It has been revealed that the collapse of a leach tank at the Ranger uranium mine in the Northern Territory was the second such incident at a Rio Tinto mine in less than a week.Rio is a majority shareholder of Ranger operator, Energy Resources of Australia (ERA).An investigation is under way at the Ranger site, inside Kakadu National Park, after a 1,400 cubic metre tank holding uranium oxide slurry and acid collapsed at the weekend.A website for the majority Rio Tinto-owned Rossing mine in the African nation of Namibia confirms a similar tank collapsed there last week.The Northern Territory Environment Centre says the similar incidents are worrying.Spokeswoman Lauren Mellor, says the incidents are worrying."It is obviously very concerning that we are seeing the same kind of failures at leach tanks at the Namibian mine, which is the largest uranium mine held by Rio Tinto, the parent company of Energy Resources of Australia," she said."Across two continents, within the same week, we have seen he same copy cat failure."It is just incredible that these types of incidents are happening on this scale."A Rio Tinto spokesman says each mine has commissioned a full investigation of the incidents to determine the causes and contributing factors. The company says it is important that the investigations run their full course.Territory Mines and Energy Minister Minister Willem Westra van Holthe says the Ranger uranium mine is one of the most regulated mines in the world and is a safe place to work.He says there have been been minimal changes in the amount of radioactivity recorded at the mine site since the spill.