I dont know where you got the 7000 tons per train from, Mitchbut...

I dont know where you got the 7000 tons per train from, Mitch
but here's rio's train stats from about 2010 in the Pilbara.

"Each train has over 200 wagons totaling nearly 30,000 tons with a train every half hour and a train is about 2 kilometres long."

Ore carriages carry about 100 tons each.
If you look at the notice below you can see they did 100 cars in a trail run so their minimum train (at 100 cars x 100t ) would be about 10,000 tons and you'd expect them to do better than the trail run by a fair margin as they "ramp up".

Here's a notice from September
Karara mine of Gindalbie Metals have commenced operations with ore trains running daily to the car dumper at Geraldton Port. On September 23rd ACN4144 & ACN4171 with 100 ore cars [50 two packs] and ACN4149 DPU locomotive on rear ran as a trial to mine in the evening. Earlier in the day ACN4148 & ACN4151 had run 78 loaded ore cars to the dumper. Karara mine site has a large stock pile of iron ore and are in a position to rapidly ramp up production.

choo choo.