Genesis, geological significance and metallogentic potentiality of A -type granites in the Awulale area of the western Tianshan, Xinjiang

The Qunji albite porphyry contains high SiO2(65.30% similar to 76. 93%), Na2O + K2O (6. 02% similar to 9. 66%) and FeOT/MgO (6.01 similar to 21. 4) and low A(12)O(3) (9. 82%similar to 15. 64%), Ca0 (0.47%similar to 1. 84%), Mg0 (0. 13% similar to 0. 45%) and is enriched in Th, U, Ta, Zr, Hf, Ga and Y. The porphyry has high Zr (468 x10 -6 - 707 x10, Y (20. 7 x10(-6) similar to 91. 4 x 10(-6)), Nb (21. 3 x10(-6) similar to 57.7 x 10(6), Ga (11.2 x 10(-6) similar to 19. 7 x 10(-6)) and Ce (36.7 x 10(-6) similar to 98.2 x 10(-6)) concentrations. Zircons from the porphyry are calculated to have saturation temperature >880 degrees C. All of these indicate that the Qunji albite porphyry has an affinity of A -type granite. The porphyry has low I-Sr(0. 70203 similar to 0.70549) and positive ENd (t = 303 Ma) value ( +4.1 to +5.2), and the whole rock Pb isotopic compositions are plotted in the field between the mantle and lower crust, indicating that the Qunji albite porphyry is likely sourced from the lower crust. The Qunji albite porphyry is therefore ascribed to the partial melting of the lower crust that was stimulated by the underplating basaltic magma from the asthenosphere, indicating an extension setting of this region in the late Paleozoic. The Qunji albite porphyry has potential of Cu mineralization. Zircons from the albite porphyry have low Ce4+/Ce3+ (19. 5 similar to 93. 0) with a mean value of 39. 6. The presence of euhedral and subeuhedral pyrite in the matrix indicates low oxygen fugacity of magma when the porphyry formed. The Cu mineralization was likely developed in a transition from oxidized S to reduced S, indicating that the parental magma of the Qunji albite porphyry is "dry", which has little potential for economic important porphyry Cu deposit