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Experimental studies on Magnesite Genesis - Application to the Magnesite Deposits Associated with Ultramafic Rocks
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A series of experiments were conducted using natural samples (rock and mineral powders) as starting materials. The experimental temperatures were varied from 35° to 300°C at intervals of approximately 50°C and normal and elevated pressures (500 and 1000 bars). At higher pressures, the XCO2 in the fluid phase was also varied.
These studies have shown that magnesite and quartz can be formed directly by the interaction of CO2-bearing water vapour and ferromagnesian minerals (olivine, orthopyroxene) without passing through the intermediate serpentine stage. The temperature conditions at which these reactions take place is between 150 and 250 °C at 500 bars total pressure with XCO2 in the fluid phase greater than 0.015. The presence of Na+ salts enhances these reactions.
The presence of calcite-aragonite-quartz-aluminous hydroxide gel-limonite (birbirite) cap rock intersected by a network of magnesite veins in Dodkanya and surrounding areas has been explained on the basis of experiments with natural hornblende, the major Ca2+-bearing mineral in hornblende-peridotites. Hornblende, under hydrothermal conditions, breaks down to calcium silicate hydrate (CSH). CSH, being unstable in the presence of CO2, inverts to CaCO3 (calcite/aragonite) and quartz. Mg2+ in trace quantities stabilises aragonite.
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