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The skarn type copper deposits are widespread in the Jiurui district in the Middle-Lower Yangtze River metallogenic belt. This paper reports a detailed study on mineral chemistry, and H, O, S and Pb isotopic compositions on skarn silicate and sulfide minerals in the three major skarn dominant deposits (Wushan, Dongleiwan and Dengjiashan). The Wushan skarn deposit is characterized with prograde garnet-dominated and clinopyroxene limited skarns with average andradite content of 83% and hedenbergite content of 10%, whereas the Dongleiwan and Dengjiashan deposits are featured with retrograde skarn alteration with abundant hydrous minerals such as epidote and chlorite. The garnet and clinopyroxene compositions show 59% andradite and 15% hedenbergite for the Dongleiwan skarns, and 43% and 22% for the Dengjiashan skarns respectively. The pistacite components (Ps value) defined as Fe 3 + /(Fe 3 + + Al) and Fe 3 + /Fe 2 + value of epidote are 0.12 and 1.63 for the Wushan skarns, 0.30 and 32.73 for the Dongleiwan skarns, and 0.17 and 42.85 for the Dengjiashan skarns. It is suggested that the prograde skarn mineralization in the three deposits was all formed in a relatively oxidizing environment, with the Wushan showing the highest oxidation potential and the Dengjiashan having the least oxidation potential. However, in the retrograde skarns, the Dongleiwan and Dengjiashan deposits show higher oxidation potential than that of Wushan. The three deposits show similar sulfur isotopic compositions of − 2.9 to + 1.4‰ and similar lead isotopic compositions with 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios of 17.900 to 18.205, 15.538 to 15.649 and 38.170 to 39.025, respectively. All the three deposits should have similar magmatic origin for the ore-forming materials based on their S and Pb isotopes. The oxygen isotopic compositions of the prograde and retrograde fluids in the three deposits show some differences, with δ 18 O Fluid values of + 8.13‰ and + 7.81‰ for the Wushan, + 6.47‰ and + 2.33‰ for the Dongleiwan, and + 8.27‰ and + 4.43‰ for the Dengjiashan. But the hydrogen isotopic compositions are similar for the prograde (− 65 to − 31‰) and retrograde (− 64 to − 33‰) fluids. Therefore, the fluid origins and evolution may be different in each deposit. The hydrothermal fluids for the prograde skarns in all three deposits were likely derived from magmatic–hydrothermal sources, but the Dongleiwan and Dengjiashan show a higher proportion of meteoric water input in the retrograde stage. Considering the similar average prograde temperatures (574 to 560 °C) as calculated from coexisting garnet–clinopyroxene pairs, and similar retrograde temperatures (281 to 246 °C) as calculated from chlorite chemistry for the three deposits, we suggest that the trigger for deposition of sulfide ores in the Wushan garnet-dominated skarn deposit was mainly caused by system cooling with temperature drop along with magmatic intrusion and crystallization process. The Dongleiwan and Dengjiashan skarn deposits constitute a well developed retrograde skarn system with abundant epidote, chlorite, quartz and calcite, which probably caused by fluid mixing of high-temperature saline magmatic–hydrothermal fluids with cooler, oxidizing and dilute meteoric water. [ABSTRACT FROM AUTHOR]

A mineralization zone exists in the Middle and Lower Yangtze River (MLYR) region. Previous studies have shown that this zone might be caused by the rich ejection of magma in the Mesozoic. We have applied the teleseismic tomography method to determine a 3-D P-wave velocity structure of the mantle down to 500km depth beneath this region by using 14,740 P-wave arrival times collected from 519 teleseismic events recorded by 46 portable and 47 static seismic stations located in this region. The relative residual times used for the tomography are calculated by the modified multi-channel cross-correlation method which increases not only the efficiency but also the data precisions up to 0.01s. The grid space is set as 1°×1° horizontally and 50–100km vertically. Our tomographic results show that the lithosphere with high velocity anomalies is separated into two parts: one locates above the depth of 100km and the other at the depths between 250km and 400km, and the asthenosphere with low velocity anomalies locates between these two parts of lithosphere, which indicates that the lithosphere delaminated together with the asthenosphere upwelling. The detachment of lithosphere might relate to the subduction of the western Pacific slab. Therefore, our study provides clear evidence to geoscientists for understanding the deep dynamic process beneath this region and a three-stage geodynamic process is developed based on the new evidence. [ABSTRACT FROM AUTHOR]