Please note: Bring a bottle of water for the experiment. About 1 litre will do.
Jock’s Route: Pettigrew’s Magnesite EarthCache
This geocache is of significant historical interest. It is one of many way-markers along the route traveled by Sir Percy FitzPatrick and his faithful dog, Jock. 'Jock of the Bushveld' is a book written by Percy FitzPatrick, a transport rider, about his adventures with Jock, a Staffordshire Bull Terrier. It takes place in the Lowveld during the time of the gold rush in the 1880's and is well worthwhile reading. Pettigrew road was mentioned a few times in the book.
The History:
After the discovery of the Kaapsche Hoop and Barberton gold fields in 1882, and the subsequent establishment of Barberton town in 1884, the need for a shorter route between these areas and Delegoa Bay was felt. The existing Nellmapius road over Burger’s Hal and Pretoriuskop was just too far. The demand for transport increased and one of the first to use the new route between the Lebombo mountains and Barberton, was Robert (Bob) Pettigrew.
He was originally from Rutherglen, Scotland, and came out to this country on the boat 'Earl of Southes' arriving in Durban on 8 October 1868. In 1870 he moved to the McCorkendale Settlement, near Lake Chrissie, where he became a farmer and businessman. When gold was discovered in the De Kaap valley in 1884 he moved to the Lowveld.
Pettigrew improved the road from the Lebombo mountains via Malelane, Kaapmuiden, Low's Creek and Noordkaap to Barberton, which became known as Pettigrew's road.
Pettigrew's Nek lies on the tarred R38 about 5 km South of Kaapmuiden in the Mpumalanga Province of South Africa. Almost a century later, road signs were erected and Pettigrew's Nek was officially named in 1987. It is not much of a 'Mountain Pass' but as the name implies, simply traverses a rather innocuous neck.
This piece of the road was especially difficult as it lies in a tsetse fly “belt” and when it rains, the exposed magnesite deposits becomes very slippery, almost like soap, which resulted in the transport riders always had to spend more time crossing the ridge.
White veins of magnesite in altered olivine-rich dunite of the Budd layered utramafic complex. The magnesite is exposed in a road cutting through Pettigrew’s Nek, about 3 km south of Kaapmuiden.
The Geology:
Important deposits of magnesite were first recorded in the north eastern sector of the Barberton Greenstone Belt in the Kaapmuiden-Hectorspruit magnesite field where the first mining took place in 1906 (Hall, 1907; 1918; Strydom, 1998). Initially the magnesite was required for the manufacture of cement, but subsequently it was used for refractory products, especially bricks in the steel industry, as well as a range of other products, including additives in fertilizer and animal feeds, and as magnesium sulphate (MgSO4) in paper production and MgO in the chemical industry. Geologically the magnesite occurrences, like those of the chrysotile asbestos deposits, are all located in rocks associated with layered ultramafic complexes. A number of deposits, (including Strathmore, Bald Hill, and Budd) are located in what was termed „ore zone‟ serpentinite (Viljoen and Viljoen, 1970). The ore zone serpentinites are the result of alteration of dunites and provide the primary source of magnesium and a suitable environment for the development of stockwork fractures wherein the magnesite occurs as veins. The age of the magnesite formation has been determined as being 2 990 Ma (Toulkeridis et al., 1993) suggesting that the magnesite post-dated the structural and metamorphic events that affected rocks in this sector of the Barberton Greenstone Belt between 3 230-3 107 Ma. The only other magnesite deposit to have been mined occurs in the Sugden Ultramafic Complex also on the northern flank of the Barberton Greenstone Belt (Anhaeusser,1963). The deposit, also known as the Bomvu Ridge Mine, produced high-grade supergene-enriched haematite ore. 22 occurrence of all the magnesite deposits in the northern and north eastern parts of the Greenstone Belt has led to the suggestion that climatic influences may have played a role in their development. The deposits are generally near-surface occurrences. White veins of magnesite in altered olivine-rich dunite of the Budd layered utramafic complex. The magnesite is exposed in a road cutting through Pettigrew’s Nek, about 3 km south of Kaapmuiden. about 30 m and as a consequence of the hot and humid climatic conditions in this part of the belt the magnesium-rich olivine of the dunites was altered in the zone of weathering by meteoric waters containing CO2 (Viljoen and Viljoen, 1969)
Sources:
The History of Mining in the Barberton Greenstone Belt.
http://www.dewilde.co.za/Barberton/GoldenQuarry/THE%20HISTORY%20OF%20MINING%20%20BARBERTON%20-%20Carl%20Anhaesseur.pdf
Creation of Barberton.
https://www.umjindi.co.za/history/creation-of-barberton.html
Pioneers of the Lowveld - Gerrit Haarhoff
To log this EarthCache you have to sent me the answers to the following questions:
1. At the co-ordinates you will see a white vertical exposure of magnesite. How does this surface and particulars feels when it is dry?
2. Pour some water on the exposure. Describe how the surface has changed and how it feels now.
3. On the result of the experiments above, describe in your own words the difficulty of crossing this ridge with a transport wagon in pouring rain.
4. What is the height of the road cutting at its highest point?
Note:
Uploading photos to the cache page and awarding the EC with a Favourite Point, are the best ways to say thank you to the cache developer and to encourage others to visit the location but is only optional.
You can sent me your answers in either Afrikaans or English.
