RE: Turquoise Hill3 May 2023 22:13
evi,
The article refers to "block caving" - a new technique making lower grade deposits economic (provided they are large enough to pay back the infrastructure costs):
'Oyu Tolgoi, which Rio forecasts will be the world’s fourth-largest copper mine when it is at full production, uses a complex method that allows access to deeper deposits called “block caving”, which involves digging under the ore body, blowing gaps underneath that allows the ore to collapse and fall down funnels to a lower level where it is collected, crushed, and sent to the surface on conveyor belts.
A cost-effective way of mining large deposits less rich than those of the past, its popularity is spreading, but the technique remains a challenge. Rio found early on that its ore collapsed all too well. Then there’s the hefty initial investment.'