(2020) Is Pyrite an Important Sink for Mo? Evidence from XAFS, TEM and APT Analyses of Pyrite
Gregory D, Chappaz A, Atienza N, Taylor S, Perea D, Kovarik L & Lyons T
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06l: Room 2, Thursday 25th June 00:39 - 00:42
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How confident are you that the Mo(VI) species have not formed during sample handling and analysis?
This was Anthony's part of the study, I forwarded your question to him, here is his response: The samples were kept under anaerobic conditions during processing and analysis.
It is very curious that the atom probe does not show any Mo. Since the spot size for LA-ICP-MS is a bit large for framboids, have you also done any imaging (i.e. electron microprobe) to confirm that the framboids had low Mo relative to the matrix (vs. just this one extracted needle)? Also, can you rule out oxidation of Mo during sample processing?
We actually had 6 needles from the same framboid, we just showed data from one for simplicity, I fairly confident that we didn't miss Mo held in pyrite but we may have missed Mo rich "nuggets" within the framboid. Your second question is similar to the one by George Helz, I forwarded it to Anthony who did that part of the study, here is his response: The samples were kept under anaerobic conditions during processing and analysis.
Great talk Dan! It's nice to see what happened to all the Mo that was detected by LAICPMS. Since Mo is possibly not associated with pyrite, can Mo still be used as a proxy for paleoenvironments? Is the organic matter that Mo seems to be associated with, representative of the ocean chemistry?
The Mo proxy still works fine but it does change a bit our interpretation of what processes are causing the Mo enrichment and our understanding on how Mo can be re-mobilized.
I am wondering if you saw any evidence of framboids being encased by biofilm like that in this paper: A high-resolution chemical and structural study of framboidal pyrite formed within a low-temperature bacterial biofilm L. C. W. MACLEAN et all 2008 Geobiology? Could the biofilm EPS account for the Mo?
I saw no evidence of it but I also wasn't really looking I was focused on the sulfide and when we did the lift out with the FIB we didn't really preserve the edges. Also, the samples were set in epoxy and carbon coated for SEM so biological films would have been difficult to identify.
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