Canada-based Torex said the group of about 20 unionised workers blocked the mine's main gate, demanding a change in their labour union. Earlier, the company had met with the workers and informed them that it did not have the authority to effect such a change, and that it would have to be done through a government sanctioned process, it said.

The protest has been peaceful, but with no unionised workers on site, Torex has shut down the processing plant.

"Government authorities have been on site, and are working to establish their approved process for resolving disputes as to which union will represent the site workers," Torex CEO Fred Stanford said.

ELG hit commercial production early last year, and has been ramping up since then. Torex has forecast gold sales of 350,000-380,000oz for 2017, with a recovery processed grade of 2.67g/t, and all-in sustaining costs of US$775-825 per ounce. However, it expects to be on the lower end of the production range and higher end of costs, due to a heavy rainy season.