The Guangshigou uranium deposit, northern Qinling Orogen, China: a product of assimilation-fractional crystallization of pegmatitic magma

Yuan, Feng, Liu, Jiajun, Carranza, Emmanuel John M., Zhai, Degao, Wang, Yinhong, Zhang, Shuai, Sha, Yazhou, Liu, Gang, and Wu, Jie (2018) The Guangshigou uranium deposit, northern Qinling Orogen, China: a product of assimilation-fractional crystallization of pegmatitic magma. Ore Geology Reviews, 99. pp. 17-41.

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Abstract

Uranium mineralization associated with biotite pegmatites occurs in the Shangdan triangular domain of the northern Qinling Orogen, constituting a significant uraniferous province. The Guangshigou deposit is the most productive uranium deposit in this area. Several Caledonian intrusions were emplaced within the ore district including the Huichizi granite (HG, 441.1 +/- 1.3 Ma), Damaogou granite (DG, 420.9 +/- 1.3 Ma), biotite pegmatite (BP, 415.6 +/- 1.5 Ma), and muscovite-biotite pegmatite (MBP, 412.1 +/- 1.4 Ma). Based on uranium concentration, each BP displays two different zones, i.e., an uranium-bearing zone (UBP hosted at the contact zone) and a non-mineralized zone (NBP hosted in the non-assimilation zone). Two magmatic pulses are distinguished. The Early Silurian HG was derived from a low degree of partial melting of thickened lower basaltic crust interfused mantle-derived materials following the subduction of the Shangdan Ocean. The Late Silurian-Early Devonian intrusions exhibited the same source region but formed during the weakening of convergent action. Fractional crystallization of high-K granitic magma (DG) produced a set of fractionated pegmatites, whereas UBP deviates from a normal magma evolution trend due to country rock contamination in the hybrid zone.

Most of the U in UBP is hosted in primary uraninite. The biotite gneiss (BG) is the most favorable country rock for uranium mineralization. Bulk assimilation of country rock is driven by reactions during xenolith melting and pegmatitic magma crystallization. The mineralization occurs at the assimilation/hybrid zone, e.g., the contact zone between BP and BG, as well as the partially assimilated xenoliths.

The enrichment of contact-hosted peritectic biotite and increase of FeOT, MgO, TiO2, MnO, LILE (i.e., Rb, Ba, K), HFSE (i.e., Nb, Ta) contents and initial Sr-87/Sr-86 ratios as well as decrease of epsilon(Nd)(t) values in BP arose from chemical interaction (assimilation/hybridization) with the country rock. The reactive bulk assimilation modified the normal crystallization process of pegmatitic magma. The uranium ores are the products of the assimilation fractional crystallization of the pegmatitic magma. U-F complexes were destabilized by reducing fluorine activities during the formation of peritectic biotite in the assimilation/hybrid zone, triggering decrease of U solubility and saturation.

Item ID: 55619
Item Type: Article (Research - C1)
ISSN: 1872-7360
Keywords: Guangshigou uranium deposit, Granitic pegmatite, Biotite gneiss, Assimilation-fractional crystallization
Copyright Information: © 2018 Elsevier B.V. All rights reserved.
Funders: Major Basic Research Program of People’s Republic of China (MBRP), National Natural Science Foundation of China (NNSFC) Key Program, China Geological Survey (CGS), State Administration of Foreign Experts Affairs, China (SAFEAC), China University of Geosciences (CUG)
Projects and Grants: MBRP Grant No. 2014CB440903, NNSFC Key Program 41730426, CGS 12120114014401, SAFEAC Grant No. B07011
Date Deposited: 19 Sep 2018 09:03
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040201 Exploration Geochemistry @ 100%
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