Silbermann, 39, will move to a newly created role as executive chairman and will retain his board seat.
Brent for August settlement dipped 0.8% to $117.05 a barrel on the ICE Futures Europe exchange.
Gold was at $1 820.88 an ounce.
Brockman, 81, is suffering from dementia and undergoing home hospice care, according to his lawyers.