Tsodilo Resources Limited said in an update that the ground magnetic and gravity surveys on kimberlite BK16 have been completed. This initial grant to Bosoto (Pty) Ltd of prospecting license PL 369/2014 became effective on October 1, 2014 and is valid for 3 years.
The company said 51 line km of high intensity magnetics was completed and 441 survey stations for the detailed gravity survey were read while the geophysical surveys indicate a size for the BK16 kimberlite pipe of between 4.8 and 5 hectare in size, an increase from the 3.5 ha historical reported size.
Tsodilo added that the modelling of ground geophysical data has highlighted the internal structure of the kimberlite and revealed Bosoto is now planning a diamond core drill program to provide a robust geological model of the kimberlite.
Previous exploration over the kimberlite has indicated that BK16 is 3.5 ha in size. This was based on wide spaced survey grids. Bosoto’s more detailed program was conducted in order to more accurately obtain the estimated size of the pipe. The ground geophysical surveys included a high intensity ground magnetic survey and a closely spaced gravity survey covering a 1 km² grid central over the pipe.
The company’s magnetometers used for this stage of the project were a Proton Precision G856 Geometric instrument for the base station and a Cesium Vapor G858 Geometrics (‘Walk magnetometer’) for collection of the data. The magnetic data was surveyed on lines 20 meters apart and readings were collected every 5 seconds.
In addition to the magnetic survey a detailed ground gravity survey was conducted over the same 1 km² block. For this a Sintrex CG-3 Autograv gravity meter was used taking readings every 50 meters on lines 50 meters apart. A Leica differential GPS was used to measure the elevation of the gravity station.
All data was processed and modelled using in-house Geosoft and Potent software respectively.
The magnetic and gravity data had excellent overlap showing that the size of the kimberlite is between 4.8 and 5 ha in size with a high level of confidence. These data also highlighted important different geophysical zones within the kimberlite, most likely associated with different kimberlite facies, which with drilling will assist in developing a robust geological model.
Based on the gravity data there is a possible extension of the pipe towards the southeast which is 2.5 ha in size. The magnetic results over this extension are not conclusive and this area will have to be tested by drilling.
BK16 is part of the Orapa Kimberlite Field (“OKF”) in Botswana. The OKF lies on the northern edge of the Central Kalahari Karoo Basin along which the Karoo succession dips very gently to the SSW and off-laps against the Precambrian rocks which occur at shallow depth within the Makgadikgadi Depression.
The OKF includes at least 83 kimberlite bodies, varying in size from insignificant dykes to the 110 ha AK1 kimberlite which is Debswana’s Orapa Mine. All kimberlite intrusions are of post-Karoo age. Of the 83 known kimberlite bodies, nine, AK1 (Orapa, Debswana); AK6 (Karowe, Lucara Diamond Corporation); BK1, BK9, BK12 and BK15 (Damtshaa, Debswana); DK1 and DK2 (Letlhakane, Debswana); BK11 (Firestone Diamonds), are currently or have been mined.
The magnetic and gravity data will be further analyzed adding the details of the historical holes to construct a 1st pass model. Bosoto then plans to enter in a core drilling program over the next 6 months, using its own diamond drill rigs, before utilizing LDD (‘large diameter drill’) holes for evaluation purposes.
“We are very determined to move the evaluation along at an accelerated pace. In 2013, the OKF area produced 12,926,500 carats and we are keen to be a part of the area’s production” commented Dr. Mike de Wit, Tsodilo’s President and COO.