186 W. II. WEED MINERAL VEINS ENRICHED BY St T LPHtDES 



is also abundant. The composition of a surface water filling a mine shaft 

 130 feet deep, noted by Haworth,* the spring water of unquestioned su- 

 perficial character from Missouri, analyzed by Hillebrand,t and a great 

 many analyses of vadose waters, published by Emmons J and various 

 other writers, establish this fact beyond a doubt. 



If other proof were needed, the stalactites formed in mines afford con- 

 vincing evidence of the solubility of metallic sulphides in deoxidized 

 waters. Stalactites of blende and of galena are found in the mines of 

 Missouri. The percolating waters of many copper mines deposit stalac- 

 tites of hydrated iron oxide, and of copper and aluminous sulphates. 

 Such deposits have been found in the Copper Queen mine near Bisbee, 

 Arizona, and at Butte, Montana. Douglas describes a spring water 

 which oozes from feldspathic rocks at the copper basin, Yavapai county, 

 Arizona.^ On exposure to the air an insoluble mass separates out which 

 has the composition given below : 



Silica 7.17 



Iron and alumina 16.21 



Copper oxide 64.40 



Sulphur trioxide 12.22 



In time this sludge is converted into a mixture of carbonate of copper 

 and alumina that binds together the gravel into a conglomerate. 



Sulphide of zinc unquestionably formed by the action of cold sulphu- 

 retted water coming in contact with an aqueous solution of zinc sulphate 

 has been found at Galena, Missouri. The deposit was amorphous, and an 

 analysis by J. Dawson Hawkins showed the following composition : || 



Silica 1.49 



Fe 1.79 



Zn , 64. 17 



Sulphur 32.86 



free.. 0.082 



Total 100.392 



DEPOSITION OF MATERIAL FROM SOLUTION IN THE ENRICHMENT ZONE 



When the waters holding the metals in solution trickle down into 

 cracks and crevices of the underlying pyritous ore the ferric sulphate is 

 reduced to ferrous sulphate, and the gold, silver, and copper are pre- 

 cipitated.^ 



• Geology of lead and zinc district of Chorokoo county, Kansas, 1884, p. 34. 



t Am. Jour. Sei., vol. xlii, May, 1892, p. 418. 



I Mines of Custer county, Colorado, Seventeenth Ann. Rep. U.S. Geol. Survey, 1896, p.411etseq. 



§ Trans. Am. Inst. Mining Engineers, February, 1899, p. 25 of pamphlet edition. 



|| Malvern W. lies : Engineering and Mining .Journal, vol. 49, March . r >, 1899, p. 499. 



flVogt: J)as Huelva Kiesfeld, Zeitschrift fur Praktische Geologic, July, 1899, p. 250. 



