El Niño is part of the South Arturo property, which itself is a joint venture between Premier Gold Mines (40%) and Nevada Gold Mines (60%).
Premier officials said high-grade ore is now being processed; it is projecting the mine will surpass production expectations for the year as it was anticipating only pre-production ore in 2019. South Arturo's guidance was previously estimated at 5,000 to 10,000oz whole-year.
While the underground element of El Niño is online, the initial phase of pit development is still in process, the company said, along with multiple drill programmes and geotechnical drilling for a proposed phase 3 pit project.
Ore from EL Niño is processed at Barrick's neighboring Goldstrike facility.
Nevada Gold Mines, which is operated by Barrick, is a JV between it and Newmont-Goldcorp.
Premier Gold Mines currently has one other producing gold mine, the underground Mercedes gold-silver operation in the Sonora state of Mexico.