Overview
Stage | Preliminary Economic Assessment |
Mine Type | Open Pit |
Commodities |
|
Mining Method |
|
Processing |
- Electric furnace
- Dewatering
- Vacuum filtration
- Filter press plant
- Spiral concentrator / separator
- Flotation
|
Mine Life | 19 years (as of Jan 1, 2021) |
The PEA utilizes one out of four deposits currently owned by Woxna under granted exploitation concessions, where two of the other deposits also have indicated and inferred mineral resource estimates offering potential upside for further expansion in future development or studies.
The Kringel deposit has already been developed as an existing mine with a partially exploited open pit and is the only deposit used as a basis for the Project in the PEA. A modernized processing plant, tailings storage facility (TSF), office and workshop buildings exist adjacent to the Kringel resource, are fully connected with power and water services, and are currently under care and maintenance. |
Latest News | Leading Edge Materials Announces Filing of Preliminary Economic Assessment Report for Woxna Graphite Anode Project July 26, 2021 |
Source:
p. 19
The ‘Woxna Graphite Project’ is owned by Woxna Graphite AB a 100% owned Swedish subsidiary of international Leading Edge Material Corp.
Deposit Type
- Metamorphic
- Contact-metasomatic
- Hydrothermal
Summary:
The Woxna Graphite Project comprises four exploitation concessions (146.71 ha) over the Kringelgruvan (Kringel), Gropabo, Mattsmyra and Mansberg graphite deposits.
The local geology for all four of the Woxna Graphite deposits has been reported in this technical document in support of the re-estimation of the Woxna Graphite Mineral Resources in totality. However, for the purposes of the PEA, the Kringel graphite deposit local geology is summarised as follows:
• the mineralisation is hosted by a sequence of steeply dipping metasedimentary and metavolcanic units metamorphosed to sillimanite grade and intruded by igneous units ranging from alkali pegmatite to granite;
• the local geology within the exploitation area is dominated by steeply-dipping, calcareous quartz-rich meta-tuff, with interbedded metasedimentary units and cross-cutting pegmatite;
• trace to massive graphite mineralisation in two discrete tabular zones is developed in association with pegmatitic intrusions;
• the mineralisation is tabular in shape, and occurs late in the structural history, postdating and crosscutting any remnant tectonised and metamorphosed lithologies;
• the graphite is considered hydrothermal/metasomatic in nature; and
• the Kringel deposit area has variable cover of 2 m to 15 m of Quaternary age glacial moraine.
Mineralisation - Kringel
Generally, graphite is developed as an accessory mineral as laminated aggregates dispersed through schistose and siliceous metamorphic rocks.
The genesis of graphite mineralisation identified and historically exploited at the Woxna Graphite Project area is predominantly considered hydrothermal and/or metasomatic. The mineralisation is associated with pegmatite intrusions that are interpreted to be the heat and metasomatising fluid source during contact metamorphism of the PaleoProterozoic age host meta-argillites and meta-tuffites (Claesson et al., 1988; Claesson et al., 1989a; Claesson et al., 1989b).
The nature of the graphite mineralisation at Kringel is summarised below:
• the Kringel mineralisation was intersected on all the drilling sections suggestive of continuous mineralisation over the concession area;
• the mineralisation is tabular and conformable with steeply dipping host metasediments and metavolcanics;
• the mineralisation is known to extend to at least a depth of 150 m below the surface; • the mineralisation strikes eastwest (E-W), and dip varies between 60 °and 80° to the south;
• grade distribution varies both laterally and vertically;
• based on grade distribution six main higher grade Type A zones have been identified with a cut-off grade of 7% Cg;
• outer, lower grade Type B domains (<7% Cg cut-off grade) were identified within which 11 small mineralised envelopes/bodies exist;
• faulting of the orebodies is apparent;
• the mineralised envelopes/bodies vary in width 5 m to 15 m (averaging 10 m);
• coarse, medium and fine-grained graphite is developed as blebs in monomineralic zones . Parts of the mineralised zone contain wispy pyrrhotite (FeS2). The combination of both graphite and pyrrhotite is the cause of the strong geophysical response to ground electromagnetic techniques applied during early exploration;
It is the opinion of the Reedleyton that the nature and genesis of the mineralisation at all 4 deposits is adequately understood and that the exploration programmes conducted were appropriate to the style of the deposit (with the addition of the geophysical data) and the genetic geological model. The exploration programme has proved successful and can be adapted to other graphite deposits in the region.
The overburden is composed of Quaternary aged glacial moraine ranging in thickness from 0.5 m to 20 m over Kringel area with an average thickness of 3.5 m.
Mineralisation - Mattsmyra
At Mattsmyra, Graphite mineralisation occurs in prehnite-bearing meta-tuffs, garnetiferous meta-argillites and pegmatitic gneiss in at least three discontinuous, stratiform graphite-pyrrhotite horizons. Three types of mineralisation have been distinguished:
• Medium- to coarse-grained, with most grains and aggregates 0.7–1.5 mm in length;
• Fine-grained with pyrrhotite; most grains are <0.5 mm in length;
• Very fine-grained impregnations associated with magnetite; most grains are <0.3 mm in length.
Mineralisation – Gropabo
At Gropabo, Graphite mineralisation is present in two discrete zones and is developed over 480 m of strike length and varies up to 100 m in width. The graphitic horizons are separated by argillic metasedimentary units and pegmatite intrusions. The grade of the mineralised horizons is strongly dependent on the degree of pegmatite intrusion. Some of the pegmatites contain graphite, but not in economic quantities.
Mineralisation - Mansberg
At Mansberg, Graphite mineralisation occurs in migmatised metasedimentary rocks containing feldspar porphyrobalsts and pegmatitic schlieren. Ill-defined banding of phlogopite-, quartz- and graphite-rich layers may be present. The mineralised zone is interpreted to dip about 60ºSW (Claesson, 1992). The graphite is relatively coarse-grained along shears, but is generally medium- to coarse-grained flake (typically 0.3-0.6 mm in length, but up to 2.5 mm) and intergrown with silicates including prehnite; it may be associated with variable amounts of magnetite, pyrrhotite, pyrite, chalcopyrite and galena.
Summary:
The mine design, scheduling and costing for the Woxna Mine was undertaken by independent mining specialist MPlan. The selection of the most appropriate and cost effective method of mining was based on both historical information, the characteristics of the mineralisation and testwork results. A Basis of Design (BoD) was prepared which provides an effective tool to clearly present the 2021 decisions, assumptions and specifications that were used to develop the mining scenario for Kringel deposit at the Woxna Mine.
The Kringel deposit geometry combined with a relatively flat topography favours surface mining methods which was the historical method of mineralisation extraction. Different mining methods were considered, and two approaches were used to rank the mining methods and to evaluate their technical feasibility and relevance, namely the University of British Columbia (UBC) method and the Nicholas method. The top-ranking method proved to be surface mining at the planned mining production rate objective of 160 kt RoM per annum delivered to the primary crusher or RoM pad stockpiles. The reference point at which RoM is defined is at the point where the RoM is delivered to the Woxna Concentrator, i.e. primary crusher or RoM pad stockpiles.
The life of mine (LoM) is 15-years, and the life of project (LoP) is 19-years with the Woxna Concentrator feed from stockpiles in the last few years. A RoM graphite grade of 10.2% C on average over the first 15-years of production is planned. During that time, Type B mineralised rock will be stockpiled in order to be processed during the final years of the LoP. In total the LoP production plan will generate approximately 258,152 MtC in concentrate.
The stripping ratios vary throughout the scheduled LoM and range from 7.84 in Year 1 reducing gradually to 1.52 in Year 15.
A slope design safety analysis was undertaken to determine an optimal slope that will achieve the best safety factor as well as ensuring the best mineralisation mining recovery, and financial return in the context of maximising graphite production. The pit slopes will incorporate single benches with face height to a maximum 10 m in the waste for a safe mining operation. The graphite mineralisation benches height will depend on the morphology of the mineralisation domains and will have a maximum height of 5 m, in accordance with the size of the excavator selected for mining. Overall slope angles achieved for the Woxna Mine open-pits will be flatter than the maximum inter-ramp angle listed, due to the inclusion of access ramps and safety berms.
Overall open-pit design parameters:
- Maximum bench height in overburden - 10 m;
- Maximum bench height in graphite - 5 m;
- Face angle - 80 degrees;
- Berm width - 5 m;
- Ramp width - 15 m;
- Ramp gradient - 10%;
- Final slope angle - 62 degrees;
- Minimum mining width - 40 m.
The mine will have in average 350 work-days annually. The mining workforce will work on 8-hour shifts, with two shifts per day, seven days per week and three rotating crews working for continuous coverage.
The RoM will be extracted from the open-pit within the Kringel exploitation concession. All beneficiation and administration infrastructure are located northwest of the concession area for which surface rights permission has been secured. The mine maintenance area is located near the concentrator offices on the access road to the mine site. The explosive storage is located north of this access road within prescribed safety distances.
The mine plan begins with the mining of the east pit at a relatively high stripping ratio of 7.84 waste tonnes for each tonne of mill feed to give access to 160 kt of Type A graphite in year one. The mine plan is designed to provide 160 kt of high-grade mill feed to the mill every year until it runs out in the 16th year after which the lower grade Type B graphite that is stockpiled over the first 15-years is then fed into the mill. The production plan for the process plant continues until year 19 when the low-grade mill feed from the stockpile is exhausted.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
|
|
1
|
Cone crusher
|
|
|
|
1
|
Rod mill
|
|
2.7m x 3.75m
|
360 kW
|
1
|
Vertical mill / Tower
|
|
|
|
10
|
Jet mill
|
|
|
|
1
|
Summary:
The primary crushing was previously carried out by a mining contractor and secondary by another contractor. It is proposed that Woxna Graphite own and operate the crushing plant.
The design is based on crushing test-work by Metso in 2012. Metso reported that the sample is abrasive, but the crushability is easy. The product from this plant is 80% passing 6.35 mm to maximise the throughput of the rod mill. The crusher operates for one shift per day and feeds onto a stockpile. The RoM material is fed into the RoM bin directly by a mine haulage truck or from the RoM stockpile by a frontend loader.
The RoM material has a top size of 400 mm and is screened by a vibrating grizzly to remove minus 50 mm fraction. The oversize is fed into a jaw crusher where it is crushed to minus 50 mm. The grizzly undersize and jaw crushed products are transferred by conveyor to a triple deck vibrating screen where it is screened at 8 mm. The oversize is conveyed to a bin and then fed by vibrating feeder to a cone crusher. The crushed product is recycled back to the screen. The screen undersize, with 80% passing 6.35 mm, is transferred by conveyor to a stockpile adjacent to the crushing plant. The crushed product is reclaimed by a vibrating feeder and conveyed to the rod mill at a controlled rate.
The milling circuit consists of a rod mill in closed circuit with a spiral classifier. The crushed material from the stockpile is fed onto the rod mill feed conveyor by a variable speed vibrating feeder at a controlled rate of 21 tph. The mass flow is measured by a weightometer on the conveyor belt which controls the feed rate.
Rod milling is used to minimise overgrinding of the graphite. The mill is 2.7 m diameter and 3.75 m long, with a 360 kW motor. The mill discharge is screened by a trommel with the oversize being collected in a scats-bunker for recycling to the mill feed on a batch basis. The mill discharge is diluted and pumped to the screw classifier where to coarse sands, are returned to the rod mill for regrinding and the overflow, the fines, are transferred to the rougher flotation feed tank. The milling circuit produces 80% passing 275 µm.
Water is added to the mill feed to produce a slurry density in the mill of 80% solids.
Jet mill
A by-product of VAP is fine graphite which is micronized in a jet mill.
Processing
- Electric furnace
- Dewatering
- Vacuum filtration
- Filter press plant
- Spiral concentrator / separator
- Flotation
Flow Sheet:
Summary:
The basis for the design of the Woxna Concentrator and associated VAP (process design) is the beneficiation of:
• 160,000 tpa of RoM with a grade of approximately 9.2% C by flotation to produce-
• an average of approximately 14,730 tpa of graphite concentrate, grading 92.3% C at the Woxna Concentrator on the mine site, which is then-,
fed to the VAP which will produce an average of approximately 6,604 tpa battery grade Coated Spherical Purified Graphite (CSPG) at 99.95% C and an average of approximately 7,479 tpa micronized (by jet mill) graphite at a grade of 93% C.
The Woxna Concentrator product will undergo several beneficiation stages through the VAP to result in the final CSPG. Sequentially these stages are spheronization to produce ‘curled’ flakes of graphite; followed by thermal purification and finally coating of the purified, spheronized flakes with additional carbon to produce graphite suitable for use in battery anodes.
The envi ........

Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Graphite
|
Recovery Rate, %
| 93.8 |
Graphite
|
Head Grade, %
| 9.2 |
Graphite
|
Concentrate Grade, %
| 92.3 |
Reserves at June 9, 2021:
The economic analysis in the PEA considers only one of the four graphite deposits held by Woxna Graphite, namely the Kringel deposit for which new Mineral Resource estimates have been disclosed.
4% Cg mill cut-off grade applied for reporting purposes constrained within the MPlan 2021 pitshell.
Category | Tonnage | Commodity | Grade |
Measured
|
0.96 Mt
|
Graphite
|
9.21 %
|
Indicated
|
1.65 Mt
|
Graphite
|
9.09 %
|
Measured & Indicated
|
2.61 Mt
|
Graphite
|
9.13 %
|
Inferred
|
0.39 Mt
|
Graphite
|
8.72 %
|
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