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In orogenic gold systems, the source of the fluids and the processes leading to mobilization, transport, and deposition of gold remain debated. Most studies focus on endowed rather than on gold-poor orogenic systems to unravel the 'key' parameters of gold mineralizing processes. Here, we present stable isotope (O, H) data from the Moly-Desgagne--Guercheville fault system (gold-free to low gold endowment) in the Chibougamau area, Abitibi greenstone belt, Canada. The gold-free Moly-Desgagne showing and nearby poorly endowed Hazeur showing and Monster Lake deposit share similar features typical of orogenic systems. The stable isotope compositions of tourmaline and quartz from the Moly-Desgagne--Guercheville fault system also display similar characteristics, such as (1) temperature of vein formation of 345 [+ or -] 86 [degrees]C (1[sigma]); (2) fluid mixing between an upper crustal reservoir (low T - high [delta]D - low [delta][.sup.18]O) and a metamorphic water reservoir (high T - low [delta]D - high [delta][.sup.18]O); and (3) positive [delta][D.sub.fluid] values consistent with multiple boiling-condensation cycles related to fault-valve processes. These characteristics are similar to those from the gold-endowed Val-d'Or vein field. The difference in gold endowment between the Moly-Desgagne--Guercheville and Val-d'Or vein fields may be related to the nature of the fault system (i.e., terrane-bounding or 'intragreenstone belt') and the volume and (or) composition (i.e., gold, its ligands, C[O.sub.2]) of the fluid source rocks. Key words: Abitibi greenstone belt, Chibougamau, orogenic vein systems, mineralizing processes, hydrothermal fluid, stable isotopes (O, H) La source des fluides et les processus menant à la mobilisation, au transport et au dépôt de l'or dans les systèmes aurifères orogéniques font toujours débat. La plupart des études s'intéressent aux systèmes orogéniques riches en or plutôt qu'aux systèmes pauvres en or afin de cerner les paramètres << clés >> des processus de minéralisation. Nous présentons des données sur les isotopes stables (O, H) du système de failles Moly-Desgagné--Guercheville (sans or ou à faible teneur) dans la région de Chibougamau de la ceinture de roches vertes de l'Abitibi (Canada). L'indice exempt d'or de Moly-Desgagné et l'indice Hazeur et le gisement du lac Monster, tous deux à faible teneur, situés à proximité, présentent tous des caractères semblables typiques de systèmes orogéniques. Les compositions d'isotopes stables de la tourmaline et du quartz du système de failles Moly-Desgagné--Guercheville présentent également des caractéristiques semblables telles que 1) des températures de formation de veines de 345 [+ or -] 86 [degrees]C (1[sigma]), 2) le mélange de fluides provenant d'un réservoir dans la croûte supérieure (faible T - [delta]D élevé - [delta][.sup.18]O faible) et d'un réservoir d'eau métamorphique (haute T - [delta]D faible - [delta][.sup.18]O élevé) et 3) des valeurs positives du [delta][D.sub.fluide] concordant avec plusieurs cycles d'ébullition-condensation associés à des processus de << soupape de faille >>. Ces caractéristiques sont semblables à celles du champ filonien riche en or de Val-d'Or. La diférence des teneurs en or entre les champs filoniens de Moly-Desgagné--Guercheville et de Val-d'Or pourrait être reliée à la nature du système de failles (c.-à-d. bordant des terranes ou à l'intérieur d'une ceinture de roches vertes) et au volume ou à la composition (c.-à-d. or, ligands de l'or et C[O.sub.2]) des roches sources des fluides. [Traduit par la Rédaction] Mots-clés : ceinture de roches vertes de l'Abitibi, Chibougamau, champs filoniens orogéniques, processus de minéralisation, fluide hydrothermal, isotopes stables (O, H), 1. Introduction The term 'orogenic gold deposit' (or orogenic vein system) was introduced by Groves et al. (1998) to designate quartzcarbonate lode gold deposits formed in active convergent (synorogenic) tectonic [...]

The ca. 2680 Ma Upper Beaver deposit is an Archean intrusion-related gold–copper deposit located in the Abitibi greenstone belt, Ontario. The deposit is associated with the Upper Beaver Intrusive Complex, which was emplaced in the hanging wall of an extensional listric fault rooted in metavolcanic rocks of the ca. 2704–2695 Ma Blake River assemblage. The fault formed during the development of an overlying basin of fluvial metasedimentary and alkalic metavolcanic rocks of the ca. 2679–2669 Ma Timiskaming assemblage. The Upper Beaver deposit was subsequently rotated to its current position during the formation of a post-Timiskaming fold, the Spectacle Lakes Anticline, associated with the development of the Larder Lake–Cadillac deformation zone, located 7 km south of the deposit. The Upper Beaver deposit is overprinted by the axial planar cleavage of the anticline but is less deformed than other gold deposits located along the deformation zone. Alteration and other pre-existing planar anisotropies enhanced strain partitioning and the development of folds and fabrics in strained mineralized zones of the deposit. Steeply dipping, sericite-altered mineralized zones developed a continuous foliation surrounding boudinaged and recrystallized quartz–calcite–anhydrite veins, whereas strong, shallowly dipping, stratiform, and skarnoid mineralized zones developed a wavy disjunctive cleavage and deformed mainly by folding. The mineralized zones acted as pre-existing anisotropies during deformation and their orientation and composition were key factors in the development of structures at the Upper Beaver deposit, which can be used as a guide for interpreting the development of structures in similar but more complexly deformed deposits along major deformation zones. [ABSTRACT FROM AUTHOR]