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Metallurgy The Wetar copper deposits contain impurities which attract significant smelter penalties. Various alternative processing routes which effectively remove and handle the impurity levels are being considered and investigated by Finders Resources for the extraction of saleable copper products from the Wetar Ore, namely: · Production of a bulk flotation concentrate on site, for shipping to a hydrometallurgical plant using proprietary third party hydrometallurgical technologies to produce high quality copper metal: · Production of copper cathode on site using heap leaching and solvent extraction - electrowinning (“SX-EW”), following initial test results which indicated acceptable recoveries using either naturally occurring or proprietary bacterial leaching techniques. A summary of these process alternatives is provided below. Flotation : hydromet : leaching Flotation Testwork Initial flotation testwork undertaken in Adelaide by Optimet, an independent metallurgical testwork laboratory, on behalf of BMI in 1991 on massive and breccia ore types from the Kali Kuning resource area on massive sulphide (2.75% Cu) and breccia (3.98% Cu) samples indicated that copper recoveries in excess of 85-87% could be obtained in concentrates grading 26-29% Cu, 2% As, 0.2% Sb, 75g/t Hg, 1g/t Au, 160-190g/t Ag, 0.5-0.6%Pb, 0.7-2.7% Zn, 38-39% S, 350-450 ppm Bi, 350-440 ppm Ni, 60-90 ppm Co, <20 ppm Cl and <100 ppm F. Recoveries of greater than 90% were obtained in rougher concentrates grading around 20% Cu. Best flotation performance was achieved at a 40 micron p80 grind size, pH 11.8, 30 minutes conditioning time, sodium ethyl xanthate collector and sodium metabisulphite collector. A new program of flotation testwork was conducted in late 2005 and during early 2006 by Optimet on composites of fresh diamond drill core provided by Finders Resources from the Kali Kuning and Lerokis resource areas. The objective of this testwork was to confirm the concentrating characteristics of the two resource areas and to produce sample concentrate that could be used for preliminary bench scale concentrate treatment process testwork for both ore areas. The Optimet flotation testwork on Kali Kuning succeeded in producing close to target of at least 90% copper recovery to a copper rougher concentrate grade at 15.7% Cu, which is only slightly lower grade than the 20% Cu obtained in 1991 testwork on a different head sample. Selected concentrate impurity and other element assays were 1.6% As, 2600 ppm Sb, 45 g/t Hg, 1.8 g/t Au, 127 g/t Ag, 0.6% Pb, 2.6% Zn, 42%S, 280 ppm Bi, 130 ppm Cd, 1200 ppm Ni, 130 ppm Co, <50 ppm Cl and <50 ppm F, or broadly similar to earlier testwork assays. The Optimet flotation testwork on Lerokis also produced close to target copper recovery and grade at 88.9% copper recovery and 15.1% Cu rougher concentrate grade respectively. However zinc was a significant impurity at 7.2% Zn and 90.4% zinc recovery, with zinc depression not being successful. Selected concentrate impurity assays were 1.0% As, 1500 ppm Sb, 37 g/t Hg, 1.7 g/t Au, 38 g/t Ag, 1.2 % Pb, 7.4 % Zn, 43%S, 320 ppm Bi, 440 ppm Cd, 700 ppm Cr, 460 ppm Ni and 100 ppm Co. Compared with Kali Kuning, Lerokis copper rougher concentrate had much higher zinc and lead assays but slightly lower arsenic and antimony grades. A preliminary mineralogical assessment study was carried out on Kali Kuning flotation feed in September 2005 and a subsequent follow-up study was carried out on in July 2006 on Kali Kuning (2.55% Cu) and Lerokis flotation feed (1.97% Cu) and corresponding rougher concentrate samples. This work was performed by G&T Metallurgical of Kamloops, British Columbia, who are well known for their application of mineralogy to optimisation of grind and flotation conditions. The studies showed that flotation feed mineralogy was dominated by pyrite (77-82%) and gangue (13-15%) followed by chalcopyrite (1.8-3.8%), chalcocite (1.7-1.9 %), sphalerite (0.3-1.7%) and tennantite/enargite (0.4-1.1%). In the rougher copper concentrates formed at a p80 grind size of 40 microns, the pyrite dominance (48-64 %) continued, but copper minerals (30-40%) and sphalerite (2-12%) were substantially upgraded relative to gangue minerals (2%). Major copper minerals in the concentrate included chalcopyrite (10-26 %), chalcocite (7-14 %) and tennantite/enargite (5-8 %). The extensive liberation of pyrite in the concentrate suggested that grind size might be coarsened, but recent testwork by Optimet suggests that any increase in grind size is likely to be limited. Recent engineering studies by Intermet Engineering Pty Limited in association with continuing flotation optimisation testwork by Optimet on a fresh master composite (3.4% Cu) as well as on individual composites (2.8 and 3.8% Cu) from Kali Kuning have confirmed that rougher concentrate production aimed at maximum copper recovery will provide better returns than cleaner concentrate production when followed by downstream hydrometallurgical treatment. Other recent Kali Kuning flotation results suggest that flotation economics are likely to be improved by a slightly coarser primary grind (p80 of 53 rather than 40 microns), addition of lime in the grind to precipitate water-soluble copper and shortened conditioning time (5 rather than 30 minutes). Optimum rougher flotation conditions for Kali Kuning have been defined by Intermet as follows: grind in lime pH 11.5; target grind size P80 53 microns; SMS dosage 500 g/t; SEX (sodium ethyl xanthate) dosage 300 g/t added stepwise through flotation; 35 g/t MIBC frother addition; total reagent conditioning time 5 minutes; and total flotation time 25 minutes Limited recent additional testwork on an aged Lerokis sample has confirmed reductions in copper recovery and concentrate grade due to sample ageing in the field, and further assessment of the ageing rate of Lerokis material will be required. Ageing testwork under simulated tropical conditions on Kali Kuning fresh ore sample has shown moderate ageing effects with a 2% loss in copper recovery after 4 weeks and possibly higher losses after longer periods of ageing. Ore stockpile management to limit ROM storage to 2 weeks before flotation will be an important part of mill design and operational requirements. Effects of ore ageing within exposed areas in the open pit have yet to be addressed. Recent tests on the possible use of sea water for flotation have found that sea water causes poor flotation performance due to pH buffering effects. Further testwork will be necessary if sea water is to be considered as a possible future processing option. However, it is understood from Finders that adequate freshwater supplies are expected to be available. Vendor thickening and filtration tests have been completed on Kali Kuning rougher flotation concentrate by Outokumpu and Larox respectively. Thickening tests have also been completed on flotation tailings. High thickener underflow densities were achieved for both concentrate and tailings including 80% solids for concentrate at a flocculant dosage of 20 g/t and 77% solids for tailings at a flocculant dosage of 10 g/t. A low filter cake moisture content of 7% was also obtained in the filtration tests, although with a slightly hazy filtrate. Hydrometallurgical Process Testwork Arsenic, mercury and antimony contaminants in copper concentrates are difficult to successfully and/or economically remove using conventional pyrometallurgical processing routes to produce copper metal. In this context, Finders Resources commenced preliminary testwork to establish the indicative amenability of three different hydrometallurgical treatment processes to extract copper from Wetar Kali Kuning and Lerokis rougher copper concentrates. These processes all produce high grade copper with the arsenic and mercury typically rejected to the leach residue, allowing them to be handled in an environmentally acceptable manner. By-product zinc recovery was not considered in the preliminary testwork but has been considered in subsequent testwork. The first round of testwork involved concentrate samples of 5kg or so that had been produced from Optimet rougher flotation testwork at a p80 grind size of 40 microns being sent to the proprietors of the three processes. Preliminary batch scale hydrometallurgical copper extractions obtained by the three different concentrate treatment options varied from a disappointing low of 76% for one process to a highly encouraging 95% for the other two processes, Xstrata’s Albion process and Outokumpu’s HydroCopper process respectively. These results indicated that the Wetar rougher concentrate is technically amenable to high copper extractions, despite the high pyrite content of the concentrate. A second round of testwork has also been completed on rougher copper concentrate samples prepared by Optimet from a Lerokis composite. The Lerokis concentrate contained a much higher level of zinc (7.7% Zn) than the earlier Kali Kuning concentrate (2.4% Zn). Nevertheless, leaching test results were good with high recoveries of both copper (93-98%) and zinc (96-99%) being achieved. One process supplier also conducted additional testwork which demonstrated the ability to economically produce by-product cathode zinc by SX/EW treatment of the copper raffinate. The other process supplier suggested further testwork would be needed to confirm the potential for production of by-product zinc oxide. The extent of recovery of silver and gold has varied substantially between the two processes. One process yielded combined silver and zinc recoveries of only 9% and 49% respectively. The other process yielded almost quantitative recovery of silver and would expect to obtain similar high recovery of gold. Detailed operating cost information based on manning, reagent and power usage has been provided by both concentrate leach process suppliers. One process supplier has also provided capital costs based on recent Australian construction costs whilst the other process supplier has provided capital costs based on recent European construction costs. Leaching Bottle roll leach tests on minus 2mm crush yielded 29% (Lerokis 2.8% Cu) to 45% (Kali Kuning 2.2% Cu) copper recovery after 50 days. Column leach tests on agglomerated minus 6mm crush in a 1-m column have to date yielded between 30% (Lerokis 2.8% Cu) and 70% (Kali Kuning 2.0% Cu) copper recovery after the first 50 days. Phase 1 BioHeap amenability tests have been carried out on minus 2mm crush samples of Kali Kuning (2.1% Cu) and Lerokis (2.4% Cu) ores after grinding to a P80 of 80 microns and adapting the milled ore to BioHeap chalcopyrite specific bacterial culture. After only 6 weeks of leaching a copper recovery of 81% was obtained from Kali Kuning at an acid consumption of 12 kg/t. Corresponding copper recovery from Lerokis was 58% at nil acid consumption. Leaching was continuing. A Phase 2 test work proposal for 60 to 240 days of leaching involving 3 crush sizes x 3 columns at 1 m high for Kali Kuning, 1 crush size x 1 column at 5 m high for Kali Kuning, and 1 crush size x 1 column x 1 m high for Lerokis has been proposed. The high copper recovery obtained from column leaching of Kali Kuning samples is currently under review, pending resolution of substantial differences in head assays of duplicate samples submitted to different assay laboratories. Duplicate head assays have ranged from the order of 2.0 to 3.3% Cu, suggesting significant variability in ore composition under current sampling techniques. Investigation work is continuing. Although copper recoveries from heap leaching are likely to be much lower than from concentrate leaching, substantially lower capital and operating costs are likely to make heap leaching an especially attractive option, provided that reasonable leach recoveries can be achieved. The main drawbacks to a heap leach operation on Wetar Island are likely to be the need to ensure the development of environmentally acceptable arsenic disposal and acid mine drainage controls. The surprisingly limited rate of pyrite oxidation to date and the potential to keep close control over leach solution movement within both the Kali Kuning and Lerokis mine sites provide encouragement that a relatively simple solution will be found to these issues. However, more advanced 2-m or higher column leach test results and appropriate environmental modelling will be needed before a clear-cut choice of on-site heap leach SX/EW processing versus on-site concentrate production and off-site concentrate leaching is available. |
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