Application of near infrared sensors to preconcentration of hydrothermally-formed copper ore

Article© 2015. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Near infrared sensors can be a very useful technique for the qualitative analysis of complex ores, and thus could be useful for the preconcentration of ores. In this paper, individual particles of hydrothermally-formed copper ore sampled from a mine in the Los Pozos mining district, northern Chile, were classified as product, middling and waste based on their near infrared response. The classification of copper bearing minerals (product) from gangue (waste) was considered for vibration combination bands at longer wavelengths from 2000 to 2400 nm. This region exhibits characteristic features for carbonates and hydroxyl gangue bearing minerals. The near infrared features at 1400 and 1900 nm were not considered favourable for classification and subsequent discrimination because they can be influenced by moisture and other environmental factors and are easily suppressed by iron-rich minerals. Two near infrared preconcentration strategies were applied for particle discrimination. Results indicate that targeting only the calcite (carbonate) dominated particles for discrimination as waste provided the best option for preconcentration. The near infrared discrimination analysis correlates well with mineralogical (QEMSCAN® and XRD) and elemental (XRF) data classification. The results indicate that near infrared spectroscopy is a suitable preconcentration method for supergene copper ore

Petrographic features as an effective indicator for the variation in strength of granites

AcceptedArticlethis is the author’s version of a work that was accepted for publication in Engineering Geology. A definitive version was subsequently published in Engineering Geology, http://dx.doi.org/10.1016/j.enggeo.2016.01.001The textural characteristics of four different granites from the lower Himalayan regime in north-western Pakistan have been examined in relation to their effect on the mechanical nature of rock. Detailed petrographic examination and subsequent quantitative QEMSCAN analysis provide better understanding of the difference between their textures. Three of the granite types are slightly altered (Grade-II) whereas the other has a higher degree of alteration and corresponds to alteration Grade-III. The mechanical properties determined for each granite type include: unconfined compressive and tensile strength, elastic modulus, P-wave velocity, Schmidt hardness and dry density. Statistical analyses, combined with post-test petrography, demonstrate textural control on mechanical properties. The important petrographic characteristics influencing mechanical behaviour include modal concentration and grain size of individual minerals, mean grain size of rock and distribution of grain size within a rock. Recrystallization of minerals along boundaries has a pronounced effect on increased strength of granites. Texture, however, has a significant influence on the variation of strength of granites with similar alteration grade.Commonwealth Scholarship Commission, U

Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1–2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10–50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110–220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement

Crystal mush dykes as conduits for mineralising fluids in the Yerington porphyry copper district, Nevada

Porphyry-type deposits are the world’s main source of copper and molybdenum and provide a large proportion of gold and other metals. However, the mechanism by which mineralising fluids are extracted from source magmas and transported upwards into the ore-forming environment is not clearly understood. Here we use field, micro-textural and geochemical techniques to investigate field relationships and samples from a circa 8 km deep cross-section through the archetypal Yerington porphyry district, Nevada. We identify an interconnected network of relatively low-temperature hydrothermal quartz that is connected to mineralised miarolitic cavities within aplite dykes. We propose that porphyry-deposit-forming fluids migrated from evolved, more water-rich internal regions of the underlying Luhr Hill granite via these aplite dykes which contained a permeable magmatic crystal mush of feldspar and quartz. The textures we describe provide petrographic evidence for the transport of fluids through crystal mush dykes. We suggest that this process should be considered in future models for the formation of porphyry- and similar-type deposits

QEMSCAN® automated mineralogical analysis of PM2.5 and PM4: a preliminary study of underground coal mine dust from Poland and Slovenia

Determining the physical and chemical properties of airborne dusts in occupational settings is essential for assessing their potential toxicity as well as the effectiveness of respiratory protective equipment and dust mitigation measures. Here, we report the first successful QEMSCAN® automated mineralogical analysis of potentially toxic PM4 and PM2.5 dust from deep coal mines in Poland and Slovenia. QEMSCAN® was setup to automatically delimit 100,000 ‘particles’ per sample, based on average atomic number contrast, subject these to X-ray elemental analysis at points in a grid pattern (0.5 µm spacing), assign a mineral name to each point and then output the results as particle size, shape, mineralogy and mineral associations data and as mineral maps. The dusts were prepared as dispersions on a polyethylene sheet so that coal particles, with a slightly higher BSE signal, could be recognized from their substrate. Samples were analyzed repeatedly and in different orientations to determine the effects of sample geometry and topography. QEMSCAN® mineral identifications were manually checked using standard SEM X-ray elemental analysis. From a pilot study of Polish and Slovenian coal dust samples, PM4 and PM2.5 contain varying proportions of coal, quartz and other silicates, sulphides, sulphates, carbonates, oxides and other minerals, and notable concentrations of fly-ash particles. That some of these components may be toxic when inhaled, particularly the quartz and fly-ash, highlights the need for larger scale and wider ranging studies. The further potential of the newly developed QEMSCAN® methodology is discussed.European Union funding: 75420

The fusion crust of the Winchcombe meteorite: a preserved record of atmospheric entry processes

Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity.Science and Technology Facilities Council (STFC): ST/V000799/

Late Cretaceous (Maastrichtian) shallow water hydrocarbon seeps from Snow Hill and Seymour Islands, James Ross Basin, Antarctica

Fossil hydrocarbon seeps are present in latest Cretaceous (Maastrichtian) volcaniclastic shallow shelf sediments exposed on Snow Hill and Seymour Islands, James Ross Basin, Antarctica. The seeps occur in the Snow Hill Island Formation on Snow Hill Island and are manifest as large-sized, cement-rich carbonate bodies, containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves. These bodies have typical seep cement phases, with δ13C values between 20.4 and 10.7‰ and contain molecular fossils indicative of terrigenous organic material and the micro-organisms involved in the anaerobic oxidation of methane, including methanotrophic archaea and sulphate-reducing bacteria. On Seymour Island the seeps occur as micrite-cemented burrow systems in the López de Bertodano Formation and are associated with thyasirid, solemyid and lucinid bivalves, and background molluscan taxa. The cemented burrows also have typical seep cement phases, with δ13C values between 58.0 and 24.6‰. There is evidence from other data that hydrocarbon seepage was a common feature in the James Ross Basin throughout the Maastrichtian and into the Eocene. The Snow Hill and Seymour Island examples comprise the third known area of Maastrichtian hydrocarbon seepage. But compared to most other ancient and modern seep communities, the James Ross Basin seep fauna is of very low diversity, being dominated by infaunal bivalves, all of which probably had thiotrophic chemosymbionts, but which were unlikely to have been seep obligates. Absent from the James Ross Basin seep fauna are ‘typical’ obligate seep taxa from the Cretaceous and the Cenozoic. Reasons for this may have been temporal, palaeolatitudinal, palaeobathymetric, or palaeoecological

Visualisation, quantitative mineralogy and matrix-inclusion separation of pottery using QEMSCAN: examples of medieval and post-medieval pottery from Somerset

AcceptedPublished as chapter in Sibbeson E, Jervis B, Coxon S (eds), Insights from Innovation: New Light on Archaeological Ceramics, St Andrews, The Highfield Press, 97-117. ISBN 9780992633646abstract not availabl

An imported flanged rimsherd discovered on the early medieval site of Kilree 3, Ireland: a study in archaeological deposition and provenance using automated SEM-EDS analysis (QEMSCAN)

The investigations presented here were prompted by the discovery of a red slip flanged rimsherd at the site of an Early Medieval double enclosure at Kilree 3, near Kilkenny town in the southeast of Ireland, in 2008. The sherd's initial classification as African Red Slip Ware (henceforth ARSW) Form 91C was based on its distinctive profile (see Kelly 2010; also independently identified by Doyle - 2009, 19), representative of the classic African flanged bowl, and on its fine red fabric. ARSW Form 91C was produced in northern Tunisia, in the 6th century AD, where it constituted a late form in the lengthy production series of ARSW. Considering the ensuing distance between the bowl's source of production and its final depositional context (in which it stands out as an exotic import), a detailed examination of the sherd's fabric (including Polarised Light Microscopy, Laser Raman Spectroscopy and automated SEM-EDS using QEMSCAN technologies) was conducted to verify the bowl's suspected origin. These investigations sought to identify the component minerals, to quantify their proportions and to highlight textures through compositional mapping. The results of the mineralogical studies are presented here with a view to contributing to the emerging narrative instigated by the discovery of the sherd and to allow for further comparative studies within the growing corpus of such fabric analyses.2021-07-15 JG: PDF resubmitte