|Abstract||Under favourable geological, climatic, topographic and hydrological conditions, the weathering of carbonate-hosted, sulphide deposits may result in the formation of economically significant direct
replacement and/or wallrock replacement nonsulphide base metal deposits (Hitzman et al, 2003; Simandl and Paradis, 2009; Paradis et al. 2010).|
Nonsulphide deposits were the main source of zinc in the 19th century. Due to the development of
differential flotation and other metallurgical innovations during the early 20th century, the interest of explorationists shifted to sulphide ores. For a variety of environmental and economic reasons, nonsulphide deposits are again representing
attractive exploration targets; however, they are commonly overlooked. The discovery rate of nonsulphide deposits in British Columbia will depend largely on the ability of the explorationists to recognize nonsulphide zinc and lead minerals, and to
understand the mobility of base metals in near surface environments and the parameters that cause their precipitation as base metal carbonates, silicates or oxides.
The Cariboo terrane of central BC (Figures 1 and 2) hosts several well known base
metal mineral deposits, including polymetallic Ag-Pb-Zn (±Au) veins, carbonate and sediment-hosted massive sulphides [i.e., Zn-Pb Mississippi Valley-type (MVT), sedimentary exhalative Zn-Pb-Ag (SEDEX), Besshi-type massive sulphides (VHMS)], and gold
placers. Carbonate-hosted nonsulphide base metal deposits are commonly overlooked.
Excellent examples of Zn-Pb sulphides and "mixed ores" (rocks consisting of sulphide and nonsulphide minerals) crop out on the Cariboo Zinc property (Figures 2 and
3). Mineralization is concentrated along a favourable northwest-trending, dolomitic belt about 8 km long (Figure 3). It consists of pervasive fine-grained sulphide and nonsulphide disseminations and aggregates forming pods and masses, sulphide- and
nonsulphide-bearing quartz (±calcite) veins, and crackle breccias. Sulphides are galena, sphalerite, and trace amounts of pyrite. Nonsulphides are smithsonite, hemimorphite, cerussite, hydrozincite, and possibly anglesite. The main showings, from
west to east, are Canopener, DeBasher, Flipper Creek, Dolomite Flats, Main, Gunn and Que (Figures 4, 5, 6, 7, 8 and 9).
In most occurrences, the spatial continuity and/or the close spatial relationships in combination with morphological
similarities between sulphide and associated nonsulphide zones suggest direct-replacement of sulphides by nonsulphide base-metalbearing minerals. The main exposure at the Gunn showing is an excellent example of a carbonate-hosted, nonsulphide,
base-metal deposit formed by the direct replacement of sulphides.
The area was covered by detailed gravity survey (Luckman, 2008). The determination of physical characteristics of mineralized (Pb-Zn sulphide and nonsulphide) rocks will be useful
for the design of future exploration programs and for re-interpretation of existing gravity surveys. Mineralogical, geochemical and isotope studies are underway.