ANOMALOUS GRAPHITE AT THE BELVIDERE MOUNTAIN SERPENTINITE, VERMONT

The Belvidere Mountain serpentinite is part of a chain of Taconic-age ophiolites that stretches from the southern Appalachians to Newfoundland. Asbestos-bearing rocks in the serpentinite have been quarried here for over a century. On the north wall of the C-area quarry there is a fault zone containing anomalous graphite-bearing rocks (Van Baalen et al., 1999). This zone is about 15 feet wide and extends to the top of the quarry wall, about 90 feet, and has a strike of 5° and a dip of 85°W. Graphitic rocks within the fault zone are bounded on the east side by the asbestos-bearing serpentinite and on the west side by massive, gray-weathering antigorite. As far as we know, this occurrence is unique in the quarry. However, extensive quarrying activity has not only wiped out evidence of its original extent, but may have destroyed evidence of similar occurrences within the quarry. The foliated rock from the graphitic zone is dark gray and has a greasy luster. In thin section, we estimated 20% opaques finely disseminated, but also concentrated in submillimeter veins.

Geochemical studies will help to determine the origin of this graphite. We first separated the graphite from the serpentinite host rock using a combination of dilute HNO₃ and concentrated HF. The graphite remained as an insoluble residue. X-ray powder diffraction revealed a broad, weak X-ray peak near the known graphite peak at 26.38° 2θ. This could be explained by poorly crystallized graphite that does not diffract strongly. An exploratory study using mass spectrometry was then undertaken. The mean δ¹³C value attained from this study was –16.77 ± 0.1 per mil, implying that there is a significant organic carbon component in the graphite.

The graphite may have been precipitated from C-O-H fluids moving along a fault zone from a carbonaceous source in the underlying Hazen's Notch or overlying Ottauquechee Formations (Gale, 1980). For example, the Cambrian Ottauquechee Formation is characterized by black graphitic quartz-sericite phyllite and schist and by massive beds of dark-gray quartzite (Albee, 1957). This mechanism could possibly be similar to that for New Hampshire graphite veins described by Rumble and Hoering (1986). Further work to test this theory is currently in progress.