A Discussion on Genetic Mechanism of the Kuerqis Iron Deposit in Fuyun County, Xinjiang

The large iron deposits in the southern margin of Altay had been studied systematically, but researches on some small Fe-rich type such as Kuerqis iron deposit are still obviously insufficient. In this paper, a study of the chronology and genetic mechanism to supply basic information for regional metallogeny and mineral assessment is documented. The Kuerqis iron deposit is located in the Erqis tectonic belt in the southern margin of Altay. The field investigation suggests that the deposit is dominantly related to hydrothermal activity of granitic porphyry besides the volcanic sedimentary genesis, meanwhile the iron deposit was destroyed by monzonitic granite. The ages of two granite intrusions in the deposit area and S isotope composition of pyrites in ore were determined by Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS) and MAT 251 EM Mass Spectrograph. The ²⁰⁶Pb/²³⁸U ages of 18 data points of zircons in granitic porphyry concentrated on the concordia line range from 273 Ma to 282.6 Ma and the weighted average age is (278.7±0.94) Ma with MSDW=1.6. The ²⁰⁶Pb/²³⁸U ages of 12 data points of zircons in monzonitic granite concentrated on the concordia line range from 271.8 Ma to 276.8 Ma and the weighted average age is (274.1±1.1) Ma with MSDW=0.47. δ³⁴S in pyrites varies from -7.2‰ to 0.7‰ and most are negative and near 0. The characteristic of δ³⁴S perhaps reflects the significant exchange of S isotope between magma from deep source and wall-rocks or the earlier sedimentary iron deposit during ascending magma. The mineralization prominently occurred in the hydrothermal period of granitic porphyry. Combined with former studies, it suggested that two granite intrusions in the deposit area intruded in a plate extension environment during the early-Permian when granite intrusions developed widely in the southern margin of Altay. Moreover, the extensive mineralization of iron and other elements perhaps occurred in this granitic event.