I think these higher figures are being used as a maximum figure...

I think these higher figures are being used as a maximum figure if they put on the electricity rather than use generators for the first 18 months to 2 years, use of mining contractors rather than own mining equipment and the purchase of new mineral processing equipment. There is plenty of second hand near-new equipment in the USA so considerable savings can be made. It might also be the figure that includes some of the capex for the stage two expansion to 3 Mtpa. You need bigger transformers for the electrics and then a lot of other engineering stuff that will be needed down the track. It's better to plan for that in stage 1 to get savings during an expansion. An extra dollar spent in stage 1 will save $4 in the expansion. Wait and see what the announcement says.

It is better to talk high and come in lower - brokers and shareholders like that. (How many projects has BHP had cost overruns and their share price gets pushed down - deadly for a smaller company). It will still be a low cost / premium price product due to the low silica/aluminium(very important) / phosphorous. Current spot price for this product is around $200/t. So it won't take long to pay off the plant.