Many mining and exploration firms, and even some large electronics firms, are scouring the world for deposits of the rare metal tantalum.
Tantalum is the only known substance that will lie flat as a capacitor on a circuit board in electronic devices. It is therefore in great demand in the electronics industry, which produces many devices and instruments that are thin or miniaturized.
The price of tantalum pentoxide is almost US$40 per lb., and it is now sometimes referred to as a precious metal. If new global resources of this valuable metal are not soon found and if substitutes are not developed, tantalum’s price will certainly rise.
Geologists are not tuning into the fact that the largest and highest-grade tantalum deposits occur in highly evolved and fractionated pegmatite dykes that contain higher-than-normal concentrations of the tin mineral cassiterite and the lithium mineral spodumene. Anomalous concentrations of beryl, an ore of beryllium, are also a favourable indicator for tantalum in pegmatite containing tin-lithium.
Tantalum prospectors might be interested to know that the Tanco mine, a well-known past producer of high-grade tantalum in Manitoba, started out as a potential tin mine. It later became a lithium mine, and thence a producer of tantalum and cesium. Also, the Greenbushes pegmatite zones in Western Australia first drew interest as a tin prospect, and then became a lithium producer. Today, the area contains the largest tantalum mine in the world.
In the Brazil Lake area of Yarmouth Cty., N.S., tantalite, the major ore of tantalum metal, occurs in large pegmatite dykes containing high concentrations of tin (cassiterite), lithium (spodumene) and beryllium (beryl). Some local, private firms prospecting these large pegmatite bodies have identified tantalite concentrations in high-grade spodumene-cassiterite phases of highly fractionated and sheared zones. In one area, float boulders containing up to 12% tantalum pentoxide have been found. This is one of the highest-grade tantalum discoveries ever made in Canada.
Future prospectors for tantalum and other rare metals associated in pegmatite bodies such as cesium, zirconium, beryl and rubidium should note that tantalite can sometimes be confused with cassiterite; both are characterized by metallic or sub-metallic shades of black to reddish-black, and, when occurring as small disseminations, it is almost impossible to distinguish between the two. Tantalite also looks like the common titanium mineral ilmenite.
Significant tantalum discoveries can be made simply by assaying for the metal if tin is known to occur in altered pegmatite dykes. Many firms are elated to receive assays of only 600-800 parts per million tantalum pentoxide in pegmatite dykes. However, such low concentrations are difficult to discern in a hand specimen.
In a humid climate, weathering commonly causes black tantalite crystals to turn orange-brown or red-brown; this is because the mineral generally contains manganese-iron concentrations. Cassiterite, on the other hand, is inert to weathering and will not be corroded by surface exposure. This weathering of tantalite has been key to locating tantalum mineralization in the Brazil Lake area.
As seasoned prospectors know, mineral-metal associations are important in the discovery of new deposits. It is a widely held suspicion that assessing the tin-tantalum connection will lead to new tantalum resources in pegmatites. There is no better place in North America to achieve this than in the highly tin-mineralized areas of Nova Scotia and New Brunswick.
— The author is the president of Nova Scotia-based Ecum Secum Enterprises.
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