Carbon Isotope Geochemistry of Archean Carbonaceous Horizons in the Timmins Area
F.-W. Wellmer, U. Berner, H. Hufnagel, H. Wehner, 1999. "Carbon Isotope Geochemistry of Archean Carbonaceous Horizons in the Timmins Area", The Giant Kidd Creek Volcanogenic Massive Sulfide Deposit, Western Abitibi Subprovince, Canada, Mark D. Hannington, C. Tucker Barrie
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Two types of Archean kerogenic-graphitic facies associated with base metal mineralization, and considered to be coeval with them, can be observed at three localities in the Timmins area: the Kidd Creek deposit, the Chance deposit, and the Rusty Hill occurrence. The type A facies normally has S13C values between -18 and -33 per mil and shows little or no correlation with values for total organic carbon; the S13C values for type B facies are more negative and lie between -29 and -48 per mil and show a positive, nonlinear correlation with values for total organic carbon. Kidd Creek argillites belong to type A. They resemble normal Archean argillites and have S13C values ranging from -19.3 to -26.4 per mil. Type B horizons occur close to the Chance deposit and the Rusty Hill sulfide occurrence and are also associated with base metal mineralization at other locations. Type B facies grades laterally into type A. Facies of both types also occur at stratigraphically different horizons. Both facies cover the same range of H/C ratios. Low H/C ratios <0.02 are observed over the whole range of S13C values, indicating that alteration during metamorphism cannot explain the differences in isotopic compositions. The large range of S13C values is interpreted to reflect primary differences during deposition. The more negative S13C values are thought to be associated with hydrothermal activity in small, restricted basins, in which methane recycling in the anoxic bottom waters is the principal pathway for bacterial biomass production. The isotopic signature is believed to result from organic matter synthesized by several different pathways, including H2S chemosynthesis, methylotrophy, and photosynthesis.
In contrast, type A carbonaceous argillites, such as those at Kidd Creek, are believed to indicate larger basinal settings in which organic matter is synthesized by assimilation of atmospheric and/or hydrothermal CO2 by C3 photosynthetic pathways in oxic surface waters with only minor methane recycling. Carbon isotope anomalies indicating mineralization were observed only in type B horizons, such as those at Chance. The smaller, isolated basins better preserve a record of methanogenesis associated with submarine volcanic exhalations. Despite the different carbon isotope signatures, the narrow range of the sulfur isotope data for the Chance mineralization, as well as inorganic geochemical data for the argillites, is consistent with the Chance deposit being part of the much larger Kidd Creek hydrothermal system. No kerogenic-graphitic horizons in large sulfide systems resulting in economic ore deposits have been studied in enough detail to understand the primary controls on the distribution of carbon isotopes fully. In large sulfide systems, the relationship between sulfides, methane recycling, and S13C value distribution is more complex and may reflect mixing of carbon sources and alternating successions of bacterial biomass, generated in the deeper part of the water column, and phytoplankton from the euphotic zone.
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The Giant Kidd Creek Volcanogenic Massive Sulfide Deposit, Western Abitibi Subprovince, Canada
ARCHEAN Cu-Zn deposits are among the most important mineral deposit types in Canada. The Superior province of Canada contains nearly 80 percent of the known Archean Cu-Zn deposits in the world (about 100 of 125 deposits). These deposits are concentrated in 10 separate mining camps, including Sturgeon Lake, Manitouwadge, Mattagami Lake, Chibougamau, Joutel, Val d’Or, Bous-quet, Noranda, Kidd Creek, and Kamiskotia (Fig. 1 and Table 1). A few deposits in rocks of similar age and composition are also known in the Slave province, the Churchill province, and in the Archean of Western Australia, southern Africa, China, and Brazil. Known deposits of this age worldwide account for more than 650 million metric tons (Mt) of massive sulfides, containing 10 Mt of Cu metal, 29 Mt of Zn, 1 Mt of Pb, 33 Mkg Ag, and 750,000 kg Au. The giant Kidd Creek volcanogenic massive sulfide deposit in the western Abitibi subprovince of Canada is the largest known deposit of this age currently in production. The Superior province is the world’s largest exposed Archean craton, occupying an area of more than 1.5 million km2, bounded by the Trans-Hudson orogen to the west and the Grenville province to the east. A number of distinct subprovinces are recognized, assembled into east-west-trending granite-greenstone terranes and metasedi-mentary belts (Fig. 1). The granite-greenstone terranes are composed of gneissic rocks of plutonic origin, supracrustal rocks of dominantly volcanic origin, and a variety of syn- to late kinematic granitoids. Volcanic rocks comprise about 12 percent of the total area. The greenstone belts have been described variously as successive lateral accretions of volcano-plutonic arcs, oceanic islands, oceanic plateaus, and rift-related assemblages (e.g., Langford and Morin, 1976; Percival and Card, 1985; Ludden and Hubert, 1986; Ludden et al., 1986; Card, 1990; Jackson and Sutcliffe, 1990; Williams, 1990; Corfu, 1993; Heather et al., 1995; Jackson and Cruden, 1995). The metallogenic history of the Superior province has been described in detail by Franklin and Thorpe (1982) and Poulsen et al. (1992).
The Abitibi subprovince (94,000 km2) is the largest of the greenstone belts. It contains the major gold and base metal mining camps in Canada (Fig. 2), with production and reserves totaling more than 480 Mt of massive sulfide and 4,700 t of Au. Metal production in the western portion of the Abitibi greenstone belt is dominated by the Timmins region, which historically has accounted for 37 percent of the total gold production