2IO NEW YORK STATE MUSEUM 



Information as to the general distribution and features of the 

 pyrite deposits in Jefferson and St Lawrence counties has recently 

 appeared in a report ^ by A. F. Buddington, prepared under the 

 direction of the State Geological Survey during the summer of 191 7. 

 A brief description of the principal ore deposits of the district were 

 contributed by the writer to the Engineering and Mining Journal 

 (December i, 191 7). 



Nature of the deposits. The pyrite deposits are usually spoken 

 of as veins, but they are really bands or zones of the country gneisses 

 and schists impregnated with the sulphide and more or less vitreous 

 quartz. The mineral occurs in two forms : as finely di Added particles 

 more or less evenly distributed through the gangue and as aggre- 

 gates of coarser grains and crystals in bunches, veinlets and stringers 

 of more irregular distribution. Some of the ore contains little else 

 than fine granular pyrite in a gangue consisting of feldspar, quartz 

 and mica, with usually considerable amounts of chloritic material 

 of secondary origin. In other examples the ore is a network of small 

 stringers or veinlets intersecting the gneiss or is made up of alternating 

 bands of sulphides and country rock, in both of which types the 

 p^nrite is much coarser than in the disseminated ores. As a rule 

 the grade of the ore depends upon the extent to which the veining 

 and banding occurs. The disseminated variety unmarked by these 

 features rarely contains more than ten or fifteen per cent of sulphur. 

 The richer grades, in which there is a considerable percentage of 

 coarse pyrite, average 25 to 30 per cent sulphur. 



Some pyrrhotite is usually present along with the p3.T:ite. It is 

 rarely intermixed with the latter, but tends to segregate in a sepa- 

 rate part of the deposit, for example, along the walls or in inde- 

 pendent bodies. It is much less common than the other sulphide 

 and rarely is found in any considerable bodies. In sulphur content 

 the pjorhotite ores are practically on a par with the pyrite ores, not- 

 withstanding the wide difference in composition of the two 

 minerals. 



The pyrite deposits show marked persistence along their strike, 

 and where they have been mined underground they have been 

 found to be persistent on the dip as well. The thickness, however, 

 is usually small comipared with other dimensions. In most localities 

 they are not more than 15 to 20 feet thick, measured from wall to wall. 

 A maximum thickness of 40 feet is found in parts of the Anna mine, 

 near Hermon, and 80 feet is reported to have been found in one of 

 the deposits at PyTites. In the long stretch in which the deposits 



^ N. Y. State Defense Council Bui. i, Albany, 1917. 



