Deflation, loam and dry stream sediment samples involve the collection of dry sample material from the optimal sample location. The sample is dry sieved by hand to reduce the initial sample volume, generally using a 2 000 μm oversize sieve and 425 μm undersize sieve. Sieve sizes may, however, be varied depending on the particle size distribution of the sample medium.
Wet stream sediment samples are collected from suitable trap-sites in active drainages. The sample material is washed and sieved generally using a 710 μm oversize sieve and 300 μm undersize sieve. Heavy minerals are concentrated from the smaller screen fraction using a mechanical hand-jig. The oversize (710 μm to 2 000 μm) fraction is generally also concentrated on a 450mm diameter, 710 μm sieve. Where heavy minerals are observed in the oversize fraction they are also collected. Using this method, initial sample volumes may be reduced by a factor of more than 100. These samples are dried in the field and re-bagged prior to consignment.
Rock chip samples involve the collection of sample material from a selected lithological horizon, either derived from drill chips or surface outcrops using a geological hammer.
All samples are submitted to an independent laboratory in Cape Town for processing and recovery of heavy mineral concentrates. These concentrates are then transferred for mineral extraction, surface texture descriptions, and (where appropriate) mineral analysis.
A 100,000 tonne bulk sampling program was carried out on the Mothae Project between January 2007 and May 2009. The objectives of this program were to validate the grade estimates of prior investigations, to collect a sufficient parcel of diamond to enable an initial assessment of diamond value, and to determine whether the diamond population of the Mothae Kimberlite contained a significant component of Type IIa (nitrogen free) diamonds, which, if present, can potentially enhance the economic potential of a Kimberlite. During the latter part of the bulk sampling program, a preliminary delineation drilling program was completed in order to create a preliminary model of the pipe and determine its tonnage potential. The bulk sampling and delineation drilling program is described below and has been compiled from internal Company technical reports. The results of this work and conclusions and estimates drawn therefrom have not been independently reviewed.
A total of 99,959 wet tonnes (82,328 dry tonnes) of Kimberlite were sampled and processed from 5 of the 6 Kimberlite domains identified within the Mothae Kimberlite. Samples were extracted using conventional truck and shovel mining. Near surface Kimberlite at Mothae has been weathered to the extent that it is 'free-digging' and does not require drilling and blasting to extract or primary crushing to process.
Sample material was processed through a 30 tonne per hour dense media separation plant to produce a heavy mineral concentrate. All material less than 2mm was rejected to tailings, and all material greater than 18 mm was crushed and reprocessed. The heavy mineral concentrate was then divided into coarse (-16 mm to +8 mm), medium (-8 mm to +3.5 mm) and fine (-3.5 mm to +2 mm) fractions and these fractions passed over a continuous grease belt for diamond recovery. Material greater than 16 mm in size was hand sorted.
Recovered diamonds were classified on the basis of size, weight, crystal form, color, and clarity. Larger stones suspected of being Type IIa diamonds were tested using 3,000 angstrom wavelength ultraviolet light.
During the course of the sampling program, it was recognized that multiple passes of the heavy mineral concentrate through the process plant and grease belt was required to achieve acceptable diamond recovery. The processing protocol was modified accordingly, and grease belt tailings were processed through an X-ray diamond recovery unit as an audit. Poor diamond recoveries on a single pass over the grease belt are believed to result from mineral coatings on the diamonds which results in the need for additional scrubbing to ensure the diamonds are sufficiently clean to adhere to grease.
Industry standard security measures for Kimberlite processing and diamond recovery were rigorously maintained throughout the program. Recovered diamonds were stored on site during diamond classification work and then removed from site to a secure location.
In total, the bulk sampling program yielded 8,899 diamonds with a total weight of 3,873.21 carats (based on the sum of individual stone weights). Grades obtained for individual samples range from 1.52 to 7.08 cpht on a dry tonnage basis. The average grade for the entire bulk sample is 4.70 cpht. The weight of diamonds per sample is based on the sum of individual weights determined for all stones recovered. The following table sets out the processing results for individual bulk samples.
|Sample||Stones||Carats||Carats/stone||Wet sample weight (t)||Dry sample weight (t)||Dry sample grade (cpht)|
*RCA = Recrush material (+ 16 mm DMS sink and 8 - 20 mm DMS float) treated between Phase 1 and Audit.
** All/Mix = General spillage, stones cannot be allocated to an individual sample.
A 15 hole, 2,452m NQ core delineation drilling program was completed between December 2008 and February 2009. Drill core was logged on site with an emphasis on characterizing the nature of Kimberlite / wall rock contacts and the nature of the transition from weathered Kimberlite to unweathered Kimberlite. In general, the contact between the Kimberlite and adjacent wall rock was observed to be very sharp. Likewise, the transition from weathered free digging Kimberlite to hard unweathered Kimberlite was observed to be abrupt, commonly occurring over less than one meter. Variations in types of Kimberlite present in each hole were also noted in the core logging program, particularly on holes that were positioned to cross the transition between various Kimberlite domains identified at surface. Additional drilling and detailed core logging, geochemical analysis and petrographic analysis will be required to develop a model of the internal geology of the Mothae pipe.
Density measurements were systematically taken at 10m intervals to develop a density model of the pipe. Drill holes were surveyed using a magnetic survey tool. Results of down-hole surveys were adequate for measuring hole inclination variations, but produced erratic results for azimuth variations. The azimuth survey data were therefore not incorporated into development of the pipe shape model.
Drill hole and surface mapping information was input into GEMS modeling software to generate a pipe shape to a depth of 200m. The pipe was subdivided into 3 zones for the purpose of tonnage and grade modelling: 1) South Zone (encompassing Kimberlite domains A, C, F and G), representing approximately 60% of the total volume of the body - the majority of the bulk samples taken to date derived from this zone; 2) North Zone (encompassing Kimberlite domain E), comprising approximately 14% of the pipe - represented by one bulk sample (E1A); and 3) Neck Zone (encompassing Kimberlite domain H and unassigned Kimberlite), comprising approximately 26% of the body - not represented by any bulk samples. The estimated overall pipe volume to a depth of 200m is 16.25 million cubic metres ("MCM"), which includes 1.76 MCM of near surface, weathered free digging Kimberlite. Based on the density model developed from drill core measurements this volume of Kimberlite represents 38.62 Mt, which includes 3.36 Mt of near surface, weathered free digging Kimberlite.
This global tonnage estimate was made to enable the Company to better assess the potential of the Mothae Kimberlite and does not constitute a resource estimate as defined by National Instrument 43-101. There can be no assurance that additional drilling will confirm this estimate of geologic potential or lead to the identification of a resource as defined by National Instrument 43-101.
Diamond grades have been estimated for weathered Kimberlite in the North and South Zones based on the bulk sample data presented in the above table. The estimated grade for the South Zone is 4.09 cpht, calculated as an area weighted average of sample grades for each of domains A, C, F and G, respectively. The estimated grade for the North Zone is 2.30 cpht and is based entirely on sample E1A. Due to the increased hardness and likely reduced efficiency of diamond recovery from unweathered Kimberlite, the sample grade values cannot be directly extrapolated to the unweathered portions of the respective Kimberlite domains. Recoverable grade estimates for this material based on size distribution modelling and comparison to recoveries at the Letseng Diamond Mine are approximately 40% lower than those of the weathered Kimberlite. No grade information is available for the Neck Zone. When combined with tonnage estimates, grade values yield an estimated total diamond content for the South and North zones of 0.69 million carats, of which 0.09 million carats occur within near-surface weathered Kimberlite material.
Grade estimates and estimates of contained diamond do not constitute a resource estimate for the Mothae Kimberlite as that term is defined by National Instrument 43-101. Estimates of diamond grade, contained carats and global tonnage for the Mothae Kimberlite have been made by the Company to assess the geologic potential of the Mothae Kimberlite so as to guide decisions about additional evaluation work. There is no assurance that continued evaluation work will confirm these estimates of geologic potential or that such work will result in defining a resource or reserve for the Mothae Kimberlite as those terms are defined by National Instrument 43-101.
The parcel of diamonds recovered to from the Mothae bulk sample program (3,873.21 carats) displays a very coarse stone size distribution, reflected in a high proportion of large stones. The results suggest very similar frequencies of large stones (in the +5 to +20 carat categories) to what would be expected in the same mass of Kimberlite from the Letseng Diamond Mine. This information, in conjunction with the recovery of a broken Type IIa diamond that originally exceeded 44 carats in size indicates very good potential for very large Type IIa diamonds similar to those recovered at Letseng. Test work undertaken to date indicates that overall approximately 24% of the examined Mothae diamonds are of the Type IIa variety. The highest proportion of Type IIa diamonds (43%) was observed in the largest size fraction examined (+23 Diamond Trading Company ("DTC") sieve class).
Valuation of the Mothae bulk sample diamond parcel by Galaxy Diamond Expertise SA ("Galaxy") in June 2009 yielded an average price of US$437 per carat.
Diamond value modelling was undertaken by combining size frequency distribution models of the total parcel recovered to date from Mothae, with modelled diamond prices per DTC size category. This is important as actual parcel estimates do not account for the probable presence of large, potentially high value stones that can have a considerable influence on average diamond value. The modeled run of mine diamond value estimate by Galaxy in June 2009 is US$559 per carat. In its June 2009 valuation and modeling work, Galaxy noted fragments of the large Type IIa stone which originally exceeded 44 carats (noted above) and observed that, had the stone not been broken, the modeled value estimate would be significantly higher.
Limitations of Bulk Sample Inferences and Estimates made from the Mothae Bulk Sampling Program
The inferences and estimates made from results of the bulk sampling program have the following limitations:
The information in this section which is of a scientific or technical nature has been derived in part from the technical report entitled "Mothae Kimberlite Project, Lesotho, Independent Technical Report" dated February 12, 2007 prepared by Dr. Norman Lock (BSc, PhD, CGeol FGS, MGSSA, PrSciNat) of MSA Geoservices (Pty) Ltd., who is a "qualified person" within the meaning of this term in National Instrument 43-101. A copy of the report is available on SEDAR at www.sedar.com.