Geology of the Witwatersrand Supergroup
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Geology of the Witwatersrand Supergroup

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Questions and Answers

What type of environment did the West Rand Group develop in?

  • Glacial ice sheet
  • Continental river system
  • Volcanic island arc
  • Shallow marine shelf (correct)

    • Which geological feature primarily consists of shales, quartzites, and minor conglomerates?

  • West Rand Group (correct)
  • Witwatersrand Supergroup
  • Dominion Group
  • Central Rand Group

    • What geological process fragmented the basement into discrete blocks leading to sub-basins?

  • Sedimentation
  • Volcanic activity
  • Erosion
  • Compressional tectonics (correct)

    • Which formation is essential for mineralization in the Witwatersrand Supergroup?

    <p>Central Rand Group</p> Signup and view all the answers

    How were the gold-bearing conglomerate reefs in the Central Rand Group characterized?

    <p>They can be correlated in the seven major goldfields.</p> Signup and view all the answers

    What type of sedimentation occurred during the formation of the Witwatersrand Supergroup?

    <p>Foreland basin sedimentation</p> Signup and view all the answers

    Which group within the Witwatersrand Supergroup contained predominantly arenaceous rocks?

    <p>Central Rand Group</p> Signup and view all the answers

    What timeframe did the sedimentation of the Witwatersrand Supergroup occur?

    <p>3.0 Ga to 2.7 Ga</p> Signup and view all the answers

    What type of mineralization is characterized by visible gold in quartz veining within highly fractured and brecciated black chert?

    <p>Zwartkoppie section type</p> Signup and view all the answers

    Which formation is associated with the tight anticlines observed in the geological section through the Sheba mine?

    <p>Zwartkoppie Formation</p> Signup and view all the answers

    What is suggested by the lack of evidence for ore types merging with depth or along strike at the Sheba-Fairview Complex?

    <p>The hydrothermal mineralizing system is compositionally uniform.</p> Signup and view all the answers

    Which of the following is NOT one of the five styles of mineralization identified in the Sheba-Fairview Complex?

    <p>Fractures in limestone</p> Signup and view all the answers

    Which type of ore deposits commonly occurs in shoreline and fluvial environments?

    <p>Heavy minerals like gold and diamonds</p> Signup and view all the answers

    What primary characteristic distinguishes sedimentary ore-forming processes that are syngenetic?

    <p>Ores are part of the sedimentary sequence.</p> Signup and view all the answers

    The presence of which mineral indicates arsenopyrite-rich layers at the contact of the hornfelsic Fig Tree Group?

    <p>Chert</p> Signup and view all the answers

    Which group mainly comprises the argillaceous rocks located to the south of the Sheba Fault?

    <p>Fig Tree Group</p> Signup and view all the answers

    Which of the following statements accurately describes orogenic gold deposits?

    <p>They are commonly located within Archean terranes on cratons.</p> Signup and view all the answers

    What is a characteristic feature of gold deposition at the camp scale?

    <p>Spatial relation to large-scale bends and faults.</p> Signup and view all the answers

    Which of the following greenstone belts is recognized as one of the oldest and best-preserved mineralized greenstone belts?

    <p>Barberton Greenstone Belt.</p> Signup and view all the answers

    Which structural feature is important for the formation of orogenic gold deposits?

    <p>First-order transcrustal fault zones.</p> Signup and view all the answers

    What type of geological feature do major gold deposits in the Kaapvaal Craton commonly associate with?

    <p>Clusters of mines along main faults and shear zones.</p> Signup and view all the answers

    In which regions can orogenic gold deposits be found?

    <p>In various cratons, including West African and Kaapvaal Cratons.</p> Signup and view all the answers

    What role do anticlines and synclines play in the context of gold deposits?

    <p>They create favorable conditions for gold deposition.</p> Signup and view all the answers

    How do major faults influence the occurrence of gold deposits?

    <p>They create pathways for gold-bearing fluids.</p> Signup and view all the answers

    What type of fluid flow is driven by rock compaction in a fold and thrust belt?

    <p>Orogeny-driven fluid flow</p> Signup and view all the answers

    Which type of fluid flow occurs in the ocean crust due to high heat flow at mid-ocean ridges?

    <p>Thermally driven fluid flow</p> Signup and view all the answers

    What is a primary driver of hydrothermal fluids responsible for creating hydrothermal ore deposits?

    <p>Thermal gradients</p> Signup and view all the answers

    In what geological setting does thermally driven fluid flow occur within a permeable unit?

    <p>Within a rift system</p> Signup and view all the answers

    What presence indicates a typical appearance of H2O-CO2 bearing fluid inclusions in rock?

    <p>Phase separation</p> Signup and view all the answers

    Which fluid flow mechanism is likely to enhance ore deposits due to thermal activity?

    <p>Temperature-induced movement</p> Signup and view all the answers

    What drives the movement of fluids in response to rock stress during orogeny?

    <p>Rock compaction</p> Signup and view all the answers

    What characteristic is typical of the Main Reef conglomerate?

    <p>It has relatively large pebbles, often up to 5 cm in diameter.</p> Signup and view all the answers

    What is the average gold grade present in the Main Reef on the Central Rand?

    <p>Less than 4 g/t using a 3 g/t cut-off.</p> Signup and view all the answers

    Which mineral is commonly found enriched in gold within the Witwatersrand gold-bearing conglomerates?

    <p>Pyrite.</p> Signup and view all the answers

    What defines the relationship between the Main Reef and the Main Reef Leader?

    <p>The Main Reef and Main Reef Leader were the first to be mined.</p> Signup and view all the answers

    What is the primary difference between the Carbon Leader Reef and the Main Reef?

    <p>The Carbon Leader Reef has visible gold and high gold grades.</p> Signup and view all the answers

    What role do evaporites play in mineral deposit formation?

    <p>They serve as sealing layers.</p> Signup and view all the answers

    What is the relationship between red beds and copper sources?

    <p>Red beds leach copper from the basement.</p> Signup and view all the answers

    Which component is crucial for the formation of ore deposits according to the model proposed?

    <p>Redox reactions</p> Signup and view all the answers

    Which condition is more favorable for hosting larger mineral deposits?

    <p>Closed systems</p> Signup and view all the answers

    What is the significance of sulfur in the context of evaporites and ore deposits?

    <p>Sulfur from evaporites supports mineral leaching.</p> Signup and view all the answers

    What main factor influences fluid circulation in the basin according to the content?

    <p>Evaporite presence</p> Signup and view all the answers

    What does lack of evaporites mean for ore deposits?

    <p>It reduces the chances of attaining ore deposits.</p> Signup and view all the answers

    How do reducing strata contribute to mineral deposit formation?

    <p>They serve as a seal to trap liquids.</p> Signup and view all the answers

    In the context of the Central African Copperbelt, what does the term 'closed system' imply?

    <p>It is isolated and contains a stable environment.</p> Signup and view all the answers

    What characterizes alluvial diamond deposits along the Orange River?

    <p>Diamonds are trapped in gravel terraces from sediment abandoned by the river.</p> Signup and view all the answers

    Which factor primarily controls sediment sorting in beach environments?

    <p>Wave dynamics and tidal fluctuations.</p> Signup and view all the answers

    What is the primary source for alluvial diamond deposits?

    <p>Kimberlite formations.</p> Signup and view all the answers

    What defines placer deposits associated with heavy minerals?

    <p>Source fertility influences mineral concentration.</p> Signup and view all the answers

    Which environment is likely to contain heavy mineral sand deposits?

    <p>Shoreline and eolian environments.</p> Signup and view all the answers

    In what type of geological setting are beach-related black sand deposits found?

    <p>Coastal environments influenced by wave action.</p> Signup and view all the answers

    Which of these minerals often forms in significant concentrations in placer deposits?

    <p>Ilmenite–zircon.</p> Signup and view all the answers

    What happens to diamonds over time as river systems evolve?

    <p>They become trapped in stable sediment formations.</p> Signup and view all the answers

    What is the relationship between diamond deposits and kimberlite?

    <p>Diamond deposits are derived from kimberlite through weathering and transport.</p> Signup and view all the answers

    Which of the following describes the term 'placer processes'?

    <p>Methods by which sedimentary minerals are concentrated in the environment.</p> Signup and view all the answers

    What determines the movement of grains in the bed load?

    <p>Entrainment</p> Signup and view all the answers

    Where are heavy mineral concentrations likely to be found along a dune?

    <p>In the trough or scour ahead of the dune</p> Signup and view all the answers

    How do rounded gold grains on small-scale cross bed foresets form?

    <p>As a result of settling sorting</p> Signup and view all the answers

    What is a distinguishing factor of deposition at an aggrading point bar along a meander channel?

    <p>Concentration of dense, heavier minerals</p> Signup and view all the answers

    In the context of placer deposits, what role do scours along the bottom of a channel play?

    <p>Aid in the concentration of heavy minerals</p> Signup and view all the answers

    How does the shear velocity at the dune crest affect grain sorting?

    <p>Encourages entrainment of larger, lighter grains</p> Signup and view all the answers

    What characterizes the microenvironment in the trough forming ahead of the dune?

    <p>Locally turbulent</p> Signup and view all the answers

    What mineral is commonly mentioned in relation to heavy mineral concentrations in meandering river channels?

    <p>Cassiterite</p> Signup and view all the answers

    In what geological feature is the concentration of heavy minerals typically observed as the river channel meanders?

    <p>Convex banks</p> Signup and view all the answers

    What effect does non-turbulent flow at the dune crest have on grain sorting?

    <p>Facilitates the transportation of heavy minerals</p> Signup and view all the answers

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    Description

    This quiz explores the geological features and processes of the Witwatersrand Supergroup, including the West Rand Group and Central Rand Group. Test your knowledge on sedimentation types, mineralization formations, and the characteristics of various geological formations within this significant region.

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