The inferred resource is 642,359 tonnes at 3.33 grams per tonne gold for 68,731 ounces of gold, using a 1.3gpt cut-off.
The resource comprises primarily fresh ore, with small portions of oxide and transitional ore.
First Au completed a backdoor listing in June last year, and discovered Gimlet in late 2018.
The resource was announced after only two reverse circulation drilling programs.
"From listing on the ASX in June last year, to soon after making a gold discovery at Gimlet with its first drill program, we now have a maiden JORC resource, which is a significant achievement for the company in such a short timeframe," First Au chairman Bryan Frost said.
"And with the work currently underway in preparation for our next drilling campaign, there is a good feeling in the company that Gimlet will produce even more excellent results."
Gimlet is just 15km outside Kalgoorlie and is within trucking distance of the Mungari, Lakewood, KCGM, Kanowna Belle and Paddington mills.
The project neighbours Intermin Resources' 289,000oz Teal project.
First Au will spend the next six months testing anomalies and depth extensions.
The company raised A$5.3 million when it listed last year and had $2.5 million cash at the end of March.
Shares in First Au were unchanged at 1.7c today, valuing the company at $4.7 million.