Botswana Diamonds said kimberlite was intersected at shallow depth in two out of three drill holes by way of visual inspection at its Marsfontein play in South Africa.
The kimberlite was believed to be associated with the existing high-grade Marsfontein pipe, the company said.
Kimberlite is an igneous rock that can contain diamonds.
At the nearby Thorny River project, geological structures 'consistent with kimberlite emplacement' were encountered in two holes.
More detailed ground mapping and geophysics would better define targets for further drilling, Botswana Diamonds said.
At 1:20pm: (LON:BOD) Botswana Diamonds PLC share price was +0.33p at 1.1p