scholarly journals Helium-ratios of rocks and minerals from the diamond pipes of South Africa

1936 ◽  
Vol 154 (882) ◽  
pp. 385-413 ◽  
Keyword(s):  
South Africa ◽  
Igneous Rocks ◽  
Basal Complex ◽  
Kimberlite Magma

It is well known that the diamond pipes of South Africa are occupied by kimberlite in varying states of brecciation and decomposition, together with inclusions of widely different sizes, shapes, and petrographic types. Indeed, so many of the “phenocrysts” of kimberlite are xenocrysts transported from below that it is difficult to determine the composition of the essential kimberlite magma which was responsible for the perforation of the crust and the formation of the pipes. The larger inclusions— commonly referred to as “nodules”—can be conveniently divided into three groups, according to whether they represent: 1—strata now removed by denudation which were penetrated by the uppermost parts of the pipes; 2—formations now exposed in the walls of the pipes opened up by mining, including granites, gneisses, and amphibolites belonging to the Pre-Cambrian basal complex; and 3—metamorphic and igneous rocks brought up from below.

Lithostratigraphy of the Mesoproterozoic Donkieboud Granodiorite (Komsberg Suite), South Africa and Namibia

2020 ◽  
Vol 123 (3) ◽  
pp. 421-430
Author(s):  
Y. Abrahams ◽  
P.H. Macey
Keyword(s):  
South Africa ◽  
Stress Field ◽  
Mineral Assemblage ◽  
Chemical Weathering ◽  
Significant Contribution ◽  
Border Region ◽  
Igneous Rocks ◽  
Crustal Material ◽  
High Grade ◽  
Regional Stress

Abstract The Donkieboud Granodiorite pluton forms an extensive intrusion across the border region between South Africa and southeast Namibia. The mesocratic grey, weakly to moderately K-feldspar porphyritic biotite ± hornblende ± orthopyroxene granodiorite represents the most extensive member of the late- to post-tectonic Komsberg Suite (~1 125 to 1 105 Ma) which intruded as sheet-like bodies into the older high grade paragneisses and orthogneisses (~1 230 to 1 140 Ma) of the Kakamas Domain of the Mesoproterozoic Namaqua-Natal Province. The Donkieboud Granodiorite comprises three main textural variations namely:a porphyritic to weakly porphyritic, relatively undeformed rock with randomly orientated ovoid and twinned feldspar phenocrysts;a weakly- to well-foliated gneiss with between 3 to 10% feldspar phenocrysts set in a medium-grained matrix anda patchy metamorphic charnockite variety. Large inclusions of the strongly foliated Twakputs (~1 210 Ma) and the Witwater (~1 140 Ma) garnetiferous granite gneisses occur within the Donkieboud Granodiorite and mafic xenoliths are common. The Donkieboud Granodiorite is variably deformed ranging from unfoliated to being gneissic. The foliation developed during its intrusion into an existing but waning regional stress field with the strain increasing towards the contacts with the surrounding country rocks. Subsequent km-scale open folding resulted in the reorientation of the gneissic foliation and locally, intense reworking of the fabrics along the margins of the folds. In places, the Donkieboud unit is crosscut by discrete mylonitic shears with a west to northwest trend. U-Pb zircon dating of the Donkieboud Granodiorite samples yielded concordia ages of between 1 118 and 1 107 Ma. Overall the Donkieboud Granodiorite has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic xenoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant amount of chemical weathering. The εNd values of -1.15 and -0.11 and TDM values of 1 615 and 1 505 Ma are typical of the Komsberg Suite and indicate a significant contribution of older crustal material to the magma of the Donkieboud pluton.

Lithostratigraphy of the Naros Granite (Komsberg Suite), South Africa and Namibia

2021 ◽  
Author(s):  
P.H. Macey ◽  
R.J. Thomas ◽  
H.P. Smith ◽  
D. Frei ◽  
PJ. le Roux
Keyword(s):  
South Africa ◽  
Partial Melting ◽  
Mineral Assemblage ◽  
Chemical Weathering ◽  
Biotite Granite ◽  
Igneous Rocks ◽  
Coarse Grained ◽  
Southern Margin ◽  
A Minor ◽  
Significant Chemical

Abstract The Naros Granite occurs as a large, northwest-trending ovoid batholith roughly 30 km long and 15 km wide straddling the Orange River border between South Africa and Namibia, 25 km northeast of Onseepkans. It consists mainly of a leucocratic to mesocratic grey, coarse-grained equigranular hornblende-biotite granite-granodiorite that is locally mildly feldspar porphyritic. Small, ovoid mafic autoliths are common and characteristic of the Naros Granite. The composition of the unit varies from granite to granodiorite with a minor leucogranitic phase observed along the southern margin of the batholith. Hornblende and biotite are ubiquitous mafic minerals but small amounts of orthopyroxene occur locally. The Naros Granite has yielded tightly-constrained U-Pb zircon ages between 1 114 Ma and 1 101 Ma. The Naros Granite is generally unfoliated to weakly deformed with only localised shearing along contacts with the surrounding country rocks giving rise to orthogneissic fabrics. It has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic autoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant chemical weathering. The Naros Granite is the youngest and most evolved member of the ~1.11 Ga Komsberg Suite, a collection of late- to post-tectonic I-type metaluminous, intermediate to felsic, biotite ± hornblende granitoids and their charnockitic equivalents that have intruded the older pre-tectonic gneisses of the Kakamas Domain of the Namaqua Metamorphic Sector.

Igneous Rocks

2018 ◽  
Author(s):  
Alex Maltman
Keyword(s):  
South Africa ◽  
Melting Point ◽  
Ground Surface ◽  
Igneous Rocks ◽  
The Other ◽  
Magma Chambers ◽  
Molten Material ◽  
The Earth ◽  
Cape Peninsula ◽  
Initial Melting

Igneous rocks were once molten. This is a simple statement, but it’s exactly what sets them apart from the other two great divisions of rocks: sedimentary and metamorphic. So, deriving from the Latin word for fire—ignis, the same word that gives us ignition—igneous rocks are associated with heat. Some are simply solidified lava, but most originated by slowly cooling below the Earth’s surface. Thanks to erosion through time of the overlying material, such rocks are now widespread at the Earth’s surface and consequently underlie many of the world’s vineyard regions, from Washington State to the mountains of Hungary, from Lodi, California, to the Cape Peninsula of South Africa. Although it gets warmer with depth everywhere across the Earth, generally the weight of the overlying rocks makes the pressure too great to allow melting, so as a rule the rocks below our feet are solid. In some places, however, the heat increases so rapidly that temperatures can reach over 600°C at just a few kilometers below the ground surface, a temperature at which some rocks are molten, even under pressure. The initial melting usually takes place in and below the lower part of the Earth’s crust, but the molten rock then rises, typically to reside tens of kilometers or so below the surface, though less under volcanically active areas. Such depths may seem large to us, but seeing as its well over 6000 kilometers to the center of the Earth, geologically they are pretty close to the surface. In other words, the igneous rocks we now see at the surface did not form incredibly deep in the Earth’s interior; they were nowhere near Earth’s core, as some writings claim. We call this underground molten material magma. People seem to like the word. Not only does it appear on wine labels, but it is also the name of a number of wine shops, bistros, and various drinks. It exists in the Earth in magma chambers. It would be simplistic to picture these as some sort of enormous underground caves filled with liquid rock: there may be patches that are wholly liquid, but almost certainly there will be plenty of solid matter, minerals that are below their melting point.

Primary baddeleyite (Zr02) in kimberlite from Benfontein, South Africa

1984 ◽  
Vol 48 (347) ◽  
pp. 257-261 ◽  
Author(s):  
D. E. Scatena-Wachel ◽  
A. P. Jones
Keyword(s):  
South Africa ◽  
Trace Elements ◽  
Electron Microprobe ◽  
Minor Element ◽  
Kimberlite Magma

AbstractBaddeleyite was found during an electron microprobe study of kimberlite from the Benfontein Sills, which are famous for their igneous carbonate and cumulus features. Based on its close textural association with both groundmass and cumulus oxides (spinels, ilmenite, perovskite), the baddeleyite appears to be primary and crystallized directly from the kimberlite magma. The baddeleyite is remarkably pure, with average ZrO2 and HfO2 of 96.4±1.3 and 1.72±0.08 wt. % respectively. Minor element ranges found were: TiO2 0.32–0.80, CaO 0.31–0.80, FeO 0.43–1.31, MgO 0.06–0.24, SiO2 0.04–0.19, Cr2O3 0–0.07, and Al2O3 0–0.10 wt.%. Several additional trace elements were sought (Ce, Cs, Mn, Nb, Nd, Sr, Y, Yb, and U) but were not detected.

scholarly journals Witwatersrand composite paleoplacers

2021 ◽  
Vol 63 (4) ◽  
pp. 8-22
Author(s):  
V. A. Stepanov
Keyword(s):  
South Africa ◽  
Heavy Fraction ◽  
Igneous Rocks ◽  
Ore Formation ◽  
Gold Particles ◽  
Useful Components ◽  
Gold Silver ◽  
The World ◽  
Factual Data ◽  
Alluvial Formation

Background. The Witwatersrand gold province located in South Africa is the richest in the world. The Witwatersrand deposits are composite, where osmirids and diamonds are mined along with gold, silver and uranium. The genesis of the Witwatersrand deposits is controversial. Most local geologists support the hypothesis of the presence of paleoplacer deposits with subsequent metamorphic transformation of ore-bearing conglomerates. In addition, there are aeolian, hydrothermal-sedimentary, hydrothermal-sedimentary-metamorphic and magmatic models of ore formation.Aim. To establish the genesis of the Witwatersrand deposits.Materials and methods. Analysis of published literature and factual data.Results. Osmirids and diamonds are mined along with gold, silver and uranium from the composite Witwatersrand deposits. Such a set of useful components is not known in any of the deposits of magmatic or hydrothermal genesis. Considering the confinement of useful components to conglomerates, the detrital nature of most of the gold grains and the presence of various accompanying minerals in the heavy fraction, characteristic of igneous rocks of felsic, basic and ultrabasic composition, the hypothesis of the primary alluvial nature of the deposits of the Witwatersrand province looks the most reasonable.Conclusions. The factual material indicates an alluvial origin of the Witwatersrand deposits with subsequent metamorphic transformation of ore-bearing reefs. The primary alluvial formation of ore-bearing conglomerates is indicated by the confinement of gold and uranium to channel facies with a tendency to accumulate in the basal horizons of the reefs, the presence of rounded gold particles bearing the traces of transportation in alluvial flows, as well as a set of minerals in the heavy fraction of concentrate, characteristic of placers.

Time and Latitude in South Africa

1972 ◽  
Vol 1 ◽  
pp. 27-38
Author(s):  
J. Hers
Keyword(s):  
South Africa ◽  
Cape Town ◽  
Astronomical Observations ◽  
Royal Observatory ◽  
The Republic ◽  
Astronomical Determination ◽  
Limited Accuracy ◽  
Better Than

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.

Combining Professional Interests and Travel: People to People Citizen Ambassador Program

2011 ◽  
Vol 1 (2) ◽  
pp. 47-54
Author(s):  
Alex Johnson ◽  
Amanda Hitchins
Keyword(s):  
South Africa ◽  
Health Education ◽  
Communication Disorders ◽  
Social Conditions ◽  
Speech Language Pathologists ◽  
Exchange Program

Abstract This article summarizes a series of trips sponsored by People to People, a professional exchange program. The trips described in this report were led by the first author of this article and include trips to South Africa, Russia, Vietnam and Cambodia, and Israel. Each of these trips included delegations of 25 to 50 speech-language pathologists and audiologists who participated in professional visits to learn of the health, education, and social conditions in each country. Additionally, opportunities to meet with communication disorders professionals, students, and persons with speech, language, or hearing disabilities were included. People to People, partnered with the American Speech-Language-Hearing Association (ASHA), provides a meaningful and interesting way to learn and travel with colleagues.

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