Structural Sequence and Its Relationship to Sulphide Mineralization in The Ordovician Lush's Bight Group of Western Notre Dame Bay, Newfoundland

CIM Bulletin, 1972


Mafic volcanic rocks ,of the Lower Ordovician Lush's Bight Group are located in the northwestern part of t he eugeosynclinal belt of t he Newfoundland Appalachian System. The group is flanked on the northwest by upper greenschist to low amphibolite facies Eocambrian-Cambrian metasedimentary and metavolcanic rocks, and is overlain to the sout heast by a sequence of sandstones and mafic to silicic volcanic rocks of Silurian age. The group consists predominantly of pillow lava with lesser amountr;> of pillow breccia and aq uagene tuff. All of the volcanic rocks have undergone a single penetrative deformation in probable Lower Devonian t ime that produced a chlorit e-grade foliation and close to tight major upright folds. This foliation locally post-dates an earlier foliation in planar zones of coarse-grained chlorite schist. The schist zones have a resultant compo- M. J. KENNEDY J. R. DeGRACE M. J. KENNEDY, a native of England, obtained his B.A. at Trinity College, Dublin in 1963 and his M.A. and Ph.D. from the same university in 1966. After working on polydeformed Dalradian and Moine rocks in Ireland, he moved to the Geological Survey of Canada as an N.R.C. Postdoctoral Fellow and worked on the polydeformed Fleur de Lys Supergroup of Newfoundland. He is now studying structural relationships between metamorphic rocks in east-central Newfoundland. He joined Memorial University as an Assistant Professor in 1967 and became an Associate Professor in 1971. His main interests are structures in metamorphic rocks and their relationship to plate movements. He is currently president of the Newfoundland Section of the Geological Association of Canada. J. R. DeGRACE, a native of Ontario, received a B.Sc. (Eng.) at Queen's University in 1969 and an M.Sc. at Memorial University in 1971. He was attached to Nolan, White and Associates, St. John's, in 1971 and is now with the Mineral Resources Division, Newfoundland Department of Mines, Agriculture and Resources. PAPER PRESENTED: at the 74th Annual General Meeting of the CIM, Ottawa, April, 1972. KEYWORDS: Geology, Ore deposits, Structural geology, Sulphide mineralization, Lush's Bight Group, Newfoundland, Appalachians, Volcanic rocks, Notre Dame Bay, Fabric relations, Folding. CIM TRANSACTIONS: Vol. LXXV, pp. 300-308, 1972. 42 site schistose fabric which is broadly concordant with the outcrop of major lithologic sub-divisions of the Lush's Bight Group. The schist zones are interpreted to represent early shear belts in which an early foliation has been folded and transposed by the later regional penetrative deformation of the area. The regional penetrative fabric was crenulated and then folded into major steeply plunging open fol ds with associated segregation kink bands. Sulphide mineralization (pyrite, chalcopyrite, minor sphalerite) is economically significant only in the schist zones and chalcopyrite is enriched in the hinges of the latest folds. It is postulated that the sulphides are pretectonic to t he development of the schist zones in which they are now concentrated and were later remobilized in these zones during subsequent folding.
Keywords: schist, Ordovician, Notre Dame Bay, King's Point, Pillow Lavas