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The Val-d'Or vein field (VVF), located in the southern Abitibi subprovince (Québec, Canada), is host to ~ 47 Moz gold and is therefore an example of a greenstone-hosted orogenic gold district. Gold is contained in quartz-tourmaline-carbonate veins that cut As-poor intermediate to mafic volcanic and intrusive rocks, including dioritic, granodioritic and gabbroic sills, dikes, stocks, and plutons. Five investigated orebodies (Goldex, Triangle, Plug #4, Pascalis Gold Trend, Beaufor) host gold in vein- and wallrock-hosted pyrite-rich sulfide aggregates (> 95 vol%) that show a porous core domain (Py1), with abundant inclusions of carbonate, silicate, and Fe-oxides up to several tens of µm in size. A homogeneous pyrite rim domain (Py2) surrounds Py1 and contains most of the gold as native gold and polymetallic (Au-Ag-Te-Bi) inclusions, primarily calaverite and petzite. The two pyrites show different Au and As contents (Py1 = Au ≤ 30 ppm; As ≤ 67 ppm; Py2 = Au ≤ 1250 ppm; As ≤ 550 ppm). Pyrite shows a ubiquitous shift in δ34S values of up to + 3.0‰ from Py1 (δ34S = − 0.4‰ to 5.8‰, n = 32) to Py2 (δ34S = 0.0‰ to 6.3‰, n = 59) and records a small, slightly negative Δ33S signature between – 0.20‰ and 0.01‰. The δ34S shift suggests that removal of reduced sulfur species from auriferous hydrothermal fluids causes the formation of inclusion-hosted gold in Py2 by a decrease in the fluid sulfur fugacity (fS2) through wallrock sulfidation of Fe-oxides. The shift also correlates with locally enriched Co and Ni concentrations in Py1 (< 1 wt%), compared to lower, oscillatory zoned concentrations (< 0.1 wt%) in Py2, respectively, indicating an overall decrease in fluid oxygen fugacity (fO2). Contemporaneously, a decrease in fluid tellurium fugacity (fTe2) drives polymetallic inclusion-hosted gold formation in Py2, initially as calaverite followed by increasingly Ag-bearing petzite and hessite. The multiple sulfur isotopes and trace element compositions recorded in pyrite in the VVF indicate that a homogeneous fluid reservoir introduced gold-sulfide complexes. Even if considered a localized process at the ore-shoot scale, fluid-wallrock sulfidation reactions can lead to a coupled decrease in fS2, fO2, and fTe2 of auriferous hydrothermal fluids in a greenstone-hosted As-poor gold district. [ABSTRACT FROM AUTHOR]

The Canadian Malartic gold deposit was produced by a hydrothermal system that altered the host metasedimentary rocks of the Pontiac Group, metavolcanic rocks of the Piché Group, and associated porphyritic intrusions and mafic dykes. The isotopic footprint in Pontiac metasedimentary rocks is marked by an increase in δ2H values from − 91‰ near mineralization to background values of ca. − 59‰, whereas δ18O values remain relatively constant near 10‰. The isotopic footprint in mafic dykes is marked by an increase in δ2H values from − 84‰ near mineralization to background values of ca. − 73‰, and a decrease in δ18O values from 9.8‰ near mineralization to background values of ca. 8.3‰. Kriging of oxygen and hydrogen isotopic compositions around the Canadian Malartic deposit delineates the isotopic footprint of the deposit. In greywackes, the − 59‰ δ2H isopleth encircles the mineralized domain and is elongated towards the northwest and southeast. In mafic dykes, the − 73‰ δ2H isopleth encircles the mineralized domain as well as a large area to the south and southeast, whereas the 8.3‰ δ18O isopleth encircles the center of the mineralized system and extends over an area towards the southeast. Host rock oxygen and hydrogen isotope compositions therefore define a cryptic alteration footprint up to 2.5 km outside of the Canadian Malartic deposit. The isotopic composition of the metamorphic fluid in equilibrium with the average least altered greywacke at upper greenschist to amphibolite conditions of ca. 550 °C is approximately δ18O = 8.6‰ and δ2H = − 19‰. This is close to the composition of the mineralizing fluid at the Canadian Malartic deposit reported by previous studies. Fluid/rock oxygen and hydrogen isotope exchange modeling indicate that the isotopic footprint formed at relatively low fluid/rock ratios up to 0.5 at temperatures near 350–400 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The La Pointe gold deposit is hosted in Archean rocks near the boundary between the La Grande and Opinaca subprovinces. • It is interpreted as a disseminated, pre-peak metamorphic orogenic gold deposit. • The La Pointe deposit is overprinted by higher, amphibolite-grade, and late retrograde metamorphism. The La Pointe gold deposit is hosted by Neoarchean rocks metamorphosed to the amphibolite facies, straddling the boundary between the La Grande and Opinaca subprovinces, in Eeyou Istchee Baie-James (Québec, Canada). The deposit consists of two zones, Zone 25 and Zone 26, which are oriented WNW-ESE (S 1) and have been deformed and folded by the main regional deformation (S 2). Zone 25 is hosted by biotite-rich paragneiss of the Laguiche Complex (2710–2671 Ma) and the mineralization consists of disseminated native gold along with arsenopyrite, pyrrhotite, chalcopyrite and minor pyrite. The mineralization is associated with recrystallized alteration consisting of quartz, phlogopite, dravite ± titanite, microcline, muscovite and calc-silicate veins. Native gold occurs as inclusions in the metamorphically annealed alteration assemblages and at the margin of arsenopyrite. The low content of gold in arsenopyrite suggests re-equilibration at peak conditions during arsenopyrite recrystallization (325–531 °C) which expelled and crystallized native gold. Zone 26 is hosted in a grunerite-altered BIF of the Yasinski Group (2751–2725 Ma) and is characterized by disseminated pyrrhotite-arsenopyrite-löllingite-chalcopyrite in calcic amphibole-biotite-garnet-tourmaline ± chlorite host rocks. Native gold occurs as inclusions in peak metamorphic minerals (hedenbergite, garnet), or at the contacts between löllingite cores and arsenopyrite rims. The La Pointe deposit is interpreted as pre-peak metamorphic, disseminated orogenic gold deposit, subsequently overprinted by higher, amphibolite-grade, and late retrograde metamorphism. [ABSTRACT FROM AUTHOR]

Tourmaline, scheelite, and magnetite from orogenic gold deposits (n = 22) and glacial sediments (n = 5) of the Val-d'Or mining district (Québec, Canada) were investigated by Electron Probe Micro-Analyzer (EPMA) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) in order to determine their chemical signature and to assess their potential as indicator minerals for gold exploration. Three types of tourmaline are recognized. Type I tourmaline from deposits hosted in felsic and intermediate-composition calc-alkaline rocks has low contents of V, Cr, Mn, Fe, Co, Ni, Zn, and Sn and a high content of Mg compared to Type II tourmaline from deposits hosted in mafic tholeiitic rocks. Type III tourmaline from deposits located at the contact between mafic metavolcanic and metasedimentary rocks shows a chemistry similar to Type I tourmaline with slightly higher Li, Mn, and Pb contents. Tourmaline from orogenic gold deposits is characterized by lower contents of Zn, Cu, Sn, and Pb compared to data from tourmaline associated with Cu-Zn, Pb-Zn-Cu, and Sn mineralization. Till tourmaline carries the chemical signature of that from orogenic gold deposits with a majority having the signature of Type I tourmaline. Orogenic gold deposits scheelite from the Val-d'Or district hosted in calc-alkaline intrusions of intermediate composition displays high Na, REE, and Y contents compared to scheelite from sediment- and mafic-hosted gold deposits. Till scheelite carries the chemical signature of that from orogenic gold deposits. Although rare in orogenic gold deposits of the Val-d'Or district, hydrothermal magnetite in the gold veins is characterized by higher Cr, Zn, Mn, K, Ca, Ti, and Al than magmatic magnetite found in dioritic and gabbroic host rocks. Magnetite associated with gold mineralization forms fine, disseminated grains, suggesting that the coarse-grained magnetite recovered in till does not originate from the gold veins. Till tourmaline and scheelite carry the signature of the orogenic gold deposits and can thus be used for exploration in overburden sediments. • Till tourmaline has the same compositional signature as orogenic gold tourmaline. • Till scheelite is chemically similar to orogenic gold scheelite. • Till magnetite does not originate from the Val-d'Or gold deposits. • Tourmaline and scheelite in till are good indicator minerals for orogenic gold deposits. [ABSTRACT FROM AUTHOR]

This study evaluates the applicability of the clumped isotope thermometry to mesothermal hydrothermal systems (5–10 km depth; 250–450 °C). We measured Δ 47 , δ18O and δ13C of calcite as well as δ18O of cogenetic minerals from typical quartz-calcite ± tourmaline±chlorite orogenic veins from the Neoarchean Augmitto-Bouzan orogenic gold deposits (Abitibi, Canada). Our findings show that caution is required when utilizing the clumped isotope thermometry in the study of old mesothermal deposits. Temperatures calculated from Δ 47 values are systematically and significantly shifted to low temperature, i.e., ∼150 °C rather than the ∼350 ± 50 °C expected for orogenic gold deposit formation and documented using oxygen isotope equilibrium between mineral pairs. We show that the low temperatures estimates resulted from solid-state reordering that occurred in calcite grains during the cooling history of the vein-hosting rocks. Because the fast cooling rates required to preserve the initial temperature of calcite formation in mesothermal hydrothermal systems are geologically unrealistic, we suggest that refractory minerals (i.e., minerals with higher blocking temperature such as magnesite, dolomite, ankerite) should be investigated to apply clumped isotope thermometry in such context. [ABSTRACT FROM AUTHOR]