Stratigraphy and geochemistry of the Rusty Lake Greenstone Belt adjacent to the Ruttan Mine, Manitoba
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Date
1979
Authors
Jackson, Michael Ralph
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Abstract
Greenstone belts in the Churchill Province of northern Manitoba, of probable Aphebian age, are hosts to massive sulphide Zn + Cu deposits. Towards the southeastern end of the Rusty Lake greenstone belt, 14 miles east of Leaf Rapids, the rocks consist of a metamorphosed sequence of mafic, intermediate, and felsic volcanics and derived volcaniclastic sediments. Mapping was carried out adjacent to the Ruttan Mine for an area of roughly 4 square miles, to outline the volcanic stratigraphy. 123 samples were collected in conjunction with the mapping and chemically analyzed for major elements, Cu, Zn, and S, and were studied in thin section. Mafic flows made up a large portion of volcanic rock types (30% of map area). Felsic volcanics (dacite to rhyolite tuffs, lapilli tuffs, crystal tuffs, agglomerate, and flows) are dominantly fragmental and make up 13% of the area. Intermediate composition volcanics (andesite to dacite tuffs, lapilli tuffs, crystal tuffs, agglomerate, flows) are almost entirely fragmental and make up 7% of the map area. Volcaniclastic sediemtns (33% of area) are a complexly interstratified sequence of sandstones, siltstones, conglomerates, and debris flow breccias. The volcanics at Ruttan are geochemically similar to other PreCambrian volcanic suites. Compared with modern volcanic associations, the Ruttan volcanics most closely resemble the differentiated suites typical of modern island arcs. However, at Ruttan total Fe and MgO are significantly higher, probably as a result of alteration and metasomatism, and Na2O and K2O are lower than island arc regimes, probably an effect of PreCambrian alteration. There appears to be a somewhat higher proportion of dacite-rhyolite to andesite than in most Archean volcanic assemblages... Exploration for massive sulphide deposits should be concentrated within differentiated basaltic to rhyolitic volcanic suites having similar lithological and geochemical characteristics as those at Ruttan.