On the Conditions of Formation of Gushan Iron Ore Deposit

【摘要】 <正> On the basis of its geological characteristics,the Gushan iron deposit should be assignedto voleano-hydrothermal type with hematite-quartz as its principal mineral assemblage.Ironconcentration of the ore solution has been estimated from the ratio of hematite to quartz inthe ore.By using experimental and thermodynamic data,the solubility of ferro-minerals atelevated temperatures and pressures have been calculated in the system FeO-Fe₂O₃-NaCl-HCl-H₂O.The effects of T,P,pH,fo₂ and total Cl concentration on the solubility of ferro-minerals are discussed.Thermodynamic calculations based on presumed physieo-chemical con-ditions for the ore solution are in good agreement.with geological observations.The calcula-tion shows that ferro-minerals were deposited at logfo₂=-21～-25,log（mHCl+mH+）=-2.5～-3,P=1—0.75（or 0.5）kb,and T=400°—350℃.It is believed that the original solutionwas an acid NaCl-bearing solution of magmatic derivation.However,iron in the solution wasenriched with falling temperatures by dissolving pre-existing ferro-minerals in consolidatedrocks rather than extracting directly from the magma.Either temperature（below 400℃）orpressure decrease may result in the precipitation of ferro-minerals from the solution,but theFe/Si ratio in the ore is dependent mainly upon pH.The widespread siliceous veins of laterstages are a reflection of decreasing acidity of the solution.An increase in fo₂ will also favorthe deposition of ferro-minerals.The hypabyssal occurrence and the existence of the Huang-maqing sandy shale have contributed greatly to the formation of hematite.更多还原

【Abstract】 On the basis of its geological characteristics,the Gushan iron deposit should be assigned to voleano-hydrothermal type with hematite-quartz as its principal mineral assemblage.Iron concentration of the ore solution has been estimated from the ratio of hematite to quartz in the ore.By using experimental and thermodynamic data,the solubility of ferro-minerals at elevated temperatures and pressures have been calculated in the system FeO-Fe₂O₃-NaCl-HCl- H₂O.The effects of T,P,pH,fo₂ and total Cl concentration on the solubility of ferro- minerals are discussed.Thermodynamic calculations based on presumed physieo-chemical con- ditions for the ore solution are in good agreement.with geological observations.The calcula- tion shows that ferro-minerals were deposited at logfo₂=-21～-25,log（mHCl+mH+）=-2.5～ -3,P=1—0.75（or 0.5）kb,and T=400°—350℃.It is believed that the original solution was an acid NaCl-bearing solution of magmatic derivation.However,iron in the solution was enriched with falling temperatures by dissolving pre-existing ferro-minerals in consolidated rocks rather than extracting directly from the magma.Either temperature（below 400℃）or pressure decrease may result in the precipitation of ferro-minerals from the solution,but the Fe/Si ratio in the ore is dependent mainly upon pH.The widespread siliceous veins of later stages are a reflection of decreasing acidity of the solution.An increase in fo₂ will also favor the deposition of ferro-minerals.The hypabyssal occurrence and the existence of the Huang- maqing sandy shale have contributed greatly to the formation of hematite.更多还原