Early Archaean (3.26 Ga) volcanogenic massive sulphide (VMS) deposits located within the low strain and very-low metamorphic grade Strelley greenstone belt, East Pilbara, Western Australia, contain exceptionally well-preserved sulphide textures which are directly analogous to those formed in black smoker chimneys at present-day submarine hydrothermal vents. The VMS deposits are associated with seafloor alteration zones in and below silicacarbonate laminites, at the top of a pile of tholeiitic to calc-alkaline intermediate and felsic volcanic rocks with trace element abundances indicative of modem subduction-related processes. VMS mineralization comprises Zn-rich sulphide lenses with significant Cu and barite, and variable Pb and Ag, above Cu-rich stringer zones, all of which are similar to Phanerozoic VMS deposits. Sulphide-sulphate mineralization implicates hydrothermal discharge into sulphate-bearing ocean waters.
The spatial distribution of mineralization is a foremost concern in regional exploration, research, and mine resource assessment. Here we use Fry analysis as a complement to structural geology and geostatistical methods. Fry analysis uses a geometrical method of spatial autocorrelation for point data. For n points there are n 2 -n spatial relationships and, because of the square function, the method yields interpretable results with small as well as large data sets. Fry analysis is an alternative to variography for directional studies. At the regional scale, Fry analysis can assess distribution patterns of mineralization and potential controlling structures. At the deposit scale, the characteristics of zones of mineralization such as direction, spacing, high-grade ore direction, and grade distribution can all be deduced.
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