<p> The Potterdoal volcanogenic massive sulphide deposit is hosted by a tholeiitic/komatiitic succession located in northern Munro Township, Ontario. An integrated surface and drill core study of this property was undertaken to document the three dimensional structure and stratigraphy of the deposit. Petrography focused on mineralogical changes associated with the hydrothermal alteration within specific units. Several geochemical methods were used to determine the effects of hydrothemal alteration (as quantified by elemental mobility) as well as source magma affinities and tectonic setting. Based on this information, a model for ore genesis was developed. </p> <p> The Potterdoal deposit is hosted by volcanic rock of an iron tholeiite affinity, emplaced within an ocean floor rifting environment. The chemistry of the tholeiites shows similarities to that of large deposits like Kidd Creek, but lacks the felsic component of bimodal volcanism. It is suggested that felsic volcanics are absent because the local crust did not achieve sufficient thickness to allow partial melting of lower crustal material. </p> <p> The deposit consists of a stockwork zone overlain by an extensive massive sulphide lens which lies along a scarp structure defmed in the paleosurface. Stockwork mineralization is narrowly confined to conduits within a fault breccia in the footwall Ore Flow. gabbro, and widens into an overlying tectonic breccia. Sulphide paragenesis appears to be controlled by the thermal solubilities ofthe sulphide minerals, and consists of pyrite, sphalerite, pyrrhotite and chalcopyrite in both stockworks and the massive sulphide lens. The lens occurs at the top of the tectonic breccia near the paleo-seawater interface, and formed by direct replacement of the tectonic breccia. The lens locally exhibits ore grade base metal values (i.e. combined Cu and Zn content of at least 3% ), and shows an upward and outward gradation from chalcopyrite to sphalerite-dominated ore. These features suggest that exhalation of the hydrothermal system was focused into local vent sites. </p> <p> Mass change associated with the hydrothermal alteration envelopes surrounding Ore Flow fault breccia conduits involve loss of Si, Ca, Na and Sr, and gain of Fe, Mg, K, Cu and Zn. These changes are attributed to fluid-rock reactions which are consistent with hydrothermal alteration associated with other VMS deposits, The genetic model suggested for the Potterdoal deposit involves a hydrothermal system driven by heat from the intrusion ofthe Munro-Warden Sill at a high stratigraphic level. The relatively small size of the deposit is probably due to the rapid cooling of the sill, which shortened the life-span of the hydrothermal system. The primary source of metals was the upper portion of the Munro-Warden Sill, as indicated by the high degree of pervasive hydrothermal alteration of this part of the gabbro. </p> <p> Drill core information has also revealed the importance of the Buster Fault in the construction of the currently exposed Potterdoal stratigraphy. Thrusting subparallel to bedding along the Buster Fault during the Kenoran compressional event(~2.6 Ga) was responsible for the local repetition of tholeiitic flows, and has effectively removed the deep footwall rocks originally associated with the Potterdoal mineralization. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19667 |
| Date | 09 1900 |
| Creators | Epp, Mark |
| Contributors | Crocket, James, Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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