Franco-Nevada said the terms were the same as the $178 million precious metals stream it signed in September with First Quantum Minerals' (CN:FM) to help it fund the acquisition of a further 10% of Cobre Panama from LS-Nikko Copper.

Franco-Nevada said it expected to fund the combined $356 million without a syndication partner after CEF Holdings, previously named as a possible one-third partner, was unable to put a suitable structure in place to participate.

The company has an existing precious metals stream over First Quantum's 80% interest in Cobre Panama and had funded $727 million of that $1 billion commitment by the end of 2017.

The incremental 20% stream differs because Franco-Nevada is funding the full amount upfront and the ongoing payment for deliveries is based on a percentage of the spot price.

The $5.5 billion development project in Panama has overcome logistical challenges and is about 60% complete, and expected to produce about 300,000 tonnes per annum of copper over a 40-year mine life.

Franco-Nevada CEO David Harquail said phased commissioning was expected later this year and Cobre Panama was expected to "add materially" to the streaming company's growth profile from 2019.

Franco-Nevada shares dropped 3.42% to C$94.51 yesterday, a mid-point in its 52-week range.