Geological Excursion to Bonnievale, Robertson and Montagu - May 2025

Date: 9 - 11 May 2025

Planning is underway for a two-day excursion to experience the “Geology of Bonnievale, Robertson, Montagu and the Keisie Valley” from Friday to Sunday morning, 9 - 11 May 2025. Participants will overnight in Montagu and return home on Sunday morning.

Excursion Highlights

The excursion will provide insight into the geological history and outcrops of:

• The Malmesbury Basement (>600Ma)

• Jurassic Enon conglomerates/sediments

• Olivine-melilitite pipe-like intrusives into the Witteberg Group

• An opportunity to stand on the hanging wall of the Worcester fault with views over the Ashton and Robertson Breede River Valley

Other localities and stops of interest will be visited, providing a rich geological journey.

Estimated Costs

• Van Loveren wine tasting and snack meal: R200

• Accommodation (Montagu Caravan Park bungalow, 2 nights): R450 per person per night

• Protea Farm tractor trip, potjiekos lunch and wine tasting: R480

• Registration and Guidebook: R120

Total estimated cost: R1700 per person, plus meals, refreshments, and fuel. Geoexcursion participants will be responsible for booking their own Montagu accommodation.

Highlight Outcrop:

The Goedemoed olivine-melilitite outcrop on the slope of Elandsberg exhibits columnar jointing from the contraction of cooling magma as it crystallised. This unique intrusion, dated at 63.7 ± 1.3 Ma (Duncan et al., 1978), is part of an arc of olivine-melilitite intrusions located at Heidelberg, Robertson, Lambert's Bay, Sutherland, and areas in Bushmanland and Namaqualand. These intrusions are typically found off-craton in mobile belts surrounding the ancient stable Archean Kaapvaal Craton, known for its deeper-seated kimberlites like Kimberley, Finsch, Cullinan, and Venetia diamondiferous kimberlites.

Guided by Geologist Jean Malan, who brings a wealth of knowledge about the area, this excursion promises to be a valuable experience for all participants.

More Information of Interest:

• Protea Farm - Montagu Tractor Trips: proteafarm.co.za/tractortrip/
• Information on Montagu: montagu.org.za/information/cogmanskloof/
• Further Reading on the Cape Fold Belt:
  • CT Min Soc - Cape Fold Belt
  • Stories in Stone: Western Cape Geology