156 Scientific Intelligence. 



2. A Study of the Magmatic Sulphide Ores ; by C. F. Tol- 

 MAN, Jr.. and A. F. Rogers. Leland Stanford Junior University 

 Publications, 1916, 76 pp., 20 pis., 7 figs. — The authors define 

 " magmatic deposits " as those segregations of ore-minerals that 

 take place under the influence of, or closely connected with, the 

 molten stage of the parent rock. Ore accumulations accompanied 

 by destructive pneumatolytic action, or those formed by hydro- 

 thermal solutions, are not to be classed as magmatic deposits. 

 Typical magmatic deposits are confined to the basic rocks. Their 

 study has led to the hypothesis that *' the magmatic ores in gen- 

 eral have been introduced at a late magmatic stage as a result of 

 mineralizers, and that the ore-minerals replace the silicates. This 

 replacement, however, differs from that caused by destructive 

 pneumatolytic or hydrothermal processes in that quartz and 

 secondary silicates are not formed at the time the ores are 

 deposited. 



It is conceived that the process of formation of plutonic rocks 

 consists of stages and that rock differentiation and ore formation 

 are the results of an orderly series of events. The stages in the 

 norites and gabbros which contain the magmatic sulphide ores are 

 as follows : 



(1) The first minerals to form are olivine, pyroxenes and feld- 

 spars. 



(2) Magmatic alteration of the silicates, as the change of pyrox- 

 ene to hornblende, often takes place prior to the formation of the 

 ore-minerals. 



(3) Later magmatic products include interstitial pegmatite 

 material, interstitial quartz, tourmaline, garnet, analcite, epidote 

 and calcite. 



(4) The introduction of the ores by mineralizers is later, in 

 general, than the minerals of group (3) and is unaccompanied by 

 any secondary silicates. 



(5) Pegmatite dikes often come later than the magmatic 

 deposits of the basic rock itself. 



(6) Hydrothermal alteration, subsequent to magmatic ore 

 deposition and which in general is insignificant, includes the 

 development of chlorite, tremolite, anthophyllite, sericite and 

 serpentine. 



(7) Lastly downward enrichment and oxidation may take place. 

 The second part of the paper is taken up with a discussion of 



various deposits of magmatic ores and the third part contains the 

 summary of the characteristics of magmatic ores and various 

 theoretical conclusions. - w. e. f. 



8. Origin of Massive Serpeyitine and Chrysotile- Asbestos^ 

 Black Lake-Thetford Area, Quebec ; R. P. D. Graham, Econ. 

 Geol. xii, 154-202_, 1917. — The author presents a summary of the 

 geological structure of this important asbestos field and examines 

 in detail various theories concerning its history. Some of his 

 more important conclusions follow. The serpentine area has been 

 derived from the alteration of original peridotites. A cross-section 



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