Just a disclaimer that this is my own completely amateur work for information sharing purposes only, and I do not have a significant amount of knowledge on MSI and HSI. I am simply consolidating my opinions and findings in writing for my own clarity, and I might as well share it. Do your own research.
Because of the lack of effective geophysical surveying methods for identifying pegmatite and in particular, fertile or Li-bearing pegmatite, there has recently been a lot of work put into finding technology that could aid in exploration of LCT pegmatites. One of the most promising methods is Hyperspectral and
Multispectral imaging, typically using data from ASTER or Sentinel-2. These satellites have sensors than can detect a wide range of light including infrared, split into 13 bands (each band represents a set range on the electromagnetic spectrum), and display these bands through RGB channels to make a nice colourful picture that a toddler (me) could read.
The way specific wavelenghts of light bounce off different surfaces of the earth gives hints as to what kind of matter the light interacted with. Rocks, vegetation, water, and most importantly minerals - each have specific light reflectance or absorption behaviours at different wavelengths. In the case of geology, the intensity of the signal can be dependant on the texture and surface area of the lithology.
Spodumene and pegmatitic minerals show energy absorbance features in short-wave infrared (SWIR) wavelengths, in particular around 2.2 - 2.4 microns. The Sentinel-2's B12 band has a bandwidth of 2.072 - 2.312 microns. This means that unfortunately, it isn't possible to get a narrow enough reading for specific minerals such as spodumene, without a hyperspectral sensor (very expensive). There can be lots of noise and false positives from the other minerals and rocks on the ground, which is why MSI is only a part of the solution. However, we can still get a general signature that can represent the type of geology an area hosts, as long as we view the signature in conjunction with our own knowledge of both the ground and targets.
This is why we should compare spectral features with regional shapes and emplacement habits of known pegmatites (northeast southwest trend, parallel or sigmoidal shape, injected parallel to the shearing and foliation of surrounding host metasedimentaries) to ensure we are only considering pegmatites and aren't taking the noise into account.
https://www.mdpi.com/2072-4292/13/18/3688In our case at Uis, we are lucky that there is very little vegetation that would hinder the topographical view of pegmatite outcroppings throughout the land package. This makes it easy to see all potential exploration targets, and their dimensions at surface. We can use the SWIR (B12) band on
Sentinel-2 satellite imagery of Uis to find and compare mineral and textural signatures, that are comparable to known spodumene-bearing pegmatite signatures. For example, we can use the B1/C1 pegmatites and spodumene-rich artisinal mine workings as reference.
The main goal from all of this is simply to differentiate the pegmatite outcropping, from surrounding granites, sediment cover, and overburden.Which in many cases within our tenements, is hard to tell from just true colour satellite. The aim is to find tonnage and scale, not mineralsation, but at the same time we won't consider lone targets that don't show a potential mineralisation signature.
Again, specific mineralsation (i.e. spod) is not guaranteed from similar signatures, but it is a positive sign that the geology of the target peg is worth putting a drill hole into.
Before -
After -
What a difference
Circled white is the lovely deep green signature of Andrada's B1 pegmatite, that we now know is rich in spodumene at surface and below. So it would be logical to look for varying brightness of this colour, but over Askari's pegmatite looking intrusions.
Note: We are looking for weaker signals than B1 and C1. This is because during sampling and previous artisinal mining of those pegmatites, fresh rock and minerals have been upheaved and piled onto the surface. This abundance of loose, unweathered, fresh broken rock creates a much stronger texture and larger surface area, increasing the intensity of the signal. This is also shown in numerous small dots of bright green, that are actually small old mine workings with piles of pegmatitic minerals around it. So while Andrada's pegmatites might show an intense green glow, we just need the colour signal.
Now, considering only EPL 8535, we'll take a look at the size of just 3 of the many larger potential ore bodies that fit the regional emplacement trend. I'll use the rough, rounded down dimensions of the outcrop and then assume a conservative 150m down-dip extension for volume, and use the generic specific gravity of 2.7. I believe at least one of these is a target of the current drilling program.
#1 - 1200m x 50m x 150m (24.3Mt).
This one is assuming a strike of outcrops join as the same body continues beneath a layer of overburden. A small mine working is right next to the body that displays a bright green signature. Rock chips from the old mine workings returned up to 1.8% Li2O.
#2 - 1800m x 70m x 150m (51Mt), + extras (74.7Mt total)
This one has some sections that look to be covered by soil, and sediment deposition from a river. Can't be bothered finding the tonnage if all those smaller surrounding pegmatites were to be included lol
#3 - 900m x 60m x 150m (21.9Mt)
~450m strike each, range from 50m to 90m wide, average about 70-80m
The resolution is too low to really identify any of the more medium-small sized outcrops, but there is an abundance of them scattered around the place, as well as lots of larger bodies, but inclusion of all of them would be superfluous to the point of this post. Just from these examples, we can see the scale is impressive. As a sidenote, I believe the down-dip extension of the pegmatite will be deeper than the 150m used (V1/V2 is double that), but I'd rather be conservative.
It's also important to note that because these pegmatites are likely formed from anatexis of surrounding rock, and are not necessarily related to the granites that are nearby, there is no difference in degree of magma complexity/fractionation relative to distance between the body and the granite, as you would find in a typically zoned pegmatite swarm. This means that economic pegmatites are not spatially restricted to any area within the swarm, assuming they're in contact with the Li-rich metasediments they formed from. However, there is evidence that pegmatites emplaced directly within granites are usually more crudely zoned, and not economic, as the granites have more of a REE geochemical profile. Though, there are some huge looking potentially pegmatitic bodies that are emplaced
between the granite and metasediments, in contact with both. Although I am not considering these (due to the unlikely chance of decent lithium concentration), there is the small chance they could be mineralised because of their contact with the metasediments. For example:
With a strike of 1400m and width of 200-400m, the tonnage could be upwards of 100mt. Red/grey granite on the right side, Zerrissene group metasediments on the left. It also follows the northeast sigmoidal host rock trend, which is why I believe it to be potentially pegmatitic, rather than granitic itself. Still, we'll say that mineralisation is unlikely here.
Confidence in the continuation of pegmatite at depth comes from relevant regional examples of already delineated ore bodies (B1/C1, V1/V2 and surrounding). All pegmatites of the Cross Cape-Uis Belt are the same age (~500 Ma), originating from the Damara Orogeny. Almost all pegs follow the same regional extensional deformation and shearing (i.e. the pegmatite melt filled in the gaps when the ground was being lightly pulled apart). This results in belt-wide anastomosing of host rock and pegmatite, with outcrops sometimes coalescing at depth, like at V1/V2.
As seen here from Andrada's PEA, based on historic drilling, the pegmatites proximal to V1/V2 also follow their surface expression consistently down-dip, or join up with others at depth. This is further evidence for below surface continuation of body. In total all these wireframes add up to ~206mt, which is Andrada's JORC exploration target.
The great thing about the pegmatites at Uis is that, for Askari, the deposit scale of tonnage is already great. All that is needed is confirmation of the mineralsation aspect from assay or core visuals. And there are some early good signs nearby indicating we may see mineralisation at depth - see the spodumene in Andrada's core from B1/C1 below, posted on their twitter.
We know that if just one of our larger pegmatites is mineralised, we may quickly have a decently sized (20mt+), shallow deposit. If more than a couple are well-mineralised, then just from looking at one portion of the 8535 tenement, there is end-goal, blue sky potential for 100mt and beyond,
as long as all these assumed factors come together. Is it unlikely? We should assume yes, though it's hard to assign a likelihood to something so intangible to us shareholders. Obviously it is unknown. There is no reason why it
ought to be the case, but there really isn't a reason why it
can't be possible. It is a punt at the end of the day, but one that I am invested in.
Anyway this ramble ended up being much longer than it should be, but I hope it was of benefit to someone. Let's see what the drill bit tells us, that's all that really matters at the end of the day.
Cheers x
Some references and further reading
https://www.sentinel-hub.com/explore/eobrowser/https://link.springer.com/article/10.1007/s00710-018-0569-8https://www.sciencedirect.com/science/article/abs/pii/S0024493717303432?via%3Dihubhttps://pubs.geoscienceworld.org/canmin/article-abstract/57/5/737/573904/Characterization-of-one-of-Africa-s-giants-the-V1https://andradamining.com/company-documents/2022-04%20ATM%20RNS%20Uis%20Phase%202%20PEA%20website.pdfhttps://www.sciencedirect.com/science/article/pii/S0034425721005101?via%3Dihub
