THE HELICOPTER WAS BEING OPERATED ON A VISUAL RECONNAISSANCE/ORIENTATION FLT WITH A PLT & A POLICE AGENT ABOARD. WHILE FLYING AT ABOUT 200 FT ABOVE THE FONTE RIVER (FOLLOWING A VALLEY), THE HELICOPTER COLLIDED WITH A POWER LINE THAT CROSSED THE RIVER. DURING IMPACT, THE MAIN ROTOR SYSTEM SEPARATED & THE HELICOPTER CRASHED IN DENSE JUNGLE. NO PREIMPACT MECHANICAL PROBLEM WAS EVIDENT.