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Geologic Overview of the Carlin Trend Gold Deposits

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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Geologic Overview of the Carlin Trend Gold Deposits

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  1. Pukyung Nat. University Maeng-Eon Park Geologic Overview of theCarlin Trend Gold Deposits

  2. Purpose • To understand sedimentary rock–hosted deposits  • To understand Carlin trend gold deposits  • Search whether to apply or not Carlin type deposits in Korea

  3. Sedimentary rock-hosted deposits Distal disseminated deposits Carlin-type Au deposits

  4. 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,…

  5. Location of Carlin type deposits Carlin trend

  6. Geological map, Carlin trend, Nevada

  7. Stratigraphy • Robert Mountain Formation • Popovich Formation • Rodeo Creek Unit old young

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

  9. 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

  10. 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°

  11. Alteration • Decalcification, Decarbonization • Argilic alteration • Silicification

  12. 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

  13. Schematic model for the development of a Carlin-type gold deposit

  14. 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

  15. 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

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

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