Petrogenesis Of Late Meosozoic Granitoid Rocks In Dahutang Tungsten Ore Field, Jiangxi Province

The Dahutang tungsten deposit, discovered in 2010, is one of the largest W deposits in the world. The deposit is genetically associated with a Late Mesozoic granitoid complex, and composed of three orebodies with distinct styles of mineralization, i.e., veinlets-disseminated ores hosted in Proterozoic granitoids, breccia pipe-hosted ores and quartz-vein swarms cut granitoid complex. This dissertation studies petrogenesis of the Late Mesozoic granitoids and relationship with W mineralization at Dahutang, by integrative analyses on LA-ICP-MS zircon U–Pb dating, whole-rock geochemical data, and Sr-Nd-Hf isotopic data from these granitoids.Main phases of the Dahutang granitoid complex include heterogranular granite, dosemic biotite-granitic porphyry and biotite-granitic porphyry. Heterogranular granite intrusion with zircon U-Pb age of 157.2±3.5Ma emplaced as stock with a 0.5¹0m thick feldspar-quartz shell, associated with stringer-stockwork W mineralization. Porphyritic biotite granite stocks with zircon U-Pb age of 153.2±3.9 Ma intruded heterogranular granite intrusion, and are associated with W-Cu vein swarms. The last phase is biotite granitic porphyry with U-Pb age of 155.9±3.1Ma, which intrude the cryptoexplosive breccia-pipe with Cu-W mineralization. Geochemically, these granitic rocks are peraluminous（with ASId=1.1¹.2）and were characterized by enrichments in Rb, Th, U and K, and depletion in Ba, Sr and Ti. Their REE patterns show enrichment in LREE and a strong negative Eu anomaly. The geochemical data suggest that the rocks are typical crust-derived S-type granites. These granitic rocks yielded initial 87Sr/86 Sr of 0.7139 to 0.7344, εNd（t） of-9.2^-6.9 and εHf（t） of-2.54^-9.63, falling on the mixing line of the meta-sedimentary rocks and meta-basalts from the Proterozoic Shuangqiaoshan Group in the Sr-Nd and εHf（t）-U-Pb age diagrams. These isotopic data suggest that the Dahutang granitoids were derived from remelting of the Proterozoic basament of the Shuangqiaoshan Group, which are identical to Neo-proterozoic ages of interited zircons and crustal Hf model ages for these granitoids.Regional geochemical analyses indicate that both the meta-sedimentary rocks and meta-basalts of the Shuangqiaoshan Group are enriched in metal W（9.13 ppm） and Cu（84.2¹74ppm）, compared with the crust in east China. Remelting of the source likely provided W and Cu in the granitoids necceassry for the formation of the Dahutang W-Cu deposit.The estimation of magmatic H₂ O indicate that these granitoid magmas are rich in H₂O（>4.0%）, which inevitably reach water saturation and dissolve the ore-forming fluids when they ascend upwards. The estimated f O₂ increased with successive emplacement of magmas that formed heterogranular granite and biotite-granite porphyries with time. Such changing in f O₂ resulted in early-stage W enrichment and mineraization related to heterogranular granite and late-stage Cu enrichment and mineralization related to biotite-granite stocks.The Dahutang granitoid rocks show geochemical affinity with collision-related granitoids, but formed in intra-continent environment in East China. Lithosphere thinning is reagrded to trigger melting of the Neoproterozoic crustal basament.