466 EDWARD STEIDTMANN 



Coleman interprets the deposit as a marginal magmatic segregation 

 from the peridotite. 



Collins^ finds that the pre-Cambrian rocks in the region between 

 Lake Nipigon west of Clay Lake, a distance of about 220 miles, 

 include Keewatin and Huronian altered acid and basic intrusives, 

 volcanic tuffs, chlorite, and sericite schist with bands of conglomer- 

 ate, graywacke, phylHte, quartzite, and jaspilite; Laurentian 

 granites, syenites, and diorites intrusive into the Keewatin; post- 

 Keewatin eruptives, gabbro, mica syenite, acid porphyries, and 

 granite; flat-lying Keweenawan impure dolomite and sandstone, 

 and post-Keweenawan diabase intrusive sheets. 



Collins^ reports that the pre-Cambrian rocks between the Pic 

 and Nipigon rivers of the north shore of Lake Superior include 

 Laurentian granite, gneisses, and syenite; Keewatin graphitic 

 gneiss, quartzite, arkose, amygdaloids, and basic and acid schists; 

 Keweenawan red arenaceous dolomite, and diabase intrusives; 

 eruptives of unknown age, viz., syenites, diorite, pegmatite, 

 and diabase. 



ColHns^ states that the cobalt silver ores of northern Ontario are 

 associated with diabases. The diabasic magma has acted as a 

 mixture of two rock species, diabase and aplite, whose segregation 

 was controlled by the rate of cooHng, no separation having taken 

 place in rapidly cooled rocks. The aplites show differentiation into 

 quartz veins, and still later quartz calcite veins. The diabase 

 contains some chalcopyrite, the aplite still more, while an even 

 higher percentage is contained in the quartz calcite veins. Neither 

 silver nor cobalt were found in the diabases. 



Harvie^ states that the succession of Keewatin, Laurentian, and 

 Huronian rocks of the Oposatica district, about 40 miles east of 



' W. H. Collins, "A Geological Reconnaissance of the Region Traversed by the 

 National Transcontinental Railway between Lake Nipigon and Clay Lake, Ont.," 

 Canada Geol. Surv. Branch, 1909. 67 pp., 2 pis., i fig., 2 maps. 



2 W. H. Collins, "Report on the Region Lying North of Lake Superior betwen Pic 

 and Nipigon Rivers, Ont.," Canada Geol. Survey, 1909, 24 pp., i map. 



3W. H. Collins, "Quart? Diabases of Nipissing District," Econ. Geol., V, No. 6 

 (1910), 538-50. 



■•Robert Harvie, "The Telluride Ores at Oposatica," Jour. Can. Mining Inst., 

 1911, pp. 164-70. 



