Wigu Hill, Tanzania
The Wigu Hill Rare Earth Element ("REE") Project is a light rare earth element deposit and a large carbonite complex with bastnaesite mineralization. The licence area covers 142km2. Initial grab samples yeilded results as high as 27.25% TREO. Montero released an initial NI 43-101 Inferred resource estimate of 3.3Mt at 2.6% LREO5 including 510K @ 4.4% LREO5 on 2 of 10 possible drill targets. Further exploration drilling to add to the current resource is underway. Click the title to download and view the NI-43-101 Report
Montero revised a portion of its initial NI 43-101 compliant Inferred Mineral Resource estimate of 3.3M tonnes at 2.6% LREO5 (Light Rare Earth Oxides) for the Tembo and Twiga Zones. The updated resource estimate is only for the Twiga Zone and is based on data from the initial 15 core boreholes (1,560m) used in the initial resource estimate and data from infill drilling of 17 boreholes at 25m intervals (986m) completed in 2012. The data used in the revised Twiga Zone overall resource has outlined a higher grade REE deposit for this zone on the south-eastern ridge of the Wigu Hill carbonatite complex. A total Inferred Mineral Resource of 1.9 M tonnes at a grade of 2.7% LREO5 has been estimated from the preliminary and infill drilling of 32 boreholes (2,546m) for the Twiga Zone to a depth of 50m. A sensitivity analysis at a cut-off grade of 3% LREO5 has shown that the Inferred Mineral Resource contains a higher-grade portion consisting of 0.47 M tonnes averaging 5.2% LREO5. The independent estimate was prepared by AMEC Earth & Environmental Services (UK) Limited (AMEC). See full news release.
The carbonatite complex has been know since the 1950s and sampled many times by various mining and scientific organisations. A summary is listed below:
- Early 1950 - discovery of the deposit by the geological survey
- 1957 - New Consolidated Goldfields examined the hill for rare earth
- 1973 - The area was explored by Molycorp Minerals
- 1987 - Tanzanian-Canadian Agrogeology project examined the area for phosphate potential
- 2000 - The area was examined by P.R. Siegfriend
- 2007 - BGR assessed the project on behalf of the Tanzanian government
- 2008 - Montero entered into an agreement with RSR in 2007
- 2009 - Reconnaisance sampling and mapping of the Wigu Hill complex commenced
- 2011 - Montero listed on the TSX.V in February and exploration commenced
The Wigu Hill Property is a large, REE enriched carbonatite with dolomitic vein system which cut into Precambrian gneisses. The deposit type would be best described as a high level, carbonatite hosted REE dike deposit. The principally coarse-grained carbonatite dikes largely contain dolomite, bastnaesite and quartz.
Mineralization is mainly concentrated in the carbonatite dykes although the surrounding country rocks appear to have low grade REE mineralization of unknown extent and grade. The REEs occur predominantly in the minerals bastnaesite, monazite and synchysite, although others such as parasite and goyazite have also been encountered. The carbonatite dykes that host the REE are typically 0.6-8.0m wide and can be traced intermittently over distances of over 700m. The deposit is a LREE dominated which is characteristic of most carbonatites. Sampling to date has revealed grades averaging over 7% total rare earth oxide (TREO), with individual samples up to 26.2% TREO.
Exploration to date has revealed the delineation of 2 defined shallow resource areas and at least 3 additional potential resource target areas that have seen geological mapping, trenching and drilling, namely: Twiga, Tembo, and Tumbili, Lower Nyati and Upper Nyati, respectively;
Resources defined at Twiga and Tembo Targets:
- Inferred Resource of 3.3 M tonnes at 2.6% TREO at the Twiga and Tembo targets (by AMEC, refer news releases September 12, 2011, October 24, 2011);
- Inferred Resource at the Twiga Target of 1.9 M tonnes at a grade of 2.7% LREO5 (Light Rare Earth Oxide) from the preliminary and infill drilling of 32 boreholes (2,546m). See news release.
- Inferred Mineral resource at the Twiga Target contains a higher-grade portion consisting of 0.47 M tonnes averaging 5.2% LREO5 to a depth of 50m and cut-off grade of 3% LREO5 (refer news release August 6, 2013). This was based on 32 core boreholes (2,546m) at 25m intervals. This outlined the potential for a small high-grade open pit mining operation within the larger resource (detailed in an independent technical review by Turgis Consulting).
Potential Resource Targets identified:
- Lower Nyati target - mapping, grab sampling (refer news release April 2, 2012, April 12, 2012), trenching and initial core drilling of 1030m at 100m intervals (refer news release April 10, 2012) at the Lower Nyati Target have identified a potential REE resource target of 20 million tonnes. A proposed core-drilling program of 20 infill and exploration drill holes (5,200m) was designed and access roads and drill pads constructed.
- Upper Nyati target - geological mapping and grab sampling have shown that the REE mineralisation on the Lower Nyati Target extends to the Upper Nyati target to the top of Wigu Hill.
- Tumbili target - mapping, trenching (1,190m) and drilling (1,525m) have identified a potential high grade REE resource target in the western portion of the Tumbili Target.
The Wigu Hill Rare Earth Project does not contain a mineral reserve and is not currently in production. Any decision to place the Wigu Hill Rare Earth Project into production requires the support of a feasibility study prepared in accordance with National Instrument 43-101. At this time the Company has completed a series of laboratory and pilot scale testwork, but this does not satisfy the requirements of a feasibility study. Accordingly, any decision to commence production on the Wigu Hill Rare Earth Project is neither imminent nor assured, and investors cannot assume that the Wigu Hill Rare Earth Project hosts an economic mine at this time.
Metallurgy, on Wigu Hill material
An update on the mineral processing and metallurgical testwork performed to date on the bastnaesite-rich carbonatite material from the Wigu Hill Rare Earth Project in Tanzania. In early 2010, Montero approached Mintek, an internationally recognized metallurgical research and testwork facility in Johannesburg, South Africa, to test the Wigu Hill carbonatite for recovery of Rare Earths. Mintek has over 25 years of experience working performing research and testwork developing economic process routes for various Rare Earth mineralizations.
Montero’s strategy is to become the first Rare Earth (“REE”) materials producer in Africa which required embarking on a series of early-stage metallurgical testwork on the mineralised carbonatite material from Wigu Hill. Early in 2010, the initial mapping of Wigu Hill demonstrated a potential for a significant REE mineralized system. The major challenge would be the mineral beneficiation, hydrometallurgy, and production of saleable rare earths. A research program to identify, test and determine the critical path to rare earth production was the justification for starting the testwork in parallel with such an early stage in the exploration program. In 2010, Montero established a team led by Mike Evans that worked with Mintek on an extensive literature research program to identify:
1) a minerals processing route to produce a bastnaesite mineral concentrate and 2) a hydrometallurgical process route for the production of saleable rare earth products.
Montero delivered the first representative bulk sample to the Mintek facility in Johannesburg on June 2010 followed by a second sample in July 2011. These unweathered, course grained bastnÃ¤site-rich samples were taken from trenches and pits in the Twiga and Tembo Zones where Montero has subsequently completed a NI 43-101 Inferred Resource Estimate (see news release dated 12/09/2011).
1) Preliminary Minerals Processing Testwork to produce a bastnaesite mineral concentrate
The basnasite-rich samples from Wigu Hill were initially sent for mineralogical analysis, crushed, assayed by element and chemical analysis, and then subjected to a mineral processing testwork program which included tests such as; screening, gravity separation, magnetic susceptibility, X-ray sorting, and flotation. The objective was to upgrade the run of mine (ROM) mineralized carbonatite material to a bastnÃ¤site-rich mineral concentrate. This mineral concentrate potentially could be sold “as is” to downstream REE processors, or alternatively, become a feed stock to a hydrometallurgical refinery designed to process this bastnÃ¤site concentrate into a variety of saleable rare earth chemical products. At present, this testwork program on mineral processing remains in progress.
2) Preliminary Hydrometallurgical Refinery Testwork to produce saleable Rare Earth chemicals
The detailed literature work enabled the team to develop a hydrometallurgical flowsheet with a two-stage Rare Earth Refinery recovery process;
- Stage 1 Refining – The leaching of the bastnäsite mineral concentrate from the mining and mineral processing plant followed by a precipitation stage to produce a Mixed Rare Earth Oxide (“MREO”) or chloride saleable product, and;
- Stage 2 Refining –The continued processing of the MREO concentrate solution and the extraction via Solvent Extraction (SX) and/or Ion Exchange (“IE”) technology to separate the individual REE’s.
To view a conceptual illustration of the flowsheet currently being evaluated click here
Stage 1 Refinery Testwork
Leaching tests were performed using a variety of leaching lixiviants. From this testwork program, it was determined that a leach process using hydrochloric acid (“HCl”) was the most efficient for the Wigu Hill bastnÃ¤site-rich material. Acid consuming gangue material is dissolved using hydrochloric acid in order to expose the bastnäsite-rich material. The residue is then leached with caustic soda to remove the silica and expose the rare earths minerals for subsequent dissolution in a further hydrochloric acid leach. Following the success of this initial test work program, a second stage program was completed, and more recently, a third stage of leaching tests is currently being performed to provide further optimization information for the leaching process. The third stage optimization tests will provide a definitive process route for the leaching of the Wigu Hill mineralized carbonatite.
The results to date are encouraging. In addition to optimizing the main leaching processes, the testwork program included detailed mineralogy of the residues from the various process stages. Testwork also evaluated the potential for recycling the spent hydrochloric acid and caustic soda reagent streams, modelling the process with SysCAD mass balance software. SysCAD was used to model the bulk leaches and the phases to produce a MREO saleable product. The final product of this process will also provide a feed solution for the Stage 2 Refining testwork.
Stage 2 Refinery Testwork
Montero and Mintek will embark on a testwork program that will commence in early 2013 to define the process route to take the MREO feedstock and produce individual, pure rare earth chemicals. On completion of this testwork program, the target is to complete a feasibility study for the Stage 2 Refinery and the upgrade of the Stage 1 Refinery to a larger production of REE chemicals.
The Stage 1 hydrometallurgical Refinery optimization testwork is targetted for completion by year end and presented by Mintek for evaluation by Montero. This will generate sufficient data to form the Design Basis for a Feasibility Study. The deliverables of this feasibility study will be a “Demonstration Plant” for a Leaching and Mixed Rare Earth Oxide (“MREO”) refinery facility targeting the production of 3,000-5,000 tpa of MREO chemical products for sale. The facility will also provide pregnant solution for solvent extraction testwork leading to the Feasibility Study of the Stage 2 Refinery that will target production of the individual rare earth chemicals for sale.
Montero has an expert metallurgical and hydrometallurgical team to undertake this work.