Koppamurra, in South Australia's boarder region with Victoria, has grown over 25% since mid-2022 to 101 million tonnes grading 818ppm total rare earth oxide,
up from 81.4Mt at 785ppm TREO.
The indicated resource is now 40% larger: 63Mt at an increased grade of 839ppm TREO.
Acting managing director Rick Pobjoy said as confidence in the resource grows, so too is the in-situ grade.
AR3 has also delivered an expanded exploration target for Frances and Dovetail covering areas already drilled between 330Mt and 1.4Bt, an increase of 536% at the upper end of the range.
It has focused on less than 5% of its land holdings so far.
The company says all the signs suggest Koppamurra is the heart of a globally significant rare earth mineral province with "multigenerational" potential.
It benefits from being in a tier one mining jurisdiction, and AR3 believes it offers the twin upsides of both rapid, low-cost growth and rehabilitation.
The company is planning infill drilling at Frances to expand its inventory of both light and heavy REEs.
Pobjoy said buyers have already come calling given it is one of the few advanced ionic clay-hosted rare earth deposits located outside of China or Myanmar.
Clay-hosted deposits are often cheaper and easier to produce than other hard rock REE deposits.
AR3 is also stepping up work on an emerging REE clay target at Massie Creek in far north Queensland, after promising sampling last year.
Shares in AR3, which have traded in a range of A18-80c over the past year, were up 1% this morning at 25c, valuing the company at $32 million.
The company started the year with $9 million cash.