Fluorspar mining firm Tertiary Minerals (LON:TYM) said fourth phase drilling at its MB project in Nevada had increased the size of the deposit.
Four step-out holes were sunk in the programme, which aimed to test the grade at the newly discovered western area, and thick mineralised intersections were found, the company revealed.
The assays will now be incorporated into an economic evaluation of the project, which last year saw a 132% increase in the contained fluorspar in a JORC estimate.
The higher confidence indicated category now houses 6.1mln tonnes at 10.8% fluorspar and inferred 80.3 million tonnes grading 10.7%, at a 9% cut-off.
The results included 89.91 metres grading 12.02% calcium fluoride (CaF2) from 120.4m depth.
Another hole had 137.16m grading 11.54% CaF2 from 53.34m depth, including 32m grading 15.81% calcium flouride from 185.93m.
Managing director Richard Clemmey told investors: "Results from the Phase 4 drilling programme continue to grow the known size of the MB deposit, proving both lateral and depth extension of significant fluorspar mineralisation in the Western Area which still remain open in all directions.
"We now look forward to incorporating these results into our economic evaluation of the project and progressing with the next phases of development this year."
Notably, the firm also said that ore-grade molybdenum (Mo) had been uncovered at the base of one hole, which provides a future exploration target.
Tertiary said the priority was now to move to the nest stages of development at MB in 2016 - metallurgical testwork, economic modelling, scoping study and mine permit planning.