Latest drilling was headlined by 153m grading 0.47 grams per tonne gold and 0.1% copper from surface.
"We are expanding the size of El Palmar, and therefore its value, with virtually every hole," Sunstone managing director Malcolm Norris said in an ASX release.
"There is also growing evidence of higher-grade copper domains with in-excess of 0.2% copper and gold in-excess of 0.35gpt.
"This should deliver a highly attractive gold-equivalent result once we have metallurgical results in hand.
"The combination of the scale and the grades we are generating at El Palmar shows that this is clearly becoming a very valuable project…"
Further assays are awaited from El Palmar and Sunstone's other exploration project, Bramaderos - where initial met work results are also due.
Sunstone said it has about A$26 million in cash and equities.