GEOLOGICAL SURVEY DEPARTMENT

(Director: T.P. Machacha)

. ';,., j,'\'

ANNUAL REPORT

OF THE

GEOLOGICAL SURVEY DEPARTMENT

FOR THE YEAR

1994

Published By

The Director Geological Survey Department

Private Bag 14, Lobatse, Botswana With the authority of

The Minisily of Mineral Resources and Water Affairs Republic of Botswana

; .

1. GENERAL

The Geological Survey Department remained within the Ministry of Mineral Resources and Water Affairs, and continued with its main functions of gathering, assessing, advising on, and distributing all data reiated to the rocks, mineral deposits and groundwater resources of Botswana.

The Departmental organisational structure continued to consist of the Directorate, four operational divisions of Regional Geology, Geophysics, Economic Geology and Hydrogeology with an Administrative Division. Support to the main divisions was provided by the Drawing Office, Technical Records and Library, Chemistry Laboratory, Mineral Dressing Laboratory, Vehicle Workshop, Drilling Section and Carpentry Workshop.

There was a full establishment of professional staff throughout the year with no major ehanges in personnel. A number of staff successfully completed training courses overseas and returned to Lobatse to continue with their professional duties. Others remained overseas on full-time training courses.

Within the Economic Geology Division the evaluation of industrial minerals continued to be given priority with extensive investigations in the Dukwe-Matsitama, Selebi-Phikwe and Palapye areas. The writing of a monograph on gold in Botswana continued. The exploration for base and precious metals in the greenstone belts of NE Botswana continued with fieldwork in the Maitengwe and Vumba Greenstone Belts.

Mineral exploration by the Private Sector continued at a very high level throughout the year. At the beginning of 1994 there were 381 active prospecting licences that increased to 528 licences by the year's end. 349 of the licences were for precious stones (diamonds), 160 for base and precious metals and 19 for other minerals. Of particular significance was the shift in gold exploration away from the greenstone belts of NE Botswana towards the centre of the Kalahari where it is thought that there may be a new Witwatersrand Basin concealed beneath the Kalahari Group and Karoo Supergroup cover. More interest is also being shown by the Private Sector in the exploitation of industrial minerals, both to meet the demands of the local market, and for export.

Within the Hydrogeology Division nluch of its work continued to be concerned with the implementation or monitoring of six major groundwater projects. Five of the projects involve consulting companies and one (the TGLP Ghanzi/Makunda Groundwater Project) is bcing undertaken by Department staff. Additionally there are four ongoing groundwater research programmes that will eventually lead to a better understanding of the groundwater resources of Botswana, also improving the techniques used to find this precious resource, One such project, the GRES-Phasc 2 Project commenced in 1993 and is examining groundwater recharge in parts of the Kalahari. This project involves close collaboration between the Hydrogeology Division and Dutch hydrogeologists. The Division continues to monitor the groundwater resources that are presently being used; a National Monitoring Network is being fully computerised. The archiving of all borehole records continued and the upgrading of the computer listing of all water boreholes in Botswana also continued. A new project aimed at reducing the risks of environmental pollution caused by the uncontrolled disposal of waste commenced in the middle of 1993. Professional advice on groundwater was given to other public bodies throughout Botswana.

There was a fourfold focus to the work of the Geophysics Division throughout 1994. There was geophysical participation into major groundwater projects, either by monitoring/quality control of contracted geophysic.al work on projects managed by consultants (Matsheng, Middlepits/Makopong TGLP Projects, Dukwi Well field Extension and Maun Groundwater Project), or by undertaking fieldwork for in-house groundwater projects, such as the Ghanzi/Makunda TGLP Project. Secondly, there was technical monitoring and quality. control on the EEC-funded Ghanzi-Chobe Fold Belt triaxial aeromagnetic survey. Response of the Private Sector to receiving the survey data, after it was placed on open file, was very significant. Thirdly there is on-going research, such as the digital compilation of all airborne geophysical data for Botswana into a coherent GlS database and the operation and maintenance of the Global Telemetry Seismic Network (with the United States Geological . Survey). Finally the training and localisation of the Division's staff with the help of CIDA continue. Two Canadian nationals remained in post throughout the year.

'I'bero wa, a ,imilar fourfold focus to the work of Ihe Regional Geology Division in 1994. The Division's principal function continued to be the routine geological mapping of Botswana at various scales with the preparation of geological maps and accompanying reports. In 1994 there was mapping in the Mosetse, Lake Ngami, Molepolole, Letlhakeng and Selebi Quarter Degree Sheets (for published geological maps at a scale of I: 125 000). There was also mapping/compilation of sheets 17, 18, 29 and 32 of the 1:250 000 maps of the Kalahari Series. Three 1: 125 000 geological maps (Dautsa, Ramsden and Ngwako Pan) were printed and Bulletins 37 and 38 were published. Bulletin 39 is in press. Only a limited amount of geological mapping in urban areas was undertaken. Secondly, there was on-going collaborative geological research with a number of other geological institutions. A number of gebchronology programmes were started as well as palynological investigations of the Karoo Supergroup rocks of Botswana. Thirdly the archive of unpublished data continued to be computerised and rationalised. Finally staff training continued, both in Botswana and overseas. The training was, in part, undertaken by BGS as part of UK SUppOlt to the Geological Survey Department.

Besides providing various rock, mineral and other chemical analyses for the various Divisions within the Department, the Chemistry Laboratory also undertook similar work for many outside customers, including the Police and the Department of Water Affairs. Similarly the Mineral Dressing Laboratory' provided thin sections and polished samples to staff within the Department and to many outside institutions. A wide range of technical services was also provided by the Laboratory to customers that included the University of Botswana and many consulting firms. The Drawing Office continued to prepare all the geological maps produced by the Department for printing at tbe Government Printer. Most of the diagrams for publicatIon were also completed in the Drawing Office. The Depaltment's library acquired many new technical books as well as receiving a large number of consultants reports related to work in Botswana. Over 30 international periodicals are regularly received.

There are now seven operational drilling rigs in the Drilling Section, although most are old. One new rig, a Smith R7 6GC, was acquired in 1994. This is a multipurpose rig that initially will undertake drilling into the Kalahari Group and Karoo

2

Supergroup strata as part of the GRES-PHASE 2 Hydrogeology research project.

The Depmiment's use of computers continues to increase and new computing equipment was received by all Divisions and Sections in 1994.

2. FINANCIAL SUMMARY

2.1 Recurrent Budget

Departmental expenditure under the consolidated fund (Head 100, Part 2) is summarised in Table 2.2.

2.2 Development Budget

Departmental expenditure under the Development Fund (Head 101, Part 2) for the year was Pll 675 475. Actual expenditure by subbead for the period 1994/95 is shown in Table 2.1.

Table 2.1 The Geological S~rvey Department's Development Fund

Sub-Head

201

202

215

216

3.

Description Amount (Pula)

Oil & Gas 500000 Stratigraphical Drilling TGLP I 750000 Groundwater Surveys Geological 548786 Survey Buildings Groundwater 8876689 Protection Studies Total 11 675475

STAFF TRAINING AND LOCALISATION

In this year's Annual RepOlt individual Divisions and Sections have itemised the details of their training and localisation programmes within the accounts of their year's work.

5.

5.1

HYDRO GEOLOGY DIVISION

Introduction

The Hydrogeology Division of the Geological Survey Department has the following duties:

• Responsibility for investigation of, and exploration fot groundwater resources on a regional basis.

~ Protection of water resources with special emphasis on groundwater.

• The promotion of the advancement of applied groundwater research.

The investigation and exploration of grollndwater resources involves the assessment of their potential in terms of quantity and quality for development. In addition the Division is responsible for gathering, collecting, archiving and analysing/interpreting data and information on groundwater levels and quality, abstraction where possible, as well as borehole information such as borehole construction and chip samples from government and private boreholes. All this information is stored in the National Borehole Records Archive, the Groundwater Computer Banks and the Drill Sample Store. All the information is readily available to the general public on request. Work on groundwater level monitoring data analysis has been started. Data and information review and interpretation from our National Archive and Drill Sample Store is planned to be started in mid-1995 when the present workload from on-going projects will be reduced.

The project "Protection of Water Resources/Waste Management" is progressing. The Geological Survey Department is implementing the sub­project, "Protection of Water Resources in technical co-operation with the Geological Survey of Germany (BGR). Work is progressing well. However, the project has been extended by 6 months from 2 years to 2.5 years in order to be able to attend to requests from the district councils to conduct hydrogeological studies on proposed waste disposal sites. Recommendations will be given on the necessary measures to be taken to minimise possible water pollution.

The research project, Groundwater Recharge and Evaluation Studies-Phase Il (GRES-Il) experienced some unforeseen field logistical problems related to equipment used in the project and due to field conditions. The project has been delayed by four months resulting a total delay of eight months sinee

the project was started in November, 1992. The Division's intemal research programmes continued with a study on the hydrochemistry of the saturated zone in selected areas of the Kgalagadi, south-wcst Botswana by Mr T. Molebatsi.

The Division continues with its training programmes in line with its localisation plan as well as work perfonnance improvement. Messrs G. Nkala and K. Mokokwe were awarded their M.Sc. Hydrogeology degrees once their respective project thesis were evaluated. Mr T. Molebatsi succcssfully completed his M.Sc. Hydrogeology programme at the University College London in the United Kingdom in September, 1994. Mr N. Ramotsoko successfully completed his Diploma in Groundwater Technology at the Northern Alberta Institute of Technology in Canada in May, 1994, while Mr 1. Setlhomo continues with his Diploma in Groundwater Technology at the same Institute. Hc is expected back in September, 1996. Mr E. Selaolo continues as a research fellow in the GRES-II project. He will be involved in the projcct until the end of the project in November, 1996. In addition to the above training, staff within the Division have attended various short specialised courses and conferences as a measure to improve performance on the job.

5.2 Development Projects

5.2.1 Groundwater Studies and Protection

5.2.1.1 Matshcng Groundwatcr Investigation

Project Duration: Total Project Cost: Consultants:

Drilling Contract: Project commencement:

14 months 1'6300000 Wellfield Consulting (Pty)Ltd. Gaborone. OD Drilling (Pty) Ltd. I" June, 1994

The project aims at assessing the groundwater potential for the Matshcng Area. The project area comprises about 9 OOOkm' around the villages of Hukuntsi, Lehututu, Lokgwabe and Tshane.

Tenders were submitted to the Central Tender Board on 31 January 1994. Evaluation of tenders was subsequently carried out, after the tenders were opened by the Central Tender Board, and completed on 10 March 1994. Six companies submitted tenders. The project was awarded to Well fields Consulting Services on 27 April 1994.

The project started on I June 1994 after one month's mobilisation. The drilling contract was awarded to OD drilling on 18 October 1994; drilling in the area started in November 1994. At

IS

the end of December 1994 the following activities were completed: data review, main geophysical data interpretation and calibration, remote sensing and the first part of a botanical survey. Drilling of ten shallow boreholes (average depth of 40m for the purpose of calibration of geophysical data and shallow geology), and one deep borehole to a depth of 460m for the purpose of gaining knowledge about the hydrogeology of the deeper strata was done. Of the ten shallow borcholes only one obtained reasonable quality (fresh) water with a yield of 4m31h. The deep borehole struck groundwater at 450m depth with a yield of 20m3/h. However, the water is saline.

5.2.1.2 TGLP Ghanzi/Makunda Groundwater Potential Survey

Project duration Total project cost: Consultant:

Drilling:

Drilling supervisors:

Project commencement:

21 months PS 800000 Project is conducted in-house by GSD Personnel 1. Pula Groundwater Developers. 2. Dewet Drilling 1. Geoflux (Pty) Ltd. 2. Water Surveys (Pty)Ltd. December 1992

The project was initiated to assess the groundwater potential of an area covering 22 000 km' situated in the Ghanzi District which stretches from the Namibian boarder to almost the Central Kalahari Game Reserve. The core issues to address in this study are groundwater salinity and amount of groundwater.

During the year a complete assessment of archival data has been undeltaken and complementary field data collection has been finalised. Hence, an inventory report detailing the data and an initial analysis was produced. This report also outlined the additional data collection which was required before a final assessment could be made. As a result a second phase, including borehole siting, drilling, test pumping and water sampling was initiated. The contracts for the drilling contractor supervisors and the drilling contractors were awarded at the beginning of October 1994 and the field activities started on 10 October 1994.

By the end of the year a revised conceptual model was formulated for the project area, and 29 boreholes were drillcd. A substantial amount of data, relating to the project drilled boreholes, was still outstanding. In particular the test pumping

16

data, the hydro chemical data and the isotope analysis of groundwater were outstanding. Drilling and testing and analysis of collected data is ongoing.

Out of the 29 boreholes drilled, 17 had a yield of more than Im 3/h with a maximum of 60m 31h and an average of 14m'/h. The rest of the boreholes are either low yielding with a yield of less than Im3/h, or dry.

The groundwater salinity ranges from 300 mgll to 4 OOOmgll, although the water is generally of good quality.

5.2.1.3 TGLP Toteng/Sehitwa Groundwater Survey

Project Duration: Total Project Cost: Consultant: Drilling: Project commencement:

16 months P3 500000 Geoflux (Pty) Ltd Dewet Drilling. 29 May 1991

The project aimed at assessing the groundwater potential of the Hainaveld area in south-east Ngamiland District. The consultant submitted the completely corrected version of the final report in September 1994, and it was accepted by the client. The required number of copies were submitted by the consultant.

This study identified two types of aquifers in the area. A fractured quartzite which gives very variable yield, ranging from 0 to 80m'/h The high yields are where extensive, open fractures are found. Another type of aquifer is Kalahari Group sand, which has a uniform yield of 5 to 10 m'/h. Difficulties when drilling are expected in this formation, due to the loose sand which tends to collapse during air percussion drilling.

Generally, the groundwater salinity is between 2 000 and 10000 mg/l, which makes it unsuitable for dome~tic use, but suitable to varying degrees for watering livestock.

A public presentation of the project results has been given in Maun and the project is now completcd.

5.2.1.4 Mmamabula Groundwater Resources Investigation Project Phase Il, Khurutshe Area

Project Duration

Total Project Cost: Consu!till1ts :

25.5 months (+2.5 months extension) PlO 000 000 Bureau de Recherche Geologiques et Minieres

(BRGM). Orleans, France.

Drilling Contractor : Pula Groundwater Developers (Pty) Ltd.,

Project commencement: October 199 I (Consultancy) Septcmbcr 1992 (Drilling and Test Pumping):

The corrected versions of maps were submitted towards the end of 1994. The final reports have been distributed to the concerned authorities and final payment was made to the Consultant in February 1995. The main aim of the project was to assess, quantitatively and qualitatively the groundwater resources in the Mrnamabula) Khurutshe area, that can be economically developed. The main target aquifers of the project were, as follows.

• Sandstones of the Ntane Sandstone Formation and the Mmamabula Formation of the Karoo Supergroup, both of fractured/porous type.

• The fractured rock type aquifers of the Waterberg Group and post-Waterberg Group intrusive rocks.

A total of 36 exploration boreholes (average depth of 250m) and ten production boreholes were drilled. The exploitable groundwater resources were evaluated over an area of I 100 km' by means of groundwater flow modelling, which was restricted to the Ntane Sandstone Formation aquifer (lOOm to 130m thick) and to some blocks in the Mmamabula sandstone's aquifer (60m thick). The Waterberg Group and post-Waterberg intrusive rocks were not modelled due to thcir poor hydrogeological characteristics. The Mmamabula Formation sandstone's aquifer is not accessible in most of the area, as the top of thc formation can be as deep as 650m. Thc Ntane Sandstone aquifer is the most interesting aquifer in the area, in terms of continuity, .location, depth (120 - 300m) and hydraulic properties (hydraulic conductivity, K, of 100 - 500 x 10.6 m/s, average yield of production boreholes of more that 50 m3/h, up to 80 m'/h). The groundwater quality is very good in most parts of the modclled area, with Total Dissolved Solids (TDS) values ofless than 500 mg/1.

For the calculation of renewable groundwater resources, recharge estimates were made using several methods. Three sets of recharge values have been filled in the rccharge zones, giving averages in the whole area of 1.5, 3.5 and 4.9 mm/yr. Exploitable resources were estimated over an area of I 100 km', using a two dimensional

finite difference model. Five exploitation scenarios were run as follows;

Scenario 1 - continuous increase of abstraction over five years up to 16 mm'/year (1826 m'Jh).

Scenario 1 bs - continuous increase of abstraction over ten years up to 32 mm'/year (3252 m'/h).

Scenario 2 - continuous increase of abstraction over three years up to 9.6 mm'/year (1096 m'Jh), followed by rotate abstraction periods. Simulation rotate periods are of three months each with an average abstraction rate of 228 m3Jh (2 mm'/year) that corresponds to a total abstraction volume of I mm 3 per year.

Scenario 3 - is similar to the Scenario 2 but with an abstraction rate of 571 m3Jh i.e. total annual volume 2,5 mm3

,

Scenario 4 - continuous increase of abstraction during three years up to 11 mm'/year (1256 m'Jh).

Recovery during four years. Abstraction during one year up to 571 m'Jh (total abstraction 5 mm' per year). Recovery during 16 years. Abstraction during three years up to 1712 m2Jh (15 mm' per year). .

Scenario 5 - is a mixture of scenario 4 and scenario 2. In this scenario, continuous abstraction rates are the same as scenario 4 but the recovery period is replaced by a lower abstraction rate of2 mm'/year.

Scenario I is not viable since the maximum drawdown is 35m, which is one third of aquifer thickness and recovery does not take place within 20 years of stopped abstraction. The other scenarios are acceptable. However, any scenario will entail groundwater mining. Three areas have been proposed for future wellfields. Two are located in the Leshibitse - Kgorotlhwe - Temesele area and the third area is located in the Makhujwane area,

5.2.1.5 Middlepits/Makopong Groundwater Potential Survey

Project Duration Total Estimated Cost: Consultants:

Drilling Contractor :

Project commencement;

14 months P4 850 000 Water Surveys Botswana (Pty) Ltd. TGB Drill Contractors Botswana (Pty) Ltd and Puia Groundwater Developers (Pty) Ltd. September 1992

17

Table 5.1 Maximum aquifer depletion resulting/rom the 5 abstraction scenarios in the 3 proposedfuture wellfie!ds.

Scenario I Ibs 2 3 4 5

K Max in 10-6m/s 62.5 125 250 250 500 250 250 250 250 250 Unconfinned S 2% 2% 20/0 10/0 2%, 2% 2% 2% 2% 2% Av. recharge (mm/y) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Max discharged(m3/h) 1826 1826 1826 1826 1826 3652 1096 1096 1712 1712 Timeofmax. 5 5 5 5 5 10 3 30 28 12 drawdown (years)

Depletion max (m)

Wellficld A 16 12 10 16 9 35 6 7 7 6

Wellfield B 9 15 8 34 4 5 7 8 Wellfield C 4 5 4 11 0 0 2 2

Pessimistic K values of250 x 10" mls have been retained in (he best areas where K values up (0 424 x 10" mls have been noted.

The draft final report was received in May 1994 and has been thoroughly reviewed. Though it was due for submission in revised final format in September 1994, it was submitted in February 1995. The drilling programme (37 boreholes) finished in October 1993, and the test pumping programme (ll tests) was completed in early November 1993 . All boreholes have been accurately levelled and positioned.

Table 5.2 A summmy of the water quality in 37 boreholes of the MiddlepitslMakopong.

Borehole Phase I Phase 2 Total

Makopong TOLl' area

Dry 0 1 1

Brackish 0 0 0

Saline 6 7 13

Middlepits/Tsabong West TOLl' area

Dry 3 3 6

Brackish 0 5 5

Saline 7 5 12

Total 16 21 37

18

Brack2000 - 5000 mgll sait, saline >500 mgll salt

Oood potential for a substantial groundwater resource has been identified beneath, and adjacent to the existing Makopong and Tsabong-West TOLl' ranch block clusters. However, the salinity of the groundwater in these areas is well beyond the tolerance of livestock (salinity always in excess of 40 000 mg/l TDS) rendering the resource useless for livestock ranching unless expensive desalination technology is applied. Drilling to the 350m level in the T,abong-West TOLl' area did not reveal a deep groundwater resource.

Five brackish boreholes with salt content tolerable to cattle (less than 3 000 mg/l TDS) have been drilled within the Middlepits ranch block cluster midway between Khuis and the RAD settlement of Khawa. Individual yields vary from seepage to 25 m3/h (averaging 9 m3/h). The water is struck in the 80 to 120m depth range. Deeper drilling should be avoided as the salinity of subsequent water strikes rapidly increases to intolerable levels. To the north­west the ground water is generally saline and unusable but "pockets" of water tolerable for cattle are found in the vicinity of Khawa (less than 8 000 mg/l TDS). This NW-SE axis within the general Middlepits TGLP area represents the only part of the whole investigation area where scope for successful1ivestock ranch development exists with respect to reasonable groundwater potentiaL

There is possibility of a deeper, less saline resource at depths of about 400m within, and adjacent to the Gemsbok National Park although this does not extend eastward to the defined TGLP areas. Likewise shallow brack and potable groundwater (upper 120m) is known in the area west of Khawa, just outside the survey area.

5.2.1.6 Pollution Protection of Water ResourceslWaste Management

The overall objective of the project is to reduce the risk of environmental pollution caused by uncontrolled disposal of wastes. The objectives of the sub-project "Pollution protection of Water Resources", which is implemented by the Geological Survey Department - Botswana in technical co-operation with the Bundesanstall fur Geonuissenschaften' und Rohstoffe (BGR)­Germany, are to produce 18 vulnerability maps at a scale of 1 ;50 000 in major settlements, and a national vulnerability map of Botswana at a scale of I: I 000 000. Training of local counterparts as part of institutional building within the Division is another objective of the project. The project was started in June ! 993 and is scheduled for completion in December 1995.

An evaluation system for groundwater vulnerability mapping was reviewed. The vulnerability maps at a scale of 1:50 000 of the Lobatse-Otse, Gaborone, Ramotswa-Mogobane and Molepolole sheets were completed with their respective accompanying reports. They were supplemented by a manual for vulnerability mapping. Copies were made and distributed to the relevant authorities. The results and recomniendations were to be discussed with. the relevant councils in February 1995. Four vulnerability map sheets were contracted out to Water Surveys Botswana and the completed work paid for from foreign funds. The consultant completed rhe Ramotswa-Mogobane sheet.

Work on vulnerability mapping and reporting of Pilane, Kanye and PaJapye areas is on~going.

Work is also on-going on the Pilane case study which was identified for improvement of an existing landfill. The site was hydro geologically investigated using various scientific methods (electromagnetics, soil sampling, drilling and borehole tests). Report drafting is on-going.

Meetings have been held with seven town and district councils in Botswana in order to create public awareness and collect data. This was done in

co-operation with the Waste Management sub­project staff.

Advice on selecting suitable landfill and burial sites was given to councils in the following areas; Lobatse, Ramotswa, Tlokweng, Gaborone, Molepolole, Ghanzi, and Mahalapye and to the Lobatse Tannery.

The sub-project protection of Water Resources has been extended by six months in order to cope with requests from district councils, for conducting hydrogeological studies on proposed waste disposal sites. Recommendations will be given so as to minimise possible groundwater pollution.

S.2.1.7 National Borehole Records Archive Project-Phase II

Project duration Total project cost: Consultants:

Project commencement:

5 months 1'217420 Knight Piesold Botswana JanuaJY 1994

A project Memorandum was prepared and submitted to MMR W A in November 1992 and approved in early 1993. The TOR were prepared, submitted to MMRWA and funds approved in December, 1993. The contract was awarded to Knight Piesold Botswana (Ply) Lld in January 1994. During the course of the project, the following tasks were accomplished:

• A total of 3 284 borehole records were added to the database.

• A total of 5 784 boreholes were plotted on borehole location maps.

• The records were also checked for data entry mistakes, duplication or even triplicate boreholes.

A total of 80 boreholes could not be plotted since they had no information which could be used to determine location details. At the end of the project the backlog had been cleared. The final report was submitted to the client (GSD) in June 1994 and the project completed.

5.2.2 Groundwater Research Programmes

5.2.2.1 Hydrochemistry "of the saturated zone in selected areas of the Kalahari, south­west Botswana

The study aimed' at determining the origin and evaluation of the hypersaline groundwaters found in the lower Karoo Supergroup sandstone aquifers of the area west of Tsabong. The study was

19

completed in Septembcr 1994. The following are conclusions from the investigation.

The groundwater chemistry and isotopic compositions show that Tsabong groundwaters are of meteoric origin, recharged from a previous, wetter climatic regime. Groundwater gets older along the postulated regional flow line (i.e. from north-east to south-west), but salinity does not progressively increase along this line. The positive linear relations between Na+ and cr and between CI- and S04 -2 and the irregular relation between 180 and CI' indicate that dissolution of salt evaporites is the major salinazation mechanism. Thus groundwater chemistry is greatly influenced by reactions between infiltrating water and the Kgalagadi surficial deposits. Precipitation of salt evaporates is likely to have preceded the last pluvial period (about 8 000 years before present). Since the Kgalagadi sediments were partly deposited under lacustrine environments, it is concluded that during the disappearance of these lakes, hot and dry climatic conditions resulted in salt precipitates. Subsequently, those CI' salts were dissolved by intermittent wet periods.

The distinct stable isotope composition differcnces between present day rainwater and the studies groundwater imply that present-day recharge is unlikely. Stable isotope compositions for groundwater are more negative than those for pre~ent-day rain water, indicating that groundwater was recharged undcr cooler climatic regimes than at present.

The Na+ICI- molal ratios are close to unity, indicating dissolution of halite. SO, -2 and C I' correlate well, indicating that S04 -2 is also a product of the CI' -salt dissolution. Mg+', Ca 2 and HC03 . concentrations result from reactions between recharging rain watcr and ubiquitous carbonate minerals. Mg+2 /Cai2 molal ratios are significantly greater than unity. This indieates that MgCO, dissolution is predominant over that of CaCO,_.

Anomalous nitrate concentrations arc attributed to biological processes in the soil and also to contamination from animal waste,

The erratic charact~r of groundwater chemistry along an assumed flow line indicates that either there is no hydraulic continuity, or groundwater is virtually stagnant. Thc high groundwater salinities indicate that the sub-basin is not being flushed. Evidently this erratic character shows that

20

groundwater chemistry is controlled by process on a local scale.

Given the presence of ubiquitous shales, rock­water interaction and cation exchange are considered as minor salinization processes.

5.2.2.2 Groundwater Recharge and Evaluation Studies - Phase II (GRES-II)

The project officially started in November 1992 and is scheduled for eompletion in November 1996. The aim of the second year programme was to improve the knowledge concerning the hydrogeology, with particular reference to flow pattern analysis and recharge process in the Letlhakeng-Botlhapatlou (LB) and Matsheng areas. To do this, isotope-physical and hydrochemical tracer techniques and modelling of the saturated and unsaturated flow were used. The aim of the training programme was to further strengthen the research and research training capacity of the Geological Survey Department and the UB­Geology Department, and as it turned out, also the Free University Amsterdam, The Netherlands.

Recharge studies in the Letlhakeng-Botlhapatlou area continued during the second year of the project. A finite-element groundwater model of the Mmamabula aquifer was constructed and soil moisture transport studies were carried out. Three scientific papers were produced on recharge rates based on the chloride mass balance method, chemical and isotope physical approach. Present­day recharge rates range from I to 10mm/year, whereas a minimum long-tenn average rate to the aquifer for the last 15 000 years is calculated as 1.5mm/year. Based on different approaches it can be concluded that there is recharge to the aquifer at the fringe of the Kalahari. Results of the studies were presented during conferences in Austria and Australia.

During the second half of 1994 a hydrogeological Ihydrogeochemical sampling programme was carried out in the Matsheng area with the assistance of Wellfield ConSUlting Services. After analyses of the samples, data will be interpreted and fUither recharge studies will follow.

The quality of monitoring of moisture content, soil suction and groundwater levels has been improved. The monitoring network for rainfall, groundwater

levels, soil moisture and soil suction was extended for more detailed studies of groundwater recharge. Groundwaters in the Letlhakeng-Botlhapatlou area

appear to be recharged by rainfall with long duration and high intensity. On-the-job training of

GSD staff and University of Botswana students is on-going. Training has been given specifically on the vacuum distillation and drilling techniques -Hollow stem auguring and advanced sampling (coring) techniques.

Vrije University Amsterdam: The Project Co­ordinator has been exposed to the management of a research project .of ,this magnitude. Two Dutch MSc students have been involved in the construction of a finite-element groundwater model of the Letlhakeng-Botlhapatlou area and in soil­moisture transport studies.

A delay of about four months was encounte,ed with the drillings in the Letlhakeng-Botlhapatlou area. Time was needed for the niaintenance of apparatus and replacement of broken glassware. Delays were also due to experimental problems during the second year programme. As a result of these delays and the unforeseen heavy involvement of both Dr Beekman and Mr Selaolo in supervision of the drilling programme, all other related activities are also running behind schedule. The total delay of executing the GRES 11 programme, including the delay of the first year programme, is at present eight months,

5.2.3 Groundwater Resources and Basin Monitoring

Monitoring has continued throughout the year. There has been an increase in our monitoring network due to the addition of new boreholes and rainfall recorders in the Letlhakeng-Botlhapatlou and Matsheng areas, as necessitated by the Groundwater Recharge and Evaluation Studies Phase 11 Project (GRES 11). The National Monitoring Network is as follows:

Serowe : 38 borcholes + 2 wells. Includes 9 production boreholes, 2 automatic recordcrs, 6 dry/blocked & I rain gauge

Palapye: 14 boreholes. Includes 7 production boreholes, 2 recorders.

Ramotswa: 40 boreholcs + well. 9 production boreholcs, 3 automatic recorders, 8

blocked/dry, I rain gauge

Mochudi: 13 boreholes. Includes 4 production boreholes, 3 automatic recorders, 2 dry boreholes, 1 rain gauge.

Malotwana: 17 borehoIes. Include production boreholes, 3 automatic recorders, dry/blocked hole, I rain gauge

4

MoIepolole/Mochudi: 45 boreholes. Includes 9 production boreholes, 5 automatic recorders, 4 dry/blocked boreholes, 2 rain gauges.

Metsemotlhaba : 13 boreholes. Includes 3 production boreholes, 2 automatic recorders, 2 dry/blocked boreholes, I rain gauge.

Pitsanyane/Nnywane: 33 boreholes. Includes 2 production boreholes, 4 automatic recorders, 4 dry/blocked boreholes, I rain gauge.

Lobatse Treatment Ponds: 6 boreholes. Includes 2 blocked boreholes.

Kanye : 67 boreholes + 2 wells. Include 10 production boreholes, 5 automatic recorders, 3 rain gauges.

LetlhakenglBotlhapatlou: Includes 10 automatic recorders, dry/blocked.

59 boreholes. I production, I I

Seleka Farm: 25 boreholes. Includes 2 automatic recorders, 2 dry/blocked holes 5 production boreholes.

Mmamabula: 46 boreholes. Includes 12 production boreholes, 10 automatic recorders, 4 rain gauges.

The National Monitoring Network now comprises 419 monitoring boreholes, 62 production boreholes, 51 automatic water level recorders and 13 rain gauges.

The computer database using dBase III +, which was designed and installed for the monitoring and rainfall data, consists of the wellfield and borehole location data, the water level measurements, date and time of measurements and the rainfall amount, date and duration. Data for all the wellfields/aquifers have been input to the database.

Basic hydro graphs can be produced and, where data is available, rainfall histograms.

Due to logistical problems associated with remoteness and difficult access of the TGLP areas investigated for groundwater resources potential, as well as staff shortages, it has not been possible to incorporate any boreholes drilled in such areas into the monitoring network. Therefore our monitoring network has morc or less remained as previously reported.

5.2.4 Drill Samples Store

There are 35 and 34 full pallet boxes of sludge samples for Government and Private boreholes respectively. These figures represent an increase of

21

5 and 3 full pallet boxes, respectively, during the reporting period.

At the end of the year the Department had a total of 191 822 and 144 285 chip samples from Government boreholes and private boreholes respectively. There has been a marked improvement in the bottling of sludge samples during the reporting period as a result of the involvement of two Tirelo Sechaba participants in the drill sample store.

The number of samples received in the period 1990-1994 is shown in Figure 5.2. Figure 5.1 shows cumulative government and private samples received since 1990 up to the reporting period.

5.2.5 National Borehole Records Archive and Computer Data Bank

Much work was carried out by the consultants, Knight Piesold (Pty) Ltd from January to May 1994. The work involved upgrading the records as well as plotting boreholes on location maps. A total of 3 284 borehole records were added to the database, while a total of 5 784 boreholes were plotted on borehole location maps.

The number of private water boreholes registered by the Geological Survey is 255. Of the 255 boreholes, 119 were plotted on location maps and 88 were input to the eomputer after the completion of the Borehole Records Archive Project (earried out by the consultant). The records in the database now total 15 933. This figure includes 3 284 boreholes input by the consultant and 88 input by the Geological Survey during the reporting period. Figure 5.3 shows the number of private water boreholes registered from 1985 to 1994.

5.3 Consulting Services for Government and the Public­Membership on Committees and Boards

Professional and technical advice continues to be an integral part of the activities of the Division. Consultants have continued to use thc National Borehole Records Archive and Database during the implementation of groundwater exploration and roads construction projects throughout the country. The general public have also been provided with

borehole infonnation, on request, for their intended water supply and livestock watering.

The Hydrogeology Division continues to give the Department of Water Affairs Technical Assistance in connection with groundwater exploration and development projects. Assistance was given to the

22

completed Molepolole/Mochudi Groundwater Exploration Project. Assistance was also given to the following on-going projects; Palla Road Groundwater Exploration Project, Dukwi Wellfield Extension and Resource Evaluation Project, Letsibogo Dam Investigation Project and the North-South Carrier Project. Technical Advice was also given on the planning of the proposed Maun Groundwater Investigation Project. The Division will play a role in the steering committee of this project.

Technical advice was given to the Ministry of Local Government Lands and Housing in connecrion with hydrogeological studies on proposed waste disposal sites in towns and district councils. This advice is provided by the team implementing the "Protection of Water Resources" sub-project of the project "Protection of Water Resources/Waste Management". Technical advice has been provided to the councils in the following areas; Lobatse, Ramotswa, Tlokweng, Gaborone, Molepolole, Ghanzi and Mahalapye as well as the Lobatse Tannery.

The Division continues to give technical advice to the Water Apportionment Board on the control of groundwater production and monitoring of well fields in Orapa, Jwaneng, Paje and Seleka, as well as pollution monitoring of the Morupule Power Station area. The Department, through the Hydrogeology Division, continued to sit on the following steering committee meetings; Interministerial Water Supply and Sanitation Committee and Debswana Water Supply Committee.

5.4

5.4.1

Staff Movements and Staff Training

Staff Assignments and Staff Movements

Mr P. Phofuetsile continued to act as Head of the Hydrogeology Division, while Mr E. Selaolo continued to be involved as a research fellow in the Groundwater Recharge and Evaluation Studies Phase II (GRES-I1). Mr Phofuetsile was assisted by Mr J R Anscombe who left the Department in October 1994 at the end of his term of contract. Mr Phofuetsile continued with the supervision of the Mmamabula Groundwater Resources Investigation Project-Phase I1, Khurutshe area. The project was officially completed with the submission of the final report and the appendices, at the end of the rcporting year.

Mr M. Morosini, a project hydrogeologist, continued to supervise and guide the

implementation of the TGLP Groundwater Potential Survey south-east o/Toteng-Sehitwa. The project final report was submitted in 1994 when the project officially closed. Mr Morosini was also involved in the implementation of the TGLP Gl'Oundwater Potential Survey-Ghanzi/Makunda Project as project manager.

Mr G Salas, project hydrogeologist who was involved in planning and execution of the TGLP Groundwater Potential Survey-Ghanzi/Makunda project returned to Australia in February 1994 at the end of his two year term of contract.

Mr S Leech arrived in Botswana in January 1994 to rcplace Mr Salas. He is involved in the TGLP Groundwater Potential Survey Project as project hydrogeologist. He is on a two-year contract.

Mr G Nkala has been involved in the implementation of the TGLP Groundwater Potential Survey project.

Mr K Mokokwe was involved in the execution of the sub-project Protection a/Water Resource of the project Protection qf Water Resources/Waste Management. He is receiving on~the-job training in the project.

Mr T Molebatsi successfully completed his MSc hydrogeology programme at University College, London, UK in September 1994 and returned to Botswana. He was then assigned to the Middlepits/Makopong TGLP Grollndwater Potential Survey Project to monitor its completion. He was also assigned to supervision of the project, Matsheng Area Groundwater Investigation as a local counterpart to the Project Hydrogeologist, Or J Timm.

Or Timm, Project Hydrogeologist, joined the Depaltment in October 1993. He was assigned to the planning and supervision of the project Mafsheng Area Groundwater investigation.

The two junior hydrogeologists, Messrs I Mab"a and M Magowe arc receiving on-tile-job training in the projects Protection of Water Resources/Waste Management and TGL? Groundwatcr Potential Survey, respectively.

Ms R Hargreaves, on British (ODAl secondment, continued to be ill charge of the groundwater monitoring unit. She also trained Mr N Ramotsoko as the head of the Groundwater Monitoring Unit. Her contract ends in March 1995.

Mr T Kgole continued to head the Borehole Records Archive, Database and Drill Sample Store.

Mr T Ntesang and Mr B Mohamadi were also involved in the Borehole Records Archive and Drill Sample Store, respectively, with the assistance of a trainee technical assistant, Ms L Ntu.

Mr N Ramotsoko returned to Botswana in May 1994 after successful completion of his diploma studies in Groundwater Technology in Canada. He was then assigned to the Groundwater Monitoring Unit to receive on-the-job training as the Head of the Unit. He is earmarked to take-over from Ms R Hargreaves. The following technicians were involved in the groundwater monitoring programme; K Leetile, J Phiri, L Keareng, L Mutukwa. Mr S Mandla, Trainee Technical Assistant, is receiving on-the-job training in the sub-project Protection of Water Resources.

5.4.2 Staff Training

Mr E Selaolo continues to be involved in the GRES-Il project as a research fellow. Messrs P Phofuetsile and G Nkala attended a training course on Groundwater Resources Assessment at the Water Depaltment of BRGM in Orlcans, France from 31 january 1994 to 26 February 1994. The training session was organised within the framework of the Mmamabula Groundwater Resources Investigation-Phase ll, Khurutshe Area. Mr Phofuetsile also attended a course on the establishment of Environmental Information Systems in Berlin, Germany from 6 to 26 November 1994. Mr G Nkala also attended a coursc on Project Planning and Appraisal from 30 May 1994 to 24 June 1994 and another on Monitoring and Evaluation of Projects fi'ol11 31 October 1994 to 18 November 1994, both at IDM in Gaborone. Mr Mokokwe attended a course on Project Planning and Appraisal from 30 May 1994 to 24 June 1994 at lDM in Gaborone and another on Applications of Remote Sensing to Protection of Natural Resources in Harare, Zimbabwe from 29 October to 30 November 1994. Mr T Molebatsi returned from London in September 1994 after successful completion of his MSc in Hydrogeology. He attended a course on Monitoring and Evaluation of Projects from 31 October to 18 November 1994 at lDM in Gaborone. Mr I Mabua attended a course on Waste Management from 6 April to \2 May 1994 in Nijkoping, Sweden, while Mr M Magowe attended a course on Applications of Remote Sensing to Protection of Natural Resources from 29 October to 30 November 1994 in Harare, Zimbabwe.

23

Mr N. Ramotsoko successfully completed his diploma course in May 1994 at the Northern Alberta Institute of Technology in Edmonton, Alberta, Canada. Mr J Setlhomo continues with the same course in Edmonton. Mr Ramotsoko returned from Canada in May and assumed the duties of a Technical Officer. From II to 15 July he attended WITS Team leaders Seminar at IDM in Gaborone.

Messrs Mabua, Mokokwe, Busch and Phofuetsile attended a workshop on Integrated Water Resources Management from 17 to 18 March 1994 in Kanye and Gaborone.

5,5 Reports and Publications

The following reports and publications were completed and published during the course of 1994.

• Mabua I, Mokokwe K & Busch K. Protection of Water Resources against Pollution by Vulnerability mapping. Proceedings of an Integrated Water Resources Management Workshop. Department of Environmental Science and Geology, University of Botswana.

• Mokokwe K, Mabua I, Manda S, Busch K & Stampe W. Groundwater Pollution Vulnerability map of Lobatse Area. Unpublished Geological Survey report.

• Mokokwe K, Mabua I, Manda S, Busch, K & Stampe W. Groundwater Pollution Vulnerability map of Molepolole Area. Unpublished Geological Survey repOlt.

• Mokokwe K, Mabua I, Manda S, Busch K & Stampe W. Groundwater pollution Vulnerability map of Molepolole Area. Unpublished Geological Survey report.

• Mokokwe K, Mabua I, Manda S, Busch K & Stampe W. Water Survey Botswana Groundwater Pollution 1994 Vulnerability map of Ramotswa Area. Unpublished Geological Survey repolt.

• Molebatsi T. Occurrence and Origin of Saline Groundwaters of the Tsabong region, South­west Botswana. University College London. In fulfilment of MSc degree in Hydrogeology.

• Mokokwe K. Water Quality in Streams near a Domestic Landfill at Lucas Heights. University of Technology, Sydney, Australia. In fulfilment of MSc degree in Hydrogeology.

• Nkala G. Hydrogeology and PreliminalJ' Modelling Results of the Seleka Farm Aquifer.

24

University of Technology, Sydney, Australia. In fulfilment of MSc degree in Hydrogeology.

• Beekman H E & Selaolo ET 1994. Long term average recharge of a shallow groundwater system in Botswana - A hydrochemical and isotope physical approach. Paper presented at the Water down under '94' conference in Adelaide, Australia: Nov 21-25 1994. Paper published in Proc. Vo!. 2A, 157-162.

• Gieske A S M, Selaolo, E T & Beekman H E. Tracer interpretation of moisture transport in a Kalahari sand profile. Paper presented at The first international symposium on application of trace in arid zone hydrology in Vienna, Austria; Aug 21-25, 1994, 11 pp. (in press).

• Selaolo E T, Gieske, A S M & Beekman H E. Chloride deposition and recharge rates for shallow groundwater basins in Botswana. Paper presented at the Water down under '94 confcrencc in Adelaide. Australia Nav 21-25 1994. Paper published in Proe. Vo!. 2B, 501-506.

~

-ll. E ~ ~

~ ~ ~

iil '0 ffi ~

E ~ c m·

~ ~

E ~ ()

w

'" 0 = '" 0 ~

'0 ii; ~

E ~ z

~

-ll. E ~ ~ ~ ~

c '0 ~

~

ffi ~ 0

~

'" E ~

z

Fig. 5.1 Numoor of sludge samples for the year 199(.1994 25

20433

20

15

10

5

oLJ~~~~~~~~~~~_1 1991 \992 1993 1994

Year ill Govt samples ~ Private samples

Fig. 5.2 Cumulative number of sludges for the year 1990-1994 210

200

190 ----" 191822 180 185394

170 Govemment samples

~ 160

"~09O 163328 ~ c 150 144285 ~ ~ 150886 0 140 = f- ~ 130 122723

120 11583~- . V Pnvale samples 110 103536 100

90 1989 1990 1991 1992 1993 1994

Year

Fig. 5.3 Number of private boreholes registered for the year 1985·1994 500

400

321 334

300 252

242 245

200

100

O. 1985 1986 1987 1988 1989 1990 1991 1992 1993

Year

1995

255

1994

25

6. GEOPHYSICS DIVISION

6.1 Introduction

The unofficial mandate of the Geophysics Division remains:

• Repository for all geophysical data collected in the country

• Assist other Divisions within the GSD and departments within the Government

• Act as technical monitor on various Government-funded projects

• Research into the applicability of various geophysical techniques within the range of geological environments found in Botswana.

The CUlTent focus of the Geophysics Division may be summarised as:

• Hydrogeology (groundwater) projects with technical monitoring and quality control on several GSD and DWA contracted projects. This includes providing all personnel and equipment on geophysical aspects of the Ghanzi-Makunda TGLP Groundwater Investigation Project, as well as technical monitoring and advise on the Matsheng and Middlepits-Makopong TGLP projects, and the Dukwi Well field Extension and Maun groundwater development projects.

'. Technical monitoring and quality control on the Ghanzi-Chobe Fold Belt triaxial aeromagnetic survey during the first half 1994. This project was specifically aimed at mineral exploration incentive for the private sector, although the data will also be significant in several groundwater exploration and evaluation projects being conducted by GSD and DWA. Response of the private sector to receiving this data once placed on open file was considered very significant. Further, similar projects in western Ngamiland are now in the planning stage.

• Several research projects arc either underway or in advanced planning stages. These include a digital compilation of all airborne geophysiCal data in Botswana into a coherent geographic infon,.,ation systems (GIS) database, a catalogue of borehole geophysical responses in various lithologies . throughout Botswana, and operation and maintenance ofthc Global Telemetry Seismic Network in conjunction with the United States Geological Survey.

• Practical 'hands-on' training continues in the Geophysics Division as part of 'he CIDA-

26

funded geophysics localisation prqject, with each of the Batswana geophysicists and technical officers undertaking or scheduled to undertake various geophysical/geological tasks. Training programmes for each officer within the Division have been initiated and arc currently proceeding on schedule. Programmes have been designed to enable each officer to acquire experience with as many geophysical techniques as possible.

Campbell and GJedhiII have continued to fill line positions in their respective roles as Principal and Senior Geophysicist in the ongoing Canadian International Development Agency (CIDA) -funded Geophysics Localisation project. The Canadian cooperants will continue carrying out several work programs involving field geophysics and data analysis I interpretation. Geophysical work over the past year has concentrated on the Ghanzi-Makunda TGLP Groundwater Investigation project and the Ghanzi-Chobe fold belt aeromagnetic survey. Gledhill's post as Senior Geophysici,t was officially localised in December, with Gledhill stepping aside out of a line position to one of advisor. KoosimiIe has assumed the regular duties and responsibilities of the Senior Geophysicist within the Division.

There are currently five Batswana professional geophysicists in the Division, with support from four geophysical tcchnicians (Jaba, Bantshang, Moncho and Ramaselaga), one elcctronics technician (Obotsang) and one technical assistant (Ditlhogo). Two of the professional geophysicists (Koosimile and Ngwisanyi) are fulfilling duties as Senior Geophysicist and Geophysicist I respectively under the recently approved Government of Botswana schemes of service. The three remaining geophysicists (Koketso, Kwadiba and Holmes) are currently out of the country pursuing their respective M.Sc. in Geophysics. Two trainees (Tladi and Kebadire) are completing a course in electronics technology (Cambrian College in Canada), and should return to Botswana and the GSD in mid- I 995 and mid-1996, respectively.

The Geophysics Division is therefore not scheduled to reach its full staff complement until mid- I 996 with the return of Koketso and Kwadiba from Ireland, andlor mid-1997 with the return from Canada of Kebadire. Only two field seasons remain in which either the professionals or the technicians can receive sustained, prac"tical handsMon training in field geophysics methodology from the Canadian cooperants. However, significant training

efforts are now being successfully undertaken by either or both of the senior Batswana Geophysicists (Koosimile and Ngwisanyi). This process should continue to expand and develop, thus ensuring project sustainability as the Canadian cooperants inevitably depart.

Advice is regularly being provided to the GSD on a number of matters. These include, but are not necessarily restricted to the following: groundwater geophysics, geophysics applied to both economic and regional geology as well as urban and geotechnical investigations. Also regularly provided is hardware and software computer and electronic technical support to the Department as a whole. In addition, the Principal Geophysicist helped the GSD and MMR W A in promotion of mineral investment opportunities in Botswana to overseas interests.

The breadth of technology transfer to GSD personnel is evidenced by the range of topics that are being supervised by the Canadian cooperants and by the short COurse offerings. Further technology transfer to the Geophysics Division, besides interpretation and project management skills, has been and is being developed in the area of advanced computer manipulation of geophysical data. An increased emphasis on digital data handling will make much use of the recently installed mapping systems, local area networking facilities, UNIX-based workstations and other computer systems at the GSD.

6.2

6.2.1

Development Projects

Ghanzi-Makunda TGLP Project

This project is being carried out by the GSD on behalf of the Ministry of Agriculture whose purpose is to evaluate the groundwater potential of the areas identified as TGLP ranches. The Division is also committed to devise the best or optimal strategies for geophysical borehole siting besides identifying those methods that can locate groundwater related structures. Reduction and processing of gravity data continued throughout the year and a report on the gravity data acquisition, processing and corrections was completed in the last quarter of the year. Data correctionl reduction and (preliminary) interpretation of time-domain electromagnetic ('I'D EM) profiling and sounding as well as aeromagnetic data processing and interpretation continued. Additional TDEM data acquisition was also conducted during the reporting year. Hori.zontal-Ioop electromagnetic (HLEM) profiling was initially carried out with the purpose

of confirming borehole siting methodology for possible perched aquifers at particular locations in the project area, and to compare frequency based EM systems to time domain EM systems.

The last quarter of the year saw the Geophysics Division stretching its meagre resources to mobilise two crews for 'exploration' borehole siting in the project area. HLEM (Max-Min 1-8) and ground magnetics used to site drill targets led to significant water strikes.

A final draft report, entitled Regional Gravity Studies of the Ghanzi-Makunda TGLP Block, on the gravity data acquisition, proeessing and corrections undertaken since the projecfs inception was completed.

6.2.2 Geophysical Consultancy to the Hydrogeology Division and the Department of Water Affairs

The Geophysics Division continued to monitor the geophysical output of various consultants engaged in groundwater resource evaluation and exploitation/development projects conducted on behalf of the Department of Water Affairs (DWA) and the Hydrogeology Division of the GSD. These projects are: .

• Mmamabula Phase 11 (Khurutshe area) GSD • Poliution Protection of Water Resources

GSDIBGR • Palia Road Phase II DWA • Dukwi Wellfield Extension DWA • Molepolole Mochudi DWA • Middlepits-Makopong TGLP GSD/MoA • Matsheng TGLP GSD/MoA

6.2.3 Ghanzi-Chobe Fold Belt Aeromagnetic Survey

A fixed-wing, very detailed high' resolution aeromagnetic survey was carried out over approximately 42,000 km' in the Ghanzi and Chinamba areas within the Ghanzi-Chobe Fold Belt of north-western Botswana. In total, 19 I ,640 line kilometres of detailed triaxial (four magnetometers operating simultaneously to measure vertical, horizontal and longitudinal gradient of the earth~s total field) was acquired along traverses spaced at 250m intervals, 80m above ground level mean terrain clearance. Data acquisition was completed in April and ali data and maps were delivered to the GSD in August though the final report was not delivered until December.

The final processed line and grid data in ASCII code and Geosoft compatible format (XYZ and

27

GRD fonnats) were delivered on CD ROM and Exabyte cartridges The calculated derivatives were supplied in Geosoft compatible format on CD ROM and Exabyte eartridge. These products are:

• Reduetion-to-the-Pole • Apparent Magnetic Susceptibility • Digital Tenain Model • Total Gradient • Euler Deeonvolution

Euler deconvolution was supplied as Au/oeAD *.DWG files to interface with' ER Mapper as an overlay to the gridded images.

The digital data comprising this survey amounts to some 14,000 Mb of data contained on twenty-two (22) CD ROMs (each 550 Mb in capacity) and duplicated on eight (8) Exabyte tapes (each 2.3 Gb capacity).

Maps delivered were base maps, total magnetic intensity and vertical gradient contour and profile maps, and total magnetic intensity and vertical gradient colour maps.

The bulk of the data processing on this project was completed in Botswana. The final computations of Euler deconvolution, magnetic susceptibility and analytic signal, as well as the plotting and printing of final maps was done in France.

Besides the aeromagnetic data, the Geophysics Division received specialised computer hardware (SUN workstation) and software (ER Mapper and GMI-Pack·modules) for use in the interpretation of the results of this and other surveys.

Analog and digital data sets have been released to mining and exploration companies as well as academic and research institutes. An overwhelming interest in the data has been registered by various parties.

6.3

6.3.1

Internal Projects

Maun Groundwater ExploratiOn and Resource Assessment

A short project of shallow, high resolution reflection seismic profiling work was conducted in the Maun area. Some 5,200 metres of profiling were completed across the Thamalakane Fault zone. Although thisw'as being done as part of a University of Botswana staff development fellow's M.Sc. thesis project, the results will be of direct significance to the Maun groundwater project, and will be made available to the DWA.

28

The Geophysics Division has assisted the DWA in preparing the technical terms of reference on both the aeromagnetic survey and the overall Maun project. The Division will also assist in evaluating the submitted tenders and the subsequent tender awards.

6.3.2 Francistown GPR Survey

Early in the year there suddenly appeared a 12m deep hole on the grounds of the Nyangabwe Hospital in Francistown. Desk top studies indicated that the hospital has been constructed atop old gold mine workings and that the hole in the ground was likely one of the shafts thought to exist in the immediate area. At the request of DABS and the Mines Department a geophysicist from the GSD was asked to assist in identifying the positions of the remaining shafts. A ground penetrating radar (GPR) survey was recommended.

The Geophysics Division facilitated contracting the services of a consultant to conduct the GPR survey. Twelve anomalous zones were identified, some within the building complex. Excavation of the sites outside the hospital buildings revealed that the sources of the anomalies were buried construction material, scrap metal contained in old pits and even a previously unknown electrical cable. Several large voids were, however, found coincident with the geophysical anomalies and these required back filling in order to stabilise the ground.

Those short project launched the Geophysics Division into a new field of near surface geotechnical studies. In future major construction work will require thorough geotechn ical investigations and the Geophysics will be there to provide assistance in monitoring and guidance as it does not have at present the resources to actually perfOlm the site investigations.

6.4

6.4.1

International Projects

Global Telemetry Network

Co-operation

Seismograph

The Global Telemetry Seismograph Network (GTSN) is a co-operative project between the United States Geological Survey (USGS) and countries in Africa and South America. The purpose of the project is to obtain and exchange in a timely manner seismological data of high quality and reliability. Data is eollected by sensors in a borehole near Magotlhwane and transmitted by radio link to the GSD where it is processed and transmitted by fibre optic link (in real time mode)

Precambrian Research Quarterly Journal of Engineering Geology Tectonophysics Water Resources Research

8.4.2 Records

Consultants' reports received during the year were as follows.

Anglo American Corporation of South Africa (Pty) Ltd

Debswana Diamond Company (Pty) Ltd Orapa and Letlhakane Mines. Orapa 1992 Water Supply Investigations. Volume I Main RepOlt CED/06S/92 September 1992. GC 1411 SI1 a.

Debswana Diamond Company (Pty) Ltd Orapa and Letlhakane Mines. Orapa 1992 Water Supply Investigations. Volume 2, Appendix I (Geophysical Survey) & Appendix 2 (Borehole construction and logs). Report CED/06S/92 September 1992.

Debswana (De Beers Botswana)

Water right for Orapa Mine. GClS/411.

Orapa Mine: Orapa Wellfields assessment of computer modelling and groundwater resources projections. Appendix to monitoring report II. Technical Note TN/005/92 May 1992. GClS/4/3.

Repolt on activities and work carried out for flow improvements from the Okavango Delta. July 1993. GC IS/5/1.

Debswana Diamond Company (Pty) Ltd Orapa 'and Letlhakane Mines. Orapa Hydrogeological desktop study 1993. Phase I. GC IS/5/2.

Debswana Diamond Company (Pty) Ltd Orapa and Lellhakane Mines. Recommendations for the dewatering of the Letlhakane Mine based on 1993 modelling. GClS/5/3a.

Northern Well field Monitoring Report 26. January­June 1993. Executive Summary. GClS/5/3.

BRGM (Bureau de Recherches Geologiques et Minieres)

Evaluation of groundwater resources Letlhakeng-Botlhapatlou Groundwater Inception Report. March 1990. GC23/9/2.

(GSI0) Project.

Evaluation of groundwater resources (GSI0) Letlhakeng-Botlhapatlou Groundwater Project Monthly Progress Reports 1-4 from 15 February to 19 April 1991. GC23/9/2a·n.

60

Monthly Progress Report 2 from IS March to 15 April 1990.

Monthly Progress Report 3 from 15 April to 15 May 1990.

Monthly Progress Report 4 from 15 May to 15 June 1990.

Monthly Progress Report 5 from 15 June to 15 July 1990.

Monthly Progress Report 6 from 13 July to 17 August 1990.

Monthly Progress Report 7 from 17 August to 14 September 1990.

Monthly Progress Report S from 14 September to 12 October 1990.

Monthly Progress Report 9 from 12 October to 15 November 1990.

Monthly Progress Repolt 10 from 15 November to 14 December 1990.

Monthly Progress Repolt 11 from 14 December to IS January 1991.

Monthly Progress Report 12 from 18 January to 22 February 1991.

Monthly Progress Repolt 13 from 22 February to 22 March 1991.

Monthly Progress Report 14 from 22 March to 19 April 1991.

The Lands area water supply study TB 10/31l2/90-91 Inception RepOlt. March 22 1991. GC23/9/3.

Burrow Binnie Ltd

North-South Carrier Consultancy. Pipe material Report. July 1993. GC24/312.

Pre-implementation selection. Module

North-South CatTier Pre-implementation ConSUltancy. Raw water/treated water option. Module Report. June 1993. GC24/3/2a.

North-South CatTier Pre-implementation Consultancy progress report. GC24/3/2b.

Earth Resources Consultants

Consolidated village water supply emergency programme. Group 1I villages, Molapowabojang, Rakhuna, Ngwatsau, Mogoreapitse, Motsentshe and Mookane. Draft Report. GC20/3/4.

Consolidated village water supply emergency programme Group II villages, Molapowabojang,

Rakhuna, Ngwatsau, Mogoreapitse, Motsentshe and Mookane. Final Report Vol.!!I. GC20/3/5.

Geollux

Integrated rural village water supply programme: siting of boreholes and supervision of drilling, construction and pumping test works in Sekoma Village. Final report. February 1994. GC72/4/l.

Groundwater Consulting Services

Tutume water supply investigations. Phase I1I. Final report Vol.! - text. June 1994. GCS2/4/1.

Tutume water supply investigations. Phase Ill. Final report Vol.I1 - figures. June 1994. GCS2/4/la.

Tutume water supply investigations. Phase III. Final report Vol III - Raw data. June 1994. GCS2/4/lb.

Water Resources Consultants

Integrated rural village water supply programme. Tender TBIO/3/lS/92-93. Final Report Vol. 1

Groundwater Investigations and Development in Mmaphashalala, Central District. March 1994. GC53/5/1.

Water Surveys Botswana

Tsodilo Hills water supply investigation. Final Report. February 1994. GC69/6/1.

Integrated rural village water supply programme. Kagkae Village. Final Report. March 1994. GC69/6/2.

8.4.3 Reports and publications

The following Departmentalreports and maps were published during 1994.

(1) Reports

• Annual report for 1993. • The geology of Botswana. (by J N Carney, D

T Aldiss & N P Lock). Bulletin 37. • The geology of the Topisi area (by R M Key,

R B M Mapeo, HEM Van Zyl, R L Hargreaves, H Holmes & A Golding). Bulletin 3S.

• The geology of the Marico River area (by G Nkala & R M Key). Bulletin 39.

(ii) Maps

• Areas held under reconnaissance permits, prospecting licences and mining leases as at 1 January 1994 (l:2 000 000).

• Areas held under reconnaissance IlI..1I'Illits1

prospecting licences and mining Icnses u.~ lit I July 1994 (l:2 000 000).

• 1:125000 Geological map of the Ngwako Pan area (QDS 2022D &2023C).

• I: 125 000 Geological map of the Dautsa area (QDS 2022C).

• 1:125 000 Geological map of the Ramsden area (QDS 2121C).

• 1 :50 000 Groundwater Vulnerability Map Sheet 2525B I Lobatse.

• 1:50 000 Groundwater Vulnerability Map Sheet 2525B2 Lobatse.

• 1:50 000 Groundwater Vulnerability Map Sheet 2525B3 Lobatse.

• 1 :50 000 Groundwater Vulnerability Map Sheet 2425D3 Mogobane

• 1:50 000 Groundwater Vulnerability Map Sheet 2425D4 Ramotswa

Sales of Departmental publications realised approximately PS 201 while about 703 publications were distributed free of charge and on exchange. The following internal reports were filed during the year.

• Key, R M, Lesole, L & Semele, D. Report on the cored borehole drilled by the Geological Survey Department near Shadishadi. RMK/54/94.

• Lesole, L. Report on a field trip undertaken in preparation for thc volcanic geology course. LLlI/94.

• Lesole, L. A report on a site investigation in Thema at the proposed site for Lobatse's new sports complex. LLl2/94.

• Lesole, L. Report on a field visit to Kang to investigate rock mined in Kang Pan for use as gravel for the new road. LLl3/94.

• Mapeo, R B M. The structure of Archaean and Proterozoic rocks and the evidence for thrusting in South-east Botswana: an abstract. RBMIl2/94.

• Mapeo, R B M, Key, R M & Walraven, F. Geochronology of the Mmathethe Granite, South-east Botswana. RBM/l3/94.

• Ngwisanyi, T H & Jaba, B C. Gravity survey in the Kuke area (1994): field report.

• Salas, G. TGLP Ghanzi-Makunda Groundwater Survey: geological framework and hydrogeological targets. A desktop study. GS/I/94.

• Tidi, J. A report on geological investigations in the Tsabong area. JT/l/94.

• Tombale, R A. Historical development of the Botswana Geological Survey. ARTIl4/94.

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8.5 Drilling and Mechanical Section

8.5.1. Introduction

The Drilling and Mechanical Section has the main responsibility for providing drilling services to all the field divisions of the Geological Survey Department. Drilling production was again severely hampered by the condition of much of the existing drilling fleet with a number of very old and obsolete rigs. As such drilling rigs were constantly under mechanical repair in 1994. Therefore most of the drilling projects were not completed within the specified and expected time. The poor condition of the rigs also meant that several drilling projects from the 1993 drilling plan had to be carried over into the 1994 drilling plan. At the end of 1994 the drilling fleet consisted of 8 rigs. These are:

Coring Rigs

Tone I

Tone Il

Longyear 44

Edson 6000 w series

R7,6GC

R6,6GC

Soil Test (auguring) Rigs

Ranger I

Proline

There are three reliable rigs in the fleet: the Edson 6 000 w series, R6,6GC and R7 6GC machines. The rest need to be boarded and urgently replaced.

8.5.2 Drilling Projects - 1994

Several boreholes were sited at various places throughout the country. These boreholes were sited by various field division of this department and were of different interest ranging from mineral exploration (Industrial and Economic Minerals); groundwater levellmonitoring and underground water ~echarge; field mapping support and lithologicallstratigraphical boreholes; and investigating geophysical anomalies. No soil auguring was carried out this year although a lot is expected next year when the GRES PHASE Il Project continues its drilling activities in the Letlhakeng/Botlhapatlou and Tshane areas. Projects carried out in 1994 by each rig are as follows. .

LONGYEAR 44 Rig - Segwagwa Pan

The Regional Geology Division sited one stratigraphy borehole (expected total depth of

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about of 600m) at Segwagwa Pan. At the end of December 1994, the borehole was down to 304m. Down-time was experienced because the gearbox broke and it took a long time to be replaced. Other accessories also gave some problems that were quickly resolved. This hole will be continued in 1995.

R7,6GC rig (GRES II Rig) - LetIhakeng IBotlhapatlou

This new rig was fully employed by the GRES II project throughout the year in the Letlhakeng/Botlhapatlou area. A new sampling system was introduced by the project staff (Advance Sampling). This system worked inside the hollow stem augers ordered from Australia by the project. The idea was to sample loose and undisturbed sediments. This sampling technique was rather successful and the only problem encountered was when ca1crete or sifcrete was intresected. With this sampling system, four boreholcs were sampled at the following places, Setshe, Mamonageng and Legape. All these boreholes were to be sampled down to a maximum depth of SOm. The deepest one (41.6Sm) was at Mamonageng. DTH boreholes were also drilled in the same areas. Three boreholes of 90m each were drilled at Setshe near the GRES II project weather station. One borehole each was drilled at Legape 28m and Mamonageng 118m. A month's work was lost at Legape when the engine on the rig seized. During this period, one rig was brought in to continue with drilling activities in the project. The engine was replaced by a new one but not much work could be carried out as this was time to close operations for December holidays.

R6,6GC Rig - Pilane

This is a new rig that was purchased from R,SA and received in early August 1994. This rig was commissioned at Pilane on the German Solid Waste Disposal project. Five DTH boreholes were drilled near the new dumping site. One borehole was drilled down to 34m and the others down to 80m. Three cored boreholes were also drilled in the same area, each down to 30m. This project was successfully completed on time. This rig was then moved to the GRES II project operation in the Letlhakeng/BotIhapatlou to continue with the DTH operations.

EDSON 6000w Series Rig - Pall. Road & GRES Il Project •

This rig started the 1994 drilling one deep cored borehole at Palla Road, jointly for the Regional

Geology Division and the Department of Water Affairs. This borehole was drilled within a major groundwater project area supervised by Water Affairs. The cored borehole was stopped at a depth of 573m after passing through artesian saline water in Ecca sandstones. The artesian water lies below a major fresh water aquifcr within Lebung Group sandstones. Every precaution had to be taken to stop the saline water contaminating the overlying fresh water which is a major source of water for Mahalapye. After completion of this borehole, the rig was moved to Letlhakeng/Botlhapatlou to help in the GRES II operations. This rig drilled one cored borehole to a depth of 497m.

TONE 1 & 1I - Dipotsana & Moshaneng

These two rigs continued shallow drilling operations for Regional Geology Division at Dipotsana. This project was carried over from the 1993 drilling programme. Six boreholes were drilled at Dipotsana with varying depths from 45m to 90m. One rig,(TONE I) developed a gearbox problem and it was brought back to headquarters for repairs. On completion of the Dipotsana project, TONE II was moved to Moshaneng to drill one cored borehole with an anticipated depth of between 60m and 80m. This borehole was completed down to 42m. The crew then moved to join other crews in the GRES II project operations.

8.5.3 Staff

The staff of the Drilling and Mechanical Section at the end of 1994 is shown in Table 8.8

8.5.4 Annual Production

A summary of the drilling completed by the Drilling Section in 1994 is shown in Table 8.9.

8.5.5 Outstanding Drilling Projects - 1994

1. One cored borehole at Segwagwa for the Regional Geology Division had reached 304m by the end of 1994. The borehole will be completed during 1995.

2. One cored borehole for the Geophysics Division to a depth of 300m at Molapowabojang to be used to test geophysical logging equipment

3. Four DTH boreholes of depths of about 250m for the Hydrogeology Division in the GhanzilMakunda Project area for monitoring and recharge studies.

4. Forty boreholes in various locations to be flushed on behalf of the Hydrogeology Division.

S. One cored borehole of 1000m to be drilled at Makunda jointly for the Regional geology and Hydrogeology Divisions.

6. Three DTH boreholes with depths of 300m to be drilled in the Pitsanyane Basin for the Geophysics Division.

7. Four cored boreholes with depths of about 40m to be drilled at Tlapana to investigate industrial minerals for the Economic Geology Division.

Table B.B The staff of the Drilling Section

Officer Post

Vacant Chief Technical Officer D4

CKMpelege Principal Technical Officer Cl

TB Sekgopa Principal Technical Officer Cl

M Ntloedibe Senior Technical Officer C2

M Raditladi Senior Technical Officer C2

M Molatlhegi Senior Technical Officer C2

K Babitse Senior Technical Assistant 83

[ Ludick Senior Technical Assistant 83

Table 8.9 Completed drilling by each rig in the

Drilling Section in 1994.

Rig Total meterage

core DTH Soil test

Tones I & 422 2

R7,6GC 416 68.9

R6,6GC 129 394

Longyear 304

Ranger I

Proline

Edson 1173 6000W

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