AUT.a. BLACK SANDS FROM IDAHO SHANNON, 15 



ent in the sands examined and that, if these similar minerals occur 

 at all, it is only as rare and scattered crystals. 



MONAZITE. 



The presence of monazite in heavy sands in Idaho was first recog- 

 nized by Lindgren * in the gold placers of the Boise Basin, where 

 he found it as a resinous brown mineral in subangular grains in 

 part exhibiting crystal faces. Roughly quantitative analyses by 

 Hillebrand made upon the purified sand showed the principal con- 

 stituents to be phosphoric acid and cerium earths, with a small 

 amount of thorium. The absence of yttriinn earths showed that 

 xenotime probably was absent. Later, Day in his work on the black 

 sands of the Pacific Slope,^ reported the mineral from 37 localities 

 in 10 counties in Idaho. Some of these are in error, since several 

 of the sands listed are from Snake River localities and a reexamina- 

 tion of the same samples failed to detect any monazite. Schrader ® 

 has recently described the occurrence of monazite in Nez Perce 

 County in northern Idaho. 



The monazite occurs most abundantly in the gold-placer region 

 about Centerville, in Boise County, and preparations were made 

 some years ago by the Centerville Mining and Milling Company 

 to recover and clean the sand for market. The plant which was 

 built was burned before any important production had been made 

 and the commercial outlook was not sufficiently bright to encourage 

 its rebuilding. The Idaho monazite is seemingly lower in its content 

 of thoria, which is the only valuable constituent, than similar sands 

 from Brazil, with which it can not compete in the very limited 

 market. 



The work of the several investigators who have examined the 

 Idaho monazite-bearing area seems to indicate conclusively that the 

 monazite is an original mineral present as an accessory constituent 

 in the granitic rock of the great central Idaho batholith and it is 

 probably more or less present in every drainage basin within this 

 great granitic area. Lindgren panned crystals of both monazite and 

 zircon from angular granite soil formed by disintegration of the 

 granite on slopes where these minerals could have no other source. 



During the present examination monazite was noted abundantly 

 in sands from Grimes Creek and elsewhere near Centerville and from 

 Idaho City, in Boise County, from Pierce City and Orofino, in 

 Clearwater County, and from French Creek, in Nez Perce County. 

 It is a noteworthy fact that in the examination of Snake River sands 

 from nine localities in five counties no trace of the mineral was 

 found. 



• Lindgren, Waldemar, U. S. Geol. Survey, 18th Ann. Rept., pt. 3, pp. 677-670, 1898. 



• Day, D. T., and Richards, R. H., Mineral Resources U. S. for 1905. U. S. Geol. Survey, 

 1906, pp. 1195-1201. 



• Schrader, F. C, Bull. U. S. Geol. Survey No. 430, p. 185, 1910. 



