I believe the quartz is found in only the fine to medium grained diorite that hosts the quartz veins that were believed to be emplaced by hydraulic fracturing. Thus measuring the volume of quartz in fine-grained diorite should give you an approximate volume for the mineralized envelope. My understanding is that the gold tends to cluster at the interface of the quartz/diorite boundaries explaining why the zones of massive quartz may contain much lower grades than the quartz-diorite zones.

Best,

Scott