REPORT OF THE CHIEF ASTRONOMER 7G5 



SESSIONAL PAPER No. 25a 



or to absorption at the earth's surface. Allowing for that fact, it seems probable 

 that none of the more widely distributed igneous rocks carries much more than 

 one per cent of its own weight in volatile matter directly derived from the 

 earth's interior. 



It follows that an enormous amount of water, carbon dioxide and carbon 

 and sulphur compounds may be given off each time that geosynclinal sediments 

 have been assimilated by molten and then crystallized magma. From each cubic 

 mile of assimilated sediments about six per cent by weight of liquids and 

 gases must be dissolved in the syntectic magma and, as crystallization proceeds, 

 a large part of this fluid must be expelled. 



In less important degree we may expect that the remelting or solution of an 

 igneous rock by an intrusive magma should cause the evolution of some of the 

 fluid matter which had been, as it were, frozen into the solid rock. Lincoln has 

 aptly called such fluids ' repressed emanations.'* Gautier's and Brun's experi- 

 ments show that many and probably all igneous rocks give off gases on being 

 highly heated.f Reheating after cooling causes the renewed emanation of gases. 

 Volatile matter trapped in crystallized secondary granite may thus be driven off, 

 if that granite be dissolved in a younger molten magma with subsequent 

 crystallization of the syntectic. 



The stoping hypothesis in its broadest statement demands, therefore, that 

 post-Archean, batholithic granites, syenites, and diorites should be accompanied 

 by special evidences of fluid emanations. 



These fluids were deposited and buried in the strata. They have been 

 resurrected in their activity. They have ' risen again,' both literally and 

 figuratively; they may be called ' resurgent ' emanations. The 'repressed' 

 emanations of secondary igneous rocks may similarly be liberated by the distill- 

 ing action of younger magma; as these fluids become revivified in their geologi- 

 cal activities they may be regarded as forming a second kind of 'resurgent' 

 emanations. All ' resurgent ' emanations are of secondary origin and, therefore, 

 stand in contrast to ' juvenile ' emanations, namely, those which, for the first 

 time, have issued from the earth's interior and become geologically active on or 

 near the surface. Magmatic emanations are, apparently, divisible into two 

 great classes, both of which should be recognized in complete discussions of 

 ore-deposits. 



That the stoping hypothesis stands this further test seems to the writer 

 entirely clear. The prevalence of quartz veins and pegmatites in the walls and 

 roofs of actual granitic, syenitic, and dioritic stocks and batholiths, and the 

 intensity of the contact metamorphism produced by the intrusions of, and 

 especially the emanations from, these rocks are facts as familiar as the com- 

 parative rarity of quartz veins and pegmatites about gabbroid masses and the 

 comparative feebleness of the contact metamorphism produced by gabbros. The 



*F. C. Lincoln, Economic Geology, Vol. 2, 1907, p. 268. 



t A. Brun, Archives des Sciences Phys. et nat. Geneva, May and June, 1905 and 

 November, 1906; A. Gautier, Annales des Mines (6), Vol. 9, p. 316, 1906, and Econ. 

 Geol., Vol. 1, 1906, p. 688. 



