Mantra Resources Updates On MRE At Nyota Prospect, Tanzania
Mantra Resources Limited (Mantra Resources) has updated mineral resource estimate (MRE) for its Nyota Prospect, part of the wholly owned Mkuju River Project (MRP) in southern Tanzania. This MRE comprises 15.3 million tonnes averaging 504 ppm for 17.0 million pounds of U3O8 classified into the Indicated Resource category, plus Inferred Resources of 29.1 million tonnes averaging 430 ppm for 27.6 million pounds of U3O8 at a lower cut-off grade of 200 ppm U3O8.
The updated MRE has been prepared by independent consultants CSA Global Pty Ltd (CSA) and is reported in accordance with the Canadian National Instrument 43-101.
The updated MRE includes the available results of infill and extension drilling conducted during 2009 and is based on new data from a total of around 26,000 meters of drilling completed by the company to early November 2009.
It should be noted that the results from the exploration drilling program, including the significant area of mineralization identified at Nyota NE, have not been included in the December 2009 update of the MRE.
The current phase of exploration drilling will be concluded in December and followed by a further revision of the MRE in the March quarter of 2010. The revised MRE will include the exploration drilling data and the remainder of the infill drilling and trenching results that are still pending.
Mantra Resources’ Joint Managing Director Robert Behets said: “This updated Mineral Resource Estimate and the recent exploration success at Nyota NE clearly demonstrates the significant potential of Nyota and the broader MRP. As a result of the company’s fast-track approach to the exploration and appraisal of the Project, the resource base has grown rapidly. Given the extensive target areas still to be tested, we are confident that ongoing work has the potential to continue to deliver exploration success and resource growth into the future.”
The Board has taken great encouragement in these results and has elected to defer the completion of the Pre-Feasibility Study (‘PFS’ or ‘the Study’) until the MRE updates from December 2009 and Q1 2010 are fully integrated into the Study. It is anticipated that the PFS will now be concluded in the March quarter of 2010.
Project Location and Geology
The Mkuju River Project is located in southern Tanzania, around 470 kilometers southwest of Dar es Salaam.
The MRP lies within the Karoo Supergroup sediments of Permian to Jurassic age. The host stratigraphy is a series of sub-horizontal, very coarse, feldspathic, arkosic sandstones with minor inter-bedded claystones and siltstones. The sediments are interpreted to have been deposited within a braided fluviatile system.
The Nyota Prospect, located in the north-western portion of the MRP, is divided in a northern area characterised by steep sided hills and valleys and a southern area which has less prominent topography.
Mineral Resource Estimation by CSA
The updated resource modelling for the MRP on the Nyota Prospect has been completed for the A, C and D areas of mineralization.
The uranium mineralization has been interpreted to lie within sub-horizontal sedimentary units bound by claystone bands. Surface geological mapping combined with drill hole logging and down-hole geophysical conductivity data was used to define the sedimentary depositional units. The clay rich base of each significant sedimentary unit was interpreted in 3-D on N-S 50 meter spaced cross sections. The average dip of the clay bedding horizons ranges between 3 to 5 degrees towards the N or NNE direction.
The sedimentary units were linked across all deposits by surface mapping. A total of 10 units were identified. Each unit has been assigned a unit number which was used in the block modelling and drill hole flagging processes.
A specialised Datamine down-hole compositing process (CompSE) was used to define downhole mineralization intercepts at various U3O8 cut-off grades over a minimum vertical thickness of 3 meters. Within the sedimentary units, the 80 ppm U3O8 cut-off was determined to be the ‘natural’ boundary between ‘mineralized’ and ‘un-mineralized’ material. Within each sedimentary unit the top of mineralization, based on the 80 ppm U3O8 cut-off, was interpreted on the N-S 50 meter cross sections. The drill hole samples were coded with the unique sedimentary unit identifier.
Surface wireframes were created from the sedimentary basal and U3O8 mineralization strings. The wireframes were extended 25 meters along and across strike past the outer edge of the zones of mineralization. In minor instances where internal mineralization continuity based on geological control was interpreted to exist, it was extrapolated up to 200 meters along strike and 100 meters across strike.
A topography digital terrain model (‘DTM’) was provided by Mantra Resources. Photomap International Inc completed an aerial survey in November 2008 and provided colour aerial photography, digital ortho-photos and a DTM covering a 14 kilometer by 14 kilometer area. The DTM was completed at 10 meter grid intervals producing one meter contours. The DTM was verified on-site by a number of surveyed traverses.
In areas where surface mapping or trench sampling indicated that the mineralization extended from the drill hole intercepts to the surface, the interpretation was extended to include the surface mineralization. All mineralization located in the top two meters of each deposit, was coded as ‘trench’ and estimated as a separate grade population.
A volume block model was constructed, using the basal and mineralized wireframe surfaces, trench and topographic surface. A parent block size of 10 meters x 10 meters x two meters (X x Y x Z) was applied. Sub blocking was applied down to the smallest cell size of 2.5 meters x 2.5 meters x 0.5 meters (X x Y x Z), in order to represent mineralized volumes with appropriate accuracy.
Preliminary economic analysis estimated the potential mineable cut-off for this style of deposit to be between 150 to 200 ppm U3O8. Hence the resource was modelled using a relatively conservative 200 ppm U3O8 lower cut-off.
QA/QC information for all assay and geophysical data types was reviewed and showed acceptable levels of precision and accuracy. Comparison between assay and geophysical results for samples containing both methods of grade measurement, within the 200 ppm U3O8 mineralization volumes, was completed and showed a very good comparison with assay data >150 ppm U3O8.
A probability modelling technique was used to define the mineralized volume within the 80 ppm U3O8 mineralized envelope that exceeded 200 ppm. The defined blocks were coded for grade estimation using the samples within the 200 ppm composite intervals defined by the CompSE process.
Statistical analysis of the samples within the 200 ppm composite intervals defined by theCompSE process was completed for U3O8. Top cuts were applied separately for drill hole and trench data. The top cuts applied to the drilling data were 3,000 ppm U3O8. The trench data was cut at 3,000 ppm U3O8 for Area A and 5,000 ppm U3O8 for Area C, no top cut was required for the Area D trench data.
Geostatistical analysis was completed for Area A. A close spaced 10 meter and 20 meter cross was drilled specifically for geostatistical analysis. Variograms were successfully modelled indicating a population nugget of 7% with an along strike N-S range of 137 meters, a cross strike E-W range of 55 meters and a vertical range of 6 meters. The Area A variogram parameters were applied to Areas C and D. No variograms were obtained for the surficial mineralization zones.