The company's ongoing two-rig RC drilling program along the 3km-long Lords Corridor has generated more than 12,000m of core since February.
Initial assays from the first 11 holes have delivered hits such as 134m grading 1.9 grams per tonne gold from 24m, including 20m at 5.9gpt from 80m from infill drilling at Orion that tested the down-plunge high-grade portion of the lode.
Extensional drilling 40m to the west returned 28m at 1.2gpt from 112m, including 4m at 3.8gpt from 132m.
Alto said it had confirmed multiple mineralised structures at Orion, both within the granodiorite intrusion and on the contact between the granodiorite and ultramafic.
Orion remains open down-dip and down plunge.
Additionally, a hole into below the Lord Henry pit returned a promising 12m at 6.1gpt from 40m, including 4m at 16.8gpt.
The work has intersected multiple stacked lodes outside the resource envelope, with high grades within primary mineralisation.
Step-out drilling at Havilah has also grown that prospect 100m to the north-west, with results such as 12m at 1.2gpt from 76m, including 4m at 3gpt.
The company has around 10,000m of RC drilling to complete, while a 3000m diamond drilling program is expected to begin in June.
Alto said the outstanding assays would likely see a revised, expanded program.
Project resources are estimated at 331,000 ounces at 1.7gpt.
Westgold, which has two mills within 150km of Sandstone, recently picked up an 8.6% stake in Alto at 7.9c per share from Middle Island Resources, which secured its shares for 9.5c last October, plus some shares that were purchased on market.
Middle Island attempted a 4.8c all-scrip takeover of Alto in 2019, while Australia's Habrok Mining and China's Goldsea Australia Mining attempted cash bids of 7c and 7.5c last year.
The stock has traded between 6-15c over the past year.
Alto's shares hit 11.5c in early trade, and the stock was up 10% to 9.9c later in the session, valuing it at $44.5 million.
