no. 1835. RELATION OF BORNITE AND CHALCOCITE— LANEY. 521 



practically all the ore deposits of the Piedmont and Southern 

 Appalachian regions. 



The relations of ore to the gangue, and of the gangue minerals to 

 each other are strong evidence against the assumption that the two 

 sulphides are secondary minerals. It has been stated before that the 

 ore is so complexly and intricately associated with the gangue min- 

 erals that no other conclusion than that of contemporaneous deposi- 

 tion seems tenable. If chalcocite and bornite of the intergrown type 

 are secondary minerals, the whole vein, gangue and all, is secondary. 



The minerals of the deposits, both gangue and ores, as a group, with 

 the possible exception of the chalcocite, if they can be said to be char- 

 acteristic of any one portion of a mineral vein, would probably be 

 typical of the deeper vein zone. 1 These are, so far as has been deter- 

 mined, quartz, calcite, epidote, chlorite, specularite, bornite, chalco- 

 cite, a very little chalcopyrite, albite, and orthoclase. It must be 

 stated that feldspar of any kind in direct association with the sul- 

 phides is rare, but good examples were found at the Seaboard mine, 

 where the feldspar is a plagioclase, probably albite; at the Holloway 

 mine, where both plagioclase and a pink feldspar, which is appar- 

 ently orthoclase, occur; and at the Copper King mine, where the 

 feldspar is albite. Feldspars, however, are very abundant in many of 

 the veins, especially in lean or barren portions. In such occurrences 

 the mineral is generally albite or an acid oligoclase. In certain por- 

 tions of the veins at the gold mine near Redbank, Virginia, and Hol- 

 loway mine in North Carolina, pink feldspar occurs in association with 

 quartz so as to strikingly resemble a pegmatite. This is generally 

 not closely associated with the ore, but at times, especially in the Hol- 

 loway mine, it carries a small amount of the sulphides. It usually is 

 found in barren portions of the vein or as stringers running off from 

 the vein into the country rock. 



Origin of the ores. — The origin of these ores is a more difficult ques- 

 tion than one might at first suspect, and is as important as difficult. 

 The country rock is by far too basic to have afforded the vast amount 

 of quartz in the veins. Neither can the underlying quartz porphyry 

 be looked to as the source, since this rock is also older than the veins 

 and is itself cut by numerous quartz veins similar in all respects to those 

 in the andesite and the andesitic tuff, except that they contain but 

 little or no calcite and epidote and probably no copper ores. Some 

 source, therefore, outside of and much younger than the country rocks 

 must be looked for. The only rock in the region which apparently 

 meets the conditions is the granite. This granite is highly quartzose, 

 younger than the rocks in which the ore deposits occur, was not in- 



i Waldemar Lindgren, Relation of ore deposition to physical conditions, Economic Geology, vol. 2, 1907, 

 pp. 105-127. 

 W. II. Emmons, A genetic classification of minerals, Economic Geology, vol. 3, 1908, pp. bll-627. 



