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Contrasting trace and rare earth element characteristics in different types of Fe-Mn carbonates associated with stratiform Ag-Pb-Zn mineralization from the Lengshuikengore district, Jiangxi Province: Implication for their genesis and depositional environment

Li Qing,Jiang Shao-Yong
tate Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, PR China

In this study, we performed a systematic trace and rare earth element analysis for the bedded Fe-Mn carbonate rocks related to the stratiform Ag-Pb-Zn mineralization in the Lengshuikeng ore district, Jiangxi Province, South China. Three types of Fe-Mn carbonates are distinguished, namely, the massive, breccia, and vein types. Both carbonate and silicate fractions in the samples are analyzed for their trace and rare earth element concentrations using a step acid-leaching technique. Our results show that the carbonate fractions in the massive type samples show the lowest REE concentrations but pronounced positive Eu and Y anomalies with Eu/Eu* value from 1.3 to 6.2 and Y/Ho value from 40.1 to 59.5, and similar characteristics are also shown for the silicate fractions in the massive type samples (Eu/Eu*=1.0-6.7, Y/Ho=20.7-55.1). These REE characteristics are similar to those of Sedex type massive sulfide deposits worldwide, and we suggest that the massive type Fe-Mn carbonate rocks were likely formed from an exhalative volcanic-hydrothermal fluid feedering the depression basin of a volcanic lake. The high concentrations of redox-sensitive elements and ratios such as U/Th, V/Cr and V/V+Ni indicate a dysoxic environment for the Fe-Mn carbonate deposition. In contrast, the breccia type and vein type Fe-Mn carbonate samples show different trace and rare earth element features from those of massive type samples, and they are more similar to the volcanic rocks and magmatic-hydrothermal fluids in the Lengshuikeng ore district and may reflect strong overprinting from volcanic and sub-volcanic magmatism related to the porphyry type mineralization in the district. 

Keywords:e-Mn carbonates; trace and rare earth elements; stratiform Ag-Pb-Zn orebody; Lengshuikeng ore district; South China

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