EXHIBIT 99.1

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that this Amendment No. 22 to the statement on Schedule 13D is being filed with the United States Securities and Exchange Commission on behalf of each of the undersigned pursuant to Rule 13d-1(k) under the United States Securities Exchange Act of 1934, as amended.

Dated: May 13, 2019 

Glencore AG
By:	/s/Nicola Leigh
Name:	Nicola Leigh
Title:	Authorized Signatory
By:	/s/Patrick Huber
Name:	Patrick Huber
Title:	Authorized Signatory
Glencore International AG
By:	/s/Martin Haering
Name:	Martin Haering
Title:	Officer
By:	/s/Peter Friedli
Name:	Peter Friedli
Title:	Officer
Glencore plc
By:	/s/John Burton
Name:	John Burton
Title:	Company Secretary