Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) was examined as a tool for measuring isotopic variation as a function of ablation depth in unpolished zircon from an Archaean metasediment specimen. This technique was able to identify micrometre‐thin (> 3 μm) isotopically distinct mineral domains characterised by ca. 100 Myr younger 207Pb/206Pb ages associated with 2s age uncertainties as low ~ 0.2%, as well as elevated U content relative to grain interiors (up to an order of magnitude). Our calculated drilling rate suggests that each laser pulse excavated depths of ~ 0.06 μm. Ages resolved through the LA‐ICP‐MS methods overlap the 2s uncertainties of 207Pb/206Pb ages measured using SIMS depth profiling on the same zircon population. The rims were further evinced by the detection of relative enrichment (> 3 orders of magnitude) in REE in the outermost micrometres of the same zircon, measured using a different and independent LA‐ICP‐MS depth profiling technique. We propose a LA‐ICP‐MS U–Pb technique capable of quickly identifying and quantifying rims, which are indication of late, yet geologically significant, fluid events that are otherwise undefined.

Basement-hosted uranium deposits of the Patterson Lake corridor are located on the southwestern margin of the Athabasca Basin in atypical hosts: altered and metamorphosed granite, granodiorite, and ultramafic to mafic rocks. Fluid inclusions record incursion of two fluids, NaCl- and CaCl2-dominant, at temperatures up to 250°C and approximately 1 km into the basement during episodic brittle reactivation of high-strain-ductile to brittle-ductile structures, in particular late west- and north-northwest-striking brittle conjugate faults that crosscut the Athabasca sandstone. Isotopic data from pyrite and tourmaline record basinal fluid-rock interactions under fluctuating pressure and oxidizing to reducing conditions. New 3-D geophysical modelling illustrates linkages between the surface architecture and lower crust to mantle and influence of the Clearwater Domain granitic intrusions on the ore systems. High radiogenic heat production from these intrusions and other ca. 1.8 Ga felsic intrusions contributed to a prolonged, elevated geothermal gradient under the Proterozoic basins that permitted shallow (less than 3 km) depths of mineralization.

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Depth profile techniques for U–Pb geochronology and rare earth element (REE) geochemistry were conducted on unpolished, Archean zircon with metasomatic rims from metasedimentary rocks within the Horseshoe Lake greenstone belt, western Superior Province, Canada. These zircon crystals are shown to have isotopically distinct rims (typically <5 μm thick) compared with the interiors of the crystal. Secondary ion mass spectrometry (SIMS) U–Pb depth profile analyses of the rims define two different 207Pb/206Pb age populations at ca. 2920 and 2869 Ma, which are >100 million years younger than the cores. The 207Pb/206Pb rim ages can be temporally correlated with regional magmatism and with a later, potentially Au-bearing, hydrothermal event synchronous with greenschist-facies metamorphism and regional deformation. Notably, the zircons do not record evidence of local ca. 2741–2715 Ma magmatism manifested by the emplacement of a quartz–feldspar porphyry dike swarm. Laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) REE depth profile analyses on the same unpolished zircon show that the rims are commonly characterized by low Th/U ratios, elevated Hf, and variable REE concentrations in comparison with the interior of the grains. The variations in rim and core chemistry suggest that these elements, along with common Pb, were mobilized by fluids and interacted with zircon in the metasediments, resulting in the production of the metasomatic rims. In summary, this paper shows that depth profiling techniques applied to unpolished zircon can be useful to elucidate the tectonic, and potentially metallogenic, history of a complex Archean terrane.

The TGI-4 Lode Gold project, which comprises numerous site-specific and thematic research activities, covers the entire spectrum of crustal settings for lode gold deposits, from orogenic banded iron formationhosted and greenstone-hosted quartz carbonate vein-type gold deposits formed deep in the crust (&amp;gt;5 km), to intrusion-related deposits that are formed at shallower crustal levels (~2-5 km), and to deposits formed at or near the seafloor. Herein we synthesize a number of important project contributions that have significant implications for on-going mineral exploration for hidden deposits. Among the key findings is a newly established link between major faults, their early evolution, syntectonic magmatism and synorogenic sedimentary basin evolution, and gold metallogenesis in various greenstone belts. The revised model incorporates a phase of tectonic extension-a distinct feature recognized in gold-rich settings worldwide-that is applicable to mineral exploration targeting across the Canadian Shield. Importantly, the simultaneous multidisciplinary study of a number of large banded iron formation-hosted gold deposits and districts allows for the development of a unifying genetic model for such deposits that integrates critical structural, stratigraphic, hydrothermal, and metamorphic elements. Several key features that are common to all of the studied deposits, but elements specific to dominantly banded iron formation-hosted gold deposits or to deposits that are only partly hosted in banded iron formation, were also established. The Lode Gold project also bridges a major knowledge gap by characterizing a spectrum of "unusual" or "atypical" gold deposits in the Superior Province. The new and revised models incorporate synvolcanic as well as pre-deformation and synorogenic synmagmatic or intrusion-related gold deposits that represent a large part of the newly discovered resources in the Canadian Shield in both "brownfield" and "greenfield" exploration environments.