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Pukyung Nat. University Maeng-Eon Park. Geologic Overview of the Carlin Trend Gold Deposits. Purpose. To understand sedimentary rock–hosted deposits  To understand Carlin trend gold deposits  Search whether to apply or not Carlin type deposits in Korea.

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Presentation Transcript
purpose
Purpose
  • To understand sedimentary rock–hosted deposits

  • To understand Carlin trend gold deposits

  • Search whether to apply or not Carlin type deposits in Korea
sedimentary rock hosted deposits
Sedimentary rock-hosted deposits

Distal disseminated deposits

Carlin-type Au deposits

what is carlin type deposit
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,…
stratigraphy
Stratigraphy
  • Robert Mountain Formation
  • Popovich Formation
  • Rodeo Creek Unit

old

young

geological history
Geological history
  • The Antler events
    • Compressional tectonism, folding,
    • Imbricate thrusting
  • The Permian Sonoma events
    • Uplift, folding
  • The Sevier orogeny
    • Folding, thrusting
characteristics
Characteristics
  • Host rocks
    • Fine-grained, laminated dolomatic limestone which contain some silt
    • Age : Cambrian~Triassic
  • Structural setting
    • High-angle, normal fault

increased host-rock permeability,

creating breccias

    • overthrust belt
slide10

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 : 500~800 bar, 2~3km
    • Low Salinity : 1~7% Nacl equiv.
    • Temp. : 180~245°
alteration
Alteration
  • Decalcification, Decarbonization
  • Argilic alteration
  • Silicification
metallization
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
exploration guides
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
summary
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
slide16

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