the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Jun 2025
Petrophysics-guided reprocessing of legacy seismic data to improve mineral exploration targeting in the Irish Zn-Pb Orefield
Abstract. The Limerick Syncline, part of the Irish Zn-Pb Orefield in southwest Ireland, represents a geologically complex and relatively underexplored region, despite hosting several significant mineral deposits, e.g., Stonepark and Pallas Green. The mineralogy and stratigraphic setting of the sulphide mineralisation in the Limerick Syncline are generally similar to other Irish-type deposits. However, a thick volcanic sequence overlies and interfingers with the carbonate host rocks, mineralisation and alteration. This setting has posed significant challenges to seismic imaging in the region, despite being a powerful technique for mineral exploration. As a result, the overall structural setting of the area has remained poorly understood. This study presents an optimised seismic processing workflow tailored to these geological complexities and applied to the legacy 2D seismic reflection profile LK-11-02. The workflow integrates newly acquired downhole and laboratory P-wave velocity data with first-arrival travel-time tomography to enhance the accuracy of the velocity model used for post-stack migration. This resulted in better signal recovery and enhanced reflector coherence, in particular, reflection continuity. As a result, imaging of key stratigraphic boundaries and carbonate-volcanic interplay geometries was enhanced, along with clearer reflection amplitude changes associated with known stratigraphic units. Acoustic impedance analysis using laboratory density data enabled a better understanding of the origins of seismic reflectivity and a more confident geological interpretation of the laterally variable lithologies. The migrated section reveals previously unrecognised major structural features in the Limerick Syncline, enhancing our geological understanding of the region. It highlights the potential of applying this workflow to seismic reflection methods, improving its use as a mineral exploration tool in the Irish Zn-Pb Orefield and similar volcanic-influenced regions.
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RC1: 'Comment on egusphere-2025-2512', Samuel Zappalá, 13 Jun 2025
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Dear authors,
the proposed manuscript is well written and the proposed idea interesting and useful, but I have some questions and concerns regarding the innovation of the work and the evaluation of some of the proposed solutions that need to be addressed. You can find them in the following lines together with some smaller suggestions to increase the clarity of the text and of the figures. I hope my comments will help you to improve the clarity of your work.
The abstract, introduction and geology are very well written and to the point. The rest of the text will benefit of some shortening, especially the velocity analysis and the discussion chapters are too long and present details that are not useful with some repetition. The velocity/lithologies comparison appears too detailed considering that is not showing any strong evidence and it is not used on the interpretation or the results, I would remove most of its description (comprised figure 5) and talk about the useful results in just 1-2 phrases.
From the manuscript appears that the main change you applied in the seismic processing is the velocity analysis that follow this scheme: the petrophysical velocity analysis from the cores is validated using the two available sonic logs. The starting model for the tomography is based on the petrophysical velocity analysis from the cores. The stacking velocity model is computed with semblance analysis and corrected according to the tomography model. If I understood correctly, a structured summary of these steps will help the reader to better understand it.
Related questions:
(1) the petrophysical velocity analysis from the cores matches only partly the sonic logs with a big number of outliers (see figure 4b after 300 m of depth or the low measurements coherency in figure 4a), you justify this behavior in the text with understandable reasons, but how do you handle the problem? Or you just ignore it?
(2) have you tested different starting model for the tomography (simpler or more complex)? Did you remove the petrophysical constrains to evaluate if they are really influencing the final tomography results? did you evaluate how much it is sensible to the inaccuracies in the velocities from the core samples?
(3) why did you not use a smoothed version of the tomography model for stacking the data (at least for the shallow depth) instead than computing another velocity model with semblance analysis?
(4) did you try to use constant velocity stack analysis instead than semblance? It is usually effective in hardrock domain but I am not sure what will be better in this mixed case.
(5) it is not clear what velocity model you are using for the migration, is it exactly the same one that you use for the stacking?
You should compare the migrated section resulting from your proposed approach with the one from the newest dataset (dataset 2) and not with the old one (dataset 1) for 2 main reasons: (1) Dataset 2 supposedly shows better results since it has a more recent processing and (2) dataset 2 is the starting data you used for your sections. It would be interesting and useful to compare also the velocity model used from the previous study that you use for comparison.
What you are comparing now (Figures 9a and b) just shows that two different processing returns two different results, nothing new in seismic. The differences between the two processing flows are too many to be able to state that they are due to the proposed velocity approach. They could as well be due to the pre-stack applied processing before your work, or to the different applied migration method and not related at all to the velocity analysis that you performed. So, this point (that I would say is the core of the manuscript) needs to be strengthened.
In the title you say “petrophysics-guided reprocessing” but only the velocity analysis is partially guided from the petrophysical data, everything else is a basic seismic processing flow.
Figure 6 needs some work to be clearer. In general, the figure is too small and is not possible to see what you describe in the text. (1) Boreholes are too thin and they have no frame making difficult to identify them when they overlap with the tomography section. (2) Some of them is plotted behind the tomography and overlap is not visible at all making impossible the comparison. (3) Do you need to plot the whole depth of the boreholes’ velocities? There is nothing to compare them below the tomography model and they do not give any useful information. (4) get rid of the single rays propagating deeper in the model, they are very confusing and not trustable. Once you clean up the figure you can add some zoom in window to highlight the details you are describing in the text. Use this figure to show the quality of your velocity model and how it benefitted from the petrophysics data.
In chapter 4.2 It is not clear how you measure the acoustic impedance, you talk in the text about acoustic impedance related to the different formations but how do you calculate it? Is it computed considering the interfaces for each borehole? Is it an average of all density/velocity values for those formations? Is it between each measured point? Explain it more in detail.
Technical corrections
Line 43 – It should be (Eaton et al., 2010).
Line 48 – It should be (Wilkinson et al., 2015).
Line 52 – what do you mean by “1000 line-km”?
Figure 1 – Very nice figure, just some comment. a) and b) should be bigger and bold, but you can actually remove them and just refer to Ireland map as an inset. You may also add a thin black frame to the all figure, but this is just an aesthetical thing. Modify the caption as “…showing the seismic lines, the drill holes…”. Highlight the seismic line that is used in the manuscript (i.e. write in red LK 11-02 on the figure).
Line 86 – It should be (Chew et al., 2009).
Figure 2 – It is not clear what is the transparent pink that cut through the other formations. Write it in the caption.
Along the manuscript use or the full names for the geological formations or their abbreviations and be consistent both on the text and in the figures/tables, now you are switching between them and this makes it difficult to follow it. If you want decide to use the abbreviations keep their full name only the first time (in the geological chapter).
Instead than table 1, a figure showing the boreholes lithological sections will add useful information and it will be easier to follow.
Line 145 – move the sonic log information on chapter 3.1
Line 158 – “Robertson Geo Mining & Minerals” should be a reference? I cannot see it in the reference list.
Line 177 – seismic data – give more information regarding the acquisition. How heavy the seismic vibrators are? What kind of sweep are they generating? What frequency range is used? What sampling rate is used? What maximum and average offset is recorded? How is the raw data quality?
Line 196 and table 2 - What type of velocity analysis has been performed in dataset 1 and 2?
Figure 4 – make the figure bigger or increase the font size of the text in the figure, it is too small to read. You are again using different names for the stratigraphic units, I would suggest to use the abbreviations.
Line 257 – it should be (Lees and Miller, 1995).
Line 276 – It should be (Sleeman et al., 1999).
Line 355 – I do not see these reflections observed between the CDPs 720 and 1130 and between 1130 and 1335, around 300 to 500 ms that you refer to. There is some discontinue reflection but hard to define them.
Figure 8 – Is it migrated or unmigrated? I cannot see many differences from the one in figure 9b.
Line 356 – I am not so confident about the R3 reflection on the north. It is clearly visible the northern part but it is not easy to follow it after CDP 250. You should move the second arrow closer.
Line 368 – You cannot refer to figure 9c before you refer to figure 9a (or to figure 9 in general).
Figure 9 – In the legend you write the name of the formations to indicate what is a horizon. Write if it is Top or Bottom of the formation.
Line 404 – I do not see any light green horizon in the figure, maybe the light blue.
Line 408 – There is any information about these faults in literature? If yes it will be useful to reference them.
Line 439 – Which dominant frequency are you considering in your calculations?
State clearly the uncertainty of your interpretation, especially for the reflections that are not intersected by the boreholes and for the faults.
Line 466 – it should be (Fusciardi et al., 2003).
Line 572 – de Morton 2015 (1) is not in the text.
Line 646 – You should distinguish the two Slezak 2023 references according to the authors guidelines.
Citation: https://doi.org/10.5194/egusphere-2025-2512-RC1
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