Genesis of the Lakang'e porphyry Mo (Cu) deposit, Tibet: Constraints from geochemistry, geochronology, Sr-Nd-Pb-Hf isotopes, zircon and apatite

The Lakang'e porphyry Mo (Cu) deposit, intermediate to large in size, is located in the eastern part of the southern Gangdese metallogenic belt. It is associated with a Miocene granodiorite porphyry (GDP). The alteration styles are mainly potassic and phyllic alteration, with minor argillic, chlorite, and carbonation alteration. In this study, we present whole-rock geochemical compositions, zircon LA-ICP-MS U-Pb data, zircon Hf isotope analyses, and zircon and apatite major and trace element compositions for the ore-bearing GDP and postmineralization quartz diorite porphyry (QDP) to constrain the formation of the Lakang'e Mo (Cu) deposit. The ore-bearing GDP, with a zircon U-Pb age of 13.83 0.20 Ma, was intruded after mineralization by the QDP, which was emplaced at 13.00 +/- 0.16 Ma. The GDP and QDP are high-K calc-alkaline series rocks with adakite-like features characterized by high contents of K2O and Al2O3, high Sr/Y ratios, strongly fractionated REE patterns, LILE enrichment, and HFSE depletion. The GDP and QDP have relatively low (Sr-87/Sr-86)i values (0.7051-0.7054) and high epsilon Nd(t) values (-0.87 to 0.59). Zircon grains from the QDP have high epsilon Hf(t) values (7.0-9.6), while zircon grains from the GDP show large epsilon Hf(t) variations ranging from -4 to 9.6, indicating that the magma source of the orebearing GDP included more continental crust than that of the postmineralization QDP. The zircon Ce4+/Ce3+ and Eu/Eu* ratios and apatite Mn and SO3 contents indicate that the postmineralization QDP had higher oxygen fugacity than the ore-bearing GDP. The oxygen fugacity of the ore-bearing magma present during apatite crystallization (generally below the Ni-Ni-O (NNO) buffer), was lower than that present during zircon crystallization (above the hematite-magnetite (HM) buffer). The F, Cl, and S contents in apatite show that the GDP and QDP were F and S rich and that the GDP had a higher F content than the QDP. A high oxygen fugacity, a Fand Srich magma and a Mo-rich crustal source were the key factors for the formation of the Lakang'e porphyry Mo (Cu) deposit. (C) 2020 Published by Elsevier B.V.

Automated summary

The Lakang'e porphyry Mo (Cu) deposit is located in the eastern part of the southern Gangdese metallogenic belt, with mainly potassic and phyllic alteration styles. The ore-bearing GDP and postmineralization QDP show differences in geochemical compositions and formation ages, indicating a more continental crust source for the GDP. Oxygen fugacity, fluorine and sulfur richness, and a molybdenum-rich crustal source were crucial factors for the formation of the deposit.