|The new find, a 104 carat diamond. Image: Supplied|
The rock is about the size of a 50 cent coin and is the fourth stone over 100 carats Lucapa has found this year.
In February, it uncovered a 404-carat rock at the same mine, worth more than $20 million, the biggest diamond ever found in Angola.
The company's share price jumped 32 per cent on the back of that announcement.
Chief executive officer Stephen Wetherall believed the company was on the cusp of discovering the original source of the stones, which could make it a takeover target for some of the largest diamond miners in the world.
He explained the size, shape, and roughness of the large stones found recently suggested they had not travelled far from their original seam, while stones found further from their source generally had more polished surfaces and a rounded shape.
"It just seems that every corner we turn we seem to trip over a large recovery," Mr Wetherall said.
"We are quite excited because when you recover these large diamonds, they generally don't travel very far and if we're going to be recovering these in the source, most certainly we will have one of the most special diamonds in the world."
Mr Wetherall said the quality of the gemstones was exceptional.
"The normal average dollar per carat of diamonds in the world is only $US120 per carat," he said.
"Our average US dollar per carat is $2,100, so it's almost 20 times the average price.
"It certainly improves the economics and viability of the source that we are searching for."
Mr Wetherall would not speculate on how much the latest 104-carat find would fetch at auction, but said it was worth many millions of dollars.
"Most certainly I am in awe," he said.
"Diamond prices have been under a little bit of pressure but the industry as a whole has been a safer bet than some of the other commodities.
"Diamonds still remain a very good investment and if we tap the source, it'll be an exceptional investment."
The diamond would likely be cut into one large polished stone with a number of smaller peripheral stones.