THE MINING AND QUARRY INDUSTRY I906 ,39 



There are abundant evidences that the ore deposits have origi- 

 nated by a process of replacement. The cores of schist show grada- 

 tion from the central unaltered nuclei outward into the rich hema- 

 tite. Specimens of the ore may be found that still show the band- 

 ing and cleavage characteristic of the schist. The presence of 

 graphite, which would naturally be the most resistant of the minerals 

 to solvent action, furnishes a clue to the origin of the ore even when 

 all the other primary constituents have been removed. The rela- 

 tively high percentages of silica and lime in the one are likewise 

 suggestive in that connection. 



As to* the source from which the ore has been derived, Prof. 

 C. H. Smyth^ jr has given an explanation that accords best with the 

 geological phenomena surrounding the occurrence. Though based 

 principally on observations made at the Old Sterling mine, the theory 

 is equally applicable to the Caledonia ore body and in fact to all of 

 the deposits in the district. Briefly stated, it ascribes the formation 

 of the ore to the circulation of underground waters which have dis- 

 solved the iron-bearing minerals from the adjacent rocks and de- 

 posited their burden in the form of oxid and carbonate when they 

 came in contact with the limestone. The source of the iron is to be 

 traced to the presence of pyrite and magnetite in the schist. There 

 are bands of schist impregnated with pyrite in the vicinity of the 

 Caledonia mine, as well as at the Dickson and Old Sterling mines. 

 These pyritic bands are developed on a large scale throughout the 

 Grenville schists of St Lawrence county and have for a number of 

 years been the object of mining. By oxidation, the iron would be 

 brought into solution as ferrous and ferric sulfates. Free sulfuric 

 acid would also result and would react upon the veins and dissemina- 

 tions of magnetite in the schist. On coming in contact with the 

 limestone, the solutions would be decomposed, the iron being pre- 

 cipitated as carbonate or limonite, while at the same time the lime 

 carbonate would pass into solution. By subsequent alteration the 

 carbonate and limonite have been changed to hematite. Residual 

 masses of unaltered carbonate are occasionally found in the Cale- 

 donia mine. The iron has been precipitated in part in the body of 

 the schist, without the agency of limestone. 



• Dickson mine. The Old Sterling Iron Co. has recently re- 

 opened this property, which has been inoperative for several years. 

 The mine is situated on the southwestern end of the belt in which 



I N. Y. State Mus. 47th An. Rep't, 1894. p. 692. 



