It said surface samples had returned assays up to 1.88g/t gold and 648g/t silver, and samples 600m east along strike from previous drilling returned up to 0.57g/t gold, 347g/t silver and 1.2% zinc.
The company said it had also discovered the new North vein, 400m to the north-east on the adjacent Cervantes property it acquired in August, with initial sampling results including up to 3.01g/t gold, 196g/t silver, 0.4% lead and 1.08% zinc.
"We believe additional high-grade mineralisation may well be discovered at Santa Maria," president and CEO Warren Rehn said.
Golden Minerals expects to compete an updated PEA this quarter, incorporating results of a drilling programme that started last August.
A 2017 PEA estimated $1 million capex for a 200 tonne per day underground operation, producing 2 million ounces of silver and 6,800 ounces of gold over a 3.2-year mine life.
The project's current resource comprises an indicated 180,000 tonnes at 304g/t silver and 1.4g/t gold plus an inferred 120,000t at 343g/t silver and 1g/t gold.
Golden Minerals has a remaining US$1.2 million to pay under its option to acquire 100% of Santa Maria.
The Colorado-based company had $2.7 million in cash and equivalents and no debt at the end of March.
It reported a positive net operating margin of $1.1 million related to the lease of its oxide plant during the quarter.
It expected to spend about $1.5 million in the year to March 31, 2019, on exploration and property costs primarily at its Mexico assets including Santa Maria.
Shares in the company closed up more than 5% on Friday to 30.02c.