Search

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Goldcorp High-Grade zone at the Red Lake mine has reserves (proven and probable) established at 1.775 million tons (Mt) at an average grade of 80.6 g/t Au. New U-Pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich Goldcorp High-Grade zone. The results show that the main stage of the high-grade mineralization in the High-Grade zone formed before 2712 Ma and that a second stage of gold mineralization, much smaller in terms of total gold content but spectacular in terms of grade, formed after 2702 Ma. This second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the Cat Island pluton (2699 Ma), approximately 7 km east of the deposit, or by the ca. 2.63 to 2.66 Ga postorogenic regional thermal event indicated by hornblende, muscovite, and biotite Ar-Ar cooling ages from the Uchi subprovince. It is proposed that the main stage of high-grade mineralization formed between ca. 2723 to 2712 Ma, possibly synchronous with emplacement of the Dome and McKenzie Island stocks, the Abino granodiorite, and Hammell Lake batholith, as well as with penetrative D2 main-stage regional deformation. Lamprophyre dikes spatially associated with the deposit postdate main-stage mineralization by at least 10 m.y. A postore granodiorite dike from the Madsen mine, the second largest deposit in the district, was dated at 2698 ± 1 Ma. This age is similar to a postalteration and late-deformation diorite dike at the Creek zone showing near the former Starratt-Olsen mine, which was dated at 2696 ± 2 Ma. The crosscutting relationships confirm that the main stage of mineralization at the Madsen mine is pre-2698 Ma. A folded and metamorphosed polymictic conglomerate located stratigraphically above the Campbell-Red Lake deposit, and deposited after ca. 2747 but before... [ABSTRACT FROM AUTHOR]

Integrated mapping, structural analysis, and U-Pb geochronology of the Committee Bay area, Nunavut, establish a record of Neoarchean crustal growth followed by penetrative Paleoproterozoic deformation. Supracrustal rocks include a lower ca. 2.73 Ga mafic-ultramafic volcanic-dominated sequence, a middle, economically significant 2.71 Ga intermediate volcanic-bearing sequence with intercalated sulphidized, gold-bearing iron formation, and an upper <2.69 Ga clastic ± komatiite-quartzite sequence. Following an 80 million year hiatus, this succession was intruded by voluminous ca. 2.61-2.57 Ga granodiorite-tonalite-granite ± diorite, which do not appear to have thermally or tectonically affected the supracrustal belt. Instead, three generations of structures record polyphase Paleoproterozoic deformation of the region. D1 structures are consistent with a doubly vergent structural fan developed at ca. 2.35 Ga in response to the Arrowsmith orogeny that affected the western Rae margin. Penetrative D2 structures dominate the map pattern and include northeast-trending, southeast-dipping folds and fabrics within which gold is localized. The general southeast dips of S2 and inclined, northwest-vergent attitude of F2 reflect northwest-directed shortening at 1.84-1.82 Ga. The absence of syn-D2 plutonic rocks in the west and central Committee Bay belt support amphibolite-facies metamorphism as a response to crustal thickening, which, in turn, led to syn-D2 crustal melting in the east. Regionally extensive upright to northwest-vergent D2 structures and associated ca. 1.85-1.82 Ga tectonometamorphism across the Rae craton are attributed to an early stage of the Hudsonian orogeny involving microcontinent collision(s) with its southeastern margin. D3 folds and dextral shearing at ca. 1780 Ma accommodated localized, late-stage compressional strain during final amalgamation of Laurentia. [ABSTRACT FROM AUTHOR]

Laser ablation inductively coupled plasma multi-collector mass spectrometry (LA-MC-ICP-MS) allows rapid, in situ, highly precise measurements of Cu isotope ratios of native Cu and Cu-bearing minerals. However, the National Institute of Standards and Technology Cu-metal isotope standard NIST SRM976 that is commonly used to calibrate LA-MC-ICP-MS Cu isotope measurements of native Cu is no longer available. We have investigated the suitability of four Cu metal materials, SSC-1, SSC-3 and SSC-4 (cathode Cu metal rods) and CUPD-1 (Cu anode sawings), originally developed by the Canada Centre for Mineral and Energy Technology (CANMET) as certified reference materials for trace element analysis, as Cu isotope reference materials for LA-MC-ICP-MS analysis and solution nebulization (SN) of Cu. The Cu isotopic composition and homogeneity of these four materials were characterised by SN- and LA-MC-ICP-MS, and are reported for the first time. The bulk Cu isotopic compositions, expressed as δ 65 Cu SRM976 in per mil (‰) relative to NIST SRM976 with combined uncertainties ( U , k = 2), of SSC-1, SSC-3 and SSC-4, determined utilizing SN-MC-ICP-MS, are identical within analytical uncertainty at 0.03 ± 0.07‰ ( n = 29), 0.04 ± 0.04‰ ( n = 28), and 0.05 ± 0.08‰ ( n = 29), respectively; the composition of CUPD-1 is 2.14 ± 0.08‰ ( n = 28). The compositions are 0.01 ± 0.07‰ ( n = 29), 0.04 ± 0.06‰ ( n = 29), 0.03 ± 0.06‰ ( n = 28) and 2.15 ± 0.06‰ ( n = 28), respectively, relative to the European Reference Material ERM®-AE633 Cu isotope standard. The Cu isotope homogeneity of the four new reference materials was assessed by determining whether multiple individual in situ Cu isotope measurements made by LA-MC-ICP-MS analysis (43 µm spot size), using each of the other three reference materials as a calibrator, approximate a single normal distribution. We also investigate whether there are statistically significant differences between the mean δ 65 Cu values of three independent data sets for each of the Cu isotope reference materials using one-way analysis of variance (ANOVA). Normality tests (graphical assessment of normal distribution quantile-quantile plots, and the Shapiro-Wilk, Jarque-Bera and reduced chi-squared statistic tests) show that: 1) the Cu isotope data acquired on SSC-1, SSC-3, SSC-4 and CUPD-1 do not depart significantly from a normal distribution, 2) the scatter of the Cu isotope data is due to analytical uncertainty with 95% confidence, and 3) there are no other significant sources of scatter; e.g. heterogeneity of the reference materials. The results of one-way ANOVA reveal that the mean difference of the δ 65 Cu value for each of the reference materials SSC-1, SSC-3, SSC-4 and CUPD-1 is statistically not significant at the 0.05 level. The mean δ 65 Cu SRM976 values with combined uncertainties ( U , k = 2) of SSC-1, SSC-3, SSC-4 and CUPD-1, determined by LA-MC-ICP-MS using each of the other three reference materials as a calibration standard, are 0.03 ± 0.09‰ ( n = 132), 0.05 ± 0.09‰ ( n = 154), 0.03 ± 0.09‰ ( n = 144) and 2.14 ± 0.10‰ ( n = 106), respectively. These values are in agreement with those determined by SN-MC-ICP-MS analysis at the 95% confidence level and have excellent precision (2 s.d. ≤ 0.10‰). These results suggest that SSC-1, SSC-3, SSC-4 and CUPD-1 can be considered isotopically homogeneous at a spatial resolution of 43 μm, and they are suitable reference materials for calibration and quality control of in situ and solution nebulization Cu isotope analyses of Cu., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Yang, Jackson and Skulski.)