Exhibit 99.1

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that this Amendment No. 21 to the statement on Schedule 13D is being filed with the Securities and Exchange Commission on behalf of each of the undersigned pursuant to Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended.

Dated: September 14, 2017

Glencore AG
By:	/s/ David Streule
Name:	David Streule
Title:	Officer
By:	/s/ Stephan Huber
Name:	Stephan Huber
Title:	Officer

Glencore International AG
By:	/s/ Robin Scheiner
Name:	Robin Scheiner
Title:	Officer
By:	/s/ Shaun Teichner
Name:	Shaun Teichner
Title:	Officer

Glencore plc
By:	/s/ John Burton
Name:	John Burton
Title:	Company Secretary