Re-equilibration of fluid inclusions in crystals takes place by loss or gain of solvents and solutes from fluid inclusions and by changes in their volumes. Volume change of fluid inclusions are primarily dictated by e...Re-equilibration of fluid inclusions in crystals takes place by loss or gain of solvents and solutes from fluid inclusions and by changes in their volumes. Volume change of fluid inclusions are primarily dictated by elastic properties and available slip planes of host crystals. In the present study, the phase-behavior of fluids entrapped in co-precipitated calcite and barite is studied. While calcite contains only biphase fluid inclusions, barite has predominantly monophase fluid inclusions. Fluid inclusion petrography, microthermometry and leachate analysis are used to establish the nature of entrapped fluids and entrapment temperature is substantiated through independent sulfur isotope geothermometry using coexisting barite and pyrite. Phase transitions in the monophase fluid inclusions in barite are explained in terms of over-pressuring of fluids in these fluid inclusions relative to fluids entrapped in calcite owing to the low bulk modulus of barite.展开更多
The Damiao Fe-Ti-P deposit,located within the Damiao anorthosite complex in northeastern China,features Fe-Ti oxide ores and nelsonites that occur as irregularly inclined stratiform-like bodies,lenses,or veins with sh...The Damiao Fe-Ti-P deposit,located within the Damiao anorthosite complex in northeastern China,features Fe-Ti oxide ores and nelsonites that occur as irregularly inclined stratiform-like bodies,lenses,or veins with sharp contacts against anorthosite and gabbronorite.This deposit is characterized by abundant titanomagnetite that hosts diverse ilmenite exsolution textures,including blocky,lamellar,and cloth-like forms.In this study,we investigate the geochemistry and mineralogy of ilmenite exsolutions in titanomagnetite to understand their formation mechanisms and implications for the ore-forming process.Detailed petrographic observations and electron microprobe analyses reveal that the exsolution textures result from multiple mechanisms:oxy-exsolution due to titanomagnetite oxidation;subsolidus re-equilibration between magnetite and ilmenite involving elemental diffusion of Fe,Ti,Cr,Co,and Ni;and exsolution related to lattice defects caused by rapid cooling.Thermodynamic modeling using Gibbs free energy calculations,and the QUILF program indicates that blocky,lamellar,and cloth-textured ilmenite exsolutions formed at temperatures above and below the solid-solution solvus under decreasing oxygen fugacity.Additionally,our results indicate that the exsolution of zircon and pleonaste at ilmenite grain boundaries is attributed to the saturation and precipitation of elements like Zr and Al,due to the oxidation of titanomagnetite,rather than interactions between ilmenite and adjacent clinopyroxene.Reconstruction of the cooling history suggests that the oxygen fugacity of oxide-apatite gabbronorites was significantly higher than that of Fe-Ti-P ores.This confirms that increasing oxygen fugacity during magma evolution promoted immiscibility,leading to the formation of nelsonitic melts and ultimately the development of Fe-Ti-P ores.展开更多
The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area ...The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area where the WNW-trending compression-shear type fault of the Indosinian epoch intersected the NE-trending tenso-shear type fault of the Yanshanian epoch. The orebody appeared in a chambered or wedged form. The mineral composition is relatively complex. On the southeastern border of the orefield there have developed intermediate-acid anatectic magmatites of the Mesozoic Era. Three-phase inclusions (Lco2, Vco2 and LNaCl-H2O) comprise over 50%, associated with vapor phase consisting of H2O, CO2, CO, CH4, N2 and H2. The ore-forming fluids can be divided into 2 stages (the early and the late). The samples are projected in the area of mixture of initial magmatic and meteoric water on the δD-δ18O diagram, suggesting two types of mineralization, i.e. the re-equilibrated magmatic-hydrothermal type and the circulating geothermal water type of a meteoric water source. The mineralization occurring in this orefield might be a superimposition of 2 tectono-magmatic activities (the Indosinian and Yanshanian movements). Therefore, it is considered a superimposed B-S type gold orefield.展开更多
基金support by the mining geologists of the Geology and Exploration Division of the HGML at Hutti
文摘Re-equilibration of fluid inclusions in crystals takes place by loss or gain of solvents and solutes from fluid inclusions and by changes in their volumes. Volume change of fluid inclusions are primarily dictated by elastic properties and available slip planes of host crystals. In the present study, the phase-behavior of fluids entrapped in co-precipitated calcite and barite is studied. While calcite contains only biphase fluid inclusions, barite has predominantly monophase fluid inclusions. Fluid inclusion petrography, microthermometry and leachate analysis are used to establish the nature of entrapped fluids and entrapment temperature is substantiated through independent sulfur isotope geothermometry using coexisting barite and pyrite. Phase transitions in the monophase fluid inclusions in barite are explained in terms of over-pressuring of fluids in these fluid inclusions relative to fluids entrapped in calcite owing to the low bulk modulus of barite.
基金funded by the National Natural Science Foundation of China(grant 42102094)Natural Science Foundation of Hebei(Grant D2022402028).
文摘The Damiao Fe-Ti-P deposit,located within the Damiao anorthosite complex in northeastern China,features Fe-Ti oxide ores and nelsonites that occur as irregularly inclined stratiform-like bodies,lenses,or veins with sharp contacts against anorthosite and gabbronorite.This deposit is characterized by abundant titanomagnetite that hosts diverse ilmenite exsolution textures,including blocky,lamellar,and cloth-like forms.In this study,we investigate the geochemistry and mineralogy of ilmenite exsolutions in titanomagnetite to understand their formation mechanisms and implications for the ore-forming process.Detailed petrographic observations and electron microprobe analyses reveal that the exsolution textures result from multiple mechanisms:oxy-exsolution due to titanomagnetite oxidation;subsolidus re-equilibration between magnetite and ilmenite involving elemental diffusion of Fe,Ti,Cr,Co,and Ni;and exsolution related to lattice defects caused by rapid cooling.Thermodynamic modeling using Gibbs free energy calculations,and the QUILF program indicates that blocky,lamellar,and cloth-textured ilmenite exsolutions formed at temperatures above and below the solid-solution solvus under decreasing oxygen fugacity.Additionally,our results indicate that the exsolution of zircon and pleonaste at ilmenite grain boundaries is attributed to the saturation and precipitation of elements like Zr and Al,due to the oxidation of titanomagnetite,rather than interactions between ilmenite and adjacent clinopyroxene.Reconstruction of the cooling history suggests that the oxygen fugacity of oxide-apatite gabbronorites was significantly higher than that of Fe-Ti-P ores.This confirms that increasing oxygen fugacity during magma evolution promoted immiscibility,leading to the formation of nelsonitic melts and ultimately the development of Fe-Ti-P ores.
文摘The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area where the WNW-trending compression-shear type fault of the Indosinian epoch intersected the NE-trending tenso-shear type fault of the Yanshanian epoch. The orebody appeared in a chambered or wedged form. The mineral composition is relatively complex. On the southeastern border of the orefield there have developed intermediate-acid anatectic magmatites of the Mesozoic Era. Three-phase inclusions (Lco2, Vco2 and LNaCl-H2O) comprise over 50%, associated with vapor phase consisting of H2O, CO2, CO, CH4, N2 and H2. The ore-forming fluids can be divided into 2 stages (the early and the late). The samples are projected in the area of mixture of initial magmatic and meteoric water on the δD-δ18O diagram, suggesting two types of mineralization, i.e. the re-equilibrated magmatic-hydrothermal type and the circulating geothermal water type of a meteoric water source. The mineralization occurring in this orefield might be a superimposition of 2 tectono-magmatic activities (the Indosinian and Yanshanian movements). Therefore, it is considered a superimposed B-S type gold orefield.
