Volcanogenic massive sulphide (VMS) deposits
VMS deposits are base +/- precious metal-rich mineral deposits hosted by submarine volcanic sequences. They are generally formed by the exhalation of hot, metal rich fluids into cold seawater surrounding volcanic vents on the seafloor. These deposits have strong connections with the modern day "black smoker" deposits formed at spreading ridges.
The deposits represent major sources of copper, zinc, lead, gold and silver in a high grade:low tonnage ratio. Gangue minerals exist in the form of quartz, chlorite, barite, gypsum and carbonate. VMS deposits are found in most parts of Canada, and are significant producers in British Columbia, Manitoba, Ontario, Quebec, New Brunswick and Newfoundland.
VMS deposits tend to be restricted to one or more volcanic horizons. In the case of the Noranda camp, these episodic events commonly used pre-existing vent structures, which led to vertical stacking of ore bodies in the volcanic sequence. VMS deposits tend to occur in clusters, as the volcanic system typically forms multiple vents along the seafloor.
The stockwork zone beneath VMS deposits forms the conduit through which metal-rich fluids rise and produces a zone of semi-massive stockwork mineralization. Hydrothermal alteration forms a pipe around the stockwork zone and typically grades from an inner chloritized zone to an outer sericitic zone. A mound structure (see diagram) typically forms as the hydrothermal fluids exhale and is slowed by the presence of eruption breccia at the vent. This allows the formation of chimney structures, which collapse and add to the amount of sulphide breccia, further slowing the exhalation of later fluids, giving fluids time to cool and mix with seawater and increasing sulphide precipitation into the mound.
VMS mineralization is the primary target on the Company's McFauld's Lake area projects.
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