302 NEW YORK STATE MUSEUM 



and again the fracturing may extend over a width of many feet, 

 with a corresponding enlargement of the deposit. The cross-fracture 

 in the EUenville mine shows extreme variation in this respect, 

 ranging from a few inches to 15 or 30 feet in width. It would appear 

 this quartzite has accommodated itself to stress by irregular, spas- 

 modic movements, indicative of no definite mobility under the 

 conditions, but on the other hand a great resistance to the crushing 

 forces. 



The sulphide minerals do not appear to have replaced the quartz- 

 ite to any extent. The fragments of rock embedded in the ore 

 preserve their singularity and the contact line is abrupt. It is 

 possible that some of the pjnrite which occurs in disseminated crystal 

 particles within the quartzite, as well as an ingredient of the ore, 

 may have been deposited by such process, but the main bodies of 

 sulphides bear little evidence of it. 



The introduction of the ores was preceded by extensive deposition 

 of quartz, which constitutes the single important gangue material. 

 It is a white or clear vitreous quartz frequently developed in good 

 crystals. 



The ore. The metallic minerals are represented by sphalerite, 

 galena, chalcopyrite and pjrrite, and most of the ores are mixtures of 

 these different materials. Sphalerite is the most abundant mineral 

 as well as the chief element of value in the ores; but in the early 

 days mining seems to have been directed rather to the extraction 

 and saving of the galena. The latter fluctuates in its proportions 

 and is much more uncertain in its distribution, having a tendency 

 to occur in independent aggregates. Masses of galena are encoun- 

 tered that are practically free of admixture, up to one-half of a ton 

 in weight. Chalcopyrite also varies greatly in its occurrence and 

 seems most abundant in the EUenville mine, where it forms crystal 

 aggregates in vugs, with vein quartz as a later deposit. 



The variation between the different components is so marked 

 that .chemical analysis of samples gives little idea of the actual 

 "conditions in a large way. Only extensive sampling of the mines 

 or actual runs can supply the basis for estimating the average con- 

 tents of the ores in the different properties. In the Simimitville 

 mine of the St Nicholas Zinc Co. the preliminary sampling, as 

 reported by Mr Kirby Thomas, showed the following percentages: 



Iron 



3-54 



Lead 



12.88 



Zinc 



20.73 



