Butler and Schaller — Thaumasile. 131 



Art. XVII. — Thaumasite from Beaver County, Utah;* by 

 B. S. Butlek and W. T. Schallek. 



Introduction. 



The interesting mineral thaumasite was first described in 

 1878 by Baron von Nordenskioldf from material collected at 

 the copper mines of Areskuta, Jemtland, Sweden. Since that 

 time it has been noted from other localities in Sweden and in 

 1896 it was described by S. L. Penfield and J. H. Pratt, from 

 Berber's quarry, West Paterson, New Jersey. The latter 

 locality is the only one where it had been noted outside of 

 Sweden, previous to the one here' described. 



During the summer of 1909 one of the authors (B. S. Butler) 

 while engaged in a geological survey of the Frisco district, 

 Beaver County, Utah, found a mineral of unusual appearance 

 which on examination in the office proved to be thaumasite. 

 The mineral was found in the Old Hickory mine of the Majes- 

 tic Copper Company, located in the Rocky Range, Rocky dis- 

 trict, Beaver County, Utah, about four miles northwest of the 

 town of Milford on the Salt Lake, Los Angeles and San Pedro 

 Railroad. 



Geological Occurrence. 



The Rocky Range is built up at the southern end, where 

 the mine is located, of a series of interbedded dolomitic lime- 

 stones and quartzites of probably Carboniferous age which 

 have been intruded by monzonite. The intrusion of the mon- 

 zonite has produced typical contact alteration of the limestone, 

 resulting in the formation of magnetite, garnet and pyroxene 

 with some pyrite and chalcopyrite. At the Old Hickory mine 

 the limestone for several feet from the contact has been largely 

 replaced by magnetite, with a small percentage of the contact 

 silicates, and sulphides of iron and copper. As the distance 

 from the contact increases the amount of magnetite decreases 

 and the contact silicates become coiTespondingly more abun- 

 dant, and these in turn give place to the carbonates composing 

 the limestone. The zone of magnetite carrying copper values 

 as chalcopyrite and secondary alterations of this mineral 

 (covellite, chalcocite and copper carbonate) has furnished the 

 ore that has been shipped from the mine. In the general 

 vicinity of the mine and especially to the north and northwest, 

 there are veins in the limestone from a fraction of an inch to 

 upwards of a foot in width, composed of a dense white mate- 



* Published by permission of the Director of the IT. S. Geological Survey. 

 t Comptes Rendus, vol. lxxxvii, p. 313, 1878. 



