The maiden indicated and inferred resource for Piedmont's North Carolina ground is 16.19 million tonnes at 1.12% lithium oxide for 182,000t of contained lithium oxide or 450,000t of lithium carbonate equivalent, using a 0.4% cut-off.

Just over half of the resource sits in the indicated category.

The resource sits within Piedmont's Core property, which is only 5km from the historical Hallman-Beam lithium mine, and is the first resource estimate completed in the past years in the Carolina tin-spodumene belt.

CSA Global has also estimated an exploration target of 4.5-5.5Mt at 1.1-1.2% lithium oxide for Core.

Piedmont president and CEO Keith D Phillips said the maiden resource had surpassed the initial exploration target of 10-15 million tonnes at a grade of 1-1.25% lithium oxide.

"The resource will underpin the upcoming scoping study, which we believe will reflect the significant advantages associated with our unique location," he said.

"There are many interesting lithium projects being advanced around the world, but Piedmont has the only project based in the industrial heartland of the United States and the cradle of lithium production, with all the economic and strategic benefits that derive from that position.

"With regional exploration progressing and constructive conversations ongoing with numerous local land owners, we are optimistic that this initial resource will be just the beginning, and that Piedmont is well-positioned to develop a world-class, low-cost integrated lithium business in the United States."

Foster Stockbroking head of research Mark Fichera said the updated exploration target had the potential to boost the Core resource to at least 20Mt.

"It would potentially provide a 20-year mine life at 1Mtpa, should all such resource eventually convert to reserves," he said.

"Additionally the company is undertaking a drill campaign on the promising Sunnyside property which also has potential to add more tonnage to the Piedmont project."

Foster placed its speculative buy rating and A30c price target for Piedmont under review.

Shares in the company rose by 5.5% this morning to 19c, giving it a market capitalisation of just over $100 million.