The Navan Orebody is a world-class carbonate-hosted Zn-Pb deposit comprising complex tabular lenses within Lower Carboniferous limestones and excluding depletion, would be over 130Mt in size. Detailed descriptions of the geology are available in a number of publications of which Ashton et al., (2015) is the most recent. The discovery of the Tara Deep satellite and outline geology are summarized in Ashton et al., (2018). Central Ireland comprises generally flat lying sequences of Lower Carboniferous limestones with common inliers of sedimentary Lower Palaeozic and Devonian rocks. The limestones are cut by numerous, locally syn-depositional NW to ENE trending major normal faults and these control the location of several carbonate hosted Zn-Pb deposits, of which Navan is by far the largest. In eastern Ireland, the Carboniferous Limestones are part of the Dublin Basin, a significant feature that after extensional basin-margin faulting and later Hercynian inversion, exposes some large Lower Paleozoic inliers at its margins and exhibits some outliers of Namurian and later Permo-Triassic sediments. The Navan Orebody is located on the footwall (northern) side of a major south-dipping normal fault that constitutes a basin margin controlling feature. The orebody itself is controlled by a complex array of Lower Carboniferous normal faulting and slides on the uplifted footwall of this major fault. The orebody generally dips at about 10-15 degrees to the WSW and comprises several, locally stacked, tabular stratiform to stratabound lenses, oriented in general concordance with the host limestones. The mineralisation ranges from a few meters to over 70m in vertical thickness. A major slide and overlying debris flow cuts the orebody obliquely and is also mineralized. The orebodies are effectively masked from the surface by a thick succession of deep-water calc-turbidites that comprise the Dublin Basin. Although there are number of significant lenses and fault blocks at Navan, >95% of the mineralisation occurs as sphalerite and galena in partly dolomitized limestones as complexly-textured replacements, veining and open-space infill where Zn:Pb ratios are typically around 4 or 5 to 1. Gangue mineralisation comprises subsidiary calcite, pyrite, marcasite, dolomite and barite. The remainder of the mineralisation occurs as massive pyritic lenses containing sphalerite and galena hosted by debris-flow conglomerates that overlie the deposit. This material contains often abundant fine-grained pyrite which has the potential of degrading the normally excellent metallurgy if not blended with normal run of mine ore.

Boliden Tara Mines is an underground zinc and lead mine producing 2.6 million tonnes per year with an annual development schedule of 13km and nearly 250km of active tunnels it is classed as the biggest zinc mine in Europe and one of the largest in global comparison. Tara Mine uses Drift and Slash and Long Hole Stoping as its main mining methods and has a current depth of around 1km. In most areas of the mine open-stopes are designed parallel to the strike direction of the orebody such that in-stope development is sub-horizontal, whereas in the upper-near surface sections the open stopes are along dip and may necessitate slightly more complex development. In both cases, ore thicknesses up to about 20m can be mined via a single footwall drift with blast-hole drilling drilled upwards. Thicker ore necessitates hanging-wall drifts. In both cases, development is advanced to the end of the stope, and a slot crosscut created from where a raise is blasted using longhole techniques to the orebody hanging wall. Subsequent longhole blasting opens up a slot over full stope width and subsequent long-hole blasting creates a blasted ore muck pile in the developing stope which is mostly mucked-out using remote control and increasingly tele-remote operations. Areas of weak ground, often related to faulting may occur in the back and/or sidewalls of stopes. These are secured using various cable bolts patterns. Once a stope is complete, it is backfilled with hydraulically placed cemented sandfraction tailings and then the intervening pillars are mined employing broadly similar methods. Stopes vary from 12 to 20m in width. Areas of drift height ore are extracted by low profile open stoping and referred to as ‘Drift and Slash’ stopes. The Mineral Reserve quantity represents an equivalent amount for 7 years of full production. However, with planned conversion of Mineral Resources it has the potential to be extended further. Tara Q4 2021 disturbances in production - Water inflow from pilot hole for ventilation shaft, starting Nov. 20; - Production partially resumed Dec. 10; - Fire in underground conveyor Dec. 27; - Q1 2022 production at reduced capacity; - Milled volume ~10 % lower than 2021 average; - Zn grade ~0.5 percentage point lower than 2021 average; - Normalization during Q2 2022; - Tara Deep – full access to exploration drift during second half of 2022. Production was halted for just over two weeks in Tara at the end of the year as a result of increased water inflows in the mine. The event will impact exploration efforts toward the Tara Deep mineralization in 2022.

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Ore processing in the mill is achieved by grinding, flotation, and dewatering. The finely ground ore slurry is pumped from the grinding circuit to flotation cells where lead concentrate is recovered firstly and then followed by zinc concentrate. Following flotation, concentrates are dewatered using thickening and filtration in Metso pressure filters. Within the flotation cells, galena (Lead sulphide) and sphalerite (Zinc sulphide) are differentially separated, while undesirable minerals such as pyrite are depressed. Once the target minerals have been extracted the waste stream, otherwise known as tailings is cycloned to separate the coarse sand fraction from the finer slimes fraction. The coarse fraction of tailings is stabilised, chemically and physically, by mixing with cement and is pumped underground to backfill mined out areas. The remaining fines fraction tailings is pumped as an aqueous slime to the Tailings Storage Facility (TSF) located 3 km north of the processing plant ........