The regional geology consists of an east-west trending schist belt of Precambrian and Palaeozoic meta-sedimentary and volcanic rocks. The schist is intruded by Cretaceous granitic rocks along with Tertiary dykes and plugs of intermediate to mafic composition. Tertiary and Quaternary sedimentary rocks with coal-bearing horizons cover portions of the older rocks (Wahrhaftig, 1968). More than a dozen VMS prospects are found within the Bonnifield District.
The massive sulphide mineralisation is most commonly located in the upper portions of the Totatlanika Schist which is of Carboniferous to Devonian age. Several gold-quartz vein deposits are also found in the district and are associated with metamorphic rocks and felsic dykes within the contact zone of a Cretaceous plutonic complex. Figure 1 illustrates the regional geology and location of major VMS deposits.
Preliminary analysis of the geologic setting of the Bonnifield District and the Dry Creek and West Tundra Flats deposits indicates that the Red Mountain Project has the volcanic, geochemical, alteration and sulphide assemblage characteristics of a very shallow water, boiling hydrothermal system. Such conditions enhance the prospectivity for gold-rich VMS systems since gold is transformed into a bisulphide complex that has inverse solubility and is precipitated only on oxidation of the fluid, usually at the top of massive sulphide deposits or in the immediate hangingwall sediments. Conversely, a shallow water setting will suppress the deposition of copper and it is likely that copper will only be a by-product of the deposits with any copper enriched zones likely detached from the remainder of the base metals. Shallow water settings typically also contain VMS mineralisation with relatively low zinc/lead ratios and enriched silver. Additional discoveries in the Bonnifield district are therefore likely to be similarly rich in zinc, lead and silver as the existing deposits at Dry Creek and West Tundra Flats with good potential for gold rich zones in the tops of the deposits and into the hanging wall.
Above: Geologic map of the Wood River area from Dusel-Bacon et al, 2012 (Economic Geology 107:1403-1432) showing the location of White Rock’s tenements outlined in blue and the Dry Creek and West Tundra Flats (WTF) deposits.