K&K most economical underground mining methodFirst , a quick powerpoint refresher on underground mining scenarios with relative costs.
https://www.edrsilver.com/_resources/UG-OTR061212-RWS.pdf
Since the Kansoko and Kakula resources are relatively flat-lying (average dip between 13 to 16 degrees) and wide (kakula indicated resource is up to 2 km wide in places), they lend themselves to the most economical form of underground mining, which is room and pillar.
Room and pillar mining has a high resource recovery rate (around 90% of the resource is recovered) and allows for a lower grade cutoff. As a guess, I think we will see a resource cutoff of about 1.4% Cu as that non-round number has been presented as a specific scenario by Ivanhoe in the past. There obviously is some significance to that number and I'm guessing it is from a preliminary run through of a model.