1084 A TREATISE ON METAMORPHISM. 



furnished by two sets of fissures, but, as suggested by Jenney," partly 

 by the mingling of two different kinds of waters, thus giving conditions 

 favorable for precipitation. 



In the Enterprise mine, at Rico, Colo., described by Richard, 6 the ore 

 bodies are in vertical veins and in flats under shales. While a set of cross 

 veins is barren, "the rich ore bodies overlie them in the contact zone.'" 

 Below the shale it is common to find ores of more than average grade in 

 the pay veins where they are broken by the cross veins. It is believed the 

 explanation of these relations is the reactions resulting from the mingling of 

 the solutions of the "verticals" with the inclined cross veins. With this 

 Ransome's recent studies accord. He says: "Large bodies of workable 

 sulphide ore occur only where the solutions in the lode fissures have had 

 opportunity to mingle with laterally moving solutions in the blanket " d 



The silver-lead deposits of the Aspen district of Colorado, described 

 by Spurr, furnish an instance of very probable precipitation of rich ore 

 shoots by the mingling of solutions. Spurr states that generally an ore 

 body is "found at the intersection of two faults, one of these faults usually 

 dipping steeply, while the other is much flatter." For this "the explana- 

 tion is offered that by the mingling of solutions which had previously 

 flowed along different channels the precipitation of metallic sulphides was 

 brought about." c 



Probably the rich shoots of gold ore in the Sierra Nevada, which, 

 according to Lindgren, pitch to the left as one looks down the vein, further 

 illustrate the principle of precipitation by mingled solutions. For the most 

 part, Lindgren makes no statement as to the relations of ore shoots and 

 lateral seams. However, on Canada Hill vein there are "occasional rich 

 bunches at the intersections" of the two systems of veins/ 



«Jemiey, W. P., The lead and zinc deposits of the Mississippi Valley: Trans. Am. Inst. Min. 

 Eng., vol. 22, 1894, pp. 189-190, 221. 



& Packard, T. A., The Enterprise mine, Rico, Colo.: Trans. Am. Inst. Min. Eng., vol. 26, 1897, pp. 

 906-980. 



cRickard, cit., p. 977. 



d Eansome, F. L., The ore deposits of the Eico Mountains, Colorado: Twenty-second Ann. Rept. 

 U. S. Geol. Survey, pt. 2, 1901, p. 301. 



"Spurr, J. E., Geology of the Aspen mining district, Colorado: Mon. U. S. Geol. Survey, vol. 31, 

 1898, p. 234. 



/Lindgren, Waldemar, The gold-quartz veins of Nevada City and Grass Valley, California: 

 Seventeenth Ann. Rept. IT. S. Geol. Survey, pt. 2, 1896, p. 195. 



