Stock in the company was trading as much as 25% down this morning.

Rex MD Mark Parry resigned, effective today, with the company citing changes in its strategy to develop the Hillside copper project in South Australia.

In the interim period, Rex chairman David Carland will move from a non-executive role to operate in an executive capacity.

“Given the delay to the feasibility study to concentrate attention on a smaller-scale start-up, the managing director’s role will take on a new focus during this period,” Carland said.

“In view of this Mark has decided to step down.

“The company would like to thank Mark for his efforts since he joined the company in September 2012. We wish him well in his future endeavours.”

Although feasibility work at Hillside is largely complete, the company has moved to extend the study to pursue lower capital options.

The work will consider an operation smaller than the base case scenario previously contemplated for a 15 million tonne per annum operation.

The extended feasibility study will consider a smaller initial footprint for the pit, lower cost options and operational design scenarios that will focus on efficiencies including dilution control during mining.

The alternative development options will be overseen by an advisory board that will report directly to Carland and the Rex board.

The news follows on an update from the company last week, confirming state government approvals for open pit and underground development at Hillside.

The approvals followed a 3.5-year review process, including community consultation and input.

Hillside has been proposed as an open pit mine supplemented by underground operations, with a mine life of more than 15 years.

Reserves stand at 180Mt at 0.5% copper, 0.1 grams per tonne gold and 14.4% iron.

Resources total 337Mt at 0.6% copper, 0.14gpt gold and 15.7% iron.

Under the current plans copper-gold and iron ore concentrates will be transferred through a 12km slurry pipeline from the processing plant to the port of Ardrossan.

The company has also considered an engineering, procurement and construction process with pricing from Korean contractors.

Shares in Rex were last trading 20.8% lower at A30.5c.