Stratigraphic controls on sediment hosted copper mineralization in the transition zone of the Munster Basin, Ireland

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Date
2019-04
Authors
Muhammad, Zahida Zakari
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University College Cork
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Abstract
The Transition Zone in the Munster Basin, which marks the transition between oxidized and reduced facies, hosts widespread copper mineralization which have been subject of much research and controversy. Mineralization is believed to have been due to bacteriogenic sulphide from reduced sea water sulphate mixing with upwelling metal bearing mesothermal fluids and pervasive alteration of feldspars upward and laterally. This thesis attempts to address controversy and improve on previous knowledge by studying stratigraphic controls on focusing fluid flow and localizing mineralization using a transect of the stratigraphic horizon in Mount Corrin/Dereenalomane area in the West Carbery district. Negative sulphur isotope values (δ³⁴S = -11.2‰ to -15.1‰) dominate the middle of the horizon with positive values (δ³⁴S= +0.5‰ to +13.2‰) at the bottom and top, implying both bacteriogenic and hydrothermal sources. Pervasive sericitization, chloritization, white mica, muscovite, and opaques (rarely copper sulphides) observed in petrographic analysis suggest hydrothermal alteration and/or weathering. Microtextural studies show replacement textures in the sequence Chalcopyrite-pyrite, chalcocite-bornite-covellite, covellite. Whole rock analysis revealed Si and Na stripping, progressive alteration in the fine- grained rocks at the base and top of the horizon; high chemical variation and signatures in the coarse-grained middle beds contain the highest concentration of ore grade mineralization (10.2 wt% Cu in one sample, >1000ppm). The findings propose mineralization is diagenetic to epigenetic where fluid ingress was likely through a fault, moving through both primary and secondary porosity accompanied by element leaching and exchange. The Variscan Orogeny remobilized and reactivated fluids. Coarse grained reduced porous sandstones containing most mineralization were mixing sites while the barren fine-grained oxidized purple rocks act as traps. Although the type of mineralization is similar to the Kupfershiefer type, its complexities make it a prime candidate for further research and highlight its uniqueness for other world analogues.
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Stratigraphy , Munster Basin , Transition zone , Copper mineralization
Citation
Muhammad, Z. Z. 2019. Stratigraphic controls on sediment hosted copper mineralization in the transition zone of the Munster Basin, Ireland. MRes Thesis, University College Cork.