Actually, businesses outsource skills development. That's a problem, and it is a trend that has developed in the industry over the last few years. However, subcontractors also have access to the mine. They are usually the ones providing training in the mines for large mining corporations. Some agreements on training are in place between subcontractors and large mining companies.
That's also a way for large mining companies to recruit. They entrust subcontracting companies with recruitment. These subcontractors are therefore responsible for recruiting and training workers. Once those workers have been trained, large mining companies coach the employees and bring them on board.
That system has developed over the last few years. I can't say that this is the best practice, but it is how mining companies have decided to recruit.