Abstract
Many analytical techniques for trace element analysis are available to the geochemist and geometallurgist to understand and, ideally, quantify the distribution of trace and minor components in a mineral deposit. Bulk trace element data are useful, but do not provide information regarding specific host minerals—or lack thereof, in cases of surface adherence or fracture fill—for each element. The CAMECA nanoscale secondary ion mass spectrometer (nanoSIMS) 50 and 50L instruments feature ultra-low minimum detection limits (to parts-per-billion) and sub-micron spatial resolution, a combination not found in any other analytical platform. Using ore and copper concentrate samples from the Olympic Dam mining-processing operation, South Australia, we demonstrate the application of nanoSIMS to understand the mineralogical distribution of potential by-product and detrimental elements. Results show previously undetected mineral host assemblages and elemental associations, providing geochemists with insight into mineral formation and elemental remobilization—and metallurgists with critical information necessary for optimizing ore processing techniques. Gold and Te may be seen associated with brannerite, and Ag prefers chalcocite over bornite. Rare earth elements may be found in trace quantities in fluorapatite and fluorite, which may report to final concentrates as entrained liberated or gangue-sulfide composite particles. Selenium, As, and Te reside in sulfides, commonly in association with Pb, Bi, Ag, and Au. Radionuclide daughters of the 238U decay chain may be located using nanoSIMS, providing critical information on these trace components that is unavailable using other microanalytical techniques. These radionuclides are observed in many minerals but seem particularly enriched in uranium minerals, some phosphates and sulfates, and within high surface area minerals. The nanoSIMS has proven a valuable tool in determining the spatial distribution of trace elements and isotopes in fine-grained copper ore, providing researchers with crucial evidence needed to answer questions of ore formation, ore alteration, and ore processing.
Highlights
IntroductionSystematic analysis of trace elements (or isotopes) in ore samples is beneficial on multiple fronts
Systematic analysis of trace elements in ore samples is beneficial on multiple fronts.Valuable geochemical insight may be gained by detailed analysis of ore deposits at every scale, from regional trends useful for mineral exploration down to the nanoscale deportment of trace elements.The association of certain trace elemental or isotopic components in a mineralized system may aid Minerals 2019, 9, 336; doi:10.3390/min9060336 www.mdpi.com/journal/mineralsMinerals 2019, 9, 336 in determining ore genesis timelines, mineralization conditions, source rocks, and subsequent alteration via interaction with hydrothermal fluids or metamorphism—just to name a few
This study presents just a few examples of beneficial trace element/isotope analyses, including examples of both geochemical and economic interest
Summary
Systematic analysis of trace elements (or isotopes) in ore samples is beneficial on multiple fronts. Advantages include multicollection capabilities (seven detectors on the 50L instrument at the Centre for Microscopy, Characterisation, and Analysis (CMCA) in Perth, Western Australia); interchangeable ion sources (Cs+ for organics and anions, O− for most cations); mass resolution to 0.1 atomic mass unit (amu); low minimum detection limits; and excellent spatial resolution ( to 40 nm). Applications include 34 S/32 S in sulfides and sulfates (e.g., References [13,14], 18 O/16 O in meteorites (e.g., Reference [15]), 13 C/12 C and 15 N/14 N in biological samples (e.g., Reference [16]), and 207 Pb/206 Pb dating of zircon and baddeleyite [17] In this contribution, we document how nanoSIMS mapping represents a scale-appropriate analytical technique that can provide an advanced understanding of the physical state of trace elements of interest in complex ores and their processing materials. These are, in turn, a necessary pre-requisite for future extraction of potential by-products and for efforts to reduce or eliminate deleterious components in final concentrates
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