The nine-year project that could begin production in the second half of 2024 is flagged to produce a total of 337,000t of zinc in concentrate, 78,000t of lead in concentrate and 3.2 million ounces of silver - with mining at a rate of 800,000t per annum and processing at 520,000tpa.
All-in sustaining costs are put at 60c per pound.
Alta's scoping work used a zinc price of $1.29/lb, versus the current spot price of about $1.46/lb.
Annual free cashflow is expected to average about $67 million during the "peak" production period 2026-2031.
The venture's internal rate of return is put at 50%.
The development will feature underground crushing, concentrate processing housed in a factory, and no waste dumps or tailings disposal at surface - with all tailings being cemented and deposited underground in new and historical stope voids as paste fill.
Alta reported the proposed underground mining operation at Gorno "is considered to be of medium risk from a technical mining operations standpoint".
The scoping work for Gorno used a resource of 7.79Mt grading 6.8% zinc, 1.8% lead and 32 grams per tonne silver.
Alta's exploration target at Gorno totals an additional 17.4-22Mt at 8.5-10.4% zinc.
Permitting work is ongoing.
Alta started the current quarter with A$2.3 million cash.
Alta's forerunner Energia Minerals arrived at Gorno in 2014 with Euroz and Alexander Burns the key parties involved in an $8.15 million funding package back then to get the venture underway.
Shares in that raising were priced at 2.5c each, the equivalent of 37.5c today given a 15-for-1 consolidation undertaken earlier this year.
Burns put in $2.5 million in that raising and became the company's executive chairman, with he having enjoyed a big win in 2010 with an iron ore play in Mauretania when Sphere Minerals was taken over for US$514 million by Xstrata.
Burns transitioned to non-executive chairman 12 months ago, with mining engineer Geraint Harris becoming Alta's managing director in September 2019.
Shares in Alta were up 1% to 8c in early trade, capitalising the company at $23 million.
