Magmatism And Genesis Of Multi-stage Porphyry-like Granite In The Giant Dahutang Tungsten Deposit,Jiangxi Province

Dahutang tungsten deposit,located in the eastern part of Jiuling polymetallic ore concentration area of Jiangnan orogenic belt,is one of the largest tungsten deposits in the world.There are many Yanshanian granites in this area,and there are still controversies and deficiencies in the study of magmatic sequence and source characteristics.For porphyritic granites closely related to mineralization,it has been found that there are two stages of magmatic intrusion,namely,Shimensi?northern region?porphyritic biotite granite?150.0Ma?and Shiweidong?southern region?porphyritic dolomite granite?144.2Ma?.We have identified porphyritic dimica granites in the southern region.Their structures,structures and mineral assemblages are similar to those of the former two,but their mineral contents,especially feldspar and mica,are obviously different.From porphyritic biotite granite to porphyritic dimica granite to porphyritic dolomite granite,plagioclase and biotite content decrease in turn,and dolomite content increases in turn.In this paper,the petrology,chronology and geochemistry of three stages of porphyry-like granite in the area are systematically studied,the magmatic sequence of porphyry-like granite in the area is determined,the petrogenesis and metallogenic significance are discussed,and the following main achievements and understandings are obtained.Zircon and monazite of porphyritic dimica granite give crystallization ages of128.6¹30.0Ma and 128.3Ma,respectively.They were formed in the Early Cretaceous and are products of the third stage of regional porphyritic magma intrusion.The third-stage porphyritic granites are characterized by high SiO₂,Al₂O₃,K₂O and low TiO₂,MnO and CaO.They belong to high-K calc-alkaline,strongly peraluminous and highly differentiated S-type granites.The peraluminous degree of rocks in the southern region is higher than that in the northern region.The magma source area is mainly the upper crust Proterozoic Shuangqiaoshan Group strata,but its source rock composition is not uniform:porphyritic biotite granite originates from partial melting of mudstone and complex sandstone of Shuangqiaoshan Group,and also partially from metabasic rocks;porphyritic dolomite granite and porphyritic dimica granite are formed by partial melting of mudstone-rich rocks,and the latter has a small amount of new mantle source.The diagenesis and mineralization process of Dahutang porphyritic granite can be summarized as follows:under extensional tectonic environment,the deep melting of W-rich Shuangqiaoshan Group strata provides material basis for diagenesis and mineralization high crystallization differentiation of magma,which makes W in magma highly enriched reductive and peraluminous magmatic fluid exsolution provide favorable physical and chemical conditions for the formation of rock mass and W migration ore-bearing.Fluid evolution,carrying W to the surrounding rock migration and enrichment of mineralization in the favorable ore-hosting part of the surrounding rock.Comprehensive studies show that the Dahutang porphyritic granite is the product of at least three stages of magmatism and formed in the post-orogenic intracontinental extensional tectonic environment.These three stages of magma intruded extensively in the region,bringing about a huge amount of mineralizing material W.The superimposition of regional multi-stage highly differentiated magmatism and its associated mineralization resulted in the super-large tungsten polymetallic deposit in Dahutang.