Heart of Gold EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This Earthcache is located in the car park close to the entrance of the Gold Reef City theme park. It is safe to do, but on weekends, school holidays and public holidays, you may find yourself in the middle of a throng of muggles waiting to enter the park
This information has been gleaned from the voluminous data available from the Annual Financial Reports of Crown Mines Ltd and smaller mining companies absorbed into it.
It was the largest gold mine in the Witwatersrand Basin for almost 60 years. On 1 July 1909 seven mining properties were amalgamated to form Crown Mines Ltd, which covered an area some 8.2 km east-west by 5.1 km north-south. The mine was served by 57 shafts (surface, subsuface, inclined, vertical. There was over 1600 km of drives, raises and cross cuts excavated (all in the early part of the 20th Century! A recor monthly production of 420 000 tons of ore was excavated in August 1938 with a record annual production of 4.28 million tons in 1938. At it's peak 27811 people were employed. Operations were ceased in March 1977. During operation, 162 905 millions tons of ore was milled and 1 412 171.7 kg of gold (i.e. 45 402 590 oz) delivered at a rate of 8.67 gm/ton. Crown Mines have been considered a leading gold producer of all time.
Although gold is prevalent in the geological strata (banket and conglomerate layers) in this region, probably more so than almost anywhere else in the world. No one in 100% certain as to exactly why it was deposited here in such concentrations, and not elsewhere.
This marks the location of the vertical shaft (Shaft No.14) was sunk by Crown Mines Limited many years after their amalgamation, on 1 July 1909, on the outcrop and upper deep level mines. It is situated 2.79 km south of the outcrop (the Main Reef outcrop that is) and attained a vertical depth of almost one kilometre (980 metres) below the surface. It was supplemented later by No. 14A sub-vertical shaft which was 560 metres deep, between 19 level and 29 level and by shaft No. 14B sub vertical shaft, 860 metres deep, between 29 level and 47 level and by R2 sub incline shaft which is 1320 metres long and runs down the incline of the Main Reef between 47 level and 62 level. The bottom of the R2 sub incline shaft is at a distance down the reef of 5.49 kilometres from the surface outcrop of the Main Reef (see George Harrison Park Earthcache), and at a vertical depth of 2 875 metres below the surface (well below sea level!). An intricate system of pulleys and winches had to bring ore to the surface, and miners did not descend in a single hoist.
(Acknowledgments: guidebook to Sites of Geological & Mining Interest on the Central Witwatersrand.; Geological Society of South Africa; 1986).
This shaft (#14) was separated from the nearby #5 shaft (located at Crown Station) by the South Rand Dyke – an igneous intrusion of dolomitic nature. The lower levels of the R2 sub inclined shaft reach all the way to the Vierfontein Dyke system, with mining actually occurring below the dyke where the Main Reef Leader continued.
Evidence of the rich mining history can be seen in the area around here with the large number of mine dumps evident. There were many more mine dumps around Joburg, but with the high cost of deep mining, the improvements in reclamation of gold from ore and economics of gold mining, it has become economically viable to “mine” the mine dumps for gold and many mine dumps have been remined and “re-deposited south of Joburg towards Ergo generally between Heidelburg and Nigel.
The theme park does cost to enter, but there is, apart from traditional thrill rides (many with a mining theme), the opportunity to explore the heritage of the Joburg mining history; see a gold pour (i.e. a gold bar being poured from the molten state); go underground down the #14 shaft (please include photos in your log if you do this) and see the mint. In actual fact, the EragonSaphira geocoin (South Africa’s first wholly produced geocoin) bears the Gold Reef City mint logo on the reverse as it was produced through them. There is also an interesting gemstone store inside the complex with many interesting examples of geological interest. A great view of Joburg, the mine dumps, surrounding shafts and general orientation, can be obtained from the top of the large Ferris wheel too.
Parking and entrance to the cache is free – and parking is also secure – the nearby Apartheid Museum (also at an entrance fee) is another worthwhile addition to any tourist (or local visitors) itinerary.
In order to qualify to log this cache, you need to answer the following questions and email the cache owner. Any logs not accompanied by an email will be deleted. Also note that we are not looking for a geological thesis – just your own investigation and learning based on your knowledge and observation. And we trust that you enjoy and learned something.
1) Take a photo of you and your GPSr at the park with some point that interested you visible. See a sample photo of the “miner” as an idea. Photos inside the park are also acceptable (especially the Mint or shaft or gold pour area) if you decide to go inside. [Optional]
2) Look at the nearby mine dumps – what colour are they – try and explain the colouration and shape (why are the tops flat and not pointed). Explain what material would be extracted from the rock mined and "left" in the mine dump, and what would have been taken away and "used".
3) Gold here is found in situ (i.e. still where it was originally formed after geological activity millions oif years ago) in the rock and needs to be mined out. In many other areas alluvial gold was found and panned out of rivers (e.g. in Pilgrim's Rest and Barberton areas - also the 1849 Californian gold rush). Why do you think that that gold got into the rivers, but was not present in rivers here in the Witwatersrand?
4) Look at the mine head gear – bonus for anyone who knows the name of the “wheels” at the top of the headgear (just for interest – and to impress the cache owner ;)).
5) Explain the evidence of Joburg’s gold mining beginnings from observation’s that you have made on your trip to and from this cache site (or visit to the city). Examples you can look for are (but not limited to) – street names; evidence of mines; geological observations; suburb names; business names; slogans etc. This is what is known as human (or social) geography and makes use of geographical evidence to give an indication of activities or history of an area. An example is that a name like Olifantsfontein (Elephant “Spring”) indicates the likelihood that Elephants were found there when spring was first discovered or settled. We are not expecting too much here – but give what you felt relevant.
There are a number of other Earthcaches in this area that really explain a lot of the associated geology in more detail (e.g. Contorted Beds in Braamfontein GC1BTDQ and The Original Golden Beatle? GC1D9HC) that are really worthwhile following up on (or at least reading the descriptions) if you would like a more detailed insight into the geology of the area.
Additional Hints
(Decrypt)
Erzrzore gb fraq lbhe rznvy!