from ODIRILE TOTENG in Gaborone, Botswana Botswana Bureau GABORONE, (CAJ News) - THE world's most valuable diamond mine is transitioning from open pit to underground operations following an investment of US$1 billion (BWP 13,6 billion). The board of Debswana, a 50:50 joint venture between De Beers Group and the Government of Botswana, announced it had