Evolution acquired an economic interest in Ernest Henry in November 2016 for 100% of future gold and 30% of future copper and silver produced within an agreed life of mine area. Outside the life of mine area, Evolution’s interest was a 49% interest in future copper, gold and silver production from Ernest Henry.
On 17 November 2021, Evolution announced the acquisition of 100% of Ernest Henry. Evolution’s interest in Ernest Henry transitioned to 100% legal ownership of the underlying asset on 6 January 2022. The economic interest in Ernest Henry on a 100% basis transferred to Evolution on 1 January.
The Ernest Henry operations extend across eight (8) current mining leases all owned by Ernest Henry Mining Pty Ltd.
Summary:
The Ernest Henry Deposit is an Iron Oxide Copper Gold (IOCG) hosted within a sequence of moderately SSE-dipping, intensely altered Paleoproterozoic intermediate metavolcanic and metasedimentary rocks of the Mt Isa group. Copper occurs as chalcopyrite within the magnetite-biotitecalcite-pyrite matrix of a 250 x 300 m pipe like breccia body. The breccia pipe dips approximately 40 degrees to the South and is bounded on both the footwall and hanging wall by shear zones. The main orebody starts to split from the 1575 level into a South-East lens, and from the 1275 level into the South-West lens. Both lenses are separated from the main orebody by waste zones, termed the Interlens and South-West Shear Zone, respectively. The orebody is open at depth.
The Ernest Henry copper-gold deposit is hosted in a hydrothermal breccia pipe plunging at roughly 45 degrees to the south, bounded between two shear zones. At depth, the orientation of shearing appears to be having a greater effect on the orebody and the primary mineralised lenses are becoming more elongate north-south, separating into discrete pods and lenses.
The Ernest Henry deposit is hosted entirely in felsic intermediate metavolcanic rocks, within a unit of the Mount Fort Constantine Volcanics, circa 1800 to 1750 million years. Regionally these lithologies lie adjacent to a large meta-diorite body which traverses the deposit from the south-west to the north-east. Timing of mineralisation at the Ernest Henry deposit is commonly accepted by many workers as occurring between regional D3 through to D4 deformation events circa 1530 to 1500 million years.
The orebody plunges moderately for more than 1500m towards the south-east and is situated between two controlling shear zones, the Hanging Wall Shear Zone (HWSZ) and Footwall Shear Zone (FWSZ), which separate the brecciated plagioclase rich felsic intermediate metavolcanic rock suite from adjacent intercalated meta-sediments.
Mineralisation has been intersected down plunge to depths lower than the 400 level, some 1800m below surface. The current ‘Life of Mine’ area from which Ore Reserves are reported extends down to the 1125 level. Below the 1125 level drilling becomes more sparse and the orebody is less understood. The region between the 1125 level to the 875 level is the focus of the next phase of mining on which a Pre-Feasibility Study has commenced. The figure below illustrates the extent of the orebody and the likely extensions to reported Ore Reserves once the PFS is completed.
The main orebody starts to split from the1575 level into a South-East (SE) lens, and from the 1275 level into the newly defined South-West (SW) lens. Both lenses are separated from the main orebody by waste zones, termed the Inter-lens and South-West Shear Zone (SWSZ), respectively.
The SE lens appears to be maintaining relatively consistent boundaries and thickness from the 1575 level down to 1250 level. Limited drilling at depth indicates the lens volume may be reducing with depth. The SE lens has not yet been closed off at depth by drilling. Additional drilling scheduled in 2022 will test the down-dip extent of the SE lens.
Data from the recent, and ongoing, infill drilling campaign has resulted in some distinct changes to the orebody definition and quality. In particular, the further elongation of the orebody below the 1275 level and the identification of the low-grade SWSZ. This shear zone falls within the current SLC design and will impact the estimated drawn tonnes and grade for all levels below the 1250 level.
Mineralization is associated with a matrix supported hydrothermal breccia that is enveloped by crackle veined potassium feldspar altered meta-volcanic rocks. The matrix is largely composed of magnetite, quartz, biotite, chalcopyrite, pyrite, fluorite, gold, molybdenite, uraniferous minerals and potassic feldspar. Other gangue minerals in the matrix consist of chlorite, calcite, dolomite, barite, apatite, muscovite, garnet, scapolite, sphene, rutile and tourmaline.
Chalcopyrite, the only copper mineral observed within the primary orebody, and pyrite are the only significant sulphide minerals within the orebody. Chalcopyrite is fine to medium grained, anhedral and commonly occurs as disseminated grains attached to magnetite and/pyrite. Chalcopyrite and pyrite are contained mostly within the breccia matrix, comprising 1% to 20% of the matrix volume.
Gold occurs about 98% of the time in the form of native gold-electrum (65-95wt % Au), other minor contributions come from sylvanite, auriferous cobaltite, pyrite and chalcopyrite. It is believed that gold precipitation was closely associated with, but preceded some of the chalcopyrite deposition, as indicated by the lower gold and copper ratios of late-stage chalcopyrite rich veins. Although the Ernest Henry orebody contains arsenic, fluorine and uranium minerals, they typically fall below product thresholds, and aren’t considered deleterious.
The Ernest Henry deposit is approximately 250m x 300m in plan at the current mining position but becomes elongated and lenticular at depth. The longer axis is parallel with the bounding shear zones. The deposit dips at 40 degrees to the south, extending from 60m under a sedimentary blanket to beyond 1600m in depth. Below 1575 RL a secondary lens is partitioned to the southeast appearing to be strongly influenced by the shearing. The current EHM resource estimate reports blocks below 1705RL that form a contiguous mineable entity above a 0.7 % Cu cut-off.