| Sanandaj-Sirjanin zone(SSZ) is the major component of Zagros collisonal orogen, which is formed by the collision of Arabian Plate and Iranian Plate in late Cretaceous or Oligocene-Miocene, Iran. There are a lot of large MVT Pb-Zn deposits(occurrences), including Iran Kuh, Emarat, Ahangaran, Tiran et al, which constitute the Malayer-Esfhan carbonate-hosted Pb-Zn metallogenic belt. The past work for the deposits of the belt was weak, and focused on the largest Irankuh deposit. Characteristics of these deposits and the ore-forming fluid propetry are unclear. The source of the ore-forming fluid and materials lack discussion, and the genesis of other deposits in Malayer-Esfhan carbonate-hosted Pb-Zn metallogenic belt is unclear and need to make a comparision. In addition, compared with the typical MVT deposits, there is a lot of quartz in the gangue mineral of these deposits; which hasn’t been explained in the past research. So we choose the Emarat Pb-Zn deposit and Ahangaran Pb(Cu) deposit to study by field geological profile, fluid inclusion research and stable isotope C, H, O, S, Pb test work to make clear of the characteristics of geology and mineralization, the source of ore-forming fluid and materials and the cause of much quartz in the gangue minerals. By the comparison of regional Pb-Zn deposits, we can confirm the genetic relationship of these deposits.Study shows the host rock of the Emarat and Ahangaran deposits is the Early Cretaceous limestone and orebodies of themt are shown as steeply-dipping, tabular veins parallel to the stratigraphic bedding. The ore minerals of Emarat are composed of galena, sphalerite and pyrite, and the gangue minerals contain quartz,and calcite. While the ore minerals of Ahangaran are composed of galena, chalcopyrite, pyrite and a little tetrahedrite, and the gangue minerals contain quartz, dolomite, barite and calcite. Mineralization of them were classified into two stages. For Emarat Pb-Zn deposit,(1) pre-ore stage, shown as replacement of the host limestone by fine-grained quartz and pyrite;(2) ore stage, coarse-grained quartz + sphalerite + galena + calcite as veins filling in silicified(by pre-ore stage quartz) limestone. For Ahangaran Pb(Cu) deposit,(1) pre-ore stage, composed of fine-grained quartz, which replacing limestone strongly;(2)ore-stage, shown as carbonate + barite + coarse-grained quartz + galena + chalcopyrite + pyrite+tetrahedrite. Study of fluid inclusions in Emarat Pb-Zn deposit shows the metallogenic fluid is H2O-Na Cl system. The homogenization temperatures range from 132 ℃ to 225 ℃ and the salinities vary from 18% to 24 wt% Na Cl. The fluid inclusions have high Na+ and Cl- contents with high Na+/K+ ratios(average 29) and low Ca2+, Mg2+, K+, and SO42- contents. These features are similar to those of basinal brine. The δ18OV-SMOW of quartz ranges from 18.6‰ to 20.7‰, and consequently the calculated δ18OH2O values of the parent fluid are between 2.84‰ and 9.12‰. The δD values of the parent fluid are between-76.2‰ and-57.5‰. Study of fluid inclusions in Ahangaran Pb(Cu) deposit shows that the metallogenic fluid is Cl--SO42--Na+-Ca2+-Mg2+ system. The homogenization temperatures range from 108℃ to 209℃ and the salinities vary from 7.2% Na Cl to 28.5%Na Cl, which suggests a characteristic of low temperature and medium-high salinity. The δ18OV-SMOW of quartz is between 17.2‰ and 18.3‰, and the δDV-SMOW is between-77.7‰ and-68.7‰. The δ 13 C V-PDB of calcite ranges from-3.0‰ to-1.7‰ and the δ18OV-SMOW ranges from 17.8‰ to 20.1‰. Combined with the study of C-O and H-O isotopes and fluid inclusions of other deposits in Malayer-Esfhan carbonate-hosted Pb-Zn metallogenic belt, we find the ore-forming fluid has the features of basinal brine, which leads to the part dissolution of carbonate during the water/rock interaction during its transporting. In Emarat Pb-Zn deposit, The δ34S values of sphalerite and galena ranges from 2.6‰ to 10.3‰. This may indicate that the reduced sulfurs in the deposit were generated by thermochemical sulfate reduction. The 206Pb/204 Pb, 207Pb/204 Pb, 208Pb/204 Pb rations of galena are 18.4112 ~ 18.4157, 15.6472~15.6497, 38.5642~38.5808, respectively. In Ahangaran Pb(Cu) deposit, The δ34S value of barite ranges from 18.7‰ to 22.7‰ and sulfides range from-3.1‰ to 9.7‰, which indicates the reduced sulfur is probably the result of biological sulfate reduction(BSR) and thermochemical sulfate reduction(TSR). The 206Pb/204 Pb, 207Pb/204 Pb, 208Pb/204 Pb rations of galena are 18.4083~18.454, 15.6512~15.6548, 38.5628~38.5515, respectively. The sulfur isotope composition of the deposits in Malayer-Esfhan carbonate-hosted Pb-Zn metallogenic belt is different, but overall, the reductive sulfur is probably from the early cretaceous Marine sulfate, which was dissolved by the stored water in carbonate-hosted rock, and provided reductive sulfur by biological sulfate reduction(BSR) and thermochemical sulfate reduction(TSR). The characteristics of lead isotope in different deposits are very similar, which indicates the lead may be derived from the crustal rocks that experienced orogeny.The geology and mineralization characteristics, the property of the ore-forming fluid, the source of ore-forming fluid and materials of the deposits in Malayer-Esfhan carbonate-hosted Pb-Zn metallogenic belt are similar, which indicates the formation of the deposits is the product of the same metallogenic system. The ore-forming fluid of different deposits,that have different mineral and metal combinations did not show obvious differences. The occurrence of large numbers of quartz in the gangue mineral may result from a rapid decrease of temperature during interaction between the relatively hot(>200℃) ore-forming basinal brine and the cold host rocks. |
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