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Semelhante a EH_Fall16_Research
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EH_Fall16_Research
- 1. EDS Microanalysis of sediment samples derived from the Lower Chlorite-Muscovite Unit of the Evington Group, Fluvanna County, Virginia Ericka Hayes Earth and Environmental Science EES 489 Dr. Haley
- 2. Big picture question: In an area such as the Piedmont of Virginia, which has sparse outcrops on which to use for geologic maps, can we use stream sediments from small watersheds as a proxy for formation outcrops?
- 3. Contributed by: Rebecca HymanContributed by: Rebecca Hyman Contributed by: Rebecca Hyman Woodson Creek
- 9. Tourmaline? Element Apparent Concentration Wt% Wt% Sigma Oxide Oxide % Number of Ions B 3.00 B2O3 9.66 2.88 O 47.81 31.00 Na 2.16 1.87 0.05 Na2O 2.52 0.84 Mg 3.76 3.63 0.05 MgO 6.02 1.55 Al 18.87 16.78 0.07 Al2O3 31.70 6.45 Si 17.96 17.85 0.08 SiO2 38.18 6.59 Ca 0.69 0.52 0.03 CaO 0.73 0.13 Ti 0.59 0.52 0.03 TiO2 0.86 0.11 Fe 9.18 8.03 0.08 FeO 10.33 1.49 Total: 100.00 100.00 20.05 (Cation sum) (Na,Ca)(Mg,Al,Fe2+)3Al6(BO3)3Si6O18(OH)4 Element Apparent Concentration Wt% Wt% Sigma Oxide Oxide % Number of Ions B 3.00 B2O3 9.66 2.88 O 47.81 31.00 Na 2.16 1.87 0.05 Na2O 2.52 0.84 Mg 3.76 3.63 0.05 MgO 6.02 1.55 Al 18.87 16.78 0.07 Al2O3 31.70 6.45 Si 17.96 17.85 0.08 SiO2 38.18 6.59 Ca 0.69 0.52 0.03 CaO 0.73 0.13 Ti 0.59 0.52 0.03 TiO2 0.86 0.11 Fe 9.18 8.03 0.08 FeO 10.33 1.49 Total: 100.00 100.00 20.05 (Cation sum) Number of Ions 2.88 31.00 0.84 1.55 6.45 6.59 0.13 0.11 1.49 20.05 (Cation sum)
- 10. Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 (Na,Ca)(Mg,Al,Fe2+)3Al6(BO3)3Si6O18(OH)4 Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 Oxide Oxide % Number of Ions B2O3 9.66 2.88 31.00 Na2O 2.52 0.84 MgO 6.02 1.55 Al2O3 31.70 6.45 SiO2 38.18 6.59 CaO 0.73 0.13 TiO2 0.86 0.11 FeO 10.33 1.49 % Oxides # of ions
- 12. Muscovite KAl3Si3O10(OH)2 Chlorite (Mg,Fe)6AlSi3O10(OH)8 Muscovite MuscoviteMC C C
- 13. FeMg Muscovite Element Apparent Concentration Wt% Wt% Sigma Oxide Oxide % Number of Ions O 45.44 24.00 Mg 1.73 1.73 0.03 MgO 2.87 0.60 Al 19.46 17.51 0.06 Al2O3 33.08 5.48 Si 21.07 21.56 0.07 SiO2 46.12 6.49 K 3.00 2.37 0.03 K2O 2.86 0.51 Ti 1.20 1.10 0.03 TiO2 1.84 0.19 Fe 11.37 10.29 0.08 FeO 13.24 1.56 Muscovite: KAl3Si3O10(OH)2 Phengitic Muscovite: K(Al,Fe,Mg)2(OH)2(Si,Al)4O10 Ernst 1963 Element Apparent Concentration Wt% Wt% Sigma Oxide Oxide % Number of Ions O 45.44 24.00 Mg 1.73 1.73 0.03 MgO 2.87 0.60 Al 19.46 17.51 0.06 Al2O3 33.08 5.48 Si 21.07 21.56 0.07 SiO2 46.12 6.49 K 3.00 2.37 0.03 K2O 2.86 0.51 Ti 1.20 1.10 0.03 TiO2 1.84 0.19 Fe 11.37 10.29 0.08 FeO 13.24 1.56
- 14. Mineral Albite Amphibole Biotite Chlorite Clinozoisite Epidote Garnet Hematite Hornblende Ilmenite Magnetite FeMgMuscovite PotassiumFeldspar Pyroxene Quartz Rutile Sphene Tourmaline Zircon >5µm 125µm 230µm Unit
- 15. Summary • EDS proved to be an effective method analyzing loose sediments • 13 minerals previously unidentified in the Evington Group • Future studies • Questions?
- 16. References Deer, W. A., R. A. Howie, and J. Zussman. An Introduction to the Rock- forming Minerals. London: Mineralogical Society, 2013. Print. Ernst, W. G. "Significance of Phengitic Micas from Low-Grade Schists." The American Mineralogist 48 (1963): Web. Krumbein, W.C. "Manual of Sedimentary Petrography." Society for Sedimentary Geology (SEPM), Print. Severin, Kenneth P. Energy Dispersive Spectrometry of Common Rock Forming Minerals. Dordrecht: Kluwer Academic, 2004. Print. Smith, James William., R. C. Milici, and S. S. Greenberg. Geology and Mineral Resources of Fluvanna County. Charlottesville: n.p., 1964. Print.
Notas do Editor
- EDS = Energy dispersive X-ray spectroscopy
- My contribution is to analyze sediments derived from a single formation to characterize the composition of that formation
- The area of study and sampling site was determined by Rebecca Hyman, using GIS to select a sampling site exclusively from the Lower Chlorite-Muscovite Unit of the Evington Group, Fluvanna County, Virginia. My project was to evaluate and analyze the sample to provide diagnostic compositional information
- Riverbed sediments were separated by sieves into size classes and we analyzed classes >5um to 230um >5um rock fragments 125um smaller fragments and some individual minerals 230um individual mineral crystals or minerals separated from lager fragments
- Since our sample was dominated by Quartz and Micas, we used tetrabromethne 2.95 specific gravity in our heavy mineral separation to isolate less common minerals such as Zircon which has a specific gravity of 4.6.
- Maps and silver paint to navigate the stub Optical identification attempts, by using paint relocate specific grain once color and orientation is lost in the SEM (could use grids in future but $$) Exploring the stub…. Lighter the color the more atomic mass the darker lighter atomic mass But identifying minerals is not always simple….. Tools and resources are crucial to indentification Dichotomies key from “Energy Dispersive Spectrometry of Common Rock Forming Minerals.” Chemical analysis form Deer, Howie and Zussman’s “Into to Rock forming minerals”
- Heavy A 230um_Rutile_2016-10-27_18-53-56 Spectrum: Mineral comcentration (counts per second per electron-volt by kilo-electron volt) (20keV) Blue Rutile is simple enough to identify due to its simple formula and crystal structure Similarly Quartz SiO2 How to identify more complex minerals?? (next slide)
- Heavy mineral separation 230um Tourmaline More difficult due to element substitutions and the limitations of the SEM (Boron) sometimes Aztec-EDS would identify B and at times we would have to tell the system to calculate for B to get an accurate identification. (W/o B the tourmaline samples would appear to be Cordierite which is a mineral formed under high pressure and heat conditions similar to those along deep faults at plate boundaries) (next slide)
- Heavy A 230um_Cordierite_Tourmaline_2016-11-08_12-29-09 Steps: Add Boron if the SEM failed Specify # of oxygen Compare % oxides, once similar mineral is identified… compare # ions (next slide example)
- Talk through comparison SiO2 38.18 range of a Tourmaline is 31-36 so 38 isn’t unreasonable Al2O3 31.70: range 22-46 Compare ions to Formula…. (Na, Ca)= 0.97 (Mg, Al, Fe)= 3.49 B= 2.88 Si= 6.59 How do we distinguish different minerals in the case we are looking at a fragment? (next slide) Aztec Mapping
- CLEAN B 125_Site 5_2016-10-17_15-31-30 Ilmenite and Quartz
- Linescan for very complex samples that are hard to distinguish Compare 2 formulas: Both contain Al, Si, O The main differences are the presence of Fe and Mg Difficult without chemical analysis, traditional methods crush and analyze SEM allows us to analyze specific minerals
- Unique Muscovite samples, misleading and frustration because published wasn’t high in FeMg Analysis by Ernst in 1963 “Significance of Phengitic Micas from Low-Grade Schists.“ published finding of FeMg rich Micas found in California around the time of the Geology and Mineral Resources of Fluvanna County bulletin was being published. Thus the researcher of the bulletin would not have known. Limitations of thin sections and compare findings (next slide)
- Shaded portion to show what was published for the formation Larger rock fragments vs individual minerals Weathering, outcropping, thin sections