Had they wanted *just* the resources in itself, they could just do it like western countries; extract the hell of it and do fuck all with the infrastructure (probably beyond a road to the port).
Investment in africa could mean trillions of dollars to chinese companies, and that's where the real money is at. When african countries signed a "low-interest" loan deal to build an expressway, those deals often include employing chinese construction companies, buying china-made construction material, using china-made equipment, designed by chinese engineers and supervised by chinese laborer, with african labors tend to do manual labors and the few african engineers trained by the chinese so they could do tier-1 technical support when the chinks move on to another project.
Which means chinese construction companies get fat contract to build said expressway, chinese truck companies get to sell more trucks, chinese factories get to sell more construction material and more chinese get job opportunity and keep the unemployment in check. Basically the money trickle back down. To the chinese (and the african would get enough for them to feel good for themselves).
In the grand scheme of things, chinese-built power plants would power chinese-owned factories, using china-made machinery to produce stuff that would be transported to chinese-built port, using china-made trucks plying their way on chinese-built expressway. In africa
On the up side, that level of participation means that the projects do get done. It's unlike previous financing model where african countries go to the world bank to borrow money for construction project and world bank would simply release money under the assumption that if the government became a guarantor, they would oversee shit being done. It may works in more advanced/mature countries (like how Japan financed part of the first shinkansen line with loans from the world bank), but that definitely not happening in africa