Conroy Gold’s exploration programme at its Clontibret gold target has to date resulted in a JORC compliant total resource of over 1 million ounces estimated over 20% of the Clontibret gold target area.
An antimony mine was worked at Clontibret, County Monaghan in the early 1800’s. The antimony mine shafts were dewatered in the 1950’s and back channel samples assayed leading to the first discovery of gold in the area with grades of up to 34.98 g/t recorded. Subsequent drilling in the vicinity of the antimony mine tested positive for gold but the assessment of grade was hampered by poor recovery.
Modern drilling techniques employed by Conroy Gold resulted in good recovery with grades comparable to those recorded in the back channel samples.
The local geology at Clontibret consists of Ordovician sedimentary rocks, which lie some 1,500 m north of the regional-scale Orlock Bridge Fault. The stratigraphy is made up of alternating units of argillite (shale or siltstone) and arenite (greywacke or sandstone) rocks. The mineralisation in Clontibret occurs in two styles - high grade lodes and a disseminated stockwork zone.
Drilling and trenching elsewhere in the remaining 80% of the Clontibret target has also intersected gold.
The Company is now planning its first operational gold mine on 20% of the Clontibret area.
Mine scoping studies have been completed by independent consultants Tetra Tech with positive technical and financial results. The scoping studies concentrated on the high grade lode zones and some higher grade zones within the stockwork. A minimum mining width of 2 metres, a long term gold price of US$1,372 and a cut-off grade of 0.60 g/t gold was used. This resulted in total contained resource of over 600,000 ounces (259,956 ounces indicated, 341,148 ounces inferred). See table below:
Prepared by Tetra Tech according to Australasian Joint Ore Reserve Committee (JORC) Guidelines as part of the scoping study
Resource on 20% of the Clontibret gold target
For the purposes of the study a conventional open pit operation based on a long term gold price of US$1,372/Oz resulted in contained gold of 441,200 Oz. Parameters includes a head grade during mine life of 1.53g/t gold, a process rate of 800,000 tonnes per annum, an assumed overall gold recovery of approximately 85 per cent and a mine life of 11.2 years with in-situ gold averaging over 50,000 Oz per annum in the first five years. Capital costs (including sustaining capital) were estimated at US$77.8 million, with a payback period of two years.
|NPV (8) (US $ M)
|Gold Price (US$)
The economic evaluation was based on a pre-tax financial model, taking a base case price for gold of US$1,372/Oz over the 11.2 year mine life. This gave a 49.4 per cent Internal Rate of Return (IRR) and a Net Present Value (NPV), at 8 per cent discount rate, of US$72.3 million.
On this basis an initial process was proposed: after conventional crushing, milling and flotation to produce a bulk sulphide concentrate containing the majority of the gold, the bio-oxidation process will then convert the majority of the sulphides in the concentrate to oxide. This will then permit a conventional Carbon in Leach (CIL) and elution process for the recovery of gold to be employed. See Figure below for a schematic of this process. A comprehensive test work programme will be carried out to fully assess the metallurgical characteristics of the ore prior to finalising the process.
The scoping study concluded that biological oxidation is an appropriate technology to be considered for treating the ore, as the Clontibret ore is refractory in nature; with the bulk of the gold occurring as sub-microscopic inclusions within arsenopyrite
On this basis an initial process was proposed: after conventional crushing, milling and flotation to produce a bulk sulphide concentrate containing the majority of the gold, the bio-oxidation process will then convert the majority of the sulphides in the concentrate to oxide. This will then permit a conventional Carbon in Leach (CIL) and elution process for the recovery of gold to be employed. A comprehensive test work programme will be carried out to fully assess the metallurgical characteristics of the ore prior to finalising the process.
The biooxidation process is for the pre-treatment of refractory ores and concentrates ahead of a conventional leaching for gold recovery. The gold in these ores is encapsulated in sulphide minerals such as pyrite, arsenopyrite and pyrrhotite thus preventing the gold from being leached. The process destroys the sulphide minerals and exposes the gold for subsequent leaching thereby increasing the overall gold recovery that can be achieved.
The process has many real advantages over alternative refractory processes such as roasting or pressure oxidation.
- Improved rates of gold recovery
- Significantly lower capital cost
- Low operating cost
- Robust technology that is suited to remote locations
- Low levels of skills required for operation
- Environmentally friendly
- Ongoing process development and improvement
- Backed by over 25 years of operating knowledge by an experienced team
Golder Associates have completed preliminary environmental studies at the Clontibret gold project and have now initiated detailed environmental monitoring and site assessments, which are a key element in the planning process for mine development. Ecological studies have also commenced, surface water monitoring locations have been established and a weather station has been installed.
Other aspects of the detailed environmental assessments will include hydrology, hydrogeology, socio-economic, soil and land uses, historic environment and cultural heritage, air quality, noise and vibration, nature conservation, landscape and visual impact, traffic and transportation, consultation with stakeholders, treatment processes, tailings disposal and a detailed restoration plan.
Further Potential at Clontibret Gold Target
The ore system remains open at Clontibret with potential for expansion of the resource. Gold has been intersected in other areas in the remaining 80% of the Clontibret target (e.g. 11 m @ 5.34 g/t Au and 21 m @ 1.82 g/t Au)