* Nexen pipeline may have been leaking for over two weeks

An oil sands pipeline rupture that has coated a large swath of muskeg south of Fort McMurray with bitumen, sand and salty water may have gone undetected by an automated monitoring system for more than two weeks, Nexen executives say.

The exact time and cause of the massive spill is still under investigation. The leak was discovered on July 15 by a worker at the Long Lake oil sands project. On Wednesday, Chinese-owned Nexen Energy ULC revealed the leak may have started as long ago as June 29. The company’s computerized monitoring system failed to detect the breach.