The preflight, engine runup and initial takeoff were uneventful. At approx 600 ft agl the engine sputtered for two or three seconds then stopped. The pilot turned back toward the runway but was too low. He crash landed in a gravel quarry after clipping power lines. No engine abnormalities were noted during a subsequent engine teardown. The reason for the engine failure could not be determined. The operator believed that either the mixture control had backedoff during the climb ot that the parachutist in the front rt seat had inadvertently pulled the mixture off with a piece of her equipment during the climb, causing the power loss.