Heavy Minerals in Provenance Studies

Abstract

Heavy minerals are sensitive indicators of provenance. Over 30 translucent detrital species are of common occurrence, many of which have characteristic parageneses. However, because they are also sensitive to the processes of weathering, transportation, deposition and diagenesis, the heavy-mineral suite of an arenite does not necessarily accurately reflect the source-area mineralogy. In most cases, the effects of weathering at source and transportation are minor, but hydraulic controls at the time of deposition and subsequent diagenesis (intrastratal solution) can cause major modifications. Hydraulic effects may be countered by the determination of hydraulic ratios or by using only those minerals whose proportionns are not granunalize controlled, as shown by scatter plots. Intrastratal solution is diagnosed by grain-surface etching and by the occurrence of more diverse suites in lowpermeability units (eg concretions, shales) compared with adjacent friable sands; different diagenetic settings are characterised by different orders of mineral stability. The most effective method to counteract problems of intrastratal solution, and indeed of hydraulic controls, is to examine the varieties of one mineral species (a 'varietal study') because this minimises density and stability contrasts. Varietal studies may be addressed either by the classical methods of optical differentiation, or by more sophisticated techniques such as cathodoluminescence, radiometric dating, or particularly electron microprobe analysis.