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Geol 5320 Advanced Igneous and Metamorphic Petrology

Geol 5320 Advanced Igneous and Metamorphic Petrology. Modeling the Petrology and PGE Reef Mineralization of the Sonju Lake Intrusion. December 7, 2009. Sonju Lake Intrusion. The Sonju Lake Intrusion. From MGS Map M-71 (Miller et al., 1989).

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Geol 5320 Advanced Igneous and Metamorphic Petrology

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  1. Geol 5320 Advanced Igneous and Metamorphic Petrology Modeling the Petrology and PGE Reef Mineralization of the Sonju Lake Intrusion December 7, 2009

  2. Sonju Lake Intrusion

  3. The Sonju Lake Intrusion From MGS Map M-71 (Miller et al., 1989)

  4. Modal Variation and Cumulus Texture Cumulus Mineral Mode Modal Variations Modal Rock Names Cumulus Code Leucogranite Quartz ferromonzonite Apatitic olivine ferromonzodiorite Apatite olivine ferrodiorite Ol-bearing oxide gabbro Ol-bearing gabbro Troctolite- augite troctolite Dunite Melatroctolite PCFOAg PCFOAh PCFoi PC(O)fi POcfi O OP

  5. Cryptic Variation

  6. Sheet-like Geometry of the Sonju Lake Intrusion Estimation of Bulk Composition Becomes a 1-dimensional problem >10 km 1 km >20 km

  7. Bulk Intrusion Composition = Parent Magma Liquid Line of Descent Calculated by summing composition of rock column above a specific horizon Sc 34 V 192 Cr 111 Co 75 Ni 185 Rb 20 Sr 233 Ba 171 Y 20 Zr 114 Nb 17 Hf 3.1 La 14.7 Ce 33.4 Sm 4.1 Eu 1.6 Tb 0.8 Yb 2.1 Lu .32 SiO2 47.6 TiO2 2.28 Al2O3 14.0 FeOt 14.7 MnO 0.21 MgO 8.3 CaO 9.4 Na2O 2.47 K2O 0.55 P2O5 0.30 Volatiles 0.20 Total 100.0 mg# 50.2 = moderately evolved olivine tholeiitic basalt From Miller and Chandler (1998) and Miller and Ripley (1997)

  8. Fractional Crystallization Modelling CHAOS 2 (NIELSEN, 1990) Model Parameters : fO2 = -2 log QFM; trapped liquid = 20%

  9. Discovery of Stratiform PGE Mineralization Skaergaard Intrusion 0 100 200 300 400 500 600 Cu (ppm) Feb. 1999

  10. Outcrop Sampling PGE Reef

  11. SLI Chemostratigraphy From Miller (1999)

  12. Evolution of Sulfide in the Sonju Lake Intrusion

  13. Exploration Drilling by Franconia Minerals July 2002

  14. Core Logging and Sampling Plagioclase 65-73% Sampling Regime Phase 1 – 1’ sample every 10’ Phase 1- continuous 1’ across PMZ 423 Total Whole Rock Analyses 1 cm

  15. Detailed Geochemical Profiling of the PMZ

  16. Meters above Cu-Au break Cu-Pd Ratios SL02-1 SL02-1 Cu/Pd Precious Metals Zone (PMZ) Pd(ppb) after Barnes et al. (1993)

  17. PMZ Metallogenesis • What was the PGE mineralizing agent? Cu-Fe Sulfide - close physical association of PGM and “cumulus” chalcopyrite • Why the paucity of sulfide in the PMZ? Sulfide dissolution by deuteric and low-T hydrothermal fluids – dissolution and replacement textures in sulfide associated with silicate alteration; secondary pyrite above PMZ • Are the stratigraphic variations in grade primary? Yes for Pd & Pt, not for Cu and Au – Pd and Pt concentrations correlate to subtle silicate layering; textural evidence of unreactive PGM; experimental evidence of Au and Cu mobility in oxidizing fluids

  18. PGE Mineralizing Agent? Cu-Fe Sulfide? Fe-Ti Oxide??? Data from SL02-1 PMZ 0 to 105m below Cu-Au Break

  19. “Cumulus” Sulfide in the PMZ Meters above Cu-Au break SL02-1 SL02-3 SL02-2 Bn Cp 100 um Cp Precious Metals Zone (PMZ)

  20. Paucity of Sulfide in PMZ? PGM Chl-Act Uralite UralitizedAugite

  21. Mobility of Sulfide

  22. Desulfurization and Oxidation of Cu Sulfide

  23. Are Metal Offsets Primary? • Kinetic Model • Preservation of variable degrees of disequilibrium • during sulfide liquation • Controls on Equilibrium • Sulf/Sil distribution coefficient • Diffusivity of metals in silicate • melt • Nucleation density of sulfide • droplet • Size/Growth rates of sulfide • droplets • Settling rate of sulfide (strain • rate of silicate melt)

  24. Relationship of PGE to Modal Variations in the PMZ Plagioclase Augite Fe-Ti Oxide

  25. Correlation of Leucocratic Gabbro to Skaergaard Platinova Reefs From Andersen et al. (1998)

  26. Restite PGM / Resorbed Sulfide 50 um 50 um Augite Augite Cp Actinolite Augite Cp Augite Pd-Sb Pd-Sb Chlorite- Actinolite Plagioclase 50 um Pt-Pd-As Cp

  27. Correlation by Secondary Pd Peaks

  28. Mineralization Model “Downer” Stage PGE scavenging of magma column complete Initial sulfide saturation Upgrading sulfide in intercumulus magma

  29. Dsulf/sil~104-108 Rapid Diffusion Dsulf/sil~102 Slow Diffusion

  30. Mineralization Model “Upper” Stage

  31. Comparing the SLI to other PGE reefs Skaergaard-type Offset Classic Meters above sulfide increase

  32. IF ONLY.....

  33. PGE reefs

  34. PELE – MELTS-based Modeling Program developed by Alan Boudreau

  35. Oxygen Buffers MH - magnetite-hematite 4 Fe3O4 + O2 = 6 Fe2O3 NiNiO nickel-nickel oxide 2 Ni + O2 = 2 NiO FMQ fayalite-magnetite-qtz 3 Fe2SiO4 +O2 = 2 Fe3O4 + 3 SiO2 WM wustite -magnetite 3 Fe1-xO + O2 ~ Fe3O4 IW iron - wustite 2(1-x) Fe + O2 = 2 Fe1-xO QIF quartz-iron-fayalite 2 Fe + SiO2 + O2 = Fe2SiO4 Common fO2 range for magmatic conditions arc non-arc

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