Genesis of the Sinongduo Carbonate-hosted Pb-Zn-Ag Deposit in the Central Lhasa Terrane,Tibet

The Sinongduo mining region includes two types of mineralizations:the epithermal and the carbonate-hosted PbZn-Ag deposits.Despite being studied for many years,the ore formation process and genesis of the carbonate-hosted Pb-Zn-Ag deposits remain poorly understood.The Pb-Zn-Ag ore bodies occur as veins and are hosted by limestone and dolostone of the Permian Xiala Formation.Three sulfide mineralization substages have been identified at the Sinongduo carbonatehosted deposit.Indium coupled with Cu,Co and Sn was incorporated into sphalerite as substitutions:2Zn^(2+)?Cu^(+)+In^(3+),(3n/2+1)Zn^(2+)?Co^(2+)+n In^(3+)or(2n+1)Zn^(2+)?Co^(2+)+n(Cu^(+)+In^(3+))(n>1)and 4Zn^(2+)?Sn2++2In^(3+).Sphalerite and pyrite in the mineralization stage displayδ^(34)S values in a narrow range of+5.7‰to+11.3‰,which are similar to those of Palaeocene igneous rocks,indicative of a magmatic source of sulfur.We present systematic carbon-hydrogen-oxygen isotope results that further support a magmatic source for the ore-forming fluids that were influenced by meteoric water.Furthermore,the Pb isotope compositions of sulfide minerals in the Sinongduo carbonate-hosted deposit overlap with the values of coeval Linzizong volcanic rocks and are similar to those of Indian Ocean sediments,indicating upper crustal sources of metals.We conclude that the Sinongduo carbonate-hosted Pb-Zn-Ag deposit is a medium-to low-temperature magmatic-hydrothermal deposit related to Linzizong magmatism.

An experimental study on metal precipitation driven by fluid mixing: implications for genesis of carbonate-hosted lead–zinc ore deposits

A type of carbonate-hosted lead–zinc(Pb–Zn)ore deposits, known as Mississippi Valley Type(MVT)deposits, constitutes an important category of lead–zinc ore deposits. Previous studies proposed a fluid-mixing model to account for metal precipitation mechanism of the MVT ore deposits, in which fluids with metal-chloride complexes happen to mix with fluids with reduced sulfur, producing metal sulfide deposition. In this hypothesis, however, the detailed chemical kinetic process of mixing reactions, and especially the controlling factors on the metal precipitation are not yet clearly stated. In this paper, a series of mixing experiments under ambient temperature and pressure conditions were conducted to simulate the fluid mixing process, by titrating the metal-chloride solutions, doping withor without dolomite, and using NaHS solution. Experimental results, combined with the thermodynamic calculations, suggest that H_2S, rather than HS^-or S^(2-),dominated the reactions of Pb and/or Zn precipitation during the fluid mixing process, in which metal precipitation was influenced by the stability of metal complexes and the pH. Given the constant concentrations of metal and total S in fluids, the pH was a primary factor controlling the Pb and/or Zn metal precipitation. This is because neutralizing or neutralized processes for the ore-forming fluids can cause instabilities of Pb and/or Zn chloride complexes and re-distribution of sulfur species, and thus can facilitate the hydrolysis of Pb and Zn ions and precipitation of sulfides. Therefore, a weakly acidic to neutral fluid environment is most favorable for the precipitation of Pb and Zn sulfides associated with the carbonate-hosted Pb–Zn deposits.

Research Progress of the Mineralization of Carbonate-Hosted Pb-Zn Deposits in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province, Southwest China

The Sichuan-Yunnan-Guizhou （SYG） Pb-Zn metallogenic province in the western Yangtze Block, is a key component of the low-temperature metallogenic domain in South China. In this area, more than 400 Pb-Zn deposits have been discovered, and the total proven reserves are up to 260 million tons with lead and zinc grade reaching 10%, even up to 30%.