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Lawley C.J.M.,Geological Survey of Canada | McNicoll V.,Geological Survey of Canada | Sandeman H.,Geological Survey of Canada | Pehrsson S.,Geological Survey of Canada | And 4 more authors.
Precambrian Research | Year: 2016

Archean greenstone belts host a significant proportion of the world's gold, typically in deposits that formed late during greenstone belt formation and cratonization. However, this is not always the case and, in the multiply reworked western Churchill Province (wCP), orogenic lode gold deposition post-dates greenstone belt formation by nearly one billion years. The spatial link between Proterozoic gold and Archean greenstone belts in the wCP is thus particularly striking although its significance is still not fully understood. The Meliadine gold district (2.8 Moz contained Au in reserves, plus an indicated and inferred resources of 5.8 Moz Au) represents an important example of this deposit style and is hosted within the Rankin Inlet greenstone belt (RIGB), which occupies a critical, but controversial position along the largely inferred boundary between the Hearne craton and the Chesterfield block. RIGB felsic volcanic rocks (ca. 2.66 Ga) are structurally intercalated, and broadly coeval, with mafic volcanic and volcaniclastic rocks (2.66-2.64 Ga), turbidite (≤2.66-2.64 Ga), argillite, auriferous banded iron formation successions and syn-volcanic granodioritic to tonalitic intrusions (2.67-2.64 Ga). Neoarchean basaltic to andesitic volcanic rocks possess calc-alkaline to primitive arc-like tholeiitic magmatic affinities along with lesser MORB-like basaltic compositions. Geochemically evolved lavas yield depleted 144Nd/143Nd ratios (εNd2.66 Ga = -1.1 to +1.6) that reflect variable interaction with an evolved and hitherto undocumented Meso- to Neoarchean basement underlying the RIGB, whereas transitional, arc-like primitive tholeiitic and MORB-like basaltic samples overlap with the Nd isotopic composition of depleted mantle at ca. 2.66 Ga (εNd2.66 Ga = +1.6 to +2.7). These Neoarchean volcano-sedimentary panels represent the main auriferous rock package within the Meliadine gold district and are intercalated with deformed Paleoproterozoic conglomerate (≤2.50 and ≤2.155 Ga). The latter are, in turn, unconformably overlain by a geochemically distinct pillowed-basalt sequence and a unique carbonate-siliciclastic package that presumably represent the remnants of Paleoproterozoic basins and are not known to host gold. The geological setting of gold deposits thus likely reflects this favourable Neoarchean lithostratigraphy in addition to metamorphism and fluid focusing along the reactivated faults during the collision of the Hearne and combined Chesterfield block-Rae craton at 1.90-1.85 Ga. © 2016.


Lawley C.J.M.,Geological Survey of Canada | Dube B.,Ressources Naturelles Canada | Mercier-Langevin P.,Ressources Naturelles Canada | Kjarsgaard B.,Geological Survey of Canada | And 2 more authors.
Journal of Geochemical Exploration | Year: 2015

The geochemical and mineralogic signature, or hydrothermal footprint, at Banded Iron Formation (BIF)-hosted gold deposits has great potential as an exploration tool at district- to deposit-scales. The Meliadine Gold District (MGD) is one of Canada's largest emerging BIF-hosted gold districts (2.8 Moz contained Au in reserves, plus an indicated and inferred resource of 5.8 Moz Au). Rocks are variably altered (silicified ± sulphidized ± sericitized ± carbonatized ± chloritized) adjacent to BIF-hosted replacement-style gold mineralization and auriferous greenstone-hosted quartz (±. ankerite) veins cutting mafic volcanic rocks, interflow volcaniclastic rocks and turbiditic successions. Hydrothermal altered and veined rocks provide a visual guide to ore and are spatially associated with anomalous pathfinder element concentrations (Au-As-Te-Bi-Sb). These geochemical anomalies are typically defined using a preferred threshold concentration for each element, or ratio, of interest. However, the conventional approach inadequately accounts for the multivariate nature of ore signatures and the inherently imprecise boundary between barren and mineralized rock. Herein favourable pathfinder element enrichment and hydrothermal alteration intensity are integrated and mapped using a conditional probability-based model in an effort to further highlight the complementary nature of multivariate datasets and to define fuzzy footprints. Key hydrothermal alteration mineral and element assemblages associated with gold are enriched from 10s to 100s of metres adjacent to ore zones and provide a vector to gold ore. We demonstrate that the accuracy and precision of portable X-ray fluorescence (pXRF) spectrometry on drill core surfaces is sufficient to map these multivariate and fuzzy hydrothermal footprints from the rock record, but at a fraction of the cost and time compared to conventional whole-rock analyses. © 2015.


Bendaoud A.L.,Universite de Sherbrooke | Ouzzane M.,Ressources Naturelles Canada | Aidoun Z.,Ressources Naturelles Canada | Galanis N.,Universite de Sherbrooke
Journal of Applied Fluid Mechanics | Year: 2011

Frost accumulation due to moist air flowing on a refrigeration coil cold surface impacts negatively on performance. The frost layer growth has an insulating effect in terms of heat transfer and causes the increase of the air pressure drop by blocking the free flow area across the coil. In this paper a new modeling approach, accounting for heat and mass transfer as well as the hydrodynamics of the problem, is proposed. A related FORTRAN program was developed, allowing the study of a large range of complex refrigerant circuit configurations. This model predicts the dynamic behavior of a refrigeration coil under dry and frosting conditions. Comparisons were made based on the frost mass accumulation and pressure drop across the coil and the results were found to agree reasonably well with experimental results reported in the literature. The model was then applied to study an evaporator typically employed in supermarkets. In terms of refrigerant temperature glide, it was shown that the glide decrease with time because of the decrease of the refrigeration capacity of the coil during the frosting. Further, the air pressure drop is strongly affected by the variation of the free flow area.


Lapointe-Garant M.-P.,University of Quebec at Montreal | Huang J.-G.,University of Quebec | Gea-Izquierdo G.,University of Quebec at Montreal | Raulier F.,Laval University | And 2 more authors.
Global Change Biology | Year: 2010

In this paper, we present a new approach, based on a mixed model procedure, to quantify the tree-ring-based growth-climate relationship of trembling aspen along a latitudinal gradient from 46 to 54 °N in eastern Canada. This approach allows breaking down the growth response into general intersite and local climatic responses, and analyzing variations of absolute ring width as well as interannual variations in tree growth. The final model also integrates nonclimatic variables such as soil characteristics and the occurrence of insect outbreaks into the growth predictions. Tree level random effects on growth were important as intercepts but were nonsignificant for the climatic variables, indicating that a single climate-growth relationship was justified in our case. The response of tree growth to climate showed, however, a strong dependence on the spatial scale at which the analysis was performed. Intersite variations in tree growth were mostly dependent on variations in the thermal heat sum, a variable that showed low interannual and high intersite variation. When variation for a single site was analyzed, other variables showed up to be important while the heat sum was unimportant. Finally, future growth under six different climate change scenarios was simulated in order to study the potential impact of climate change. Results suggest only moderate growth increases in the northern portion of the gradient and a growth decrease in the southern portion under future climatic conditions. © 2009 Blackwell Publishing Ltd.

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