The Geologic Feature Of Porphyry Metallogenic System And Ore-controlling Factor Of Thick-great-rich Skarn Orebody In Jima, Tibet

We have achieved a great breakthrough in prospecting at Jima copperpolymetallic deposit which is a large deposit of economically significance andscientific significance at Gangdese metallogenic belt. The identified resource reserveof copper, molybdenum, lead, zinc, gold and silver have reached large-scale. It is atypical, representative and unique deposit at Gangdese metallogenic belt.Based on thesystem summary of the latest exploration and research of Jima mining area, we putforward that Jima copper polymetallic deposit is porphyry mineralization system thatis related to porphyry mineralization. We also finished the geological characteristicsof mining area research, ore geological characteristics research, distribution ofore-forming elements research, diagenetic geochronology research, material sourceresearch, origin and evolution of ore-forming fluids research, fissure(veins) systemcharacteristics research and other researches on rock and ore controlled structure,theseall achieved fruitful research results.However,there are still some important questionsthat demand prompt solution. This paper aimed at solving practical scientificproblems, systematicly collates and summarizes the geologic feature of Jima porphyrydeposit system, according to fully understand of geological background.It alsocomprehensively and systematicly studys and analysises the characteristics of thethick-large skarn orebody and rich orebody, explores the ore-controlling mechanismand establishes the corresponding magma-ore-controlling model. The acquiredrecognization as followed:The Jima porphyry metallogenic system is made up of copper polymetallicorebodies in skarn, copper and molybdenum (gold and silver) orebodies in hornfels,molybdenum (copper) orebodies and independent gold orebodies in peripheralstructural alteration zone. The main structures of skarn ore are dense disseminated,lumpy,veiny, The main structures of porphyry and hornfels are disseminated-veiny.Main ore minerals include chalcopyrite, bornite, molybdenite, chalcocite, tetrahedrite, galena, sphalerite, native gold, the gangue mineral mainly are skarnminerals and quartzs with small amount of anhydrite,calcite, fluorite and otherminerals. Ore-forming elements of copper polymetallic orebody originate in skarnexhibit zoning characters such as Mo+Cu±Au±Agâ†'Cu±Mo±Au±Agâ†'Pb+Zn+Cu±Au±Ag±Moâ†'Au±Ag±Cu along from emplacement center tocontect zone of skarn-marble and marble; Ore-forming elements of copper andmolybdenum (gold and silver) orebody originate in hornfels exhibit zoning charactersas ‘up copper down molybdenum’; molybdenum (copper) orebodies originate inporphyry are deep concealed orebodies, the attitude of orebodies are nearly uprightcylindrical, mineralization concentrates at the top of and internal of porphyry;Independent gold orebodies originate in peripheral structural alteration zone can bedivided into independent gold orebodies originate in skarn, independent goldorebodies originate in slate–hornfels, independent gold orebodies originate in quartzdiorite porphyry according to host surrounding rock and occurrence state.We delineate skarn copper-molybdenum orebody and skarn lead and zincorebody base on cut-off grade of general industrial indicators and delineate skarncopper, molybdenum, lead, zinc bonanza base on bonanza indicators. According to theresearch of distribution on the plane and output features in profile of thick-greatorebody and bonanza,we suggest that enrichment center of thick-great orebodiesaccord with that of bonanza, thick-great orebodies mainly distribute at three areas:1)porphyry contact zone in the center of mining area;2) inside the Tongshan glidingbody at southern of mining area;3) Niu Matang at the northern of mining area. Theore-controlling mechanism of different part of thick-great-rich orebody is different, itcan be summed up: Contact zone ore-controlling, gliding body ore-controlling andanticline ore-controlling.