Assessing Hydrothermal Alteration Effects on Bulk-Rock Geochemisry

Abstract

An important step in studying volcanic processes is to understand the sequences along which the magmas evolve. Chemical variations within a group of major and trace elements are usually the result of magma evolution processes. The majority of the trends observed for these two groups of elements against the differentiation index clearly demonstrate that the magma modification process is dominated by crystal-liquid segregation. Studies of the chemical changes imposed on the volcanic rocks from the study well has been vital in quantifying element mobility. The latter has proved to be an important tool in getting a better understanding of the hydrothermal alteration processes affecting the volcanic rocks from well OW-910. The concept of scattering of elemental concentration has proved that some mobilisation has occurred and this principle can successfully be applied, though to a limited extent, to equally assess the effects of hydrothermal alteration on both major and trace element geochemistry. It has been satisfactorily established that mobile elements display some leaching by hydrothermal fluids, even though the degree varies. Immobile elements, on the other hand have remained relatively inert, thus do not appear to be affected by fluid components of alteration processes.