Ann: Maiden resource drilling completed at Oxley Potash Project, page-6

Might aswell take the shovel and dig some up as some results are from surface. Bhp deposit is 1km underground.   

I don't think capex is the problem as the fertiliser industry is worth $175 billion and this deposit is close to ports etc. you should probably Google feldspar and Brazil fertiliser technology and read a few articles.

Here is one article.

http://news.mit.edu/2014/new-source-potassium-fertilizer