EXHIBIT 99.1

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that this Amendment No. 24 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: April 7, 2020

Glencore AG
By:	/s/ Stephan Huber
Name:	Stephan Huber
Title:	Officer
By:	/s/ Martin Häring
Name:	Martin Häring
Title:	Director

Glencore International AG
By:	/s/ John Burton
Name:	John Burton
Title:	Director
By:	/s/ Peter Friedli
Name:	Peter Friedli
Title:	Officer

Glencore plc
By:	/s/ John Burton
Name:	John Burton
Title:	Director
By:	/s/ Peter Friedli
Name:	Peter Friedli
Title:	Officer