African Aura Mining Inc., the TSX-V (AUR) and AIM (AAAM) listed exploration and development company focused on gold and iron ore in sub-Saharan Africa, announces the results of an independent Mineral Resource Estimate for the Company's 100% owned New Liberty gold project located in western Liberia.
- Resources and grade increased to 1.51 million ounces at 3.78 g/t Au
- 5,599,000t at 4.17 g/t (for 751,000 ounces) in the indicated category; and
- 7,040,000t at 3.40 g/t (for 762,000 ounces) in the inferred category
- Entire indicated resource is within potential open pittable depth from surface
- Management is targeting a production profile of approximately 100,000 ounce per year for the open pittable material
- Deposit remains open at depth and along strike
- Resource model will be incorporated into a Preliminary Economic Assessment
The resource estimate was undertaken by AMC Consultants (UK) Limited ('AMC') in accordance with the requirements of National Instrument 43-101 "Standards of Disclosure for Mineral Project", of the Canadian Securities Administrators ("NI-43-101"). It incorporates all the results from drilling as at 14 September 2010, being 175 holes for 27,736 meters and was calculated on the basis of a 1.0 g/t cut-off grade.
The Preliminary Economic Assessment of the New Liberty mine is being carried out by AMC and is expected to be complete by the end of 2010.
Luis da Silva, Chief Executive of African Aura, commented:
"We are delighted that the resource estimate offers the opportunity to achieve our objective of developing an open pit gold mine with the potential to produce approximately 100,000 ounces per year. We are particularly pleased with the much higher grade of 4.17 g/t for the 751,000 ounces in the indicated category, all of which are within an open-pittable depth of 200m from surface. New Liberty remains open at depth and we anticipate that, in line with similar Archaean age gold projects around the world, substantial further resources may be defined by deeper drilling in future.
In light of New Liberty's size, high grade, excellent metallurgy and potential production profile the project is on the cusp of becoming a very significant gold deposit in West Africa and we look forward to updating shareholders in due course."
The total resource estimate of 1.51 million ounces of gold grading 3.78 g/t is comprised of 5,599,000 tonnes grading 4.17 g/t (for 751,000 ounces) in the indicated category and 7,040,000 tonnes grading 3.40 g/t (for 762,000 ounces) in the inferred category. The indicated resource has been projected to an approximate depth of 200 metres below surface. The inferred resource remains open down dip and open along strike.
Resource estimation parameters
- The estimates of mineral resources were calculated in accordance with NI 43-101 and carried out by Chris G Arnold BSc (Hons), MSc, MAusIMM (CP) of independent consultants AMC.
- A total of 175 diamond drill holes have been completed at New Liberty for 27,736m, the majority of which have been utilised in the Mineral Resource estimate. The drilling has been carried out with holes typically inclined at -60°, resulting in intersection angles generally being 75% of the true width. Down hole surveys have been carried out on all of the holes and core recovery averages over 90%.
- The resource estimation has been based on interpretations using integrated geological and grade information recorded from diamond core logging and assaying. Most of the resource interpretation, modelling and estimation work was conducted using Datamine geological and mine planning software package. The database was subject to a series of standard validation procedures, and twenty percent of the data was randomly selected for validation against source information.
- The interpreted mineralised zones present as strongly planar shapes striking generally slightly south of east and dipping between 60° and 80° to the south. The geological and mineralisation shapes were formed into solid triangulated wireframes, which were filled with model cells based on parent cell XYZ dimensions of 10m x 10m x 20m. Cells were permitted to reduce to 5m, 2.5m and 10m in the X, Y and Z dimensions respectively in order to better represent the geometry of the mineralisation. The model was coded to reflect individual mineralised zones, as well as to distinguish between weathered and unweathered material, using an interpreted top-of-fresh surface based on geological logs. A triangulated surface of topography was used to constrain the upper bounds of the model.
- Samples were coded by mineralisation zone and weathering in a manner consistent with the cell model. Statistical analysis was conducted on one metre composites within different subsets extracted from the coded sample file (e.g. by mineralisation zone). The results of the statistical analysis demonstrated that the mineralised zones have a range of mean grades (from 1.61g/t Au to 6.47g/t Au), but the corresponding coefficients of variation fall within a relatively narrow window (1.18 - 1.53). All zones exhibit some bimodality in their distributions, and this is attributed largely to the short scale grade variability within zone intersections, where low grade samples interfinger with strongly mineralised samples. A recognised high grade shoot character of the mineralisation may also contribute to the bimodality.
- Statistical analysis was used in conjunction with a spatial assessment of high grade samples to determine individual high grade cap values for each mineralised zone, for use during grade estimation. Variographic analysis was conducted on all mineralised zones with sufficient composites, and three of these two returned structures suitable for modelling.
- Gold grade estimation was conducted from one metre composites, using Ordinary Kriging in those zones for which variogram parameters were generated. For the other more extensive zones, variogram parameters derived from the combined mineralised zone data set were applied, while for the remaining zones with relatively fewer intersections, inverse distance squared weighting was applied.
- The resource model was populated through grade interpolation into parent cells, under hard-bounded zonal control, using 50m x 80m x 10m (strike / dip / cross plane) search ellipsoids, aligned in the average plane orientation of each zone. Cells not estimated in the first pass were estimated by subsequent passes with expanded search ellipses.
- In 1999, five drill-core samples were submitted to Lakefield Research Limited of Ontario, for mineralogical examination and subsequently metallurgical and environmental testing, and in 2006 Mintek of South Africa completed metallurgical testwork on 126 core samples from four drill holes. The principal conclusions of metallurgical testwork conducted in 1999 were that the gold is strongly associated with silicate minerals and, less commonly, with sulphides, within altered mafic to ultramafic rocks, and that gold extractions of between 79.5% and 96.9% are achievable, depending on the sample. Furthermore, some of the gold may be recoverable by a gravity method, suggesting potential for pre-concentration of the sample prior to leaching. The 2006 work confirmed the responsiveness to gravity recovery, suggesting that greater than 50% gravity recovery is achievable, and an overall recovery of 93% can be obtained by a combination of gravity and carbon-in-leach (CIL) processes. In addition comminution characterisation tests showed the material to be of medium hardness and lower abrasiveness.
- No assumptions have been made in the resource estimate about mining or processing methods.
Quality assurance / quality control ("QA/QC") and chain of custody
- QA/QC analyses for the period 2005-2010 were undertaken by AMC in preparation for resource estimation. The progressive introduction of QA/QC procedures included the standard implementation of field duplicates (quarter core and crushed), blank samples, standards and laboratory repeats, as well as specific programmes of re-assaying and umpire laboratory assaying.
- Diamond drilling at New Liberty was supervised by African Aura's geologists. Core and core blocks are placed in core boxes by the driller. Upon reception in the core shed on site, core was cleaned or washed, if required, and core blocks were checked by African Aura staff. The core was then photographed wet and dry in a frame to ensure a constant angle to and distance from the photographer. Magnetic susceptibility readings were taken every metre. Geotechnical logging was carried out, taking records of casing size, bit size, depths, intervals, core loss/gain, core recovery, weathering index, RQD, fracture index, jointing and joint wall alteration and a simple geological description recorded. For oriented core more detailed point data based depth, alpha and beta angles of fabrics were recorded. Geological logging then follows as from-to data, containing depths, rock codes and brief descriptions of the lithological units and angles of contacts. Bulk density measurements were also taken.
- The core was transferred to the core saw shed for cutting. Splitting was done using spoons or trowels on unconsolidated material, with half the diameter of the sample being removed for assay. Solid core was sawn in half with a core saw and each sample interval placed in a plastic bag and a sample ticket included with the sample. The bag was labelled with hole number and sample number using a marker pen.
- Prior to shipment, final checking was carried out in the presence of a Senior Geologist and two field assistants to ensure sample IDs were correct, samples were intact and there were no omissions. Quality control standards and blanks samples were inserted at pre-determined intervals at this point. For all holes drilled since 2009, samples were sent from site on a complete hole basis directly to the OMAC preparation facility in Monrovia, along with documentation, which acts as a receipt and sign back. Sample transfer and delivery to the OMAC laboratory in Ireland was then monitored and tracked via their website until assays were released. OMAC is accredited by Irish National Accreditation Board to ISO 17025 and fire assay is included in the Schedule of Accreditation.
- Pulp weights sent from Liberia for analysis were between 100 and 200g. On arrival of the 150-200g portions of prepared pulp at OMAC, samples were checked against the submission sheet, logged into LIMS, and homogenised to prevent segregation that might have occurred in transit. Large consignments of samples (>300) were split into smaller sub-batches of 200 samples for convenience of processing. This practice was introduced in 2008 and prior to that every consignment was treated as a single batch.
- Samples were weighed, mixed with flux and fused in clay crucibles. Lead buttons produced after fusion were cupelled, forming dore prills that were digested in aqua regia, and digests are analysed for gold using a Varian AA Spectrometer. Samples were analysed in lots of 50 and included 44 original samples, 4 duplicates, one CRM and a blank.
A technical report prepared by AMC entitled "New Liberty Gold Project, Liberia, West Africa - Technical report on Additional Drilling and Estimated Resources" will be filed on SEDAR at www.sedar.com within 45 days of this release.
The Qualified Person responsible for preparing the resource estimate and the technical information presented in this press release is Mr C G Arnold, BSC(Hons),MSc, MAusIMM (CP) of AMC Consultants (UK) Limited.
About the New Liberty Project
The New Liberty gold deposit is a classic Archaean shear zone hosted greenstone gold deposit with a strike length of 1.75km, located in western Liberia. The project has a current resource of 1.51 million ounces at a grade of 3.78 g/t, comprised of 5,599,000 tonnes grading 4.17 g/t (for 751,000 ounces) in the indicated category and 7,040,000 tonnes grading 3.40 g/t (for 762,000 ounces) in the inferred category.
The best drill intersect from New Liberty is currently 8.45 g/t Au over 37m from 55m depth and the deposit, which crops out at surface, remains open at depth. Metallurgical testwork undertaken by the Company on drill core from New Liberty has indicated a non-refractory ore with excellent expected recoveries of up to 93%.
A Preliminary Economic Assessment by AMC Consultants (UK) Limited is presently underway that will contribute to a Bankable Feasibility Study for an open pit gold mine targeting 100,000oz annual production.
New Liberty is one of a series of gold deposits, including the Ndablama and Weaju prospects, located within the Company's 457km2 'Class A' 25 year renewable Mining Licence. Geologically, Archaean greenstone belts are known to host major gold mines in Canada, Australia, the Democratic Republic of the Congo and Tanzania. The Company considers that the Archaean geology of the Man Craton of west Africa is one of very few provinces globally that is highly prospective, but has yet to be systematically explored.
Source: African Aura Mining Inc.