Tango was not able to meet the criteria of the conditional sale within the allotted time frame. The agreement has now lapsed and the disposal will not proceed.
Firestone’s Botswana operations, including its interest in the low-grade high-value BK11 mine, are currently under care and maintenance.
The failed disposal would have no impact on its cash position. At the end of the year, the group expects to have a cash balance of US$9mln, not including the US$15mln standby facility or proceeds of the disposal.
Firestone is currently focused on the completion and commissioning of its Liqhobong Diamond Mine in Lesotho with initial production expected to begin in the last quarter this year.
The group said it remained committed to seeking ways of advancing or unlocking the shareholder value from its Botswana assets, which it continues to believe have value.
Shares fell just over 3% to 44.5p.