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The ivory has been confiscated from poachers or recovered as a result of natural deaths or government-sanctioned elephant culls, officials said.
Zimbabwe says it needs to raise extra funds to deal with its burgeoning elephant population, which at about 100,000 is one of the largest in Africa.
Adult elephants consume about 100 to 300 kgs of food a day, studies have shown, and officials say their growing numbers are straining the impoverished country's resources and posing a threat to plant life.
Some $30 million is required each year for conservation of the animals and anti-poaching in Zimbabwe, but Vitalis Chadenga, director-general of the Parks and Wildlife Management Authority, told Reuters the current budget was "very far from there".
"There is a point where our elephant population can get so much to a point where they self destruct and this is happening in some of the parks," he said.
In 2008, Zimbabwe was allowed to conduct a one-off sale of 3.9 tonnes of ivory by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the international group that governs trade in plants and animals.
Plagued by corruption, Zimbabwe provided detailed documents to CITES showing how the money raised from the sale went directly into conservation.
Zimbabwe faces an October deadline to make its request to CITES if it wants to quickly sell the tusks.
However, conservationists worry the sale could fuel demand for ivory, especially in the fast-growing emerging economic powers of Asia where it is often used in carved ornaments.
Although elephants are prolific in Zimbabwe, poaching and a loss of habitat have made them a threatened species in large parts of Africa.
A global ban on the ivory trade was imposed in 1989 and was widely credited with stemming the relentless slaughter of African elephants in countries such as Kenya.
Occasional auctions from African government stockpiles have since been sanctioned.
Chadenga said the global ban was not working.
"We have not had a legitimate sale of ivory now but we continue to have an upsurge in poaching," he said.