The zircon U-Pb age and geochemical characteristics of ore-bearing granite in the Niuduo graphite deposit eastern Tibet

There may be a crystalline graphite ore belt from Chaya to Zuogong in eastern Tibet, which has great potential for prospecting.Three graphite orebodies were discovered from north to south, i.e., Niuduo, Diguo and Qingguo.The latest geological survey shows that the Niuduo graphite deposit is expected to reach the scale of large-scale deposits, but the theoretical research work remains very insufficient.In this paper, based on the basic geological characteristics of the mining area, the authors studied the petrology, petrogeochemistry and zircon U-Pb chronology of the ore-bearing rock mass.The results show that the ore-bearing granite has the characteristics of K-rich, peraluminium, calc-alkaline S-type granite, and the REE distribution curve is right-inclined LREE enrichment type, with obvious LREE fractionation and obvious negative Eu anomaly.Trace element characteristics show that high field strength elements such as Nb, Ba, Sr, P and Ti are deficient, especially Ti, while large ion lithophile elements such as Rb, K and U are relatively enriched.Zircons in the samples have obvious oscillatory zones with high Th/U ratios(generally higher than 0.4), suggesting typical magmatic zircons.The ²⁰⁶Pb/²³⁸U age of zircons determined by LA-ICP-MS is 258.1+1.9 Ma, MSWD=3.5(n=35), and the age of zircons is Late Permian.Geochemistry shows that the Niuduo granite originated from partial melting of continental crustal complex sandstone, and the diagenetic temperature was relatively high.It may have been formed by collisional orogeny resulting in crustal thickening, warming and remelting.