An investigation of some sulfide deposits of the rambler area, Newfoundland

Abstract

The geology of the Rambler area, Newfoundland, is described. The rocks of the area consist mainly of ultramafic and tholeiitic pillow lavas and associated pyroclastic rocks. Clastic sedimentary rocks, acidic lavas and pyroclastics, and thin units of an acidic ‘chert-like’ rock are interbanded with the lavas and pyroclastics. Metadolerite dikes intrude all other rocks in the area. The field and petrographic relationships suggest that the area has undergone at least three deformational and two meta- morphic events. The first deformational event was mainly constrictive and produced rock fabrics which locally approach those of L tectonites; mineral and particle lineations are abundant. This deformational event was accompanied by meta- morphism to the quartz-albite-epidote-almandine subfacies of the greenschist fades. Structures produced by the first deformational event were folded by at least two later deformations into earlier tight, northeast plunging, isoclinal folds which were followed by development of open recumbent folds. A second metamorphic event which appears to have post dated the folding, attained conditions of biotite grade green- schist metamorphism. Major and trace element data are presented for the country rocks. The tholeiitic lavas are chemically similar to present day ocean floor basalts and the ultramafics to rocks described from the Komatii formation in the Barberton Mountain Land, South Africa, by R.P. Viljoen and M.J. Viljoen in 1970. The association of ultramafic lavas, ocean floor type lavas basic pyroclastics, ' chert - like' sediments, acidic lavas and low potassium basic intrusives (metadolerites) suggests that the Rambler area represents an ancient ocean floor complex - probably part of an ophiolite complex. The geology and mineralogy of several of the sulfide deposits are described, their textures being explainable in terms of the deformational and metamorphic events affecting the area. The sulfide deposits have been deformed and metamorphosed during the first constrictive deformation and their textures are the result of recrystallization under conditions of the biotite grade greenschist facies of metamorphism. Fluidinclusion filling temperatures on the quartz gangue in remobilised sulfide veins gave temperatures (uncorrected for pressure) of crystallization of 145~330 C. The geochemistry of the East Mine ore body is described and the genesis of the sulfide deposit s is discussed in the light of the geochemical and petrological data. Although it is difficult to establish clearly the mode of formation of the highly metamorphosed and deformed sulfide deposits the bulk of available in formation favours a 'syngenetic’ rather than an ' epigenetic replacement’ mode of formation.