Types,characteristics,and time-space distribution of molybdenum deposits in China
【摘要】：正Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous. increasing demand for Earth resources.China possesses the largest Mo reserves in the world(exceeding 19.6 Mt).The major ore deposits are of porphyry,porphyry-skarn,skarn,vein,and sedimentary types.Porphyry molybdenum deposits contain 77.5%of the Chinese Mo reserves,with lesser amounts in porphyry-skarns(13%),skarns(5.1%).and veins(4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical.The six Mo provinces are in the Northeast China,Yanliao.Qinling-Dabie,middle-lower Yangtze River Valley,South China,and Sanjiang areas.We rec- ognize six ore-forming periods:(1)Precambrian(541 Ma).(2)Palaeozoic(541-250 Ma),(3)Triassic(250-200 Ma), (4)Jurassic Early Cretaceous(190-135 Ma),(5)Cretaceous(135-90 Ma),and(6)Cenozoic(55-12 Ma).The abun- dance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism.involving interactions between the Siberian,North China,Yangtze,India,and Palaeo-Pacific plates.Precambrian molybdenum deposits are related to Mesoproterozoic volcanism in an extensional setting.Palaeozoic Cu-Mo deposits are related to calc-alkaline granitic plutons in an island arc or a continental margin setting.Triassic Mo deposits formed in the syn-collision postcollision tectonic set- ting between the Siberian and North China plates and between the North China and Yangzi plates.Jurassic Early Cretaceous molybdenum deposits formed along the eastern margin of Asia and are associated with the palaeo-Pacific plate-subduction tectonic setting.Cretaceous Mo deposits are related to high-K calc-alkaline granitic rocks and formed in a lithospheric thin- ping setting.Cenozoic molybdenum deposits formed in a collision setting between the Indian and Eurasian continents and the subsequent extensional setting.