Research On Metallization Of Zhijiadi Epithermal-type Ag-Pb-Zn Deposit In Shanxi, China

Zhijiadi large Ag-Pb-Zn deposit is one of the most representative epithermal depositson north margin of Huabei platform， and it locates on Taibaiwei Mountain Mesozoiccolcano Basin of Lingqiu County， Shanxi. New phenomenon of deep ore body with newcharacteristics and metallization are observed based on exploration work carried in themining district recently， both of which provide new exploration material for the study ofZhijiadi ore deposit geology and its mineralization pattern. Based on new progress ofexploration of the mining district， geological survey of the deposit and achievements ofprevious study， this study systematically dissects Zhijiadi deposit.Taibaiwei Mountain Mesozoic volcano Basin is characterized by double layerstructure， which comprise Archean metamorphic basement at its bottom and lateProterozoic-Paleozoic sedimentary layer at its top. Volcanic series of the mining districtwere defined as late Jurassic Baiqi formation (J3b2)， and zircon grains of the volcanicseries were separated for U-Pb isotope age using LA-ICP-MS. Quartz porphyry，Rhyolite porphyry and granite were formed in135±0.76Ma，135±0.76Ma and136±0.55Ma respectively. Temporal and spatial relationship of thesevolcanic-subvolcanic rock series of the mining district is the products of an identicalmagmatic process， which represent an important tectonic-magmatic-metallization eventin early Cretaceous.Breccia pipe zoning patterns of the mining district is proposed. Hydrothermalchannel phase is recognized from the bottom of④ore-bearing breccia pipe in the miningdistrict for the first time. Systematic study has been taken on the structure andmineralization characteristics of the differrent position of the ore-bearing breccia pipe，and4phase zone are distinguished from bottom to tope， such as the channel phase， thebreccia phase， the fracture phase and crack phase. Fracture phase and breccia phase arethe major position of ore， and the channel phase could lead to porphyry-likemineralization in the deep.Vertical mineralization and alteration model of the mine is constructed based onmineralization types， hydrothermal alteration， mineral-assemblages and mineralizingelement assemblage.4units could be recognized from top to bottom. Zone I is Mn gossanzone which is the alteration halo of Mn (Ag) and could be treated as prospecting criteria. Zone II is fracture system controlled mineralizing veins zone with Ag and Pb (Zn) asmineralizing elements. Zong III is vein and cylinder type mineralized zone. Both veintype ore and cylinder type ore are produced in this zone， which is the major mineralizedzone of the mine with Ag， Pb and Zn as mineralized elements. Zone IV is amineralization zone with characteristics similar to porphyry. Low grade ore displayingstock veinlet structure and disseminated texture is produced in the inner and outer contactzone of quartz porphyry and quartz porphyritic breccia， especially the in the intersectionof contact zone and fracture structure. This model systematically discovers the verticaldistribution law of3mineralizing types in the mining area.Zhijiadi Ag-Pb-Zn deposit metallization model is proposed. As is suggested by traceelements patterns of ore and minerals，3mineralizing types are produced by theevolution of a same ore-forming fluids system， which is characterized by medium-lowtemperature and low salinity. Systematic analysis of S-Pb isotope and D-O isotope offluids-inclusion suggest that ore-forming material mainly derives from magma， whilemineralization fluids is mingling product of magmatic fluids and atmospheric water. Thispaper propose Zhijiadi vein-breccia-porphyry3in1metallization model and discovertheir inner connection.We propose4criteria as Zhijiadi Ore prediction symbols， including Mn-Aggossan， quartz porphyry， mineralization-alteration zoning patterns and volcanictectonic. We not only confirm that quartz porphyry is ore-forming geological body， butalso propose3mining targets based on new recognition.