The airline transport pilot reported that he was taking cargo to a remote mining airstrip under the provisions of Title 14, Code of Federal Regulations Part 91. He said during the landing roll, the main landing gear wheels encountered several soft spots, and he had difficulty maintaining directional control. The nose wheel encountered rough and soft terrain near the edge of the airstrip and collapsed rearward, damaging a fuselage structural bulkhead. The pilot stated that there was no preaccident mechanical problems with the airplane, and that in retrospect, it would have been beneficial to have a wider runway and more experience in that type airplane.