The Citronen Deposit is interpreted as belonging to the SEDEX deposit class, forming syn-depositionally with sedimentation.

SEDEX deposits are formed in submarine environments by the precipitation of sulphides from metal bearing fluids introduced onto the seafloor through underlying fractures which act as metal-bearing fluid conduits. Large amounts of sulphur are precipitated principally as pyrite and focused around vent areas or ‘mounds’ on the sea floor. Base metal (Zn + Pb) bearing sulphides at Citronen are predominantly located within laminate horizons surrounding these larger sulphide accumulations.

Mineralisation at the Citronen Fjord Zn-Pb Deposit comprises several distinct sulphide mounds containing massive and net-textured pyrite-rich mineralisation, interpreted to represent the focal point of fluid influx, flanked by pyritic laminated sulphides that are locally sphalerite and galena-rich. These laminated sulphides host the majority of economic grade mineralisation.

The deposit consists of multiple sulphide mounds forming in three lateral positions (“vents”), defined as the Discovery, Beach and Esrum ore bodies.

The mineralisation is hosted within two fine- grained sedimentary units, separated by a mass carbonate debris flow. The majority of mineralisation is stratiform, with semi-massive net-textured to massive sulphides accumulating in the core of the mound structure. Structurally controlled stock-work style mineralisation is present within the carbonate debris flows, with the most notable termed the XX ore body. The stratiform mineralisation has been identified from outcrop to a depth of approximately 500 metres, with the mineralisation open at depth. Level 1 is located predominantly within the Discovery ore body, Level 2 is evident discontinuously across all three ore bodies and Level 3 contains the largest volume of sulphides, with a lateral extent of over 3,000 metres between the Beach and Esrum ore bodies.

The mineralisation is pyrite dominated with variable amounts of sphalerite ((Zn/Fe)S) and lesser galena (PbS) present as sulphide species. Minor chalcopyrite (CuFeS2) has been documented and interpreted as having formed during remobilisation and enrichment of primary stratiform-hosted mineralisation. No economically significant Cu or silver (Ag) has been identified to be associated with the sulphide mineralisation.

Primary mineralisation is generally fine to medium grained, weakly to moderately laminated and bedded parallel with regionally deposited sediments. Gangue mineralogy is primarily silt and clay from mudstones deposited contemporaneously with sulphide mineralisation.

The ore body’s nature and orientation is well understood and the room and pillar mining method has been selected as the most appropriate for this style of deposit.

With the mining method being room and pillar, a recovery factor of 100% recovery was assumed as ore loss should be negligible provided that a tele-remote bogging system is used for the recovery of the ore drive strip material. The likelihood of ore loss would increase if a line of site remote bogging system was used.

All mining has been planned for conduction via development jumbo and, as such, minimal overbreak (i.e. unplanned dilution) outside of the planned dilution skin is expected. As a result, no tonnage factors were applied to this design.

Open pit mining operations have been scheduled to commence at the end of the life of the underground mine in Year 11 (3.3 Mtpa scenario).

The open pit mining rate to continue to maintain a total ore feed rate of 3.3 Mtpa to the process plant until the open pit is depleted. Mining will utilise 10 x 60t haul trucks and excavators until the point where the project is closed out, subject to the discovery of additional resources.

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Dense Media Separation (DMS)
DMS performance at a 2.96 to 3.10 separation SG provides recoveries in excess of 97% of lead and zinc to the sinks plus the -1.0 mm fines product bypass throughout the size ranges tested.

The DMS feed bin discharges at an approximate average of 375 t/h by belt feeders to a wet feed preparation screen that removes all -1.0 mm material, with the screen oversize feeding into the DMS cyclone feed hopper.

The DMS cyclone pump feeds -38+1 mm material combined with dense medium to the DMS cyclones. The DMS cyclone overflow is stripped of medium on a drain-and-rinse dual screening system with screen oversize conveyed to the external floats stockpile. The DMS cyclone underflow is stripped of medium on a drain rinse screen system, and the screen oversize is conveyed to the sinks (ball mill feed) bin.

The DMS feed fines are separated at the wet feed preparation screen. Sixteen percent of the ore feed weight reports as -1 mm fine ........