(ShareCast News) - Shares in AIM-listed miner Botswana Diamonds fell more than 12% on Tuesday, as the company announced that drilling has started on the kimberlite pipe.The miner has started to drill on the the kimberlite pipe AK22 on its PL260 licence in the Orpa area of Botswana, part of a joint venture with Alrosa, a diamond producer.On the 9 September the company said two core holes will be drilled on the kimberlite AK 22.The company said it will provide further details on its proposed drilling campaign on the PL135 licence in the Gope region in due course.Shares in Botswana Diamonds were down 12.5% to 1.40p at 1426 BST.