Implications of Major and Trace Element Migration in Altered Granites for Hydrothermal Alteration and Granite-Related Uranium Mineralization in the Sanjiu Ore Field, South China

Xu Chen,Biguang Jiang,Jinning Qin,Debao Meng,Chunhua Wen,Bin Li

doi:10.3390/min12020144

Xu Chen, Biguang Jiang + Show 4 more

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https://doi.org/10.3390/min12020144

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Abstract

The recently discovered Sanjiu ore field (SJOF) is a granite-related uranium ore field located in the middle of Zhuguangshan (South China). The relationship between hydrothermal alteration of granite and uranium mineralization in the SJOF is crucial yet understudied. In this study, the major- and trace-element contents of granite samples (fresh granite, altered granite, and tectonites) with different uranium contents were analyzed by using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma–mass spectrometry (ICP–MS). The analytical results show a relative increase in Si, S, Ca, Pb, Mo, and Sb content in altered granites and tectonites, relative to fresh granites. During the mineralization stage, the increase of the aforementioned elements is related to various hydrothermal alterations (e.g., silicification, carbonation, sulfation, etc.) and newly formed minerals (e.g., microfine crystalline quartz veins; calcite agglomerates or fine veins; and metal sulfides, such as pyrite). There is a concomitant relative decrease in Na, K, Al, Fe, Mg, and other elemental contents that may be due to mineralogical alteration processes, such as biotite to chlorite, feldspar-group minerals to clay minerals, and redox of Fe-bearing minerals. The LREE/HREE ratio in altered granites decreases significantly with the increase in uranium content, suggesting that a low LREE/HREE ratio may be a prospecting indicator. The normalized trace-element patterns of mineralized granite (ore) and the relatively high U content of fresh granite imply that granitic rocks may be the primary uranium source in the SJOF. The uranium mineralization is mainly concentrated in the redox zone that occurs at a depth of 100−300 m. The redox zone is characterized by the most developed hydrothermal alterations and enrichment of trace elements, including W, Mo, Sb, Li, and the HREE.

Highlights

The results show that the major element and U
The analysis show that the average LREE/HREE ratio of ore-bearing altered granites (OBS) (2.53) and pitchblende
We have found the the following to be true: (1) The Sanjiangkou granite with high U content (14.6–22.4 ppm) was the main U source of Sanjiu ore field (SJOF). (2) The large-scale hydrothermal alterations promoted the release and migration of active U, and the superimposed hydrothermal alterations facilitated the enrichment of U. (3) The multisource mineralizing fluid, which was rich in oxygen and uranyl U, continuously extracted and/or transferred high-abundance trace elements in granite while flowing upward along mineralizationcontrolling faults [50,51]

Summary

Introduction

The uranium (U) deposits in China are generally hosted by four types of rocks: granites, volcanic rocks, carbonaceous–siliceous–pelitic rocks, and sandstones. The granite-related U deposits comprise about 35% of the U reserves in China [1]. The Zhuguangshan composite granitic batholith (ZCGB) is an important U host in South China, as it is associated with most of the identified granitic U resources. The Sanjiu ore field (SJOF) is located in Zhuguangshan between the Lujing ore field and the Chengkou ore field in the middle of the ZCGB (Figure 1). Zhuguangshan composite granitic batholith (ZCGB) is an important U host in South

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