Hi Hotrod, My understanding of the reefs is that generally all the gold is housed in the top 20cm or so of the quartz vein right next to the dyke irrelevant of the thickness of the vein. To mine it to minimise dilution, maximise recovery and minimise cost each reef has its own method based mainly on the angle from horizontal thus whether the broken vein rock from blasting will self roll down or needs mechanical assistance.
But generally there are 2 scenarios in any reef (whether at A1 or MS or RoD) being either below 45 degrees or above. Obviously anything above 45 will generally roll down under gravity. Those reefs that are 30deg or lower (most rock breaks at 30 and 60 degrees and the dykes broke across themselves and sit vertically) can be mined as follows:
Imagine the reef as a table top sitting at 30deg from horizontal. Develop a main drive along the lower long side (low to no grade) big enough for rail and services like air. Off that at 10m centres develop drives in the vein at an apparent dip up within the table and about 3 of them to the edge of the table top. Join them at the end of the fingers. This finger raise development is in higher grade.
the connection between the finger raises is only the thickness of the vein. It is drilled and blasted and scraped down in slices retreating back down the fingers. If the vein is 1m thick it is removed at 1.2m thick. If it’s half a m thick then only 0.7 m is extracted etc. so this grade is high.
So, irrelevant of vein thickness or angle, it’s down to grade and dilution and tonnes per shift cost.
So just saying one vein or another is economic or uneconomic is too uneducated an approach.
Each vein might or might not be economic.
