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The East Branch Brook (EBB) metagabbroic dykes, host to a portion of the Clarence Stream gold deposit, are situated within the contact metamorphic aureole of the Middle Devonian I-type Magaguadavic Granite on the northwestern margin of the post-orogenic Saint George Bathohth. They are highly deformed, light- (type I), intermediate- (type 2) to dark-coloured (type 3) dykes containing auriferous quartz veins that occupy brittle to ductile northeast-trending shear zones in shallow marine, hornfelsed, volcaniclastic, sedimentary rocks of the Silurian Waweig and Oak Bay formations. The shear zones parallel the regional structure as a result of proximity to the faulted boundary (Sawyer Brook fault) between the Ordovician St. Croix terrane to the northwest and the Silurian to Early Devonian Mascarcne Basin to the southeast. Geochemical studies of the EBB dykes indicate that three pulses (Fe-rich. intermediate, and Mg-rich) of subalkaline to slightly alkaline continental tholeiitc magmas were generated in a transpressional environment during the Early Silurian to Early Devonian Positive eNd values indicate their derivation from a partially depleted mantle source during faulting and nft-related events  Although the geochemical data (Fe- and Ti-depletion) indicate calc-alkaline affinity for the nearby Bocabec intrusive complex, eNd values and primitive mantle-normalized spider diagram patterns are similar to those of the EBB dykes. In contrast, the St. Stephen Intrusion appears more primitive with within-plate tholeiitic to slightly alkalie affinity   RESUME  Les dykes metagabbroiques du ruisseau East Branch, qui abritent une partie du gite aurifiere dc Clarence Stream, sont situees a l'inteneur de 1'aureolc de metamorphismc de contact du granite du Devonian moyen de type 1 de Magaguadavic sur la limite nord-ouest du batholithe postorogenique de Saint George. Il s'agit de dykes extrememeni deformes de teinte pale (type 1) et intermediaire (type 2) a foncee (type 3) renfermant des filons de quartz aurifere qui occupent des zones de eisaillement cassantes a deformables, orientees ver\ Ic nord-est. dans des roches sedimcntaires volcanoclastiques a comeenncs marines peu profondes des formations silunennes de Wawcig el d'Oak Bay. La proximile de la limite faillee (faille du runsseau Sawyer) entre le terrane ordovicien de St. Croix, au nord-ouest et le bassin du Silurien au Devonien inferieur de Mascarenc. au sud-est, a amene les zones du eisaillement a longer parallelement la structure regionale. Des eludes geochimiques des dykes du ruisseau East Branch revelent que trois impulsions (composante riche en Fer. composante intermediaire et composante riche en Mg) de magmas tholeutiques continentaux, allant de subalcalins a legerement alcalms sont survenues dans un environnement transpressionnel pendant la periode du Silurien inferieur au Devonien inferieur. Les vateurs positives de eNd lemoignent de leur provenance d'un manteau particllement appauri pendant la formation de failles et des phenomenes apparcntes a une distension   Meme les donnees geeochimiques (appaurassement en Fe et en Ti) revelent unc affinite calcoalcaline du complexe intrusif proche de Bocabec. les valeurs de eNd et les configurations de diagrammes en araignee normalisees du manteau primitif sont analogues a celles des dykes du ruisseau East Branch Par contre, l'intrusion de Saint Stephen semble plus primitive avec une affinite mira-plaques allant de tholenlique a legercment alcaline   Traduit par la redaction

atlantic geology

Geochemistry and petrogenesis of the East Branch Brook metagabbroic dykes in the Sawyer Brook fault zone, Clarence Stream gold prospect, southwestern New Brunswick