CEMEX loader opr was moving flyash from mat'l storage bldg to hopper. Raw mat'l del driver, ind. o/o contracted w/ Tri-State Carriers(TSC), entered mat'l storage area & exited his tractor, preparing to unload. Loader reversed to get another load & impacted the tractor, striking the driver. MSHA issued Contr ID B0350 to TSC under protest as it is not a contr on CEMEX mine site.