Andy Well Mining Pty Ltd, a subsidiary of Meeka Metals Limited (Meeka Metals), owns 100% of all Exploration Licenses, Mining Leases and mineral rights for the Project. Andy Well Mining Pty Ltd was acquired by Meeka Metals in February 2021 from Silver Lake Resources Limited (Silver Lake). The Project is managed by Meeka Metals.
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Summary:
Project scale geology consists of Archean aged high Mg Basalt units intruded by north-south striking porphyry intrusives. These are cross cut by east-west striking Proterozoic dolerite dykes. The mineralized quartz vein cross cuts the Archean units but not the Proterozoic dykes.
Andy Well is located at the northernmost end of the north-north easterly trending Archaean Meekatharra- Wydgee greenstone belt, within the Youanmi Terrane. The belt comprises a succession of metamorphosed mafic to ultramafics, felsic and sedimentary rocks interpreted to belong to the Norie Group formerly Luke Creek and Mount Farmer Groups.
The Andy Well local stratigraphy is comprised of a north-northeast striking, sub-vertical (~80º) dipping, Achaean volcano-sedimentary package. The stratigraphy youngs toward the West based on sedimentary textures and immobile element geochemistry of basalts. The local package follows a general transition from a basaltic subaqueaous lava sequence at its base which becomes mafic volcaniclastic dominated before transitioning to a siliciclastic sequence of agrillites and arenites to the west of the Great Northern Highway.
The lowermost unit in the local sequence is a voluminous gabbro unit which is generally massive with a leucocratic texture at its core. West of this unit, a series of at least 3 distinct >200m thick basalt episodes have been recognised texturally and geochemically within the local sequence which are themselves comprised of multiple individual lava flows. Flows generally show a fractionation from high- Mg bases to lower Mg flow tops with flow contacts recognised as having a spatial relationship with the mineralised structures of Wilber, Judy and Suzie lodes.
The high-Mg basalts are typically chlorite-carbonate altered, however replaced by a strong chlorite- sericite-carbonate-pyrite alteration when sheared. Sometimes talc and biotite are included in this assemblage. Coarse bladed amphiboles may overprint basalts for several metres on the margins of the shear structures but are not preserved within the shearing itself. Original volcanic textures are preserved away from shearing including pillow and variolitic textures in basalts.
Towards the top of the basaltic sequence, mafic derived volcaniclastic sediment becomes more abundant interfingered with thin basalt flows. An ultramafic unit exists towards the top of the volcaniclastic sequence and approximately marks the transition to a siliciclastic dominated domain.
Above the ultramafic, a unit of black shale and laterally equivalent massive pyrite up to 8m thick occurs within fine grained silty arenites and argillites. A 2-5m garnetiferous mafic sediment can be used as a marker within the sedimentary package.
Minor Archaean dolerites are present generally parallel to stratigraphy and most obvious within the sedimentary sequence. Felsic intrusive cross cut stratigraphy at all levels. An older dacitic porphyry has been reported which is itself cut by earlier quartz feldspar-phyric porphyry. Intrusives are typically normal to stratigraphy and have an affinity to intrude along basalt flow boundaries. Porphyries are most abundant within the basaltic sequence and scarce within sediments. Rare lamprophyre has been recorded. East-west Proterozoic dykes crosscut all units approximately perpendicular to stratigraphy within the mine area.
It is interpreted that shearing at Andy Well has developed adjacent to (and in response to) movement along the Mount Magnet Shear zone, which is located ~1km to the east. Shearing along the northeast-southwest trend is likely to have exploited lithological contacts due to rheological contrast between differing basalt flow compositions. Strain appears to have been preferentially accommodated in fractionated magnesium rich basalt flow bases, which contain a higher proportion of ductile alteration minerals such as chlorite and talc compared to more robust brittle flow tops.
The Wilber Shear is a 2-5m intensely sheared zone within a broader 20-60m wide zone of foliation. The shear dips 80°?295° with an early foliation S1, dipping 84-90°?108-114°, overprinted by a penetrative S2 foliation that dips on average 80°?295°. Kinematic indicators inside the shear zone suggest it is dominated by combined reverse-sinistral movement. Younger fold and crenulation cleavage events have little impact on the quartz reef and shear zone. Minor normal block faulting offsets the reef in some areas <5m. The dominant sinistral-reverse movement observed in the Wilber Shear zone is permissive for Wilber being an extension shear vein or riedel shear opening. The Wilber Shear is one of several similar sub-parallel northeast-southwest shear structures approximately 200m apart. A north-south structure orientation is also evident in magnetic images and appears to have dextrally offset northeast-southwest structures in places by up to 100m. The north-south structures appear to define the northern and southern strike extents of the lodes and dextrally offset the northeast-southwest shears.
The gold mineralisation at Andy Well is orogenic shear hosted, narrow high-grade quartz reefs. Economic mineralisation has so far been identified within five parallel north-northeast trending quartz reefs; Wilber, Judy North, Judy South, Suzie and Jenny.
A geochemical affinity for basalt host rock/contact is also likely to be significant for mineralisation as grade is less abundant within sheared porphyry host rock.
Vein mineralogy is predominantly quartz-calcite-chlorite+/-fuchsite associated with minor disseminated pyrite with lesser amounts of chalcopyrite, galena and sphalerite. Gold is frequently visible and finely dispersed throughout laminated, breccia and massive quartz types as well as with a lesser pyrite and other sulphides. Gold grades within veining are in general above 30g/t, whilst grades outside of veining but within the mineralised envelope are in the order of <0.3g/t Au.
Mineralised veins are interpreted petrographically as a space-filling. During flow of the hydrothermal fluid through the open structure, slivers of altered wall were scavenged into the structure, and suffered replacement to form fine-grained fuchsite + chlorite in stylolitic trails. Ongoing mild deformation caused partial recrystallisation of the vein quartz, forming finer-grained sutured mosaics.
Historical production was principally sourced from the Wilber Lode, a sub-vertical slightly west-dipping laminated quartz vein commonly 0.4 to 1.5m in width with a well-developed boudinage texture. It forms an extensive and largely continuous sheet of mineralisation, which is currently defined over 600m strike and 700m down dip, remaining open at depth.
Summary:
Crushing
The Project will use three-stage crushing to produce P80 of 13.5mm feed for the milling circuit.
The nominal crushing rate is 150tph with double shift operation and 76% crusher utilization. Crushed ore more than the mill requirement overflows the fine ore bin (FOB). Alternatively, the crushed ore is stockpiled by pulling out overflows from the FOB by a front-end loader. The FOB is normally kept full by operating the crushing circuit at a rate exceeding the milling capacity. This allows for crusher maintenance shutdowns when required, without interruption of milling operations.
Crushed ore is withdrawn from the fine ore bin using two belt feeders with variable speed drives. The speed of the belt feeders is controlled by a process loop to the weightometer located on the mill feed conveyor. The mill feed rate is automatically controlled to the selected mill feed rate.
The crushed ore is transferred from the fine ore bin discharge belt feeders to the mill feed conveyor. The mill feed conveyor is fitted with a walkway to one side and a dual idler weightometer linked to the fine ore belt feeder VSD to control the mill feed rate.
A ball mill kibble is located above the mill feed conveyor to feed grinding media to the mill.
A lime silo and feeder are located above the mill feed conveyor. Bulk quicklime is delivered to site and pneumatically transferred to the lime silo. The lime is fed by a variable speed screw feeder onto the mill feed conveyor at a rate controlled by a pH loop in the first leach tank.
Milling and Classification
The milling circuit comprises a single stage 3,850kW ball mill, fitted with rubber liners, discharge trommel and operating in closed circuit with cyclone classification. The mill discharge density is controlled by water addition to the mill feed chute, regulated using a flowmeter and flow control valve. The mill discharge slurry flows through the trommel screen into the mill discharge hopper fitted with a level indicator. The slurry level in the mill discharge hopper is maintained constant by a level control loop to the VSD on the cyclone feed pump motor.
The mill discharge slurry is pumped to a cluster of 10” cyclones for classification to oversize (product which is at the P80 of 75µm for the leach circuit) and coarse undersize. Operation of the cyclones is monitored by a slurry flowmeter and pressure transmitter. The cyclone feed density is regulated by water addition to the mill discharge hopper using a flowmeter and flow control valve.
A fraction (~25%) of the cyclone underflow (coarse fraction) flows to a gravity feed splitter box and will then gravitate back to the ball mill via a pipe and boiler box arrangement. The rest of the cyclone underflow will gravitate back to the ball mill feed chute.