Botswana said it would do 40 reverse circulation boreholes to a depth of 30 metres
The company said the first four holes had intersected kimberlite at predicted thicknesses and depth but did not release actual results.
The programme is expected to be completed within four weeks.
After Botswana has completed drilling activities and received the necessary regulatory approvals within the next three months, it will start the bulk sampling programme.
In the meantime, the company is refurbishing a nearby diamond processing plant to process the bulk sample kimberlite.
In June, Botswana completed Thorny River's technical and economic study, which indicated potentially positive economics using the top end of the 46-74 carats per hundred tonnes grade and US$120-220 per carat value ranges.
Botswana Diamonds' shares rose 5.17% Monday to 76p, with shares up 12% since the start of the year, but down 20% in the past six months.