The company said directional diamond drilling had continued to intersect multiple zones of high-grade zinc mineralisation, within and below the Santander pipe target.
Among the highlights, Trevali hit 64.6m at 7.26% zinc from 556.95m, including 6.5m at 20.4% zinc, 0.43% copper and 18.48g/t silver.
"From our initial discovery drill hole in February 2008, Trevali has enjoyed almost 10 years of accretive resource growth and replacement at Santander," president and CEO Dr Mark Cruise said.
"Given the coarse style of the mineralization, absence of significant amounts of barren sulphide and location immediately adjacent to the mine infrastructure, the Santander pipe forms a compelling high-priority target."
Two surface and two underground drill rigs are continuing to drill to delineate the system.
Further underground drilling at the Magistral trend immediately west is expected to expand and upgrade its existing resource.
The company had record income from its four commercially producing operations in the September quarter, up 250% to US$28.4 million compared with the third quarter in 2016.
Santander produced 14.6 million payable pounds of zinc, 3.9Mlb lead and 194,214oz of silver during the period, at head grades of 4.13%, 1.04% and 1.26oz/t respectively.
Trevali had $105.7 million cash at the end of September however there was a net loss of 1c per share mainly due to the acquisition of Glencore's (LN:GLEN) African zinc mines.
Shares reached C$1.43 intraday in Toronto but closed down around 2% to $1.36.