Geology of the Gullsbridge copper deposit, central Newfoundland

Upadhyay, H. D. (1970) Geology of the Gullsbridge copper deposit, central Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis deals with (i) the geological setting of the Gullbridge copper deposit at Mineral Point, (ii) the petrography of various rock types occurring within the Gullbridge mine area, (iii) textural relationship among various ore and gangue minerals, (iv) ore genesis, and (v) a sequence of geological events concerning the ore body. -- The Gull Pond area is underlain by predominantly volcanic and pyroclastic rocks that range from Ordovician to Silurian in age. The ore body occurs within mafic volcanic rocks of the Roberts Arm Formation of probable Middle Ordovician age. These rocks are regionally metamorphosed to greenschist facies grade. They were intruded by granite-diorite bodies during the Devonian period. Numerous faults of regional scale traverse the Gull Pond area. One fault, which is only partly defined, is assumed to pass through Mineral Point. -- The ore body has a somewhat lenticular form with a northeasterly trend and a westerly dip. It was disrupted by several faults that were, at a later stage, intruded by predominantly mafic dykes. The sulphides are associated with cordierite, andalusite, and anthophyllite assemblages. The host rock for the ore body is a chloritic cordierite rock that contains the cordierite-andalusite assemblage. This is bounded on both sides by cordierite-anthophyllite rock. Hydrothermal activity involving chloritization, silicification, and sericitization affected the zone which is now occupied by the ore body. -- The opaque minerals occurring in the ore samples include chalcopyrite, pyrrhotite, and pyrite with subordinate magnetite, ilmenite, hematite, sphalerite, galena, and one unknown mineral referred to as "X". The sulphides have replaced some of the pre-existing gangue minerals. Several textures of special interest are described. -- On the basis of meager petrochemical data, a subtractive metasomatism, accompanied by contact metamorphism, of metabasalts is suggested as a process for the origin of the cordierite-andalusite and cordierite-anthophyllite assemblages. Despite rather non-conclusive evidence, the author proposes a modified volcanic exhalative origin of the ore body whereby the sulphides were remobilized and emplaced along the assumed fault zone at Mineral Point. -- Four phases of deformation have been recognized in the rocks underlying the mine area. A sequence of geological events and their time relationships to various ore and gangue minerals is presented. Suggestions are made for further geological investigation of the Mineral Point - Southwest Shaft area.

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