"can someone tell me again, why we're so certain or expect to find the holy grail?" with the Carbonatites. It's a great question. I will do my best to explain how I see it.
First up - we cannot be certain that the Carbonatites are the "holy grail" - ie the source of the Mangaroon region Rare Earths. However, it does look extremely likely.
All known Rare Earth ironstones are associated with nearby Carbonatite magma intrusions. The richest Rare Earths deposits in the world - Mt Weld in WA (owned by Lynas) and Mountain Pass in Nevada USA are Rare Earth deposits which are part of a major Carbonatite magma intrusion.
This article is an interesting description of the Mt Weld deposit: http://portergeo.com.au/database/mineinfo.asp?mineid=mn770 Note that this was discovered through an aeromagnetic survey - just like the one completed by Dreadnought at Mangaroon. Similar to Mangaroon, the magnetic anomalies were from Carbonatite magma intrusions which were mostly NOT visible at the surface - because millennia of erosion and weathering had buried them under debris ("regolith").
In fact the weathered material at Mt Weld has some of the richest Rare Earth deposits - because the weathering process, as the Carbonatites break down, can concentrate the Rare Earth content.
Just like Mt Weld, the Carbonatites at Mangaroon are deeply weathered and mostly covered in regolith. At Mangaroon this is described as "calcrete" - material made from eroded/weathered rocks stuck together by Calcium Carbonate. They only outcrop at the surface in two places - the C3 and C4 Carbonatite targets. Assays from those outcrops confirm Carbonatite with significant Rare Earth content. However, the magnetic data for all the targets is similar, and they are close to each other, so it is a good bet that C1, C2, C5 and C6 are similar.
The Ironstones at Yin - and the Ironstones at Hastings' Yangibana project - are all from "dykes" - thin intrusions of magma which have penetrated through other rock. https://en.wikipedia.org/wiki/Dike_(geology).
Those dykes will have come from a major magma chamber/intrusion. Figure 1 in DRE's 1 Feb Announcement gives the picture.
Prior to Dreadnought's discovery of the Carbonatite intrusions, it was thought that the Yangibana dykes must have come from Carbonatite buried somewhere much deeper down - because they couldn't be found.
I suppose it is still possible that this is the case - or that there are other near surface Carbonatite sources which have not yet been found. However Carbonatite is quite rare. https://en.wikipedia.org/wiki/Carbonatite
It is therefore far more likely that the Yamgibana and Yin Ironstones are indeed from Dykes which were sourced from the Carbonatite intrusions found by DRE.
The only other question would be - are the Rare Earths in the dykes (at Yangibana and Yin) somehow better quality/more concentrated than the Rare Earths in the Carbonatite source. The Porter Geo article I referenced earlier (http://portergeo.com.au/database/mineinfo.asp?mineid=mn770) explains that the Mt Weld deposits were strongly influenced by leaching from groundwater: "The leaching of carbonatite by groundwater coupled with mineral alteration (such as alteration of pyrochlore) resulted in the preservation of a residuum rich in primary igneous apatite with high REE contents."
The ways in which Rare Earths end up being concentrated in commercially viable deposits is still not fully understood. Here is a great article about that: https://www.science.org/doi/10.1126/sciadv.abb6570
However it states that: "It has long been established that REE deposits are associated with late hydrothermal activity in and around carbonatites" Note that the article also explaIn that an ideal commercial deposit would be higher in Nd and Pr because these are minerals which will be in high demand for the magnets needed in high efficiency electric motors: "Any deposit mined for Nd will always contain more Ce than Nd and often more La as well (2, 7). This presents a challenge for geologists, who now must find not just deposits rich in REE, but deposits that have proportions closest to industry needs. Demand for electric vehicle motors is forecast to increase in the coming decades. Therefore, deposits should have as much Nd and Pr as possible compared to La and Ce, with a sprinkling of Dy to make the perfect REE combination for magnets."
The big selling point of the HAS Yangibana Ironstones is that they are indeed high in Md and Pr. Fun fact: the assays DRE now has for Yin show the same thing: "Assays up to 16% TREO with an average NdPr ratio of ~30%, nearly double the global average and similar to the Hastings Technology Metals Ltd (ASX.HAS, Mkt Cap $450M) world-class Yangibana Rare Earths Project located ~25kms away." source: https://hotcopper.com.au/threads/ann-assays-confirm-yin-as-a-high-grade-rare-earth-discovery.6863275/
This is really good! It is also a huge advantage for DRE that Hastings has already done the hard work needed to understand the metallurgy here - ie how to extract the commercial minerals from the base material. I think it is extremely significant that one of the first things DRE did was to test the metallurgy/extraction from the Yin Ironstones. Their Announcement of 1 September last year is a must read: https://hotcopper.com.au/threads/ann-encouraging-results-for-rare-earths-at-yin.6260294/
So, friend Swisskid, nothing is "certain" about that "holy grail" - but DRE has systematically investigated this in a truly intelligent way and the results to date have (in my opinion) hugely increased the chances.
What we know:
Rare Earth Ironstone deposits are all associated with Carbonatite intrusions
DRE has identified 6 probable Carbonatite intrusions - two of them confirmed so far. There are no other known Carbonatite intrusions in the region, which makes it likely (though till not certain) that the DRE Carbonatite intrusions are the source of the regional Rare Earths
The Yin ironstones assayed so far are at least as good in. RE content as those at the HAS Yangibana project, and very similar in composition.
We know that DRE understand the metallurgy required
The initial drill results at Yin are actually better than anything HAS has found at Yangibana
Nothing is a safe bet in mining exploration, but my personal opinion is that DRE is now looking highly likely to have a major commercially viable Rare Earths discovery - with a fair chance that it will be world class.
Note: Don't get too excited by the $8.7 billion market cap of Lynas, because their value is also based on the fact that they have spent 10 years perfecting the difficult process of actually refining Rare Earths - at their LAMP plant in Malaysia. DRE is an explorer - not a miner - and certainly not a processor. However, the Mangaroon Rare Earths project could still have a value many times the current market cap of DRE, so in my view, the share price growth we have seen is just the beginning.
(Disclaimers - it's still speculative, and you need to make your own decision about risk vs reward.)
(20min delay)