THE APPLICATION OF PORTABLE X-RAY DIFFRACTION TO QUANTITATIVE MINERALOGICAL ANALYSIS OF HYDROTHERMAL SYSTEMS

Abstract

X-ray powder diffraction (XRD) is a well-established tool in the study of hydrothermal systems, as it allows for the identification and quantification of mineral assemblages. Through the quantification of alteration mineral assemblages geologists can characterize the geometry of a deposit or geothermal system and draw inferences regarding the fluid evolution and environmental conditions of deposition ( e.g. , pH, T). Traditionally, XRD devices have largely been restricted to laboratories; however, advances in XRD sample holders and X-ray sources have allowed for the development of portable XRD (pXRD) devices. This paper assesses the validity of the Olympus Terra pXRD instrument for qualitative and quantitative studies of hydrothermal systems through comparisons with data from laboratory XRD (Empyrean II diffractometer) and XRF techniques for both synthetic mixtures of natural minerals and a variety of samples from the Kulumadau epithermal gold deposit, Woodlark Island, Papua New Guinea. Diffractograms of synthetic mineral mixtures with known concentrations of quartz, kaolinite, muscovite, albite, and pyrite were analyzed quantitatively using the Rietveld-based Siroquant technique and showed good overall agreement for both devices, with the exception of muscovite, which encountered accuracy issues at concentrations R 2 values of >0.92 for all major mineral phases ( i.e. , >5%). With the exceptions of pyrite and magnetite, minor to trace minerals ( i.e. ,