Met tests augur well for Cerro de Maimon

Results from metallurgical tests point to higher recovery rates at the advanced Cerro de Maimon copper-gold project in the Dominican Republic.

In July, a resource update prepared for Globestar Mining (GMI-V) showed significantly more oxide material in the deposit than had been outlined, and now SGS Lakefield Research has recovered 45% more gold and 8.7% more copper from samples of supergene-enriched mineralization.

Situated in the Maimon volcanic belt, Cerro de Maimon is a stratabound exhalative massive sulphide deposit that has been both supergene-enriched and oxidized near-surface. The metallurgical tests focused on sulphide material only because previous studies on oxides yielded 90%-plus recovery rates for each of gold and silver.

Copper recoveries from supergene-enriched material are estimated at 93.8%, versus 86.3% previously, and gold recoveries are pegged at 53.8%, compared with 37.1%. Improvements are also indicated for zinc, which rose to 92.8% from 82.8%, and silver, which increased to 68.5% from 65%.

Also, copper recoveries of 85% were obtained from samples of primary material — 2.7% more than before. Recoveries of zinc, gold and silver are still being refined. Once finished, all the results will be incoporated in a new resource estimate.

Sulphide minerals in the primary zone are finely disseminated in the host sericite schist and occur in the form of pyrite, chalcopyrite, bornite, sphalerite, galena and tetrahedrite. Copper and zinc are bound closely together and, before the recent tests, could not be floated into separate concentrates.

Chalcocite and covellite partially replace chalcopyrite, sphalerite and bornite in the zone of secondary enrichment. The process locally enriched copper grades to 10%, with 2-3% being the average in unaffected material.

Fragments in the oxide cap consist of sericite schist, chert and/or quartz cemented in a matrix of goethite, hematite and corkite (a weathering product of galena). Weathering deepens in places to 35 metres below surface but averages 20 metres.

Overall, the deposit strikes for 1.2 km in a southeasterly direction and plunges at a shallow angle to the southeast. The plunge is greatest near the surface, where the deposit thickens to a maximum of 40 metres.

At last report, measured and indicated sulphide resources stood at 4.7 million tonnes grading 2.8% copper and 1.74% zinc, plus 35 grams silver and 0.96 gram gold per tonne. Similarly categorized material in the oxide cap stands at 664,000 tonnes averaging 63.8 grams silver and 2.54 grams gold.

The estimates are based on cutoff grades of 1% copper for sulphides and 1 gram gold for oxides. When the former is halved, the volume of sulphide material jumps to 6.3 million tonnes and metal grades decrease by 14-19%; the same process increases the volume of oxide material to 1.1 million tonnes and reduces metal grades by about 30% for each.

Consultants Pincock Allen and Holt are incorporating the new metallurgical results and will include those arising from the ongoing tests on primary material into a new resource estimate. The update is part of an ongoing feasibility study.

Although excluded from the independent investigation, Globestar envisions the inclusion of several satellite deposits in the planned open-pit operation. Among them is Loma Pasada, which is 15 km away and host to an inferred resource of 1 million tonnes grading 2.2% copper and 0.75% zinc.

Globestar has a half-stake in Cerro de Maimon but owns surrounding concessions outright. A private, arm’s-length U.S.-based company holds the remaining interest in the former, subject to a 10% management fee to Globestar and a provision of $750,000 for project development. Thereafter, funding is to be provided on an equal basis.

The original owner, Falcondo, an 85%-owned subsidiary of Falconbridge (FL-T), retains a 2% net smelter return royalty. It also is owed payments of $790,000; half of these payments is due one year after the completion of a feasibility study, whereas the other half is due a year after the start of commercial production.