Currently the line from Olympic Dam to Northern terminal station...

Currently the line from Olympic Dam to Northern terminal station is privately owned by the mine (BHP), built by WMC when OD was initially being constructed.

http://www.electranet.com.au/network_mapState.html

It is 275kV and has no tower capacity for an additional load in bound to BHP. BHP have negotiated with Electranet to sell the line to them and/or get an augmentation built to accomodate the new load at OD after its expansion, and/or get the 132KV backup line from Pimba (Woomera) upgraded to 275kV.

EN are (however) the most expensive line constructor in Aus.

Many many plants have struggled to get connection agreements and or line construction at reasonable rates, often getting the construction done by others (Transfield, United etc)

I think current BHP planning is a 300-600mW plant fired by a spur gasline, as an alternative to increased transmission.

If the GEO's build to Olympic Dam, then they can replace OD's requirements of 105-125 mW and the line essentially drops to zero load, and if they supply up to 250Mw by back loading the line.

Would need significant load protection infrastructure, as the circuits would be heavily loaded at the 250Mw level, but would be the cheapest logical route to market.

Yes, still requires $700+m for new lines and requires BHP to take some operating risk in allowing others to use their line.