Difficult Metallurgy and Similar Projects Polymet Mining has a good site and quite a few technical papers on the low grade Northmet project, interesting reading.
Western Minerals Technology
The Application of Activox® to Nickel - Cobalt - Copper Concentrates
https://www.wmt.com.au/activox-nicocu.html
LionOre Mining
Selkirk Mine
The Selkirk deposit is a shallow plunging zone of massive sulphide mineralization. It is approximately 200 meters long, 100 meters wide and up to 25 meters thick; and has a “U” shaped cross-section. The orebody plunges to the southwest and is dissected through the center by north-west striking vertical dyke. The depth of the bottom of the known massive sulphide orebody is 150 meters below surface. While the bulk of the orebody comprises massive sulphide, it is surrounded by a halo of disseminated sulphide nickel mineralization of varying thickness.
The massive sulphide orebody has a very consistent grade of between 2.6% and 2.7% nickel and 1.6% copper. The surrounding disseminated mineralization averages less than 1% nickel. Mineralogically, the massive sulphides comprise approximately 77% pyrrhotite, 10% pentlandite, 10% magnetite and 3% chalcopyrite, making them difficult to upgrade. However, the Selkirk in-situ massive sulphide is of sufficiently high grade to feed directly into the BCL smelter. Consequently, the massive sulphide orebody is being completely mined out from hangingwall to footwall, leaving sufficient pillar support to ensure safe working conditions.
Ground based geophysical surveys combined with in-hole geophysical probing of previous surface diamond drill holes was completed in 1997. The objective was to determine the potential for further massive sulphide mineralization down plunge of the current massive sulphide orebody. No massive sulphide continuity was evident but the area is still considered prospective and indicates that there is an anomaly containing lenses, pods and stringers of mineralization. The anomaly will continue to be investigated. The current orebody is surrounded by approximately 5 million tonnes of disseminated ore which also extends down plunge. The viability of mining this material, particularly if a concentrator is established at Phoenix, needs to be investigated.
Mining at a rate of approximately 60,000 tonnes per annum results in a remaining four year mine life. There are currently 248,000 tonnes of ore in the proven and probable reserve categry.
Rock mechanics modeling is taking place to investigate the potential for partial extraction of approximately 100,000 tonnes left as pillars once the mining of the massive sulphide orebody is
Phoenix Mine
The deposit, located 15 kilometers north of Selkirk, comprises a series of semi-parallel, near vertical discontinuous massive sulphide lenses and veins. This can obtain up to 8% nickel surrounded by disseminated ore and also low grade zones within which grades average less than 0.4% nickel. Mineralogically, the sulphides comprise over 70% pyrrhotite, 20% pentlandite and 7% pyrite. In 1992, a trial pit operation, together with an innovative dry magnetic treatment plant confirmed that the Phoenix orebody could be viably developed into an operational mine. The feasibility study identified a resource of 43 million tonnes grading 0.40% nickel and 0.26% copper. Geophysical exploration in 1997 identified three areas of potential mineralization for detailed follow-up exploration. Exploration drilling has completed 17 of 29 scheduled holes. The intersections have confirmed a similar style and tenor of mineralization to that found within the existing mineralized resource. Resource information was updated increasing the original estimated mineable reserve from 15.2 million to 19.6 million tonnes, of which 18.2 million tonnes remained at the end of December 1997 inventory. The present planned remaining mine life is approximately 12 years. However, there is excellent potential for additional ore reserves at Phoenix. The magnetic separation plant will be expanded during 1998 to increase annual Phoenix concentrate production to 120,000 tonnes. Ongoing metallurgical testwork is encouraging and indicates that an on-site concentrator, could increase recovery of nickel and copper from feed, to warrant project justification. Grid power and a tar road between Francistown and Selkirk as well as Phoenix will be established in 1998. The Botswana Government is currently investigating the establishment of an untreated water supply between the Shashe dam and Phoenix. The official published ore reserves will be reassessed and updated during 1998. The table below does not include results from the 1997 and current exploration drilling program.
Polymet Mining –Northmet Project
HYDROMETALLURGICAL PROCESS DEVELOPMENT AT POLYMET MINING CORPORATION'S NORTHMET PROJECT
https://www.polymetmining.com/press_releases/technical%20papers3_13_00.html
NorthMet Project Pre-Feasibility Study Completed
https://www.polymetmining.com/press_releases/press_releases07_20_01.html