RE: 100yrs ago up to 70g AU a tonne2 Apr 2021 11:27
10+ decades ago, they had very basic mining and extraction methods and hit 77g a tonne. With modern techniques you could achieve upwards of 50% greater recovery. I am no mining expert but over 100 yrs ago surely levels of AU within rock that were not visible to the naked eye would have been completely missed and unrecoverable as they did not have the ability to crush, refine and extract that we do today.
These old timers were following very distinct and strong veins of gold through the rock, all other material was discarded to spoil heaps. It may have received some crush and washing but very rudimentary, certainly no where near what can be achieved with modern milling and heap, leach, gravity etc extraction methods