Dear all,
I have done XRF analysis of unconsolidated fluvial sediment samples and found that CaO wt% is much more higher. I have calculated the weathering indices as per the formula given in Excel sheet. However, I found less CIA value due to higher CaO* value (higher than Na2O value). So, I have taken Na2O value instead of CaO* while calculating corrected CIA. I would be extremely grateful to you if you kindly help me with the followings.
Do the calculation of CIA corrected is ok? If not, pls let me know the correct procedure.
What would be the correct way to calculate other weathering indices viz., WIP, CIW, PIA?
Looking forward to your kind suggestions in this regard!!!
Thanks & regards,
Ashok
You can follow the answers to questions from the links:
https://www.researchgate.net/post/H...ration_and_other_weathering_indices
https://www.researchgate.net/post/W...of_protolite_in_metamorphic_rocks/1
excuse me, these links:
https://www.researchgate.net/post/How_to_calculate_Chemical_Index_of_Alteration_and_other_weathering_indices
https://www.researchgate.net/post/What_is_the_best_method_for_determining_the_source_of_protolite_in_metamorphic_rocks/1
Dear Roman Terentiev,
Thanks for your information. I am getting higher value of CaO due to the presence of calcrete nodules (CaCO3) in my sample. We generally follow the following formula to calculate CaO*.
CaO* = mol CaO - mol CO2 in calcite- mol CO2 in dolomite x 1/2 - mol P2O5 in apatite x 10/3
I could not be able to get CO2 percentage through XRF. So, I deducted the mole of P2O5 in Apatite and found that CaO* value is higher than the the mole of Na2O. It has been mentioned in few papers (link given) that if the molar value of CaO* (after deduction) is higher than that of Na2O, we will have to consider Na2O value instead of CaO*. So, I have followed this principle to calculate CIA (corrected). I would be extremely grateful if you kindly let me know whether this calculation is correct or not. If not, pls let me know the best possible solution of my problem by going through my data (attached excel file).
Looking forward!!
Regards,
Ashok
http://www.sciencedirect.com/science/article/pii/S0883292704001635
http://www.nature.com/articles/srep06868
Dear Ashok Shaw,
I think you are operating correctly. However, it is better to check your calculations with the involvement of other rock data. For example, to choose carbonate-free sediments, and then to compare the obtained data on carbonate-rich and carbonate-free sediments from the studied Formation.
Best Regards,
Roman
Dear Roman Terentiev,
Thank you for your kind reply. I am thinking about doing the XRF of the same samples again after removing Carbonates since CaO% is affecting the percentage of other oxides, especially SiO2%. And it is affecting the correct interpretation of Provenance or tectonic setting. I am not sure whether my thinking is correct or not. If so, I need a procedure where I can remove the carboanates from the samples before doing the XRF analysis.
Kindly let me know your suggestion.
Best regards,
Ashok
Dear Ashok,
A good idea! On the technology of carbonate removal is better to ask analysts. Probably, chlorohydric acid (HCl) is needed here.
When excluding carbonate calcium, it is necessary to normalize to 100% to facilitate comparisons between analyses. Try using the attached program.
Best regards,
Roman
CIA = {Al2O3 / (Al2O3 + CaO* + Na2O + K2O)} x 100
PIA = {(Al2O3 – K2O) / ((Al2O3 - K2O) + CaO* + Na2O)} x 100
CIW = {Al2O3 / (Al2O3 + CaO* + Na2O)} x 100
CIW´ = {Al2O3 / (Al2O3 + Na2O)} x 100
In the above equations the major oxides are expressed in molar propotions and CaO* is the content of CaO incorporated in silicate fraction. McLennan (1993) proposed an indirect method for quantifying CaO content of silicate fraction assuming reasonable values of Ca/Na ratios of silicate material. Procedure for quantification of CaO content (CaO*) of silicate fraction involves subtraction of molar proportion of P2O5 from the molar proportion of total CaO. After subtraction, if the “remaining number of moles” is found to be less than the molar proportion of Na2O, then the “remaining number of moles” is considered as the molar proportion of CaO of silicate fraction. If the “remaining number of moles” is greater than the molar proportion of Na2O, then the molar proportion of Na2O is considered as the molar proportion of CaO of silicate fraction (CaO*).
@ Ashok Shaw
Yes , the procedure of McLennen ( 1993) ,, if the sediment or rock samples not have NaCl as halite, in this case CaO not equal Na2O....
i think we need to clean the crushed samples first to remove the salt.
and i think better to remove the carbonate and analysis only the less than 2 micron clay fraction.
sorry I mean if the sediments have halite,difficult to consider CaO =Na2O
better to remove carbonate minerals and evaporat minerals.
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