This is the most logical answer to why the 10% (or 19%) partner is putting up the bulk of the money to make this project feasible - rebuilding roads, a power plant and airport. China get a stake in a potentially billion+ dollar mine; they already have a pre-existing agreement with DRC to spend billions on infrastructure; these improvements will make possible other potential mining projects in the region, that they could also have a stake in; the resource will likely end up in China, where it is most required (see below); but ultimately, they will be the eventual owners of the mine itself.
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This is an old chart (the only one I could find), but note that while China had the most capacity, they were actually the 4th biggest producer. I expect things were different in 2016.
One concern I have, which I think this was pointed out once already, but ignored - the wording of:
"Separate to this agreement, Dathomir and Cominiere have agreed that Dathomir will facilitate the rehabilitation of the road from Lubumbashi to Manono and the Mpiana Mwanga hydroelectric power station." - it does not explicitly say that China will foot the bill.