Geological characteristics and metallogenic potential of Paleocene granodiorite in Azhaxiang, southern Gangdese, Xizang

The Gangdese magmatic arc belt in Xizang is an important copper producing area in China. The Azhaxiang study area is located in the eastern part of South Gangdese porphyry copper belt, an area of extensive Paleocene magmatism. However, the relationship of Paleocene magmatism to copper mineralization and the metallogenic potential of the Paleocene rocks is not well understood. A better understanding of the nature of the Paleocene magmatism is important to guide prospecting in this area. In this paper, we analyzed the magmatic origin, petrogenesis, and tectonic setting of the Azhaxiang granodiorite using geochronology, petrochemistry, and zircon isotopes combined with oxygen fugacity to analyze the metallogenic potential. LA-ICP-MS zircon U-Pb dating results show that the pluton was formed in the Paleocene (64.55±0.93 Ma). The rocks are calcalkaline, and the average REE (including Y) is 94.01×10⁻⁶, enriched in K, U, Rb, Ba and LREEs, depleted in Nb, Ta, Ti, Zr and HREEs, without obvious negative Eu anomalies. The average Rb/Sr and Nb/Ta is 0.20 and 11.89 respectively. The ε_Hf(t) value is +10.7~+13.3, the t_DM2 is 285.5~453.4 Ma, I_A=490, I_T=484. The crystallization temperature of zircon in the pluton is about 700℃, which indicates that the magma originated from the partial melting of the newborn crust in the subduction environment, and a small amount of mantle material added. It has typical characteristics of I-type granite. It is inferred that it was formed in the island margin arc tectonic setting before compression and subduction collision. Combined with the contribution of high oxygen fugacity, mantle, and fluid, it shows that the area has good metallogenic potential for deep-seated copper and gold resources.