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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-Fe_2O_3-NaCl-HCl-H_2O.The effects of T,P,pH,fo_2 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 logfo_2=-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 fo_2 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.
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. Irroncentration of the ore solution has been estimated from the ratio of hematite to quartz. and the thermodynamic data, the solubility of ferro-minerals atelevated temperatures and pressures have been calculated in the system FeO-Fe_2O_3-NaCl-HCl-H_2O.The effects of T, P, pH, fo_2 and total Cl concentration on the solubility of ferro- minerals are discussed. Thermoodynamic calculations based on presumed physieo-chemical conditions for the ore solution are in good agreement. with geological observations. calcifications shows that ferro-minerals were deposited at logfo_2 = -21 ~ -25, log ( mHCl + mH +) = -2.5 ~ -3, P = 1-0.75 (or 0.5) kb, and T = 400-350 ° C.It is believed that the original solution was an acid NaCl-bearing solution of magmatic derivation. However, iron in the solution wasenriched with falli ng temperatures by dissolving pre-existing ferro-minerals in consolidated rocks rather than extracting directly from the magma. Either temperature (below 400 ° C) 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 on pH. The widespread siliceous veins of lasterstages are a reflection of decreasing acidity of the solution. Increase in fo_2 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