Evidence for late-paleozoic brine migration in Cambrian carbonate rocks of the central and southern Appalachians: implications for Mississippi Valley-type sulfide mineralization

Journal Article · Fri May 01 00:00:00 EDT 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90222-5· OSTI ID:6894394

Hearn, Jr, P P; Sutter, J F; Belkin, H E

Many Lower Paleozoic limestones and dolostones in the Valley and Ridge province of the central and southern Appalachians contain 10 to 25 weight percent authigenic potassium feldspar. This was considered to be a product of early diagenesis, however, /sup 40/Ar//sup 39/Ar analyses of overgrowths on detrital K-feldspar in Cambrian carbonate rocks from Pennsylvania, Maryland, Virginia, and Tennessee yield Late Carboniferous-Early Permian ages (278-322 Ma). Simple mass balance calculations suggest the feldspar could not have formed isochemically, but required the flux of multiple pore volumes of fluid through the rocks, reflecting regional fluid migration events during the Late-Paleozoic Alleghanian orogeny. Microthermometric measurements of fluid inclusions in overgrowths on detrital K-feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100/sup 0/ to 200/sup 0/C and freezing point depressions of -14/sup 0/ to -18.5/sup 0/C. The apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby Mississippi Valley-type (MVT) deposits suggests that the regional occurrences of authigenic K-feldspar and MVT mineralization may be genetically related. This hypothesis is supported by the discovery of authigenic K-feldspar intergrown with sphalerite in several mines of the Mascot-Jefferson City District, E. Tennessee. Regional potassic alteration in unmineralized carbonate rocks and localized occurrences of MVT mineralization are both explainable by a gravity-driven flow model, in which deep brines migrate towards the basin margin under a hydraulic gradient established during the Alleghanian orogeny.

• Research Organization: Geological Survey, Reston, VA (USA)
• OSTI ID: 6894394
• Journal Information: Geochim. Cosmochim. Acta; (United States), Vol. 51:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
APPALACHIAN MOUNTAINS
CARBONATE ROCKS
BRINES
MIGRATION
ROCK-FLUID INTERACTIONS
DIAGENESIS
GEOCHEMISTRY
MINERALIZATION
ARGON ISOTOPES
CAMBRIAN PERIOD
CHEMICAL COMPOSITION
INCLUSIONS
ISOTOPE RATIO
MASS BALANCE
MICROCLINE
MINERALOGY
SULFIDE MINERALS
CHEMISTRY
FELDSPARS
GEOLOGIC AGES
ISOTOPES
MINERALS
MOUNTAINS
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
580400* - Geochemistry- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)