EXHIBIT 99.1

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that this Amendment No. 23 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.

Date: June 19, 2020

Glencore AG
By:	/s/ Stephan Huber
Name:	Stephan Huber
Title:	Director
By:	/s/ Martin Haering
Name:	Martin Haering
Title:	Director
Glencore International AG
By:	/s/ Martin Haering
Name:	Martin Haering
Title:	Officer
By:	/s/ John Burton
Name:	John Burton
Title:	Director
Glencore plc
By:	/s/ Ivan Glasenberg
Name:	Ivan Glasenberg
Title:	CEO
By:	/s/ John Burton
Name:	John Burton
Title:	Company Secretary