A new geological map of the Abitibi Subprovince
By Jean Goutier and Mario Melançon
|Next March, at the annual convention of the Prospectors & Developers Association of Canada (PDAC 2007), in Toronto, a preview version of the new geological map of the Abitibi Subprovince will be unveiled. This geological region, one of the most prolific in the world in terms of gold, copper, zinc and silver production, is the largest Archean volcanosedimentary belt in the world (~2.7 billion years). The new map will therefore highlight new exploration sectors, mainly for copper, zinc, gold and silver.
This new version of the geological map of the Abitibi Subprovince substantially updates previous editions by the MER-OGS (1984) and Hocq (1990). The most significant changes are in the northern portion of the Abitibi Subprovince. They include:
- identification of an old volcanic sequence dated at 2791 Ma (in the past, the oldest known rocks were 2730 Ma in age);
- recognition of nine episodes of volcanism and two episodes of sedimentation;
- better distinction between types of plutons; and
- extension of the alkaline volcanics of the Chapais-Chibougamau area to the west.
New dating of volcanics containing lenses of massive sulphides (Cu-Zn-Ag-Au) highlights the presence of new episodes of polymetallic mineralization, such as at 2736 Ma (Gémini-Turgeon), 2721 Ma (Estrades), 2718 Ma (Gonzague-Langlois) and 2706 Ma (Abcourt) as opposed to classical episodes, at 2730-2725 Ma (Normétal-Joutel-Selbaie-Matagami) and 2701-2697 Ma (Horne, LaRonde). Some areas also display geological characteristics (lithology and age) analogous to those of the rock hosting the giant Kidd Creek Cu-Zn-Ag deposit in Ontario.
Other dating shows that the episode of alkaline volcanism and deposition of alluvial-fluvial sediments in the northern portion (Haüy and Waswanipi formations) is not as old as expected (~2690 Ma rather than 2715-2705 Ma). These rocks are therefore close in age to the Timiskaming-type sedimentary and volcanic rocks in the southern portion of the Abitibi Subprovince that are associated with major structures and many gold deposits (e.g. Kirkland Lake area in Ontario ). Accordingly, in the north, the shearing bordering these rock types represents corridors prospective for the discovery of new gold deposits.
The synthesis map emphasizes regional correlations, new U-Pb dating and geology issuing from recent work by Géologie Québec, which is available in SIGÉOM. It features a legend showing the temporal correlations between the volcanic, plutonic and sedimentary units. This version will be used as a base for a small-scale georeferenced map.
For details about new dating in the Abitibi Subprovince, please see the following documents: RP-2005-01, RP-2005-02, RP 2006-04.