Publication Type:Book Chapter
Source:The physical environment of the city of Greater Sudbury, Ontario Geological Survey, Toronto, ON, Canada, Volume 5, p.21-55 (2002)
Keywords:base metals, bedrock, Canada, Chelmsford Formation, copper ores, dikes, eastern canada, faults, gneisses, gold ores, granites, Huronian, igneous rocks, impact features, intrusions, metal ores, Metamorphic rocks, metavolcanic rocks, migmatites, mineral assemblages, Mineral exploration, mineralization, nickel ores, Onaping Formation, Ontario, Paleoproterozoic, Petrology, plutonic rocks, Precambrian, proterozoic, quartz veins, silver ores, Sudbury Igneous Complex, Sudbury Ontario, sulfides, upper Precambrian, veins, volcanic rocks
The bedrock of the former Regional Municipality of Sudbury occurs within 3 Precambrian structural provinces of the Canadian Shield. These structural provinces are defined by the last orogenic event to affect them. Rocks to the north, northwest and northeast are within the Superior Province (Kenoran Orogeny, 2500 Ma), those at the southeastern margin are within the Grenville Province (Grenvillian Orogeny, 1000 Ma), while the majority of the rocks are in the Southern Province (Penokean Orogeny, 1900 to 1700 Ma). The first two provinces comprise an assortment of felsic and mafic gneissic rocks, schist, mafic and granitic bodies and mylonite. In the Southern Province, where most of the rocks are Paleoproterozoic (2500 to 1600 Ma), there are 3 principal elements: 1) sedimentary and volcanic rocks of the Huronian Supergroup and Nipissing Gabbro; 2) the Sudbury Basin consisting of breccia and sedimentary rocks of the Whitewater Group; and 3) the Sudbury Igneous Complex surrounding the Sudbury Basin as an elliptical collar (58 by 28 km). The Sudbury Basin, Sudbury Igneous Complex and an outer zone of brecciated footwall rocks (Sudbury Breccia) comprise the Sudbury Structure. Mineralization in the area includes 1) copper, gold, silver and nickel in volcanic rocks at the base of the Huronian Supergroup; 2) copper-nickel-platinum group elements mineralization in early Paleoproterozoic mafic intrusions, Nipissing Gabbro and the Sudbury Igneous Complex; and 3) zinc-lead-copper-gold deposits (Errington-Vermilion) and hydrothermal base-metal and precious-metal veins in the Whitewater Group. The Sudbury Igneous Complex, which contains the only deposits that are currently economic, consists of 4 units, from bottom to top: Contact Sublayer (a xenolith-bearing norite), norite, quartz gabbro and granophyre. Radiating and concentric dikes of quartz diorite, called offsets, intrude footwall rocks and are related to the Sudbury Igneous Complex. There are 4 types of magmatic sulphide deposits, consisting mainly of pyrrhotite, pentlandite and chalcopyrite: 1) Sudbury Igneous Complex-footwall contact deposits (Ni>Cu) are in depressions in the contact, with mineralization in the Contact Sublayer and in the underlying footwall, especially in the Footwall Breccia; 2) footwall deposits (Cu>Ni) occur below footwall contact deposits and are commonly hosted by Sudbury Breccia; 3) offset deposits (Ni = Cu) in radial and concentric dikes; and 4) sheared deposits, representing faulted and remobilized Sudbury Igneous Complex-footwall contact deposits. In the footwall contact and offset deposits the ores were precipitated as an immiscible sulphide from a sulphur-saturated Sudbury Igneous Complex melt whereas, in the footwall deposits, the fluids are the fractionated derivatives of footwall contact deposits. The geological history of the area can be separated into 3 different periods of activity which occurred 1) before, 2) during, and 3) after the Sudbury Event (1850 Ma). 1. Evidence that the Sudbury Structure was the site of a paleodome prior to the Sudbury Event includes uplift of the Levack gneiss complex, radial and concentric disposition of Matachewan dikes about the Sudbury Igneous Complex, the trend of early Paleoproterozoic mafic intrusions and the trend of Matachewan dikes intersecting at the dome and felsic plutons intruding the south flank of the dome. Also the absence of Nipissing Gabbro between Huronian outliers and Sudbury Igneous Complex implies nondeposition or erosion of the Huronian Supergroup. Folding occurred about east to northeast-trending axes and locally about north-northeast and north-northwest-trending axes. 2. The Sudbury meteorite struck the paleodome forming a crater, Sudbury Breccia, shatter cones, planar deformation features in quartz and feldspar, magma and/or melt (Sudbury Igneous Complex) and the Onaping Formation. 3. Post-Sudbury Event activity includes displacement of the South Range by a southeast-dipping zone of reverse shear, folding (south of the North Range) about northeast-trending axes and more widely spaced n rthwest-trending axes, regional alkali metasomatism, batholith emplacement and intrusion of 2 sets of mafic dikes.
GeoRef, Copyright 2018, American Geological Institute.<br/>2004-050599<br/>Elliot Lake Group<br/>Hough Lake Group<br/>Nipissing Gabbro<br/>Onwatin Formation<br/>Quirke Lake Group<br/>Vermillion Formation