Eight shallow holes have been completed to date in what's called the Apartadero zone and five assays were received.
Highlights include 3.5 metres (m) at 3.5 g/t (grams per ton) gold and 1.6 g/t silver.
In another hole, there was 18.5 metres at 0.8 g/t gold and 5 g/t silver.
"We were very pleased to encounter gold grades in some of the early shallow reconnaissance holes," said Tawn Albinson, the president of Prospero.
"The drill plan developed with Fortuna was designed to get a handle on structural controls on the highest priority targets before deeper drilling."
"We now see a strong correlation between the presence of black jasperoids after limestone and grade.
"A few more shallow holes will be required over the next two weeks to get a decent picture of the strike and dip of what we think are the controlling structures."
The drilling of Petate is being carried out as part of the firm's reconnaissance campaign evaluation financed by its strategic partner Fortuna Silver Mines over three of Prospero's projects.
Prospero shares were unchanged at C$0.16 each.