Thursday 5 April 2018

Gold Bearing Witwatersrand Conglomerate from the Robinson Deep, Johannesburg

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The above specimen of Witwatersrand reef gold ore was mined in the Robinson Deep gold mine, operational between 1898 and 1966.

This specimen is part of my gold collection, see here

The Robinson Deep was indeed deep, reaching 8,380 ft. below the surface. The specimen is typical of Witwatersrand conglomerate, having quartz pebbles which are bound in a gold bearing matrix. The gold is very finely disseminated within the matrix, associated with pyrite. Under the microscope, very small specks of auriferous pyrite can be seen.

The Robinson Deep is located at  Johannesburg, Johannesburg District (Central Rand), Witwatersrand field, Gauteng Province, South Africa. This 1903 map shows the Witwatersrand gold field's location -


I was given the specimen in 1967 by a nice old lady, Mrs. Ford. She was my sister Janet's piano teacher in the 1960s. Mr. & Mrs. Ford went on a "Grand Tour" after they were married in the early 1950s (they were posh), and visited Johannesburg, between other "exotic" locations. They went to the Robinson Deep gold mine and were given a sample of "reef" during the mine-tour.

The specimen is 6 x 4.5 x 3.5 cm and weighs 94 grams. Here's a 27 second video -




Similar specimens of Witwatersrand conglomerate can be seen on-line at Mindat , at USGS and here.

Interesting references on the geology of the Witwatersrand gold field -

  • Kirk et al. in American Scientist “The Origin of Gold in South Africa” Nov 2003 (PDF)
  • Laurence J. Robb and F. Michael Meyer “The Witwatersrand Basin, South Africa: Geological framework and mineralization processes” from Ore Geology Reviews June 1995 (PDF)
  • P.R.Janisch "Gold in South Africa" J. S. Afr. Inst. Min. Metaff., vol. 86, no. 8 Aug. 1986. pp. 273-316 (PDF

Here's some history of the Robinson Deep gold mine -


Two Ndau migrant labourers (named No.1139 & No.5122) from southern Mozambique endure 95 degree heat and 100% humidity, more than a mile underground down the Robinson Deep gold mine. This classic photo by Margaret Bourke-White was used in LIFE magazine 18 Sep 1950.

Here's a couple of short films about winning gold from the reef. They're cringe-worthy in their absence of mention of Apartheid, and that the actual source of the immense wealth was the labour of the true owners of the land.....




Above, the headgear at Robinson Deep Gold Mine, Johannesburg 1905. Below, a stereo photo of gold bullion produced by the mine in 1910. Use crossed-eyes to see the 3D image of 5012 ounces of gold, worth today £4.87 million.







from - Transactions of the Manchester Geological Society, Volume 28, June 1903

For those with an appetite for conglomerate, here's a closer look at the specimen. Video 18 seconds -


This specimen is part of my gold collection, see here


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