Stellar Diamonds (LON:STEL) chief executive Karl Smithson said it is “highly encouraging” that the Droujba kimberlite in eastern Guinea extends to 388 metres and remains open at depth.
Previously the pipe, which covers 3 hectares at surface, had been intercepted at 222 metres.
Stellar said today it has doubled the scope of its drilling programme to 12,000 to discover whether Droujba’s two hypabyssal kimberlites coalesce at depth.
Bulk sampling will take place on site once the plant is relocated from the company’s Bomboko project, also in Guinea.
At the same time 268 kilograms of drill core has been sent for micro-diamond analysis. Previous tests on 400 kilograms of kimberlite returned 952 diamonds.
Chief Executive Karl Smithson said: "The drilling programme at Droujba is progressing well and the significant intersection of kimberlite at a depth of 388m is considered to be highly encouraging in terms of the potential tonnage of the Droujba pipe.
"Based on the interpretation of the drilling data the company has elected to double the current 6,000m drilling programme in order to model the ore body to depth and, in tandem with further microdiamond sampling and a surface bulk sampling programme, establish an initial inferred resource estimate by the end of the first quarter of 2012. I look forward to updating shareholders in due course."
Discovered in the 1960s by the Russians, Droujba was mined down to 20 metres, and it was believed there was nothing below that depth.
Stellar has embarked on an aggressive drilling programme, that also includes the Tongo prospect in Sierra Leone, funded by £6.2 million cash call completed in March.