38 NEW YORK STATE MUSEUM 



o£ the ore is placed in the later and lower temperature stage of 

 serpentinization, rather than, as at Edwards, in the earlier, high- 

 temperature stage following diopside formation, the entire process of 

 mineral formation is ascribed to deep-sea^,ed conditions and mag- 

 matic agencies rather than to the more superficial conditions and 

 agencies by which the formation of the serpentine is often explained. 



At Schwarzenberg, in Saxony, pyrite-blende deposits occur in 

 silicate aggregates formed by the contact metamorphism of lime- 

 stones by granite. The metamorphic silicates are considerably 

 altered and an entire bed may be converted to chloritic or serp- 

 pentinous aggregates.^ The sulphides which have formed after the 

 primary silicates and, apparently, after these have been altered to 

 hydrous silicates, surround and penetrate them, as in the ores at 

 Edwards. 



Very similar are the zinc ores of Rafvala, Sweden, where again 

 the sulphides surround and penetrate the corroded contact silicates. 

 Here, again, according to Beck ^ the sulphides are later than the 

 silicates but with no definite evidence as to how much later. 



Many ores of copper, lead, zinc, gold and silver, occurring in the 

 Cordilleran region, are related in origin to the Edwards zinc deposits, 

 though, as a rule, of vastly later geological date, much greater com- 

 plexity of mineral composition and, probably, formed at less depth. 

 But in the derivation of the ore-bearing solutions from granitic, 

 monzonitic or other magmas, and the deposition of the metals in 

 limestones, b}^ replacement, at and near the contacts, there is very 

 marked resemblance of a fundamental kind. Descriptions of the 

 western deposits are so numerous that extended reference is out 

 of the question, but the exhaustive reports of Lindgren,^ Lindgren, 

 Graton and Gordon* and of Ransome and Calkins^ may be 

 mentioned. 



In these western ores, the sulphides are often so intergrown with 

 contact metamorphic minerals as to lead to the conclusion that they 



^ Beck, R., Ueber Erzlagerstatten von Schwarzenberg; Zeits. d. Deutsch. 

 Geol. G'es., 1900, 52, pp. 58-60; also, Erzlagerstatten, 3te Auflage, 1909, i, 

 pp. 124-28. 



2 Beck, R., Ueber die Gesteine der Zinkblendelagerstatte Langfallsgrube 

 bei Rafvala in Schweden ; Tschermak's Min. & Pet. Mitth., 1901, 20, 

 pp. 382-89. 



2 Lindgren, W., The Copper Deposits of the Clifton-Morenci District. 

 Arizona; Prof. Paper U. S. G. S. No. 43, 1905. 



* Lindgren, W., Graton, L. C. & Gordon, C. H., The Ore Deposits of New 

 Mexico; Prof. Paper U. S. G. S. No. 68, 1910. 



5 Ransome, F. L., & Calkins, F. C, The Geology and Ore Deposits of the 

 Coeur D' Alene District, Idaho; Prof. Paper U. S. G. S. No. 62. 1908. 



