Mineralization processes at the Daliangzi Zn-Pb deposit, Sichuan-Yunnan-Guizhou metallogenic province, SW China: Insights from sphalerite geochemistry and zoning textures

Abstract

The Daliangzi deposit is the second largest Mississippi Valley-type (MVT) Zn-Pb deposit in the Sichuan-Yunnan-Guizhou metallogenic province (SYG), SW China. However, detailed mineralization processes that occurred at different ore-forming stages and spatial locations are poorly understood. In this contribution, we report LA-ICP-MS trace element spot analysis and elemental mapping of sphalerite to reconstruct the mineralization processes. Three stages of sphalerite (SpI–SpIII) with different colours and crystallographic morphology have been identified in Daliangzi. Generally, the colloform SpI is enriched in Cd, Pb, Ag, Sb, As, and Tl. The crystalline SpII is relatively concentrated in Fe, Cu, Ga, Ge, and Mn. The colourless SpIII is depleted in most of the analysed trace elements. Trace elements were incorporated into sphalerite in various ways. For instance, Ge may be incorporated in the SpI by direct substitution of Ge4+ + □ ↔ 2Zn2+ but via coupled substitution of Ge4+ + 2Cu+↔ 3Zn2+ in the SpII and SpIII, and also can enter the SpIII as Ge-bearing mineral micro-inclusions. The temperature and sulfur fugacity estimations based on the sphalerite trace element contents show that the SpI was precipitated in a high-temperature condition with fluctuating sulfur fugacity. The SpII was crystallized during a dramatic decrease in temperature and sulfur fugacity, while the SpIII was formed in a low-temperature environment at the end of the mineralization. Combined with the growth histories of the typical zoning textures, we inferred that (i) the Cd-rich SpI with colloform texture precipitated from a rapid fluid mixing process triggered by the pulsed ingress of metal-rich fluid in open spaces with abundant organic matter; (ii) the SpII with high Ge content crystallized from a slow fluid mixing process associated with the temperature decrease and low organic matter abundance. Especially, the Ga-rich subtype with typical rhythmic bands formed from a self-organizing process that occurred in a closed environment under the stratigraphic unconformity; (iii) the pure SpIII probably formed by the replacement and recrystallization as late fluids flowed through the early sphalerite generations along fissures.