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.