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Louise Soroka and Nathan Coleman Cadet Gold Synthesis Project

Australian Government Geoscience Australia. Classifying Granites after (Champion & Cassidy, 2001). Louise Soroka and Nathan Coleman Cadet Gold Synthesis Project. Aims of this slideshow. To describe the method of classification by (Champion & Cassidy, 2001)

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Louise Soroka and Nathan Coleman Cadet Gold Synthesis Project

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  1. Australian Government Geoscience Australia Classifying Granites after (Champion & Cassidy, 2001) Louise Soroka and Nathan Coleman Cadet Gold Synthesis Project

  2. Aims of this slideshow • To describe the method of classification by (Champion & Cassidy, 2001) • Present this method in an interactive format • Give examples of granites and by what processes they were classified • Applying this knowledge to various data

  3. There are five main granite groups • High Ca • Low Ca • Mafic • Syenite • High-HFSE • (Since our Geodynamic synthesis charts did not include the High-HFSE group it won’t be discussed in length here)

  4. Altered Sample • Syenite • Mafic • Low Ca • High Ca A flow chart approach has been achieved by discriminating the group of a granite in the following order

  5. Note of importance! • Some granites are much harder to classify than others! • When using the discriminate charts some granites will not fall into only one group and will require interpretation as to which group it fits best

  6. -L.O.I (> 2-3) -Anomalous ASI, S, CO2, Na2O, K2O Discriminating Granite Flow Chart Yes No Sample has been altered • High Na2O + K2O (>10) • High Na2O versus K2O -High Ce & K2O (K 3-5, Ce 100-500) -Low to moderate MgO (< 1-2) This chart is to be used in conjunction with scatter- plots from Champion & Cassidy 2001. Yes No Syenitic -High to very high Fe, Y, Zr -Very low Al2O3, K2O, Rb, Pb * Yes No High-HFSE Several major outliers should indicate a negative choice in that category -Low to moderate SiO2 (<72), K2O (<4) -Low to moderate Zr (<200) -High Ni to low SiO2, mg# (>30), -High MgO (>0.6) Yes No Mafic -High K2O (>4), K2O/Na2O -High Rb (>150), Th (>30-40), Zr and Ce to low Si -Moderate to low Na2O (<4) • Moderate-high Y (>10) • TiO2 and Sr not very discriminating No Yes High Ca Low Ca

  7. Scatter plots The Previous chart is only a guideline. If any of the geochemical values are borderline then they should be checked with the scatter plots. (Champion and Cassidy 2001)

  8. Geochemistry Basics • A Low SiO2 (under 65) is a strong indicator that the granite is probably Mafic (or Syenitic) • A mid range of around 69-71 SiO2 means it could be Mafic or any of the others, esp. High/Low Ca • SiO2 does not separate High from Low Ca • However K2O and Na2O are great separators of High and Low Ca • Some studies won’t take REE data but elements like Rb, Th, Y can all be good indicators of granite group

  9. Now to the fun part! What type of granite is the sample TIMB? A) High Ca B) Mafic C) Syenite D) Low Ca E) None of the Above (Relevant scatter plots are on next slide) (Doumbia et al. 1998) Senegal, West African Craton

  10. Granitoids of the southeastern Yilgarn Craton Black = High Ca Red = Low Ca Blue = Mafic Pink = High-HFSE (Champion and Cassidy 2001)

  11. Did you get the answer as B) Mafic? • Yay! Good job!

  12. The sample TIMB was classified as Mafic because… • Syenite was discounted as Na2O +K2O was low • A low SiO2 set it well apart of the High and Low Ca region • A medium MgO value set it somewhat apart from the other classifications • It had a low values for K2O and REE Zr Cross checking with the scatter plots confirms our classification

  13. Another question What type of granitoid is the sample MG11? A) High Ca B) Mafic C) Syenite D) Low Ca E) None of the Above (Relevant scatter plots are on next slide) (Downes et al. 1997) Margerides, French Massif Central

  14. Granitoids of the southeastern Yilgarn Craton Black = High Ca Red = Low Ca Blue = Mafic Pink = High-HFSE (Champion and Cassidy 2001)

  15. Did you get the answer as D) Low Ca? • Awesome!

  16. The sample MG11 was classified as Low Ca because… • High SiO2 and moderate-low MgO discounted Mafic classification • High K2O and moderate-low Na2O places MG11 in Low Ca cluster • REE values also indicated Low Ca e.g. High Rb and Sr

  17. Contradictions • But what about the Th value? • Th value strongly indicated High Ca classification, but with most of the Geochemistry pointing towards Low Ca this did not change our result.

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