Genesis of the vein-type Gaocheng Ag-Pb-Zn deposit in the western Guangdong Province of China and its implication for regional exploration

Abstract

Abstract The Daganshan region in the western part of the Guangdong Province is an important mineralised area containing W, Sn, and Ag–Pb–Zn occurrences. Although vein-type Ag-Pb-Zn deposits are usually spatially related to W-Sn and Sn deposits, the genetic links between them are still not understood. The newly discovered Gaocheng deposit is a typical vein-type Ag-Pb-Zn deposit in this region, which is hosted predominantly by a Silurian biotite monzogranite and to a lesser extent by a Late Cretaceous quartz porphyry . Here, we present new Rb-Sr dating of sphalerite, fluid inclusion microthermometry, and H-O-S isotopic geochemistry of the deposit, and whole-rock major and trace elements geochemistry of the mineralised quartz porphyry. The aim is to better understand the genesis of the Ag-Pb-Zn mineralisation and its link with W, and Sn deposits in the region. The sphalerite Rb-Sr age is 90 ± 6 Ma, indicating that mineralisation is Late Cretaceous similar to that of the quartz porphyry. Three vein sets have been recognised around the quartz porphyry comprising early arsenopyrite–pyrite–quartz veins crossed by sulphides–quartz–Ag veins and late (non-mineralised) calcite–quartz–fluorite veins. The fluid inclusions have homogenisation temperatures of 360–300 °C with salinities of 8.2–6.4% NaCl equivalent for the first vein set, 320–240 °C with salinities of 6.5–4% NaCl equivalent for the second vein set, and 220–160 °C with a corresponding salinity of 4.2–3.4% NaCl equivalent for the late vein set. This indicates a gradual decrease of temperature and salinity of the mineralising fluids. The composition of the vapour accompanying the saline fluid in the inclusions is H 2O with minor amounts of CO2 and CH4, which indicates that the mineralising fluid included H2O–NaCl(–CO2–CH4). The fluid inclusions in the early vein set assays +6.52 - +6.13‰ δ18OH2O and –91 - –85‰ δDH2O, and the fluid inclusions in the mineralised second vein set contains +5.72 to +2.41‰, δ18OH2O and −72 to −42‰ δDH2O. These data indicate that the mineralised fluids represented by the stage I and II vein sets included magmatic fluids that were gradually contaminated by meteoric fluids. The magmatic source of the mineralising fluid is also indicated by the narrow range of δ34 S values between −2.2 and −2.4‰. The whole-rock analyses show that the Late Cretaceous quartz porphyry is a highly fractional peraluminous granite , similar to the W- and Sn-related granites in the Daganshan region. The Gaocheng vein-type Ag-Pb-Zn deposit is therefore genetically related to the Late Cretaceous quartz porphyry and shares similar geochemical characteristics at Sn-bearing granites in the Daganshan region and is also prospective for Sn mineralisation.