The only known concentration of carbonatite complexes in North America is in northern Ontario and western Quebec, in a petrographic province here named the Ontario Carbonatite Province. This petrographic province has some 50 known carbonatite complexes over an area of 1.3 million km 2 . Almost all of the carbonatite bodies occur along recognizable major tectonic features, three of which are most probable, and one predicted. According to their ages, the carbonatite bodies belong to four groups; the two younger groups, dated 120 and 570 m.y., are restricted to the Ottawa graben, whereas the two older groups, dated 1,100 and 1,700 m.y., are situated along the Kapuskasing High and the Albany Forks and Carb structures. All four structures are major tectonic features probably related to the Mid-Continent High. No carbonatite complexes have been recognized to date along the Mid-Continent High in Minnesota and Wisconsin, but their existence is predicted.A number of complexes were examined for their mineral potential. They all contain apatite in the carbonatite phase, in amounts of 5 to 25 percent, and some contain significant enrichments of apatite through leaching out of carbonates.Such enrichment occurs on the Cargill complex, located on a branch structure off the Kapuskasing High. The complex contains a unique, very high grade residual phosphate deposit associated with a well-developed karst topography now buried under glacial lake clays. During karst development carbonates were dissolved from the carbonatite, and residual minerals, mainly apatite, were concentrated in sink holes and troughs. Sorting and reworking of apatite-rich residuum by surface and subsurface water formed concentrations of nearly pure apatite sand, locally several tens of meters thick. Unusual concentrations of rare earth minerals are present in a discontinuous thin blanket of secondary weathering products on top of the residuum. Widespread occurrences of vermiculite suggest further possible economic potential.

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