proceedings: geological society 485 



F. C. Schrader: A sulphide-hearing monzonite from Arizoym. A 

 description of a monzonite was given, in which pyrite, chalcopyrite, 

 and molybdenite are disseminated throughout the entire rock, appar- 

 enth' as original constituents. Green copper stains are quite common 

 on the rock, and a few mining prospects have been started. 



Discussion: A. C. Spencer said that in his study of the disseminated 

 copper ores of Ely, Nevada, the microscopic examination had led him 

 to infer at first that the copper minerals in these bodies had been 

 deposited as original constituents. He had later come to the conclusion 

 that his first impressions were wrong. Schrader said that in his speci- 

 mens the copper ores occupied an interstitial position as regards the 

 quartz and feldspar. In similar California occurrences described by 

 Turner the same relations had been found. From such relations the 

 original nature of these constituents had been inferred. 



REGULAR PROGRAM 



J. B. Mertie: Copper and gold deposits of the Koisina-Kuskulana 

 District, Alaska. The Kotsina-Kuskulana District lies on the south 

 flank of the Wrangell Mountains. The geologic column in this area 

 is as follows: At the base there is a formation composed essentially 

 of tuffs, interbedded lavas, and basic intrusives, with which are associ- 

 ated minor amounts of argillite and limestone. Fossils from the 

 sedimentary members have been determined to be of Carboniferous 

 age. Overlying this conformably is a series of altered basaltic lava 

 flows, about 6,500 feet thick, which are designated as the Nikolai 

 greenstone. Lying upon the Nikolai greenstone without apparent 

 disconformity is the Chitistone limestone, a formation of upper Triassic 

 age about 700 feet thick. This grades upward into thin-bedded lime- 

 stone and shale, likewise of upper Triassic age, which comprise probably 

 about 5,000 feet of sediments. The youngest hard-rock formations of 

 the area include massive conglomerates, sandstone, and limestone of 

 upper Jurassic age, which lie unconformably on all the underlying 

 formations. Glacial and recent stream gravels occur along the drain- 

 age channels. Dioritic rocks intrude all the formations up to and in- 

 cluding the upper Triassic sediments. 



The copper deposits occur in the basal formation, in the Nikolai 

 greenstone, and to a minor extent in the Chitistone limestone. The 

 copper minerals commonly found are bornite, chalcocite, chalcopyrite, 

 malachite, azurite and native copper, but not all of these are found in 

 any one deposit. The gangue minerals are quartz, epidote, and calcite. 

 The loci of the copper deposits are shear zones. The ore-bodies are 

 irregular in shape and of doubtful persistence. Five tj^pes of ore de- 

 posits are recognized. All of these types, with the exception of the 

 native copper deposits, are thought to be primary. The presence of a 

 quartz-epidote gangue in much of the ore, considered in relation to 

 numerous quartz-epidote veinlets which have their maximum develop- 

 ment in the vicinity of the dioritic intrusives, leads to the belief that the 

 ore deposits are connected genetically with the intrusive rocks. The 



