Geologic%20Overview%20of%20the%20Carlin%20Trend%20Gold%20Deposits

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Geologic Overview of theCarlin Trend Gold
Deposits

• Pukyung Nat. University
• Maeng-Eon Park

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Purpose

• To understand sedimentary rockhosted deposits
• ?
• To understand Carlin trend gold deposits
• ?
• Search whether to apply or not Carlin type
  deposits in Korea

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Sedimentary rock-hosted deposits
Distal disseminated deposits
Carlin-type Au deposits
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What is Carlin-type deposit?

• Hosted sedimentary rocks
• Carbonate-replacement gold deposits
• Micron size ? invisible gold
• 70 of U.S. and 10 world (1998) ? 3rd producing
  region in the world
• China, Australia, Spain, Russia,

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Location of Carlin type deposits
Carlin trend
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Geological map, Carlin trend, Nevada
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Stratigraphy

• Robert Mountain Formation
• Popovich Formation
• Rodeo Creek Unit

old
young
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Geological history

• The Antler events
• Compressional tectonism, folding,
• Imbricate thrusting
• The Permian Sonoma events
• Uplift, folding
• The Sevier orogeny
• Folding, thrusting

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Characteristics

• Host rocks
• Fine-grained, laminated dolomatic limestone which
  contain some silt
• Age CambrianTriassic
• Structural setting
• High-angle, normal fault
• ?increased host-rock permeability,
• creating breccias
• overthrust belt

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• Igneous rocks
• Alkaline igneous intrusion
• Granodiorite to granite
• Occurrence of gold
• In Pyrite, arsenian pyrite
• Au is associated with anomalous concentrations of
  As, Sb, Ba,Ti, Hg
• Fluid-inclusion geochemistry
• (Average)
• Depth 500800 bar, 23km
• Low Salinity 17 Nacl equiv.
• Temp. 180245

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Alteration

• Decalcification, Decarbonization
• Argilic alteration
• Silicification

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Metallization

• (During hydrothermal system)
• Pre-ore stage
• Jasperoid replaced carbonate
• Gold ore stage
• Quarz veins and silicified breccias formed
• Post-ore stage
• Calcite vein formed
• Contain barite, orpiment, reagar, stibnite,
  cinnabar

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Schematic model for the development of a
Carlin-type gold deposit
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Exploration guides

• Silty to argillaceous, thinly laminated, marine,
  carbonate rocks or carbonate-bearing
  silicilclastic rocks
• An area that has undergone extensional tectonics
• Concurrent mid-to upper-crustal plutonism
• The occurrence of W, Mo deposits
• Jasperoid
• The characteristic trace-element suite of Au, As,
  Sb, Hg, Tl

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Summary

• Carlin-type deposits formed above active,
  deep-penetrationg extensional faults where
  plutons were emplaced into the middle and upper
  crust in regions of thick marine
  carbonate-siliciclastic sequences by
  overthrusting
• slightly to highly acidic, low-salinity,
  high-CO2, high H2S fluids
• depths of up 3km by high density, CO2 bearing
  fluid inclusion

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• Gold precipitation was related to a mixing
  process, and , for the most part, was not due to
  boing