How do you know BHP are not interested in negotiating use on their rail line?
They are negotiating with FRS and with Atlas.
All the signs point to me that BHP are negotiating with BRM.
There is political pressure on BHP from the WA government to negotiate access with some juniors. If they do so with BRM it will help BHP and their PR.
It is confidential at present.
It is not a certain deal, but I beleive a deal is possible.