From this site : https://atlanticptyltd.com.au/projects/windimurra/geology-reserves-resources

"The vanadium titanomagnetite (VTM) bearing **bro is deeply weathered down to about 50 metres below the present surface. From fresh rock, weathering passes upwards through a zone of saprock up to 5 metres thick, into saprolite (30 metres to 40 metres thick), then to a mottled clay zone 3 metres to 10 metres thick. A lateritic caprock up to 5 metres thick has largely been eroded except in the vicinity of Hawkstone Ridge. The base of complete oxidation is about 30 metres below surface."

Let's break down the different layers of this rock deposit in simpler terms:

Fresh Rock: This is the original, unweathered rock deep below the surface.

Saprock: Just above the fresh rock, there is a zone called saprock, which is partly weathered rock. This layer is about 5 meters thick.

Saprolite: Above the saprock, there's a thicker layer called saprolite, which is more weathered and looks more like soil than rock. This layer is 30 to 40 meters thick.

Mottled Clay Zone: On top of the saprolite, there is a mottled clay zone. This is a mix of clays that look blotchy or spotted, and it's 3 to 10 meters thick.

Lateritic Caprock: The topmost layer is called lateritic caprock. This is a hard, iron-rich layer that formed at the surface. It used to cover the whole area but has mostly been eroded away, except in some places like Hawkstone Ridge. This layer is up to 5 meters thick.

Base of Complete Oxidation: This is the point down to which the rock has been completely weathered and oxidized. This base is about 30 meters below the surface.

So, if you were to dig down from the surface, you'd first hit the lateritic caprock (if it's still there), then the mottled clay zone, followed by the saprolite, the saprock, and finally the fresh rock at the bottom.

Mottled clay zone can mix with the saprolite layer to some extent. Here’s how it works:

Saprolite is a weathered layer that still retains some of the original rock structure but is more like soil. It’s typically where minerals like vanadium can be found because it's a transitional zone between rock and soil.

Mottled Clay Zone is a more weathered layer of clay that sits above the saprolite. It has a blotchy appearance due to varying degrees of oxidation and other chemical processes.

Due to the natural processes of weathering and erosion, it's possible for the mottled clay to mix with the saprolite layer below it. This mixing can occur through:

Chemical Weathering: Elements from the mottled clay can leach down into the saprolite, altering its composition.Physical Processes: Erosion and other geological activities can cause some of the mottled clay to physically move down into the saprolite layer.

So, it's feasible that the vanadium, which you believe is concentrated in the saprolite, could be found intermixed with materials from the mottled clay zone. This blending can complicate extraction and processing but is a common occurrence in deeply weathered geological formations.

The presence of too much mottled clay could indeed impact a salt roast recovery process. Here’s how:

Impurities: Mottled clay can introduce impurities that interfere with the chemical reactions necessary for the salt roasting process. These impurities can affect the efficiency of vanadium extraction.

Consistency: The clay's fine particles can create a less consistent feedstock, leading to uneven heating and reactions during roasting. This inconsistency can reduce the overall effectiveness of the recovery process.

Binding Agents: Clays can act as binding agents, making the mixture more difficult to handle and process. This can lead to clumping, which impacts the uniformity of the roasting process and reduces the contact between the vanadium-bearing minerals and the salts used in roasting.

Refractory Material: Some clays are refractory, meaning they resist chemical breakdown at high temperatures. This resistance can inhibit the necessary chemical transformations needed to recover vanadium effectively.

Dilution: The presence of significant amounts of clay can dilute the concentration of vanadium in the feedstock, requiring more processing effort and potentially more reagents to achieve the same recovery levels.

In summary, if the mottled clay content is too high, it can negatively impact the salt roast recovery process by introducing impurities, causing inconsistency in the feedstock, binding the materials, resisting chemical breakdown, and diluting the vanadium concentration. These factors can collectively reduce the efficiency and yield of the vanadium recovery process.

The fortunate thing with ChatGPT, Pi AI, Perplexity et al is there is no need to rely on anonymous 'Eddie the Experts' on message boards weighing in with commentary as it can be easily interrogated. The process failures at Windimurra could just as likely be put down to the above complexities in mining & treating the ore body such as that found at Windimurra, with negligible negative implications due to 'head grade' at all. There could have simply been too much clay to process economically, particularly when the Vanadium price dropped below break even point.

Not to mention the fire, were a root cause analysis done as to why the project eventually failed.

Windimurra fire damage 'extensive' Tue 11 Feb 2014