The Ozango Project lies to the west of the city of Huambo in central western Angola and covers a vast landholding of 3670 square kilometres. Infrastructure is very good, with the national highway running through the northern portions of the concession. This is paralleled by a railway that runs to the deep water Atlantic port of Lobito some 250 kilometres to the west. A recently completed hydroelectric power plant currently has its power running to the coast along the same route. The city of Huambo is 70 kilometres away with all of the usual amenities, including an international airport.
The Ozango Project is 70% owned by Rift Valley Resources in a local subsidiary. The other 30% is owned 10 % by Ferrangol P & P SA as a strategic government partner and 20% by Angolan investors.
The geology of the project area comprises Archean greenstone and Paleoproterozoic granites with Cenozoic carbonatite and kimberlites. Gold, copper, rare earths, phosphate, manganese, tungsten and uranium have all been identified at surface, within the project area. The most advanced prospects with the concession are the Catabola copper/gold prospect, the Longonjo rare earths Prospect and the Bongo gold prospect.
Ozango Project Location Map
The Bongo prospect, within the eastern reaches of the Ozango Project, straddles a set of parallel fault zones hosted in the Paleoproterzoic metasediments and has gold mineralization identified in soils, rock chipping and stream sediment sampling. Satellite imagery has mapped the fault structures. Panned concentrates have returned visible gold from streams along the 10 kilometres of strike length.
Bongo Sheer Zone looking to the South West
ABOUT THE CATABOLA COPPER/GOLD PROSPECT
The Catabola prospect covers an approximate area of 180 square kilometres, comprising numerous copper-gold (plus iron and uranium) prospects. Four distinct target areas have been delineated to date: Cassenha Hill, Cambumbula, Caluvi Hill and Cativa. These targets are located along a contact between Paleoproterozoic granite and metasedimentary rocks. Quartzite hosted-hosted iron oxide, copper, gold mineralization has been identified across the target areas in soils and in trenching and in oxide material from adits at Cassenha Hill
The Project area consists of Archaean/Palaeoproterozoic greenstone rocks that have been intruded by Cretaceous felsic volcanics, carbonatites and kimberlites. These rocks are considered highly prospective for REE, phosphate, copper, iron ore and gold. To date, however, this area has seen very little modern exploration.
The Catabola copper-gold target comprises an area of approximately 180km2 with two separately identified mineralized structures both trending northwest to southeast, approximately 5 kilometers apart (figure 1)
- Zone 1 – Cassenha Hill Copper-Gold Prospect: Centered on historic small scale copper mining at Cassenha Hill.
- Zone 2 – Cambumbula Iron Prospect: A recently discovered major zone of iron rich altered metasediment with associated weakly anomalous copper-gold values.
FIGURE 1 – CATABOLA COPPER/GOLD TARGET AREA
CASSENHA HILL COPPER-GOLD PROSPECT
During late 2015 and early 2016 the Company completed site works (drill pads and access roads/tracks) and a maiden diamond drilling programme at Cassenha Hill. The work included the rehabilitation of 12km’s of gravel road from the town of Catabola, made ready the Cassenha Hill camp and purchased consumables and equipment for the maiden drilling campaign. Details and results from the drilling campaign are available for viewing in the “Investors” section on the company’s web page under “ASX Announcements”.
FIGURE 2 – CASSENHA HILL COPPER/GOLD PROSPECT
FIGURE 3 – DRILL HOLE LOCATION PLAN
FIGURE 4 – DRILL SECTION – LOOKING NORTH WEST
Copper workings at Cassenha Hill in the 1940s and 1950s included 7 shafts and some 29 adits extending over a length of 1.6 kilometers. The copper mineralisation is hosted by siliceous metasediments and occurs in brecciated and gossanous quartz-magnetite-barite veins in a major, steeply dipping and strongly altered/weathered shear zone. The zone has been traced by surface mapping and prospecting over a strike length of some 5 kilometers but may well be considerably longer.
The separate Caluvi Hill and Cativa prospects located northwest and southeast of the Cassenha Hill zone respectively may well be one and the same giving an approximately 14 kilometer long potential strike length of prospective ground. The Cassenha Hill shear structure has been described by SRK Consulting (2010) as a broad zone up to 150 meters wide within which individual copper bearing veins, typically 10-30 meters wide and several hundred meters long, occur in an enechelon pattern. Previous exploration work conducted at the Cassenha Hill prospect includes regional rock chip sampling, soil and stream sediment sampling, surface trenching and underground adit channel sampling.
Competent Person Statement
The exploration results contained within is based on and fairly represents information compiled by Mr Greg Cunnold who is a member of the Australian Institute of Mining and Metallurgy. Mr Cunnold is a director of Rift Valley Resources Ltd and has consented in writing to the inclusion in this ASX Release of matter based on the information so compiled by him in the form and context in which it appears. Mr Cunnold has sufficient experience relevant to the style of mineralisation and type of deposit under consideration to be qualified as a Competent Person as defined by the 2012 Edition of the “Australian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves”.
About the Longonjo Magnet Metal Prospect
The Longonjo prospect is located within the Ozango Project area 50km west of the regional city of Huambo. It is located proximal to good infrastructure including roads, towns and recently recommissioned railway infrastructure which links to the deep water Atlantic port of Lobito.
The geology is typical of REE mines and prospects globally including Lynas Corp’s Mt Weld deposit in Western Australia, Peak Resources’ Ngualla deposit in Tanzania and similar to Arfura’s Nolans Bore Project.
Figure 2 Carbonatite Vent – National Highway to Port (319km)
Metallurgical Drilling and Trenching
A soil geochemical sampling program undertaken at Longonjo over an area of 6km2 and defined a large robust 3.5km long and 1.7km wide +0.5% REO geochemical anomaly which remains open to the west. A follow up trenching and pitting program carried out to test the bedrock within the soil anomaly returned highly encouraging results of up to 18.9% TREO from the pit bedrock samples.
First pass exploratory drilling conducted at the Company’s Longonjo prospect in 2014 (see ASX announcement “Initial Metallurgical Results from Longonjo Prospect – 7th May 2014”) tested the centre of the geochemical anomaly and returned high grade rare earth assays from every hole. From a total of 168 composite samples generated during the campaign, the highest grade returned was 11.32%, the lowest 0.45%, with an average of 2.96% TREO over all the samples.
The distribution of the high value neodymium and praseodymium rare earths in the mineralization was found to be substantial, accounting for more than 75% of the in-situ value as shown graphically in Figure 3.
Figure 3 – In-Situ Value Distribution
(Source: Metals Pages – 16th November 2016)
Neodymium and Praseodymium metals are essential for the production of high strength permanent magnets. They are used in wind turbines, MRI machines, electric motors, drones, mobile phones, computers and many more technology and industry applications.
Following on from these encouraging results, a surface trench sampling program (see Figure 4) was undertaken to provide a suitable sample for metallurgical testwork. The program provided a composite of approximately 58kg sampled from 4 to 6 metres in depth (below the top soil) along an 80 metre long trench. Analysis of the homogenised trench sample returned a grade of 6.47% REO. Mineralogical examination confirmed the rare earths to be primarily hosted within monazite.
Figure 4: Trenching at Longonjo
The company engaged Specialist Metallurgical Consultant, Mr Gavin Beer, to interpret previous metallurgical testwork and undertake a Metallurgical Desktop Study.
The study encompassed:
- Interpretation of the previous testwork undertaken.
- Development and recommendation of a process flowsheet.
- Develop a preliminary mass and energy balance.
- Development of the preliminary equipment list.
- Determine major equipment required.
Beneficiation testwork was undertaken on the trench composite sample (see ASX announcement “Metallurgical Testwork Update Longonjo Prospect – 27th August 2015”) and successfully demonstrated that the mineralization can be physically upgraded producing concentrate grades of up to 19.4% REO.
A beneficiation process (Figure 5) was subsequently developed that incorporating the following stages:
- Crushing and grinding.
Figure 5: Block flow diagram of the tested beneficiation flowsheet
Hydrometallurgical testwork was undertaken on a composite flotation concentrate evaluating various extraction routes. As the rare earths are largely associated with refractory monazite minerals, a “cracking” process is required in order to extract the rare earths. Two cracking processes were tested:
- A sulphuric acid bake at elevated temperatures followed by water leaching.
- A caustic conversion using hot caustic soda followed by hydrochloric acid leaching.
The results are summarised in Table 1 with respect to the dissolution, or “recovery”, of key rare earths and gangue elements to the leach solution.
Table 1: Acid Bake and Caustic Conversion Results
|Acid Bake Route||83.7||77.5||89.1||89.0||14.7||45.0||39.5|
|Caustic Conversion Route||64.1||27.5||90.1||90.0||76.4||70.2||56.8|
The acid bake route was selected for the following reasons:
- Achieved good dissolution of the high value Nd and Pr rare earths
- Lower dissolution of gangue metals such as iron, thorium and uranium
- Lower reagent consumption
- Simple and proven flowsheet that has been demonstrated commercially. The simplified hydrometallurgical route is shown in Figure 6.
Figure 6: Block flow diagram of the recommended hydrometallurgical flowsheet
(tested stages shaded)
The overall recommended flowsheet is shown pictorially in Figure 7
The proposed final product is a mixed rare earth carbonate that will be sold or toll treated at a third party refinery. There is also the potential to create greater revenue should the company decide to build an extraction facility to produce separated rare earth oxides on the back of the proposed hydrometallurgical plant.
Figure 7 – Overall Flow sheet
The Desktop Study referred to in this report is based on high level technical and economic assessments, and is insufficient to support estimation and economic assessments, and is insufficient to support estimation of Ore Reserves or to provide assurance of an economic development case at this stage, or to provide certainty that the conclusion of the study will be realised.
Competent Person Statement
The exploration results contained within this ASX Release is based on and fairly represents information compiled by Mr Greg Cunnold who is a member of the Australian Institute of Mining and Metallurgy. Mr Cunnold is a director of Rift Valley Resources Ltd and has consented in writing to the inclusion in this ASX Release of matter based on the information so compiled by him in the form and context in which it appears. Mr Cunnold has sufficient experience relevant to the style of mineralisation and type of deposit under consideration to be qualified as a Competent Person as defined by the 2012 Edition of the “Australian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves”.
The information also relates to Metallurgical Test-work is based on and fairly represents information compiled and / or reviewed by Mr Gavin Beer who is a Member of The Australasian Institute of Mining and Metallurgy and a Chartered Professional. Mr Beer is a Consulting Metallurgist and a full-time employee of Met-Chem Consulting Pty Ltd. Mr Beer has sufficient experience relevant to the activity which he is undertaking to be recognised as competent to compile and report such information. Mr Beer consents to the inclusion in the report of the matters based on his information in the form and context in which it appears.