Thursday, April 03, 2008

Southern African Development Community Geology Map

The CGS is in the process of completing a new map of the geology of the SADC (Southern African Development Community) countries. The map will be at a scale of 1:2 500 000 and will be based on a lithostratigraphic legend.

During the mid-1990s, the Mining Coordination Unit of the SADC countries included, amongst others, a Geology Subcommittee which initiated several specific cooperation projects. These resulted in several publications synthesising the occurrence of diamonds, gold and copper in the SADC region, geophysical and seismological maps of the SADC area, maps depicting the pre-Kalahari stratigraphy, a Kalahari isopach map, as well as other publications and databases. In addition, a stratigraphic working group was established to facilitate a comparison of the stratigraphy of the various countries. At the time it was considered to be potentially a valuable tool for mineral exploration in the area.

This project culminated in the publication of a comparative stratigraphic chart of the geology of the SADC countries in 1998. The chart, compiled by Frikkie Hartzer of the CGS and published by the CGS on behalf of SADC, was a cooperative effort by the geological community of southern Africa. In this chart the actual geological units as portrayed on the various regional 1:1 000 000- and 1:2 000 000-scale geology maps were plotted on the same chronological space, showing time and duration of intrusion, sedimentation or eruption.

The success of this project led to the decision to compile a new geology map covering the entire SADC area. Although there are specific maps of the area currently available, such as the Geology Map of Africa at a scale of 1:5 000 000, the Tectonic Map of Africa (1:5 000 000) and a Mineral Resources Map of Africa (1:5 000 000), there is no specific geology map of the area at a scale of 1:2 500 000 based purely on a lithological classification, as opposed to a tectono-stratigraphic, tectonic or a chronostratigraphic classification. The basic principle for the production of such a map has always been that, since geological units are not bound by geographic borders, a uniform map would enable the geological community to correlate units across the borders and synthesise the various names given to similar units in different countries.

The CGS offered to facilitate the compilation and eventual publication of this map. Frikkie Hartzer was asked to compile the map, with the help of Pieter Bosch, who was given the responsibility to compile the data for Tanzania, and co-workers from all the SADC countries were commissioned to participate in this project.

Geographically, the SADC countries form a well-defined entity consisting of the Democratic Republic of the Congo (DRC), Angola, Namibia, South Africa, Lesotho, Swaziland, Botswana, Zimbabwe, Mozambique, Malawi, Zambia, Tanzania, Mauritius and Madagascar. In 1998, when the stratigraphic chart was compiled, the Seychelles was a member of SADC, but not Madagascar; an insert map had to be constructed for the inclusion of Madagascar.

The biggest problem facing the compilers and co-workers was the difference in quality and quantity of geological data between the various countries. Countries such as Botswana, Namibia, South Africa, Lesotho and Swaziland have recently published 1:1 000 000-scale maps which were of great assistance in the compilation. However, parts of those countries have since been remapped. A concerted effort was made to include some of this new information. Countries such as Zimbabwe, Zambia and Malawi have accumulated considerable new information in the form of mapping projects since the publication of their 1:1 000 000-scale geology maps. Several 1:100 000-scale maps of these three countries were recompiled for inclusion in the SADC map, a very time-consuming process. In the case of Tanzania, for which a geology map at the scale of 1:1 000 000 was published in 1958, a special effort was made to compile the considerable load of new information. Pieter Bosch spent several weeks at the Geological Survey in Dodoma, Tanzania, to trace and capture new information.

The geology map of the DRC has been a difficult compilation since very little new mapping has been reported recently; however, an exception was that the geology of the northeastern part of the country has been reinterpreted by the French Geological Survey (BRGM). The Geology Department of the Africa Museum in Tervuren, Belgium, cooperated in providing interpretation of the existing data, including mapping from the Pan-African West Congolian Belt in the western part of the DRC and Angola.

During the course of the project, Mozambique launched a new mapping programme that was funded/financed by institutions such as the World Bank, the Nordic Development Fund, the African Development Bank and the South African Government. In 2007 it was decided to include the new data from this project in the map and to redesign the legend accordingly.

The process followed during the compilation of the map was to begin with capturing the existing (1 or 2 million scale) map data, followed by the manual addition of new map data to enable a separate compilation for each country. The data set was then redrawn into a single data sheet, which was then scanned and vectorised. After codification, harmonising of the data was done and a single legend was designed. The construction of the legend was based on the original stratigraphic chart, but proved to be a very complicated process. Currently, the map is in the process of being checked and verified. The cartographic process has started and the date of publication is currently set for within the next few months.

In terms of the future, the project is seen as an ongoing task. Currently, the World Bank is financing an extensive geological project in Madagascar, which would greatly enhance the existing geological knowledge and change the geology map of the country considerably. Similar projects are envisaged for Tanzania and the DRC. A long-term view would be the possibility of publishing a second edition of the map once these projects have been finalised.

The SADC Geology Map is of considerable size, exceeding all standards and will be published and sold by the CGS as a set of six A0-size maps.

Source : Council for Geoscience


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