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Combined geostatistical and multifractal power-spectrum modelling of geochemical distributions can provide suitable indicators of metal dispersion, and is capable of analysing complex problems for targeting potential areas for mineral exploration. A case study analysing lake sediment geochemical data for the Gowganda area is presented and development of the methodology for spatial analysis of the data is described. The Gowganda-Cobalt area of northeastern Ontario is a textbook example of Co, Ag-Co vein-type deposit, which by 1984 had yielded one-half billion ounces of Ag. The area is also known for shear-zone-hosted Au mineralization. This paper uses the spatial and geometric distribution of lake sediment data to discriminate geochemical anomalies from background values. The application of two geostatistical techniques (spatial principal component analysis and indicator kriging) allows the estimation of geochemical distributions by utilizing their statistical and spatial properties. The newly developed multifractal power-spectrum method additionally allows for the geochemical distributions to be modelled by their multifractal Fourier-transformed power-spectrum characteristics. Verification of the estimates produced by these techniques has been enabled through spatial analysis of bedrock geology and mineral deposit occurrences in the area.

The major and trace element geochemistry of matrix materials from glaciogenic diamictites (unsorted polymictic conglomerates consisting of clasts scattered throughout a finer grained matrix) of the Neoproterozoic Port Askaig Tillite of western Scotland shows evidence of an upward change in provenance. Values for a carbonate-corrected Chemical Index of Alteration (CIA) are fairly high (∼70–80) in the lower diamictites, suggesting that they were derived mainly from an older sedimentary cover (older Dalradian Formations) that had undergone a previous weathering cycle. Low CIA values, more typical of unweathered material, were obtained from diamictites in the upper part of the formation. Thus, deposition of the Port Askaig diamictites is thought to involve a change in provenance, with unroofing of a cover of older sedimentary rocks and exposure of basement rocks. In spite of these inferred differences in provenance, diamictite materials throughout the formation have very uniform chondrite-normalized rare earth element (REE) distributions. REE distribution patterns from the diamictites closely resemble that of average post-Archean shales (PAAS), with a significant negative Eu anomaly and typical enrichment in LREE. These results, together with the presence of uniform (LaYb)Nratios throughout the formation, suggest that the sedimentary cover rocks from which the lower diamictites were derived, were themselves derived from a similar post-Archean basement. A ThScversus Sc plot suggests that siliciclastic matrix material in the lowest diamictite was derived essentially from provenances similar to PAAS. The higher diamictites appear to have been derived from a mixture of granitic material and PAAS, in a ratio of up to ca 4: 1. Sparse sedimentary structures suggest derivation of the Port Askaig Tillite from the southeast but the exact source remains unknown.