Geological Characteristics And Genesis Research Of The Tuolangla W-Mo Polymetallic Deposit,Tibet

The southern margin of the eastern section of the Gangdese belt has a strong mineralization during the late collision period during the collision between the Indian-Asian continent,forming the Nuri-Chongmuda porphyry-skarn-type copper polymetallic metallogenic bel.The Tuolangla W-Mo polymetallic deposit is located in the north-central part of the metallogenic belt.The tungsten ore body is layered and mainly distributed in the layered skarn of the granite porphyry and the Lower Cretaceous Bima Formation.The ore minerals are scheelite,chalcopyrite and a small amount of molybdenite.The molybdenum ore body is mainly layered in the layered skarn of the Bima Formation,and the vein molybdenum ore body is cut into the Dianzhong Formation of the Paleocene.The mainly ore mineral of molybdenum ore body is molybdenite and chalcopyrite.The Tuolangla W-Mo polymetallic deposit mainly develops chalcopyrite mineralization,molybdenite mineralization and scheelite mineralization.The layered skarn type ore body is mainly distributed in the interlayer fault fracture zone in the Lower Cretaceous Bima Formation.During the evolution of the skarn deposits,the main mineralization stages are scheelite mineralization in the oxide stage,chalcopyrite and molybdenite polymetallic mineralization in the quartz sulfide stage.The magmatic rocks exposed in the mining area include granite porphyry,diorite porphyry and andesitic porphyry,of which granite porphyry has the widest exposed area.The zircon U-Pb ages of the two granite porphyries are 91.43±0.69 Ma(n=16,MSWD=0.040)and 89.80±0.42 Ma(n=23,MSWD=0.073),and ?Hf(t)ranges from +7.7 to +15.4;the geochemical characteristics show that the granite porphyry belongs to the high potassium calc-alkaline series,the high field strength elements such as Nb and Ta are depleted,and the large ion lithophile elements such as K and Sr are enriched,the total rare earth elements ranges from 39.52 ppm to 81.15 ppm,La N/Yb N ranges from 17.14 to 42.80,and ?Eu ranges from 0.68 to 0.90.The above results indicate that the formation of granite porphyry in the northward subduction of the Neo-Tethys ocean,the diagenetic material mainly comes from the depleted mantle,mixed with a few crustal material.Re-Os isotopic dating of molybdenite indicats that the isochron age is 22.49±0.19 Ma(MSWD = 1.18)and the weighted average age of isotopic model is 22.5±0.17 Ma(MSWD = 1.13).The two results are consistent,indicating that the polymetallic mineralization of Tuolangla deposit occurred at the early Miocene.The temperature measurement results of quartz fluid inclusions show that the homogenization temperature ranges from 155°C to 350°C,mainly concentrated between 200°C ~270°C,and the salinity is 0.5%~33.2% Na Cleqv,mainly concentrated between 6%~11% Na Cleqv;The H-O isotopic test results of quartz show that the ?DV-SMOW range is-115‰~-50‰,with an average of-76.5‰.The ?18OH2O in the ore-forming fluid is calculated to be-0.9‰~0.7‰,with an average of-0.3‰;The results of S isotope measurement in metal sulfides shows that ?34S ranges from-12.4‰~6.3‰ with a peak of +3.5‰.The above results show that the ore-forming fluid with medium temperature and low-medium salinity are derived from magma,adding with a considerable amount of atmospheric precipitation.The ore-forming materials mainly come from the mantle and are contaminated with crustal materials.The Tuolangla W-Mo polymetallic deposit belongs to the skarn type deposit,but the ore-forming age reflected by the molybdenite is quite different from the zircon age of the granite porphyry and the diorite porphyrite,indicating that the true ore-forming rock mass has not yet exposed.The andesite in the Bima group has a large number of zircons from Proterozoic,indicating the existence of ancient crust remnants in the lower part of the metallogenic belt where the deposit is located.The magmatic intrusion in the early Miocene period caused the inclusion of Cu from the mantle source material and W-Mo from the crust source material into the ore-forming system,forming the Tuolangla deposit,which has the potential to form porphyry deposits in the deep.