Physicochemical Control of the Early Permian Xiangshan Fe-Ti Oxide Deposit in Eastern Tianshan (Xinjiang), NW China

• Published in: Journal of earth science (Wuhan, China) Vol. 29; no. 3; pp. 520 - 536
• Main Authors: Shi, Yu, Wang, Yuwang, Wang, Jingbin, Zhao, Lutong, Xie, Hongjing, Long, Lingli, Zou, Tao, Li, Dedong, Zhou, Guochao
• Format: Journal Article
• Language: English
• Published: Wuhan China University of Geosciences 01.06.2018; Springer Nature B.V; Beijing Institute of Geology for Mineral Resources, Beijing 100012, China; School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China%Beijing Institute of Geology for Mineral Resources, Beijing 100012, China%Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China
• Subjects: Ablation; Biogeosciences; Cerium; Concentrates (ores); Copper; Earth and Environmental Science; Earth Sciences; Fractionation; Fugacity; Gabbro; Gabbros; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Ilmenite; Iron; Laser ablation; Lasers; Lava; Magma; Melts; Mineral Deposits; Mineralization; Nickel; Permian; Plagioclase; Ratios; Rock; Rocks; Solidus; Sulfide; Sulphides; Titanium; Trace elements; Zircon; China; geochemistry; layered intrusion; eastern Tianshan; zircon U-Pb age; gabbros; magmatic Fe-Ti oxide deposits
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-017-0969-4

The Xiangshan mafic-ultramafic complex is one of the major Early Permian mafic-ultramafic intrusions in eastern Tianshan (Xinjiang, NW China), and consists of two major intrusive phases. The first intrusive phase is mainly gabbroic rocks hosting ilmenite mineralization, while the second intrusive phase is mainly lherzoilite associated with Ni-Cu sulfide mineralization. The Xiangshan ilmenite orebodies hosted in the Fe-Ti oxide-bearing gabbro occur along the contact between hornblende gabbros and leucogabbros. The hornblende gabbros and Fe-Ti oxide rich gabbros at Xiangshan are newly dated to be Early Permian (280.1 and 279.2 Ma, respectively). Major and trace element compositions of zircons and whole rocks from Xiangshan hornblende gabbro and Fe-Ti oxide gabbro have been measured by in situ excimer laser ablation ICP-MS. Zircon Ce 4+ /Ce 3+ ratios based on lattice-strain model and Ti-in-zircon temperatures of hornblende gabbro and Fe-Ti oxide gabbro of the Xiangshan complex are calculated to evaluate the physicochemical variations during the ilmenite mineralization. Whole-rock geochemistry and zircon trace element geochemistry suggest that Fe-Ti oxide gabbros were formed from a basaltic parent magma which had undergone a transfromation from being H 2 O-rich to H 2 O-poor. During the magmatic evolution, primitive, H 2 O-poor basaltic melts may have been replenished into the system, increasing its solidus temperature and decreasing its oxygen fugacity and H 2 O contents. This may have supperessed the Ti-rich poikilitic hornblende fractionation and promoted the plagioclase fractionation, which consequently concentrated the ore-forming components in the residual melts and generated the ilmenite mineralization.