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Zhao H.,Chinese Academy of Geological Sciences | Xie G.,Chinese Academy of Geological Sciences | Wei K.,Geological Team of Southeast Hubei Province | Ke Y.,Geological Team of Southeast Hubei Province
International Geology Review | Year: 2012

The Tonglushan Cu-Fe deposit (1.12 Mt at 1.61% Cu, 5.68 Mt at 41% Fe) is located in the westernmost district of the Middle-Lower Yangtze River metallogenic belt. As a typical polymetal skarn metallogenic region, it consists of 13 skarn orebodies, mainly hosted in the contact zone between the Tonglushan quartz-diorite pluton (140 Ma) and Lower Triassic marine carbonate rocks of the Daye Formation. Four stages of mineralization and alterations can be identified: i.e. prograde skarn formation, retrograde hydrothermal alteration, quartz-sulphide followed by carbonate vein formation. Electron microprobe analysis (EMPA) indicates garnets vary from grossular (Ad 20.2-41.6Gr 49.7-74.1) to pure andradite (Ad 47.4-70.7Gr 23.9-45.9) in composition, and pyroxenes are represented by diopsides. Fluid inclusions identify three major types of fluids involved during formation of the deposit within the H 2O-NaCl system, i.e. liquid-rich inclusions (Type I), halite-bearing inclusions (Type II), and vapour-rich inclusions (Type III). Measurements of fluid inclusions reveal that the prograde skarn minerals formed at high temperatures (>550°C) in equilibrium with high-saline fluids (>66.57 wt.% NaCl equivalent). Oxygen and hydrogen stable isotopes of fluid inclusions from garnets and pyroxenes indicate that ore-formation fluids are mainly of magmatic-hydrothermal origin ( 18O = 6.68‰ to 9.67‰, δD = -67‰ to -92‰), whereas some meteoric water was incorporated into fluids of the retrograde alteration stage judging from compositions of epidote (δ 18O = 2.26‰ to 3.74‰, δD= -31‰ to -73‰). Continuing depressurization and cooling to 405-567°C may have resulted in both a decrease in salinity (to 48.43-55.36 wt.% NaCl equivalent) and the deposition of abundant magnetite. During the quartz-sulphide stage, boiling produced sulphide assemblage precipitated from primary magmatic-hydrothermal fluids (δ 18O = 4.98‰, δD = -66‰, δ 34S values of sulphides: 0.71-3.8‰) with an extensive range of salinities (4.96-50.75 wt.% NaCl equivalent), temperatures (240-350°C), and pressures (11.6-22.2 MPa). Carbonate veins formed at relatively low temperatures (174-284°C) from fluids of low salinity (1.57-4.03 wt.% NaCl equivalent), possibly reflecting the mixing of early magmatic fluids with abundant meteoric water. Boiling and fluid mixing played important roles for Cu precipitation in the Tonglushan deposit. © 2012 Copyright Taylor and Francis Group, LLC.

Xie G.,Chinese Academy of Geological Sciences | Mao J.,Chinese Academy of Geological Sciences | Zhao H.,Chinese Academy of Geological Sciences | Wei K.,Geological Team of Southeast Hubei Province | And 3 more authors.
Ore Geology Reviews | Year: 2011

The Tonglushan ore district in the Middle-Lower Yangtze River Valley metallogenic belt includes the Tonglushan Cu-Fe, the Jiguanzui Au-Cu, and the Taohuazui Au-Cu skarn deposits. They are characterized by NE-striking ore bodies and hosted at the contact of Triassic carbonate rocks and Late Mesozoic granitoid deposits. New Sensitive High-Resolution Ion Microprobe (SHRIMP) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) zircon U-Pb, molybdenite Re-Os, and phlogopite 40Ar-39Ar ages indicate that these skarn deposits formed between 140.3±1.1 and 137.3±2.4Ma. These dates are identical to the zircon U-Pb ages for host quartz diorites ranging from 140±2 to 139±1Ma. These results confirm that both skarn mineralization and related intrusions were initiated during the Early Cretaceous. The high rhenium contents (261.4-1152μg/g) of molybdenites indicate that a metasomatic mantle fluid was involved in the ore-forming process of these skarn ore systems. This conclusion is consistent with previously published constraints from sulfur, deuterium, and oxygen isotope compositions, and the geochemical signatures, and Sr-Nd isotopic data of the mineralization-hosting intrusions. Geological and geochronological evidence demonstrates that there were two igneous events in the Tonglushan ore district. The first resulted in the emplacement of quartz diorite during the Early Cretaceous (140±2 to 139±1Ma), and the second is characterized by the eruption of volcanic rocks during the mid-Early Cretaceous (130±2 to 124±2Ma). The former is spatially, temporally and genetically associated with skarn gold-bearing mineralization (140.3±1.1 to 137.3±2.4Ma). The recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the Middle-Lower Yangtze River Valley metallogenic belt. © 2011.

Zhao H.,Chinese Academy of Geological Sciences | Mao J.,Chinese Academy of Geological Sciences | Xiang J.,Chinese Academy of Geological Sciences | Zhou Z.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Petrologica Sinica | Year: 2010

Tonglushan skam Cu-Fe (Au) deposit is located in the westernmost Daye district of MYLRB. A geochemical and Sr-NdPb isotopic studies were carried out for the Tonglushan quartz diorite, which is closely related to the deposit. The compositions of plagioclases show they are oligoclase (An =21-31). Amphiboles belong to magnesihornblend, have characteristics of low Ti (<0.2) and high Mg/(Mg + Fe) (>0.5). MF values of biotites vary from 0.58 to 0.66, suggesting biotites are Mg-riched. The rocks are characterized by SiO2 and alkaline compositions between 58.86% and 67.71%, and from 5.67% to 9.63%, respectively, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), but relative depletion in Nb,Ta,Ti elements. They have initial Nd (εNd(t) = -7.65~ -3.44), Sr (( 87Sr/86Sr)i =0. 7055~0.7069) and Pb (( 206Pb/204Pb)1=17.66-18.00, ( 207Pb/204Pb)i, = 15.49-15.56, ( 208Pb/204Pb)1 =37.73-38.19). Comparative analysis demonstrates that Tonglushan and Yangxin intrusions originated from homologous magma. The magma was from the enrich mantle of about 40km deep and at about 889°C temperature. Amphiboles and biotite thermometers estimate magma crystallized at 650-800°C and 500-630°C temperatures, under 1.49kbar pressure, corresponds to the emplacement depth of about 4.9km. Magma has a high oxygen fugacity (fo2) condition, in favor of Cu, Fe and Au ore-forming elements into melt, may be related to plate subduction.

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