The ore-forming process of the Maoping Pb-Zn deposit, northeastern Yunnan, China: Constraints from cathodoluminescence (CL) petrography of hydrothermal dolomite

摘要

Most MississippiValley Type (MVF) Pb-Zn deposits have a common host-rock lithofacies sequence known as the hydrothermal dolomite (HTD) facies; however, the spatial and temporal relationships between dolomitization and Pb-Zn mineralization remain unclear. In this paper, we report a detailed cathodoluminescence (CL) study on the HTD facies of the No. II orebody in the Maoping Pb-Zn deposit in northeastern Yunnan Province, southwestern China. The results indicate that the dolomite in the Carboniferous limestone is part of a spectrum of hydrothermal mineral deposits, and the diagenesis and mineralization processes, in which the acidity of fluids played an important role, can be divided into six steps. A dolomite prototype formed during the first and second steps. In the third step, acid fluids produced by sulfide precipitation interacted with the dolomite prototype, resulting in dissolution and alteration, thus forming cavities. The fluid that formed during the first three steps flowed along open tensional faults. Dolomitization in the first step covered most of the region of later mineralization and gradually extended toward the center of the orebody. In the fourth and fifth steps, vugs and fractures were the main pathways for fluids, with only a small volume of fluid in the fifth step. Dedolomitization occurred in the sixth step and vugs were filled mostly by calcite. However, the fact that voids are present in only a small number of vugs is indicative of fluid exhaustion. Dolomite with growth zoning is characteristic of precipitation by ore-forming fluids accompanied by pulsed filling. There is no significant correlation between vugs and the locus of mineralization. Rather, the vugs indicate that the ore-forming fluids had passed through them, and the locus of massive ore formation was the center of the migrating fluid body. The saddle dolomite was deposited during pauses in sulfide precipitation. Cathodoluminescent zonation of HFD can be used as an aid in understanding the ore-forming process and for mineral prospecting in the Maoping deposit and other MVF deposits. (C) 2015 Elsevier B.V. All rights reserved.