Behaviour of Base Metals During Partial Melting

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Introduction
This essay focuses on the Behaviour of base metals during partial melting in the upper mantle and fractional crystallization in the crustal magma. A base metal is a metal that easily oxidise and reacts with a diluted hydrochloric acid (HCL) to form hydrogen. The examples of base metals include iron, nickel, copper, zinc and lead. The Behaviour of these metals in terms of partial melting and fractional crystallization is discussed by using their partition coefficients. Partition coefficient is the ratio of concentration of an element in a mixture of a phase relative to another phase. In addition, the partition coefficient depends on pressure, the composition of the solid, the composition of the melt and the temperature (Hall, 1987). Furthermore, the Behaviour of these metals during fractional crystallization is discussed based on the results that were obtained from the study of Okataina Volcanic Center on how metals (Zn, Pb, Cu, Mo) Behaviour during crystallization and degassing of rhyolites. Then their Behaviour during partial melting is discussed based on the results that were obtained from the experiments which were done at 1.5-2.0GPa and 1300-1500ᵒC for divalent metals (Zn, Fe, Mn, Co, and Ni).
Behaviour of metals during partial melting and fractionation crystallization
Firstly, crystal fractionation is a chemical process by which the composition of magma changes due to crystallization. This is because the crystals within the magma have different compositions to the magma which leads to separation of crystals from the magma, therefore; resulting to a change of the composition of the remaining melt. Then partial melting is a process whereby a rock which is subjected to high pressure and temperature is melted in smal...

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...presence of both elements in the exsolving vapour and a vapour phase determines the ability of metals to partition out of the melt.
Conclusion
The partition coefficient of the metals with the melt determines which element will prefer to stay in the melt or move from the melt. Therefore, this describes the Behaviour of metals during partial melting and fractionation crystallization. The partition coefficient depends on pressure, the composition of the solid, the composition of the melt and the temperature. The results that are discussed above indicate that melt of are clinopyroxene rich rocks are expected to have low Mn/Fe, Co/Fe, Ni/Co, Mn/Zn and high Zn/Fe compared to peridotite(Olivine + othopyroxene) partial melts. Throughout the process of fractional crystallization the metals (Pb, Zn and Mo) partition into crystallizing minerals or remain dissolved in the melt.

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