REPLACEMENT ORE DEPOSITS IN THE SIERRA 



NEVADA 



It is well known that most of the gold deposits of the Sierra 

 Nevada occur in true fissure veins in which the quartz appears to 

 have been deposited in open cracks. This has been emphasized 

 recently in a very clear manner by Mr. Waldemar Lindgren in 

 two papers, 1 and he has also shown that the material of these 

 veins was deposited by carbonated waters containing also silica 

 and the precious metals. These waters have deposited their car- 

 bonates in very definite zones in the wall rocks, and the silica in 

 the fissures. At some points, however, in the Sierra Nevada 

 there are ore deposits which seem to have formed by the replace- 

 ment of other material. Such appears to be the Diadem lode 2 

 southwest of Meadow Valley in Plumas county. This lode seems 

 to represent a mass of dolomite and lime carbonate which has 

 been replaced by quartz and chalcedony; masses of dolomite are 

 still found on some of the levels. Iron and oxides of manganese 

 are present, and according to J. A. Edman rich selenides of gold 

 and silver combined with lead and copper occur as a rarity. 

 Some of the manganese is in the form of the silicate, rhodonite. 

 A certain portion of the lode is composed of little elliptical 

 bodies which according to Mr. Charles Schuchert of the U. S. 

 National Museum represent the silicified tests of foraminifera of 

 Carboniferous age belonging to the genus Loftusia. The shells 

 of Loftusia were originally carbonate of lime. These fossils 

 were found by Mr. J. A. Edman, the proprietor of the mine, and 

 forwarded to the Geological Survey for determination. They 

 sometimes form considerable bunches, the interspaces between 

 the elliptical tests being filled with secondary silica, or in some 



'Bull. Geol. Soc. of America, Vol. VI, pp. 221-240. 



Gold Quartz Veins of Nevada City and Grass Valley, Seventeenth Ann. Rep. U. S. 

 Geol. Surv., Part II. 



2 See Bidwell Bar folio of the U. S. Geol. Survey. 



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