1914] 



Lawson: Ore Deposition by Meteoric Waters 



231 



fessor Lawson 's strictures, the general testimony favors essentially 

 pneumatolitic methods." I am aware of the "concensus of opinion" 

 and the "general testimony," but I fail to see that it proves anything 

 scientifically. I have great respect for the gentlemen who hold this 

 prevailing opinion, but I can have no great respect for the hypothesis 

 which it embodies until the alternative one of meteoric waters is 

 negatived somewhat more definitely than by Professor Kemp's method 

 of quoting opinions. 



KNOPF'S CEITICISM 



Parage nesis of Tourmaline and Ore. — In a recent paper- 7 I pointed 

 out that the commonly accepted view, which refers the deposition of 

 the copper ores at Butte to magmatic waters, is not the only possible 

 explanation of their origin. If the quartz monzonite of Butte be 

 regarded as a laccolith resting on a floor of sedimentary rocks, which 

 have sagged below it in synclinal fashion, then the deposition of the 

 ores may be ascribed to the ascent of meteoric waters through fissures 

 traversing the hot mass. These waters would pass through and leach 

 the zone of magmatic sulfids at the base of the laccolith and deposit 

 the salts of the metals thus obtained at higher and cooler levels. Dr. 

 A. Knopf has recently reviewed-* this paper in a most kindly and 

 appreciative spirit. I accept his correction that there is evidence of 

 a certain amount of doming of the roof, though this is so slight that 

 it still leaves us under the necessity of recognizing a sag of the floor 

 to accommodate the intrusive mass. Dr. Knopf intimates that I have 

 not given due weight to his argument in favor of magmatic waters 

 based on the paragenesis of tourmaline and ore, taken in connection 

 with the concentration of the former in the aplitic magma. I may 

 also admit this charge without blushing, but after further reflection 

 I am still not satisfied that the argument is entirely convincing. It 

 may be conceded from Knopf's observations and those of Ward and 

 Granigg which he cites that the tourmaline is a concentration product 

 in the residual magma. But is it not possible that after consolidation 

 such concentrations of tourmaline may, in a laccolith which has been 

 broken by faults, be open to the attack of superheated steam rising 

 from below, and so be taken into solution again together with salts of 

 flic metals obtained by attack upon the earlier precipitated sulphids ? 

 If the sulphids remained residual with the constituents of the tourma- 



" Is the Boulder batholith a laccolith?, Univ. Calif. Publ. Bull. Dept. Geol., 

 vol. 8, no. 1, 1914. 



Economic Geology, vol. 9, no. 4, pp. 396-402. 



