Petrogenesis And Metallogenic Implications Of Late Cretaceous Granites In Dachang–Kunlunguan Ore Belt,Guangxi Province,China

The southwestern part of the South China Block one of the major Sn,W and Cu metallogenic provinces related to Mesozoic granitoid suites.However,the genetic relationship between and the magmatic suites and metallogeny is not well–constrained.Here we evaluate the petrogenesis and mineralization significance of Cretaceous granites from the Dachang–Kunlunguan ore belt in the eastern part of the province with the methods of regional geology,petrology,mineralogy,petrogeochemistry,zircon trace elements,U-Pb dating and Lu-Hf isotopes,obtaining the the following conclusions:This belt includes biotite granites formed at ca.98⁹7 Ma in the Kunlunguan Cu and W ore field,and the alkali–feldspar granites emplaced at ca.92 Ma at the Dachang Sn deposit.These granites are formed in an extensional setting.Zircon grains in the Kunlunguan biotite granites show?Hf?t?values ranging from-11.0 to-1.2 and the rocks have lower P₂O₅ contents?0.12⁰.18 wt.%?and ASI values?1.00to 1.14?,consistent with the features of I–type granites.In contrast,the Dachang alkali–feldspar granites are strongly peraluminous?ASI=1.29¹.44?with high P₂O₅contents?0.25⁰.34 wt.%?and the zircons in these rocks show?Hf?t?values ranging from-6.5 to-2.1,comparable to S–type granites.Based on the geochemical features,the Kunlunguan I–type granites are interpreted to have formed through the mixing components of the crust and the mantle.In contrast,the geochemical signature of the Dachang granites indicate partial melting of a metasedimentary source including psammitic and pelitic components.The Dachang S–type granites display high values of DI and FeO_T/MgO,low ratios of La/Yb,Zr/Hf and Nb/Ta and strongly negative Sr,Ba and Eu anomalies,suggesting that they are highly fractionated granites.Kunlunguan I–type granites are mostly unfractionated and show depletion in P and Ta with high Nb/Ta ratios?7.4¹2.1?,while Dachang S–type granites are enriched in P and Ta with low Nb/Ta ratios?<5?,indicating that magmatic–hydrothermal transition played a vital control on the enrichment of partial HFSEs in the strongly peraluminous magmas.The Kunlunguan I–type granites have high zircon Ce⁴⁺/Ce³⁺ratios?100¹000?which indicate high oxygen fugacity,explaining the formation of W and Cu mineralization.The highly fractionated Dachang S–type granites show magmatic–hydrothermal transition and low oxygen fugacity(Ce⁴⁺/Ce³⁺<100),which facilitated formation of the world-class Sn deposit.