Abstracts
Abstract
The I:asi Branch Brook (F.BB) metagabbroic dykes, hosl to a portion of the Clarence Stream gold deposit, are situated within the contact tnelamorphic aureole of the Middle Devonian I-type Magaguadavic Granite on the northwestern margin ot the post-orogcnic Saint George Bathohth. They are highly deformed, light- (type I), intermediate- (type 2) to dark-coloured (type .1) dykes containing auriferous quart/ veins thai occupy brittle to ductile northeast-trending shear /ones in shallow marine, homfclsed. voleaniclastic. scdimcniary rocks of the Silurian Wawcig 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 Karly Devonian Mascarenc Basin to the southeast. Geochemical studies of the FBB dykes indicate that three pulses (Fc-rieh. intermediate, and Mg-rich) of subalkalinc to slightly alkaline continental tholeiitc magmas were generated in a transprcssional environment dunng the Parly Silurian to liarly Devonian Positive t:v, values indicate their derivation from a partially depleted mantle source during faulting and nft-related events
Although the geochemical data (Fc- and Ti-depletion) indicate eale-alkaline affinity for the nearby Boeabcc intrusive complex, ».,,, values and primitive mantle-normalized spider diagram patterns are similar to those of the FBB dykes In contrast, the St. Stephen Intrusion appears more primitive with wiihin-platc tholciitic to slightly alkalic affinity
RESUME
I.es dykes mctagabbroique.s du ruisseau East Branch, qui abntent unc partie du gite aurifiere dc Clarence Stream, soni situees a I'intcneur de 1'aureolc de mctamorphismc dc contact du granite du Devonicn moyen de type I de MagaguadaMC sur la limiie nord-ouest du batholithe postorogenique de Saint George. II s'agit de dykes extremcmcni deformes de tcinte pale (type I) et intcrmediairc (type 2) a foneec (type 3) renfermant des filons de quart/ aurifere qui occupent des zones de cisaillement cassantes a deformables, orientccs ver\ Ic nord-est. dans des roches sedimcntaires volcanoclastiques a comeenncs marines peu profondes des formations silunenncs de Wawcig el d'Oak Bay. La proximile de la limite faillcc (faille du nnsseau Sawyer) enta* le terrane ordovicien de St. Croix, au nord-ouest. el le bassin du Silunen au Devonicn inferieur de Mascarenc. au sud-cst. a amene les zones du cisaillement a longer parallelcmcnt la structure regionale. Des eludes gcochimiques des dykes du ruisseau Fast Branch revelcnt que trois impulsions (composantc riche en fer. tomposante intcrmediairc ct composante riche en Mg) de magmas tholeuiiques continentaux, allant dc subalcalins a legcrement alcalms. sont survenues dans un environncmcnl transpressionncl pendani la periodc du Silurien inferieur au Devonien inferieur. Les vateurs positives de (;NJ lemoignent dc leur provenance d'un manteau particllement appauwi pendant la formation de failles et des phenomencs apparcntes a unc distension
Memc M les donnees (>ei>chimiques (appamnssemenl en Fc el en Ti) revelcnt unc affinile calcoalcalinc du complcxc intnisif proche de Bocabce. Ics valeurs de i\(1 ct les configurations de diagrammes en araignee normalisees du manleau prinntif soul analogues a cclles des d>kes du ruisseau last Branch Par eontrc, I'intrusion de Saint Stephen semblc plus primitive avce une affunte mira-plaques allant de tholenlique a legercment alealinc
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