The geometric mean concentration ratio (GMCR) as an estimator of hydraulic effects in geochemical data for elements dispersed as heavy minerals

Abstract

The Geometric Mean Concentration Ratio (GMCR), based on analysis of paired sediment samples from high- and low-energy environments, is proposed as an estimator of the variability introduced into stream sediment data by local hydraulic effects. Examples of its use, for W (dispersed as scheelite) and Sn (dispersed as cassiterite), indicate that variability attributable to hydraulic effects generally increases with grain size and density and can be reduced either by expressing results relative to a heavy mineral fraction (as in analyses of pan concentrates) or by use of finer sediment fractions. Used in orientation surveys the GMCR provides a guide to selection of optimum methods of sample collection and preparation to minimize hydraulic variability for elements dispersed in heavy minerals.