Shu, Qihai, Lai, Yong, Zhou, Yitao, Xu, Jiajia, and Wu, Huaying (2015) Zircon U–Pb geochronology and Sr–Nd–Pb–Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China. Lithos, 238. pp. 64-75.

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Abstract

Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U–Pb dating, trace elements and Hf isotope, and/or whole rock Sr–Nd–Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U–Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re–Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr–Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from − 0.8 to + 10.0, restricted εNd(t) values from − 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03–18.88, (207Pb/204Pb)i = 15.48–15.58 and (208Pb/204Pb)i = 37.72–38.28, in agreement with Sr–Nd–Hf isotopes reflecting the dominance of a mantle component. An integration of geochronological and isotopic data points to three stages of Mo mineralization events (i.e., Triassic, Late Jurassic, and Early Cretaceous) associated with magmas generated from three different source regions in the Xilamulun district, NE China. The variation in the origin of the magmas from which the porphyry Mo systems were generated suggests that the formation of Mo deposit lies not in the composition of magma sources. Other factors, including high magma oxygen fugacity, may have taken a fundamental role in Mo enrichment and subsequent mineralization.

Item ID:	44423
Item Type:	Article (Research - C1)
ISSN:	1872-6143
Keywords:	early cretaceous ages; Sr–Nd–Pb–Hf isotopes; oxygen fugacity; Mo deposits; Xilamulun; NE China
Funders:	National Natural Science Foundation of China (NNSFC), China Scholarship Council (CSC), Society of Economic Geologists
Projects and Grants:	NNSFC 41390443, CSC 201306010045
Date Deposited:	17 Jun 2016 05:27
FoR Codes:	04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%
SEO Codes:	84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840199 Mineral Exploration not elsewhere classified @ 50% 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
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