Manganese is one of the most widely used alloy elements in the world, essential to the manufacturing of steel. By reducing unwanted sulphur and oxygen and preventing brittleness, a stronger, longer lasting steel is produced.

Manganese is also used in the manufacture of some batteries, ceramics, agricultural chemicals, fuel, welding materials, foundry equipment and some electrical components.  The majority of GEMCO’s products are used in the international steel industry.

GEOLOGICAL PROFILE

The manganese orebody on Groote Eylandt is an undulating sedimentary layer between clay and sand beds over a terrain of much older sandstone. The orebody consists of pisolitic manganese oxides, thought to be originally formed by chemical precipitation in a wave-affected, shallow sea-floor environment during a period of rising and falling sea levels. Manganese oxides formed into pellet-like pisoliths that accumulated to form a layer of ore.  This pisolitice layer emerged from the sea during a world-wide drop in sea level and extends over a large area of the western side of Groote Eylandt.

A long period of tropical weathering saw remobilisation and recrystallisation of the manganese oxides, forming hard cemented pisolite and massive manganese oxides. Overlying clays and gravels were strongly oxidised and leached to form the iron and alumina rich laterites which are excavated off the manganese ore as overburden.

The orebody is typically mined as two different layers—a middle layer of high-grade ore and cemented and loose high pisolitice ore, and a bottom layer of high silica ore.