Abstract

At the Goodyear Prospect on the Port au Port peninsula in southwestern Newfoundland, narrow, lenticular, crustified veins occupy prominent vertical joints which strike parallel to the axis of a broad anticline in Ordovician limestone. The abundant calcite gangue exhibits excellent comb structure. Galena, the most plentiful sulphide, occurs mainly as subparallel, elongate growths of cubes oriented with trigonal axes normal to the banding of the veins. Zinc sulphide occurs principally as finely colloform-banded, brown sphalerite with bladed structure normal to the banding. An immersion medium of high index revealed wurtzite. Marcasite commonly occurs as nodules displaying concentric banding and radial fibrous structure. Properties of an anomalous variety of marcasite are listed. Pyrite in small amounts is generally associated with marcasite. Fine black powder occurring in marcasite nodules was shown by X-ray to be mainly marcasite. The paragenesis of the primary minerals is given; pyrite and marcasite, and, sphalerite and wurtzite which occur in close spatial association in the ore are believed to be essentially contemporaneous.Evidence is presented that the ores were deposited in post-upper Mississippian time under conditions of low temperature and pressure. Several textural features of the sulphides suggest the importance of colloidal phenomena. Although intrusives are unknown in the vicinity of the deposits, igneous rocks of post-upper Paleozoic age occur in a few places in Newfoundland.

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