Sulphide and sulphosalt mineralogy and paragenesis from the Sierra Almagrera veins, Betic Cordillera (SE Spain)

Abstract

The Sierra Almagrera vein-type mineralization contains base metal sulphides and Pb-Sb- Cu-Ag sulphosalts. The sulphides possess significant proportions of Ag, Sb (galena), Fe (sphalerite) and Sb, Zn (chalcopyrite). Ore microscopy and electron microprobe have revealed a mineralogical and textural variation and confirmed the presence of bournonite, boulangerite and anomalous tetrahedrite. The average sulphosalt formulas are bournonite Cu_0.98 Pb_{0. 96} Sb_0.98 S_3.04, boulangerite Pb_4.8Sb_3.8S_11.34 and anomalous tetrahedrite Ag_0.6Cu_9.7 Zn_3.6 Fe_{0. 44} Sb_3.47 S_13- The sequence of mineral deposition indicates the existance of four mineralizing stages and one supergene alteration: 1) Fe-(As); 2) Zn-Cu-Fe; 3) Pb-Sb-Cu-Ag; 4) Cu-Zn-Fe, and 5) carbonates, sulphates and supergene oxides. In broad terms, it is possible to establish the following conclusions: a) there exist a mineralogical and textural variation with depth, the Pb-Sb-Cu-Ag stage reaching the maximum development; b) a temperature decrease during the formation of sph. 1, linked to the progressive increase in Fe-content of the sphalerite has been detected; c) the compositional homogeneity of the bournonite (and the fair lack of As in the tetrahedrite) could indicate the existance of a possible tendancy to individually crystallise the Sb and As sulphosalts, according to the trend Bi → Sb → As.