Papers by Matthew Leybourne
Explore-the Journal of Science and Healing, 2016
WISHES TO THANK OUR CORPORATE SPONSORS FOR THEIR SUPPORT INTRODUCTION The determination of mercur... more WISHES TO THANK OUR CORPORATE SPONSORS FOR THEIR SUPPORT INTRODUCTION The determination of mercury contents in rocks, minerals, surficial sediments and soils is critical for a number of disciplines including the understanding of anthropogenic contributions to the environment, baseline studies, food webs, and mineral deposit formation and exploration. Many studies of Hg and Hg speciation are predicated on the basis that Hg is toxic to humans and aquatic systems, and that much of the labile Hg in the environment is of anthropogenic origin (Lacerda & Marins 1997; Martínez-Cortizas et al. 1999; Pirrone et al. 2010). Recent estimates of global Hg fluxes have suggested that anthropogenic sources are c. 2000 x 106 g annually (with large variations in estimates), reemissions of Hg are c. 450 x 106 g annually, biomass burning is c. 300 to 600 x 106 g annually, whereas geogenic sources are < 900 x 106 g and < 600 x 106 g annually for emissions to the atmosphere and oceans, respectively ...
This report has been prepared in good faith within time and budgetary limits. Due to time constra... more This report has been prepared in good faith within time and budgetary limits. Due to time constraints we have not been able to incorporate all review feedback. These limitations will be addressed in a later review and a subsequent version published.
In Iran, listvenites (fully quartz-carbonate altered peridotites) are commonly associated with La... more In Iran, listvenites (fully quartz-carbonate altered peridotites) are commonly associated with Late Cretaceous ophiolites. Despite the abundance of carbonate alteration in these ophiolites, there have been few studies of these rocks, including isotopic investigations into the source of fluids [1, 2] and element mobility due to this alteration [3]. Here, we provide constraints on the sources of altering fluid by using the stable (C, O) and radiogenic (Sr) isotopes and report on element mobility associated with listvenitazation of ophiolitic peridotite in the Hangaran area of Birjand, Iran.
Minerals
Exploration under thick glacial sediment cover is an important facet of modern mineral exploratio... more Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material. This study applies mineral liberation analysis (MLA) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy (e.g., MLA) of finer material allows for the rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Sisson W-Mo deposit has a previously documented dispersal train containing the ore minerals scheelite, wolframite, and molybdenite, along with sulfide and other accessory minerals, and was used as a test site for this study. Wolframite is identified in till samples up to 10 km down ice, whereas in previou...
The Canadian Mineralogist
We report new isotopic data for H2 and CH4 gases and Sr for groundwater collected from Jurassic K... more We report new isotopic data for H2 and CH4 gases and Sr for groundwater collected from Jurassic Kirkland Lake kimberlites in northern Ontario, Canada. Groundwaters interacting with kimberlites have elevated pH (up to 12.4), are reducing (Eh as low as the H2-H2O couple), are dominated by OH− alkalinity, and have non-radiogenic (mantle) 87Sr/86Sr values (∼0.706–0.707). Most significantly, the highest pH groundwaters have low Mg, high K/Mg, and are associated with abundant reduced gases (H2 ± CH4). Open system conditions favor higher dissolved inorganic carbon and CH4 production, whereas under closed system conditions low DIC, elevated OH− alkalinity, and H2 production are enhanced. Hydrogen gas is isotopically depleted (δ2HH2 = −771 to −801‰), which, combined with δ2HH2O, yields geothermometry temperatures of serpentinization of 5–25 °C. Deviation of H2-rich groundwaters (by up to 10‰) from the meteoric water line is consistent with Rayleigh fractionation during reduction of water to ...
The Canadian Mineralogist
Exploration for gold in Nunavut has been primarily focused on Archean greenstone belts in the nor... more Exploration for gold in Nunavut has been primarily focused on Archean greenstone belts in the north and coastal regions of the territory, resulting in large areas of underexplored terrain in the south. The Kiyuk Lake property is located in the underexplored southwest corner of the Kivalliq Region of Nunavut within the Hearne domain of the ∼1.9 Ga western Churchill Province. The property is hosted by Proterozoic calc-silicate and clastic sedimentary units of the Hurwitz Group (<2.4–1.9 Ga) and the unconformably overlying Kiyuk Group (1.9–1.83 Ga). Gold mineralization in Proterozoic sedimentary rocks is rare in the Canadian Shield, so the Rusty Zone at Kiyuk Lake presents a unique opportunity to study the enigmatic gold mineralization hosted in such sedimentary rocks. Mineralization at the Rusty Zone is hosted by an immature lithic wacke cut by thin intermediate dikes that are associated with hydrothermal breccias composed of Fe-carbonate, calcite, calcic-amphibole, Fe-sulfide, Fe-...
The Canadian Mineralogist
The MacMillan Pass District in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-... more The MacMillan Pass District in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-Pb-Ag-(Ba) deposits. Bulk geochemical paleoredox proxies (Eu/Eu*, Ce/Ce*, Mo, Re/Mo, and Ni/Co) indicate anoxic–dysoxic water column and sulfidic porewater conditions persisted during the Late Devonian deposition of the Lower Earn Group host rocks. Positive Eu/Eu* anomalies (up to 3.31) in sulfide mineralization at the Tom deposit are consistent with relatively high temperature (probably >250 °C), reducing, acidic hydrothermal fluids that infiltrated laterally through unconsolidated sediments proximal to the hydrothermal upflow zone and/or exhaled at the seafloor as moderate- to high-density brines. Molybdenum and U enrichment factors (relative to upper continental crust) and Mo/organic C values are consistent with a moderately restricted basin; Mo/C values fall between those of the Black Sea (highly restricted) and the Framvaren Inlet (moderately restricted). A Ba-rich shale was iden...
Mineralium Deposita
The proximity to metasedimentary footwall rocks relative to platinum group element (PGE) minerali... more The proximity to metasedimentary footwall rocks relative to platinum group element (PGE) mineralized intrusive rocks in the northern limb of the Bushveld Igneous Complex (BIC) has resulted in complex local contamination in the intrusions. To assess the extent of incorporation of non-magmatic material and its effects on PGE mineralization, major element, trace element, and S isotopic data were collected from drill core UMT094 on the Turfspruit farm, where core logging has shown that the mineralized Platreef, forming the Flatreef deposit, is located stratigraphically well above local sedimentary footwall rocks. The S isotopic data combined with whole rock geochemistry data (including CaO/Al2O3, (V/Ti)PM, (Ni/Cr)PM, S/Se, loss on ignition) were used to assess incorporation of a range of local footwall material. The δ34S data show a steady decrease from the footwall assimilation zone (δ34S typically + 8 to + 9‰, maximum 12‰) to near constant δ34S values (δ34S 2 for shale assimilation; ...
Minerals
Exploration under thick glacial sediment cover is an important facet of modern mineral exploratio... more Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material, however this study applies modern automated mineralogical methods (mineral liberation analysis (MLA)) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy of finer material allows for rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Izok Lake volcanogenic massive sulfide (VMS) deposit, one of the largest undeveloped Zn–Cu resources in North America, has a well-documented fan-shaped indicator mineral dispersal train and was used as a test site for this study. Axinite, a VMS indicator mineral difficult ...
The world-class Windy Craggy Cu-Co-Au deposit, northwestern British Columbia, is investigated to ... more The world-class Windy Craggy Cu-Co-Au deposit, northwestern British Columbia, is investigated to assess potential magmatic contributions to mineralizing fluids in volcanogenic massive sulphide (VMS) deposits. Windy Craggy is of particular interest for two reasons: 1) its atypically large size and high-grade; and 2) the observation of fluid inclusions with anomalously high salinities. The deposit has recorded fluids with salinities up to 17 weight % equivalent NaCl (most 6–16 weight % equivalent). The Ca/Na values in fluid inclusions determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) are greater than seawater and similar to values from other mafic-dominated VMS systems. The fluid inclusions have variable metal and metalloid concentrations, with positive correlations between Cu, Mn, Zn, Sb, Sn and Bi. Also analyzed are Windy Craggy host lithologies, including footwall argillites, relatively fresh to highly altered footwall mafic volcanic rocks and stringer and massive sulphides.These inclusions show similar trends and overlap the host rocks in Fe versus Mn and Cu versus Zn, but show clear excesses over host rocks in antimony, tin, bismuth and similar elements that are commonly ascribed as indicative of magmatic input. We suggest that these excess values strongly point to direct magmatic contributions to the Windy Craggy ore-forming fluids, as opposed to simply reflecting leaching of metals from the footwall sedimentary and igneous rocks.
Geochemistry: Exploration, Environment, Analysis
Geochemistry: Exploration, Environment, Analysis
International Geology Review
The Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabou... more The Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabound volcanogenic Cu–Zn–(Pb) ± Au-bearing massive sulphide deposits and associated zones of hydrothermal alteration. Here, we use major and trace element analyses of massive sulphides, gossans, and hydrothermally altered and least altered metamorphosed host rock (schist) from two of the deposits (Shaib al Tair and Rabathan) to interpret the geochemical and petrological evolution of the host rocks and gossanization of the mineralization. Tectonic interpretations utilize high-field-strength elements, including the rare earth elements (REE), because they are relatively immobile during hydrothermal alteration, low-grade metamorphism, and supergene weathering and therefore are useful in constraining the source, composition, and physicochemical parameters of the primary igneous rocks, the mineralizing hydrothermal fluid and subsequent supergene weathering processes. Positive Eu anomalies in some of the massive sulphide samples are consistent with a high temperature (&gt;250°C) hydrothermal origin, consistent with the Cu contents (up to 2 wt.%) of the massive sulphides. The REE profiles of the gossans are topologically similar to nearby hydrothermally altered felsic schists (light REE (LREE)-enriched to concave-up REE profiles, with or without positive Eu anomalies) suggesting that the REE experienced little fractionation during metamorphism or supergene weathering. Hydrothermally altered rocks (now schists) close to the massive sulphide deposits have high base metals and Ba contents and have concave-up REE patterns, in contrast to the least altered host rocks, consistent with greater mobility of the middle REE compared to the light and heavy REE during hydrothermal alteration. The gossans are interpreted to represent relict massive sulphides that have undergone supergene weathering; ‘chert’ beds within these massive sulphide deposits may be leached wall-rock gossans that experienced silicification and Pb–Ba–Fe enrichment from acidic groundwaters generated during gossan formation.
Geology, 2016
We want to know when plate tectonics began and will consider any important Earth feature that sho... more We want to know when plate tectonics began and will consider any important Earth feature that shows significant temporal evolution. Kimberlites, the primary source of diamonds, are rare igneous features. We analyze their distribution throughout Earth history; most are young (~95% are younger than 0.75 Ga), but rare examples are found as far back as the Archean (older than 2.5 Ga). Although there are differing explanations for this age asymmetry (lack of preservation, lack of exposure, fewer mantle plumes, or lack of old thick lithosphere in the Archean and Proterozoic), we suggest that kimberlite eruptions are a consequence of modernstyle plate tectonics, in particular subduction of hydrated oceanic crust and sediments deep into the mantle. This recycling since the onset of modern-style plate tectonics ca. 1 Ga has massively increased mantle CO 2 and H 2 O contents, leading to the rapid and explosive ascent of diamond-bearing kimberlite magmas. The age distribution of kimberlites, combined with other large-scale tectonic indicators that are prevalent only in the past ~1 Ga (blueschists, glaucophane-bearing eclogites; coesite-or diamond-bearing ultrahigh-pressure metamorphic rocks; lawsonite-bearing metamorphic rocks; and jadeitites), indicates that plate tectonics, as observed today, has only operated for <25% of Earth history.
Journal of Petrology, 2016
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Papers by Matthew Leybourne