Autori: Damian, Gh., Ciobanu, C.L., Cook, N.J. & Damian, F.
Editorial: Neues Jahrbuch für Mineralogie – Abhandlungen, 185/2, p.199-213, 2008.
Ag-Bi-sulphosalts are reported from Cu-rich ores within base metal mineralization situated beneath Au-ores below level 750-800 m in the Cremenea vein of the ªuior epithermal vein deposit, Baia Mare region, Romania. Microanalytical data show the presence of a homogeneous unnamed phase with empirical composition [(Ag0.81Cu0.12)0.93Pb0.91(Bi1.11Sb0.06)1.17(S2.98Se0.02)3], showing light Bi-enrichment relative to ideal AgPbBiS3. Intergrowths of galena and matildite with a characteristic basket-weave texture are interpreted as decomposition products of AgPbBiS3 and other phases along the PbS-AgBiS2 join. Parallel lamellar intergrowths have bulk compositions approximating Pb4Ag5.6Bi5.6S15.2. These compositions represent natural equivalents of phases synthesized in the PbS-AgBiS2 system. Although galena and matildite end-members and decomposition-products may be formed at still lower temperatures, interpretation of observed textures and microanalytical data, in combination with published phase diagrams, indicate formation of the intermediate phases at temperatures as low as 144 °C. Similarly, we interpret minimum temperatures of initial precipitation as melts (in the range 40-70 % AgBiS2) to be in the range 230–175 °C. The observed Bi excess may be a factor preventing decomposition of AgPbBiS3 into galena and matildite.
Cuvinte cheie: Şuior epithermal vein deposit, Baia Mare, Ag-Bi-sulphosalts, galena-matildite series, unnamed phases.