Petrogenesis of the quartz diorite from the Lietinggang-Leqingla Pb-Zn-Fe-Cu-(Mo) deposit in southern Tibet: Implications for the genesis of a skarn-type polymetallic deposit in the Tibetan-Himalayan collisional orogen

Abstract

The Lietinggang-Leqingla deposit is a representative skarn-type polymetallic deposit in the eastern of the central Lhasa subterrane. It comprises Pb-Zn and Fe-Cu-(Mo) mineralization that are part of the same metallogenic system. Garnet-skarn hosting Fe-Cu-(Mo) mineralization distributed in the contact zone between the Jubuzhari complex intrusions and carbonate strata of the Mengla Formation. The Pb-Zn mineralization is hosted in distal garnet-pyroxene and pyroxene-actinolite skarns, which formed in the strata of Mengla Formation. Here, we investigate quartz diorites (61.06 ± 0.93 Ma) that are related to Fe-Cu mineralization in the northern part of the mining area. The quartz diorites are characterized by low SiO2 (61.57–65.88 wt%), low K2O (2.53–3.07 wt%), and high total alkali (Na2O + K2O) contents (5.69–6.35 wt%). They are enriched in large-ion lithophile elements and light rare earth elements, but depleted in high field strength elements and heavy rare earth elements. The quartz diorites yield variably low (La/Yb)N ratios (4.29–7.07, the average value is 6.36) with moderately negative Eu anomalies (Eu/Eu* = 0.49–0.72). Furthermore, they exhibit a narrow range in (87Sr/86Sr)i ratios (0.706355–0.706807) and weakly negative εNd (t) (−2.08 to −1.57), and positive εHf (t) (+0.14 to +3.46) values. Based on the geochemical characteristics presented in this study and previously published data, we propose that the ore-forming rocks related to Fe-Cu and Pb-Zn mineralization were formed at the same time. The intermediate intrusions associated with Fe-Cu mineralization were derived from partial melting of lithospheric mantle mixed with the rejuvenated lower crustal melts, after which the mixed magma underwent minor fractional crystallization during upwelling. The felsic intrusions associated with Pb-Zn mineralization were formed by melting of mantle-derived basaltic magmas with old lower crust component contributions and which underwent extensive fractional crystallization.