Zijin Mining acquired the Timok project it refers to as Čukaru Peki last year, through the acquisition of Nevsun Resources and then Freeport-McMoRan's stake in the Lower Zone. 

EMX said it had acquired an uncapped 0.5% NSR royalty across the Brestovac licence, which contained the Čukaru Peki Upper Zone development project and Lower Zone deposit, in 2013.

It noted the royalty agreement contained a provision for the reduction of the 0.5% NSR royalty rate "under certain express and specific circumstances".

"After a thorough review of the royalty agreement and based on certain publicly available information, EMX does not believe that the circumstances which would have triggered a reduction of the royalty rate have occurred and therefore the royalty rate remains at 0.5% of NSR," EMX said.

"Furthermore, there is no mechanism for the royalty to be reduced in the future."

It said it held two further Timok royalty properties, Brestovac West and Durlan Potok. Both exploration properties are also operated by Zijin.

EMX said Zijin had accelerated the schedule for the Upper Zone and slated initial production for the second quarter of 2021, according to its annual report released in March.

"EMX has requested, but has not been provided, the supporting data and information used for either Nevsun's or Zijin's Timok project disclosures, nor does EMX have access to the property itself," it said.

"As a result, EMX has not been able to independently verify the technical information regarding Nevsun's or Zijin's disclosures on the Timok project, but EMX does consider that such information to be reliable and relevant in all material respects."

Zijin's Serbian arm Rakita Exploration has indicated a US$474 investment in constructing the mine for the Upper Zone, which was expected to produce about 79,000 tonnes of copper annually at full production.

EMX shares closed up 5.1% yesterday to C$3.68, near the upper end of a one-year range, capitalising it at $310 million (US$234 million).