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Economic Geology; November 1980; v. 75; no. 7; p. 1010-1021; DOI: 10.2113/gsecongeo.75.7.1010
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Metamorphic zonation of sulfides, oxides, and graphite in and around the orebodies at Ducktown, Tennessee

B. E. Nesbitt, and W. C. Kelly

Univ. Mich., Dep. Geol. Sci., Ann Arbor, Mich., United States

Several distinct zonations of oxide-sulfide-graphite assemblages have been identified in the wall rocks adjoining the metamorphosed massive sulfide deposits at Ducktown, Tennessee. The oxide-sulfide-graphite assemblages used to delimit these zones are as follows: pyrrhotite-ilmenite-graphite (country rocks), pyrrhotite-ilmenite, pyrrhotite-rutile, pyrrhotite-pyrite-rutile (wall rocks), and pyrrhotite-pyrite-magnetite (ore zone). The transition from the pyrrhotite-ilmenite-graphite zone to the pyrrhotite-ilmenite zone can be recognized as far as 90 m from the ore zone. The pyrrhotite-ilmenite to pyrrhotite-rutile transition occurs from 4 to 70 m from the ore. The pyrrhotite-pyrite-rutile zone is discontinuous and is only locally present immediately adjoining the ore zone. Knowledge of the P (6 kb) and T (550 degrees C) of metamorphism allows calculation of equilibria in the system Fe-Ti-O-S from available thermodynamic data. Calculations of the stabilities of various reactions as a function of f (sub S 2 ) and f (sub O 2 ) indicate that the log f (sub S 2 ) varies from --7.0 + or - 0.5 in the country rocks to --2.5 + or - 0.3 in the ore zone. The log f (sub O 2 ) similarly varies from --21.4 + or - 0.7 in the country rocks to --18.5 + or - 0.5 in the ore zone. These inferred values for f (sub S 2 ) and f (sub O 2 ) can be used to calibrate the S 2 -O 2 -ferromagnesian silicate reactions which have also taken place in these rocks. The distribution of the oxide-sulfide-graphite zones may be useful in the interpretation of the origin of metamorphosed sulfide bodies, the exploration for undiscovered deposits, and the extension of known deposits.

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 Geological Society, London, Special PublicationsHome page
G. N. Phillips, P. J. Williams, and G. De Jong
The nature of metamorphic fluids and significance for metal exploration
Geological Society, London, Special Publications, January 1, 1994; 78(1): 55 - 68.
[Abstract] [PDF]


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