Geology

The Cannington ore body lies within a sequence of rocks known as the Mount Isa Inlier. This is a large block of rocks, sitting within the Earth's crust in northern Queensland, that were formed more than about 1900 million years ago (early Proterozoic), probably mostly as sedimentary and volcanic rocks deposited on an ancient sea-floor. Massive upheavals in the Earth's crust then occurred over 100's of millions of years. The rocks were folded, and subjected to very high pressures and temperatures deep in the Earth's crust. As a result the rocks were metamorphosed or changed to gneisses and schists by about 1600 million years ago.

The Mount Isa Inlier is approximately 500 km long and up to 200 km wide. As well as the ore body at Cannington, it hosts many other important ore bodies, including the famous deposits of Mt Isa (copper, lead, zinc and silver), as well as those at Osborne (copper and gold) and Selwyn (copper and gold).

The Cannington ore body consists of high concentrations of several different metal sulfide minerals hosted by the metamorphic rocks. The most important ones are galena (lead sulfide - PbS) and sphalerite (zinc sulfide - ZnS). As well as lead, the galena also contains significant amounts of silver. However, native or metallic silver is very rare at Cannington. The ore body also contains several other non-valuable sulfide minerals, including pyrite and pyrrhotite (both iron sulfides), arsenopyrite (iron arsenic sulfide) and chalcopyrite (copper iron sulfide).

The ore body is believed to contain about 44 million tonnes of ore. On average, each tonne of ore is estimated to contain about 550 g of silver, 113 kg of lead and 47 kg of zinc.