It means that for every tonne of dirt you dig up you will reduce...

It means that for every tonne of dirt you dig up you will reduce the overall mass of material that is sent to the next stage of the process and achieve dirt with a high concentration of metal as per the values stated. The next stage of the process is typically called a smelter and they work best with low amounts of mass, like minerals that are self heat generating so you don't need to put energy into the process with low level of contaiminents. The PGM/PGE typically are recovered as a side stream if in high enough concentration because of the value of these materials $2000/oz means $2000 per every 31.1035g of metal of that species that you find is what it is valued at but as it isn't a pure PGM/PGE mine you will get credit for these materials when you sell it to a smelter. Typically they pay for the TC/TR which are the Treatment charges and Refining charges a smelter charges to process the material through their facility.