a Precambrian hydrocarbon from the Sudbury Basin, Ontario, Canada

PPL RL [224 kb] XP TL [82 kb]

Above: two photomicrographs showing brecciated, opaque anthraxolite in granular to fibrous quartz cement. Sample from the Whitewater Group, the Proterozoic sedimentary package which fills the western part of the Sudbury basin, the second-largest generally-recognized terrestrial impact structure. Nominal 40X magnification, long-axis field of view 2.7 mm, in plane-polarized reflected (left) and crossed-polarized transmitted light.

"Rock of the Month # 64, posted October 2006" ---

Anthraxolite is a relatively mature hydrocarbon phase with subvitreous lustre and pronounced fracture. This example is from Balfour township, west of Sudbury.

Thucholite is a related term for a relatively mature hydrocarbon, typically with elevated levels of minor elements. The name is derived from some of the possible constituents: THorium, Uranium, and major elements Carbon, Hydrogen and Oxygen. It has been described from unusual, relatively high-temperature environments, such as granitic pegmatites, and from the famed reefs of the Witwatersrand, the world's greatest repository of gold.

Anthraxolite and thucholite are but two names in a rather confusing, overlapping terminology for hydrocarbon species which lack the clear crystallinity of carbon polymorphs such as graphite and diamond. One such term is cannel coal
which like "jet" relates to materials formed more recently in the Phanerozoic Era, the geologically-modern realm of more diverse, abundant and larger plant life.

The sample of the Balfour anthraxolite, collected by J.M. Martins in September 1984 and described in this article, contains about 95% ovoid-angular fragments of hydrocarbon, 1-12 mm in size, of shiny black, jet-like appearance. The hydrocarbon has flat to conchoidal fracture, and indeed seems remarkably hard. A polished section was about 93% anthraxolite, plus 7% cementing quartz, and (largely within the quartz) traces of fine-grained pyrite, magnetite and chalcopyrite. Localized fracture planes cut the breccia, reducing the hydrocarbon, which behaves in a brittle manner, to shards 1-50 microns in size. The sample featured in a study of carbonaceous materials in the Precambrian, and associated with gold deposits of various ages (Wilson and Rucklidge, 1986, 1987). Raman spectroscopy of anthraxolite, and of carbonaceous matter from the host sediments in the Sudbury basin, confirmed that the material is highly-disordered carbon, unlike the crystalline graphite that can develop in high-grade metamorphism (Heymann and Dressler, 1997).

In the early years of the great Sudbury nickel mining camp, fuel and timber (often one and the same) were required in great quantities. It may have seemed providential that, at a site some 27 km west of Sudbury and 8 km southwest of Chelmsford, a "seam" of "smokeless" coal 10 feet wide was reported from Balfour township (Coleman, 1897). The seam was exposed over a length of 70 feet, true width perhaps 6-9 feet. The black rock was relatively hard, 3-4 on the Mohs scale, c.f. anthracite, 2-2.5. It (ibid., p.160) "forms small plates or irregular cubic blocks, the largest observed being three-quarters of an inch square". More veins than seams, the rock also contained quartz and scattered pyrite. The occurrence was drilled, and tests showed that the material burnt well, "after getting up a good fire it gave a brilliant blue flame and also great heat, but the waste was considerable" (ibid., pp.160-161). The carbon was probably derived from adjoining slate, which assayed 6.8% C, while the black rock itself assayed 94.92% C. The vein was later shown to continue for 100 feet (30 metres) and more from the surface, but this was not to be a repeat of the fortuitous juxtaposition of coal fields with iron ores, that had been instrumental in the Industrial Revolution in central and northern England. In the Sudbury case, it seemed that "those slates were once bituminous, and fissures in them were filled with liquid or plastic substances, now changed, as in Balfour township, to irregular veins of anthraxolite' (Coleman, 1903, p.291). The host rocks are the Whitewater Group strata which infilled the Sudbury basin, cooled after the impact. and which contain diverse, often carbonaceous sediments, and local lead- zinc mineralization (Arengi, 1977; Roussell et al., 2002). Some units of the Onaping and Onwatin formations contain several weight percent reduced carbon.

It was not long before similar solid, even glassy hydrocarbons were noted elsewhere. The occurrence of abundant hydrocarbon ("thucholite") at the Besner feldspar mine near Parry Sound, in the Grenville province of Ontario, south of Sudbury, was described by Spence (1930). This black mineral proved to be radioactive, and had been dubbed thucholite (see above) by Ellsworth in 1928, in place of the older term anthraxolite. The thucholite is usually found in oligoclase feldspar, and there are even traces of an oily substance. This seems quite surprising, in an igneous rock otherwise composed of major and accessory minerals more typical of Grenville pegmatites, such as allanite, beryl, garnet, sphene (titanite) and uraninite.

However, not all such hydrocarbons were radioactive, and the term anthraxolite persisted. Dunn and Fisher (1954) described it in vugs and fractures, disseminated and within quartz crystals (the so-called Little Falls or Herkimer diamonds) in Cambrian to Ordovician dolomites in upstate New York, U.S.A. The infilling of vugs and pockets is consistent with an early fluid state (see also Mancuso et al., 1989; Hiller and Shapiro, 2009). Parnell (1988) reported a minute (<1 micron) inclusion of native platinum in calcite inclusions within a late pyrobitumen veinlet cutting more massive bitumen, displaying that the New York anthraxolite was capable of transporting metals. The maturation of organic matter in the Precambrian has been studied in considerable detail (e.g., Hayes et al., 1983). The effect of metamorphism on hydrocarbons, diversely referred to as kerite, anthraxolite, shungite, graphite, ozokerite and asphaltite, was addressed by Lobzova and Ziborova (1988).


Arengi,JT (1977) Sedimentary Evolution of the Sudbury Basin, Ontario. MSc Thesis, University of Toronto, 141pp.

Coleman,AP (1897) Anthraxolite or anthracitic carbon. Ontario Bureau of Mines Rep. 6, 159-166.

Coleman,AP (1903) The Sudbury nickel deposits. Ontario Bureau of Mines Rep. 12, 235-303.

Dunn,JR and Fisher,DW (1954) Occurrence, properties, and paragenesis of anthraxolite in the Mohawk valley. Amer.J.Sci. 252, 489-501.

Hayes,JM, Kaplan,IR and Wedeking,KW (1983) Precambrian organic geochemistry, preservation of the record. In `Earth's Earliest Biosphere' (Schopf,JW editor), Princeton University Press, 543pp., 93-134.

Heymann,D and Dressler,B (1997) Raman study of carbonaceous matter and anthraxolite in rocks from the Sudbury, Ontario, impact structure. Lunar and Planetary Science 28, 563-564.

Hiller,JA and Shapiro,RS (2009) Detailed petrographic analysis of anthraxolite morphology in the Biwabik iron-formation, northern Minnesota. Abs. 55th Annual Meeting, Institute on Lake Superior Geology, vol.55 part 1, 83pp., 40-41, Ely, MN.

Lobzova,RV and Ziborova,TA (1988) Behavior of high-carbon solids during metamorphism. Int.Geol.Rev. 30 no.2, 187-196.

Mancuso,JJ, Kneller,WA and Quick,JC (1989) Precambrian vein bitumen: evidence for petroleum generation and migration 2 G.a. ago. Precambrian Research 44, 137-146.

Parnell,J (1988) Native platinum in pyrobitumen from Fonda, New York. Amer.Mineral. 73, 1170-1171.

Rousell,DH, Meyer,W and Prevec,SA 2002 Bedrock geology and mineral deposits. In `The Physical Environment of the City of Greater Sudbury' (Roussell,DH and Jansons,KJ editors), OGS Spec.Vol. 6, 228pp., 20-55.

Spence,HS (1930) A remarkable occurrence of thucholite and oil in a pegmatite dyke, Parry Sound district, Ontario. Amer.Mineral. 15, 499-520.

Wilson,GC and Rucklidge,JC (1986) Lithological features and economic significance of reduced carbonaceous rocks in gold deposits. OGS Misc.Pap. 130, 177-189.

Wilson,GC and Rucklidge,JC (1987) Geology, geochemistry, and economic significance of carbonaceous host rocks in gold deposits of the Timmins area. In `Geoscience Research Grant Program, Summary of Research 1986-1987', OGS Misc.Pap. 136, 241pp., 66-76.

Graham Wilson, 09-10 July 2011

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