Relationship between alteration mineralogy and lithogeochemistry associated with the Backun epithermal Au-Ag deposit

다국어 초록 (Multilingual Abstract)

Hydrothermal alteration records the effects of fluid-rock interaction, and these effects are expressed as compositional changes that can be recognized in the geochemistry of the rocks. Where compositional changes define gradients that can be related to processes that form ore deposits, they potentially provide vectors toward sites likely to contain precious metal mineralization. Alteration indices and pathfinder elements, are potentially effective for targeting of mineralized veins, involving geochemical dispersion and mineralogy.
To sum up with the geochemical dispersion, consequently simplified of K and Si enrichments and Na and Ca depletion present a larger footprint than do anomalous concentrations of precious metals, base metals, and pathfinder elements. Although most of the alteration index has been applied on VHMS deposits, the Backun epithermal Au-Ag deposit shows great possibility of application. The threshold could be the value of wall rock's alteration index, depends on the composition of forming minerals. The alteration box are most likely to be useful when epithermal deposit exploration is conducted. Clear gain or loss elements with high score of coefficients of correlation likely to be a great pathfinder. For granite, K2O, Rb, Tm, Sm, Y, Fe2O3, Ni, Co, Cd, Tl, S, Zn, Total S have not only positive strong coefficients of correlation with gold and silver, but also largely gained value toward mineralized vein. For intermediate dyke, Ni and Co have strong negative coefficients of correlation with gold and silver as well as loss of those elements, U is opposite that positive coefficient of correlation as well as gain of that element. These elements are potential pathfinder as well. Petrographic study of the paragenetic relationships between hydrothermal and supergene minerals is required to maximize the usefulness of whole-rock geochemical data (Warren et al., 2007).

목차 (Table of Contents)

• 1. Introduction 1
• 2. Geology 2
• 3. Methods 4
• 4. Ore deposit 5
• 4-1. Mining history 5
• 4-2. Petrology 8
• 4-2-1. intermediate dyke 11
• 4-2-2. Granite 16
• 4-3. Characteristics of alteration using SWIR (Short Wave Infrared) 19
• 4-3-1. Short Wave Infrared 19
• 4-3-2. Methodology 19
• 4-3-3. Applying PIMA to hydrothermal alteration zones 20
• 4-4. Geochemical dispersion 22
• 4-4-1. Mass transfer and hydrothermal alteration in epithermal environments 22
• 4-4-2. Evaluation of mass transfer in hydrothermally altered rocks 23
• 4-4-3. Molar element ratio: mass transfer and associated alteration mineralogy 35
• 5. Discussion 42
• 5-1. Sericite Index 42
• 5-2. Chlorite Index 44
• 5-3. AI (Ishikawa alteration index) 45
• 5-4. Chlorite-carbonate-pyrite index (CCPI) 47
• 5-5. Alteration box plot 49
• 5-5-1. Advantages (Large et al., 2001) 52
• 5-5-2. Limitation (Large et al., 2001) 52
• 5-6. Spitz-Darling 54
• 5-7. Alkali Index 55
• 5-8. Modified Hashimoto 56
• 5-9. Hashigushi Index 57
• 6. Conclusion 59
• References 63
• ABSTRACT 70