Figure 6b. Norseman Higginsville local and EagleEye magnetics showing structural and stratigraphic correlation.
This figure shows;
A. Local magnetics survey on the left which has been enhanced by EagleEye to define stratigraphy and lithology.
B. The central image is the EagleEye image from the Australia wide magnetics defining the high magnetics units which define the broad structure and stratigraphy.
C. The right image has been designed to define later more brittle structure and stratigraphy in greater detail.
The first point to note is that the broad outline of the Greenstone enclave within the granite has the same shape in all three plans which confirms EagleEye’s structural validity at this broad scale.
In general the Australia wide EagleEye plans define less of the stratigraphy and more through-going magnetic structures. This is to be expected as the wider survey will define the deeper magnetics and the EagleEye process includes these in its search parameters. An example of this tying together strong structures in EagleEye is seen by the strong magnetic, arcuate, NNE structure running from the centre at the bottom to the Centre right at the top. This arc is disrupted by the strong magnetics accompanying the Jimberlana dyke in the centre right.
Of interest this arc is on the outer ring of the Cauden Giant Ring Structure centered south of Southern Cross https://www.geotreks.com.au/work/giant-ring-structures/yc-3-geology-gravity-mineralisation-exploration-targeting-of-yilgarn-370km-cauden-giant-ring-structure-one-worlds-largest-meteorite-impacts/ There are some good exploration targeting areas on this plan some of which are being currently explored. What about the ones that aren’t ?!
This arc also lines up with the Eastern rim of the Ring F to the west of Norseman https://www.geotreks.com.au/work/giant-ring-structures/yn-1-norseman-an-unreported-700-km-diameter-giant-ring-structure-real-or-imaginary-impact-structure-or-superplume/. I have hypothesised that these rings are crucial for the localisation of huge volumes of outer core fluids at the surface and so they are critical for Exploration Targeting for all minerals.
This paper I wrote in 2017 gives a much better description of the topic https://www.dropbox.com/s/3x3txdvikp69c4u/YN%20%231%20Norseman%20GRS%20in%20radiometrics.docx
The EagleEye method was a bit less developed then 🙂 ! This work was done during my stint at my aborted UWA PhD and was a major source of discontent with certain individuals there – hence no PhD 🙁 .
This arcuate structure is not seen clearly in the local magnetics because the structure gets faint in the granites. However along the trace of this structure there is an increase in dark areas in the granite in the local survey.
Also the NS, main line of lode of Norseman can be seen to continue nearly unbroken right through to Higginsville under Lake Cowen. This is definitely not obvious on the local magnetics or any other plan I’m aware of.
This suggests that the EagleEye image gives a clearer definition of through-going lode structures than the local magnetics and is thus better for exploration targeting?? One could follow this line under the lake quite easily on EagleEye plan!
The EW structures are seen in all three images. however the northern one, south of Higginsville, is much stronger and disrupted in the Right EagleEye plan. What does this mean for exploration targeting. I’d be looking at its intersection with the NS lode line tomorrow!!
This figure has the same two EagleEye plans showing the stratigraphy/high magnetics on left and detailed stratigraphy/ structure in the centre. These can be compared with the geology plan on the right which is at the same scale.
The NS ‘line of lode’ can be clearly seen and the arcuate stratigraphy represented by the dark blue arc on the geology can be faintly observed on the EagleEye left plan. This will become clearer in the next post.
The geological trends to the east of Norseman continue for about 10 km into the granite. What does this mean?
At Mt Magnet this same structural anomalism into the granites was observed westward and up there the greenstone structural trend could be observed in the gneiss which was insitu replaced. Mafics were dark biotitic, and felsics were light granitic gneiss. Does this occur at Norseman? Bit of field mapping required? Lots of good ore in granite!
This figure shows the local magnetics on left and the local magnetics with an enlargement of the EagleEye Magnetics superimposed on the right.
The local magnetics has been interpreted for stratigraphic boundaries and linears. These form lines were then overlain on the now more detailed EagleEye magnetics and compared.
Observations –
The EagleEye plan is enhanced from Australia-wide, fuzzy, colour contour magnetics on which nothing resembling structural geology can be observed. That plan has been enlarged about 100 times!
When one traces the structures that are the same around the margins of the overlay it is seen that most of the structures lead into each other. This good correlation verifies the EagleEye structural geology.
The blue area in the centre of both plans correlate well.
The western margin of the Greenstone/granite boundary on the left is almost identical.
The granite east of Norseman is very similar, with the exception of the high magnetic zones within it in the EagleEye plan previously mentioned.
The broad EW Jimberlana Dyke magnetic trend is almost identical.
The strong WNW trends are similar, but sharper and more disjointed in the EagleEye plan.
The NNE linear trends correlate but the flat S trend through the centre of, and following the main ore-field, is hardly observed in the local magnetics. This is an important discovery as it throws light on another ore defining structure not recognised at Norseman – or at least not reported on. This has Exploration Targeting implications right across the Yilgarn!
I could wax lyrical all day but that is enough for now 🙂 . We’ll look more closely in the immediate Norseman area next. Will this give better detail again??
Cheers and happy structural analysing!
Bob
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