FORMATION OF SWELLING CLAY-MINERALS BY SULFIDE OXIDATION IN SOME METAMORPHIC ROCKS AND RELATED SOILS OF ONTARIO, CANADA

Sulfide minerals are commonly present in the metamorphic and igneous rocks of southeastern Ontario. They are also dispersed in the till that is the parent material for many soils in the area. When sulfides from these rocks are exposed to a humid atmosphere, bacteria (Thiobacillus ferrooxidans) proliferate and acid sulfate weathering proceeds rapidly with the formation of jarosite, for which K+ ions are provided by the alteration of micas and feldspar. Interstratified minerals occur as an intermediate stage during the transformation of micas towards swelling clay minerals, which are major constituents of the clay-size fraction. A similar transformation likely takes place in the soils of the area, in which swelling clay minerals are dominant. This hypothesis may be further supported by the presence of large amounts of goethite, a weathering (hydrolysis) product of jarosite.