I found a few examples of operations in Guinea. I consider Alufer's Bel Air, now in operation, to be a good example because the BFS has a cost estimate for 10.3 Mtpa and because the operation is very similar to that of Metro Mining in Queensland.
Metro Mining are running a 2Mtpa operation for about AU$29 / t FOB including royalties etc (US$22 / t FOB). Current manpower is about 185. Metro's BFS estimated a trans-shipment cost of AU$9 / t, say US$7 / t.
At Bel Air they mine it with surface miners into the back of trucks which haul it 10km to the port to be crushed then stockpiled. It is rehandled into barges and trans-shipped into Capesize vessels. Manpower for the current operation at 4.5 Mtpa is about 500. Their BFS operating cost estimate for 10.3Mtpa is US$25 / t FOB including royalties etc. I couldn't find their current operating cost. At Bel Air they have no other land transport costs because the deposit is on the coast.
Translating Bel Air costs to Minim Martap (MM)...let's deduct US$7 / t for trans-shipment costs (there will be no trans-shipment cost for MM as bulk carriers will be loaded at Kribi) making it US$18 / t to mine and crush, stockpile and rehandle and to get MM ore onto a ship.
Now it still has to be hauled by rail from MM and stockpiled and rehandled at Kribi. You said my first estimate was a little high (your words "I've done my own snooping and come up with better figures. (Though not dramatically so).") so let's say US$22 / t rather than the US$26 / t.
So before it leaves Cameroon US$40 / t have been spent.
Then you've got seaborne freight costs - I still reckon they're about US$23 / t - what does your CBIX site say? So all up the cost is around US$63 per tonne delivered to a Chinese customer. Let's say 10% of the bauxite (1 Mtpa) goes to the refinery in Cameroon - that makes 0.9 x 63 + 0.1 x 40 = US 61 / t. Could the refinery handle more than 10%?
Studies of 3 Mtpa operations (Garafiri, Dynamic & FAR in Guinea, Sierra Min in Sierra Leone) indicate an average cost of about US$25 / t FOB but their logistics are more complex than those of Bel Air and costs will probably be higher in the fullness of time. Manpower for FAR is estimated at 700 and for Dynamic at greater than a thousand. None of the projects are 860km from the coast.
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