<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)

The giant Kidd Creek Mine is an Archean Cu-Zn-Ag deposit in the Abitibi Greenstone belt, located in the Superior Province of Canada and is one of the largest known base metal massive sulfide mines in the world with a tonnage of 170.7 Mt (Past production, Resource and Reserve). The massive sulfides in Mine D comprise a number of ore lenses that are interpreted to be the downplunge continuation of the Central orebody from the upper mine. These are referred to as the West, Main, and South lenses. The massive sulfides overlie a silicified rhyolitic unit at the top of a mixed assemblage of rhyolite flows, volcaniclastic sediments and ultramafic flows. The sheared nature of the fragmental units in the hanging wall of the deposit, at depth, illustrates the greater deformation that has occurred than in the upper mine. Metal zonation and the distribution of Cu stringer mineralization suggest that the West and Main lenses may be part of a single massive sulfide body (Main orebody) that has been structurally dismembered. The South Lens is a detached body, separated by late faults. The large Cu stringer zone beneath the West and Main lenses has a thickness of up to 150 metres, and is much broader and structurally remobilized in Mine D partially due to a newly identified series of vertically trending offset faults, that extends along the entire length of the massive sulfide bodies. A number of features of the North, Central and South orebodies in the upper part of the mine (e.g., Se-rich halo around Cu-rich zones) have been recognized in Mine D and provide an important framework for correlating the deep orebodies with the upper levels of the mine. Drilling below the current mine levels indicates that the massive sulfide and Cu stringer zones continue below 10,200 feet (3109 m) and highlight the remarkable continuity of the deposit downplunge with no end in sight. Two main ore suites have been recognized in the upper part of the mine and in Mine D: a low-temperature, polymetallic assemblage of Zn, Ag, Pb, Cd, Sn, Sb, As, Hg, ±Tl, ±W, and a higher-temperature suite of Cu, Co, As, Bi, Se, In, ±Ni. More than 25 different ore minerals and ore-related gangue minerals are present, including Co-As-sulfides, Cu-Sn-sulfides, Ag-minerals, and selenides. The massive ores consist mainly of pyrite, pyrrhotite, sphalerite, magnetite and chalcopyrite, together with minor galena, tetrahedrite, arsenopyrite, and native silver with a quartz and siderite gangue. Despite the high Ag content of the ores, the majority of the massive sulfides are remarkably Au poor except for a local gold zone that has been recognized in the deep mine in association with high-temperature mineralization. The trace elements in the ores exhibit strong zonation and diverse mineralogy. Spectacular albite porphyroblasts, up to 1 cm in size occur in the most Cu-rich ores of Mine D which are coincident with the peak of regional metamorphism and likely represent higher metamorphic or hydrothermal temperatures. Overall the orebodies have remained remarkably similar downplunge. However, unlike the upper part of the mine, pyrrhotite is dominantly hexagonal, only tetrahedrite was observed as the dominant sulfosalt, and magnetite occurs as both blebby porphyroblasts and as abundant intergrowths with sphalerite-chalcopyrite ores and siderite. These characteristics suggest that the deep mine has been subjected to higher metamorphic temperatures, possibly related to depth of burial, and that the original hydrothermal fluids may of had a lower H2S/CO2 and/or higher temperatures.

The giant Kidd Creek Mine is an Archean Cu-Zn-Ag deposit in the Abitibi Greenstone belt, located in the Superior Province of Canada and is one of the largest known base metal massive sulfide mines in the world with a tonnage of 170.7 Mt (Past production, Resource and Reserve). The massive sulfides in Mine D comprise a number of ore lenses that are interpreted to be the downplunge continuation of the Central orebody from the upper mine. These are referred to as the West, Main, and South lenses. The massive sulfides overlie a silicified rhyolitic unit at the top of a mixed assemblage of rhyolite flows, volcaniclastic sediments and ultramafic flows. The sheared nature of the fragmental units in the hanging wall of the deposit, at depth, illustrates the greater deformation that has occurred than in the upper mine. Metal zonation and the distribution of Cu stringer mineralization suggest that the West and Main lenses may be part of a single massive sulfide body (Main orebody) that has been structurally dismembered. The South Lens is a detached body, separated by late faults. The large Cu stringer zone beneath the West and Main lenses has a thickness of up to 150 metres, and is much broader and structurally remobilized in Mine D partially due to a newly identified series of vertically trending offset faults, that extends along the entire length of the massive sulfide bodies. A number of features of the North, Central and South orebodies in the upper part of the mine (e.g., Se-rich halo around Cu-rich zones) have been recognized in Mine D and provide an important framework for correlating the deep orebodies with the upper levels of the mine. Drilling below the current mine levels indicates that the massive sulfide and Cu stringer zones continue below 10,200 feet (3109 m) and highlight the remarkable continuity of the deposit downplunge with no end in sight. Two main ore suites have been recognized in the upper part of the mine and in Mine D: a low-temperature, polymetallic assemblage of Zn, Ag, Pb, Cd, Sn, Sb, As, Hg, ±Tl, ±W, and a higher-temperature suite of Cu, Co, As, Bi, Se, In, ±Ni. More than 25 different ore minerals and ore-related gangue minerals are present, including Co-As-sulfides, Cu-Sn-sulfides, Ag-minerals, and selenides. The massive ores consist mainly of pyrite, pyrrhotite, sphalerite, magnetite and chalcopyrite, together with minor galena, tetrahedrite, arsenopyrite, and native silver with a quartz and siderite gangue. Despite the high Ag content of the ores, the majority of the massive sulfides are remarkably Au poor except for a local gold zone that has been recognized in the deep mine in association with high-temperature mineralization. The trace elements in the ores exhibit strong zonation and diverse mineralogy. Spectacular albite porphyroblasts, up to 1 cm in size occur in the most Cu-rich ores of Mine D which are coincident with the peak of regional metamorphism and likely represent higher metamorphic or hydrothermal temperatures. Overall the orebodies have remained remarkably similar downplunge. However, unlike the upper part of the mine, pyrrhotite is dominantly hexagonal, only tetrahedrite was observed as the dominant sulfosalt, and magnetite occurs as both blebby porphyroblasts and as abundant intergrowths with sphalerite-chalcopyrite ores and siderite. These characteristics suggest that the deep mine has been subjected to higher metamorphic temperatures, possibly related to depth of burial, and that the original hydrothermal fluids may of had a lower H2S/CO2 and/or higher temperatures.