"They're a long way from infrastructure"
not all that far away, 5mtpa shouldn't be a drama to get out on the rail line below.
I think the Hancock rail to abbot point allows them to get 20000t pay load trains and the 20mtpa export (allowing for Economies of scale), whereas the option below may only allow them 7000t pay load trains and may only permit them 5mtpa out of glastone.