
Mesoproterozoic graphite deposits, New Jersey Highlands: Geologic and stable isotopic evidence for possible algal origins
Canadian Journal of Earth Sciences
By: R.A. Volkert
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Abstract
Graphite deposits of Mesoproterozoic age are locally abundant in the eastern New Jersey Highlands, where they are hosted by sulphidic biotite-quartz-feldspar gneiss, metaquartzite, and anatectic pegmatite. Gneiss and metaquartzite represent a shallow marine shelf sequence of locally organic-rich sand and mud. Graphite from massive deposits within metaquartzite yielded ??13C values of -26 ?? 2??? (1??), and graphite from massive deposits within biotite-quartz-feldspar gneiss yielded ??13C values of -23 ??4???. Disseminated graphite from biotite-quartz-feldspar gneiss country rock was -22 ??3???, indistinguishable from the massive deposits hosted by the same lithology. Anatectic pegmatite is graphitic only where generated from graphite-bearing host rocks; one sample gave a ??13C value of -15???. The ??34S values of trace pyrrhotite are uniform within individual deposits, but vary from 0 to 9??? from one deposit to another. Apart from pegmatitic occurrences, evidence is lacking for long-range mobilization of carbon during Grenvillian orogenesis or post-Grenvillian tectonism. The field, petrographic, and isotope data suggest that massive graphite was formed by granulite-facies metamorphism of Proterozoic accumulations of sedimentary organic matter, possibly algal mats. Preservation of these accumulations in the sedimentary environment requires anoxic basin waters or rapid burial. Anoxia would also favour the accumulation of dissolved ferrous iron in basin waters, which may explain some of the metasediment-hosted massive magnetite deposits in the New Jersey Highlands. ?? 2000 NRC.
Additional publication details
Publication type | Article |
---|---|
Publication Subtype | Journal Article |
Title | Mesoproterozoic graphite deposits, New Jersey Highlands: Geologic and stable isotopic evidence for possible algal origins |
Series title | Canadian Journal of Earth Sciences |
Volume | 37 |
Issue | 12 |
Year Published | 2000 |
Language | English |
Larger Work Type | Article |
Larger Work Subtype | Journal Article |
Larger Work Title | Canadian Journal of Earth Sciences |
First page | 1665 |
Last page | 1675 |