PRE-CAMBRIAN CLASSIFICATION IN ONTARIO 597 



of the province as well as in the north and northwest. In the 

 southeastern section there is also a series, the Hastings, that is 

 believed to represent the Timiskamian of the north.^ 



METALLOGENETIC NOTES 



During the last decade, owing to the great progress that has 

 been made in the production of metals in Ontario, special facilities 

 have been provided for the study of pre-Cambrian rocks. Our 

 information has been much increased concerning the age relations 

 not only of the rocks that represent various epochs of this great 

 period but also of the ore deposits that are associated with them. 

 Of no other part of the continent, or of the world, has the pre- 

 Cambrian proved to be of greater economic interest. The province 

 not only has the world's greatest deposits of nickel, among which 

 have been developed mines that compare favorably in economic 

 importance with those of any other metal found elsewhere, but 

 the gold mines and the cobalt-silver areas are recognized as being 

 among the greatest known. 



From Table III it will be seen that there were at least four 

 great metallogenetic epochs during the pre-Cambrian period in 

 Ontario — Grenville, Algoman, Animikean, and Keweenawan. A 

 fifth epoch of minor importance should probably be added to 

 represent the ore bodies associated with the basic intrusives that 

 preceded the intrusion of the Algoman granite and followed the 

 deposition of the Timiskamian sediments. There is proof that 

 many important ore deposits have been removed by erosion, and 

 it seems not unlikely that the rocks of certain epochs, not now 

 productive, contained deposits which have disappeared through 

 the removal of vast thicknesses of material. 



SEQUENCE OF INTRUSION AND METAL DEPOSITION 



Table III brings out an interesting alternation of intrusion and 

 sedimentation, and the importance of the igneous rocks in the 

 formation of ore deposits. It will be seen that there are broadly 

 five great epochs of igneous activity, basic and acid rocks alter- 

 nating, viz.: (i) Keewatin, basic; (2) Laurentian, acidic; (3) pre- 

 Algoman, basic; (4) Algoman, acidic; (5) Keweenawan, basic, 



^ OnL Bur. Mines, XXII, Part II. 



