The Bakerville Diamond Digggings are located about 20km north of Lichtenburg, North West, in South Africa. The deposit lies within the Lichtenburg Diamond Fields, about 250km west of Johannesburg.
Your tasks – the C.S.I. work!
At GZ you will a encounter huge pothole - the object of this EarthCache. PLEASE BEWARE THAT THERE ARE NO BARRIERS AND THE POTHOLE IS VERY DEEP. KEEP CHILDREN AND PETS CLOSE BY AND IN CHECK!!
An added bonus here are 2 traditional caches in the immediate vicinity – 1 less than 50m away!
In order to substantiate your visit and be able to claim this EarthCache a number of questions need to be answered and submitted to the cache developer, via e-mail, to “cincolcc [at] gmail.com”
1 – In your own words explain what the sides of the pothole look like.
2 – Look at the colour and striations that you see and comment on the colour and the spacing of the striations.
3 – What do you think the striation bands are?
4 – Describe any other interesting things you saw or experiences you had on your journey to the site from the main road – especially the old buildings and people you may have met and spoken with - (you can add these to your log for others to enjoy too). Photos are always welcomed in the logs but please don’t post photos of the dunes themselves.
5 – Estimate the dimensions of the pothole – length x breadth x depth. BE CAREFUL when approaching the edge.
6 – OPTIONAL – post a photo of your team at the potholes.
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.
=======================================================================================================
General Geology
The Bakerville diamond deposit occurs on Transvaal Dolomite, an irregular dolomite bedrock with chert and dolomite. The gravel runs and patches on the alluvial deposit have potholes and large sinkholes of about 70m in depth.
The individual gravel runs are identifiable to several kilometres and are about 140m-wide. The diamondiferous gravel runs are about 3m thick.
The average thickness varies from 1m to 1.5m and is covered by lush vegetation, which prevents erosion.
TRANSVAAL DOLOMITE
The Geology of Dolomite
Ancient carbonate rocks are predominantly composed of two minerals; calcite or dolomite. When a carbonate rock is dominated by calcite (more than 95% with less than 5% dolomite), it is called limestone, when it is dominated by dolomite (the mineral) it is called dolomite (the rock). Limestone is a chemical or biochemical sediment consisting essentially of calcium carbonate primarily in the form of calcite, and minor constituents such as silica, feldspar, pyrite and siderite. Dolomite, as a rock, contains more than 90% dolomite and less than 10% calcite as well as detrital minerals and secondary silica (chert). Very few, if any, sedimentary dolomites are truly stoichiometric, encompassing the spectrum from calcium to magnesian dolomites. Researchers seem to agree that the carbonate rocks in the Malmani Subgroup are essentially dolomitic limestones (a limestone that has been incompletely dolomitized) with few limestone bands, whereas the Campbell Rand Subgroup consists of dolomite and limestone.
The onset of limestone deposition has been estimated at 2 550 Ma. The limestone precipitated in favourable environmental conditions by algal photosynthesis and inorganic precipitation. The precursor mineral to dolomite was aragonite. The limestone then underwent dolomitization in an environment where meteoric and marine water mixed and the saline brine became supersaturated with respect to magnesium and silica and undersaturated with respect to calcite thereby increasing the potential for dolomitization and chertification. Sufficient evidence exists to indicate that dolomite is syndepositional, the minerals forming contemporaneously with sedimentation.
Dolomite and limestone, with little or no impurities, are valuable industrial commodities and are used in the making of a wide range of products such as cement and glass. There are a number of large cement producing factories that can be seen from miles around when approaching Lichtenburg from any direction.
How Diamonds are Formed
Geologists believe that the diamonds in all of Earth's commercial diamond deposits were formed in the mantle and delivered to the surface by deep-source volcanic eruptions. These eruptions produce the kimberlite and lamproite pipes that are sought after by diamond prospectors. Diamonds weathered and eroded from these eruptive deposits are now contained in the sedimentary (placer) deposits of streams and coastlines.
The formation of natural diamonds requires very high temperatures and pressures. These conditions occur in limited zones of Earth's Mantle about 90 miles (150 kilometers) below the surface where temperatures are at least 2000 degrees Fahrenheit (1050 degrees Celsius). This critical temperature-pressure environment for diamond formation and stability is not present globally. Instead it is thought to be present primarily in the mantle beneath the stable interiors of continental plates.
Diamonds formed and stored in these "diamond stability zones" are delivered to Earth's surface during deep-source volcanic eruptions. These eruptions tear out pieces of the mantle and carry them rapidly to the surface, This type of volcanic eruption is extremely rare and has not occurred since scientists have been able to recognize them.
Is coal involved? Coal is a sedimentary rock, formed from plant debris deposited at Earth's surface. It is rarely buried to depths greater than two miles (3.2 kilometers). It is very unlikely that coal has been moved from the crust down to a depth well below the base of a continental plate. The carbon source for these mantle diamonds is most likely carbon trapped in Earth's interior at the time of the planet's formation.
Exploration
In the 1920s, the declared diamond production at Bakerville area was about 7.5 million ct. In the 1980s government surveys indicated the potential occurrence of diamondiferous gravels, which renewed the mining interests in the area.
Prospective properties of the historical area, however, were inaccessible to new exploration entrants until 2004, because of previous South African mineral legislation. During 2008, the Patsema area was largely explored with prime focus on the Bakerville project as the area had potential gravel runs and historical potholes. Bulk sampling was also conducted at the Zamenkomst farm during the same year. The exploration included the digging of 2,380 hand pits for assessing gravel volume; 20km of trenches for taking 264 bulk samples of about 350m³ to 500 m³; 19, 2.5m Bauer boreholes; and 571 reverse circulation (RC) drill holes.
BACKGROUND TO THE BAKERVILLE DIAMOND FIELDS
In the early twentieth century, diamonds were found in various places in the Lichtenburg district of the former Transvaal Province. However, it was only during the early 1920's that large quantities of diamonds were found, resulting in the proclamation of the Bakerville (more correctly: the Lichtenburg-diamond field) in 1926. Thousands of miners swarmed to the area in search of wealth. At the height of activity, in 1927, an estimated 90 000 people were involved at the diamond fields. Bakerville was the most important of a number of settlements where the miners congregated. It was laid out in 1927 and is named after A W Baker, the then owner of the farm Uitgevonden 355JP. As early as 1928, activities started to decline - and continued to decline. Currently only a few people are involved in diamond mining in this area.
It all started a few years earlier, in 1924, when postmaster's son Koosie Voorendyk and a couple of locals were digging a cattle dip. Suddenly a worker's eye caught a glitter in the gravel. Koosie, in great excitement picked up the stone and took it to the local science teacher, a Mr Bosnian, to put the stone through an acid test. It was a beautiful stone of three carats.
It was the richest public diggings ever mined - it was the Lichtenburg Diamond Rush of February 1926 and a population of 150 000 souls appeared as if by magic. Bakerville, or "Bakers" as it was known it the time, it is only one of several "Diggers Towns", developed in Wild West style. Bakerville was the biggest and most famous of the towns - bigger than Cape Town at the time. The diamond rush in the Lichtenburg district made many men rich but also broke thousands of hearts.
By 1928 the rush was over. Today a smattering of "bitter-einders" remain, optimists all, still digging through tonnes of gravel heaps in the never-ending search for the 'Big One'. In a second rush in 1945, production on the diggings was on the same scale as in 1925; one-hundred-and-four diggings on one farm were proclaimed.
