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The Pb Isotope Linear Array for Volcanogenic Massive Sulfide Deposits of the Abitibi and Wawa Subprovinces, Canadian Shield

By
Ralph I. Thorpe
Ralph I. Thorpe
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
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Published:
January 01, 1999

Abstract

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.

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Contents

Economic Geology Monograph Series

The Giant Kidd Creek Volcanogenic Massive Sulfide Deposit, Western Abitibi Subprovince, Canada

Mark D. Hannington
Mark D. Hannington
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C. Tucker Barrie
C. Tucker Barrie
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Society of Economic Geologists
Volume
10
ISBN electronic:
9781629490052
Publication date:
January 01, 1999

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