• journal_title：European Journal of Mineralogy
• Contributor：Matthias Krismer ; Peter Tropper
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2013/0025-2270
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：25
• issue：2
• firstpage：155
• section：Articles

Monomineralic Fe-Zn tetrahedrite-tennantite (fahlore) veins from the historic silver mines of Brixlegg in the Inn Valley (North Tyrol, Austria) show replacement textures containing a newly formed mineral assemblage (enargite/luzonite-famatinite + chalcostibite + pyrite + sphalerite ± stibnite), resulting from fahlore breakdown. In order to deduce the T-log f_S2 conditions of this reaction, appropriate mineral equilibria in the Cu-Fe-Sb-S and Cu-Zn-Sb-S systems were calculated using available thermochemical data.

The lack of thermochemical properties of famatinite (Cu₃SbS₄) made it necessary to perform a theoretical approximation, which yielded ΔG²⁹⁸_f of −402.25 kJ mol⁻¹. This estimate was combined with thermochemical data of all other phases from the available literature. In the T-logf_S2 space, phase equilibria indicate that rising f_S2 and/or dropping T lead to the breakdown of Fe-Zn tetrahedrite-tennantite. However, uncertainties stemming from the theoretically estimated thermochemical properties of famatinite place the calculated reactions near or above the S₂ condensation curve. Adjusting ΔG²⁹⁸_f of famatinite to 3–5 % more negative ΔG²⁹⁸_f values shifts the reactions towards reasonable conditions, and places the stability fields of the observed mineral assemblages within the T- logf_S2 window estimated by independent methods.

This study therefore indicates that combination of existing thermochemical data and detailed mineralogical and petrological investigations on natural enargite/luzonite-famatinite-bearing assemblages may lead to meaningful T-logf_S2 estimates. However, more experimental data on the thermochemical properties of famatinite are clearly needed.