Efficient and Accurate Identification of Platinum-Group Minerals by a Combination of Mineral Liberation and Electron Probe Microanalysis with a New Approach to the Offline Overlap Correction of Platinum-Group Element Concentrations

Abstract

Identification and accurate characterization of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding PGMs and quantifying their composition was developed. It combines a mineral liberation analyzer (MLA), a point logging system, and electron probe microanalysis (EPMA). As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that the combination of MLA, point logging, and EPMA results in the identification of a significantly higher number of PGM grains than reflected light microscopy. Analysis of PGMs by EPMA requires considerable effort due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements. X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.

Advanced Identification and Quantification of In-Bearing Minerals by Scanning Electron Microscope-Based Image Analysis

“…All quantitative analyses were performed with a focused beam at an accelerating voltage of 20 kV and a beam current of 30 nA. Interferences of the Cd–Lβ1 and Sn–LN-lines on the In–Lα line were corrected using the offline correction approach described in Osbahr et al (2015). For matrix corrections, the atomic number–absorption–fluorescence (ZAF) approach was used (Philibert, 1963; Reed, 1965; Philibert & Tixier, 1968).…”

New insights into the petrogenesis of the Jameson Range layered intrusion and associated Fe-Ti-P-V-PGE-Au mineralisation, West Musgrave Province, Western Australia

“…Magnetite, diopside and olivine from the same supplier were measured during the analytical runs to monitor instrumental drift. Mutual interferences were corrected for Zn Lβ 1 on Na Kα 1,2 , V Kβ 1,3 on Cr Kα 1 and Ti Kβ 1,3 on V Kα 1 using the offline overlap correction method of Osbahr et al (2015). Correction factors were determined with 0.0656, 0.0939 and 0.0449, respectively.…”

Record and provenance of Pleistocene volcaniclastic turbidites from the central Lesser Antilles (IODP Expedition 340, Site U1398B)

“…Matrix corrections were applied using the ZAF method. An additional correction was made for the peak overlap following the procedure described in Osbahr et al (2015). Corrections were made for the following overlaps: VKα by TiKβ1,3, FKα by FeLβ1, FKα by FeLN, FKα by CoLN and CrKα by VKβ1,3.…”