Summary:
The Prieska Deposit is a VMS-style deposit, with mineralisation defined along 2.4km of a northwest-southeast trending strike extent and down to a depth of 1.25km. Mineralisation of Cu, Zn, silver (Ag) and gold (Au) is in massive sulphides distributed as a persistent lens within gneiss rock assemblages.
The Copperton deposit is a Volcanogenic Massive Sulphide (VMS) deposit which is situated in the southernmost exposures of the north-northwest trending Kakamas Terrain, which forms part of the Mid-Proterozoic Namaqualand Metamorphic Complex.
The deposit is hosted by the Copperton Formation of the Areachap Group. The Areachap Group also hosts several other but smaller VMS deposits such as the Areachap, Boks Puts, Kantien Pan, Kielder, and Annex Vogelstruisbult deposits.
The structural sequence at the mine consists of a footwall Smouspan Gneiss Member, Prieska Copper Mines Assemblage (PCMA), which hosts the sulphide mineralisation, and the hangingwall Vogelstruisbult Gneiss Member.
The historically mined section of the deposit is confined to a tabular, stratabound horizon in the northern limb of a refolded recumbent synform, the axis of which plunges at approximately 5° to the south-east.
The mineralised zone outcrop has a strike of 2,400m, is oxidised and / or affected by leaching and supergene enrichment to a depth of approximately 100m.
The mineralised zone crops out as a well-developed gossan. It has a dip of between 55° and 80° to the northeast at surface and a strike of 130° to the north.
Recently drilling indicates that the Deep Sulphide Target has a strike length of at least 2,460m at depth.
The thickness of the mineralised zone exceeds 30m in places but averages between 7m and 9m. The mineralised zone persists to a depth of 1,100m (as deep as 1,228m in one section) after which it is upturned due to folding.
The Deep Sulphide Target area is located below the historically mined area. It comprises the steep down dip continuity ("steep limb and hinge zone”) from where it upturns to its subsequent synformal structure ("trough zone").
The morphology of the mineralised horizon in the eastern limb is well mapped out by drilling and historical mining while the western limb up dip extent is poorly tested and mapped.
The supergene sulphide zone of the +105 Block is the northernmost 1,000m portion of the total strike of the PCZM orebody. It is located from approximately 50m to 90m below surface between 1,020m and 980m AMSL. From 0 to 50m is the oxide resource portion of the +105 Block and the leach zone below this.
Trial mining on 99 Level has shown that the massive sulphide zone is composed of approximately 60% competent, albeit softer, altered equivalent of the hypogene sulphides. The remaining 40% is made up of friable soft granular supergene sulphide and clayey material. According to drilling and exposure in raise development, the proportion of supergene sulphide material increases rapidly above 99 Level.
The supergene sulphide zone in the trial mining area dips to the NE, at 40 to 55 degrees, and strike NW-SE. The mineralised zone varies in width from 1m to 8m.
Deep Sulphide
• The Deep Sulphide mineralisation is the depth extension of the stratabound, stratiform VMS Prieska Cu-Zn deposit and is hosted by the 3km thick Copperton Formation of the Areachap Group. The massive sulphide mineralisation is characterised by abundant rounded fragments of gangue material of various sizes contained in a matrix of sulphide minerals. The gangue includes fragments of both hangingwall and footwall material.
• No clear metal zonation is evident from the modelling. High Cu areas are generally not in the same place as the high Zn (with a few exceptions). • Geological data and conclusions reached were based on observations made in drill core from the Orion 2017 drilling and sampling program.
• Like many other VMS deposits, domaining for estimation is not possible using solely the geology, and the best method is therefore to utilise the assay data.
• There is a sharp decrease in the Zn and Cu grades on the boundary of the massive sulphide unit. For the construction of the wireframes, a Zn equivalent cut-off of 3.0% (Zn Eq = Zn% + (Cu%*2) for the mineralised zones was used. The Zn_Eq cut-off was used a guide for modelling rather than a strict threshold.
Dimensions
Within the Mining Right areas, the strike length of the mineralisation is 2,460m, its horizontal width varies from 410m to 870m and the down dip extent is 1,228m below shaft collar. The true thickness of the orebody varies between < 1m to 30m with an average of 7m.
+105m Level
The +105m Level resource model comprises six defined geological zones.
These are:
- Haematite-goethite-quartz oxide zone (gossan) from surface to approximately 33m;
- Clay (kaolinite)/leach zone developed in places below 33m;
- Chalcocite dominant supergene sulphide zone between approximately 42m and 70m;
- Mixed supergene sulphide zone between approximately 70m and approximately 100m below surface. This has a relatively sharp contact with the fresh underlying massive sulphides;
- Hypogene zone is the fresh underlying massive sulphides. This is limited to areas where the hypogene zone has not been mined up to the 105m Level; and
- A separate zone of elevated Cu and Zn values in the oxides (where there is adequate drilling information) in the hangingwall (HW) to the main +105m Level crown pillar is present in the northwest of the deposit or approximately 300m strike where the zone converges with the main zone towards the southeast.
All of the above six zones apart from the second (clay/leach zone), are considered as being suitable for inclusion as part of the Mineral Resource. The Oxide and HW Oxide are referred to as the Oxide Zone. The Supergene Sulphide, Mixed and Hypogene zones are collectively referred to as the Supergene Sulphide & Hypogene Zone.
Dimensions
• The strike length of the +105 Level Crown Pillar mineralisation is approximately 1,000m from the northwest to where the zone intersects the sinkholes in the southeast. The depths below surface to the upper limits are 3m and to the lower limits from 100m to 120m below surface.
• The thickness of the mineralised zone varies from 1.5m to 23m.