The Pb Isotope Linear Array for Volcanogenic Massive Sulfide Deposits of the Abitibi and Wawa Subprovinces, Canadian Shield
Ralph I. Thorpe, 1999. "The Pb Isotope Linear Array for Volcanogenic Massive Sulfide Deposits of the Abitibi and Wawa Subprovinces, Canadian Shield", The Giant Kidd Creek Volcanogenic Massive Sulfide Deposit, Western Abitibi Subprovince, Canada, Mark D. Hannington, C. Tucker Barrie
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One hundred and five lead isotope analyses have been obtained for 47 volcanogenic massive sulfide deposits and occurrences within the Abitibi and Wawa subprovinces, largely from minor amounts of galena that form an integral part of the deposits. When 52 nonanomalous compositions for the best dated of these deposits are recalculated to a uniform age of 2716 Ma, they define the Abitibi-Wawa linear array at a slope of 1.034 ± 0.062. Two-stage calculation yields an age of 4490 ± 35 Ma for the Pb isotope sources responsible for this linear array if they each subsequently evolved in a single-stage manner from a source that was homogeneous prior to about 4490 Ma. If the assumption of single-stage evolution is valid, 4490 ± 35 Ma could represent the time of a major mantle differentiation event.
The data indicate that the lead in deposits for a distance of at least 710 km from Matagami, Quebec, to the Winston Lake deposit in the Terrace Bay-Schreiber area of Lake Superior, Ontario, was derived from equivalent sources. This evidence helps confirm that the Abitibi and Wawa subprovinces, contiguous except for the Kapuskasing tectonic zone, had, at least in some respects, a common evolution history. Further study will be required to show that the Shebandowan subprovince west of Lake Superior, considered an extension of the Wawa subprovince, shared this isotopic history. The Pb isotope data for deposits in the Wabigoon and Uchi subprovinces of western Superior province, which lie to the north of the Wawa-Shebandowan belts, indicate strikingly different isotopic sources that were more isotopically evolved at a given age.
The use of data for older deposits elsewhere in the world permits initial isotopic parameters (Ao = 9.431, Bo = 10.495, Co = 29.681) to be established for the Abitibi-Wawa model at 4490 Ma. In contrast to the Wabigoon-Uchi model (formerly referred to as the “western Superior model”), the Abitibi-Wawa model is not widely applicable elsewhere in the world. However, it does yield congruent model ages for some volcanogenic massive sulfide deposits in the Yilgarn craton, Western Australia, which shows that it has validity beyond the Abitibi-Wawa greenstone belts.
Analyses for deposits of the Manitouwadge district, Ontario, and for an Archean deposit within the Grenville province east of Val d’Or, Quebec, illustrate the minor influence of high-grade, upper amphi-bolite to granulite metamorphism on Pb isotope compositions. Anomalous compositions were obtained for galenas from veins and for most low lead sulfides, such as pyrite and sphalerite. These indicate that a Grenvillian remobilization or isotopic resetting occurred throughout the Abitibi subprovince, although the character of such an event in the Matagami district, 190 km from the Grenville front, is very obscure. Other older events are also indicated by the data.
Figures & Tables
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