THE MINERALS OF IDAHO 185 



opals had been found for a distance of 250 feet on the surface and 

 the greatest depth reached in the open cuts was 20 feet. North of 

 and parallel with this ledge was another, 8 feet wide, traced for 50 

 feet, from which 1,000 carats of good opals were obtained. 840 The 

 deposits have been briefly mentioned by Lindgren, Drake, and 

 Schrader. 85 They were visited by Sterrett in 1910, when no work 

 was in progress on any of them. He gives a very complete description 

 of the deposits which is repeated below. 8 " 



Deposits have been opened on Squaw Creek and along the Cald- 

 well-Rockville road about 2 miles east of south of Sommer camp. 

 The deposit in the valley of Squaw Creek below the junction with 

 Little Squaw Creek is situated in a small rounded hill about 1 mile 

 above the ranch of Jim Keith. The elevation is about 3,500 feet 

 above sea level and that of the mountains about 1,000 feet higher. 

 The country is treeless, and low hills in the valley are covered only 

 with sage brush and a small quantity of grass. A few small pits 

 have been made on the summit of the hill and on the south side, 

 cutting into the partially disintegrated basalt in which the opals 

 occur. The basalt is highly vesicular, and under the microscope 

 is found to be composed chiefly of lath-shaped crystals of labradorite, 

 augite, and a brownish glass. The basalt is a portion of a flow 

 which partly fills the canyon of Squaw Creek and rests on rhyolite 

 and rhyolite tuff, the most important formation of the region. The 

 partially disintegrated basalt breaks up fairly easy and is removed 

 from the pits in large blocks. These blocks are broken up and the 

 opal picked out. The opal occurs as amygdaloid in the steam 

 holes and cavities in the basalt. The greater part of the cavities 

 contain no opal, and only a part of the opal is of the precious variety, 

 much of it being milky white or colorless. In some of the blocks 

 of basalt broken into, the opal is plentiful and much of it has a fine 

 play of colors. Most of the opal is in small pieces and large pieces 

 of precious opal are rare. Some of the vesicles are filled with chal- 

 cedony and opal. Fragments of chalcedony and chalcedony with 

 white opal 2 inches across were observed loose in the soil of the hill. 

 Some of this material is banded both with curved bands and straight 

 onyx bands. Similar specimens of chalcedony and white opal were 

 seen in other places in the valley. 



One of the larger mines, 3 miles west of Enterprise, contained 

 two sets of workings on different sides of a draw or valley and from 

 35 to 65 feet above the bottom of the draw. The principal workings 

 are on the west side and consist of several open cuts, the largest 

 about 50 feet long and 25 feet deep and a tunnel 40 feet long. The 



M« Geo. F. Kunz. U. S. Geol. Survey, Mineral Resources United States, 1893, p. 693. 



m Silver City folio (No. 104), Geol. Atlas United States, U. S. Geol. Survey, 1904. 



* Douglas B. Sterrett. U. S. Geol. Survey, Mineral Resources of United States, 1910, p. 872-874. 



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