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Xie J.,Hefei University of Technology | Yang X.,Hefei University of Technology | Sun W.,CAS Guangzhou Institute of Geochemistry | Du J.,Anhui Academy of Geological Survey
Lithos | Year: 2012

The Tongling district in the Lower Yangtze River belt is one of the most important Cu-polymetal producers in China. Copper-Au deposits in the region are closely related to Early Cretaceous dioritic intrusions, which can be classified into three rock associations: pyroxene diorite-pyroxene monzodiorite, quartz diorite-quartz monzodiorite and granodiorite. The dioritic rock series (SiO 2=54.6-64.5wt.%) are calc-alkaline, with high Al 2O 3 (>15.4wt.%), Ba (Ba>700ppm) and Sr concentrations (~920ppm in average), and low Y and Yb concentrations, all of which are typical for adakite. Geochemical characteristics suggest that the Tongling adakitic rocks are genetically related to slab melting and subsequent interaction with the mantle, likely during a ridge subduction along the Lower Yangtze River Belt in the Early Cretaceous. Geothermometers show high formation temperatures of 800-900°C, which is consistent with interaction with the asthenosphere mantle as indicated. The relatively low ε Nd(t) values (-11.2 to -16.7) and high ( 87Sr/ 86Sr) i ratios (0.7067 to 0.7095) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The Tongling dioritic rocks are characterized by high radiogenic Pb isotopes with ( 206Pb/ 204Pb) i=17.80-18.56, ( 207Pb/ 204Pb) i=15.46-15.60, and ( 208Pb/ 204Pb) i=37.92-38.48, which mostly plot in the field of MORB, near the intersection of EM-1 and EM-2, and are clearly different from those of the upper and lower continental crust and Dabie adakites. These exclude major contamination from the continental crust. Given that eastern China has both EM-1 and EM-2 types of enriched mantle, whereas the Tongling region is located near the transition from EM-1 to EM-2, the enriched Sr-Nd isotopic characteristics of Tongling adakites are best explained by slab melts with assimilation of enriched mantle components. © 2012. Source


Xie J.,CAS Guangzhou Institute of Geochemistry | Xie J.,Hefei University of Technology | Sun W.,CAS Guangzhou Institute of Geochemistry | Du J.,Anhui Academy of Geological Survey | And 4 more authors.
Journal of Asian Earth Sciences | Year: 2013

Permian manganese ore deposits are widely distributed in southwestern and eastern China. Guichi Permian manganese district in southern Anhui Province, central eastern China, is currently the most important manganese metal producers in eastern China. Manganese ores (MnO=18.2-45.4wt.%) in Guichi region occur in calcareous, argillaceous and siliceous Mn-bearing sequence of the Permian Gufeng Formation. In contrast to Mn-bearing rocks, the ores have higher Mn, Fe, P, Sr (more than 1500ppm) and Ni contents (>480ppm), higher Mn/Fe (>5) and Lan/Cen (>2) values, and lower Co/Ni (<0.05) ratios. The Guichi manganese deposits also have low Co/Ni (<1) and Co/Zn ratios, low in total REE contents (mostly<100ppm) with negative Eu (0.46-0.75) and Ce (0.42-0.76) anomalies. The mineralogy and geochemistry of manganese deposits in the Guichi region strongly indicate hydrothermal activities, which is supported by high paleotemperatures (49-71°C) of Permian Mn-carbonate ore and Mn-bearing carbonate. The low Ceanom. values (<-0.1) and high strontium contents indicate that the Guichi manganese deposits were formed in high-salinity and oxidative marine sedimentary environment. The Al2O3/TiO2 (9.23-48.2) and Y/Ho (25.9-44.4) ratios, REE patterns, δ13CV-PDB (-10.2‰ to 5.00‰) and δ18OSMOW (20.7-28.0‰) characteristics of Permian manganese deposits reveal a mixed Mn source of volcanic, terrigenous and organic matter. © 2013 Elsevier Ltd. Source

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