Original paper

Textural and chemical features of sphalerite from the Palai-Islica deposit (SE Spain): implications for ore genesis and color

Carrillo-Rosúa, Javier; Morales-Ruano, Salvador; Hach-Alí, Purificación Fenoll

Abstract

Sphalerite in the Au-Cu volcanic-hosted, Palai-Islica deposit appears in three locations with differences in chemistry, mainly in the Fe content: a) included in pyrite (Fe: 0.49-5.47 at.%) within the quartz veins; b) disseminated or in crustiform bands, also within the quartz veins; and c) disseminated in hydrothermally altered volcanic rocks from the deepest part of the deposit (Fe: 0.28-1.12 at.% - the only one which is cathodoluminescent). Disseminated- or crustifom band-sphalerite is the most abundant type, with two varieties: "dark" (Fe: 3.16-8.66 at.%) and "light" (Fe: 0.08-2.52 at.%). The former is associated with zones rich in gold and other metals. The Fe content of sphalerite reflects an evolution in fs2 of the hydrothermal fluids. Fe-rich, "dark" sphalerite could be related to a mixing process triggering noble- and base metal sulphide precipitation. Different types of sphalerite have significant amounts of minor elements, such as Cu (up to 1.34 at.%), Sb (up to 0.67 at.%), Sn (up to 0.31 at.%), Ge (up to 0.29 at.%), Cd (up to 0.24 at.%), In (up to 0.18 at.%), Mn (up to 0.15 at.%) and Ga (up to 0.12 at.%), some of which are elements not traditionally recognized in sphalerite. Among them, Sb, Sn, Ga-Ge and In are proportional to Cu content, and the following charge balanced coupling substitutions have been demonstrated: Sb3+ + Cu+ + Cu2+ → 3Zn2+; Sn4+ + 2Cu+ → 3Zn2+; 2Ge2+ + Ga3+ + 2Cu2+ + Cu+ → 6Zn2+. The first two substitutions have been shown to correlate with red coloration in Fe-poor sphalerite. The latter substitution, could be related to incorporation into the hydrothermal system of Ga-Ge bearing fluids from the basin. The presence of cathodoluminescent sphalerite seems interesting since it could reflect distinctive trace element content, and could help to distinguish a different type of mineralization and fluid/metal source manifested in an unexplored part of the deposit.

Keywords

sphaleriteepithermal depositspainsbsncolorchalcopyrite "disease"cathodoluminescence