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Russian Geology and Geophysics

2015 year, number 8

EVOLUTION OF MAGMATIC-HYDROTHERMAL SYSTEM OF THE KALAXIANGEER PORPHYRY COPPER BELT AND IMPLICATIONS FOR ORE FORMATION ( Xinjiang, China)

Gao Jinggang1,2, Li Wenyuan2, Xue Chunji3, Tu Qijun4, Zhao Zhanfeng3, Yang Wenping5, Li Youzhu1, N.I. Volkova6
1Changan University, 126 Yanta Road., Xian 710054, China
2Xian Institute of Geology and Mineral Resources, China Geological Survey, 438 East Youyi Road, Xian 710064, China
3State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China
4Bureau of Geology and Mineral Exploration and Development, 390 East Karamay Road, Urumqi 830000, China
5No. 11 Geological Party of the Xinjiang Bureau of Geology and Mineral Exploration and Development, 5 Beijing Road, Changji 836500, China
6V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: U-Pb SHRIMP , , Re-Os , , - , SHRIMP U-Pb age, S and Pb isotopes, Re-Os isotopes, metallogenic model, Kalaxiange’er porphyry copper belt

Abstract

The Kalaxiangeer porphyry copper ore belt is situated in the eastern part of the southern Altai of the Central Asian Orogenic Belt and forms part of a broad zone of Cu porphyry mineralization in southern Mongolia, which includes the Oyu Tolgoi ore district and other copper-gold deposits. The copper ore bodies are spatially associated with porphyry intrusions of granodiorite, quartz diorite, quartz syenite, and quartz monzonite and have a polygenetic (polychromous) origin (magmatic porphyry, hydrothermal, and supergene). The mineralized porphyries are characterized by almost identical REE and trace element patterns. The Zr/Hf and Nb/Ta ratios are similar to those of normal granite produced through the evolution of mantle magma. The low initial Sr isotope ratio I Sr, varying within a narrow range of values (0.703790-0.704218), corresponds to that of primitive mantle, whereas the εNd( T ) value of porphyry varies from 5.8 to 8.4 and is similar to that of MORB. These data testify to the upper-mantle genesis of the parental magmas of ore-bearing porphyry, which were then contaminated with crustal material in an island-arc environment. The isotopic composition of sulfur (unimodal distribution of δ34S with peak values of -2 to -4) evidences its deep magmatic origin; the few lower negative δ34S values suggest that part of S was extracted from volcanic deposits later. The isotopic characteristics of Pb testify to its mixed crust-upper-mantle origin. According to SHRIMP U-Pb geochronological data for zircon from granite porphyry and granodiorite porphyry, mineralization at the Xiletekehalasu porphyry Cu deposit formed in two stages: (1) Hercynian porphyry stage (375.2 8.7 Ma), expressed as the formation of porphyry with disseminated and vein-disseminated mineralization, and (2) Indosinian stage (217.9 4.2 Ma), expressed as superposed hydrothermal mineralization. The Re-Os isotope data on molybdenite (376.9 2.2 Ma) are the most consistent with the age of primary mineralization at the Xiletekehalasu porphyry Cu deposit, whereas the Ar-Ar isotopic age (230 5 Ma) of K-feldspar-quartz vein corresponds to the stage of hydrothermal mineralization. The results show that mineralization at the Xiletekehalasu porphyry Cu deposit was a multistage process which resulted in the superposition of the Indosinian hydrothermal mineralization on the Hercynian porphyry Cu mineralization.