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The geology of Pioneer Gold Mine, Lillooet Mining Division, British Columbia Stanley, Alan David

Abstract

Pioneer gold mine is 100 miles north of Vancouver in the Bridge River area of the Lillooet Mining Division, British Columbia. The mine has been worked extensively for more than 30 years and has produced over a million ounces of gold. The gold occurs in ribboned quartz veins which average less than three feet in width and are classified as mesothermal. The gold content of the veins is variable and it occurs, with a small amount of sulphides. Gold values greater than 0.5 oz. Au/Ton are considered economic. The Pioneer mine occurs in a northwesterly trending zone, called the Cadwallader Gold Belt, formed by the Hurley-Noel formation of sedimentary rocks and the Pioneer formation of volcanic rocks. The gold-quartz veins are genetically related to the Bralorne intrusions which occur within the rocks of this zone. There is a repetition of these formations in the Pioneer property, which can be explained by normal movement on a fault. A wide zone of serpentine marks the position of this fault, which is called the Cadwallader Break. This Break is a first order fault and can be related to second order faults formed during the same period of deformation. These second order faults are now occupied by quartz and form the veins which are mined. Planes of liquid inclusions in the quartz of the quartz veins have attitudes similar to those of the megascopic planes of rupture. These planes of inclusions were formed by the annealing of microscopic fractures in the quartz veins. The attitude of these fractures was determined by the same deformation which produced the megascopic fractures, including the 'Cadwallader Break'. The Bralorne intrusion in the mine area is composed of the Bralorne diorite and soda granite which contain albite as their only feldspar. No evidence has been formed to indicate that the intrusion is formed by the process of granitization. Sodic solutions, possibly parts of the final differentiate of the magma which formed the Bralorne intrusion have caused albitization of the intrusion and the Pioneer formation.

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