Mesoproterozoic graphite deposits, New Jersey Highlands: geologic and stable isotopic evidence for possible algal origins
2000
Graphite deposits of Mesoproterozoic age are locally abundant in the eastern New Jersey Highlands, where they are hosted by sulphidic biotitequartzfeldspar 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 δ13C values of 26 ± 2 (1σ), and graphite from massive deposits within biotite-quartz-feldspar gneiss yielded δ13C values of 23 ± 4. Disseminated graphite from biotitequartzfeldspar 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 δ13C value of 15. The δ34S 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 G...
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