The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trac...The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trace the skarn evolution.Petrographic evidence for replacement of garnet and magnetite by ilvaite in the early retrograde stage(Stage I)combined with thermodynamic modeling suggests that the alteration may have occurred at 400470°C under moderately high fO withΔlgfO(HM)ranges from 4 to 4.2.The model is based on a maximum 22 pressure of 50 MPa calculated from magmatic amphibole geobarometer.The continuous breakdown of ilvaite with quartz to form ferro-actinolite and magnetite occur in the late retrograde stage(Stage II).The reactions occurred at 400440°C under moderate fO(ΔlgfO(HM):4 to 4.4).In Stage III,the breakdown of ilvaite to form calcite,pyrite 22 and ferroactinolite depends on XCO which can be estimated to be in a range of 0.005 to 0.05,and the reaction would 2 occur at higher temperatures with increasing XCO.Under these conditions,the breakdown occurs at 270350°C and 2 low fO(ΔlgfO(HM):up to 5.2).The thermodynamic model for continuous evolution from Stage I to Stage III 22 completely records the conditions of the retrograde alteration,which is inconsistent with the thermobarometry imprints of fluid inclusions.Therefore,the petrography and phase relations of ilvaite are useful indicators of reaction conditions in various skarn deposit types.展开更多
Based on the analyses of Loss-on-Ignition （LOI）, carbonate content and sediment characteristics, this paper reconstructs the climatic and environmental evolution of the Gahai lake area since the late Last Deglacial ...Based on the analyses of Loss-on-Ignition （LOI）, carbonate content and sediment characteristics, this paper reconstructs the climatic and environmental evolution of the Gahai lake area since the late Last Deglacial Period. The results cover the late Last Deglacial Period and the Holocene. The climate was very unstable and rather arid during the late Last Deglacial Period. The Holocene can be divided into three periods： the early Holocene （11360-8240 cal aB. P. ）, which was dry but unstable and featured rising temperatures, the mid-Holocene （8240-3200 cal aB. P. ）, which was warm and wet and the late Holocene （ since 3200 cal aBP）, which was cold and dry. Results also show a warm-wet event around 1500 cal aB. P.展开更多
基金Projects(41172076,41802080)supported by the National Natural Science Foundation of ChinaProject(1212011085528)supported by Geological Survey Program from the China Geological Survey+3 种基金Project(2019CX035)supported by Innovation-driven Plan of Central South University,ChinaProject(201411025)supported by the Scientific Research Fund from Ministry of Land and Re-sources,ChinaProject(201309)supported by the Program of High-level Geological Talents,ChinaProject(201112)supported by the Youth Geological Talents of the China Geological Survey
文摘The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trace the skarn evolution.Petrographic evidence for replacement of garnet and magnetite by ilvaite in the early retrograde stage(Stage I)combined with thermodynamic modeling suggests that the alteration may have occurred at 400470°C under moderately high fO withΔlgfO(HM)ranges from 4 to 4.2.The model is based on a maximum 22 pressure of 50 MPa calculated from magmatic amphibole geobarometer.The continuous breakdown of ilvaite with quartz to form ferro-actinolite and magnetite occur in the late retrograde stage(Stage II).The reactions occurred at 400440°C under moderate fO(ΔlgfO(HM):4 to 4.4).In Stage III,the breakdown of ilvaite to form calcite,pyrite 22 and ferroactinolite depends on XCO which can be estimated to be in a range of 0.005 to 0.05,and the reaction would 2 occur at higher temperatures with increasing XCO.Under these conditions,the breakdown occurs at 270350°C and 2 low fO(ΔlgfO(HM):up to 5.2).The thermodynamic model for continuous evolution from Stage I to Stage III 22 completely records the conditions of the retrograde alteration,which is inconsistent with the thermobarometry imprints of fluid inclusions.Therefore,the petrography and phase relations of ilvaite are useful indicators of reaction conditions in various skarn deposit types.
文摘Based on the analyses of Loss-on-Ignition （LOI）, carbonate content and sediment characteristics, this paper reconstructs the climatic and environmental evolution of the Gahai lake area since the late Last Deglacial Period. The results cover the late Last Deglacial Period and the Holocene. The climate was very unstable and rather arid during the late Last Deglacial Period. The Holocene can be divided into three periods： the early Holocene （11360-8240 cal aB. P. ）, which was dry but unstable and featured rising temperatures, the mid-Holocene （8240-3200 cal aB. P. ）, which was warm and wet and the late Holocene （ since 3200 cal aBP）, which was cold and dry. Results also show a warm-wet event around 1500 cal aB. P.
