The first three step-out holes, from the 421 discovery hole drilled last year, have intersected "significant copper-gold mineralisation" including 58.1m at 4.54% copper-equivalent, or 7.19g/t gold-equivalent.
President and CEO Steve Robertson said the initial step-out drilling was important to establish the continuity of the recently discovered mineralisation in the 421 zone.
"The gold content makes this discovery even more captivating," he said.
Stardust's nearby Canyon Creek deposit has an indicated 985,000 tonne resource grading 2.92% Cu-eq and an inferred 1.98 million tonnes at 2.65% Cu-eq, announced last year.
Teck Resources made a strategic investment in the junior in December and now holds 10%, according to a June presentation.
The company's Stardust-Canyon Creek discovery has earnt it a nomination for best new discovery in the 2019 Mining Journal awards, to be announced on September 27 in London.
Sun Metals had C$6.7 million (US$5 million) in cash at May 28.
Its share price has more than doubled in the past year, from 19c 12 months ago to closing up 10.7% on Friday to 46.5c.
At that price it is capitalised about $56 million (US$42 million).