NO. 2005. 3I0UNT LYELL COPPER DISTRICT— GILBERT & POGUE. 621 



That the ore deposition was conditioned by structural features and 

 represented a combination of replacement and impregnation, with 

 predominance of the former, seems conclusive and needs no further 

 elaboration here. 



ANALOGOUS DEPOSITS. 



Cupriferous pyritic deposits of the Mount Lyell type play so impor- 

 tant a part in the world's copper reserve ^ and present features of 

 such general interest that it may be profitable to review briefly the 

 significant geological characteristics of the leading representatives. 



Ural Mountains.^— Numerous lenses and sheets of massive cupriferous 

 pyrite, occurring in schists and greenstones of the Ural Mountains, 

 contribute to the copper output of that region. The pyritic ore runs 

 about 3 per cent in copper, due to later interstitial chalcopyrite, 

 which is associated with some sphalerite and galena, and in one 

 mine, bornite. Both the wall and ore are cut by joint seams carrying 

 enrichments of chalcopyrite and tennantite mixed with white vein 

 quartz and sometimes barite; these are distinctly later than the 

 pyrite, though not necessarily attributable to the action of de- 

 scending waters. The masses are replacement deposits in the 

 schistose rocks.^ 



Norway. — Copper-bearing pyi'itic ores are extensively developed 

 in this country, the districts of greatest import being the Sulitelma, 

 north of the Arctic circle, and the Roros and the Meraker near Trond- 

 hjem in central Norway. These deposits, which are notably similar in 

 character, are lenticular masses of pyrite, with admixed chalcopyrite, 

 averaging from 2^ to 3 per cent copper, and occurring within crystal- 

 line schists alongside intrusive masses of gabbro, or soda granite. 

 The bodies are comparatively small in horizontal dimensions, rarely 

 exceeding 60 feet in width, but extend downward to great depths. 

 According to Vogt* they originated from solutions which were expelled 

 from the intruding gabbroid and related gi-anitic masses, and 

 deposited their metallic content along the slipping planes of the 

 schists durmg their metamorphism. 



Rammelsherg. — The oft-discussed deposits of Rammelsberg, in the 

 Hartz Mountains of central Germany, consisting of pyrite with chalco- 

 pyrite, galena, sphalerite, arsenopyi-ite, barite, etc., intercalated 

 in metamorphosed clay slates, have been cited ^ as analogous to the 

 Mount Lyell occurrence. According to Lmdgren and Irving,® how- 



' The importance of this type of copper deposit is apt to be underestimated in the United States where 

 copper is obtained largely from ores of an entirely different order. Abroad the dominant type of copper 

 deposit is pyritic. 



2 Turner, Mining Mag., June, 1912. 



3 Turner, Econ. Geol., vol. 7, 1912, p. 709. Knox, idem, pp. 295-297. 



* Trans. Amer. Inst. Min. Eng., vol. 31, 1901, p. 141. (See also, Weed, The copper mines of the world, 

 1907, pp. 103-106. Beck-Weed, The nature of ore deposits, 1905, vol. 2, pp. 462-465.) * 

 ' See Gregory, Australasian Inst. Min. Eng., vol. 10, 1905, pp. 179-181 

 6 Econ. Geol., vol. 6, 1911, pp. 303-313. 



