TECTONIC CONTROL OF THE ECONOMIC FEASIBILITY OF THE LIMESTONE ACCUMULATIONS IN NIGADOO RIVER SINCLINORIUM, NORTHEASTERN NEW BRUNSWICK

The rocky Brook Millstream Fault Zone (RBMFZ) is one of the major transcurrent shears of the Northern Appalachians. It probably appeared in the Early Silurian, when it controlled the subsidence of a graben-type continental basin. During the Late Silurian - Early Devonian closure of the basin, the zone was mobilized as a strike-slip discontinuity. At its eastern end it may have activated, and partly utilized, the unconformity between the Silurian Chaleurs Group and the Ordovician Bathurst Supergroup. The transpressive nature of the deformation of the rocks in the Chaleurs proto-basin resulted in the formation of the Nigadoo River Synclinorium (NRS) and a number of faults that have the orientation of the RBMF and may have similar internal structure. At the southern limb of the NRS the RBMFZ partially follows the strike of the LaPlante (LP) Formation believed to be of Pridolian age. For the most part the LP Formation comprises calcareous shales, but locally these shales contain allochthonous accumulations of limestone and coarse carbonate breccia. The breccia clasts are predominantly reefal fragments up to 0.1 m in size, included in a siliciclastic, shaly matrix. The carbonates are derived by re-sedimentation of small reefs of Pridolian age, built mainly of laminar stromatoporoids and stromatolitic algae, mudstones and biogenic and polymict breccias. The faunas and the sediments of the reefs suggest a rather low-energy environment and the associated internal breccia and mudflows suggest that the reef mounds were deposited on the upper slope of the margin of a narrow shelf. The limestones are mined by Elmtree Resources LTD in a quarry that is located close to the RBMFZ. The exposures in the quarry reveal complex folding and faulting. The tectonic features determine the economic significance of the limestone accumulations. The mapping of the area shows that the original thickness of the LP is insufficient for mining. However at particular locations, folding and strike-slip displacement multiplied the thickness of LP and made it economically feasible. Prospecting for new reserves and reevaluation of the known reserves are based on structural - geological studies.