| The Daolundaba Cu-polymetallic deposit,located in the western slope of the southern Great Xing'an Range,is a Cu-based,associated with W-Sn-Ag medium-sized deposit.Orebodies of the deposit are hosted in faulted and shattered zones,which develop within the Permian sandstone and slate and the Variscan biotite granite.The deposit includes Cu orebody,W orebody,Sn orebody,Cu-W orebody,Cu-Sn orebody,W-Sn orebody,and Cu-W-Sn orebody,with associated Ag.These ore bodies occur not only as alien symbiosis,but also intergrowth symbiosis.Systematic mineralogy,fluid inclusion,geochronology,and geochemistry were studied for the Daolundaba deposit in this paper.The deposit's mineralization process can be divided into four stages,namely,quartz-fluorite-muscovite-tourmaline-cassiterite-wolframite stage?stage I?,quartz-fluorite-wolframite-chalcopyrite-arsenopyrite-pyrrhotite stage?stage II?,quartz-fluorite-chalcopyrite-pyrite-pyrrhotite-silver-bearing mineral stage?stage III?,and calcite-fluorite-pyrite stage?stage IV?.Three types of fluid inclusions?FIs?,including liquid-rich?WL type?,gas-rich?WG type?,and daughter mineral-bearing?S type?inclusions,have been distinguished in quartz,fluorite,and calcite veins for the deposit.In general,the ore-forming fluid system belongs to an H2O-NaCl±CO2±CH4 system with high to medium-high temperature and great fluctuation of salinity.The?18OH2O and?D values of ore-forming fluids vary from-10.0‰to 7.2‰and-127‰to-819‰,respectively,and the?13C value varies from-9.8‰to-6.7‰,indicating that the ore-forming fluids mainly originated from magma with minor meteoric water added in later period.The?34S values of metallic sulfides from ores range from-7.4‰to-1.2‰,and the 206Pb/204Pb,207Pb/204Pb,and208Pb/204Pb values of metallic sulfides vary from 18.311 to 18.794,15.519 to 15.706,and 38.078 to 38.826,respectively,indicating that the ore-forming material of the deposit chiefly originated from the granitic magma.LA-ICP-MS cassiterite U-Pb age varies from 134.7±6.6Ma to 136.8±7.4Ma,and LA-ICP-MS hydrothermal monazite U-Pb age ranges from 136.1±2.1Ma to 137.7±3.2Ma,indicating that the Daolundaba deposit formed in the Early Cretaceous.LA-ICP-MS zircon U-Pb ages for the Zhangjiayingzi and Qianjinchang intrusions in the Daolundaba area vary from134±1Ma to 136±1Ma and 278±1Ma to 279±1Ma,respectively,implying that the Daolundaba deposi has a close genetic link with the Zhangjiayingzi intrusion.The Zhangjiayingzi intrusion belongs to highly fractionated I-type granite,generated in a extension environment,and was formed by partial melting of material of a Neoproterozoic orogenic belt.The Qianjinchnag intrusion belongs to unfractionated S-type granite and formed in a collisional or post-collisional environment;its source region is mainly the Neoproterozoic crust;and during the rising of the magma,the initial magma was contaminated by ancient crustal matter.The multi-stage boiling of the ore-forming fluids and the fluid mixing of magmatic and meteoric water were the dominant mechanism for the deposition of ore-forming materials. |
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