Arc magmatism drives the production of modern continental crust.However, the mode of crustal differentiation in the geologic past, particularly in the Archean, remains controversial.Herein I adopt a compositional approach to interrogate a global, igneous geochemical database (EarthChem Library) and document the evolving compositional history of basalt, andesite, and rhyolite, which represent the three main crustal building blocks.Basalt and andesite yield synced geochemical trends and progressively incompatible element-rich and compatible element-poor compositions that are consistent with extensive partial mantlemelting during the Archean.Post-Archean basaltic to andesitic rocks also tend to be more alkaline in character, which coupled with their high field-strength-and large-ion lithophile-element signature, points to the increased influence of Phanerozoic-style intra-plate magmatism on the global, rock record.Coeval rhyolitic rocks are depleted in these same elements, suggesting that post-Archean felsic magmas track the evolving compositions of their basaltic to andesitic source, which are, in turn, controlled by the partial melting trend.These complementary, or symmetric, geochemical trends between rock types shifted during the Proterozoic and heralded the onset of modern compositional relationships between crustal building blocks.
The crystal growth history of an Au-rich sedimentary pyrite nodule from the Timmins-Porcupine Au camp, Ontario, Canada, has been investigated using Electron Backscattered Diffraction and Laser Ablation Inductively Coupled Plasma Mass Spectrometry techniques to study the crystallographic processes controlling metal deportment in the pyrite structure. Results show four distinct growth stages characterized by different pyrite microstructures, crystal forms and trace element compositions. A direct link is observed between the growth of octahedral facets in pyrite and the development of primary (non-tectonic) subgrain boundaries. Furthermore, zones with a high abundance of subgrain boundaries have the highest Au, As, Ag and Cu (and other metals) contents – suggesting metal distribution is linked to the development of microstructures. Finer-grained aggregates are characterized by higher grain boundary density than in coarse areas, making higher trace element concentrations inversely proportional to grain size. Our results indicate that the high Au concentrations (~100 ppm) in pyrite represent a primary feature related to nodule growth, instead of secondary enrichment processes, and highlight the possibility that sediment-hosted pyrite nodules could represent a metal-rich geochemical reservoir for the formation of younger orogenic Au deposits.
Abstract Geochemical surveys contain an implicit data lifecycle or pipeline that consists of data generation (e.g., sampling and analysis), data management (e.g., quality assurance and control, curation, provisioning and stewardship) and data usage (e.g., mapping, modeling and hypothesis testing). The current integration of predictive analytics (e.g., artificial intelligence, machine learning, data modeling) into the geochemical survey data pipeline occurs almost entirely within the data usage stage. In this study, we predict elemental concentrations at the data generation stage and explore how predictive analytics can be integrated more thoroughly across the data lifecycle. Inferential data generation is used to modernize lake sediment geochemical data from northern Manitoba (Canada), with results and interpretations focused on elements that are included in the Canadian Critical Minerals list. The results are mapped, interpreted and used for downstream analysis through geochemical anomaly detection to locate further exploration targets. Our integration is novel because predictive modeling is integrated into the data generation and usage stages to increase the efficacy of geochemical surveys. The results further demonstrate how legacy geochemical data are a significant data asset that can be predictively modernized and used to support time-sensitive mineral exploration of critical minerals that were unanalyzed in original survey designs. In addition, this type of integration immediately creates the possibility of a new exploration framework, which we call predictive geochemical exploration. In effect, it eschews sequential, grid-based and fixed resolution sampling toward data-driven, multi-scale and more agile approaches. A key outcome is a natural categorization scheme of uncertainty associated with further survey or exploration targets, whether they are covered by existing training data in a spatial or multivariate sense or solely within the coverage of inferred secondary data. The uncertainty categorization creates an effective implementation pathway for future multi-scale exploration by focusing data generation activities to de-risk survey practices.
New geological mapping in the Tehery Lake-Wager Bay area of northwestern Hudson Bay, Nunavut, frames the emplacement, depositional, and metamorphic histories of the dominant rock types, major structures, and links to neighbouring areas of the central Rae Craton and Chesterfield Block. The area is divided into six domains (Ukkusiksalik, Douglas Harbour, Gordon, and Lunan domains presented here, and Kummel Lake Domain and Daly Bay Complex on adjoining maps) defined by large-scale structures and characterized by differing metamorphic assemblages, Sm-Nd and U-Pb isotopic data, and/or specific lithologies. Meso- to Neoarchean granitoid rocks underlie most of the area and are tectonically intercalated with Archean (volcano)sedimentary packages (Kummel Lake, Lorillard, and Paliak belts). These rocks are locally intruded by ca. 2.62 to 2.58 Ga Snow Island suite granite and cut by younger, thin, east-trending diabase dykes. Paleoproterozoic (volcano)sedimentary rocks are preserved in the Kingmirit belt (Daly Bay Complex) and in basement-cover infolds of Ketyet River group-equivalent strata (Douglas Harbour and Ukkusiksalik domains). In the south, the Daly Bay Complex (comprising mostly mafic granulite-facies rocks) and Kummel Lake Domain (a granulite-grade core complex) share some characteristics with rocks of the Kramanituar and Uvauk complexes, which may delineate the northeastern segment of the ca. 1.90 Ga Snowbird tectonic zone. The Paleoproterozoic Trans-Hudson Orogeny had widespread, penetrative structural and metamorphic effects on the area, and led to the intrusion of the ca. 1.85 to 1.81 Ga Hudson suite monzogranite and mafic ultrapotassic rocks, and ca. 1.83 Ga monzodiorite in the Ukkusiksalik and Douglas Harbour domains. The area is cut by large, southeast-trending gabbro dykes of the 1.267 Ga Mackenzie igneous event.
The Central Mineral Belt (CMB) in Labrador, Canada, hosts multiple U (±base ± precious metal) showings, prospects and deposits in metamorphosed and variably hydrothermally altered Neoarchean to Mesoproterozoic, igneous and sedimentary rocks. Previous work has recognized U mineralization locally associated with Fe-Ca and alkali metasomatism typical of metasomatic iron oxide and alkali-calcic alteration systems (IOAA) that host iron oxide-copper-gold (IOCG) and affiliated critical metal deposits. However, the type, extent and temporal or genetic relationships between the diverse Fe, Ca and alkali metasomatism and the regionally distributed U mineralization remains poorly understood. Combined unsupervised machine-learning and classification of alteration from a large geochemical dataset distinguish the main alteration phases in the CMB, identify compositional changes related to U mineralization, and infer lithological/mineralogical information from samples with censored (i.e., missing), limited and/or inaccurate metadata. Weak to intense Na and Na + Ca-Fe (Mg) metasomatism in the southwest (Two-Time and Moran Lake areas) and eastern (Michelin area) portions of the CMB pre-dates U mineralization and Fe-oxide breccia development, similar to albitite-hosted U and IOCG deposits globally. Rare earth elements and spider diagrams highlight both preservation and disruption of normally immobile elements. Principal component and cluster analysis indicate significant variations in Fe-Mg ± Na contents in the rocks from combinations of Na, Ca, Fe, and Mg-rich alteration, while protolith REE signatures can be locally preserved even after pervasive albitization-hematization. Cluster analysis identifies mineralized felsic and mafic rocks in the Michelin deposit and Moran Lake area, facilitating inference of relevant lithological/mineralogical information from samples lacking or with limited meta-data. The methods outlined provide rapid and relatively inexpensive means to optimize identification of mineral systems within large geochemical datasets, verify drill core or field observations, highlight potentially overlooked alteration, and refine economic mineral potential assessments. Based on our results and previous work, we suggest the mineral potential of the southwestern and eastern CMB needs to be re-assessed with modern exploration models for IOAA ore systems and their iron oxide-poor variants.
A detailed Re-Os molybdenite, pyrite, and chalcopyrite geochronology at five shear-hosted Au occurrences (Kenge, Mbenge, Porcupine, Konokono, and Dubwana) in the Lupa goldfield, southwestern Tanzania, is reported in this paper. Au occurrences within the Lupa goldfield share many geologic similarities with the orogenic Au deposit type and are situated within a Paleoproterozoic magmatic arc that intruded the Archean Tanzanian cratonic margin. Pyrite ± chalcopyrite ± molybdenite-bearing fault-fill veins and mylonitic shear zones crosscut granitic host rocks and are associated with the highest Au grades. Re-Os sulfide ages are deemed a suitable proxy to constrain the timing of Au based on the occurrence of Au-bearing minerals as inclusions within pyrite and chalcopyrite, whereas Au-bearing minerals filling pyrite fractures may represent a younger and undated metallogenic event.
Molybdenite at Kenge occurs as ultrafine disseminations within fault-fill veins (1953 ± 6 Ma; n = 3) that possess nominally older weighted average Re-Os ages than molybdenite hosted by stylolite-like veins (1937 ± 8 Ma; n = 7). Both sample sets are ca. 70 m.y. older than a weighted average Re-Os pyrite age from the mylonitic shear zones at Kenge and Mbenge (1876 ± 10 Ma; n = 13), which contain fault-fill veins and record the timing of mylonitization. Molybdenite at Porcupine occurs as ultrafine disseminations within quartz veins and mylonitized granite samples (1886 ± 6 Ma; n = 4) that are broadly equivalent in age to weighted average Re-Os ages of molybdenite occurring as stylolite-like veins (1873 ± 5 Ma; n = 6) and pyrite within oblique-extension veins (1894 ± 45 Ma; n = 2). Weighted average Re-Os pyrite model ages at Konokono (1880 ± 14 Ma; n = 9) and Dubwana (1905 ± 25 Ma; n = 2) are also consistent with the ca. 1.88 Ga event observed at Kenge, Mbenge, and Porcupine.
Gold occurrences in the Lupa goldfield therefore record a protracted hydrothermal history (1.95–1.87 Ga) comprising at least three temporally distinct hydrothermal events (ca. 1.95, 1.94, and 1.88 Ga), which are each represented in detail by a complex vein history that occurred at a time scale less than the resolution of the Re-Os method. The sampling of broadly contemporaneous sulfides from five shear zones suggest that mylonitic shear zones represented an interconnected network of midcrustal permeable fluid conduits at ca. 1.88 Ga that permitted the transportation and deposition of gold. Comparison between Re-Os sulfide and high-precision U-Pb zircon ages for the granitic host rocks provides unequivocal evidence for sulfidation concomitant with magmatism. However, the range of Re-Os ages argues against an intrusion-related deposit model whereby metallogenic fluids are solely derived from an individual intrusion. The regional ca. 1.88 Ga metallogenic event identified as part of this study occurred concurrently with eclogite facies metamorphism during the Ubendian orogenic cycle and provides one of Earth’s earliest temporal links between subduction zone processes and orogenic Au deposit formation during the Paleoproterozoic.
Abstract Achieving net-zero carbon emissions goals will increasingly rely on critical mineral resources while simultaneously decreasing the extraction, processing and use of hydrocarbons as the primary provider of energy. Canada is well positioned to contribute to this effort through a series of innovative policy and research initiatives, and it is Canada's goal to be a stable supplier of critical minerals into the future. To this end, Natural Resources Canada and the Geological Survey of Canada invest financial resources into critical mineral research initiatives. This research aims to generate precompetitive baseline geological, geochemical and geophysical data for large, underexplored regions within Canada, whereas targeted studies focus on mineral systems science and improved exploration models for the large variety of critical mineral resources distributed throughout Canada. These research approaches can be combined, digitally, to generate mineral potential models. These ongoing efforts by the Geological Survey of Canada enhance the viability of Canada being (or maintaining its status as) a hub for critical mineral resource development and processing well into the future.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)