Ground geophysical surveys were undertaken in September 2006. Gravity, magnetic and frequency domain electromagnetic (FDEM) surveys were carried out over the Mothae Kimberlite with the view to delineate the Kimberlite/basalt pipe contact and any internal Kimberlite phase variations that may be identifiable.
The gravity survey was conducted with data collection at 25m station intervals along 500m lines spaced 50m apart. Elevation was acquired from a Differential GPS. Bouguer gravity values were achieved using a basalt density of 2.8 t/m3.
A magnetometer was used in 'walk mode' at one second intervals along the 500m lines as for the gravity survey, with infill where required. Spatial positioning was recorded from a handheld GPS. The frequency domain electromagnetic ("FDEM") survey was undertaken. With a 40m coil separation, conductivity data were recorded at 10 m station intervals along 400m lines in the southern lobe and 250m lines in the northern lobe.
Survey results were gridded with a Kriging algorithm.
The gravimetric survey defined the Kimberlite body convincingly. The gravity signature difference between the two lobes may be explained through depth of weathering or local variations in country-rock basalt density. The total horizontal derivative ("THD") of the Bouguer gravity map shows the Kimberlite/basalt contact to closely coincide with that defined by the vertical loop electromagnetic ("VLEM") interpretation.
The Mothae Kimberlite displays two magnetic units, corresponding to the northern and southern lobes; the two lobes are continuous at depth as also shown by the gravity and VLEM responses. The apparent magnetic break in the data could be due to basalt cover. The main Kimberlite body is interpreted to narrow with depth, contrary to previous interpretation. Internal magnetic variation in the southern lobe is interpreted as possible multiple Kimberlite intrusions.
The FDEM survey successfully delineated the Kimberlite/basalt contact showing a high conductivity body continuous between the northern and southern lobes. Possible Kimberlite phase variations are also discernible within the southern lobe.
The Kimberlite/basalt contact and internal possible Kimberlite phase boundaries have been delineated successfully with the application of these three geophysical techniques. Future planning of delineation drilling and sampling programmes can now be soundly based on the outcome of these surveys.
Surface pitting and trenching has been undertaken to facilitate geological mapping. The objectives of this programme have been to establish the nature and thickness of the overburden to the Kimberlite, to delineate the Kimberlite/basalt contacts where possible and to characterize the Kimberlite and any variations internal to the pipe.
Groundwater conditions typically precluded in situ inspection of Kimberlite in pit exposures due to rapid ingress of water. Not even the cut-off drainage trench could reduce this flow which will require careful management during the proposed bulk sample programme.
The Kimberlite has been characterised as fragmental, massive volcaniclastic Kimberlite ("VK") with abundant xenoliths of basalt and common mantle material. Exposures were described as classic Tuffisitic Kimberlite Breccia ("TKB"); the distinctive magmaclastic texture comprises pelletal lapilli set in a fine grain inter-clast matrix with a mixture of country rock xenoliths.
Seven distinct Kimberlite types (Type I to Type VII) have been recorded and mapped. Discrimination at this stage is largely based on the size, shape and abundance of the magmaclasts as well as the nature and abundance of basalt country rock xenoliths. Mantle peridotite inclusions are a recognisable and measurable component in some areas of the pipe.
Broken rounded peridotite in the north of the Kimberlite clearly distinguishes the emplacement process frozen in exposed rockwall contact as turbulent diatreme activity in contrast to pyroclastic deposition from explosive volcanic processes. Close inspection of this locality also shows the intrusive nature of the Kimberlite along the joints in the basalt with spawling or stoping of the basalt recognisable in places.
There are other localities exposed in the north trench that display numerous large rounded basalt and basement gneiss xenoliths, common highly altered mantle xenoliths and abundant very large ilmenite macrocrysts (up to 3 cm) enclosed in Type VI Kimberlite. This material may represent the remnants of an early phase of TKB or hypabyssal Kimberlite breccia (HKB) emplacement and could produce above average diamond tenor.
Detailed petrographic and other laboratory studies will be required to elucidate the detailed emplacement history of the Mothae Kimberlites, at least to the extent that is required to understand the economic potential. The current interpretation shows a strong correlation between the geological mapping and ground geophysical interpretation.
Economically diamondiferous Kimberlites have to date only been found within Archaean Cratons associated with deep, cool mantle rocks. This observation has become known as "Clifford's Rule". Economically diamondiferous lamproites occur on the margins of these cratons. An Archaean Craton is that area of crystalline continental core (or Shield) greater than 2,500 Ma in age, which has remained essentially undisturbed by younger tectonism. The Mothae Kimberlite is located in the southeast portion of the Kaapvaal Craton.
Kimberlite and lamproite originate at depth in the asthenosphere (150km to 300km) and the rapidly ascending magma entrains a variety of foreign rocks and minerals (xenoliths and xenocrysts) from the substrate. Among these minerals are garnet, ilmenite, chromite and diamond.
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.