Coontail fluorite rhythmites of southern Illinois: evidence for episodic basin dewatering
Stratiform coontail ore of the Cave-in-Rock fluorite district, southern Illinois, display conspicuous, rhythmic banded textures similar to those reported in many MVT deposits throughout the world (e.g., east Tennessee, USA; Silesian-Cracow Region, Poland; and northern Baffin Island, Canada). Banding is expressed by the rhythmic alteration of two types of layers: detrital layers of fluorite mottled with particulate gangue dolomite and quartz, and layers of clear, crystalline fluorspar. Both are now composed principally of fluorite but differ in color, fabric and outline. In the past, this rhythmic banding has generally been attributed to fine-scale replacement of a primary host rock stratification or to cyclic replacement of host carbonates by a fluid of oscillating chemistry. Detailed megascopic and microscopic studies of these ores and their carbonate host real that ore bands were not derived by fine-scale in situ limestone replacement. Detrital bands contain hydraulically transported, sorted and graded, allochthonous debris derived by dissolution and disaggregation of host limestone and overlying shale. The banded fabric thus represents a cyclic interplay of chemical and hydraulic processes active during hydrothermal ore mineralization. Coontail ore bodies evidently formed in a hydrothermal spelean system, whose laterally sinuous trace reflects localization of hydrothermal activity where feeder faults intersected relatively impermeable roof-rock shales. The banded nature of these ores testifies to the ability of Mississippi Valley-type hydrothermal solutions to both create and fill their own open spaces. Moreover, the rhythmic nature of coontail ores suggests a prolonged and pulsating mineralization best explained by episodic dewatering of the Illinois Basin.
- Research Organization:
- Univ. of Michigan, Ann Arbor (USA)
- OSTI ID:
- 6875445
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FLUORITE
MINERALIZATION
PETROGRAPHY
ILLINOIS BASIN
GEOLOGIC HISTORY
GEOLOGIC FAULTS
GROUND WATER
ILLINOIS
ORIGIN
PRECIPITATION
TEXTURE
WATER REMOVAL
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM FLUORIDES
CALCIUM HALIDES
FEDERAL REGION V
FLUORIDES
FLUORINE COMPOUNDS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
HALIDE MINERALS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
REMOVAL
SEPARATION PROCESSES
USA
WATER
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)