ON THE GENESIS OF THE PYRITE DEPOSITS OF 

 ST LAWRENCE COUNTY 



BY C. H. SMYTH, JR 



In an effort to get some clue to the methods of formation of the 

 pyrite deposits of St Lawrence county, which in recent years have 

 been more extensively worked than before, the important mines and 

 several pits and prospects were visited and examined with such care 

 as limited time and the conditions of the workings permitted. The 

 expectation, based upon previous knowledge of the geology of the 

 region, that the problem would prove a troublesome one to solve 

 was fully justified by the result. A thoroughly satisfactory investi- 

 gation of the matter can be carried through only after the general 

 geology of the region is worked out in detail, but as this consum- 

 mation is doubtless remote, a statement of the results of the present 

 study seems warranted. 



The most important workings are the mine on the Cole farm,' four 

 miles northeast of Gouverneur, the Stella mines, one mile north of 

 Hermon, and the group of mines at Pyrites, or High Falls, on the 

 Grasse river, six miles south of Canton. Besides these there are 

 many smaller mines and prospects scattered over this part of the 

 county and, as the geological conditions which favor the formation 

 of the pyrite deposits prevail over a large area, it is probable that 

 many occurrences have escaped notice. 



GENERAL GEOLOGY 



The geology of the region is exceedingly complex and. for the most 

 part, as yet unstudied in detail ; but, speaking in most general terms, 

 there is an older series of highly metamorphosed sediments, crystal- 

 line limestones, gneisses, schists and quartzites, classed as Grenville; 

 cut by igneous rocks of varying character and age, but chiefly 

 granites, which are generally gneissoid. More basic rocks, diorites 

 and gabbros, are not lacking but, particularly as regards the latter, 

 are much less important than farther south, in the heart of the 

 Adirondack region. 



The typical rocks of either class, sedimentary or igneous, are of 

 course readily distinguished, but in many cases extreme meta- 

 morphism has completely obscured the original character, making a 

 positive determination difficult or even impossible. It often happens, 

 too, that a rock is of composite character as a result of injection or 

 assimilation, giving, on the one hand, a sediment more or less 



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