In Sept. 11, 2020, the Geological Society of South Africa offered a GSSA Lunchtime Talk by Mike O’Brien, P.Geo., and Matt Mullins, on the estimation of mineral resources in the historic Pering Zinc-Lead Mine in South Africa. Mike O’Brien developed an updated model of the mineral deposits of this former producing mine using Leapfrog Geo 3D. The Pering Deposit was mined between 1986 and 2003, producing 468 ktons of zinc in concentrate, and 85 ktons of lead in concentrate, from milling of 20.5 Mt of ore at an average head grade of 2.6 % zinc and 0.6 % lead. The Pering deposit was closed by BHP in 2003 as a result of low metal prices and was subsequently sold to Minéro Zinc in 2008. The remaining mineral resources were estimated at closure, in 2010, and again in 2020. This talk describes the modelling of the remaining resources in 2020.
“Key points are to use all available information: exploration, grade control, historical production, etc., to provide some form of reconciliation. On any estimation that is done a key element is integrating all that information together and experimenting with different conformations and architectures to figure out what is the most plausible and most likely, and optimize it to an extent, and ultimately to produce a holistic model that is going to be fit for purpose.”Mike O’Brien, P.Geo., Director, Red Pennant Geoscience
The technical talk can be viewed on YouTube, but to appreciate the contents, the speakers’ comments have been transcribed in the attached pdf document:
“Old properties can be resurrected and brought back to life, given the right economic conditions and certainly also given the right institutional memory in the form of data – data that’s allowed to survive in a comprehensive and copious form where people are able to remodel it after a long period of time, and also given the expertise people like Jeff Leader who are still available for us to use to better define a mineral resource and a deposit.”Mike O’Brien, P.Geo., Director, Red Pennant Geoscience
The Mississippi-Valley type Pering zinc-lead deposit is situated on the Ghaap Plateau in the Northern Cape, South Africa. It was mined between 1986 and 2003, producing 468 ktons of zinc in concentrate, and 85 ktons of lead in concentrate, from milling of 20.5 Mt of ore at an average head grade of 2.6 % zinc and 0.6 % lead. The remaining Mineral Resources were estimated at closure, in 2010, and again in 2020. This talk describes the 2020 modelling of the remaining resources.
“We did multiple pit optimizations based on different size of throughput, so anything from 1.2 to 3.6 million tons per year.Matt Mullins, Competent Person, Director, Tacoma Strategies
We changed the mining costs, the processing costs, the total costs. We changed the recoveries and we changed the revenues to determine the robustness of the pit optimization process.
In all cases we achieved positive NPVs [Net Present Values].
The NPVs were pretty healthy and considerable and we certainly had no concerns about the resource’s eventual economic extraction and to declare a reserve as well.”