Masters Theses

Date of Award

12-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Otto C. Kopp

Committee Members

Kula C. Misra, Richard W. Arnseth

Abstract

Since sphalerite is often associated with the medium to coarsely crystalline dolostones of the Upper Knox Group in East and Central Tennessee, this lithology has been investigated extensively. Past explanations for the formation of these dolostones include replacement of limestone during interaction with ore fluids, groundwater migrating through the Kingsport paleoaquifer, mixed freshwater and seawater during early diagenesis, and hypersaline brines.

The present study employs a controlled sampling method, standard petrographic techniques, cathodoluminescence petrography, and X-ray fluorescence analysis to investigate the origin of limestones and dolostones adjacent to mineralized areas. The samples came from the Coy mine, Mascot-Jefferson City district. East Tennessee, and core from the Right Fork area. Central Tennessee.

Three major lithologies were found in East Tennessee. Limestones are micrites and biointrapelsparites which are interpreted as having formed subtidally. Xenotopichypidiotopic, medium- to coarse-grained dolostones (X-H,MCd) replaced limestones after lithification, and in some cases, after silicification. The X-H,MCd were formed in two stages. During the first, zoned, subhedral rhombs (visible only with cathodoluminescence) were precipitated. During the second, anhedral, nonzoned dolomite crystals replaced the remaining chert or micritic matrix using previous rhombs as nucleation sites. Dolomitization was accompanied by an increase in K, Fe, Mn, Sr, and Br, and a decrease in Cl. Xenotopic, fine-grained dolostones (X,Fd) were probably formed penecontemporaneously with sedimentation in an intertidal to supratidal environment and were later neomorphosed under reducing conditions.

In Central Tennessee, three major lithologies were also found. Limestones and X,Fd are similar to those from East Tennessee. Idiotopic-hypidiotopic, fine- to coarse-grained dolostones (I-H,FCd) are composed of mosaics of subhedral zoned rhombs (cloudy centers, clear rims). Elemental con centrations are generally similar to those of X,Fd, but Br/Cl ratios are lower in the I-H,FCd. The I-H,FCd are interpreted as having formed during early, near-surface diagenesis.

Petrographic and elemental evidence suggest formation of the X-H,MCd of East Tennessee in a stable reducing (burial) environment by interaction of limestone or chert with hypersaline brines. Whether these brines were basinal or evaporative in origin is a matter of speculation.

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