Geological Map Of The Colony Of The Cape Of Good Hope Sheet 45 – Postmasburg – Daniels Kuil

Cartographer: Rogers, A. W.
Publisher: The Geological Commission
Price: £125 (post-free in the UK)
Publication Date: 1907
Edition: 1st edition thus
Format: Lithograph
Condition: In very good condition
Sheet Size: 73.8cm x 52.4cm

Condition:

Lithograph. Sheet Size: 73.8cm x 52.4cm. Neat ink number to lower right margin. Old fold lines. Very slightly creased, marked, dusty and rubbed. Colouration very bright and clean. A very good copy. Very scarce.

Location: Pocket RSAGEOL: SR: 002858

Geology Of The Daniels Kuil And Postmasburg Region: An Historical Overview

1. Geographic and Geological Context

Daniëlskuil is located in the Northern Cape Province of South Africa, along the eastern margins of the Kalahari Basin, approximately 150 kilometres north-west of Kimberley. Situated near the edge of the Ghaap Plateau, it lies within a transitional zone between ancient cratonic basement rocks, Palaeoproterozoic carbonate platforms, and the overlying younger Kalahari sediments. The town is known geologically for its karst features, dolomite formations, and lime mining operations.

The region holds particular significance for its exposures of the Ghaap Group, a subunit of the Transvaal Supergroup, and for its links to the ancient chemical sedimentation processes that occurred in shallow marine environments over 2 billion years ago.

2. Cratonic Foundations: The Kaapvaal Craton

Beneath Daniëlskuil lies the stable and ancient crust of the Kaapvaal Craton, one of the oldest pieces of continental lithosphere on Earth, with origins dating back over 3 billion years. Though largely buried beneath younger sediments in this area, the cratonic basement provides the tectonic stability and platform integrity that allowed for long-lasting marine sedimentation.

The Kaapvaal Craton’s relatively passive tectonic setting during the Palaeoproterozoic period permitted the formation of broad carbonate shelves, particularly evident in the Ghaap Plateau region.

3. The Ghaap Group: Marine Carbonate Deposition and Dolomite Platforms

The dominant and most geologically important unit in the Daniëlskuil region is the Ghaap Group, a subdivision of the Transvaal Supergroup, deposited between approximately 2.6 and 2.2 billion years ago.

This group is composed primarily of:

1. Campbell Rand Subgroup

• Thick successions of dolomite and limestone, interbedded with chert layers
• Deposited in a shallow, stable marine environment on the cratonic margin
• Host to karst systems, sinkholes, and natural caves formed through chemical weathering of dolomite by slightly acidic groundwater

1. Kuruman Formation (Basal Banded Iron Formation)

• Although more prominent further north in Kuruman itself, localised development of iron-rich cherty layers may occur in the Daniëlskuil area
• These formations indicate oceanic iron precipitation prior to significant atmospheric oxygenation

The carbonate rocks of the Campbell Rand Subgroup are intensely recrystallised and show evidence of diagenetic alteration, which enhances their suitability as industrial lime sources. Mining in the area has long targeted these dolomitic units for lime and aggregate production.

4. Karst Topography and Surface Features

The most visually striking geological feature in Daniëlskuil is its karst topography, a direct result of the solubility of dolomite in groundwater. The town’s name itself refers to a “kuil” (pit or hollow), specifically the sinkhole-like limestone cavity believed by local tradition to have been used as a holding cell or pit.

These karst features include:

• Sinkholes and solution cavities
• Subterranean caverns
• Natural springs, some of which have been utilised for local water supply

The karst terrain also influences soil development, water drainage, and land stability, and requires geotechnical assessment before construction or mining expansion.

5. Overlying Cover: Kalahari Group Sediments

Above the carbonate platform lies a veneer of Kalahari Group sediments, deposited from the late Cretaceous to recent times. These include:

• Wind-blown sands, forming dunes and sheet sands
• Clayey alluvium, particularly in shallow depressions and along ephemeral drainage channels
• Calcretes and duricrust layers, formed through pedogenic processes in the semi-arid climate

These younger deposits mask older formations in some parts of the region and contribute to the area’s semi-arid geomorphology and soil types.

6. Structural Features and Tectonics

Though the region lies within the tectonically stable interior, subtle structural features are evident, including:

• Gentle folding and broad warping of sedimentary strata
• Minor faulting that may influence local groundwater flow
• Possible karst collapse structures, mistaken for tectonic depressions

These structural characteristics affect aquifer recharge, mine planning, and the integrity of natural sinkholes.

7. Hydrogeology and Water Resources

The dolomitic rocks of the Daniëlskuil area host significant karst aquifers, which are valuable for local water supply. Characteristics of these aquifers include:

• Fracture- and solution-enhanced permeability
• Variable but sometimes high-yielding boreholes
• Potential for rapid contamination due to direct recharge through sinkholes

Careful groundwater management is essential in karst environments to prevent over-extraction and protect against pollution.

8. Economic Geology and Industrial Use

The region has long supported lime production, with the high-purity dolomitic limestone being used for:

• Metallurgical flux in steel and manganese smelting
• Agricultural liming agents
• Construction materials and aggregate

Mining has played a central role in the local economy, with quarries extracting both raw limestone and processed lime products for regional and national markets. The area’s geology also makes it of continued interest for geological mapping, karst hydrology, and mineral exploration.

9. Environmental and Heritage Considerations

The geology of Daniëlskuil has shaped not only the natural environment but also cultural narratives and land use. Environmental and heritage aspects include:

• Preservation of karst ecosystems, which are often fragile and support specialised biodiversity
• Protection of geological heritage features, such as the historic sinkhole and exposed dolomite cliffs
• The importance of geological awareness in managing land subsidence, water protection zones, and land development

Conclusion

The Daniëlskuil region exemplifies the geological transition from deep-time cratonic stability to Proterozoic marine sedimentation and modern karstification. Dominated by the dolomitic rocks of the Ghaap Group, it provides a unique insight into early Earth environments, carbonate platform evolution, and the processes that govern karst landscapes.

Economically, scientifically, and environmentally, Daniëlskuil remains a geologically rich and instructive locality, where the interplay of ancient bedrock and recent surface processes continues to shape both the landscape and the life it supports.

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