NO. 2005. MOUNT LYELL COPPER DISTRICT— GILBERT d POGUE. 623 



upon their final consolidation, which found congenial conditions for 

 precipitation in the more schistose phases of the alaskite-porphyry 

 where this rock presented maximum permeability and surface of 

 attack. 



Of the ore minerals pjrrite was the first to crystallize in most in- 

 stances; sphalerite, on the whole, is later. Chalcopyrite is the young- 

 est of the important minerals, forming vemlets around and in other 

 sulphides; it prefers the company of sphalerite to pyrite and shows 

 also an affinity for quartz and barite. Primary bornite is commonly 

 associated with chalcocite, and the two either take the place of chal- 

 copyrite or are intimately associated with it. Secondary bornite 

 and chalcocite are also present, but are readily distinguished from 

 the former. 



Ducktown, Tennessee} — These important deposits, which are 

 notable for successful working of low-grade ore, form lenticular to 

 tabular masses, inclosed within deeply dipping schists of sedimentary 

 origin, and represent limestone intercalations which have suffered 

 replacement by ore-bearing solutions from probable magmatic 

 sources. The primary ores consist of pyrrhotite and pyi'ite with 

 chalcopyrite and subordinate sphalerite; these are associated with 

 specularite, magnetite, actinolite, calcite, tremolite, quartz, pyroxene, 

 garnet, zoisite, chlorite, mica, graphite, titanite, and feldspar. Sec- 

 ondary enrichment has proved of importance only near the surface, 

 where chalcocitization has taken place in a narrow zone rarely over 

 a few feet in thickness, between the gossan and primary sulphide 

 zone. The Ducktown occurrence is not a strict analogue of the 

 Mount Lyell deposit, though presenting many features m common .^ 



SELECTED BIBLIOGRAPHY. 

 Fawns, Sidney. 



Some notes on the Mount Lyell Mine, Tasmania. Inst, of Min. & MetalL, vol. 4, 

 1895-96, pp. 279-289. 

 Describes briefly geology of deposits and treatment of the ores. 



Gregory, J. W. 



The Mount Lyell Mining Field, Tasmania. With some account of the geology of 

 other pyritic ore-bodies. Trans. Australasian Inst, of Min. Eng., vol. 10, 1905, 

 pp. 26-196. 29 figs., 17 plates, 1 geol. map. 



Gives results of thorough geological investigation, including detailed petrography. Contains 

 complete bibliography to year of publication. 



Mount Lyell Mining P'ield. Australasian Mining Standard, 1905 (17 numbers). 

 Same as preceding. 



1 Emmons and Laney, PreUminary report on the mineral deposits of Ducktown, Tennessee. Bull. 470, 

 U. S. Geol. Survey, 1910, pp. 151-172. 



2 From the foregoing review it is seen that the great cupriferous pyrite deposits of the world are strikingly 

 alike in their geologic relations, mineralogic content, and origin. It may therefore be generalized that any 

 region of schistose rocks (especially sericite and chlorite schists) that is intruded by a differentiated series 

 of igneous rocks, is one favorable to the occurrence of such deposits, and where in such regions gossans are 

 found, which in their outcrops show values in gold and silver and the presence of barite, lenses of cupriferous 

 pyrite at depth may be anticipated with considerable confidence. 



