For others, only need to read the underline.
You are looking for a 'negative' cerium anomaly, not a positive cerium anomaly which is what you get at surface, but weathering processes and strength of weathering a key as to whether how these develop. The positive cerium anomaly (near surface) is found in the upper part of the weathered crust (along with other light REEs, whilst the negative cerium anomaly is found in the lower weathered parts (at depth). It is a guide only but companies do use it to determine exploration effort only, and generally after finding a resource and tracking this to understand direction of ionic as drilling continues, and it is never full-proof.
Given REEs in ionic normally grade less than 0.1% (TREO), and Ce is only a part thereof, the anomaly itself is not a large feature in itself, so it is actually when you drill and assay and MET you work things out. The issue with Ce is that it is not valuable - in what I posted 1/3rd of head grade in that sample was Ce btw, but the key part been in terms of TREO only 3% of it was Ce. That itself is a good result and in itself confirms the deposit is ionic because Ce ratios tend to be higher in other resource types (in terms of TREO) - Ce leakage into the heavy REE layers is what in part drives this.
Ultimately it is about head grade and the extent to which the weathering process established an ionic resource. When I think about ionic clays it is about the process of chemical weathering of REE from the parent rock and how the REE ions, and enrichment of those REEs onto the clay surface through ion absorption occurs. And to repeat not all the resource is ionic. And ion absorption is what makes ionic resources more cost effective to process than typical clay deposits, however, ultimately economics of either depends on the extent of the higher value REEs (so the term TREO in part is a misnormer). It is why in the graph I showed some deposits could be developed regardless that TREO was less than 0.2% (and obviously some were ionic)
My understanding of the formation of ionic resources is as follows:
1. the distribution of light REEs reduce as you go deeper in ore body depth.
2. the distribution of heavy REEs increases as you go deeper in ore body depth.
3. In other words you have better rare earth differentiation through water flow through rock reaction (and weathering acts as a form of pH solution). Given how weathering happens you will have differing outcomes and compositions.
4. If weathering is particularly strongin strength and time then your light and heavy REEs will be enrinched in the same clay layer. If not as strong you have a divergence of light to heavy REEs although there will be slippage into either layer.
To you question of Ce, I presume you are referring to the term 'redox' and how that process works for Ce (since redox works mostly on Ce) - for others, redox is explained here -
Redox - WikipediaRedox has the greatest impact on Ce in ionic resources as I understand it. That means you have a positive Ce anomaly - actually enriched Ce, in the upper weathered crust, but Ce itself is a light REE so it will be found with other light REEs in that layer anyway. It is the negative Ce, or what is commonly referred to as Ce loss meaning it dives into the lower layers, that is a key as a marker for identifying ionic resources, and that is found lower down. It is also a key marker that would explain why Ce in TREO for ionic deposits in METs would be lower than what you might see for clays and say hard rock - again though it does depend on resources.
Ce and La btw are your largest component parts in any REE deposits, whether they be clay, hard rock, ionic etc etc and they are considered light REEs
At the end of the day you don't know whether a resource is ionic or clay until you do METs (PH4 or PH3 is what defines an ionic resource through METs and is generally a quick release process and obviously a low cost process). If you have to use a stronger PH solution than 3 or 4 (and it takes longer) then that becomes a costlier process and more fundamentally you will receive a lower basket price as you would also capture impurities in the solution and moreso also means you have a lower recovery rate - which impacts economics. So for clays, you probably need TREO of say 0.3% for clays to potentially be viable and that depends on REE spread of the more valuable minerals (ionic is less costly). I would be interested in this so called picture you might be alluding to as been a Ce anamoly because it is the below that decides an ionic resource. I have seen too many images by exploration companies suggesting A, and then when they explore A is not there or A is something else.
So until you drill and do METs you won't know. And the key to ionic is a number of METs been done using pH4 (or at worst pH3) solution. But if you can positively identify the marker as Ce negative then that would be a likely, and I use likely because weathering is a key and process is a key, that the area is not ionic. And Ce negative is below the surface so need to identify that marker itself. And obviously if the resource is ionic, the METs would show a low percentage of Ce in TREO, I suspect.The paper below is a nice reference:
All IMO IMO
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