Lithogeochemical techniques using immobile elements

Abstract

Elements of demonstrated immobility in hydrothermal alteration and metamorphism provide useful lithogeochemical parameters for mineral exploration in greenstone terranes. They yield precise identifications of precursor volcanic rock type and magmatic affinity, and quantitative estimates of mass, volume and mineralogical changes. Immobile incompatible elements (Zr, Y, Nb, REE) establish affinities, and monitor fractionation of compatible elements in tholeiitic and transitional volcanic suites. Mass changes in mobile components can be determined for a homogeneous rock unit or a continuous volcanic series. Mass change results also bear directly on the interpretation of REE profiles in altered rocks. Normative calculations allow chemical analyses to be portrayed as alteration minerals, which are also useful in interpreting oxygen isotope data. Immobile element techniques produce a large number of parameters that can be illustrated on maps and diagrams, and otherwise used in exploration. Usage of these techniques brings deeper insight to the evolution of volcanic stratigraphy and the hydrothermal processes that formed the alteration zones and ore deposits.