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Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins

Joseph F. Whelan, James C. Cobb and Robert O. Rye
Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins
Economic Geology and the Bulletin of the Society of Economic Geologists (August 1988) 83 (5): 990-1007

Abstract

Cleat and clastic dikes of Middle Pennsylvanian-age coal beds of the Illinois and Forest City basins of Illinois, Iowa, Missouri, and Kansas locally contain appreciable amounts of sphalerite within a kaolinite-pyrite-sphalerite (+ or - pyrite)-calcite paragenetic sequence. The sphalerite and associated minerals are of interest as a partial record of the history of fluids in the sedimentary basin and as possible indicators of Mississippi Valley-type mineralization. Moreover, zinc from the sphalerite may represent an exploitable by-product of coal mining and combustion.Pyrite is abundant in these coals both as fine-grained disseminated framboids that formed during early diagenesis and as coarser grained cleat fillings, etc., that formed much later. The delta (super 34) S values of this later pyrite, the sphalerite, and the coal organic matter range from -12 to 19 per mil. Within individual samples, however, pyrite, sphalerite, and organic matter sulfur delta (super 34) S values are nearly identical. This similarity strongly suggests related origins. The delta (super 34) S values of pyrite, sphalerite, and organic matter from coals of the Illinois basin and the central and southern Forest City basin range from -12 to 0 per mil. This range is not unique to the sphalerite-bearing coals; pyrite and organic matter from sphalerite-free high sulfur coals have similar delta (super 34) S values (Price and Shieh, 1979). We believe that sulfur produced by the breakdown of organosulfur compounds in the coal is incorporated into the epigenetic sulfides. In the northern Forest City basin, however, many samples have delta (super 34) S values between 8 and 19 per mil. These are similar to the delta (super 34) S values of sphalerite and pyrite from the Upper Mississippi Valley Zn-Pb district which lies northeast of the Forest City basin and north of the Illinois basin. This similarity suggests input from a Mississippi Valley-type hydrothermal system.Cleat kaolinite has delta D values of -36 to -24 per mil and delta (super 18) O values of 19.2 to 20.2 per mil. Assuming that clearing postdated the lignite rank of coalification implies that kaolinite was deposited between 40 degrees and 100 degrees C. At the lower temperatures, the kaolinite fluid would have had an isotopic composition similar to seawater; at the higher temperatures, it would have had a composition similar to the sphalerite-depositing fluid. Sphalerite was deposited from a fluid that was chemically and isotopically similar to the fluids responsible for the main-stage ores of the Upper Mississippi Valley Zn-Pb district (75 degrees -113 degrees C, approximately 21 equiv wt % NaCl, delta D = -65 to -3ppm, and delta (super 18) O = -0.9-9.9ppm). The isotopic compositions (delta (super 13) C = -12.4 to -2.7ppm and delta (super 18) O = 21.1-25.8ppm) and paragenetic positions of the cleat calcite samples are similar to those of the late-stage calcite of the Upper Mississippi Valley Zn-Pb and Illinois-Kentucky fluorspar districts. Calcite inclusion fluids had delta D (sub H (sub 2) O) values of -80 and -58 per mil, implying a meteoric water source. At probable temperatures of 15 degrees to 75 degrees C, this calcite formed from fluids having calculated delta (super 18) O (sub H (sub 2) O) values of -9 to 1 per mil, implying slight to moderate exchange with sedimentary rocks. The diagenetic-epigenetic history of fluids recorded by the cleat minerals probably began with a slightly evolved seawater, followed by a metal-bearing deep basin brine, and concluded with a cooler, slightly evolved, meteoric-water fluid.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 83
Serial Issue: 5
Title: Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins
Affiliation: U. S. Geol. Surv., Denver, CO, United States
Pages: 990-1007
Published: 198808
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 65
Accession Number: 1988-072822
Categories: General geochemistryEconomic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, sketch map
N36°00'00" - N40°34'60", W95°45'00" - W89°04'60"
N33°34'60" - N37°00'00", W103°00'00" - W94°25'00"
N33°00'00" - N36°30'00", W94°40'00" - W89°40'00"
N33°00'00" - N35°34'60", W96°45'00" - W90°30'00"
N38°49'60" - N41°25'00", W96°19'60" - W93°45'00"
N37°00'00" - N42°30'00", W91°30'00" - W87°30'00"
N40°25'00" - N43°30'00", W96°34'60" - W90°10'00"
N37°00'00" - N40°00'00", W102°00'00" - W94°34'60"
N36°00'00" - N49°00'00", W104°00'00" - W80°30'00"
Secondary Affiliation: Ky. Geol. Surv., USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists
Update Code: 1988
Program Name: USGSOPNon-USGS publications with USGS authors
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