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M. B. Mcclenaghan - One of the best experts on this subject based on the ideXlab platform.
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Indicator Mineral and geochemical signatures associated with the sisson w mo deposit new brunswick canada
Geochemistry-exploration Environment Analysis, 2017Co-Authors: M. B. Mcclenaghan, Michael A. Parkhill, A. G. Pronk, A A Seaman, Martin Mccurdy, Matthew I. LeybourneAbstract:An Indicator Mineral and geochemical case study was carried out around the Sisson W–Mo deposit to test modern Indicator Mineral and analytical methods and document glacial and fluvial dispersal from a significant W–Mo source. Indicator Minerals in the 0.25 – 2.0 mm non-ferromagnetic heavy Mineral fraction of till and stream sediments include the primary ore Minerals scheelite, wolframite and molybdenite, as well as chalcopyrite, joseite, native Bi, bismutite, bismuthinite, galena, sphalerite, arsenopyrite, pyrrhotite and pyrite. Indicator Minerals in c. 12 – 14 kg samples define glacial dispersal of at least 10 km down ice (SE) of the deposit and fluvial dispersal at least 4 km downstream. The presence of very coarse (0.5 – 2.0 mm) Indicator Minerals in till and stream sediments marks proximity (
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Indicator Mineral and geochemical signatures associated with the Sisson W–Mo deposit, New Brunswick, Canada
Geochemistry-exploration Environment Analysis, 2017Co-Authors: M. B. Mcclenaghan, Michael A. Parkhill, A. G. Pronk, A A Seaman, M W Mccurdy, Matthew I. LeybourneAbstract:An Indicator Mineral and geochemical case study was carried out around the Sisson W–Mo deposit to test modern Indicator Mineral and analytical methods and document glacial and fluvial dispersal from a significant W–Mo source. Indicator Minerals in the 0.25 – 2.0 mm non-ferromagnetic heavy Mineral fraction of till and stream sediments include the primary ore Minerals scheelite, wolframite and molybdenite, as well as chalcopyrite, joseite, native Bi, bismutite, bismuthinite, galena, sphalerite, arsenopyrite, pyrrhotite and pyrite. Indicator Minerals in c. 12 – 14 kg samples define glacial dispersal of at least 10 km down ice (SE) of the deposit and fluvial dispersal at least 4 km downstream. The presence of very coarse (0.5 – 2.0 mm) Indicator Minerals in till and stream sediments marks proximity (
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Indicator Mineral and till geochemical signatures of the Mount Pleasant W-Mo-Bi and Sn-Zn-In deposits, New Brunswick, Canada
Journal of Geochemical Exploration, 2017Co-Authors: M. B. Mcclenaghan, Michael A. Parkhill, A. G. Pronk, W.d. SinclairAbstract:Abstract A study of the till Indicator Mineral and matrix geochemical signature of the Mount Pleasant W-Mo-Bi and Sn-Zn-In deposits in New Brunswick, Canada was undertaken using commercially available methods. Indicator Minerals of the deposits include: cassiterite, wolframite, and molybdenite, as well as gangue Minerals topaz, chalcopyrite, galena, sphalerite, arsenopyrite, pyrite, and loellingite and secondary Pb Minerals beudantite, anglesite, plumboferrite, and plumbogummite in the 0.25–0.5 mm heavy Mineral (> 3.2 specific gravity) fraction, and fluorite in the 0.25–0.5 mm mid-density (3.0–3.2 specific gravity) fraction. The presence of coarse (0.5–2.0 mm) Indicator Minerals in till close ( 5 ppm are some of the highest ever reported for till.
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Application of Indicator Mineral methods to bedrock and sediments
2017Co-Authors: M. B. Mcclenaghan, D Layton-matthewsAbstract:Intrusion-centred Mineral districts host a diversity of ore deposits of variable metal associations, alteration assemblages and genesis. Porphyry systems represent particularly important exploration targets but the prioritization of conventional geochemical or geophysical anomalies that might represent a deposit, particularly when systems are buried under cover, is extremely difficult. Three key questions arise: (1) is the alteration (particularly when only a propylitic type is observed) related to a porphyry system? (2) how can the fertility of a system be assessed at an early stage of exploration in order to reduce exploration risk? and (3) how can the centre of the system (in 3 dimensions) be predicted ahead of extensive, potentially deep, drilling? These fertility and vectoring challenges have been the subject of recent work, primarily based on Mineral chemistry, in a series of AMIRA projects based out of the University of Tasmania, now also being continued at the Natural History Museum in London. The approach to assessing the presence of a possible porphyry system has been to establish Mineral chemical criteria that discriminate between porphyry and non-porphyry environments based on: (1) the composition of igneous Minerals (e.g. plagioclase, zircon, apatite, magnetite); and (2) the composition of hydrothermal alteration phases, particularly those developed in the propylitic domain (epidote, chlorite, magnetite, calcite, quartz). Many of these phases may be reworked via erosion into paleo or modern sediment transport systems and are thus available for assessment of catchment area fertility. Some of the characteristics of these Minerals may allow the distinction between extensively Mineralized and ostensibly barren environments (the system “fertility”); clearly these features are of significant exploration utility. The vectoring challenge has been addressed by the completion of numerous orientation studies on known porphyry systems to establish any systematic spatial variations in Mineral chemistry that may exist, primarily within the propylitic environment. These studies have shown that characteristic and, to variable degrees, reproducible patterns of major and trace element variation exist that allow effective vectoring towards the center of a hydrothermal system, as well as discrimination between porphyry-related and non-porphyry Mineral assemblages1,2. In particular, chlorite has proven to be particularly effective for prediction of absolute distances to the system center, even allowing estimation of the depth of a buried system. Both epidote and chlorite appear to contain signals that reflect the potential metal endowment of a system. The ability to define these characteristics of a system from a limited number of samples of distal “green rocks” marks a major step-change in the way that exploration for porphyry systems can be done. In this presentation, the approach and methodology are summarised and some of the major findings from this work are illustrated with examples from a number of porphyry systems worldwide
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Processing of glacial sediments for the recovery of Indicator Minerals: protocols used at the Geological Survey of Canada
Geochemistry: Exploration Environment Analysis, 2013Co-Authors: A Plouffe, M. B. Mcclenaghan, R C Paulen, Isabelle Mcmartin, J.e. Campbell, W.a. SpiritoAbstract:A successful method of Mineral exploration in glaciated terrain is the use of Indicator Minerals recovered from carefully selected glacial sediments, and subsequently traced back to their bedrock source. The successful application of Indicator Mineral methods relies on efficient and effective recovery as well as the correct identification of a wide variety of Indicator Minerals. The Geological Survey of Canada (GSC) has developed protocols for ongoing and future research projects to achieve the highest quality for reporting Indicator Mineral data. Such protocols include the use of field duplicate samples, blank samples, and base material spiked with known numbers, morphologies, species, and sizes of Indicator Minerals. Field duplicate samples serve to estimate sediment heterogeneity. Spiked samples are used to monitor the accuracy of the sample processing and Mineral identification methods for recovering specific Minerals. Blank samples serve to detect potential carry-over contamination. In certain instances, a specific sample processing order is essential and should be communicated to the commercial processing laboratory. Ore-rich samples collected near known Mineralization are to be processed last, to reduce chances of carry-over contamination. Repeated Indicator Mineral counts should be carried out on at least 10% of the heavy Mineral concentrates to measure reproducibility (precision) of the Mineral counts. All Indicator Mineral data, original laboratory reports, heavy Mineral concentrates, unmounted picked grains, and grain mounts are now archived at the GSC, using specific guidelines.
Noreen J. Evans - One of the best experts on this subject based on the ideXlab platform.
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lawsonite geochemistry and stability implication for trace element and water cycles in subduction zones
Journal of Metamorphic Geology, 2014Co-Authors: Laure Martin, Donna L. Whitney, Katherine F. Fornash, Jörg Hermann, Laure Gauthiezputallaz, Vitale A Brovarone, Noreen J. EvansAbstract:This contribution reviews the existing data on lawsonite stability and trace element geochemistry, and provides new data for metabasaltic and metasedimentary (quartzite) rocks from New Caledonia, Turkey and California. Lawsonite is a major host of REE, Sr, U, Th and Pb in basaltic compositions. Trace element-rich lawsonite also occurs in metasedimentary rocks, in which comparatively fewer phases compete for trace elements than in metabasaltic rocks. Trace element patterns in lawsonite are influenced by the coexistence or breakdown of allanite, titanite, apatite and garnet that compete for these elements in high-P metamorphic rocks. Lawsonite is restricted to cool geotherms and therefore is an Indicator Mineral for subduction-zone metamorphism. The lawsonite stability field shows a strong dependence on temperature and composition and it is largest in rocks with a high normative anorthite content and, in basaltic systems, carbon content. Along cold geotherms, lawsonite can transport water and trace elements to great depths, providing a source for these elements in the deep mantle. Along warmer geotherms, lawsonite disappears on a continuous reaction, gradually releasing water over a temperature interval of several tens of degrees. During lawsonite breakdown in complex systems, Th and LREE remain trapped in newly formed accessory allanite. However, owing to extreme LREE content, allanite has lower Pb/Ce and Sr/Nd than lawsonite, resulting in a relative enrichment of Sr and Pb compared with Ce and Nd in the fluids produced during lawsonite breakdown. Existing experimental data on the solidus of altered oceanic crust suggest that the lawsonite-breakdown reaction is within 50 °C of the solidus at sub-arc pressures of 3–4 GPa.
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Lawsonite geochemistry and stability – implication for trace element and water cycles in subduction zones
Journal of Metamorphic Geology, 2014Co-Authors: Laure Martin, Donna L. Whitney, Katherine F. Fornash, Jörg Hermann, Laure Gauthiez-putallaz, A. Vitale Brovarone, Noreen J. EvansAbstract:This contribution reviews the existing data on lawsonite stability and trace element geochemistry, and provides new data for metabasaltic and metasedimentary (quartzite) rocks from New Caledonia, Turkey and California. Lawsonite is a major host of REE, Sr, U, Th and Pb in basaltic compositions. Trace element-rich lawsonite also occurs in metasedimentary rocks, in which comparatively fewer phases compete for trace elements than in metabasaltic rocks. Trace element patterns in lawsonite are influenced by the coexistence or breakdown of allanite, titanite, apatite and garnet that compete for these elements in high-P metamorphic rocks. Lawsonite is restricted to cool geotherms and therefore is an Indicator Mineral for subduction-zone metamorphism. The lawsonite stability field shows a strong dependence on temperature and composition and it is largest in rocks with a high normative anorthite content and, in basaltic systems, carbon content. Along cold geotherms, lawsonite can transport water and trace elements to great depths, providing a source for these elements in the deep mantle. Along warmer geotherms, lawsonite disappears on a continuous reaction, gradually releasing water over a temperature interval of several tens of degrees. During lawsonite breakdown in complex systems, Th and LREE remain trapped in newly formed accessory allanite. However, owing to extreme LREE content, allanite has lower Pb/Ce and Sr/Nd than lawsonite, resulting in a relative enrichment of Sr and Pb compared with Ce and Nd in the fluids produced during lawsonite breakdown. Existing experimental data on the solidus of altered oceanic crust suggest that the lawsonite-breakdown reaction is within 50 °C of the solidus at sub-arc pressures of 3–4 GPa.
Laure Martin - One of the best experts on this subject based on the ideXlab platform.
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lawsonite geochemistry and stability implication for trace element and water cycles in subduction zones
Journal of Metamorphic Geology, 2014Co-Authors: Laure Martin, Donna L. Whitney, Katherine F. Fornash, Jörg Hermann, Laure Gauthiezputallaz, Vitale A Brovarone, Noreen J. EvansAbstract:This contribution reviews the existing data on lawsonite stability and trace element geochemistry, and provides new data for metabasaltic and metasedimentary (quartzite) rocks from New Caledonia, Turkey and California. Lawsonite is a major host of REE, Sr, U, Th and Pb in basaltic compositions. Trace element-rich lawsonite also occurs in metasedimentary rocks, in which comparatively fewer phases compete for trace elements than in metabasaltic rocks. Trace element patterns in lawsonite are influenced by the coexistence or breakdown of allanite, titanite, apatite and garnet that compete for these elements in high-P metamorphic rocks. Lawsonite is restricted to cool geotherms and therefore is an Indicator Mineral for subduction-zone metamorphism. The lawsonite stability field shows a strong dependence on temperature and composition and it is largest in rocks with a high normative anorthite content and, in basaltic systems, carbon content. Along cold geotherms, lawsonite can transport water and trace elements to great depths, providing a source for these elements in the deep mantle. Along warmer geotherms, lawsonite disappears on a continuous reaction, gradually releasing water over a temperature interval of several tens of degrees. During lawsonite breakdown in complex systems, Th and LREE remain trapped in newly formed accessory allanite. However, owing to extreme LREE content, allanite has lower Pb/Ce and Sr/Nd than lawsonite, resulting in a relative enrichment of Sr and Pb compared with Ce and Nd in the fluids produced during lawsonite breakdown. Existing experimental data on the solidus of altered oceanic crust suggest that the lawsonite-breakdown reaction is within 50 °C of the solidus at sub-arc pressures of 3–4 GPa.
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Lawsonite geochemistry and stability – implication for trace element and water cycles in subduction zones
Journal of Metamorphic Geology, 2014Co-Authors: Laure Martin, Donna L. Whitney, Katherine F. Fornash, Jörg Hermann, Laure Gauthiez-putallaz, A. Vitale Brovarone, Noreen J. EvansAbstract:This contribution reviews the existing data on lawsonite stability and trace element geochemistry, and provides new data for metabasaltic and metasedimentary (quartzite) rocks from New Caledonia, Turkey and California. Lawsonite is a major host of REE, Sr, U, Th and Pb in basaltic compositions. Trace element-rich lawsonite also occurs in metasedimentary rocks, in which comparatively fewer phases compete for trace elements than in metabasaltic rocks. Trace element patterns in lawsonite are influenced by the coexistence or breakdown of allanite, titanite, apatite and garnet that compete for these elements in high-P metamorphic rocks. Lawsonite is restricted to cool geotherms and therefore is an Indicator Mineral for subduction-zone metamorphism. The lawsonite stability field shows a strong dependence on temperature and composition and it is largest in rocks with a high normative anorthite content and, in basaltic systems, carbon content. Along cold geotherms, lawsonite can transport water and trace elements to great depths, providing a source for these elements in the deep mantle. Along warmer geotherms, lawsonite disappears on a continuous reaction, gradually releasing water over a temperature interval of several tens of degrees. During lawsonite breakdown in complex systems, Th and LREE remain trapped in newly formed accessory allanite. However, owing to extreme LREE content, allanite has lower Pb/Ce and Sr/Nd than lawsonite, resulting in a relative enrichment of Sr and Pb compared with Ce and Nd in the fluids produced during lawsonite breakdown. Existing experimental data on the solidus of altered oceanic crust suggest that the lawsonite-breakdown reaction is within 50 °C of the solidus at sub-arc pressures of 3–4 GPa.
Georges Beaudoin - One of the best experts on this subject based on the ideXlab platform.
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Chemical composition of tourmaline in orogenic gold deposits
Mineralium Deposita, 2020Co-Authors: Marjorie Sciuba, Georges Beaudoin, Sheida MakvandiAbstract:Tourmaline from 18 orogenic gold deposits and districts, hosted in varied country rocks and metamorphic facies, was investigated by EPMA (electron probe micro-analyzer) and LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) to establish discriminant geochemical features to constrain Indicator Mineral surveys for gold exploration. Such tourmaline most commonly belongs to the alkali group, with a dravitic composition. LA-ICP-MS results were investigated with binary plots and PLS-DA (partial least square-discriminant analysis). PLS-DA suggests that the major element composition of tourmaline from orogenic gold deposits is buffered by the hydrothermal fluid, whereas trace element composition is strongly controlled by the composition and the metamorphic facies of the country rocks. Contents of Sn, Ga, Ti, rare earth elements (REE), Zr, Hf, Nb, Ta, Th, and U vary with the metamorphic facies of the country rocks. Tourmaline from orogenic gold deposits has high contents of Sr, V, and Ni and low Li, Be, Ga, Sn, Nb, Ta, U, and Th compared to tourmaline from other deposit types and geological environments. Binary plots such as Sr/Li vs. V/Sn, Sr/Sn vs. V/Nb, Sr/Sn vs. Ni/Nb, and Sr/Sn vs. V/Be, as well as PLS-DA, discriminate tourmaline from orogenic gold deposits from that of other settings. Binary plots highlight a transitional variation in the trace element composition of tourmaline from metamorphic, to magmatic-hydrothermal, to magmatic environments.
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Trace element composition of scheelite in orogenic gold deposits
Mineralium Deposita, 2019Co-Authors: Marjorie Sciuba, Georges Beaudoin, Donald Grzela, Sheida MakvandiAbstract:Scheelite from 25 representative orogenic gold deposits from various geological settings was investigated by EPMA (electron probe micro-analyzer) and LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometer) to establish discriminant geochemical features to constrain Indicator Mineral surveys for gold exploration. Scheelite from orogenic gold deposits displays five REE patterns including a bell-shaped pattern with a (i) positive or (ii) negative Eu anomaly; (iii) a flat pattern with a positive Eu anomaly and, less commonly, (iv) a LREE-enriched pattern, and (v) a HREE-enriched pattern. The REE patterns are interpreted to reflect the source of the auriferous hydrothermal fluids and, perhaps, co-precipitating Mineral phases. Scheelite from deposits formed in rocks metamorphosed at upper greenschist to lower amphibolite facies have low contents in REE, Y, and Sr, and high contents in Mn, Nb, Ta, and V, compared to scheelite formed in rocks metamorphosed below the middle greenschist facies. Scheelite from deposits hosted in sedimentary rocks has high Sr, Pb, U, and Th, and low Na, REE, and Y, compared to that hosted in felsic to intermediate rocks. Statistical analysis including elemental plots and multivariate statistics with PLS-DA (partial least square-discriminant analysis) reveal that the metamorphic facies of the host rocks as well as the regional host rock composition exert a strong control on scheelite composition. This is a result of fluid-rock exchange during fluid flow to gold deposition site. PLS-DA and elemental ratio plots show that scheelite from orogenic gold deposits have distinct Sr, Mo, Eu, As, and Sr/Mo, but indistinguishable REE signatures, compared to scheelite from other deposit types.
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PCA of Fe-oxides MLA data as an advanced tool in provenance discrimination and Indicator Mineral exploration : case study from bedrock and till from the Kiggavik U deposits area (Nunavut, Canada)
Journal of Geochemical Exploration, 2019Co-Authors: Sheida Makvandi, Georges Beaudoin, M. Beth Mcclenaghan, David Quirt, Patrick LedruAbstract:Abstract Magnetite and hematite grains from the 0.25–0.5 mm and 0.5–2.0 mm ferromagnetic fractions of ten till samples collected up-ice, overlying and down-ice of the Kiggavik U deposits (Nunavut, Canada), as well as eight bedrock samples from Kiggavik igneous and metasedimentary basement and overlying sedimentary rocks were characterized for their grain size and Mineral association using optical microscopy, scanning electron microscopy (SEM) and Mineral liberation analysis (MLA). Principal component analysis (PCA) was used to evaluate the MLA data for Fe-oxide Mineral association and grain size distribution. PCA shows that Mineralogical and granulometric differences in Fe-oxides from Kiggavik igneous rocks distinguish them from that of Kiggavik metasedimentary and sedimentary rocks. In addition, The PCA results indicate that the composition and abundance of Minerals associated/intergrown with Fe-oxides are not only different in various till samples, but also in different size fractions of the same sample. Higher proportions of hornblende, quartz, gahnite, grunerite, apatite, chromite and sulfides are intergrown with Fe-oxides in the 0.5–2.0 mm till fraction, as compared to the 0.25–0.5 mm fraction in which Fe-oxides are mostly associated with pyroxene, titanite, rutile, feldspars, calcite and zircon. The Mineral associations and grain sizes of proximal bedrocks are reflected in smaller size fractions of Kiggavik till, whereas detrital grains in the 0.5–2.0 mm fraction of Kiggavik till may have originated from distal sources. PCA also shows that Fe-oxides from the Kiggavik bedrock and till can be discriminated from those of volcanogenic massive sulfide (VMS) deposits because of smaller grain sizes and higher abundances of sulfides, gahnite, axinite, corundum, hypersthene and pyroxene intergrown with VMS Fe-oxides. This study emphasizes the importance of selecting suitable representative grain size fractions of till, or other sediments, when using Indicator Minerals for exploration. The results of PCA of Fe-oxides MLA data are consistent with the results of using Fe-oxides geochemical data in provenance discrimination of Kiggavik till.
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An orientation study of the heavy Mineral signature of the NICO Co-Au-Bi deposit, Great Bear magmatic zone, NW Territories, Canada
Geochemistry: Exploration Environment Analysis, 2011Co-Authors: Isabelle Mcmartin, Louise Corriveau, Georges BeaudoinAbstract:ABSTRACT An orientation study around the NICO Co-Au-Bi deposit in the Great Bear magmatic zone of NW Territories, Canada, was initiated in 2007 to establish a practical guide to geochemical and Mineralogical exploration for iron oxide copper-gold deposits in glaciated terrain. Bedrock and till samples were collected up-ice, proximal and down-ice from Mineralization and host rocks, to characterize their Indicator Mineral signatures. Results demonstrate that gold grain abundance, size and shape, as well as magnetite and hematite composition, have the best potential to fingerprint the Mineralization at NICO. Pristine-shaped gold grains indicative of a local bedrock source and a short distance of glacial transport are relatively abundant in till samples collected immediately down-ice from several Mineral occurrences at NICO and none were recovered up-ice. Iron oxide composition using preliminary discriminant diagrams shows some potential, using Ni/(Mn+Cr) versus Ti+V plots. In particular, magnetite and hematite from till samples collected over, or directly down-ice of, the NICO deposit have lower Ti+V compositions compared to magnetite and hematite from till collected up-ice from Mineralization. Potential non-ferromagnetic Indicator Minerals are either not chemically stable in surface sediments (arsenopyrite, chalcopyrite, pyrite), not sufficiently coarse-grained or resistant to glacial transport (bismuthinite, tourmaline, ferroactinolite), not abundant enough in the Mineralized bedrock (scheelite, molybdenite, cobaltite, allanite), or not sufficiently heavy (tourmaline) to be useful at NICO but may be at other deposits in the region or elsewhere in glaciated terrain. The development of Indicator Mineral methods, together with till geochemistry, will be tested with further sampling over the Great Bear magmatic zone.
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Using magnetite as an Indicator Mineral, Step 1 : Calibration of LA-ICP-MS
2010Co-Authors: Perumala Venkata Sunder Raju, Sarah-jane Barnes, Dany Savard, Georges BeaudoinAbstract:Magnetite (Fe3O4) is a common and widespread accessory Mineral and could be used as an Indicator Mineral. Unfortunately, there is no certified matrix-match calibration material for the analysis of magnetite by LA-ICP-MS. In this paper, a description of the calibration of the Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) instrument using multiple standard reference materials is presented and compared with the Electron Microprobe (EPMA) and Instrumental Neutron Activation Analysis (INAA) techniques, which will be discussed succinctly.
R J Chapman - One of the best experts on this subject based on the ideXlab platform.
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Detrital Gold as a Deposit-specific Indicator Mineral by LA-IPS-MS Analysis
2018Co-Authors: Da Banks, R J Chapman, C Spence-jonesAbstract:Gold derived from alkalic porphyry systems in BC has previously been shown to exhibit a generic Hg-Pd signature revealed in both alloy composition and the suite of Minerals present as inclusions within gold particles. Development of an Indicator Mineral methodology based on this result has been hindered by the number of gold detrital gold grains required to confidently establish a signature, and the associated implications for the design of field exploration campaigns. Trace element analysis of detrital gold grains has been undertaken using Laser-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in an attempt to identify more elemental discriminants than has been possible by analysis using electron microprobe (EMP), and consequently reduce the sample size necessary for accurate characterization. Two LA-ICP-MS instruments have been used which collect data in different ways. The quadrupole system has been applied to all grains studied. The mass spectrometer sequentially scans the plasma stream to generate an analysis of material liberated by continual ablation. In contrast, the Time of Flight (ToF) instrument makes a single ablation, but measures all elements simultaneously. This approach has been used with only a few samples, but has generated new understanding of the heterogeneity of natural gold. Consideration of the large element suite generated by LA-ICP-MS confirmed the elemental associations previously identified, and has facilitated characterization of gold populations in terms of the binary Au-Ag alloy and occurrence of minor alloying metals. Orogenic gold grains generate analyses which lie along a Au-Ag binary mixing line, but many gold grains from alkalic porphyry systems show clear deviation from this trend. Natural gold has been shown to be highly heterogeneous at the trace element level. Comparison of results from a LA quadrupole and a ToF system revealed that only a small number of elements are homogenously distributed in Au alloy. Most are present either as local concentrations or as inclusions of Minerals too small to observe by SEM. This heterogeneity has profound implications for the interpretation of LA-ICP-MS data of natural gold generated by quadrupole systems, as the analyses obtained may be dependent upon the site of ablation within any particular gold grain. The application of LA-ICP-MS to detrital gold grain characterization during exploration does not currently offer an advantage to the established workflow of microchemical characterization which measures alloy compositions using EMP and identifies the associated inclusions using SEM. Both microchemical characterization and LA-ICP-MS approaches currently require approximately equivalent numbers of detrital gold particles to generate useful information. However, the results of this study have raised the possibility that extreme partitioning of trace elements to Mineral inclusions within the gold could form the basis of a methodology by which individual gold grains could be confidently ascribed to a specific source style.
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A new Indicator Mineral methodology based on a generic Bi-Pb-Te-S Mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada
Mineralium Deposita, 2018Co-Authors: R J Chapman, M. M. Allan, J. K. Mortensen, T. M. Wrighton, M. R. GrimshawAbstract:Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing Mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the Mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calc-alkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion Mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S Mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore Mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry Mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of Mineralization. These parameters influence both gold alloy composition and ore Mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable Indicator methodology based on detrital gold.
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a new Indicator Mineral methodology based on a generic bi pb te s Mineral inclusion signature in detrital gold from porphyry and low intermediate sulfidation epithermal environments in yukon territory canada
Mineralium Deposita, 2018Co-Authors: R J Chapman, M. M. Allan, J. K. Mortensen, T. M. Wrighton, Matthew GrimshawAbstract:Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing Mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the Mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calc-alkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion Mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S Mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore Mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry Mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of Mineralization. These parameters influence both gold alloy composition and ore Mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable Indicator methodology based on detrital gold.