Continental looking at 30Moz at Buritica

"This is a tier one orebody and I think it will at least double its size. We have probably only drilled half-way down the deposit so far. We have drill tested over 1,600 vertical metres and are stilling hitting the master veins and grade. We haven't hit the depth of where the deposit ends and we have a lot of potential along strike, and in the district. It could be 30Moz," he said.Master veins are those which run for the majority of the strike length and vertical extent. These host some 80% of the gold and Reading believes they are the feeder veins of the system.Buritica has proven and probable reserves of 13.72 million tonnes grading 8.4 grams per tonne of gold and 24.3g/t of silver for 3.71Moz gold and 10.7Moz silver. This is within a measured and indicated resource of 16.02Mt grading 10.32g/t gold and 40.8g/t silver for 5.3Moz gold and 21Moz silver, with an inferred resource of 21.87Mt grading 8.56g/t gold and 37.3g/t silver for 6Moz gold and 26.2Moz silver.The Buritica reserves extend from the 1,800m level down to the 1,000m level, with the resource model extending down to the 600m level. "We have drilled down to the 200m level and confirmed the system is wide open and high grade at depth. This is 400m below the feasibility orebody," said CEO Ari Sussman."Buritica has a 3g/t cut-off grade. At a 0.5g/t cut-off, it would have a similar amount of gold as [AngloGold Ashanti's] 28Moz at La Colosa," he added.With first gold pour less than a year away the company's market capitalisation seems relatively subdued at C$517 million and a $2.73 share price. Mining analysts have target pricing ranging from $4 to $6.75. Why the discrepancy?"Part of that could be Colombia risk and part could be execution risk. With a single assset company, the market wants to see producton before it gives the full valuation," an analyst on the visit told Mining Journal. Construction is 67% complete at Buritica, Colombia ConstructionFirst gold pour from Buritica is scheduled for May 2020 with production of up to 300,000oz/y with an initial 14-year mine life at an all-in sustaining cost of US$600/oz and initial capital expenditure of $512 million.With the mine build 67% complete, the company is a couple of months away from peak construction activity. The Higabra valley is being transformed from inaccessible scrubland to an industrial complex where prickly shrubs have given way to a prickly appearance lent it by the number of crane booms erecting the plant installations across the narrow valley. A road now cuts down the mountain connecting the plant site to the mine site and up to the paved municipal road connecting Buritica to Colombia's road system. Long gone are the days when visiting the valley required half a days' ride astride a mule.The biggest pieces, which relate to the Metso SAG and ball mills, mill rings and motors, are already on site. The mill room gantry crane will go in shortly and then the building can be enclosed. Five leach tanks have been built and just require their impellors to be fitted. With the critical path items now being completing the construction of the 110kva powerline and testing it so it can be energised later this year, the completion of the filter plant and Merrill Crowe refinery.With Continental aiming to extract an initial 2,100 tonnes per day from Buritica, a crucial aspect for COO Don Gray is advancing mine development to be able to sustain this production rate and later increase it to 3,000tpd."We will get 3,000-4,000 tonnes per stope so we will start with 30 stopes for 2,000tpd and ramp up to 40 active stopes," he said.One notes an element of pride and satisfaction in the comments of the normally unflappable Gray whose team has both developed the mining plan and trained locals to be miners and operaters of the three two-boom jumbos and five or six single-boom jumbos."People said there is no local mining workforce so we should use a contractor, but we decided to train locals as part of our social commitment, which is what a contractor would do anyway. We are achieving more than 1,000m a month of development, which surprised Newmont who thought we would be able to get less," he said.Continental established a mine training school with national training agency Sena and has already graduated a class of 99 trainees including 38 women, the first women in Colombia qualified to work underground. A second class will graduate soon.The company's commitment to sustainability caught Newmont's eye when it decided to buy a 19.9% stake in the company in May 2017. Continental partners with leading internationally recognised environmental and social development NGOs and recently placed eleventh in the index of best private social investment in Colombia based on amount invested and the quality of the investment, making it best mining company. "The top 10 companies are multi-billion-dollar companies, so we are very proud to be both the leading mining company and the leading small company," said VP external affairs and sustainability Ana Milena Vasquez."Newmont [which participates in technical, exploration and social and governance committees] was very impressed with our level of sustainability work but they have also bought a lot of rigour to our approach. They are taking some of our ideas and using them elsewhere, particularly in Peru. This will resonate through the country and inform how companies build mines in Colombia," said Sussman.OperationsSome 82% of production at Buritica will be via long-hole mining, 16% cut-and-fill and 1.6% shrinkage. Cut-and-fill will be used nearer to the surface and where there is more oxidised material near the Tonusco fault zone where ground conditions deteriorate. Continental is also planning on using a larger 2.5m stope than the 1.8m stopes detailed in the FS following successful trail stope mining in May 2016 and December 2017 which returned higher grades and tonnage than forecast by the geological model. These trials also showed the company can mine using 18m sub-level spacing rather than 15m. Some 50% of the filtered tails will be used for paste backfill with the tails to be transported back up to the mine via a tramway.The company is also reworking its approach to exploiting the orebody to improve efficiency and productivity with a mine plan update to be issued at the end of the year or early 2020. "The feasibility had some 300km of life of mine development and we are looking to reduce this by 100km, which is a significant cost saving," said Sussman."The feasibility had about 90 veins, but we have stripped this down to about 25 principal veins. The new deposit modelling incorporating fewer veins means less development is needed to prepare them. We are looking at moving ramps closer to the deposit and having fewer and shorter crosscuts. Where the master veins are far enough apart, we can bring the ramp down between them so we will need shorter crosscuts," said Gray.As the level and quantity of geological information increases, the geological understanding of Buritica continues to evolve. Newmont relogged over 100,000m of drill core to focus on the host rock and alteration to better understand the geology. Buritica sits on the all-important Miocene intrusive belt and the current thinking is that it is an intermediate sulphidation, porphyry generated CBM (carbonate base metals) vein system with a porphyry underneath. "We think a lot of pressure built in the system and was suddenly unleashed sending the fluids charging through. Veta Sur system is on the edge of the porphyry and Yaragua is in the middle," said Reading. Don Gray (right) shows analysts a BMZ in the Buritica mine, Colombia Exploration within the deposit is focused on identifying areas where the master veins intersect with northwest trending structures, identified as points of enrichment forming chimneys within the deposit and where it looks likely the company can mine greater widths. Continental calls these broad mineralised zones (BMZ) and has identified five so far. "We think there are a lot more BMZs there as there are a lot of intersecting structures, but we have to go underground to find them," said Reading.Nearby, the company also has highly prospective targets at Pegasus, which looks like the western continuation of the Yaragua system some 1.5km distant and where rock chips have assayed 234g/t. And to the south of Veta Sur, the Laurel target looks equally promising and would be very close to the underground mine operations at Veta Sur.

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