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Alteration_Mass_Balance

Alteration_Mass_Balance - Earth Sciences 4502/6510...

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Earth Sciences 4502/6510 Hydrothermal Alteration Geochemistry Part 1: Mass and Elemental Changes During Hydrothermal Alteration: Techniques, Theory, and Applications Stephen J. Piercey Department of Earth Sciences Memorial University St. John’s, NL, Canada A1B 1N3 [email protected] Wednesday, 15 August, 12
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Hydrothermal alteration and element mobility. Philosophical approach to alteration sampling. Sample screening. Methods of calculate mass and elemental change: Gresens (1968). Grant (1986) - isocon MacLean (1990) – single and multiple precursor methods. Stanley and Madeisky (1994) – PER method Other simple tools for alteration geochemistry. Alteration indexes and applications. Integration of GIS, 3D visualization, and other data to target vector. Outline Wednesday, 15 August, 12
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Element Mobility Unlike in petrological-based problems when discussing alteration we want to understand the distribution of mobile elements . We wish to define dispersion haloes of elements and identify the best elements to distinguish proximal versus distal alteration = Target Vector! (Galley, 1995) Under the right conditions any element can be mobile! Key is to understand spatial relationships and relative mobility in different ore-systems, or in presence of different ligands. Alteration is really looking at dispersal and destruction haloes ! Wednesday, 15 August, 12
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Sc Ti Zr Hf Nd U Nb Cr Mo W Sm Mn Tc Re Eu Fe Ru Os Gd Co Rh Ir Tb Ni Pd Pt Dy Cu Ag Au Ho Er Tm Yb Lu Zn Cd Hg B Al In Ga Tl C N O Si P S Sn Sb Te Ge As Se Pb Bi Po F Cl I Br At Ne He Ar Xe Kr Rn Ta Pm V Y La Pr Pa H Be Mg Ca Sr Ba Ce Th Li Na Cs La Ac K Rb LFSE REE Noble Metals Base Metals TE Vol. Elem. HFSE Wednesday, 15 August, 12
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Element Mobility Major elements : most mobile except for Al 2 O 3 , TiO 2 ± P 2 O 5 . General empirical mobility scale: Al 2 O 3 , TiO 2 < P 2 O 5 < MgO, Fe 2 O 3 , FeO, MnO < CaO < K 2 O, Na 2 O. LFSE: most mobile except Th, and to a lesser extent U. General empirical mobility scale: Th < U < Ba, Sr, Pb < Cs, Rb, K HFSE: can be considered immobile unless in presence of F-rich fluids/melts; this is rare. REE: for the most part immobile. Can be mobile with F, Cl, SO 4 2- rich fluid/melt interaction. Eu and Ce exceptions Eu in Eu 2+ state can be mobile (reducing conditions) Ce 3+ vs. Ce 4+ - Ce 4+ often ppted. from hydrothermal solutions and in sedimentary rocks can indicate oxidizing basinal conditions. Wednesday, 15 August, 12
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Element Mobility TE: variably mobile, some very immobile (Cr, Ni, V, Sc, Ti), others less so (Co, Cu, Zn, Fe, Mn) Noble Metals: very uncertain behaviour during alteration and metamorphism. Au, Ag clearly mobile, PGE???? Base Metals: clearly very mobile during alteration and metamorphism. Volatile Elements: extremely mobile and often form larger haloes than base metals.
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