Comparison of the immature profile of the laterites from the Izabal Geosol with wet and dry laterites. 

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... Resources Inc. is developing a nickel-cobalt laterite project in Guatemala, Central America, by applying existing atmospheric chloride technology to a known resource. The tropical laterite project has an inferred resource of 133 million tonnes grading 1.51% nickel, which represents ~20% of Chesbar’s land holdings in Guatemala. Within its boundaries, the Sechol area has a measured resource of 14 million tonnes grading 1.46 % nickel and 0.08% cobalt, and an indicated resource of 23 million tonnes grading 1.34% nickel and 0.08% cobalt. Notwithstanding the impressive overall resource, the company has taken an innovative approach to a laterite project and is concentrating on El Inicio, a high-grade starter pit with five million tonnes grading 2.1% nickel and 0.08 % cobalt. The process flowsheet is based on atmospheric chloride leaching in a slightly acidic magnesium chloride brine, solution purification by recycled magnesia, precipitation of a mixed nickel/cobalt hydroxide intermediate product, and lixiviant regeneration by modified pyrohydrolysis technology. Initial results suggest that >90% of the contained nickel and cobalt in the non-magnetic fraction of the feed can be recovered, with <5% of the iron leaching. A metallurgical scoping study has established preliminary capital and operating costs for a production facility at a proposed rate of 20,000 tonnes per year of nickel as the intermediate mixed hydroxide. A preliminary assessment of producing a magnesium oxide by-product has also been carried out. This paper reports on the current development of the project and highlights the advantages of working in a chloride medium at atmospheric pressure and slightly elevated temperatures. Chesbar Resources is a Canadian Exploration Company, formed in the 1930s and listed on the Toronto Stock Exchange, Canada. A joint venture agreement between Intrepid Minerals Corporation and Chesbar (75/25), known as Minera Mayamerica S.A., was originally signed in January, 1998 with the objective of exploring for gold and silver; prior to that, Chesbar had been involved in gold exploration in Venezuela. In December, 1998, Minera Mayamerica S.A. was granted the original nickel licences in Guatemala for properties adjacent to Inco’s Exmibal deposit, and in 2001, Chesbar subsequently acquired 100% of Mayamerica with the objective of establishing a nickel/cobalt production facility. A more detailed description of the geology of the Guatemalan Laterite Belt has been given in a previous publication [1]. The Sechol group of deposits comprises several large lateritic pockets, which are delimited by tectonic faults and hosted by ultramafic rocks, mainly dunites and pyroxenites, and usually strongly serpentinized. As a result of the study of several laterite profiles in the area, and using the definitions established by the North American Stratigraphic Code, a new pedostratigraphic unit was defined, The Izabal Geosol, which is composed of five pedological horizons: 3⁄4 Gossan or Iron Hat (not always present) 3⁄4 Limonitic Horizon 3⁄4 Stone Line 3⁄4 Mottled Zone Horizon (also known as the Transition Zone) 3⁄4 Saprolite Horizon. The saprolite horizon marks the bottom part of the Izabal Geosol, and lies directly over the saprock horizon which continues into the less weathered bedrock. The most complete profiles are usually present over weathered dunites and serpentinites, while on top of the less altered pyroxenites, there is usually the formation of only a limonitic zone. All of the laterite deposits in Guatemala are associated with an ophiolitic belt that probably intruded during the Tertiary Era. The young age and the petrologic composition of these ultramafic rocks, together with the climatic conditions of the area, are responsible for the formation of these immature profiles, shown in Figure 1. The extensive regional position held by Chesbar Resources Inc. within the Guatemalan Ophiolitic Belt provides the potential for similar or even larger-scale deposits than the Sechol Group which have already been identified. The 2002 exploration program identified several potential deposits within the Sechol property and in other adjacent licences. Including the work completed in the Marichaj, San Lucas and Sechol properties, Chesbar has already identified resources of 133 M tonnes grading 1.51% Ni and 0.08% Co. Currently, the company has a total of 15 claims, representing 741 km 2 of potential lateritic targets, as shown in Figure 2. In accordance with the Canadian NI 43-101 legislation, Chesbar has identified the following resources (Table I) in the Sechol Property, using a 1% Ni cut-off, a minimum thickness of 2 metres, and a dry density of 1 g/cm 3 . Within the measured resources, the start-up pit, El Inicio, with more than 5M tonnes grading 2.1% Ni and 0.08% Co has been identified, with material from this pit being used to prove the metallurgical flowsheet. Essentially, there have been four processes used for the recovery of nickel and cobalt from laterite deposits. Two of these are pyrometallurgical processes (ferronickel production and matte smelting), and are not discussed any further in the context of this paper, except to note that these processes generally treat only the higher Ni, higher Mg-content saprolite horizons. One, the Caron Process, is a hybrid, being a reduction roast followed by ammonia leaching. The fourth is the only true hydrometallurgical process, pressure sulphuric acid leaching. The latter two processes focus mainly on the lower Ni, lower Mg-content limonite horizons. Over the past decade, nickel laterites have received a great deal of attention in terms of hydrometallurgical flowsheet development. All of the processes planned or so far commercialized have been based on a sulphuric acid leach at high pressure, the Pressure Acid Leach (PAL) or High Pressure Acid Leach (HPAL), and from published information, there appears to have been very little attention given to evaluating a chloride-based approach. Various reasons have been advanced for this, such as exotic materials of construction being needed, chloride is an aggressive lixiviant with a consequent high acid consumption and leaching of most metals in the ore, difficulties with controlling iron leaching, and how to handle magnesium leaching. All of these are valid concerns, but neither are they insurmountable problems. The first, and probably most successful, laterite leach plant is that at Moa Bay in Cuba, which originally (briefly) commenced operations in 1959 [2]. The process is based on a sulphuric acid pressure leach at around 240 o C in pachuca autoclaves, and subsequent precipitation of a mixed nickel/cobalt sulphide intermediate for further refining at the Corefco (formerly Sherritt) nickel- cobalt refinery at Fort Saskatchewan, Canada. Until relatively recently, this remained the only operating pressure acid leach process for nickel laterites. An alternative process, a modified version of that first described by Caron in 1950 [3,4] and known by his name, based on ammonia/ammonium carbonate leaching of reduction-roasted laterite, has seen some commercial success, notably by Níquel Tocantins in Brazil and Queensland Nickel (BHPBilliton) in Australia, although there have been other operations using this process. Its major disadvantage is that cobalt recovery is limited, often as low as 40%. The Sechol development in Guatemala is adjacent to the Exmibal property, owned by Inco, and operated as a nickel matte smelter until it shut down in 1980. These properties border Lake Izabal (Figure 2), which is increasingly becoming a resort spot, and therefore, it was considered undesirable to consider any kind of smelting operation in such a setting. Despite the relatively high MgO content of the ore, this not only eliminated options such as ferronickel or a continuation of matte smelting, but also the roasting step which is a pre-requisite for the Caron ammonia leach process. With this in mind, attention was then turned to investigating a hydrometallurgical flowsheet, with the original intention being to follow the well-developed sulphuric acid pressure leach (PAL, HPAL) processes in Western Australia, and which Inco has planned for the Goro Project in New Caledonia. Initial scoping testwork, carried out at different testing laboratories (and hence on slightly different materials), showed that both the saprolite and the limonite horizons of the Sechol orebody were amenable to leaching with either sulphuric or hydrochloric acid, as shown below in Table II. These tests were carried out in order to give pointers as to the most attractive route to follow, and the results can be summarized as follows: 3⁄4 The highest extractions were obtained with the pressure sulphuric acid leach system, although, as can be seen, the ...