Pyrite porphyroblast paragenesis at the Cherokee Mine, Ducktown, Tennessee

Pyrite porphyroblasts up to 300 mm in size are common in the polymetamorphosed, iron-rich, stratabound, massive sulfide ore at the Cherokee Mine, Ducktown, Tennessee. These porphyroblasts contain abundant inclusions of sphalerite, calcite, and micas that are used to determine the paragenesis of the porphyroblasts and the metamorphic history of the ore deposit. The ore mineralogy at the mine is: hexagonal pyrrhotite (60%), pyrite (30%), chalcopyrite (4%), sphalerite (3 %), and magnetite (3 %) with minor galena, molybdenum, tetrahedrite, bismuth, ilmenite, and rutile. The ore body is interpreted to have been syngenetic and to have contained both primary pyrrhotite and primary pyrite: additional pyrite may have formed as crusty accretions resulting from oxidation of primary pyrrhotite shortly after deposition. The early pyrites were later deformed and acted as seeds for the formation of the larger porphyroblasts by Ostwald ripening, and by the annealing of small pyrite grains into larger porphyroblasts, during isochemical metamorphism. Sphalerite geobarometry indicates initial growth of the pyrite porphyroblasts began at 6.8± 0.8 kilobars and that many sphalerite grains underwent some degree of re-equilibration at a later stage. Fluid inclusions formed during retrograde metamorphism have salinities near 12 % NaCl with a vapor phase rich in CO₂. Pyrrhotite-pyrite compositional profiles indicate at least partial re-equilibration of hexagonal pyrrhotite down to about 270°C. At lower temperatures further compositional re-equilibration was probably prevented, because the coexisting pyrite was too refractory to release the sulfur needed for the hexagonal pyrrhotite to react to monoclinic pyrrhotite.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Geology

Department dc:contributor.department

Geology

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1984

Author dc:creator

• Brooker, Donald Duane

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/74501

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/74501