Summary:
The Omagh Gold Project lies within the Caledonian orogenic belt. The principal host rocks of gold mineralisation in the region belong to the late Neoproterozoic to Cambrian aged Dalradian Supergroup. Gold mineralisation can be characterised as Palaeozoic orogenic type and is one of several orogenic structurally controlled, mesothermal gold bearing quartz and quartz-sulphide vein systems located in the Caledonian basement rocks.
The Omagh Gold Project is hosted in the Sperrin Nappe, an SSE-verging overturned limb of an isoclinal nappe within the Lack Inlier. The metamorphic grade exposed at surface is greenschist to lower amphibolite grade. The deposit itself is hosted by the Mullaghcarn Formation that is composed of fine grained clastic meta-sedimentary rocks including psammites, semi-pelites and chlorite-rich pelites, interbedded with basic metavolcanics.
The Lack Inlier is bounded by the Cool Fault in the north and the Omagh Thrust-Castle Archdale faults in the south. Deformed graphitic schists are well developed along the Omagh Thrust, south of the Omagh Gold Project. Several ENE-trending steeply dipping faults and shear zones dissect the inlier. The NNE-trending Omagh Lineament, one of three major, parallel, basement lineaments in the region, crosses the eastern part of the Lack Inlier, in the area underlain by the north trending Omagh Gold Project vein swarm.
The Omagh Gold Project vein swarm comprises 17 named vein structures in an area of about 6 km2 . The most important of those vein structures are the Kearney and Joshua vein systems, which are the focus of the MRE described in this technical report.
The Kearney vein system is the largest mineralised vein system. It is comprised of 22 modelled sub-vertical N to NNW-trending veins that range in thickness from <0.1 m to 8.0 m. The Kearney vein system has a strike length of approximately 850 m and a maximum vertical extent proved by drilling is 337 m, it remains open at depth down plunge. The three largest veins are continuous for between 400 m and 800 m along strike. Smaller discontinuous veins may only extend for less than 80 m along strike.
The Joshua vein system is the second largest mineralised vein system. It is comprised of seven modelled sub-vertical N to NNW-trending veins that range in thickness from <0.1 m to 5.0 m. The Joshua vein system for the purpose of this report includes the closely sited Kestrel vein which is approximately 100 m to the west of the Joshua vein system. The Joshua vein system has a strike length of approximately 1 km and a maximum vertical extent proved by drilling is 200 m, it remains open at depth down plunge. The largest vein is continuous for the entire strike length of the Joshua vein system. Smaller discontinuous veins may only extend for less than 50 m along strike.
Mineralisation consists of centimetre-to-metre-scale wide brecciated quartz veins with disseminated to massive auriferous sulphides, predominately pyrite and galena with some accessory arsenopyrite and chalcopyrite. Quartz veins pinch and swell from stringers to widths greater than a metre over distances of several metres. The veins are commonly fringed by varying widths of clay gouge. Wall rock alteration in the form of sericitisation and bleaching may extend several metres into quartz-feldspar schist host rocks, depending on the degree of fracturing. The vein systems of the Omagh Gold Project are structurally controlled complex zone of quartz-sulphide mineralisation and associated alteration, along which there has clearly been tectonic movement, resulting in an irregular brecciated lattice-work of mineralised veins.
Mineralisation is primarily hosted in massive sulphides, quartz veins within the quartz breccia unit, and clay gouge. Altered wall rock may also host mineralisation depending on the degree of fracturing. Gold values are closely correlated with sulphide content.
Digitised maps of Riofinex trenches from the Kearney open pit, and underground geological maps from Galantas illustrate a complex high strain shear zone with the main tabular vein occasionally splitting into narrower veins before merging again along strike. The N to NNW trending Kearney and Joshua veins are generally at high angles to the host rock foliation, although it can vary significantly and become parallel with the veins (Shaw et al., 2022). The veins do show variations from the broad N to NNW-trend at a local scale. Notwithstanding the complexity of the shear zone, the Kearney vein system is mapped to be continuous along strike.
The Kearney vein also shows a classic pinch and swell geometry which is most evident in the underground geological map on a scale of 40 m to 60 m. The map also illustrates how thicker “swell” zones of massive sulphide and quartz breccia are connected by thinner “pinch” veins and zones of black clay fault gouge. Galantas have identified similar pinch and swell structures in the Joshua vein.
The pinch and swell structures have been described by Galantas as potential dilation zones. Dilation zones have potential for wider intervals of mineralisation and are believed to be linked on shallow N-dipping planes related to the regional SE directed thrusting. Conversely, Shaw et al. (2022) link the pinch and swell structures to continuous deformation with the narrow clay gouge rich shear zones accommodating the majority of the counter-shearing during rotation, whereas the more competent quartz breccia and massive sulphide buckled during the same rotation. They describe the shallowly N-dipping faults as post-dating mineralisation.