Lead independent director Robert Malone said: "We are pleased to put into place this next phase of what we believe to be a model succession process.

“We appreciate the ongoing veteran leadership of Boyce, and look forward to the continued success of president and chief operating officer Glenn Kellow following a recent significant increase in his responsibilities."

Kellow recently assumed executive responsibility for corporate strategy, global analytics and business development, as well as continuing to oversee all aspects of the company's global operations including worldwide sales and trading activities.

The agreement with Boyce continues his term as chairman and CEO to June 30, 2015, and as executive chairman until June 30, 2016.