Havilah Resources plans to embark on a fast-tracked study to investigate the feasibility of mining the North Portia copper-gold deposit immediately following the expected wind down of gold mining operations at Portia towards the end of calendar 2016.
This timing could take advantage of the considerable investment in mining and site infrastructure already put in place at Portia by Consolidated Mining & Civil (CMC).
North Portia lies 500 metres north of Portia and contains a JORC Indicated and Inferred Resource of 11.3 million tonnes of 0.89% copper, 0.64 g/t gold and 500ppm molybdenum.
No mining study has been carried out on North Portia to date because Havilah had planned to develop the Kalkaroo copper-gold mine first and then utilise this processing plant to treat the North Portia copper sulphide ore.
However, given the new synergies provided by the adjacent Portia gold mining operation, a preliminary scoping mining plan has been completed for North Portia based on an updated resource block model. This showed that there is approximately 3.7 million tonnes of mainly oxidised material at an average grade of 0.68% copper and 0.49 g/t gold and containing approximately 25,000 tonnes of copper and 58,000 ounces of gold, which could be accessed by removal of roughly 25 million tonnes of overburden, assuming similar pit slopes and other mining parameters to Portia.
The viability of North Portia as a stand-alone mining proposition is potentially enhanced by several positive factors:
- Comparatively low cost of mining overburden and oxidised ore due to the free-digging nature of the material and also by taking advantage of backfilling the adjacent Portia open pit with North Portia overburden.
- The soft oxidised ore will not require crushing or grinding and the planned metallurgical tests will determine the extent to which simple gravity methods can be employed to recover the copper and gold.
- All mining infrastructure and mining equipment is already in place for the current Portia mining operation and it is possible that the Portia processing plant may be suitable in part for treatment of the oxidised ore.
- The deposit lies within the existing Portia mining lease, thereby reducing the permitting task to approval of a new Program for Environmental Protection and Rehabilitation (PEPR) document. While specific to the North Portia operation, there will be considerable overlap with the approved Portia PEPR document.
Studies on mining the underlying harder sulphide ore would be delayed until such times as it is exposed in the floor of the open pit some 3 or 4 years after mining commences. A subsequent cutback to below 150m depth would be required to access at least 5 million tonnes of underlying sulphide ore, which has not been considered at this early stage. Metallurgical testwork by Pasminco showed that the primary chalcopyrite ore produced good recoveries and concentrate grades via standard flotation methods.
In order to help evaluate the viability of the North Portia project, Havilah plans to shortly commence work on the following key tasks:
- Determine recoveries of secondary copper and gold in the oxidised ore, which will require core drilling in order to obtain sufficient sample to carry out the necessary metallurgical tests.
- Undertake strategic infill RC drilling to increase the level of confidence to Measured and Indicated Resource status for the oxidised and transitional ore.
- Complete further groundwater studies to assist in the preparation of mining approval documentation.
- Geotechnical studies on available drillcore.
Commenting on the future prospects of mining at North Portia, Havilah managing director Chris Giles said: "With all mining infrastructure and plant and equipment now in place at Portia it makes sense for us to look at the viability of mining North Portia as a sequential follow on operation.
"Like Portia this will be a major overburden removal exercise and what we learn in mining the soft clay material at Portia will be able to be directly applied to North Portia to optimise the mining efficiency and safety.
"The planned metallurgical testing will establish the optimum recovery methods and will help to determine to what extent the Portia processing plant can be utilised.
"If the economics justify the mining development then when the time comes we will discuss with CMC how we can go about it to achieve a mutually beneficial outcome" he said.