May it be that BHP management has an internal limit to 100 million USD due to the today's undecided future of the Jansen potash project? Look at BHP's Annual Report 2017 from September: "Jansen is in the feasibility study phase and we continue to assess how we can reduce risk and unlock value. The current scope of work was 70 per cent complete at the end of FY2017. Work on the shafts will continue in FY2018. Once shaft excavation is complete, the shafts will be connected underground and shaft infrastructure will be installed. This falls within the current approved scope of work. Construction beyond the current scope of work will require Board approval.  With a later market window now anticipated, the Jansen Potash Project will not be brought to the Board in CY2018. In the meantime, we are considering multiple options to maximise the value of Jansen, including further improvements to capital efficiency, further optimisation of design and diluting our interest by bringing in a partner."