The resource includes an indicated estimate of 88Mt at 3.8% THM.
Scoping work is underway and infill drilling is planned next quarter.
The Port Gregory project borders Resource Development Group's Lucky Bay mine, with Heavy Minerals' scoping work to be undertaken by engineers "that worked directly" on that project within the last 2.5 years.
Water jet cutting drives current demand for garnet and is the dominant end-use in advanced manufacturing economies.
Garnet pricing increasing 20% year-on-year in the US in 2021, reaching US$325/t (garnet concentrate).
Heavy Minerals describes Mt Gregory as "world class" and believes future alluvial almandine garnet produced from the Port Gregory region can "not only help fill this supply gap but is also likely to displace inferior hard rock garnet that is less preferred by end users, typically due to its reduced recyclability".
Heavy Minerals ended the March quarter with A$2.9 million cash.
Shares in Heavy Minerals were up 12% to 28c during Monday's ASX session, capitalising the company at $14.4 million.
