The inferred 44 million tonnes grading 0.6 grams per tonne is based on a gold price of US$1300 per ounce and a cut-off grade of 0.3gpt, with Rex's development concept at Hog Ranch entailing heap leach processing.
Rex believes a cut-off grade of 0.3 grams per tonne is applicable for a "small scale operation", and that a lower cut-off could work for a larger scale operation.
The ASX-listed company said both options were under consideration.
It also pointed to the "large broad alteration system defined over a 20sq.km area" and "deeper higher grade vein hosted targets".
Previous mining at Hog Ranch is aid to have yielded about 200,000ozs of gold, with the project owned and operated by Western Mining Corporation from 1988-1994.
Rex completed the acquisition of the project last month after issuing 10 million shares to a private Australian company called Hog Ranch Group (HRG), whose eight shareholders include Rex's CEO Richard Laufmann and CFO Amber Rivamonte.
A further 20 million shares from Rex are due HRG upon resource and decision to mine milestones.
Rex's move into Nevada comes as the company slowly progresses towards potential development of the A$500 million Hillside copper project in South Australia.
Hillside is located in wheatbelt country on SA's Yorke Peninsula, with Rex saying in July the approval process for the project had thus far taken more than five years at a cost exceeding $15 million.
Rex started the current quarter with $2.7 million cash.
Shares in Rex were up 2% to 9.7c in Monday morning trading, capitalising the company at $27.5 million.