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Geology of the Deer Horn prospect, Omineca M.D., British Columbia Papezik, Vladimir Stephen

Abstract

The Deer Horn property lies astride the contact of the Coast Range batholith and a group of siliceous and shaly sediments of Jurassic or Lower Cretaceous age. The contact strikes westerly and dips about 50° to the South. The southern three fifths of the property are underlain by granitic rocks, the remaining northern part consists of slightly metamorphosed sediments striking approximately west, dipping about 70° south and believed to form an overturned syncline. The rocks are cut by two albitite dykes and several minor trap dykes. The granitic rocks are divided into two main types, "porphyritic" granodiorite and hornblende granodiorite. The latter contains the main part of the mineral deposit, and is further subdivided into several varieties produced by tectonic movements and hydrothermal alteration. Alkali metasomatism has affected both the granitic rocks and - to a lesser extent - the sediments. Some metasomatic features are discussed in detail. Two veins or vein systems, the Main and the Contact, lie in the hornblende granodiorite and in the contact zone. They strike westerly, converge towards the west and dip towards each other, forming a shallow troughlike structure. Both carry sulphides and minor tellurides with gold and silver. Scheelite occurs sparsely in the veins and in bands of epidotegarnet skarn in the sediments, being somewhat more concentrated in two areas of fine talus in the western part of the property. The Main vein is shown to be a replacement vein formed in a thrust fault. The shearing angle of the fault flattened in the more brittle contact zone, and the fault terminated in a series of complementary shears. The combination of these two factors produced the curving trough-like shape of the vein. The narrow Contact vein was formed in a later gravity fault. The zone of intersection of the two veins was highly sheared and thus rendered more permeable to the mineralizing fluids. This accounts for the numerous high-grade stringers present near the intersection. In view of the known and inferred limits of the two veins it is not expected that the ore will continue either laterally or in depth.

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