Geochemical dispersion in mineralized soils of a permafrost environment

Abstract

Abstract The Agricola Lake massive sulphide body occurs in metavolcanic rocks of Archean age in the northwestern Canadian Shield. The mineralization contains Zn, Cu, Pb, Ag and Au and, in addition, there are elevated contents of As and Hg. The area lies within the zone of continuous permafrost. The distribution of elements in soils in the vicinity of the mineralization shows the influence of three independent dispersion processes — glacial, solifluction and hydromorphic — superimposed on the primary bedrock distribution. Oxidation of sulphides has been active in the past and continues to this day. In the absence of large amounts of carbonate minerals, this has produced an acidic weathering environment. The most mobile of the elements studied — Zn — has been largely removed from the mineralized soils and dispersed a considerable distance down drainage. Au, Hg, Pb and Ag are relatively immobile and are retained in the soils overlying mineralization or in nearby, glacially dispersed detritus. Fe, Cu and As are of intermediate mobility and are deposited in the proximal portion of the drainage system. The estimated order of mobility is: Zn > Cu > Fe > As > Ag > Pb > Hg > Au. Glacial action dispersed oxidized detritus, already depleted in mobile elements. Material precipitated along the proximal portion of the drainage system shows an association of As and Cu with iron oxides and Ag and Hg with manganese oxides. In addition to the elements discussed above, Mg in soils indicates the alteration zone underlying the massive sulphide and Ca outlines the soils subject to acidic leaching.