87 



At Sudbury the basic dikes are composed of olivine 

 diabase which on weathering shows the characteristic 

 spheroidal forms. In thin sections under the microscope 

 the rock is one of the most beautiful of its class. Similar 

 dikes of olivine diabase on the Quinze river, a hundred 

 miles to the northeast of Sudbury, have been described by 

 the writer* 



In the region between Sudbury and the Quinze many 

 dikes of olivine diabase have been found as well as those of 

 olivine-free diabase. 



In the vicinity of Cobalt these dikes are rare, the only 

 one studied by the writer being the basalt-diabase of Cross 

 lake. 



Analyses. 



The following table shows the chemical composition of 

 two typical samples of the Nipissing diabase at Cobalt, and 

 that of a rather basic type of the Sudbury norite, together 

 with analvses of two later basic dikes. 





No. 1. 



No. 2. 



No. 3. 



No. 4. 



No. 5. 



SiOo 



45.20 



47.32 



3.62 



16.52 



3.32 



12.40 



9.61 



3.33 



.01 



3.40 



.67 



.04 



trace 



.0275 



.0055 



!so 



49.84 



48.06 



49.90 



T1O0 



1.47 



A1»0 3 



19.08 

 3.64 



14.64 

 7.89 

 4.98 



18.94 

 1.51) 

 6.40/ 



10.32 

 7.39 



IS. 23 



9.57 



11.55 

 7. SO 



16.32 



Fe20a 





PeO 



CaO 



MgO 



BaO 



13.54 

 6.58 

 6.22 



NaoO 



KoO 



1.08 



1.99 1 



1.28 



1.87 



1.82 

 2 25 



MdO . 





CuO 









NiO 









CoO 











P2O0.. . 





.17 



H 2 









2.57 



3.54 















9y.So 

 



100.803 

 3.01 



100.24 



100.89 



99. Od 









No. 1, basalt-diabase dike, Cross lake. Cobalt. No 2, 

 olivine diabase dike, Sudbury. No. 3, Nipissing diabase 

 cut by basalt-diabase dike at Cross lake. No. 4, Nipissing 

 diabase, on the Violet property near Cross lake. No. 5. 

 norite, more basic than the average, at Sudbury.f 



*llth Report, Ontario Bureau of Mines, pp. 227, 229. 

 fAnalyses Nos. 2 and 5 are taken from Dr. A. P. Coleman's paper in 

 the Fourteenth Report, Ontario Bureau of Mines, Part III. 



