Advanced Identification and Quantification of In-Bearing Minerals by Scanning Electron Microscope-Based Image Analysis
Abstract The identification and accurate characterization of discrete grains of rare minerals in sulfide base-metal ores is usually a cumbersome procedure due to the small grain sizes (typically <10 μm) and complex mineral assemblages in the material. In this article, a new strategy for finding and identifying indium minerals, and quantifying their composition and abundance is presented, making use of mineral liberation analysis (MLA) and electron probe microanalysis (EPMA). The method was successfully applied to polymetallic massive sulfide ores from the Neves-Corvo deposit in Portugal. The presence of roquesite and sakuraiite could be systematically detected, their concentration quantified by MLA measurements, and their identity later confirmed by EPMA analyses. Based on these results, an almost complete indium deportment could be obtained for the studied samples. This validates the approach taken, combining automated mineralogy data with electron microprobe analysis. A similar approach could be used to find minerals of other common minor and trace elements in complex base-metal sulfide ores, for example Se, Ge, Sb, or Ag, thus permitting the targeted development of resource technologies suitable for by-product recovery.
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.
Heat Recovery Systems
Geothermal energy is recovered from an underground zone of relatively hot strata via a borehole into which is inserted a heat pipe system containing a working fluid, the heat pipe system comprising an assembly of two tubes in concentric relation, the inner tube being constituted by a relatively small diameter capillary for the return of working fluid to the vicinity of the zone of the relatively hot strata. The working fluid is preferably assisted in its return under gravity by means of a pump. The system includes heat exchange means operable to recover thermal energy from the working fluid. A third and outermost tube may be used to reduce heat losses, this third tube enclosing the two tubes over all but that part of their length which is in the zone of relatively hot strata.