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In-situ mineral chemistry and chronology analyses of the pitchblende in the Shazijiang uranium deposit and their implications for mineralization TEXT SIZE: A A A
In-situ analyses are important techniques in earth science researches. However, these techniques are rarely used in hydrothermal uranium deposits in South China, which restrain the understanding of the metallogenies of hydrothermal uranium deposits. The Shazijiang uranium deposit is a famous granite-type (hydrothermal) uranium deposit in South China, but the mineral chemistry and chronology characteristics of uranium minerals are still obscure. This paper revealed the mineral chemistry and chronology of the pitchblende (uraninite) of the Shazijiang uranium deposit, by using EPMA, LA-ICP-MS and SIMS. The effects of alternation on the chemistry and chemical age of the pitchblende are discussed as well. The results of EMPA show that the pitchblende is characterized by high contents of uranium and calcium, but extremely low contents of ThO2 and rare earth elements, indicating the pitchblende was precipitated from a low-temperature hydrothermal fluid, which was characterized by high Ca ions. A comparative study of unaltered and altered pitchblende shows that alteration can cause a large amount of silicon to enter the pitchblende, replacing the uranium and lead. However, the apparent age or chemical age of the pitchblende is significantly affected by its alteration. The SIMS U-Pb age dating of the pitchblende obtained an age of 101. 4 +/- 5Ma, indicating that there is an early uranium metallogenic event of about 100Ma in Shazijinag uranium deposit. The results of LA-ICP-MS show that the pitchblende is characterized by low total amount of rare earth elements. But the chondrite-normalized patterns of rare earth elements are rich in light-REE, with obvious negative Eu anomalies. It is indicated that the uranium source rocks may be the Douzhashan wall rock granite. The extension of the lithosphere caused the upwelling of the mantle fluid which interacted with the deep uranium-rich granite, forming a uranium-rich hydrothermal fluid. The Shazijiang uranium deposit formed due to the precipitation of the pitchblende in the structural fracture zone.
 

Publication name

 ACTA PETROLOGICA SINICA, 35 (9):2679-2694; 10.18654/1000-0569/2019.09.04 2019

Author(s)

 Chen YouWei; Hu RuiZhong; Luo JinCheng; Dong ShaoHua

Corresponding author(s) 

 HU Ruizhong 
 huruizhong@vip.gyig.ac.cn  
 Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550081, Guizhou, Peoples R China
 Univ Chinese Acad Sci, Coll Earth & Planetary Sci, Beijing 100049, Peoples R China

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