230 W. LINDGREN — CALIFORNIA GOLD-QUARTZ VEINS. 



of course, frequently appear in the larpjer veins, separating them in two 

 or more parts. The heaviest veins appear to be found along the mother- 

 lode in Tuolumne and Mariposa counties, where the clean quartz often 

 reaches a width of 10 to 15 feet, and in isolated cases even more. This 

 extreme thickness seldom continues for any great distance. It may 

 probably be safely assumed that gold-quartz veins of this type cannot be 

 formed at any extreme depths below the surface, probably not below 

 10,000 feet, for at such depth open spaces could hardly exist. These 

 very large fissure veins are, however, not very abundant; a moderate 

 width of one to three feet is far more common. In many cases, indeed, 

 there are no large open spaces at all, but a network of smaller cracks and 

 fractures, in which the solutions deposited their contents. 



Association of Minerals in Gangue and Ores. 



In the predominating milky white quartz of the veins but few other 

 gangue minerals are found. Calcite, more rarely magnesium carbonate, 

 or a mixture of both, occur occasionally, but always in subordinate 

 quantities and usually concentrated near the walls. The quartz is ordi- 

 narily massive, but excellent examples of comb-structure may be found. 

 Barite * and fluorite are conspicuously absent. A white mica with pearly 

 luster is sometimes found in the quartz at some of the mines along the 

 mother-lode, and a green potassium-mica, colored by chromium, and 

 which Professor Silliman has called mariposite,'\ occurs abundantly in 

 places, though usually not in the quartz itself. Roscoelite, a vanadium - 

 potassium-mica, has been found in one place, and albite occurs in isolated 

 cases. I Rhodonite has been found in Plumas county. Titanium min- 

 erals, such as titanite, ilmenite and anatase, occur occasionally. 



The native gold is distributed through the quartz-gangue in an irregular 

 manner. The particles may be of microscopic size, or coarser, and visible 

 to the naked eye as scales, threads and smaller masses. Occasionally 

 large pieces, of all weights up to fifty pounds or more, will be found. In 

 the ores from the larger mines it is, however, rare to find the gold visible 

 to the naked eye. The gold always contains a little silver, in rarer cases 

 as much as 30 per cent. 



A variable but always comparatively small quantity of metallic min- 

 erals accompanies the gold. It varies from a fraction of 1 per cent to 

 5 or 6 per cent, but ordinarily makes up from 2 to 3 per cent of the mass 



* For rare occurrences of barite see W. Lindgren, Am. Jour. Sei., vol. xliv, 1892, p. 92, and H. W. 

 Turner, Am. Jour. Sci., vol. xlvii, 1895. 



t For analyses see H. W. Turner : " Further notes of the gold ores of California," Am. Jour. Sci., 

 vol. xlvii, 1895. 



X See the interesting paper by H. W. Turner : Am. Jour. Sci., May, 1894, vol, xlvii, p. 467. 



