Ore genesis of the unusual Talate Pb-Zn(-Fe) skarn-type deposit, Altay, NW China: constraints from geology, geochemistry and geochronology

The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen, NW China. Lenticular ore bodies occur in the Kangbutiebao Formation, a package of intermediate-felsic marine volcanic rocks and terrigenous clastic sedimentary-carbonate rocks. Skarn alteration (mainly garnet) is present in both ore and wall rocks, especially the carbonate rocks. The mineral assemblages and cross-cutting relationships of veins allow the alteration and mineralization process to be divided into four stages. From early to late, these are the early skarn (E-skarn), the late skarn with quartz-magnetite veins (QM), the quartz-sulphide (QS) and the quartz-carbonate (QC) assemblages. Quartz crystals are important gangue minerals in the latter three stages, in which four distinct compositions of fluid inclusions are identified based on petrography, microthermometry and laser Raman microspectroscopy, namely aqueous inclusions (W-type), pure CO2 inclusions (PC-type), CO2-rich inclusions (C-type) and daughter mineral-bearing inclusions (S-type). Microthermometric data and laser Raman analyses show that the quartz crystals from the QM stage contain all four inclusion types, with the W-type being predominant. Homogenization temperatures range between 271 and 426 degrees C. The salinities of the W- and C-type fluid inclusions range from 0.5 to 22.4wt.% NaCl eqv., whereas the S-type fluid inclusions in the QM stage range from 31 to 41wt.% NaCl eqv. Daughter minerals in the fluid inclusions include halite, sylvite, pyrite and calcite. Quartz from the QS stage (main mineralization stage) contains the W-, C- and PC-type inclusions, which are homogenized at temperatures of 204-269 degrees C, with salinities of 0.2-15.6wt.% NaCl eqv. Only W-type fluid inclusions have been identified in the QC stage. These yielded homogenizing temperatures of 175-211 degrees C and salinities of 1.1-9.9wt.% NaCl eqv. The C-type fluid inclusions of the main (QS) mineralization stage yield trapping pressures of 107-171MPa, corresponding to a depth of 4-6km. The sulphur isotope values (-1.7 parts per thousand and -6.6 parts per thousand) imply that the QS stage may not be directly associated with the early skarn (-7.4 parts per thousand) and quartz-magnetite stages (-4.8 parts per thousand and -5.0 parts per thousand), though the QS stage is probably dominated by magmatic-hydrothermal fluids. 40Ar/39Ar isotope plateau ages of 227.6 and 214.1Ma for biotite separated from the QM and QS stages are significantly younger than the host Kangbutiebao Formation (ca. 410Ma). The Talate Pb-Zn(-Fe) deposit is interpreted to be an unusual skarn-type system formed in a continental collision orogeny. Copyright (c) 2014 John Wiley & Sons, Ltd.