Slide 1: Technological approaches to diamond exploration on the Thorny River prospect, South Africa
Technological approaches to diamond exploration on the Thorny River prospect, South Africa James AH Campbell Managing Director, Botswana Diamonds plc African Exploration Showcase Geological Society of South Africa 12th November 2021
Slide 2: Outline
Africa Exploration Showcase: 12th November 2021 Technological approaches to diamond exploration on the Thorny River prospect, South Africa Marsfontein blow pit and dumps when active Outline ⧫ General Geology ⧫ History ⧫ Strategy ⧫ Technological Approaches ⧫ Results ⧫ Conclusion Reference: Allan, 199
Slide 3: Introduction
Introduction Photo: Andreas Stelzer Africa Exploration Showcase 2021 3
Slide 4: General Geology
General Geology ⧫ The region is underlain by the Kaapvaal craton. ⧫ In the vicinity of the Klipspringer mine, sediments of the Transvaal Supergroup occur. These comprise the Chuniespoort dolomites, basal Black Reef Formation and the pre-Black Reef units of the Wolkberg Group. ⧫ In the east, the geol
Slide 5: History
History ⧫ De Beers sampled the area during the 1970-80’s. ⧫ Klipspringer discovered in 1987 by De Beers*. ⧫ SouthernEra announced discovery of Marsfontein in 1995 and mined in JV with De Beers 1999-2000 with a payback of less than 4 days. ⧫ 970k tons produced 1.8M carats in 18-months ⧫ Three further
Slide 6: Strategy: to find another Marsfontein!
Strategy: to find another Marsfontein! ⧫ Abundant kimberlitic indicators (particularly garnet, spinel and chromium diopside) present so loam sampling is a useful reconnaissance tool. ⧫ Electromagnetics (‘EM’) produces good anomalies over the kimberlite. ⧫ Blows tend to occur on the confluence of the
Slide 7: Technological Approaches
Technological Approaches Africa Exploration Showcase 2021 7
Slide 8: Soil Sampling
Soil Sampling ⧫ Soil (loam) sampling a good first pass reconnaissance and follow-up exploration tool. ⧫ Abundant kimberlitic minerals: garnet, spinel and chromium diopside proximal to the kimberlite. ⧫ Strong halo effect: coarse grains don’t tend to travel far. Eclogitic and peridotitic garnets, chr
Slide 9: Ground Geophysics - Magnetics
Ground Geophysics - Magnetics ⧫ Magnetics tend to chiefly outline the dolerite and not kimberlite dykes as the latter are only weakly magnetic. ⧫ Magnetic susceptibility readings from drill core show that on average, the kimberlite has a susceptibility of 0.47SI with a maximum of 1.3SI ⧫ Quick and r
Slide 10: Ground geophysics – Electromagnetics
Ground geophysics – Electromagnetics ⧫ Frequency Domain Electro- magnetics (Max/Min) will outline both dolerite and kimberlite dykes. ⧫ Used in combination with magnetics, Max/Min is a useful tool in delineating the kimberlite dykes. ⧫ This technique can acquire data over multiple frequencies at var
Slide 11: Ground geophysics - Gravity
Ground geophysics - Gravity ⧫ Gravity is used where we believe there is a kimberlite blow. ⧫ Blows tend to produce gravity lows. ⧫ It is a more time consuming and complex technique and thus more costly so is restricted to specific targets. Reference: Geofocus, 2020 Africa Exploration Showcase 2021 1
Slide 12: Ground geophysics - GPRS
Ground geophysics - GPRS ⧫ A Ground Penetrating Radar System (‘GPRS’) was used to delineate the channels on the Marsfontein sheet gravels. ⧫ Quick and relatively cheap. ⧫ As the channels are relatively shallow, a higher frequency antenna would probably be required for better definition. References:
Slide 13: Ground geophysics – Induced Polarisation
Ground geophysics – Induced Polarisation ⧫ Induced Polarisation (‘IP’)was tested on the property by the Council for Geoscience (‘CGS’). ⧫ IP is a geophysical imaging technique used to identify the electrical chargeability of subsurface materials. ⧫ It is particularly focused on the chargeable materi
Slide 14: Drone Surveys
Drone Surveys ⧫ Detailed drone surveys undertaken over much of the property. ⧫ The aim of these surveys was to: ⧫ Provide accurate georeferences for groundwork, such as drilling and geological mapping. ⧫ Assess vegetation anomalies. ⧫ The tool was also helpful in the production of videos for public
Slide 15: Precision Structural Mapping
Precision Structural Mapping ⧫ Subterrane of the UK uses a combination of precision field structural geological measurements in combination with detailed ground geophysics to identify targets. ⧫ Targets are defined as buried or partially buried (potential) blows. ⧫ This is still very much work in pr
Slide 16: Spectral analysis
Spectral analysis ⧫ Terramodelling Services of Canada used machine and deep learning to delineate spectral anomalies from European Space Agency Sentinel 1 / 2 and ASTER data. ⧫ The following were assessed: ⧫ Structure ⧫ Topography ⧫ Elevation and displacement ⧫ Hydrothermal alteration ⧫ Epidote and
Slide 17: Drilling – RC Percussion
Drilling – RC Percussion ⧫ Reverse Circulation (‘RC’) drilling follows positive sampling and ground geophysical work. ⧫ Both angle and vertical holes were drilled. ⧫ The diameter of the holes was 140mm and a continuous 1m sample was taken and bagged. ⧫ Portions of these samples were washed and geolo
Slide 18: Drilling - Core
Drilling - Core ⧫ Core drilling was carried out where there was a requirement for more detailed geological data. ⧫ The core was subjected to detailed independent petrographic work. ⧫ Samples from the core were also taken for microdiamond analyses. Reference: Georoc, 2017 Africa Exploration Showcase
Slide 19: Bulk Sampling
Bulk Sampling ⧫ Bulk sampling was undertaken in an area where the kimberlite dyke swelled. ⧫ The purpose of the bulk sampling was to produce sufficient macro diamonds for preliminary grade and valuation models. ⧫ The samples were processed at an independent bulk sampling plant which included crushin
Slide 20: Results
Results Africa Exploration Showcase 2021 20
Slide 21: Mineral Chemistry
Mineral Chemistry ⧫ Around 54% of garnets fall into the G9/G5 category (garnets that originate from lherzolites and websterites). ⧫ 19% fall in the G10 field (garnets originating from harzburgites) and 7% garnets in the G10D (diamond inclusion) field. ⧫ The G10D garnets, plotting within the diamond
Slide 22: Petrography
Petrography ⧫ All kimberlite samples are Group 2 variety, coherent hypabyssal kimberlites with mineralogies dominated by calcite and phlogopite but with accessory apatite and in some samples monticellite, clinopyroxene and richterite amphibole. Fine grained perovskite and opaques are also present. ⧫
Slide 23: Diamonds: Macro & Micro
Diamonds: Macro & Micro ⧫ Select core samples were taken for microdiamond Total Diamond Content Model work and processed at an Micro diamonds combined Model uses tagged Macro and Micro classes independent laboratory. 14 All Micros A trench was excavated Modified Base BSP 12 ⧫ Model for the recovery
Slide 24: Geological Modelling
Geological Modelling ⧫ Detailed ground geophysical work supplemented by drilling results has enabled kimberlite modelling using Inversion and Forward Modelling Techniques. ⧫ Estimated volume so far of 72,000m3. ⧫ This work is being expanded to cover both the River and River Extension blows. ⧫ This t
Slide 25: Competent Persons Report (‘CPR’)
Competent Persons Report (‘CPR’) ⧫ Published in February 2018. ⧫ “Based on the exploration results to date, exploration targets have been highlighted with the following potential: ⧫ The undiluted raw in-situ grade of the kimberlite dyke sample is estimated between 46-74 cpht (1mm bcos). By contrast,
Slide 26: Conclusion
Conclusion Africa Exploration Showcase 2021 26
Slide 27: Conclusion
Conclusion ⧫ Modern diamond exploration requires the application of advanced and complimentary technologies. ⧫ These are informed by the area’s geological model. ⧫ In this case, we are looking for buried or partially buried kimberlite blows. ⧫ The level of precision required is high as the targets a
Slide 28: Acknowledgments
Acknowledgments Photo: John Shelton Africa Exploration Showcase 2021 28
Slide 29: Acknowledgements
Acknowledgements ⧫ My Vutomi colleagues: John Shelton, Linesh Lutchmansingh & Dennis Kekana ⧫ Explorations Unlimited: Prof Tania Marshall (Competent Persons Report). ⧫ Geofocus: Bjorn Harvemann & Gavin Selfe (geophysical surveys). ⧫ Subterrane: Andrew Long (detailed structural analysis). ⧫ Terramode
Slide 30: Thank You Questions & Discussion
Thank You Questions & Discussion Photo: Andreas Stelzer Africa Exploration Showcase 2021 30
Slide 31: About the Author
About the Author ⧫ James Campbell is Managing Director of Botswana Diamonds plc (a diamond development company active in Botswana, South Africa and Zimbabwe and listed on London AIM and Botswana Stock Exchange). He has spent over thirty-five years in the diamond industry in a variety of leadership r
Slide 32: 162 Clontarf Road Clontarf Dublin 3
162 Clontarf Road Clontarf Dublin 3 Ph: +27 83 457 3724 Web: www.botswanadiamonds.co.uk Twitter: @BotswanaDiamond Email: james@botswanadiamonds.co.uk Africa Exploration Showcase 2021 32