From Impact to Riches : Evolution of Geological Understanding as Seen at Sudbury , Canada

dress, I decided that I should pick something that has been a major factor, perhaps the major factor in my professional life—the world’s nickel capital, Sudbury, Ontario. On setting out in July 1957 from Britain to make a life in North America, I was fortunate to obtain a job with Falconbridge Nickel Mines Limited in one of their mines at Sudbury. In my subsequent career as a graduate student, postdoctoral fellow, and academic, I have been lucky enough to stay in close touch with the new developments in Sudbury geology as they have occurred over the intervening 45 years. The developments have been startling and I believe provide an object lesson as to how progress in our particular science commonly occurs. Therefore my intention in this address is not to discuss every aspect of the geology, but to give you a personalized view of the major jumps in our understanding about Sudbury, how they came to be made, and how one led to the other. First, a little history. The presence of sulfides was initially reported at Sudbury in an 1856 Geological Survey of Canada Report as documented in the following quotation (Report of Alexander Murray, Geological Survey of Canada, 1853–1856, p. 180–181): Previous to my visit to Whitefish lake, I had been informed by Mr Salter that local attraction of a magnet had been observed by himself while running the meridian line and he expressed it to be his opinion that the presence of a large body of iron ore was the immediate cause. When therefore, I came to the part indicated by Mr Salter, I made a very careful examination not only in the direction of the meridian line but for a considerable distance on each side of it, and the result of my examination was that the local attraction, which I found exactly as described by Mr Salter, was owing to an immense mass of magnetic trap. Specimens of this trap given to Mr Hunt for analysis and the result of the investigation shows that it contains magnetic iron ore and magnetic iron pyrites generally disseminated throughout the rock, the former in very small grains: titaniferous iron was found associated with the magnetic ore, and a small quantity of nickel and copper with the pyrites. These remarks were not followed up. It was only after sulfides were revealed in a new railway cutting in 1883 as a result of the building of Canada’s first transcontinental railroad, the Canadian Pacific, that a prospecting and staking rush started in the area. The first production at Sudbury occurred in 1886 (Fig. 1). During the late nineteenth and early twentieth centuries, laterites in New Caledonia satisfied the majority of the world’s demand for nickel, but by 1905 the sulfide mines at Sudbury had overtaken New Caledonia as the principal source of supply. Thereafter, Sudbury production waxed and waned according to demand. The early companies soon merged into what eventually became INCO Limited, but in 1928 another significant company, Falconbridge Nickel Mines Ltd., appeared on the Sudbury scene and has continued to this day. The slackening in the growth rate that is shown in Figure 1 as having set in during the 1960s, and having continued to this day, coincides with the discovery of the Talnakh deposits of the Noril’sk area, which exceed Sudbury in terms of their grade and resources of Ni, Cu, and platinum group elements (PGE). Turning to the geology, the principal aspects are summarized in chronological order in Table 1 and are illustrated in the simplified geological map appearing as Figure 2. An Archean hinterland comprising granites and felsic gneisses (shown in pink in Fig. 2) was affected by 2.46 Ga rifting that gave rise to a southern ocean. The northern margin of the rift is shown in red in Figure 2. The Huronian Supergroup, shown in yellow, comprises greenstones, greywackes, and quartzites that were deposited along the margin of the rift. North of the northern margin, the Huronian rocks form a thin shelf cover on From Impact to Riches: Evolution of Geological Understanding as Seen at Sudbury, Canada