1914] 



Lawson: Ore Deposition by Meteoric Waters 



221 



In my review of Types of Ore Deposits 2 I advanced one alternative 

 hypothesis which seems to be capable of explaining many ore deposits 

 in and about intrusive masses. I said : 



"The doctrine [of magmatie waters] remains feeble and can never attain to 

 the dignity of a scientific theory until it disposes of another possible means of 

 accounting for these ores, which has even greater claims to our attention than 

 the supposed magmatie waters. The means I refer to is the ordinary ground- 

 water as affected by igneous intrusion. The circulation of the ground-water 

 would in every case be profoundly disturbed by the injection of hot igneous 

 magmas into sedimentary terranes. The disturbance would, however, be far 

 from chaotic. The presence of the hot body would be the controlling influence 

 in determining the circulation. The circulation would always be upward on 

 the periphery of the hot mass. This would be true, not only while it was still 

 molten, but also long after it had solidified. Such a circulation of the heated 

 ground-water would be quite competent to do all that is ascribed to magmatie 

 waters, including the formation of lime-silicate zones. It would not only bring 

 to a zone of active chemical reaction the materials leached from the surround- 

 ing region, but it would attack the still hot, though solid, igneous mass itself 

 and abstract from it part of its metallic constituents. And it is significant in 

 t his connection that most of the igneous rocks that have ores either on their 

 periphery or within their mass have been subject to very severe chemical attack. 

 Until this very probable means of ore deposition at the contact of limestone and 

 igneous rocks has been disposed of, the doctrine of magmatie waters is unneces- 

 sary. It remains at best a possibility, one of the fashionable vagaries of our 

 time, not entitled to respect as a scientifically established theory. ' ' 



Lindgren's quotation of part of the last sentence of this statement 

 fails to make my position clear, and as he combats the hypothesis 

 which it expresses I feel constrained to reproduce the statement in full, 

 as the text of following discussion. His hope that I have already 

 changed my view of this question is not yet realized; and the present 

 paper is intended not only as a reply to his strictures upon the 

 alternative hypothesis, as above stated, but also as a further exploita- 

 tion of its possibilities. My only positive view in the matter is that 

 the deposition of ores by magmatie waters as a general scientific theory 

 is not yet established. I shall be glad to accept it as such when its 

 advocates shall have fulfilled the usual scientific requirement of dis- 

 proving opposing hypotheses. I agree with Lindgren's statement 3 

 that there are "three possible methods of deposition: (1) By atmo- 

 spheric waters heated by contact with the cooling porphyry, (2) by 

 ascending magmatie waters, or (3) by a mixture of both." But 

 inasmuch as meteoric waters are known to have deposited many im- 



2 Mining and Scientific Press, February 3, 1912. 



s U. S. G. S. Clifton Polio, 1905, p. 13. See also Professional Paper No. 43, 

 p. 24. 



