Geology And Geochemistry For Copper And Zinc Deposits Of Zhashui-Shanyang Area-the Importance Of Epigenetic Mineralization

Zhashan polymetallic concentration area,is located in the East part of South Qinling Orogenic belts,is famous for Lead-Zinc polymetallic ore deposits.Most of them are regarded as SEDEX deposits formed during Devonian. Recently, some advancement of exploration approves there is not only hydrothermal exhalation-sedimentary mineralization but also epigenetic mineralization, which is very important. It is very clear that the Mujiazhuang copper deposit,located in the Zhashan polymetallic concentration area, is an epigenetic one formed by fluid metasomatism during Carboniferous and the Tongmugou zinc deposit, located in the Zhashan polymetallic concentration area, is fluid matomatism reformed ore deposit based on hydrothermal exhalation-sedimentary ores or rocks on basis of researching on gological characteristics of isotopes geochemistry, fluid inclusions geochemistry, mineralization dating and event geology both the Mujiazhuang copper deposit and the Tongmugou zinc deposit in the Zhashan area. By comparing of regional geothermal events, it is put forward that the point-to-point collision between the Qinling Block Mass and the North China Plate during Carboniferous begin forming the granite in the deep interior of the Zhashan area to make this area forming high geothermal background, and forming fluid metasomatic metallogenics.It is established three more key construct-magma-geothermal events and matched mineralizationat events based on researching regional magmatism, metamorphism and chronology: the hydrothermal sedimentary event during 360～340Ma, the structurally magmatic reformation mineralization formed by the deep-derived magma activity and the geothermal activity during 320～280Ma,and the alteration .i.e the retrometamorphism happening at the fragile-ductile deforming zone within the later-stage crust water hydrothermal activity during 190～170Ma. It is discovered firstly that fluid matomatism event during 320～280Ma(Carboniferous) is very important among regional hydrothermal events.It is clear that there are two kinds of epigenetic mineralization based on researching two typical ore deposits in the Zhashan polymetallic concentration area: fluid metasomatism and fluid matomatism reformed mineralization based on hydrothermal exhalation-sedimentary ores or rocks. The Mujiazhuang copper deposit is a fluid metasomatic ore deposit which is located nearly in axialplane fracture of Jinjinghe-hujiamiao inverted anticline which is in south limb of Hongyansi-heishan composite syncline in the Zhashan area. The axialplane fracture, is a complicated structure, forms in inverted limb, has two stages construct activities: detachment early and left-lateral strike-slip fault lately. They are filled by Cu-bearing ankerite-quartz veins, but main ore bodies are located the later stage fractures. Most of ores, filled in dilatant zone of fracture, are mass and network mineralization. The scale of ore bodies depends on the property of embracing rocks: network veins ore body in fragile rocks and mass ore body in soft rocks. Biotite alteration is relation to copper mineralization. The Tongmugou zinc deposit, is located in North lamb(inverted lamb) interlays fracture of Maluping inverted syncline, is a rich zinc deposit of fluid matomatic reformed. The main ore-bearing rock is Qingshiya group of Devonian (albite slate or albite-scapolite slate), in which there are multiplayer lamellar and minutiness sphaleritite low-grade ores that it is intergrows with pelite, composes minutia lamellar and shows remains layering. Wall-rock alteration(aibite,silication, scapolite et, al) is single side nonsymmetry, It is clear that they are formed by hydrothermal exhalation-sedimentary during Devonian. Ore shoots, are located in subsidiary fracture(F3) derived from structure F2, are larger and thickness near point of intersection between F2 and F3, and are enchelon arrangement in dip. Wall-rock alteration(green color stone, mainly composed of hoepfnerite, epidote, diopside, biotite, quartz, and chlorite etc.) is around ore shoots to be distribute with symmetry, that show the block and brecciated ores of the Tongmugou zinc deposit are fluid metasomatic reformed deposit.It is discovered that ore mineral lead isotopes of the Mujiazhuang are sky-high radioactivity lead abnormal, and alteration rocks nearly ore body are also. On the contrast of both the Mujiazhuang and Cambrian ores and rocks lead isotopes composition, they are homoplasy, and it is suggested that the lead abnormal isotopes resource of the Mujiazhuang are from Cambrian.It is put forword that lead of the Tongmugou zinc deposit are also abnormal lead isotopes which are from the basis rocks like hydrothermal deposit rocks.It is approved with regional contrast research.On the basis of fluid inclusions for the Mujiazhuang copper deposit, it is showed that there were two stages of fluid evolution: the first stage is magma hydrothermal with middle temperature, middle and high salinity (CO₂)-H₂O+NaC1 fluid, its homogenization temperature are 190²65℃and salinity 12.5～35.34wt%NaCl,preture 12.8～21.3Mp, Meanwhile, a large of three faces fluid inclusions with a salty crystal coexistence to vapour face inclusions are discovered in the high and middle high temperature steps of homotemperature of fluid inclusions for the Mujiazhuang copper deposit, it is suggested that the mineralization fluid is over-saturation and occurring boilization and supposed that there is magma chamber in deep of mining area. The second stage is behind hydrothermal of magma with middle-high temperature, middle and high salinityH₂O+NaCl fluid, its homogenization temperature are 300～350℃and salinity 7.4～41.59wt%NaCl,preture 10.8～19.3Mp. On the basis of fluid inclusions for the Tongmugou zinc deposit, it shows that there is only first stage of fluid evolution, a large of three faces fluid inclusions with a salty crystal coexistence to vapour face inclusions are discovered in the high and middle high temperature steps of homotemperature of fluid inclusions for the Tongmugou zinc deposit, it is suggested that the mineralization fluid is occurred boilization. Boilization is an important mechanism of mineral matters precipitation. The process of fluid evolution is: first, with magma invasion in deeper area, hydrothermal fluid of magma mixied with strata-formed water transports up to near surface and quickly are boiling and form nonintermingle fluid, then mineral matters deposit form strangle lode ores; second, The late hydrothermal fluid of magma are boiling again to form main ores. The evolution of fluid is going along with two stages tectonic movement.On the basis of Geochemistry of fluid inclusion(fluid composition, fluid evolution, the fluid resource judged from the tracing of indifferent gas and REE), it is approved that the mineralization fluid is from the formational water(water in the strata)and magma water in the Tongmugou, and is from the magma water in the Mujiazhuang(the first stage), and is from the formational water and the deep-derived magma in the Mujiazhuang (the second stage). In addition, the hydrogen and oxygen isotopic data of the Mujiazhuang copper deposit supports the results.The biotite associated with chalcopyrite in the Mujiazhuang copper deposit, its Ar-Ar age is 323.68Ma, which represents the age of mineralization. The forming age of hoepfnerite mineral was close to the forming time of Pb-Zn deposit, and the K-Ar surface age is 293Ma. The main ore-forming age of Cu-Pb-Zn deposits in the Zhashan area is about 323～293Ma.It is supposed that Carboniferous mineralization maybe was a very important metallogenesis period in the Zhashan area. The mineralization model of epigenetic fluid matomatism, is founded according to geological and geochemistry characteristics, and suggests a new direction for ore deposits exploration.