C. H. Smyth, Jr. — Replacement of Quartz oy Pyrite. 281 



difficulties as regards concentration. In the present case, 

 while there is no obvious source for any unusual quantity of 

 alkaline carbonates, a sufficient supply might, perhaps, be fur- 

 nished by overlying shales, while the Lorraine formation might 

 be a source of hydrogen sulphide. Iron may have been origi- 

 nal in the conglomerate, or derived from overlying rocks. In 

 this connection, Doelter's* production of artificial pyrite by 

 the action of hydrogen sulphide and sodium sulphide on iron 

 carbonate is very suggestive, and may represent some approxi- 

 mation to the conditions involved in the case under considera- 

 tion. + 



If this is true, it is evident that the replacement of quartz 

 by pyrite is caused by common, rather than peculiar, agents, 

 and therefore might be expected to occur with some frequency. 

 As a matter of fact, judging from the literature of ore deposits, 

 it is by no means rare. LindgrenJ in particular has described 

 several instances within very recent years. 



But in all the cases that the writer has thus far found men- 

 tioned, the process is connected with some type of mineral vein 

 formation, where, with the hot alkaline solutions and mineral- 

 izers, and resultant powerful chemical action, it is not surpris- 

 ing to find even so resistant a mineral as quartz yielding to the 

 agents of alteration. In some of these cases it is, as in the 

 present instance, the quartz of sedimentary rocks that is 

 replaced, but always under the conditions involved in the fill- 

 ing of mineral veins. 



These conditions are so unlike those controlling the deposi- 

 tion and subsequent existence of the Oneida conglomerate that 

 the occurrence of pyrite replacing quartz in veins would hardly 

 suggest the probability of the same thing taking place in the 

 conglomerate, and explanations of the former process would, 

 doubtless, require modification before being applied to the 

 latter. 



The reagents suggested above are similar to those filling 

 veins, but in the case of the conglomerate their action would, 

 probably, be less intense, owing to lower temperatures and 

 pressures, greater dilution, and the absence of some of the 

 more powerful reagents. Compensation might be afforded by 

 the ready permeability of the formation and the large surface 

 of quartz exposed to attack, while, of course, the time factor 



* Allgemeine Cheniische Mineralogie, p. 148. 



f See a theoretical discussion of the chemistry of pyrite-quartz replace- 

 ment by C. S. Palmer, Eng. and Min. Jour., lxxix, p. 169. 



% Metasomatic Processes in Fissure Veins, Trans. Am. Inst. Min. Eng., xxx, 

 p. 615, et seq. 



Gold and Silver Veins in Idaho, 20th Ann. Eeport, U. S. Geol. Survey, 

 iii, p. 219 et seq. 



Geological Eeconnaissance across the Bitterroot Eange, etc. U. S. Geol. 

 Survey, Professional Paper No. 27, pp. 109-110. 



Am. Jour. Scl— Fourth Series, Vol. XJX, No. 112.— April, 1905. 

 19 



