Lab_6_Isotopes

# Has the cassiterite formed from high or low

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Unformatted text preview: that the temperatures are in Kelvin. Convert temperatures to Celsius. 2) What do you notice about the temperatures of the mineral pairs as one goes from the interior of the alteration zone (chlorite) to the more distal portions of the alteration zone? Why is this? (10 marks). 3) Compare the temperatures of the cassiterite ­quartz pairs to the other zones? Has the cassiterite formed from high or low temperature fluids? For the questions above please include the equations used to calculate the various parameters. Part 2. Calculating Fluid Compositions and Water Rock Interaction 1) Given the temperatures that you have calculated in Part 1 and the associated fractionation equations above, calculate the δ18Owater for each sample (10 marks). 2) Given your knowledge of ocean water, was the fluid isotopically heavier or lighter than seawater? Why do you think this is (explain)? (10 marks) 3) Using the whole rock δ18O data and the δ18O water that you have calculated for the various mineral pairs, and assuming that the initial fluid δ18O is seawater (δ18O = 0 per mil), and the δ18O of the unaltered rhyolite is +15 per mil, calculate open system and closed system water:rock ratios. Which values are higher, open system or closed system? Why? Which alteration assemblage has the highest water:rock ratios? Why? (20 marks). Equations for Fluid:Rock Interaction Water:rock interaction in a closed system (i.e., closed vessel, no fluid comes in our out of the system): W / Rclosed final initial δ 18 Orock − δ 18 Orock = 18 initial final δ O fluid − δ 18 O fluid Water:rock interaction in an open system (i.e., fluid can flow in and out of the system): initial Ⱥ δ 18 O final − δ 18 Orock Ⱥ W / Ropen = ln Ⱥ 18 rock + 1Ⱥ = ln[W / Rclosed + 1] initial 18 final Ⱥ δ O fluid − δ O fluid Ⱥ Ⱥ Ⱥ...
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