Thermodynamic Limitation Of Formation Conditions Of Ophiolite Chromite Deposite

As an important raw material for producing stainless steel products,chromite affects national production and economy.The proven reserves of chromite in China account for only one-thousandth of the world,and the prospecting of chromite is becoming increasingly urgent.If you want to find chromite smoothly,you must first understand the principle of chromite mineralization.In the past,Chromite is classified as a magmatic deposit.And the formation mechanism of ophiolite chromite is believed to be explained by the melt-rock reaction model,but the product of melt coagulum is not observed in the field.This paper believes that a large number of geological phenomena indicate that the fluid plays an important role in the formation of podiform chromite.The fluid's low viscosity and strong permeability can make up for the defects in the melt-rock model.The new fluid-rock model needs substance and data support.By observing the field characteristics of the Luobusha ophiolite-type podiform chromite in Tibet,collecting samples and observing under petrographic microscope to divide different phases.According to the observation under the microscope,the sample was analyzed by electronic probe to obtain the data to identify the original minerals in the phase zone and the minerals produced after the reaction.The two processes of fluid and rock reaction can be roughly summarized according to the contact relationship between the original mineral and the reacte mineral and the data of the electronic probe.One is the reaction of harzburgite and fluid to produce dunite and chromite.Second,the ore-lean fluid after the reaction precipitates and crystallizes at low temperature and pressure to generate low-temperature minerals.These two processes can establish detailed reaction equations based on mineral composition and mineral relationship.By looking for the applicable thermodynamic equations under high temperature and pressure and the thermodynamic parameters of the pure minerals of the main reaction,the temperature and pressure at the equilibrium of each reaction equation can be calculated.According to the equilibrium temperature and pressure data of each equation,a temperature-pressure curve can be drawn to summarize the temperature and pressure range where the two processes of fluid and rock reaction are located.Combining the previously analyzed reaction process and the characteristics of the generated mineralization can confirm the rationality of the temperature and pressure range calculated by thermodynamics.By establishing a thermodynamic model,a fluid-rock reaction model can be initially established.