Yep, in this case Saprolite is the same as Oxide. The statement above can be broken down into the following:
'Resource Estimate of 18.5Mt @ 1.1g/t Au (674,300 oz) using a 0.5g/t Au cut-off grade'.
This means that they have taken all the blocks greater than 0.5 g/t in the block model (a 3d model that is used to calculate tonnages and grades of gold deposits) and have calculated the total tonnage of those blocks and the average grade of those blocks.
'within a conceptual A$1,600/oz Au optimal pit shell'
A 'pit shell' is a rough design of an open pit that is produced to constrain mineral resources at depth. These shells are automatically produced using mining parameters and factors and a specific gold price (in this case $1600). This is a requirement by the reporting code (JORC) to ensure that companies do not report mineral resources that are not exploitable. This 'pit shell' is basically the boundary where it becomes uneconomical to mine material below (too much waste material compared to ore material). Therefore, only mineral resources above this open pit design are reported (all blocks below are ignored).
Hope that helps! Any more questions, dont hesitate to ask.
