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Review of mineral resources and ore reserves
The Phalaborwa Igneous Complex, situated south of Phalaborwa in the Limpopo province, comprises 14 distinct rock types, each with a specific mineral composition, as illustrated in Figure 2. It is a vertical volcanic pipe, roughly kidney-shaped and measuring between 1,5 and 3,5km in width and 6,5km in length. The complex consists of three conjoined lobes – namely the North Pyroxenite, Loolekop and South Pyroxenite areas.
Apatite is the only phosphate-bearing mineral in the igneous complex. Although it is sometimes present in only very small amounts, it is never completely absent and often figures as an abundant mineral constituent in the pyroxenite and foskorite rock types. Copper and magnetite are present in the Loolekop lobe and are exclusively associated with foskorite and carbonatite rock types.
As a result of exploration drilling, higher concentrations of apatite mineralisation, expressed as a percentage of P2O5, were found in the Loolekop foskorite and pyroxenite rock types, as well as in the pyroxenite rock types of the north-west corner of the North Pyroxenite lobe and the South Pyroxenite lobe. There are four mines currently operating in the Phalaborwa Igneous Complex. Palabora Mining Company (PMC) operates a copper mine in the central portion of the complex, as well as a vermiculite mine in the southern portion of the complex. Foskor operates two phosphate rock mining operations, one situated in the North Pyroxenite area and another in the South Pyroxenite area.
Foskor (Pty) Ltd has submitted all applications as required in terms of the Mineral and Petroleum Resources Developments Act (No. 28 of 2002), related to minerals and reserves. Submissions were made for four new mining rights, three of which have already been granted with the fourth in the process of being reviewed. Two submissions were made for the conversion of old order used rights to new mining rights.
The mining rights already granted are:
Mining right applications submitted and under review are:
Applications for conversion of old order used rights to new mining rights submitted and under review are:
Management is confident that the outstanding applications will be finalised and approved by the Department of Mineral Resources.
From 1950 onwards, numerous drill tests have been performed on the phosphate deposits, with the most recent drilling completed in 2006. A total of 100,544 metres were drilled to demarcate mineral resources in the North and South Pyroxenite pits. Drilling was also performed in PMC’s active tailings dam to evaluate possible mineral resources.
Samples acquired from the defined drill holes were assessed at Foskor’s chemical laboratory. Foskor is not currently undertaking any new exploration projects.
Geostatistical analysis of the drilling information was used to build 3-dimensional geological block models showing phosphate mineral distribution. The block models for the two mining areas and the tailings dam were validated by correlating the original drill-hole assay results with the estimated values determined by the geostatistical methods.
Mineral resources were classified as either measured, indicated or inferred, based on drill-hole densities, kriging efficiency parameters and the cumulative knowledge and experience of Foskor’s geologists.
Mineral resources and reserves
The mineral resources and reserves were classified according to the South African Mineral Resource Committee (SAMREC) Code. SAMREC defines a mineral resource as: ‘a concentration or occurrence of material of economic interest in or on the earth’s crust in such form, quality and quantity that there are reasonable and realistic prospects for eventual economic extraction’.
In terms of the Code: ‘the location, quantity, grade, continuity and other geological characteristics of a mineral resource are known, or estimated from specific geological evidence, sampling and knowledge interpreted from an appropriately constrained and portrayed geological model. Mineral resources are subdivided, and must be so reported, in order of increasing confidence in respect of geo scientific evidence, into inferred, indicated or measured categories’.
To elaborate, a mineral reserve is the economically mineable material derived from either a measured or an indicated mineral source. It includes diluted and contaminated materials and allows for mining losses. At minimum, an appropriate assessment for a project should be a pre-feasibility study. Alternatively, a Life of Mine Plan – detailing considerations; modifications; realistically assumed mining; and all other modifying factors such as the metallurgical, economic, marketing, legal, environmental, social and governmental impacts – should be drawn up.
The cut-off feed grade to economically produce a saleable (36,5% P2O5) phosphate rock concentrate was calculated (using methods originally made famous by leading mathematician and mining consultant Kenneth Lane). The cut-off grade currently used for the North and South mineral reserves is 5,5% P2O5, with material with a grade of between 4% and 5,5% P2O5 classified as marginal ore.
North Pyroxenite deposit
Foskor commenced mining phosphate-bearing ore from the North Pyroxenite deposit, situated in the north-western part of the Phalaborwa Igneous Complex, in 1966. From 1961 to 1977, almost 150 drill holes or 24,377 metres were drilled. Between 1980 and 1984, an additional 55 holes were drilled around the existing pit, adding a further 23,200 metres.
The lithological (rock classification) information from these holes was interpreted to build a resource mineralisation model. On this basis, the mineral resources were estimated and categorised as either measured, indicated or inferred. Design of the open pit mine was based on optimisation runs using the Whittle Optimisation Programme (i.e. a global open pit mine design system used to maximise net present values, and to balance schedules, blends and stockpiles). The North Pyroxenite mineral reserves were estimated with modifying factors at 425,8 million metric tons as at 31 March 2011.
South Pyroxenite deposit
Drilling in the South Pyroxenite area began in the late 1950s and continued into the 1960s. In the 1990s an infill drilling programme was terminated prematurely, due to financial considerations, but was completed during 2005/06. In total, 143 drill holes or 49,584 metres were drilled. Bulk and trench sampling were also done in the South Pyroxenite area.
The geological and resource models for the South Pyroxenite area were based on the exploration campaigns. The geological contacts were interpreted from the drilling data. Ordinary kriging was used to estimate the P2O5 block model values, which were finally validated through comparisons against the original drill hole data.
Mineral resources in the South Pyroxenite area were audited by Snowden Mining Industry Consulting in 2008. As at 31 March 2011, the reserves were estimated at 983,7 million metric tons.
Central area: PMC active tailings dam
Phosphate-rich tailings have been deposited in the PMC active tailings dam since the late 1970s. Foskor owns the rights to the apatite in the tailings even though the dam is located on PMC’s premises. A resource of approximately 297 million metric tons with an in situ (i.e. prior to processing) grade of 6,6% P2O5 was delineated through drilling and sampling during the 1990s.
The data collected during exploration was evaluated for geostatistical application. An oriented block model was then created and ordinary kriging was applied to estimate the grade distribution throughout the dam. The resources were categorised as measured, indicated or inferred.
In 2003, a feasibility study (carried out with assistance from Snowden Mining Industry Consultants and Rio Tinto Technical Services) to reclaim the tailings revealed that the planned capital and operating costs would exceed actual benefits. The project was aborted and PMC’s use of the tailings dam continued.
The carbonatite intrusion in the centre of the igneous complex is surrounded by apatite-bearing foskorite and pyroxene pegmatoid rock types. PMC used to mine and stockpile the foskorite and pyroxene pegmatoid rock as a by-product of mining the copper-bearing carbonatite. PMC selectively mined and stockpiled rock according to the Extension 100F Agreement between Foskor and PMC. The agreement gave PMC the right to process rocks with a less than an agreed P2O5 grade, and to retain every mineral except phosphate.
The rights to the rocks mined by PMC were determined by conventional grade control practices by PMC and monitored by Foskor. PMC commenced mining in 1965, and in 2002 the opencast mine reached its maximum planned depth of 750 metres, after which PMC developed an underground mine in the same ore body below the opencast mine. The foskorite and apatite-rich pegmatoid mined by PMC containing more than 6% P2O5 was stockpiled as foskorite stockpiles for Foskor. The majority of these stockpiles have been mined and processed during the year under review, with the remainder accounted for in the mineral resources and reserves statement.
Phalaborwa phosphate and vermiculite tailings
Currently, PMC operates an opencast vermiculite mine in the South Pyroxenite area, producing vermiculite concentrate from a nearby plant. PMC transports the high P2O5 tailings from this plant to a stockpile close to Foskor’s East Crusher. Foskor has reclaimed high phosphate tailings from this stockpile since 2006.
The estimated mineral resources and reserves reported here were reviewed and endorsed by the following competent persons:
Snowden Consulting was appointed to act as competent person in the validation of the original report compiled in 2009.
Table 1: Proved and probable mineral reserves, as at 31 March 2010*
Table 2: Proved mineral resources as at 31 March 2010
*Most recent official ore reserve calculations.