The Swiss mining giant must complete the feasibility study by January 2012 to maintain its 81.82% interest.

Australia-listed Highlands Pacific holds the remaining stake of the project and is free-carried to the completion of the study.

Xstrata has already spent close to $140 million on the project.

A prefeasibility study released two weeks ago gave the project capital costs of $5.3 billion for a 20-year operation.

The estimated capital cost includes an $803 million 160-megawatt hydro-electric scheme that will guarantee low power costs and avoid exposure to fluctuating oil prices.

The open pit project is expected to produce 930,000 tonnes per annum of concentrate containing 246,000t copper and 379,000 ounces of gold in the first eight years of its life at C1 cash operating costs of 43c per pound or $1.12/lb without gold credits.

At a rate of 60 million tonnes per annum, the operation will generate an average $933 million of free cash flow per year using Highlands Pacific's metal price assumptions of $2.50/lb for copper and $1000/oz for gold.

After the first eight years, the throughput rate will be 50Mtpa to produce 190,000tpa copper and 284,000ozpa gold at cash costs of 58c/lb copper, generating $612 million free cash flow per annum.

The joint venture partners are targeting first production in 2017 after a four-year construction period.

The project has resources of 8.1Mt of contained copper and 13.3 million ounces of contained gold.

An updated resource estimate will be released next month based on 38,000 metres of diamond drilling completed this year.

A further upgrade is expected in the June quarter next year as part of feasibility study work.

Highlands Pacific shares remain at A37.5c this morning.