Ore Petrography Using Megapixel X-Ray Imaging: Rapid Insights into Element Distribution and Mobilization in Complex Pt and U-Ge-Cu Ores

• DOI: 10.2113/econgeo.111.2.487
• Publication Date: 2016-02-22T18:03:37Z
• Authors: Kan Li; Barbara Etschmann; Nicholas Rae; Frank Reith; Chris G. Ryan; Robin Kirkham; Daryl Howard; Diogo R.N. Rosa; Carla Zammit; Allan Pring; Yung Ngothai; Antony Hooker; Joël Brugger
• Keywords: Thin section; Microprobe; Trace element

Geologic samples are extremely diverse and share a tendency for both heterogeneity complexity. This is especially true ores, which commonly result from complex interplay of processes in highly dynamic environments. In recent years, number tools allowing the chemical mapping major (e.g., mineral liberation analysis, MLA), minor electron microprobe, EPMA), trace laser ablation-inductively coupled plasma-mass spectrometry, LA-ICP-MS) elements geologic at ~1- to 50- μ m resolution over mm2 areas have seen rapid development become readily available. To date, application synchrotron-based X-ray fluorescence (SXRF) has been limited addressing key questions because low availability high cost. paper demonstrates how advances detector technology bringing new possibilities ore petrology. Millisecond dwell times allow collection thin section size maps resolutions few hours, while improvements data analysis software simplify production quantitative elemental maps.

Based on imaging six representative different commodities (Pt, U, Cu, Ge) contexts (PGE deposit; sandstone-hosted U vein-type polymetallic hydrothermal iron oxide-copper-gold (IOCG) deposit), we demonstrate that megapixel SXRF (MSXRF) can efficiently provide information necessary understand metal speciation context section-scale textural Image revealed results studied deposits, example, (1) distribution micrometer-sized Pt-rich grains Ti mobility during formation schistosity Fifield Point prospect (New South Wales, Australia); (2) presence Ge contained organic matter Hg minerals associated within quartzite clasts Lake Frome ores (South (3) confirmation two-stage enrichment Barrigao deposit, with demonstration solid solution early chalcopyrite (Portuguese Iberian pyrite belt); (4) late dissolution-reprecipitation reactions bornite Moonta Wallaroo IOCG deposits Australia). These illustrate MSXRF powerful technique locating nano- microparticles precious metals (Pt) contaminants Hg) form distinct (micro) minerals. addition, it tool understanding relatively grades (100–1,000 ppm; e.g., Ge).