I was once in the gold mines up in the mountains of the Philippines when I lived there (near Baguio). I also did some work inside of the talcum powder mines near Woodstock, VT.
The conditions in these places are highly toxic in my opinion. State regulations are probably stringent regarding the working conditions but your son could be exposed to hazardous gases and such. No telling what noxious materials he is dealing with.
If he does not improve through diet and detox (parasites, flushes etc) and proper rest and recreation then maybe have him tested for heavy metal or toxin exposure? Just a thought. Some of these poisons can really take down the adrenals/kidneys and nutritional support simply would not be enough to combat any toxic exposure.