Insights into hydrothermal controls and processes leading to the formation of the Late Ediacaran Gaoyan stratiform manganese-carbonate deposit, Southwest China

• DOI: 10.1016/j.oregeorev.2021.104524
• Publication Date: 2021-10-14T15:04:46Z
• Authors: Zhaofu Gao; Xiangkun Zhu; Dan Wang; Chenxu Pan; Bin Yan; Jin Li
• Keywords: Rhodochrosite; Carbonate minerals; Terrigenous sediment

The stratiform Mn-carbonate ore from the Gaoyan deposit occurs within terrigenous-sedimentary rocks of upper part Ediacaran Doushantuo Formation and is characterized by rhodochrosite spherulites. Here we examine effect depositional environment hydrothermal contribution based on new petrographical, mineralogical geochemical data to shed light major controls formation sedimentary Mn mineralization. significant characteristics such as high Mn/Fe ratios (average 32.07), Ba content 1940.9 ppm), positive Eu anomalies 1.38) low REE contents 51 ppm) reveal a source. Meanwhile, 87Sr/86Sr ores are substantially higher than those carbonate wall contemporaneous seawater, indicating mixing radiogenic Sr Mn-rich extraction underlying sediments. This explanation supported linear correlation between anomalies. slightly Ce anomaly most samples mirrored in negative black shale, while different provide evidence that redox cycling took place across sub-oxic anoxic/euxinic water interface. euxinic conditions, evidenced co-occurrence fine-grained disseminated pyrite framboidal aggregates diameters <5 μm) with rhodochrosite, can account for via ongoing Fe-sulfide precipitation. Calcite introduction metal-rich waters lower pH relative surface waters, together Mn-oxide reduction sulfate reduction, triggers substantial increases saturation precipitation near water–sediment Subsequently, increasing Ca2+ early diagenesis resulted kutnohorite rims. Altogether, develop model mineralization spherulites mineral phases, forming during diagenesis. Slightly carbon isotope compositions (∼–6.1‰) manganese normal dolostones (∼–4.8‰) suggest limited source oxidation organic material methanogenesis processes burial supports direct redox-stratified columns means may be mainly controlled contribution, rather seawater conditions. exploration strategies focus oxic zone alone an indication prospectivity ineffective.