Metallogenic Epoch,Genesis And Geological Significance Of The Chagele Pb-Zn Deposit,Tibet

The Chagele deposit is a skarn-type lead-zinc-molybdenum polymetallic deposit newly discovered in the western central section of the central Gangdise metallogenic belt in recent years.Research on its metallogenic age and deposit genesis will help to understand the west extension characteristics of the central Gangdise metallogenic belt.Based on the geological investigation of the deposit,this paper analyzes the granite porphyry petrology,zircon U-Pb age,main and trace rock geochemistry,Sr of the three ore sections of Chagelenan,Chagelebei and Longgen.Sr-Nd-Pb isotopic geochemistry,H-O isotopes of ore-forming fluids,and Molybdenite Re-Os isotopes,etc.The following main understandings have been obtained.The stratum exposed in the mining area mainly includes the Xia La Formation?P₂x?shallow metamorphic clastic rock and limestone,the Nianbo Formation?E₂n?and the Pana Formation?E₂p?intermediate-acid volcanic rock series and the Quaternary?Q?loose deposits.There are developed fault structures in the mining area,mainly NW-trending faults,followed by NEE-trending and north-south-trending faults,and a small-scale NE-trending ductile shear zone developed.There are two sets of granite porphyries developed in the mining area,namely,fine spots and coarse spots,which are exposed in the southern and northern sections of Chagele and the northern sections of Chagele and Longgen respectively.Strong potash feldsparization and veinlet disseminated molybdenum mineralization occurred in the small porphyry granite porphyry of the Chagelenan ore section.The metallogenic stages include four stages:I quartz-potassium feldspar stage,II quartz-molybdenite stage,III quartz-chalcopyrite-pyrite stage,and IV quartz-epodote stage.Skarnization and lead-zinc-copper mineralization develop in the fine porphyry and coarse porphyry granite porphyry of the Chagele North ore section and the coarse porphyry granite porphyry of the Longgen ore section.The metallogenic stages include?garnet-pyroxene-wollastonite stage,?epidote-actinite-chlorite stage,?quartz-chalcopyrite-pyrite stage,and?galena-sphalerite There are five stages:ore-quartz stage and V calcite-quartz stage.The fine porphyry and coarse porphyry granite porphyry in the mining area generally belong to the peraluminous high-potassium calc-alkaline-potassium basalt series granite,which is rich in alkali and aluminum,poor in titanium and phosphorus,enriched in light rare earths,and abnormally negative in europium.Among them,the fine porphyry granite porphyry zircon ²⁰⁶Pb/²⁰⁸U weighted average age of the Chagelenan mine section is 66.63±0.29Ma,and the fine porphyry granite porphyry zircon²⁰⁶Pb/²⁰⁸U weighted The average ages are 62±0.5 Ma and 62.74±0.37 Ma,respectively.The weighted average age of ²⁰⁶Pb/²⁰⁸U zircons from the Longgen granite porphyry is 62.1±0.43 Ma.The(⁸⁷Sr/⁸⁶Sr)i of the two sets of granite porphyry are 0.70967?0.71509,and?Nd?t?is-6.01?-5.81,showing the characteristics of mixed crust and mantle sources.The Molybdenite Re-Os isochron age of the Chagelenan ore section is 62.4±1.8 Ma,indicating that the metallogenic age belongs to the Paleocene and is in the early stage of steep and deep subduction of the Indian continent during the main collision period of the Indian-Asian continent.It is more closely emplaced with fine porphyry granite porphyry.The temperature measurement of fluid inclusions and the analysis of H-O isotopes show that during the first stage of the mineralization process,magmatic water is the mainstay.At the beginning of the second stage,more cyclic atmospheric precipitation is added,and at the fifth stage,the main atmospheric precipitation is basically.Comprehensive analysis shows that the Chagele lead-zinc-molybdenum deposit is a porphyry molybdenum+skarn lead-zinc-copper"two-in-one"deposit related to granite porphyry intrusions.The metallogenic model can be summarized as:the early stage of the Indian-Asian continental collision period,accompanied by the steep and deep subduction of the Indian crust below the Lhasa terrane and the rewinding of the subducted Neo-Tethys oceanic crust,triggering asthenic mantle material The upwelling caused the mantle-derived magma to invade.At the same time,the high thermal anomaly and the thickening of the crust of the Lhasa terrane induced deep melting of the crust to form crust-derived magma.The two types of magma are mixed and crystallized in the shallow magma chamber,forming a mineralized magma rich in silicon,alkali,aluminum and poor in titanium and phosphorus.When the magma chamber receives replenishment and is reactivated,the differentiated ore-forming magma invades,forming fine porphyries and coarse granite porphyries successively.After the magmatic period,the hydrothermal fluid formed porphyry molybdenum-copper ore bodies in the granite porphyry dominated by felsic wall rocks,and formed in the external contact zone of the granite porphyry dominated by carbonate wall rocks Skarn-type lead-zinc-copper ore bodies constitute a"two-in-one"metallogenic model.