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Exploration Work
The exploration component of the work completed to date included high-resolution ground geophysical surveys, excavation of a series of exploratory pits through the overburden, and petrographic, indicator mineral and geochemical analysis of kimberlite samples derived from the exploratory pits. The geophysical results, in combination with the bedrock intersections in exploratory pits clearly identified the surface outline of the pipe. Magnetic data, and the results of petrography, indicator mineral and geochemical analysis define six internal kimberlite domains. (A, C, E, F, G and H)
VLEM MAP |
KIMBERLITE DOMAINS |
BOUGUER GRAVITY MAP |
Bulk Sampling
A total of 99,959 wet tonnes (82,328 dry tonnes) of kimberlite were sampled and processed from five of the six 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 2 mm 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, which distinguishes diamonds that contain nitrogen from those that do not.
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.
Grades obtained for individual samples range from 1.52 to 7.08 cpht on a dry tonnage basis (Table 1). The average grade for the entire bulk sample is 4.70 cpht.
Table 1. Processing results for individual bulk samples of Mothae kimberlite. The weight of diamonds per sample is based on the sum of individual weights determined for all stones recovered.
Sample |
Stones |
Carats |
Carats/stone |
Wet sample weight (t) |
Dry sample weight (t) |
Dry sample grade (cpht) |
C1A |
90 |
27.86 |
0.31 |
2,035.29 |
1,837.05 |
1.52 |
C2A |
310 |
117.11 |
0.38 |
5,023.31 |
4,163.82 |
2.81 |
C2B |
211 |
75.47 |
0.36 |
1,936.18 |
1,616.89 |
4.67 |
C2C |
681 |
380.85 |
0.56 |
9,965.10 |
8,192.51 |
4.65 |
C3A |
750 |
301.22 |
0.40 |
9,569.02 |
7,781.52 |
3.87 |
G1 |
1,007 |
408.07 |
0.41 |
7,340.98 |
6,198.82 |
6.58 |
G1C |
2,529 |
1,166.97 |
0.46 |
27,162,70 |
21,970.31 |
5.31 |
F1 |
1,162 |
444.26 |
0.38 |
7,469.90 |
6,273.60 |
7.08 |
F1C |
1,519 |
715.79 |
0.47 |
18,753.24 |
15,389.95 |
4.65 |
A1A |
372 |
129.83 |
0.35 |
5,340.76 |
4,565.28 |
2.84 |
E1A |
255 |
99.61 |
0.39 |
5,362.84 |
4,338.33 |
2.30 |
RCA* |
6 |
2.60 |
0.43 |
394.35 |
394.35 |
0.66 |
All/Mix** |
7 |
3.57 |
0.51 |
|
|
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Total |
8,899 |
3,873.21 |
0.44 |
99,959.32 |
82,328.07 |
4.70 |
*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.
Delineation Drilling Program
A 15 hole, 2,452 metre 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 10 metre intervals to develop a density model of the pipe.
Drill hole and surface mapping information was input into GEMS modeling software to generate a pipe shape to a depth of 200 meters. The pipe was subdivided into three zones for the purpose of tonnage and grade modeling: (i) 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; (ii) North Zone (encompassing kimberlite domain E), comprising approximately 14% of the pipe -- represented by one bulk sample (E1A); and (iii) Neck Zone (encompassing kimberlite domain H and unassigned kimberlite), comprising approximately 26% of the body -- not represented by any bulk samples. The Mothae geology model is illustrated in Figure 3. The estimated overall pipe volume to a depth of 200 meters is 16.25 million cubic meters, which includes 1.76 million cubic meters of near surface, weathered free digging kimberlite. Based on the density model developed from drill core measurements, this volume of kimberlite represents 38.62 million tonnes, which includes 3.36 million tonnes of near surface, weathered free digging kimberlite.
Figure 3. Three-dimensional view of the pipe model for Mothae kimberlite looking west. upper surface shown represents the base of the overburden. The modelled weathered kimberlite zone is indicated in paler colours than the underlying unweathered kimberlite zones. The model extends to approximately 200 metres below the base of the overburden.
Plan Going Forward
Lucara intends to continue the development of the Mothae property. In order to evaluate the economic potential of the project, Lucara intends to enter into a pre-production mining phase. In preparation for this phase, the current process plant will be upgraded to include a large diamond recovery system, improved data capture systems and a slimes handling system.
Prior to commencement of material processing and second round of delineation drilling will be completed to upgrade the internal geological model and will provide a more accurate estimate of the tonnage and diamond content of the Mothae kimberlite. This model will be used to provide input into the preliminary mine plan which will be followed during the trial mining period.
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