Basically, with the asthetically unpleasing 'Pilbara cab'. Some have Dash-7 hoods, others, Dash-8. Apparently the former on BHP are being retired.
Hamersley Iron bought new C-636s and M-636s. They sent all of the C-636s and some M-636s to ComEng (MLW's Australia liscensee) to be rebuilt with their version of the new cab and a modified long hood, among other things. They sampled some SD-50s and GEs but obviously didn't like them, as they weren't ordered again. They retired the Alcos in 1995 after NRE and a turbocharger company made an unrefuseable offer on the 251s. The shells were trucked several hundred miles to Perth (aside from a preserved unit) for unknown reasons in 1999. Many were still there in 2002.
Mt. Newman Mining, now BHP Port Hedland, placed several orders for C-636s (some were aquired from Bechtel) and M-636s, most with HiAd trucks. Goninan (GE) eventually rebuilt all of their Alcos into Dash-7s and Dash-8s in the mid -80s to 1991? An interesting note, the hood/cabs were paced on the frame "backwards". However, the few M-636s with Dofasco trucks were retired, most scrapped in 1995/6, aside from three which are preserved. They also bought new GEs from Goninan which came with their version of the Pilbara cab.
Robe River, the last on the scene, received new M-636s, one of which was the last Century-design locomotive built (in 1980). Robe also operated C-630s from MK and C-636 from Chrome Crankshaft. In 1989, they had three C-636s from Naporano and Chrome rebuilt, one into a GE and one two as Hamersley's Alco design. In 2004, 5 unrebuilt M-636s were stored.
Rio Tinto merged Robe and Hamersley's rail operations as "Pilbara Rail"
Both groups have new GEs shipped from Erie. US SD4xs have also been down there.