Origin of Gold in South Africa

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Origin of Gold in South Africa

• By Roberta Peryea
• GEL 305

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Gold Prospecting

• 1850s
• Two Georges
• Johannesburg

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Witwatersrand basin

• West Virginia
• Gold Concentration

This place is a literal gold mine!!
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Witwatersrand basin
Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
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Formation of Basin

• River erosion
• Deposition
• Sea level fluctuation
• Basaltic lava
• Sedimentation

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Origin of Gold
PLACER THEORY

• How it works
• Gold transport
• High density
• sedimentation

HYDROTHERMAL THEORY

• How it works
• Fluid infiltration
• precipitation

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Origin Continued

• Placer Evidence
• Loss of fluid energy
• Rounded pyrite

• Hydrothermal Evidence
• Easily fractured
• Sulfur reaction

Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
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PLACER THEORY
Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
9
HYDROTHERMAL THEORY
Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
10
Which wins?

• 1. Need a smoking gun
• Date gold
• Problem with gold
• One lonely isotope
• 187Rhenium ? 187 Osmium

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New Technology
Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
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Results

• Gold from Vaal Reef
• Gold vs. Host Conglomerate

3.01 bya
2.76-2.89 bya
PLACER WINS
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Searching for El Dorado

• Where did gold flow from?
• Rhenium-Osmium isotopes
• Mantle or crust?

• Komatiites

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Komatiites

• Composition
• Formation Era
• Mantle characteristics
• Granite-greenstone belts
• Favored source

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Komatiite Sources

• Two belts
• Location
• Connections
• New tests
• New gold rush in Africa!?

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Belt Pictures
Kirk et. al., 2003. The Origin of Gold in South
Africa. American Scientist. Vol. 91 pp. 534-41
17
Lets Wrap It Up

• Tectonic Activity
• Formation of Belts
• Formation of Basin
• Flood Basalts ? Sedimentation

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ALMOST DONE!

• Two more events
• Large magma plumes
• Meteor Impact