The company deferred a $A28 billion expansion of the mine nearly two years ago, but the SA government granted the company a four-year extension of the indenture agreement to October 2016.

It was on the proviso that BHP spent around $650 million during the period on research and community initiatives.

In documents submitted to the federal Department of the Environment, BHP proposes to start construction of a heap leach trial demonstration plant within the boundaries of the current mine in July next year.

“Although still in the planning phase, the demonstration plant is likely to consist of a temporary irrigated heap leach pad containing approximately 36,000 tonnes of material, a temporary crushing facility for supply of material for the heap, ponds for capture of liquor, and associated small processing facilities for treatment of the captured liquor and recovery of residual copper, gold and silver via further downstream processing,” BHP said.

BHP said it expected any environmental impact to be negligible.

The proposed plant will run for three years from October 2016.

The timeline indicates the company will not be ready to make an expansion decision by the October 2016 deadline.

BHP shares last traded half a cent lower at $38.995.