Skip to main content
U.S. flag

An official website of the United States government

Mesoproterozoic graphite deposits, New Jersey Highlands: Geologic and stable isotopic evidence for possible algal origins

January 1, 2000

 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 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 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 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 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.

Publication Year 2000
Title Mesoproterozoic graphite deposits, New Jersey Highlands: Geologic and stable isotopic evidence for possible algal origins
DOI 10.1139/e00-050
Authors R. A. Volkert, Craig A. Johnson, Albert V. Tamashausky
Publication Type Article
Publication Subtype Journal Article
Series Title Canadian Journal of Earth Sciences
Index ID 70022284
Record Source USGS Publications Warehouse
USGS Organization Geology, Geophysics, and Geochemistry Science Center