Geologic understanding of the richly mineralized Dawson Range gold belt (DRGB) in the central Yukon, Canada is hindered by: (1) limited outcrop exposure due to thick soil cover; and (2) low resolution age-constraints despite a long history of porphyry Cu–Au–Mo deposit (PCD) exploration. Here, the well-preserved Klaza Au–Ag–Pb–Zn porphyry–epithermal deposit is used as a type-example of Late Cretaceous magmatic–hydrothermal mineralization to address the complex metallogeny of the DRGB. U–Pb zircon dating defines four magmatic pulses of Late Triassic to Late Cretaceous ages with the latter consisting of the Casino (80–72 Ma) and Prospector Mt. (72–65 Ma) suites. The Casino suite has five phases of intermediate-to-felsic calc-alkaline composition, correspond with older (77 Ma) porphyry mineralization, and displays evidence of magma mingling. The intermediate-to-mafic, slightly alkalic Prospector Mt. suite shows evidence of mingling with the youngest Casino suite phases, correlates with younger (71 Ma), intermediate-sulfidation epithermal and porphyry-type mineralization, and shoshonitic basalts of the Carmacks Group. Zircon trace element data suggest a common melt source for these suites; however, the younger suite records features (e.g., high La/Yb) that indicate a higher pressure melt source. The results from this study highlight the Prospector Mt. suite as a historically overlooked causative magma event linked to Au-rich PCDs in the DRGB and extends the temporal window of PCD prospectivity in this area. The transition from mid-Cretaceous Whitehorse suite magmas to Late Cretaceous Casino-Prospector Mt. suite magmas is proposed to reflect a transition from subduction to localized extension, which is becoming more recognized as a common characteristic of productive porphyry belts globally.

Subduction zones play a crucial role in Earth's physical and chemical dynamics, but their initiation and related magmatism remain poorly understood. This study presents new zircon U-Pb age, Hf-O isotope and whole-rock major-trace element and Sr-Nd isotope data from the Kohistan arc in northern Pakistan, a well-preserved Phanerozoic oceanic crustal arc. The Jaglot Group basalts are low-K tholeiites similar to early Izu-Bonin-Mariana forearc basalts, representing the oldest volcanic stratigraphy of the Kohistan arc. The Matum Das tonalite, intruding the Jaglot Group at similar to 155 Ma, provides a new minimum age for subduction initiation. The rapid formation of new felsic crust shortly after subduction initiation challenges existing models and indicates the need for further research into early arc-forming processes.

Charactering alteration and its geochemical signature provides critical information relevant to ore-deposit genesis and its related footprint; for porphyry-type deposits, zoned potassic-phyllic-propylitic alteration and metal enrichment are critical features. Here we integrate earlier lithological and mineralogical studies of the (10+ Moz Au) Archean Côté Gold porphyry-type Au(-Cu) deposit (Ontario, Canada) with identified alteration types to provide exploration vectors. The ca. 2740 tonalite-quartz diorite-diorite intrusive complex and co-temporal Au(-Cu) mineralization as disseminations, breccias and veins are co-spatial with ore-related alteration types (amphibole, biotite, muscovite). An early, locally developed amphibole event coring the deposit is followed by emplacement of a Au(-Cu) mineralized biotite-rich magmatic-hydrothermal breccia body and broad halo of disseminated biotite and quartz veining. These rocks record gains via mass balance calculations of K, Fe, Mg, LILE, and LREE with Au, Cu, Mo, Ag, Se and Bi. Later muscovite alteration is enriched in K, Rb, Cs, Ba, CO2, and LOI with varied Au, Cu, Mo, Te, As, and Bi values. A strong albite overprint records extreme Na gains with the loss of most other elements, including ore metals (i.e., Au, Cu). Together these data define an Au-Cu-Mo-Ag-Te-Bi-Se core co-spatial with biotite breccia versus a peripheral stockwork and sheeted vein zone with a Te-Se-Zn-Pb-As association. These features further support the posited porphyry-type model for the Côté Gold Au(-Cu) deposit.

Siderite and baryte are common non-sulphide phases in sedimentary exhalative (SEDEX) deposits, but their formation remains poorly understood. Siderite is important as an exploration vector in some deposits, whereas baryte is important as a S source in some deposits. The past-producing Walton deposit (Nova Scotia, Canada) consists of two ore types: (1) a sulphide body primarily hosted by sideritised Viséan Macumber Formation limestone (0.41 Mt; head grade of 350 g/t Ag, 4.28% Pb, 1.29% Zn, and 0.52% Cu), and (2) an overlying massive baryte body of predominantly microcrystalline baryte (4.5 Mt of >90% baryte). This study used optical microscopy, SEM-EDS, cathodoluminescence (CL), LA-ICP-MS, and SIMS sulphur isotope analysis of siderite and baryte to elucidate their origin and role in deposit formation. Siderite replaces limestone and contains ≤9 wt. % Mn, is LREE-depleted (PAAS-normalised REEY diagrams), and has low (<20) Y/Ho ratios. Sideritisation occurred due to dissimilatory iron reduction (DIR) that led to the breakdown of Fe-Mn-oxyhydroxides and organic matter, as indicated by light δ13CVPBD values and negative Y anomalies. The baryte body is dominated by a microcrystalline variety that locally develops a radial texture and coarsens to a tabular variety; it also occurs intergrown with, and as veins in, massive sulphides. Based on fluid inclusion data from previous studies, the coarser baryte types grew from a hot (>200 °C) saline (25 wt. % NaCl) fluid containing CO2-CH4 and liquid petroleum. Marine sulphate δ34SVCDT values typical of the Viséan (~15‰) characterise the baryte body and some tabular baryte types, whereas heavier (~20‰) and lighter (~10‰) values typify the remaining tabular types. The variations in tabular baryte relate to distinct zones identified by CL imaging and are attributed to the sulphate-driven anaerobic oxidation of methane (SDAOM) and oxidation of excess H2S after sulphide precipitation. These results highlight the importance of hydrocarbons (methane and organic matter) in the formation of both the siderite and the baryte at Walton and that DIR and the SDAOM can be important contributing processes in the formation of SEDEX deposits.

Peraluminous rare-metal granites and pegmatites (RMGP) formed in late-orogenic settings represent an important source of elements essential to the energy transition and the electronics industry, such as Li, Ta, Nb and Sn. However, exploration for RMGP in crystalline basement is hampered by their typically small size, lack of distinctive petrophysical characteristics, and proximity with earlier, larger barren composite granitic plutons that may mask their presence. This paper reviews the main geochemical features of late-Variscan, 315-to-310 Ma RMGP in the northern French Massif Central (FMC) to better define useful geochemical proxies relevant to exploration targeting. The northern FMC defines a ca. 150 km-long metallogenic province that hosts three types of RMGP: (i) the Beauvoir and Montebras leucogranites, (ii) the Ch & eacute;deville pegmatite field, and (iii) the Richemont rhyolite. Based on a compilation of whole-rock geochemical data for these RMGP (n = 151) and other late-Variscan peraluminous granites in the FMC (n = 1953), we examine the enrichment of rare elements (Li, F, Be, Nb, Ta, Sn, W) as well as indices of magmatic fractionation and hydrothermal alteration in these settings. The RMGP are variably enriched in Li (372-11,200 ppm; avg = 3500 ppm), F (1475-40,000 ppm; avg = 15,010 ppm), Be (3-506 ppm; avg = 107 ppm), Nb (25-200 ppm; avg = 79 ppm), Ta (23-447 ppm; avg = 116 ppm), Sn (19-13,311 ppm; avg = 1069 ppm) and W (3-312 ppm; avg = 38 ppm), of which the Beauvoir leucogranite is the most enriched. Compared to the peraluminous cordierite-biotite and two-mica granites in the FMC, the RMGP are strongly fractionated with very low Sigma(Fe + Mg + Ti), low Nb/Ta (<2), Zr/Hf (<20) and Th/U (<1) ratios, and high Rb/Sr ratios (>10). In addition to these striking features, the RMGP show a systematic spatial association with evolved two-mica granites containing elevated contents of Li (avg = 627 ppm), F (avg = 4462 ppm), Be (avg = 28 ppm), Nb (avg = 32 ppm), Ta (avg = 14 ppm), Sn (avg = 122 ppm) and W (avg = 19 ppm), which are 2-4 times higher relative to other peraluminous two-mica granites in the FMC. The emplacement of these evolved granites was synchronous with magmatism at ca. 330-315 Ma, preceding and partly overlapping the formation of RMGP. Interpolated element distribution maps from the studied areas show large geochemical halos for Li, Be, F and Sn (+/- W) around the granites spatially associated to RMGP, with concentrations exceeding ten times upper continental crust values, and extending several km from the plutons. Due to their highly-evolved character and large geochemical footprints (>10 s km(2)), the granitic plutons associated with RMGP represent pre-enriched, specialized precursors for rare-metal mineralization. Given the regional extent of evolved peraluminous leucogranites in the northern FMC, we conclude that there is a significant mineral potential for rare metals (especially Li) and that future geochemical surveys should considerer areas near specialized leucogranites as high-priority targets to search for new concealed RMGP occurrences.

Previous studies of the mid-Cretaceous (ca. 85 Ma) LCT-type Little Nahanni Pegmatite Group (LNPG; Northwest Territories, Canada) document disequilibrium textures and pervasive metasomatism associated with rare-metal (e.g., Ta, Nb, Sn) mineralization. As in other pegmatite settings, the source of the melts and the nature and origin of pervasive metasomatism remain enigmatic. To resolve these latter issues, an integrated study of bulk O and H isotope analysis of mineral separates (quartz, K-feldspar, albite, muscovite, garnet), in situ Secondary Ion Mass Spectrometry (SIMS) isotopic (O) analysis of quartz and albite, and in situ Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) trace element analysis of quartz was done in concert with cathodoluminescence (CL) imaging and petrographic observations. Quartz with elevated delta O-18 values (delta O-18(quartz) = 10 to 16.3 parts per thousand) also have high Ti-in-quartz temperatures (551 +/- 17 degrees C to 603 +/- 16 degrees C). These data along with their pristine nature from CL imaging suggest some localized melt-wall rock (WR) exchange occurred at the time of pegmatite melt emplacement. Furthermore, the elevated delta O-18 values indicate a crustal source (i.e., S-type granite) for the LNPG parental melt, which also overlaps with delta O-18(quartz) data for granitoids of the mid- to Late-Cretaceous Selwyn Plutonic Suite of this area. In contrast, the large range for delta O-18 values for metasomatic minerals, such as albite (-3.0 to +18.3 parts per thousand) indicate a complex evolution involving multiple oxygen isotopic reservoirs, in particular incursion of meteoric water previously equilibrated with metasedimentary wall rocks. Finally, the large range for mineral pairs (e.g., Delta(quartz-albite) = -5.1 to +14.3 parts per thousand) and abundance of dissolution features in late-stage assemblages unequivocally indicates that sub-solidus fluid:rock interaction was responsible for such large spreads in delta O-18 and values delta D values, although other processes (e.g., disequilibrium crystallization, thermal gradients, rapid cooling) might have also contributed, but to lesser extents.

Magmatic volatile phases play a major role in igneous systems, but indirect sampling of the magmatic fluid, especially for basic magmas, remains challenging to document. Here, we report compelling evidence of primary fluid inclusions trapped within magmatic ilmenite from two different basic intrusive settings: Armorican Massif (France) and Central Iberian Zone (Spain). Fluid inclusions have a solute chemistry dominated by sodium, calcium, chlorine, sulfur and iron, with detectable contents of metals and metalloids and thus likely record the onset of late-stage magmatic volatile saturation in these basic magmas. Hence, we argue the presence of fluid inclusions in ilmenite may be a good indicator for magma degassing in these settings and importantly records the magmatic-hydrothermal transition. Additionally, this study suggests that the trapping of the magmatic volatile phase during ilmenite (and other opaque minerals) crystallization may be more common but at present an underappreciated phenomenon in basic igneous magmatic systems. Fluid inclusions within ilmenite record primary magmatic fluids in intrusive mafic rocks and may work as a proxy for mafic magma degassing, as shown by geochemical data from inclusions in mafic samples from the Armorican Massif and the Central Iberian Zone.

The Macusani Volcanics and related rocks (SE Peru) are well known examples of erupted strongly peraluminous rare-metal rich silicic magmas. We used the phenocryst/matrix glass method to determine relevant mineral/melt partition coefficients to facilitate modeling of such systems. Concentrations of trace (Li, Be, B, Al, P, Ti, Mn, Zn, Ge, Rb, Sr, Zr, Nb, Sn, Cs, Ba, La, Sm, Eu, Gd, Yb, Ta, W, Pb and U) and major elements were measured in obsidians, matrix glasses, glass inclusions, phenocrysts and phases from biotite reaction zones by Laser-Ablation ICP-MS and Electron Microprobe Analysis. The derived phenocryst/melt partition coefficients for quartz, plagioclase, sanidine, biotite, muscovite, andalusite and ilmenite are compared with values from reference silicic magmas and literature. Mineral/biotite partition coefficients are calculated for tourmaline and hercynite. The database is then applied to model chemical fractionation in Macusani magmas. Fractional crystallization and partial melting trends (with the B concentration used as a proxy for the fraction of residual liquid) generate progressively more evolved (higher Rb, Nb, Sn, Cs and Ta and lower Sr, Ba and Pb) residual liquids. The trace element concentrations in obsidians are reproduced for 50–70% crystallization of matrix glasses from ash-flow tuffs. This demonstrates that differentiation of magmas parental to the ash-flow tuffs can generate the highly evolved obsidian-forming liquids. Based on this, we present an updated model for crustal melting and the generation of the Macusani magmas. A metapelitic component dominates the source region but calcic plagioclase cores enriched in Sr, Ba and La suggest an affiliation with mafic magmas, which were likely potassic to ultrapotassic. The presence of a mafic component is consistent with the high heat fluxes in the source region and accounts for specific magmatic variables (i.e., middle crustal anatectic zone, very reducing fO2, high F). Petrogenetic processes differ significantly between Macusani Volcanics suites and two-mica leucogranites despite both having nearly identical source rocks, mineral assemblages and compositions.

The Neoarchean diorite- and tonalite-dominated Chibougamau pluton (Canada) is ideal for case studies dedicated to the petrogenesis and timing of emplacement of fertile magmatic systems and associated Cu-Au porphyry systems. Using whole-rock analyses, geochronology, and zircon chemistry, it is determined that an early magmatic phase (pre-2714 Ma) is derived from a dioritic magma with a moderate ƒO2 (ΔFMQ 0 to +1), which is optimal for transporting Au and Cu, and that diorite is a potentially fertile magma. Field descriptions indicate that the main mineralizing style consists of sulfide-filled hairline fractures and quartz–carbonate veins. This is likely the consequence of fluid circulation facilitated by a well-developed diaclase network formed following the intrusion of magma at about 4–7 km depth in a competent hosting material. The petrographic features of fluid inclusions (FIs), considered with their microthermometric data and evaporate mound chemistry, suggest the exsolution of early CO2-rich fluids followed by the unmixing of later aqueous saline fluids characterized by a magmatic signature (i.e., Na-, Ca-, Fe-, Mn-, Ba-, and Cl-F). The type of magmatism and its oxidation state, age relationships, the nature of mineralization, and fluid chemistry together support a model whereby metalliferous fluids are derived from an intermediate hydrous magma. This therefore enforces a porphyry-type metallogenic model for this Archean setting.

Abstract The metaturbidite‐hosted, ∼380 Ma Dufferin gold deposit, Meguma terrane, northeastern Appalachian Orogen (Nova Scotia, Canada) is an orogenic gold deposit with mineralized saddle reef‐type quartz veins hosted by metasandstones and black slates in a tightly folded anticline. Together with native gold inclusions, genetically related hydrothermal carbonaceous material (CM) in veins occurs as pyrobitumen in cavities and along fractures/grain boundaries proximal to vein contacts and wallrock fragments. Integrating several microanalytical methods we document the precipitation of gold via coupled fluid‐fO2 reduction (via interaction with CM) and pH increase. These changes in fluid chemistry destabilized gold bisulfide complexes, leading to efficient Au precipitation from a gold‐undersaturated (0.045 ± 0.024 ppm Au; 1σ; n = 58 fluid inclusions) aqueous‐carbonic fluid (H2O‐NaCl‐CO2 ± N2 ± CH4). The proposed mineralization mechanism is supported by: (a) a complementary decrease in Au and redox‐sensitive semimetals (As, Sb), and increase in wall rock‐derived elements (i.e., Mg, K, Ca, Sr, Fe) concentrations in fluid inclusions with time; (b) a corresponding decrease in the XCO2, consistent with CO2 removal via reduction/respeciation and late carbonate precipitation; and (c) gold embedding in, or on, the surface of CM inside mineralized cavities and fractures. Despite mineralizing fluids transporting low concentrations of Au far from saturation, precipitation of gold was locally evidently high where such fluids interacted with CM, contributing to the overall gold endowment of Meguma deposits. This work re‐emphasizes CM as a potential prerequisite for efficient gold precipitation within the overall genetic model for similar orogenic metasedimentary settings globally where the presence and/or role of CM has been documented.

Red sandstone of the Proterozoic Aston Formation (Nunavut, Canada) is exposed in the same geographic area as the Storm Cu showing in the Paleozoic-carbonate-hosted Polaris Zn-Pb district (Arctic Canada). The similar to 800-m-thick Aston Formation experienced successive burial and exhumation episodes, with maximum burial (>3 km) at the time of the Devonian Ellesmerian orogeny. A petrographic and in situ SIMS oxygen isotope study identified redbed diagenetic events, associated fluid types and temperatures, and their relative timing. The first hematite coat (Hem1) developed in the Proterozoic. Intrusion of Proterozoic dykes and sills heated local formation water to high temperatures (130-223 degrees C), resulting in precipitation of patchy Qz1 cement in a shallow-burial environment. The Fe and Si were probably derived through alteration of non-quartz silicate detritus. In the Paleozoic, a bleaching (reducing) event removed most Hem 1; the reduced fluid may have been related to regional Zn mineralisation throughout the Polaris district during the mid-Paleozoic Ellesmerian orogeny. Ensuing pressure-solution during maximum burial was probably also Ellesmerian. A second hematisation episode (Hem 2) encloses the pressure-solved quartz-grain contacts. Coeval with Hem 2 was pervasive Qz2 cementation from a low- to mid-latitude, meteoric-derived, oxidised hydrothermal (140-180 degrees C) fluid that supplied externally derived Si and Fe, probably in the Early Carboniferous. The nature and timing of the fluid events indicated by the Aston Formation's diagenetic history closely match the fluid history recorded in both Cu and Zn mineralisation in the Polaris district. This relationship strongly supports the concept that Cu in sedimentary-rock-hosted ore deposits can be sourced from redbeds, even those whose depositional age and environment is much older than, and geodynamically unrelated to, the fluid event(s) that caused diagenetic reddening and Cu transfer from source rock to mineralising site.

The Neoarchean Windfall gold deposit, hosted in the Urban-Barry greenstone belt of the Abitibi subprovince (Quebec, Canada), represents an emerging and significant Au deposit with a resource of 7.4 Moz of Au. It is hosted in 2717 Ma bimodal volcanic rocks that are cut by several generations of calc-alkaline quartz-feldspar porphyry dikes separated into (1) a 2697.6 ± 2.6 Ma group spatially related to Au mineralization and (2) a 2697.6 ± 0.4 Ma group that truncates the earlier dikes and the Au mineralization. The Au zones are structurally controlled and localized to faults and fractures proximal to the contacts of the early quartz-feldspar porphyry dikes; these zones form thin, subvertical, and elongate lenses plunging 35° east-northeast. Gold mineralization, present as both free gold and inclusions in pyrite, occurs (1) in gray quartz veins and stockworks with pyrite and subordinate carbonate and tourmaline and (2) in pervasive to patchy sericite-silica-pyrite-carbonate ± tourmaline ± fuchsite alteration zones. The Au mineralization and associated hydrothermal alteration, along with all the host rocks that include postmineralization intrusions, are overprinted by D2 deformational features that include a penetrative fabric, shear zones, and associated folds. The spatial and temporal association of the quartz-feldspar porphyry intrusions with the Au mineralizing event at the Windfall gold deposit, along with its elemental association (Ag, As, Sb, S, Se, Bi, Te, ± Zn, Cu, Pb, Mo, W), suggests an intrusion-related model and contrasts with the more abundant orogenic gold deposits in the Abitibi greenstone belt. This interpretation has important implications both locally and regionally for Au exploration in Archean greenstone terranes.

The San Rafael Sn (-Cu) deposit, located in the Eastern Cordillera of southeast Peru, is one of the world's largest cassiterite-bearing vein systems (>1 Mt Sn produced since 1969). The deposit consists of a quartzcassiterite-chlorite-sulfide lode system spatially associated with an upper Oligocene (ca. 24 Ma) S-type granitic pluton. Based on a revised paragenetic sequence for the deposit, we interpret the temporal setting of both magmatic (biotite, K-feldspar) and hydrothermal (muscovite, adularia, cassiterite) minerals analyzed by 40Ar/39Ar step-heating and U-Pb laser ablation- inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochronology. The least-disturbed biotite sample from the megacrystic monzogranite yielded a 40Ar/39Ar plateau age of 24.10 +/- 0.26 Ma (2s), which constrains the time of cooling of the upper part of the pluton to below 300 degrees C. Greisen developed on top of the granitic cupola and its immediate metamorphic aureole dated at 24.24 +/- 0.24 Ma (2s; 40Ar/39Ar muscovite average plateau age) is interpreted to be contemporaneous with the emplacement of pre-ore quartz-tourmaline veins and breccias. In situ U-Pb dating of cassiterite, including both botryoidal cassiterite ("wood tin") and coarse-grained cassiterite in quartz-chlorite veins and breccias, constrains the timing of the main Sn ore stage to between 24.10 +/- 0.37 and 23.47 +/- 0.53 Ma (2s). Botryoidal and coarse-grained cassiterite are characterized by similar trace element compositions with fluctuating metal concentrations across growth banding, suggesting significant changes of physicochemical conditions of the hydrothermal system during cassiterite precipitation, likely caused by rapid and repeated mixing between magmatic fluids and meteoric groundwaters. Polymetallic sulfide-rich veins and quartz-carbonate veins are constrained to have formed between 22.72 +/- 0.11 and 22.29 +/- 0.24 Ma (2s), based on adularia 40Ar/39Ar plateau ages. The latter overlap partially reset 40Ar/39Ar age spectra for K-feldspar megacrysts in the host granite and thus reflect pervasive alteration by hydrothermal fluids. Collectively, the results show the magmatic-hydrothermal system spanned at least 2 m.y. with the main Sn ore stage representing <1 m.y. in the lifetime of the deposit. The latest polymetallic stages postdate the main Sn ore stage by ca. 1 m.y. and reflect the waning of the hydrothermal system, accompanied by additional incursion of meteoric groundwaters. This study provides further evidence that the present-day exposed level of the San Rafael granite was a passive host for the Sn mineralization and only provided the structural focusing for the mineralizing fluids derived from a deeper part of the magmatic system.

A comprehensive study of samples from MVT–type base-metal (Zn-Pb) deposits from across the Canadian Cordillera was done to compare and contrast features and assess their relevance in the context of sulphide mineralization. Petrography and supported CL imaging indicates early host rock dissolution to form secondary fine-grained dolostone during marine cementation is followed by multiple generations of dolomite cements (low T, fine-grained to coarser, higher T varieties) that overlaps with Zn-Pb sulphides which is succeeded by a later barren calcite stage. Ore-stage dolomite is often rich in Fe (<1.3 wt. % FeO) and hosts small sphalerite inclusions. Sphalerite-hosted fluid inclusions record Th values (77–214°C) and salinities (1–28 wt. % equiv. NaCl±CaCl2) that reflect fluid mixing with no single fluid type related to sulphide mineralization. In situ SIMS δ18OVSMOW data for dolomite and calcite (13 to 33‰) suggest involvement of several fluids (i.e., seawater, basinal, meteoric) over a large temperature range at varying fluid-rock ratios. In situ SIMS δ34SVCDT data for sphalerite and pyrite indicate a large variation (8 to 33‰), but with smaller ranges (<2 to 3‰) for the settings studied, and suggest reduced S was produced dominantly via TSR processes from homogeneous sulphur reservoirs. Together the datasets suggest involvement of several fluids in the mineralizing process with mixing of a S-poor, metal-bearing fluid with a metal-poor, S-bearing fluid.

Discriminating Archean Au deposit types and related ore-forming processes is challenging but paramount for increasing Au exploration success. This study tests the validity of applying geochemical data generated from conventional bulk versus modern in situ methods as discriminants for classifying Au deposits in the Archean Swayze greenstone belt with further comparison to other deposits in the contiguous Abitibi greenstone belt and Red Lake area (Superior Province, Canada). The study used five well-characterized Au settings, based on new mapping, as a basis for evaluating in situ (δ18Oquartz, δ33, 34Ssulfide, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of pyrite, electron microprobe analysis of gold), and whole-rock geochemical datasets to resolve whether intrusion-related Au deposits can be discriminated from orogenic-type Au deposits. Results show that the in situ methods provide insight into processes related to Au mineralization, both primary and subsequent remobilization and upgrading, and define elemental and isotopic correlations that cannot be resolved using conventional bulk methods. For example, when comparing the whole-rock to laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace metal data, only Ag, Te, and Hg show a consistent positive correlation with Au across deposit types in both data sets. Furthermore, the wholerock datasets combined with in situ isotopic analysis suggest the Archean sanukitoid-associated Au deposits represent a distinct group of intrusion-related deposits with mineralization characterized by low δ34Spyrite (<–5 to –25‰), inferred high fO2, an Hg-Te signature, and hosted in intrusions of <2690 Ma that predate shearing. The data and interpretations presented herein provide a baseline that can be widely utilized in future studies of Au deposits.

The Mississippian (Visean) Windsor Group of Atlantic Canada consists of a lower carbonate unit overlain by a thick succession of evaporite, clastic, and carbonate rocks. It hosts numerous Zn-Pb deposits, including the Scotia (formerly Gays River deposit), Walton and Jubilee deposits in Nova Scotia, and a number of occurrences on the Port au Port Peninsula, Newfoundland. Geological and geochemical studies show that these deposits share a number of important characteristics, including location on the flanks of sub-basins in carbonate rocks at the base of the Windsor Group, strong structural control on mineralization, and metalliferous fluids sourced from the underlying basement rocks. Despite these similarities, there is significant inter-deposit heterogeneity, and individual deposits can be classified as typical MVT or SedEx/CD, or deposit types transitional between these end-member types (akin to Irish-type deposits in the Irish Midlands) based on conditions at the site of mineralization. It is best to describe the mineralizing system responsible for the formation of these deposits using a mineral-system approach, focussing on regional-scale characteristics such as triggers for mineralization (e.g., edge-driven convection during transtensional tectonics) and favourable crustal architecture to transport metalliferous fluids to suitable mineralization sites. Ongoing research using state-of-the-art geochronological and geochemical techniques aims to advance the understanding of the timing and nature of mineralizing processes in the sedimentary rock-hosted Zn-Pb deposits of the Maritimes Basin.

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment.

The Wawa gold corridor, located in the Michipicoten greenstone belt of the Superior province, Canada, com-prises Au-bearing shear zones that crosscut the 2745 Ma Jubilee stock and that evolved during protracted deformation (D1-D3). Numerous generations of sulfide minerals crystallized before, during, and after these deformation events, and gold is associated with D1 arsenopyrite, D2 pyrite, and Bi-Te phases and chalcopy-rite in assemblages that crosscut D3 veins. Observations of porosity and inclusions in D1 arsenopyrite and D2 pyrite suggest these sulfides underwent coupled dissolution-reprecipitation reactions. By coupling these tex-tural observations with trace element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), it is evident that such replacement reactions generated gold from Au previously in solid solution. Conversely, textural relationships among paragenetically late gold and Bi-Te minerals are consistent with the precipitation of these phases from Bi-rich polymetallic melts. Mass balance calculations involving comparisons of the mass of Au in sulfides and the total mass of Au in their associated host rocks indicate that only D1 arse-nopyrite contained enough Au to account for whole-rock Au content and overall deposit grade. Although D1 arsenopyrite is less volumetrically abundant than the various pyrite generations present in the deposit, it is often replaced by the later pyrite types, which is compatible with higher initial volumes of arsenopyrite than what is presently observed. It is concluded that the D1 Au + arsenopyrite event was the principal Au-mineralizing event in the Wawa gold corridor and that the other gold-bearing assemblages (i.e., gold + D2 pyrite, gold + Bi-Te phases + chalcopyrite) largely represent secondary mobilization of this primary enrichment. Given that LA-ICP-MS sulfide chemistry is regularly used in orogenic Au research, the approach outlined herein to assess the relative impact of distinct Au-and sulfide-mineralizing events could easily be applied to the study of other Au deposits in which complex hydrothermal parageneses are recognized.