Controls of the mineralization in the Betts Cove ophiolite

Saunders, Cynthia Margaret (1985) Controls of the mineralization in the Betts Cove ophiolite. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (12MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The focus of this study is the Betts Cove massive sulphide deposit which is located within the Betts Cove Complex, an Ordovician ophiolite sequence that consists of, in ascending stratigraphic order, an ultramafic, a gabbroic, a sheeted dyke and a pillow lava member. The ophiolite is conformably overlain by the Ordovician Snooks Arm Group, a series of sedimentary rocks and basic to andesitic pyroclastic rocks which are intruded by diabasic sills. The ophiolite and the Snooks Arm Group are intruded by or are in fault or unconformable contact with the surrounding rock units. The pillow lava member of the ophiolite is characterized by variolitic textures which are the result of supercooling. The basaltic members of the ophiolite are characterized by unusually low TiO₂ and high Cr, Ni and MgO concentrations; they show similarities to boninites from the Western Pacific and may have formed in a supra-subduction environment. The Betts Cove sulphide deposit is located at the contact between the sheeted dyke and the pillow lava members. It consists of a massive pyrite-chalcopyrite-sphalerite body underlain by a stockwork of pyrite-chalcopyrite. The deposit has a distinctive footwall alteration zone which consists of a core of quartz-chlorite and a halo of chlorite-albite-quartz. These zones are superimposed on a background greenschist assemblage of actinolite-epidote-chlorite-albite-quartz with relict clinopyroxene commonly preserved. The footwall alteration zones can be related to the amount of water which has passed through the rock. The core zone was the area of highest fluid flux (high water/rock ratio); CaO, Na₂O, Sr, and to some extent, light rare earth elements were leached from this zone. The background assemblage was produced by a low water/rock ratio and that of the halo zone by an intermediate water/rock ratio. Fluid inclusion studies show that the fluids had a composition similar to that of seawater. The Betts Cove deposit shows many similarities to the classic Troodos massive sulphide deposits and is thought to have formed in the same way - by re-deposition of metals which were leached from the ocean crust by circulating seawater. Comparable deposits are currently being formed at the East Pacific Rise and the Galapagos Ridge. The site of upwelling of metal-bearing hydrothermal fluids, probably along faults and fracture zones, is the area of greatest fluid flux; thus the core alteration zone underlying the Betts Cove deposit is interpreted to represent the conduit for the mineralizing fluids which deposited the massive sulphide mineralization. The fluids may have been focussed along faults and permeable zones.

Actions (login required)

View Item