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.
Minor and trace elements in bornite and associated Cu–(Fe)-sulfides: A LA-ICP-MS studyBornite mineral chemistry
Abstract In situ laser ablation inductively-coupled mass spectroscopy (LA-ICP-MS) has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying Cu-sulfides from 12 deposits with emphasis on syn-metamorphic Cu–vein systems in Norway, and skarn, porphyry and epithermal systems in SE Europe. Bornite contains significant concentrations of both Ag and Bi, especially in the vein and skarn deposits studied and has the potential to be a major Ag-carrier in such ores. Concentrations of up to >1 wt.% of both elements are documented. Measured concentrations appear to be independent of whether discrete Ag- and/or Bi-minerals are present within the analyzed sulfide. Where bornite and chalcocite (or mixtures of Cu-sulfides) coexist, Ag is preferentially partitioned into chalcocite over co-existing bornite and Bi is partitioned into the bornite. Bornite is a relatively poor host for Au, which mimics Ag by being typically richer in coexisting chalcocite. Most anomalous Au concentrations in bornite can be readily tracked to micron- and submicron-scale inclusions, but bornite and chalcocite containing up to 3 and 28 ppm Au in solid solution can be documented. Selenium and Te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample. Selenium distributions show some promise as a vector in exploration, offering the possibility to track a fluid source. Bornite and chalcocite are poor hosts for a range of other elements such as Co, Ni, Ga and Ge, etc. which have been reported to be commonly substituted within sulfides. Hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary (supergene) bornite.
Archaeology and mud wall decay in a West African village
Abstract A detailed study of the processes of deterioration of mud walls and of the physical evolution and devolution of a contemporary West African village is seen to facilitate the location of decayed mud structures at a nearby archaeological site. Various climatic and pedological conditions at the site make it unlikely that such walls will be discerned. The archaeologist wishing to obtain the fullest and least biased picture of the settlement configuration of the ancient community should therefore heed all the inferential lessons to be had from a focused ethnographic investigation. Given similar climatic situations and practices of house construction, taphonomy and ethnographic analogies may both be necessary for a valid reconstruction of an archaeological settlement.