Drift prospecting; geochemistry of eskers and till in permanently frozen terrain: District of Keewatin, Northwest Territories

Abstract
Geochemical results are reported for a program that compared samples collected from eskers and adjacent till in permanently frozen terrain. Contrasting effects of disturbance on the well- and poorly sorted sediments within the active (seasonally thawed) zone are discussed. Trace element geochemistry of several textural and mineralogical fractions of each sample is reported, compared and explained. A previously known area of copper-nickel mineralization is clearly outlined by anomalies in various fractions of both till and esker samples. Other anomalies, possibly related to unknown sources, are also described. It is concluded that some potentially interesting ore minerals (sulphides and carbonates) are removed from the active zone of eskers and till by intense chemical weathering. Clays and secondary oxides that can scavenge cations released by this weathering are preferentially removed by surface runoff from mud boils on till, but are retained within the porous structure of the thawed zone of eskers. Thus, silt and clay (-250 mesh) is recommended for analysis in esker samples but must be used with caution when analyzing t ill. Heavy mineral separates from near-surface esker and till samples from permanently frozen terrain are not recommended for routine analysis. Micas, magnetite, clay, and rock fragments can reflect economically interesting mineralization, suggesting that some mineral phases in rocks adjacent to mineralized zones may be enriched in the cations characteristic of those zones. This implies that a target for drift prospecting may be larger than the mineralized zone its e lf.

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