Outcropping mineral deposits in dry climates

In the CSIRO study, 14 case histories of outcropping deposits in low-rainfall terrains were described. Of these, ten were associated with high-contrast Hg soil anomalies. 

The initial sampling delineated three high-contrast Hg soil anomalies directly over the Eastern and Western Lodes and over rocks midway between the lodes on Line 14.36 N (Fig. 12-8). Later sampling duplicated the central and eastern anomalies, but produced only low-contrast anomalies over the Western Lode. Background Hg contents of soils over footwall limestone and hangingwall slate are in the range 10-30 ppb. Copper is 

A similar relationship between Hg and target elements has been defined at the Lady Loretta deposit, also in northern Queensland (Loudon et al., 1975 Carr, 1981, 1984). Here the ore body consists of a stratiform lens, up to 40 m thick, hosted within fine-grained sedimentary rocks occurring in a steep-sided basinal structure. The ore outcrops on the western limb of this structure however, to the east, Zn and Pb sulphides pinch out rapidly, giving way to massive pyrite with interbedded dark, fine silt-shales. The ore-bearing rocks and their pyritic equivalents stand out as ridges, remnants of a 

In the above examples it is apparent that the secondary dispersion of Hg is no greater than, and commonly less than, that of the target elements. This was the case in most of 

These CSIRO examples do not stand alone in indicating a common highly-specific relationship between outcrop of weathering sulphides and the extent of anomalous levels of Hg in soils. Warren et al. (1966) compared the Hg, Pb and Zn contents in soils associated with base-metal mineralisation in British Columbia, Canada, and concluded that because anomalous levels of Hg were associated with anomalous Zn and/or Pb, there was no advantage in using Hg as a pathfinder. Friedrich et al. (1984) determined the distribution of Hg, Ba, Cu and Zn associated with Cu deposits of the Troodos Complex, Cyprus, and, on a number of profiles across faults that intersect blind mineralisation, found anomalous Hg soil contents coincident with high-contrast Zn, Cu and Ba anomalies (Fig. 12-12). 

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