Depositional controls and genesis of the Jinding sandstone-hosted Zn-Pb deposit, Yunnan province, southwest China

Jinding is a large, Zn-rich ore deposit hosted within alluvial sandstones along the margin of a continental basin that formed in the tectonic collision zone between the India plate and the Yangtze platform. Zn-Pb mineralization appears to have occurred during the early Tertiary compressional phase of this continental basin.; The Jinding orebody is hosted in the nonmarine Paleocene Yunlong Formation which may be divided into local depositional facies consisting of proximal rock slides, mid fan streamflow-dominated debris flows, fan delta and distal fan facies. High energy influx of coarse clastics and carbonate boulders adjacent to the Pijiang growth fault characterizes the Jinding host rock depositional environment. However, major orebodies are hosted in the fan delta fine sandstones and the underlying mid-fan fragment-bearing sandstone facies.; Two hydrologic systems probably were involved in the Jinding ore-forming process according to the constraints provided by fluid inclusions, O, C, Sr, S, and Pb isotopes and biomarker geochemistry. A meteoric water system was resident in the shallow part of the alluvial fan and fan-delta complex. These pore waters mixed with hydrothermal brines that developed in the deeper part of the basin and ascended to the Jinding alluvial fan along the Pijiang fault.; Fluid inclusion studies indicate that the hydrothermal fluids were basinal brines with temperatures near 150{dollar}spcirc{dollar}C and 17 to 23 eq. wt % NaCl. These fluids are characterized by an average {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}water{rcub}{dollar} value of 9.3{dollar}perthous{dollar} (SMOW), depleted {dollar}rmdeltasp{lcub}13{rcub}Csb{lcub}calcite{rcub}{dollar} values ranging from {dollar}-{dollar}18.6 to {dollar}-{dollar}25.2{dollar}perthous{dollar} with a mean of {dollar}-{dollar}22.2{dollar}perthous{dollar} (PDB), elevated {dollar}rmsp{lcub}87{rcub}Sr/sp{lcub}86{rcub}Sr{dollar} values ({dollar}>{dollar}0.7102) and homogeneous Pb isotope compositions (average {dollar}rmsp{lcub}206{rcub}Pb/sp{lcub}204{rcub}Pb=18.449, sp{lcub}207{rcub}Pb/sp{lcub}204{rcub}Pb=15.649, sp{lcub}208{rcub}Pb/sp{lcub}204{rcub}Pb=38.663).{dollar} The pristane/phytane, {dollar}rm Csp{lcub}35{rcub}/Csp{lcub}34{rcub}Csb{lcub}27{rcub}{dollar}-C{dollar}sb{lcub}28{rcub}{dollar}-C{dollar}sb{lcub}29{rcub}{dollar} gammacerane/hopane and sterane/hopane indices of the Jinding organic compounds suggest an anoxic, hypersaline and probably marine carbonate source rock. Pb isotopic data suggest that the ore fluid was well mixed during transportation without Pb contribution from the basement. Organic geochemical data suggest the source of Jinding petroleum was marine carbonate sediments. However the elevated homogeneous Sr isotope data indicate the involvement of clastic sources.; The other end member pore fluids are characterized by lower temperatures {dollar}({lcub}le{rcub}70spcirc{dollar}C) that allowed sulfate-reducing bacteria to produce H2S that was fixed as sulfide minerals with depleted S isotope values ({dollar}-{dollar}32.0 to {dollar}-{dollar}11.1{dollar}perthous,{dollar} CDT). This type of fluid is isotopically lighter in O ({dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}H2O{rcub}=1.3{dollar} to 4.8{dollar}perthous,{dollar} SMOW) and heavier in C ({dollar}rmdeltasp{lcub}13{rcub}C={lcub}-{rcub}3{dollar} to {dollar}{lcub}-{rcub}16.8perthous{dollar} PDB).; Mixing of the high temperature and high salinity metal-bearing ore fluid with lower temperature, reduced S-rich fluid resulted in sulfide precipitation in the Jinding alluvial fan/fan delta complex.