|Abstract||The Kootenay Arc (KA) hosts a large number of known base metal mineral deposit-types, such as polymetallic veins, W skarn, porphyry Mo, volcanic-hosted massive sulphide (VHMS), sedimentary exhalative
(SEDEX), and carbonate-hosted Zn-Pb (MVT/Irish-type). |
The mineral potential of the KA is higher then suggested by new discoveries and by the number of mines brought into production during the past 30 years. During that period, the emphasis was
on traditional exploration methods, such as mineral prospecting, ground geophysics, and soil and stream sediments geochemistry. The data was subjected to conventional interpretation methods and involved an aging regional geology knowledge base. The
majority of exploration programs were also targeting the most popular deposit models.
Geoscience studies done under the umbrella of the Targeted Geoscience Initiative 3 program are aiming to reinvigorate mineral exploration in KA. The new
airborne EM and MAG survey in the southern KA will provide continuous and uniform geophysical coverage over a large area (i.e., 610 km2). Integration of this data with existing regional geochemical survey (RGS) data and updated geological maps will
provide new targets for follow-up ground exploration.
The conventional KA exploration targets listed above remain valid, but innovative targets have become apparent during the new work. During the last two years, the Irish-type model was
introduced to explain the formation of carbonate-hosted Zn-Pb deposits in the southern KA, and there are numerous opportunities for further refinements. For example, shifts can be made from the traditional exploration approach focused at
sediment-hosted Zn-Pb sulphide deposits (such as SEDEX, MVT, Irish-type, and Zn-Pb ±Ag veins) to related nonsulphide Zn-Pb deposits. The latter are in most cases formed by oxidation of sulphide ore minerals in near surface conditions and involve
remobilization and focused precipitation of base and precious metals as metal silicates and carbonates. For example, the near-surface portions of carbonate-hosted sulphide deposits in the southern KA are weathered, strongly oxidized, and consist of
extensive Zn- and Pb-bearing iron oxide gossans and base metal-bearing nonsulphide mineralization. The most common nonsulphide minerals are goethite, hematite, hemimorphite, smithsonite, cerussite, anglesite, and hydrozincite. The Reeves MacDonald
(ReMac Zinc Corp.), Jersey-Emerald (Sultan Minerals Inc.), Lomond (Trophy Ridge Resources Inc.), and Oxide group of deposits (Dajin Resources Corp.) are the best examples of carbonate-hosted nonsulphide base metal (CHNSBM) deposits in the southern
KA. The shape, mineralogy and paragenesis of the known CHNSBM deposits are indicative of direct-replacement of sulphides by nonsulphide base metal-bearing minerals. Explorationists look instinctively for red gossans in the field, which are commonly
associated with near-surface oxidation of sulphides. However, Zn-rich (low Pb) CHNSBM deposits commonly form by interaction of Zn-rich fluids with carbonate wallrock (replacement process). Such deposits (consisting of “white ore”) may have been
overlooked in the past and represent new and exciting exploration targets within the KA.
Nonsulphide deposits were the main source of zinc in the 19th century. Due to 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. The discovery rate of
nonsulphide deposits in the KA will depend largely on the ability of the current generation of 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.