Scheelite skarn mineralisation has formed within the metamorphic aureole of the Carboniferous Grassy Granite where it is in proximity to the calcareous sediments and carbonates of the Lower Grassy Group. The Dolphin and Bold Head deposits are hosted in a similar stratigraphic sequence.

Mineralisation is hosted within a 100-200m thick sequence of complex skarn mineralogy with two main horizons known as B and C Lens both of 10-30m thickness separated by a similar thickness of skarn altered volcanic sediments. Skarn formation and mineralisation have occurred where carbonates come into direct contact with the intrusion, or adjacent to brittle faults intersecting the intrusion. Mineralisation in the Dolphin deposit is best developed within C Lens which has several distinct mineralogical components including a garnet hornfels, a pyroxene-garnet hornfels and banded pyroxene garnet hornfels. B Lens is an upper dolomite horizon which has been variably hornfelsed and metasomatised with sporadic mineralised pyroxene-garnet skarn.

The Dolphin deposit dips east to southeast at approximately 30° before steepening to 50° in proximity of the Decline Fault on the eastern margin of the deposit. The host stratigraphy is broadly folded by several southeast dipping open anticlines or vergence folds with wavelengths of a few tens of metres. Several major southeast and east trending normal faults associated with the folding cut the orebody into discreet fault blocks. The Northern Boundary Fault truncates the mine sequence to north juxtaposing the Lower Grassy Group against the Fraser Formation quartzite. The Mine Sequence is truncated to the south by the granite, the surface of which dips and plunges shallowly north and east.

The OC mine is proposed to be an own-operate, truck-shovel operation utilising mid-sized hydraulic excavators matched to a fleet of 75 tonne dump trucks The UG mine will be decline accessed and based on contract mining for development and ore production using standard rubber tyred diesel and electro-hydraulic underground mining equipment.

Open Cut Mining
Updates to the 2019 Mineral Reserve Estimate have been made during the current Feasibility Study, none of which are considered to result in a material variance from the original estimate of 3.0Mt @ 0.73% WO3. Technical studies into scheduling, equipment, drill and blast and power and fuel costs have resulted in minor revisions to cost estimation. Physical constraints, cut offs and mine design remain essentially the same with the most significant updates to the 2019 estimate being:
- Updated equipment list;
- Revision of ore schedule into 2 stages;
- Smoothing of the waste movement schedule to optimise mining costs;
- Increased drilling capacity with smaller holes and 100% emulsion explosives to reduce blasting effects on Grassy town and improve fragmentation;
- Updated OC cost estimation.

The majority of the waste and ore will require drill and blasting; the exception to this being old fill and marine sand material. Blasts will be engineered to ensure minimum displacement of the ore to minimise dilution and ore loss. Drilling will be carried out by 2 top hammer rigs with blast hole diameters from 102 mm to 127 mm.

The Dolphin Open Pit final pit design remains unchanged to that completed by REG and Xenith consultants using Surpac software for the 2019 Feasibility Study. The interim design to allow the installation of the Interim Membrane Wall has minor effects on the ore schedule in terms of grade timing but no effect on overall ore tonnes and grade. The pit design continues to be constrained by geotechnical domains, the existing open pit morphology and a -20m RL contour of the base of offshore marine sand. A block cut off grade of 0.2% WO3 was used to define the ore boundaries within the base and western limit of the existing open pit. A Whittle optimiser utilising Lerchs-Grossmann algorithm was used to verify the economics of the pit limit and showed the pit limits determined by the physical constraints lay well within the optimum pit extents determined by the optimiser. From the updated mine design, a production and dump schedule were produced as the basis of an economic model. Mining factors were applied to convert the in-situ tonnage and graded to a ROM tonnages and grade. The ROM Ore then formed the basis for classification as Open Cut Ore Reserves, once other modifying factors were applied.

Underground Mining
The proposed mining method is similar to the old mine, with a new decline designed to bypass the upper decline and access the lower mine and Swan areas. The decline and accesses have been designed to suit modern rubber tyred underground equipment at minimum 4.5 x 4.5 m.

Ore production assumes a combination of cut and fill (CAF), post pillar cut and fill (PPCAF) and up hole bench stoping (UHB), down hole bench stoping (DHB) and remnant up hole stoping methods. It is assumed all voids will be filled with either cemented paste fill, sand fill or waste rock. The recoveries utilised in this estimate are completely reliant on the use of consolidated paste fill. The use of consolidated paste fill represents the safest and most productive means of recovering the maximum percentage of the in-situ resources.

Remnant ore is located within areas that have been previously mined or may have been compromised by known poor ground conditions since the mine closed some 30 years ago. It is assumed that remnant ore will be mined where practicable late in any mining sequence except where the voids produced can be immediately filled to prevent subsidence and/or caving.

On mine closure the ventilation circuit was working adequately, with the air ingress of 120 m3 at the portal with unforced ventilation to the various stoping areas. All return air was collected at the -150 m level return airway and directed to twin ventilation rises on the 75m level driven by two Richardson 1615CY centrifugal fans.

It is assumed that the ventilation circuit below -140 m RL will remain intact, although is assumed to require some rehabilitation. Under the new planned underground operating conditions, the ventilation air ingress will be at the -120 m RL portal. The ventilation circuit will need to be connected from some convenient point underground to the new exhaust fan position in the completed open cut, as the original return air rises to surface (where the exhaust fans were located) will be mined out, as part of the new planned open cut to the -140 m RL. A dedicated return air rise will be required from the -150 m level to the surface either via the old -100 m level into the open cut or via a dedicated rise to surface. Currently a 135 m raise bored rise and fan (210 kW) has been included in the capital however other alternative systems require design and costing. Internal forced ventilation has been included in the operating costs and includes a 90 kW decline fan and several 55 kW face fans for development headings.

Significant modifications to the process flowsheet and plant design since the 2019 FS (ASX:KIS 3 June 2019) have been made, mainly to the gravity circuit resulting in a reduced flotation requirement. Civil construction associated with processing outside of the Gekko scope was designed and costed by BR Design. The process flowsheet design includes two stage crushing, using jaw and cone crushers, fine ore stockpile, fine vertical shaft impact crushing, coarse and fine gravity concentration using spirals and tables, dressing of gravity concentrates by flotation and magnetic separation and finally drying, blending and bagging of concentrate. Plant throughput is expected to average 60 tonnes per hour.