EXHIBIT A

FILING AGREEMENT DATED TO BE EFFECTIVE JULY 8, 2013

REGARDING JOINT FILING OF SCHEDULE 13D/A-6

The undersigned hereby agree that:

(i)

Each is eligible to use the Schedule 13D attached hereto;

(ii)

The attached Schedule 13D is filed on behalf of each of the undersigned; and

(iii)

Each of the undersigned is responsible for the timely filing of such Schedule 13D and any amendments thereto, and for the completeness and accuracy of the information therein concerning itself; but none of them is responsible for the completeness and accuracy if the information concerning the other persons making the filing, unless it knows or has reason to believe that such information is inaccurate.

Sentient Global Resources Fund III, L.P.      By: Sentient GP III, LP, General Partner             By: Sentient Executive GP III, Limited,                                      General Partner By:  _____/s/ Greg Link______ Greg Link, Director Date: July 8, 2013 Sentient Executive GP III, Limited By:  ____/s/ Greg Link______       Greg Link, Director Date: July 8, 2013 Sentient GP III, LP By:  ___/s/ Greg Link______       Greg Link, Director Date: July 8, 2013

Sentient Executive GP IV, Limited By:  __/s/ Greg Link______       Greg Link, Director Date: July 8, 2013 Sentient GP IV, LP By:  __/s/ Greg Link______      Greg Link, Director Date: July 8, 2013 Sentient Global Resources Fund IV, LP     By: Sentient GP IV, LP               its General Partner          By:  Sentient Executive GP IV, Limited,               its General Partner By:  ___/s/ Greg Link______      Greg Link, Director Date: July 8, 2013

SGRF III Parallel I, L.P.      By: Sentient GP III, LP, General Partner             By: Sentient Executive GP III, Limited,                                      General Partner By:  ___/s/ Greg Link______             Greg Link, Director Date: July 8, 2013