Geology, geochemistry, geochronology and genesis of granitoid clasts in breccia-conglomerates, MacLean Extension orebody, Buchans, Newfoundland

• Main Author: Stewart, Peter William
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1985
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/6840/; https://research.library.mun.ca/6840/1/PeterWilliamStewart.pdf; https://research.library.mun.ca/6840/3/PeterWilliamStewart.pdf

Granitoid clasts found in association with the transported orebodies at Buchans are largest, and occupy the greatest volume of the host polylithic breccia-conglomerate subunit when proximal to the greatest sulphide accumulation in the sequence of debris flow deposits. The granitoid clasts are typically the most rounded clast lithology present in the debris flow deposits. They decrease in size and volume with increasing distance from the lowermost sulphide-rich sections of the debris flow sequence. They show igneous textures and compositions ranging from trondhjemite (rare) to quartz porphyritic microtrandhjemite to aplite to granophyric aplite. All granitoid clasts have been classified into six ‘types’ based on these textural and grain size differences. The five most abundant ‘types’ are reduced to ‘granitic’ and ‘aplitic’ groups based on textural similarities. -- Hydrothermal fluids deposited calcite, barite, and quartz sericitized plagioclase grains, and chloritized all mafic phases present. Despite this alteration, and variable alkalki metasomatism (loss of K) that is presumed du to late-stage volatile loss, all granitoid clasts appear to have a common magmatic source based on similar trace element abundances. -- The ‘granitic’ group clasts are typically larger, occupy more volume and are more altered than ‘aplitic’ group clasts. The proportion of ‘aplitic’ group clasts to ‘granitic’ group clasts increases with decreasing sulphide concentration in the debris flow sequence. Similarly, the average size and volume occupied by granitoid clasts in debris flow subunits decreases with increasing distance from the sulphide-rich sections of the debris flow deposits. -- All granitoid clasts appear to represent fragments of the same magma system that produced the felsic volcanic rocks of the Buchans Group. This conclusion is based on similar mineralogical and petrographic features, and similar major and trace element abundances (especially TiO2, Zr, Y, V, Nb, Ga and REE) between granitoid clast types and the Buchans ...