain the only known occurrences of filipstadite and manganostibite (ideal formulae (Mn,Mg)2(Sb0.55+Fe0.53+)O4 and Mn72+SbAsO12 , respectively). Filipstadite from Nordmark is newly recognized, and occurs in assemblages with svabite-johnbaumite, calcite, tephroite-forsterite, phlogopite-kinoshitalite, tilasite, ±jacobsite, ±plumbian roméite, ± adelite, ± hedyphane. Manganostibite from Långban and Jakobsberg is reported for the first time, and the mineral is generally associated with katoptrite, tephroite, humite-group minerals, calcite, 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 have formed coevally with the principal ore and skam minerals at these deposits.

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 filipstadite 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 Fe2O3, 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+ + As5+ exchange mechanism, which improves the local charge-balance at tetrahedral structural sites dominated by As.

Keywords: filipstadite • manganostibite • jacobsite • katoptrite • antimony • Långban • Nordmark • Jakobsberg • Sweden

Mineralogical Magazine; June 1998 v. 62; no. 3; p. 395-407; DOI: 10.1180/002646198547666
© 1998, The Mineralogical Society
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