Some musings but definitely nothing more than that. The next two paragraphs below got out of hand.
The depth of the magenta body and its surrounding halo mean UG mining or the base of an open pit following mining of the Regolith/Saprolitic zone if that happens. (Araxa, Mt Weld are both examples where this could be possible but still have enough 'surface' ore to keep them going for a considerable time. Luni IMO suggests that more of these regolithic deposits may be found or even exist already such that UG exploitation may be decades away for Nb, REE, phosphates etc in carbonatites.
[The table in my previous post may give some support for this. The large bulk grades of some deposits probably contain some higher grade core(s)
Tapira and Bonga are possible examples. Seis Lagos is a definite candidate for #2 deposit at the moment (probably bumps Luni way out) which I thought was somewhere near Araxa but is some 3000 Kms away in NW Brazil near Colombia and Venezuela - possibly a more remote and environmentally sensitive area than Luni.]
The base for this
image comes from this 7/3/23 announcement of detailed gravity infill. Some extracts:
“Using the passive seismic data, it is possible to remove some of the effects of the basement topography. This ‘constrains’ the gravity to provide a clearer view of features below. For the first time, we believe we have possibly defined the densest part of the Luni gravity anomaly, providing a refined gravity target at depth.” Gravity data
can be strongly skewed by the depth of cover. Shallow cover over fresh rock can create a gravity high in RAW data. A correction factor is needed to 'level the playing field' and reduce or remove what may be spurious anomalies. Standard procedure for geophysicists BUT depends on the "fudge factors" used. With another 150+ drill holes available depth to fresh rock can be determined more accurately and further analysis of data done.
I doubt this information would alter the 3D inversion model too much.
Raw gravity data comes from a mix of an early 400x400m survey with density increase in December 2022 to 100x50m. [Would be interesting to see the Falcon survey data from ENR's airborne survey of the north part of Luni - Tenement boundaries and logistics of airborne surveys mean the data were collected.]
An updated 3D inversion model has now been created for the Luni area, which has utilised the recently acquired passive seismic data to help constrain the model and remove basement topography effects. This model has defined a gravity anomaly with a rhombic ‘pipe-like’ geometry, which transitions into a more significant and laterally extensive gravity anomaly at depth (‘Luni Deeps’).
This is a gravity anomaly which
may or may not be associated with mineralisation. Simply represents an initial 3D inversion model of the most dense part of the carbonatite intrusion.
The geological models for Araxa (Mt Weld and others?) show multiple phases of intrusion (and alteration) which will all have different chemical and geophysical signatures. The correlation of these two factors can be a useful exploration model (or not). Just differences that need to be tested and see what, if any, economic results drop out.
Put another way, the Luni magenta anomaly is a
model of higher density [with a fingers crossed hope it may be economic].
No really simple way to explain the Gravity inversion process as it does involve - for lay people anyway (me included) - mathematics that are beyond high school level among many other concepts. As with the 'fudge factor' mentioned above for depth corrections, there are assumptions made for generating 3D models. The accuracy of these assumptions
will impact the final result.
Links to two YouTube videos on Inversion. More available...
1
Short and pretty good IMO for the basics .
2
Much longer for those who are interested. More math and something I haven't finished watching yet.
For anyone who has followed exploration plays for a long time the concept of an anomaly (geology, geophysics, geochemical etc) needs to pass the drill test. Feedback from the drilling can be used to modify the model.
From a previous post:
What does the footprint of surface drilling tell us about this model? Since I last played with this the yellow boundary has extended to the SW and probably swings up in the direction of, and beyond, hole L1.If the early inversion model is correct there is a zoned core of higher density material with lighter material (current near surface high Nb zones) which may extend to depth.
Perhaps a revised model is needed?======================================
Seis Lagos to Araxa
====================
Latest sentinel pass of Luni - West Arunta area 9/3/24
Next on 14th.
(20min delay)