Mapping of metavolcanic, metasedimentary, and metaplutonic rocks in the vicinity of the Northeast Margaree River, west-central Cape Breton Highlands, has been carried out on 1:10 000 and 1:25 000 scales. The Jumping Brook metamorphic suite (redefined) consists of a lower unit of metabasalts and associated pyroclastic and sedimentary rocks (Faribault Brook metavolcanics), overlain by quartz-rich sedimentary rocks with local conglomerate and tuff (Barren Brook schist), and semi-pelitic to psammitic schists (Dauphinee Brook schist), which grade into porphyroblastic schists ranging up to staurolite-kyanite grade (Corney Brook schist). Medium grained amphibolite (George Brook amphibolite) with relict dioritic texture is common in the sequence and probably represents synvolcanic intrusions. The Belle Cote Road gneiss, an Ordovician-Silurian tonalitic to granodioritic orthogneiss considered part of the Pleasant Bay Complex, forms an elongated belt through the central highlands. These units can be traced from the Cheticamp River into the central highlands in the area bounded by Highland and Fielding roads. They are intruded by a range of foliated to undeformed Silurian to Devonian granitoid rocks. Massive sulphide deposits, common in the vicinity of Faribault Brook, are localized near the transition from metavolcanic to metasedimentary rocks. However, shearing has remobilized sulphides in some deposits, while others are associated with unrelated, later shear zones. The age of the volcanic and sedimentary protoliths of the Jumping Brook metamorphic suite is not known, but a Lower Paleozoic age, previously considered unlikely, now appears possible.

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Early Ordovician (late Arenig) graptolites are identified from strata near the Northwest Gander River of the Exploits Subzone which were previously considered to be of Silurian and/or middle Ordovician age. A second locality within a graphitic shale yields a Middle Ordovician (Caradoc) graptolite assemblage, suggesting that it is equivalent to the Lawrence Harbour Formation. The fossiliferous units are associated with antimony prospects and have fundamental implications regarding structural interpretation and age of mineralization. The early Or dovician occurrence is similar both in terms of age and biogeographic affinity to that from a fossiliferous greywacke unit which overlies ophiolites at Coy Pond to the south. This apparently confirms that early Ordovician rocks within the Exploits Subzone were formed in high latitudes along the southeast margin of Iapetus and suggests the possibility of widespread turbidite deposition at that time, possibly related to a major tectonic event. On a repere des graptolites de l'Ordovicien inferieur (Arenig tardif) dans des couches gdologiques proches de la riviere Northwest Gander de la sous-zone d'Exploits, qui etaient auparavant considerees comme un secteur de la periode du Silurien ou de l'Ordovicien moyen. Un deuxieme emplacement a l'interieur de schiste graphitique a donne une zone d'assemblage de graptolites de l'Ordovicien moyen (Caradoc), ce qui laisse supposer qu'elle equivaut a la Formation Lawrence Harbour. Les unites fossiliferes sont associees a des zones d'interet d'antimoine et elles ont des repercussions fondamentales en ce qui touche ['interpretation structural et Page de la mineralisation. La venue de l'Ordovicien inferieur est semblable, tant du point de vue de Page que de l'affinite biogeographique, a celle d'une unite de grauwacke fossiliere qui recouvre des ophiolites a Coy Pond, au sud. Ce fait semble confirmer que les roches de l'Ordovicien inferieur a l'interieur de la sous-zone d'Exploits ont ete formees a de hautes latitudes le long de sud-ouest de la rive d'lapetus et il permet de supposer la possibility d'une sedimentation repandue de turbidite a cette epoque, possiblement reliee a un evenement tectonique marquant.

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