Ann: JORC Resource Estimate , page-8

The grade may be lower than Lihir, but is metallurgical much cheaper and easier to treat. Lihir's ore is refractory and needs pressure autoclaves to heat up the sulphides and break them open to enable cyanide to contact the gold particles and dissolve them. Robust's gold and silver is free milling oxide deposit which is already broken open and will dissolve on contact with cyanide with simple mixing. Big difference to the development schedule and cost of development.