the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Jan 2023
Structural framework and timing of the Pahtohavare Cu ± Au deposits, Kiruna mining district, Sweden
Ervin Veress
Joel B. H. Andersson
Olof Martinsson
Tobias E. Bauer
Abstract. As part of a larger mineral systems approach to Cu-bearing mineralization in northern Norrbotten, this study utilizes structural geology to set the classic Pahtohavare Cu ± Au deposits into an up-to-date tectonic framework. The Pahtohavare Cu ± Au deposits, situated only 5 km SW of the Kiirunavaara world-class iron oxide apatite (IOA) deposit, have a dubious timing and their link to IOA formation is not constrained. The study area contains both epigenic Cu ± Au (Pahtohavare) and iron oxide-copper-gold (IOCG, Rakkurijärvi) mineral occurrences which are hosted in bedrock that has been folded and bound by two shear zones trending NE-SW and NW-SE to the east and southwest, respectively. Structural mapping and petrographic investigation of the area reveal an anticlinal, noncylindrical, SE-plunging fold geometry. The cleavage measurements mirror the fold geometry which characterizes the fold as F2 associated to the late phase of the Svecokarelian orogeny. Porphyroclasts with pressure shadows and mylonitic fabrics observed in thin section indicate S0/S1 is a tectonic fabric. The epigenetic Pahtohavare Cu ± Au mineralization sit in brittle-ductile structures that cross cut an earlier foliation and the F2 fold, indicating that the timing of the deposits occurred syn- to post-F2 folding, at least ca. 80 Myr after the Kiirunavaara IOA formation. A 3D model and cross sections of the Pahtohavare-Rakkurijärvi area and a new structural framework of the district are presented and used to suggest that the shear zones bounding the area are likely reactivated early structures that have played a critical role in ore formation in the Kiruna mining district.
-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(2947 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2947 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Leslie Logan et al.
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-1475', Pietari Skyttä, 17 Feb 2023
General comments
The topic is interesting and relevant for understanding the relationships between different deposits types and their regional structural framework, which eventually, will aid in exploration of new deposits. The paper fits well the scope of the journal. There is new data, but it is unclear how representative it is (see P2 and comments to Fig. 3 below). The manuscript is written in a clear and understandable way.
However, the manuscript has several major shortcomings associated with i) defining the key questions, ii) presentation of the data and iii) subsequent structural interpretation (see points P1 to P5 below). As such, the new structural interpretations may not be verified from the presented evidence, and their correlation with regional geology, and further utilization in solving the relationships of the diverse mineralization of the study area are not justified. For the above reasons, the paper needs substantial improvement, and another round of review.
- P1: The study is not motivated as no specific research questions have been stated: The overall global IOA vs. IOCG problematics is described, but the manuscript does not state which are the key questions or hypotheses in applying or testing the concept to the area of the present study.
- P2: The required geological background to justify the research questions (P1) is not provided.
- In particular, the regional alteration-structure-mineralization features are mentioned (lines 22-23. 24-26, and later in Section 2.1), but their mutual relationships and role in formulating the research questions is not explained. Information such as that on lines 302-305 should be included in the introduction.
- The structural description only characterizes bulk shortening directions of the main orogenic phases, but largely lacks information about the structural geometry and the character of the faults (trends, dips, kinematics, timing) and their relationship with alteration and stratigraphy. This information is required to justify the presented crustal evolution models (Fig. 6), as the model heavily leans on the presence of an extensional fault networks and reactivations along the included faults (which is justified as such!)
- P3: The introduction is missing the statement of the main outcome of the work (claim); presently the phrasing is (l. 56) “… investigation was conducted…”, which leaves the work unmotivated. Please state clearly the main outcome of the work and its local and global significance, with respect to both the overall geological understanding and applicability in exploration (if any)
- P4: Presentation of input data: The presented structural interpretation (Figs. 3, 5) is not backed up by the description of the used data, as the spatial location and coverage of the outcrop observations and the drill-hole data is missing. No geophysics or other supporting information is provided either. There is a significant mismatch between that presented on maps and stereograms (see comments for Fig. 3 in particular). The location and largely also the orientation of the field and microscopic photos are missing. Introduction of structural data is not systematic (see e.g. comments regardings lines 156-167)
- P5: Structural interpretation: The lack of spatial data for the used input points (P4) makes it impossible to evaluate the validity of the structural interpretation. There are inconsistencies regarding the geometry of interpreted cross-sections, modelled anticline (antiform) and the orientation distribution of the bedding data. Reasoning behind the presented kinematic interpretations of the shear zones are not given in adequate detail (e.g. lines 191, 268)
Specific and technical comments:
Line 21: Start the introduction with i) the global IOA-IOCG problematics, then proceed to ii) Kiruna deposits and geology, and based on these, develop research questions that can be a) used to improve the understanding about the IOA vs. IOCG in the Kiruna area (relevant questions are stated on lines 305-309, and should be included in the introduction; see P1), and b) solved with the available dataset and methods.
Lines 34-37: These relate to the implementation >>> move to lines 55-59 (original line numbering)
Line 112: change “direction” to “orientation”
Line 113: Please indicate the trend of the conjugate faults.
Line 115: A word appears to be missing in the title
Lines 116-117; 127-128: Please go directly to the point/subject in the first sentence of the section (applies to other sections as well). Now the first sentences are “empty”, which reduces the effectivity of the writing.
Line 118: “Rektor” is not shown on map. Please make sure all the locations cited in the text are visible on the figures.
Line 121: “formation” of what? Please explain!
Line 133: unclear, please rephrase!
Line 142: Include “Kiirunavaara Group” in the legend of Fig. 3.
Line 144,149, 252 + others): “Above the Luossavaara formation are a series….”. This is not good English, please rephrase to e.g. “ The Luossavaara Fm is overlain by ….”
Line 146: Move the reference to the structural character of the unit in a new Section (2.2.2) explaining the local structure
Lines 156-167: Include this in a new section, which should include, in the following order: i) the relevant structural geometry of the area, with particular emphasis on the faults, ii) the known kinematics of the faults, iii) the known ages of the faults (and other deformation)
Line 163: “central Kiruna” >>> please be more specific and refer to a feature annotated on the map
Line 165: “… kinematics…” but along which structure, please explain!
Line 180: “… coeval with syn-volcanic faulting…” >>> Is this 1.90 or 1.89 Ga; please add an age.
Line 191: What is the dip and kinematics of this shear zone? (If known from earlier work)
Line 194: Please explain in adequate detail which is the structural and lithological control. Later on (lines 198-200) there is some reference to hot lithology, but this is too far away from the statement on line 194 to be followed, and the type of structural control is not described. This is highly relevant for this investigation, as your work needs to either confirm or disprove the earlier interpretations, which can then be further used in confirming the working hypotheses (or questions) presented in the introduction.
Line 206: What are these localities? How are the input data distributed with respect to the mapped structure? This is a crucial issue to show as the reliability/uncertainty of the map is largely dependent on the input data; is the fold structure (hinge, both limbs) and all/some of the faults covered by field observations (or drill hole data (see line 218).
Line 211: What is the purpose of the sampling, how many samples were taken in total? Are (all) the samples oriented (many of the sections in Fig. 4 show no orientations)?
Line 218: From where are the drill holes? Show on a map/sections!
Lines 232-233: Remove the first line; this is already told.
Lines 237 + 238: See comments for Fig. 3 regarding the geometry of the antiform. Parasitic folding should follow the overall geometry of the fold, and as such does not explain the scatter in bedding orientations. Please also be more specific in the description: e.g. Do not use “somewhat irregular” but instead describe the style of scatter or clustering on the stereograms, and link that specifically to the limbs and the hinge domain of the fold.
Line 239 + 245: Location of the Pahtohavare open pit + Saarijärvi is not shown on the maps. Please add this information.
Lines 255-259: These belong to the discussion (normally no references allowed in the results). What is non-coaxiality of strain based on? I can’t see the evidence.
Line 263: Where is this shear zone, please indivcate!
Line 264: “mineral lineation … shows a moderate oblique-reverse movement…” >>> not true as it only shows the relationship between the horizontal and vertical slip, NOT the shear sense, which needs to be derived from shear-sense criteria
Line 268: “sinistral oblique-reverse” >>> With respect to what deformation zone? What is the evidence? To me the NNW-SSE carbonate veins in Fig. 3D indicate vein-opening due to dextral slip along the bounding NW-SE fault/shear zone.
Line 271: Where are the tension gashes documented?
Lines 273-274: This is background information which needs to be moved to the Geological setting (see main comment P2b)
Lines 292- …: The discussion is quite unfocused and repetitive with earlier parts of the manuscript as the research questions are not adequately defined (P1)
Lines 276-280…: This can’t be linked to the figures nor evaluated as no spatial reference to the DHs is given in this manuscript (see P4).
Lines 333-335: The relationship between the vein orientations and the derived kinematic interpretations or the kinematically linked faults/shear zones is either vague or not given at all (see also line 268).
Line 341: What actually are the Pahtohavare deposits like? Now the geometric style of the deposits are just very roughly indicated in Fig. 7, whereas other figures only show their location.
Lines 349-358: This information needs to be used in defining the research questions in the introduction, and the essential details needs to be included. For example, earlier considerations about the crustal level vs. the style of deformation need to be included as they are required in correlating the results of this investigation with the regional geology.
Line 384: Add the name of the SZ on the map.
Comments to figures (many of which are linked to general comments P1-P5)
Fig. 2:
- Please provide a cross-section to illustrate the relationship between the stratigraphy and the structure e.g. across the Luossavaara deposit. Annotate the Luossavaara deposit on this map (see Fig. 7)
- What is the character of the ENE-WSW trending fault which separates the Kiruna and Luossavaara deposits? Are the Kiruna and Luossavaara deposits initially part of the same lens/layer, and later split into pieces? Or is the fault syngenetic + later reactivated?
- Legend: Loussavaara Fm >> Luossavaara Fm
Fig. 3:
- Is there some geophysics available to support the map, or is it solely based on mapping data?
- What is the distribution of the structural data?
- Please include the location of the input data points; both surface mapping and drill-hole (DH) data? This could also be presented as a separate “data map”, but preferably included into the existing map; there should be space for it.
- What explains the presence of sub-vertcal NE-SW and ESE-WNW foliation planes? They are not compatible with the distribution of the bedding data (and hence indicative of the presence of bedding-parallel foliation); are they spatially associated with the faults?
- Structural interpretation and correlation between the structural data shown on the map and the stereograms (plots hereafter):
- Very few tectonic symbols (bedding, foliation) are shown on the map. Together with the missing information about the input data used in compiling the map (structural point data, geophysics, level maps from the mine etc…), it is impossible to judge the reliability of the structural interpretation.
- No sub-horizontal bedding data is shown on the map (min dip value on the map is 40), but the plot shows a cluster with ~9 reading with a mean 180-190/30 (dipdir/dip) orientation. These data should locate on the southern limb of the fault, but the bedding dips in Section A-A´ of Fig. 5 show that all the dips on the southern limb of the anticline are steep.
- Should the sub-horizontal cluster of bedding data (see previous point) be including in defining the statistical fold axis (β)? This question relates to understanding the geometry of the anticline:
- The southern limb of the anticline appears to be separated from the hinge and northern limb by a fault. Should the geometry of these domains be treated separately instead plotting a common β -axis for all the bedding data?
- What causes the) is “flat-topped” character of the anticline (Section A-A´ in Fig. 5)? Flattening of the fold hinge along Section A-A´from SE to NW is not justified as shown above.
- Is there sedimentary way-up data? Should the “anticline” be “antiform”?
Fig. 4:
- Orientations and sampling sites are largely missing and should be included.
- The figures are jumping back and forth from topic to another; please restructure to explain the geometries of the structural elements and their (cross-cutting) relationships, then proceed to the evidence about localized deformation (shearing, faulting), including the shear sense criteria
- The character of the highlighted clasts in Fig. d are not discernible from the figure
- Add reference to the orientation of the thin section, and the interpreted sense of shear for figs. e) + f). Moreover, show the spatial context of section by indicating their occurrence on a map / cross-section. Within these, the microphotographs are not useful.
Fig. 5:
- This is a nice 3D-illustration
- The moderately SE-dipping fault in Section A-A´ doesn’t intersect the section in the 3D-model. Please revise /extend.
- What is the character of the discordant bottom contact of the pillow basalt; tectonic or depositional unconformity? Please explain and annotate in the figure accordingly.
Fig. 6:
- This tectonic sketch should cover the same area as Fig. 7 as the latter encloses also the major IOA deposits, which are not presented here. For this reason, this figure is not motivated in providing improved understanding about the relationship between the different deposits types (Pahtohavare & IOAs), which in the beginning of the abstract is stated to be one of the major unknowns of the area, and as such, main aims of the study.
The same scale problem applies to correlation with Fig. 1: Which of the WNW-ESE faults in Fig. 1 corresponds to the northern WNE-ESE fault in Fig. 7?
>>> This is in fact a critical point for understanding the primary (syn-depositional) fault network and their potential control over the deposition of the supracrustal rocks:
- The northern WNW-ESE fault constrains the lateral extent of the Hauki, Matojärvi and Luossavaara FMs so that they occur only to the north of the fault
- By contrast, the depositional basin defined by the two opposingly dipping, WNW-ESE trending normal faults in Fig. 6a would suggest that the above FMs should have been deposited to the south of the northern WNW-ESE fault in Fig. 6. Northerly dip for both WNW-ESES trending normal faults in Fig. 6a could be more compatible with respect to the spatial distribution and thickness of the presented stratigraphic units.
- a): The age should be max. 1.89 Ga = age of the oldest supracrustals
- Please clarify the timing relationship between the 1.87 Ga deformation event (Gig. 6b) and the deposition of the 1.89-1.85 Ga rocks; is there ongoing deposition at the time of this deformation event? In particular one would expect deposition of syn-faulting (1.87Ga) strata into the releasing bend of the N-S strike-slip fault (presently just teh Rakkurijärvi deposit is localized into this site).
- Please replace symbols for the deposits so that the symbol better illustrates the location, shape and orientation of each deposit, as far as possible, in the given scale. This needs to be in line with the information presented in Fig. 7.
Citation: https://doi.org/10.5194/egusphere-2022-1475-RC1 -
AC1: 'Reply on RC1', Leslie Logan, 27 Feb 2023
Dear Dr. Skyttä,
On behalf of all co-authors, I would like to thank you for your comments and review. We will respond to you as soon as we have received comments from the second reviewer and editor regarding the manuscript. Thank you for your consideration.
Kind regards,
Leslie Logan
Citation: https://doi.org/10.5194/egusphere-2022-1475-AC1 - AC3: 'Reply on RC1', Leslie Logan, 22 May 2023
-
RC2: 'Comment on egusphere-2022-1475', Giovanni Musumeci, 05 Apr 2023
General comments
The subject of manuscript is interesting and potentially of wide audience.
However, in the present form the manuscript is not suitable for publication for the following reasons:
- the text is difficult to understand, and some sections are very confusing;
- tectonic structures are poorly described. In particular faults and shear zones are not adequately described;
- the interpretation of the stereonets (fig 3A-C) does not seem exact; It should be revised and discussed in more detail, (see comments in the annotated text, figure 3);
- some structural terms are cited inappropriately or not proven (e.g. mylonitic);
- a clear and exhaustive description of relationships between mineralizations and stuctures is completely lacking;
- several statements in the “Discussion section” seem speculative;
- some figures (Figure 1 - 3) are poorly mentioned in the text and some localities and/or mineralizations are not reported in these figures;
- the photos in figure 4 illustrating the meso and microstructures are of very low quality. This makes comparison with the text very difficult.
Specific comments
Given the subject of the manuscript (structures and mineralization), I suggest that the authors review the organization of the text in the following way and order:
1) detailed description of the tectonic structures (foliations, faults, fractures) at the meso and microscale. Interpretation of structural data should be revised, in particular as regard relations between bedding and cleavage;
2) detailed description of the mineralizations (mineralogical association, host rocks, style of deposit, type of veins, deformation) with high quality meso and microphotos;
3) exhaustive description of the geometric and spatial relationships between mineralizations and tectonic structures;
4) the “Discussion section” should be re-organized on the basis of these data.
This order of presentation of analytical data would allows
(i) the authors a better formulation of the "Discussion section" and
(ii) a clear understanding for the reader
Other comments and technical correction are reported in the annotated text.
- AC4: 'Reply on RC2', Leslie Logan, 22 May 2023
-
AC2: 'Comment on egusphere-2022-1475', Leslie Logan, 14 Apr 2023
Dear Dr. Skyttä and Dr. Musumeci,
Thank you both for your comments on the manuscript. Overall, both reviews indicated a lack of clarity in the organization and language of the manuscript. We will edit the manuscript according to your input to improve the content, flow, and structure of the writing. Additionally, an important point was brought up that the research question was unclear and unmotivated. Below is a revised statement that we will incorporate into the introduction section to improve on this point.
Research Question:
The main purpose of this study is to determine the relative timing of the formation of the Pahtohavare Cu ± Au deposits (which is currently unknown) by a structural investigation of the area and contextualizing the structural results within the district and regional tectonic evolution. This is significant to the local scientific community because there is limited structural information published from the Pahtohavare area (Martinsson et al., 1993), while several studies have been carried out around the Kiirunavaara deposit and the region between Kiruna town and Kurravaara (Vollmer et al., 1984, Wright 1988, Grigull et al., 2018, Andersson et al., 2021). It also is significant to the broader scientific community because there are currently no studies from the Kiruna mining district (which contains the type locality for Kiruna-type IOA deposits) that assess the timing of IOA versus IOCG mineralization within the context of the Svecokarelian orogeny. The results from this work add important data to the debate about the genesis of IOA and IOCG deposits and whether they necessarily form coevally and under the same tectonic conditions. This study has important implications for exploration by providing insight into the structural vectors to Cu ± Au ore in Norrbotten and in districts that host both IOA and IOCG deposits.
In addition, both reviews highlighted shortcomings in the descriptions of the structural features in the area. We will work to improve the presentation of the structural features in Figure 4 by bettering the resolution (where possible), description, georeferencing, and adding more content where needed. Furthermore, it was indicated that the stereonets and map in Figure 3 need more discussion and transparency. For this we have two initial comments. First of all, the authors chose originally to simplify the reporting of the structural measurements on the geologic map to avoid confusion and keep a clean appearance. However, we will work to incorporate more spatial data to the map so that the stereonet data, spatial data, and supporting descriptions can be more easily matched. Secondly, it should be noted that the overall outcrop coverage is quite low, averaging less than ca. 5%. As a result, the representation of bedding in the southwestern limb of the anticline is restricted to the outcrops exposed at the Southern Pahtohavare open pit, while the northeastern limb bedding measurements come from minor tuffitic and chemical sediment interlayers within the Peuravaara formation (composed mainly of basaltic lava). Attached you can find two additional subfigures that will be added to the manuscript. A) An aeromagnetic anomaly map showing the enhanced vertical component (dzdz) of the total magnetic intensity. The shear zones, faults, and ore deposit localities from Fig. 3 have been added for easier correlation between figures. Data source: Geological Survey of Sweden. Data processing by T. Rasmussen, and B) the geologic map from Fig. 3 showing all bedding and cleavage measurement localities, observation points, and outcrop exposure (occasionally boulders, data from the Geological Survey of Sweden) in the Pahtohavare-Rakkurijärvi area.
The authors will continue to work to revise the manuscript according to the reviewer comments. Thank you for your input.
Kind regards,
Leslie Logan
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-1475', Pietari Skyttä, 17 Feb 2023
General comments
The topic is interesting and relevant for understanding the relationships between different deposits types and their regional structural framework, which eventually, will aid in exploration of new deposits. The paper fits well the scope of the journal. There is new data, but it is unclear how representative it is (see P2 and comments to Fig. 3 below). The manuscript is written in a clear and understandable way.
However, the manuscript has several major shortcomings associated with i) defining the key questions, ii) presentation of the data and iii) subsequent structural interpretation (see points P1 to P5 below). As such, the new structural interpretations may not be verified from the presented evidence, and their correlation with regional geology, and further utilization in solving the relationships of the diverse mineralization of the study area are not justified. For the above reasons, the paper needs substantial improvement, and another round of review.
- P1: The study is not motivated as no specific research questions have been stated: The overall global IOA vs. IOCG problematics is described, but the manuscript does not state which are the key questions or hypotheses in applying or testing the concept to the area of the present study.
- P2: The required geological background to justify the research questions (P1) is not provided.
- In particular, the regional alteration-structure-mineralization features are mentioned (lines 22-23. 24-26, and later in Section 2.1), but their mutual relationships and role in formulating the research questions is not explained. Information such as that on lines 302-305 should be included in the introduction.
- The structural description only characterizes bulk shortening directions of the main orogenic phases, but largely lacks information about the structural geometry and the character of the faults (trends, dips, kinematics, timing) and their relationship with alteration and stratigraphy. This information is required to justify the presented crustal evolution models (Fig. 6), as the model heavily leans on the presence of an extensional fault networks and reactivations along the included faults (which is justified as such!)
- P3: The introduction is missing the statement of the main outcome of the work (claim); presently the phrasing is (l. 56) “… investigation was conducted…”, which leaves the work unmotivated. Please state clearly the main outcome of the work and its local and global significance, with respect to both the overall geological understanding and applicability in exploration (if any)
- P4: Presentation of input data: The presented structural interpretation (Figs. 3, 5) is not backed up by the description of the used data, as the spatial location and coverage of the outcrop observations and the drill-hole data is missing. No geophysics or other supporting information is provided either. There is a significant mismatch between that presented on maps and stereograms (see comments for Fig. 3 in particular). The location and largely also the orientation of the field and microscopic photos are missing. Introduction of structural data is not systematic (see e.g. comments regardings lines 156-167)
- P5: Structural interpretation: The lack of spatial data for the used input points (P4) makes it impossible to evaluate the validity of the structural interpretation. There are inconsistencies regarding the geometry of interpreted cross-sections, modelled anticline (antiform) and the orientation distribution of the bedding data. Reasoning behind the presented kinematic interpretations of the shear zones are not given in adequate detail (e.g. lines 191, 268)
Specific and technical comments:
Line 21: Start the introduction with i) the global IOA-IOCG problematics, then proceed to ii) Kiruna deposits and geology, and based on these, develop research questions that can be a) used to improve the understanding about the IOA vs. IOCG in the Kiruna area (relevant questions are stated on lines 305-309, and should be included in the introduction; see P1), and b) solved with the available dataset and methods.
Lines 34-37: These relate to the implementation >>> move to lines 55-59 (original line numbering)
Line 112: change “direction” to “orientation”
Line 113: Please indicate the trend of the conjugate faults.
Line 115: A word appears to be missing in the title
Lines 116-117; 127-128: Please go directly to the point/subject in the first sentence of the section (applies to other sections as well). Now the first sentences are “empty”, which reduces the effectivity of the writing.
Line 118: “Rektor” is not shown on map. Please make sure all the locations cited in the text are visible on the figures.
Line 121: “formation” of what? Please explain!
Line 133: unclear, please rephrase!
Line 142: Include “Kiirunavaara Group” in the legend of Fig. 3.
Line 144,149, 252 + others): “Above the Luossavaara formation are a series….”. This is not good English, please rephrase to e.g. “ The Luossavaara Fm is overlain by ….”
Line 146: Move the reference to the structural character of the unit in a new Section (2.2.2) explaining the local structure
Lines 156-167: Include this in a new section, which should include, in the following order: i) the relevant structural geometry of the area, with particular emphasis on the faults, ii) the known kinematics of the faults, iii) the known ages of the faults (and other deformation)
Line 163: “central Kiruna” >>> please be more specific and refer to a feature annotated on the map
Line 165: “… kinematics…” but along which structure, please explain!
Line 180: “… coeval with syn-volcanic faulting…” >>> Is this 1.90 or 1.89 Ga; please add an age.
Line 191: What is the dip and kinematics of this shear zone? (If known from earlier work)
Line 194: Please explain in adequate detail which is the structural and lithological control. Later on (lines 198-200) there is some reference to hot lithology, but this is too far away from the statement on line 194 to be followed, and the type of structural control is not described. This is highly relevant for this investigation, as your work needs to either confirm or disprove the earlier interpretations, which can then be further used in confirming the working hypotheses (or questions) presented in the introduction.
Line 206: What are these localities? How are the input data distributed with respect to the mapped structure? This is a crucial issue to show as the reliability/uncertainty of the map is largely dependent on the input data; is the fold structure (hinge, both limbs) and all/some of the faults covered by field observations (or drill hole data (see line 218).
Line 211: What is the purpose of the sampling, how many samples were taken in total? Are (all) the samples oriented (many of the sections in Fig. 4 show no orientations)?
Line 218: From where are the drill holes? Show on a map/sections!
Lines 232-233: Remove the first line; this is already told.
Lines 237 + 238: See comments for Fig. 3 regarding the geometry of the antiform. Parasitic folding should follow the overall geometry of the fold, and as such does not explain the scatter in bedding orientations. Please also be more specific in the description: e.g. Do not use “somewhat irregular” but instead describe the style of scatter or clustering on the stereograms, and link that specifically to the limbs and the hinge domain of the fold.
Line 239 + 245: Location of the Pahtohavare open pit + Saarijärvi is not shown on the maps. Please add this information.
Lines 255-259: These belong to the discussion (normally no references allowed in the results). What is non-coaxiality of strain based on? I can’t see the evidence.
Line 263: Where is this shear zone, please indivcate!
Line 264: “mineral lineation … shows a moderate oblique-reverse movement…” >>> not true as it only shows the relationship between the horizontal and vertical slip, NOT the shear sense, which needs to be derived from shear-sense criteria
Line 268: “sinistral oblique-reverse” >>> With respect to what deformation zone? What is the evidence? To me the NNW-SSE carbonate veins in Fig. 3D indicate vein-opening due to dextral slip along the bounding NW-SE fault/shear zone.
Line 271: Where are the tension gashes documented?
Lines 273-274: This is background information which needs to be moved to the Geological setting (see main comment P2b)
Lines 292- …: The discussion is quite unfocused and repetitive with earlier parts of the manuscript as the research questions are not adequately defined (P1)
Lines 276-280…: This can’t be linked to the figures nor evaluated as no spatial reference to the DHs is given in this manuscript (see P4).
Lines 333-335: The relationship between the vein orientations and the derived kinematic interpretations or the kinematically linked faults/shear zones is either vague or not given at all (see also line 268).
Line 341: What actually are the Pahtohavare deposits like? Now the geometric style of the deposits are just very roughly indicated in Fig. 7, whereas other figures only show their location.
Lines 349-358: This information needs to be used in defining the research questions in the introduction, and the essential details needs to be included. For example, earlier considerations about the crustal level vs. the style of deformation need to be included as they are required in correlating the results of this investigation with the regional geology.
Line 384: Add the name of the SZ on the map.
Comments to figures (many of which are linked to general comments P1-P5)
Fig. 2:
- Please provide a cross-section to illustrate the relationship between the stratigraphy and the structure e.g. across the Luossavaara deposit. Annotate the Luossavaara deposit on this map (see Fig. 7)
- What is the character of the ENE-WSW trending fault which separates the Kiruna and Luossavaara deposits? Are the Kiruna and Luossavaara deposits initially part of the same lens/layer, and later split into pieces? Or is the fault syngenetic + later reactivated?
- Legend: Loussavaara Fm >> Luossavaara Fm
Fig. 3:
- Is there some geophysics available to support the map, or is it solely based on mapping data?
- What is the distribution of the structural data?
- Please include the location of the input data points; both surface mapping and drill-hole (DH) data? This could also be presented as a separate “data map”, but preferably included into the existing map; there should be space for it.
- What explains the presence of sub-vertcal NE-SW and ESE-WNW foliation planes? They are not compatible with the distribution of the bedding data (and hence indicative of the presence of bedding-parallel foliation); are they spatially associated with the faults?
- Structural interpretation and correlation between the structural data shown on the map and the stereograms (plots hereafter):
- Very few tectonic symbols (bedding, foliation) are shown on the map. Together with the missing information about the input data used in compiling the map (structural point data, geophysics, level maps from the mine etc…), it is impossible to judge the reliability of the structural interpretation.
- No sub-horizontal bedding data is shown on the map (min dip value on the map is 40), but the plot shows a cluster with ~9 reading with a mean 180-190/30 (dipdir/dip) orientation. These data should locate on the southern limb of the fault, but the bedding dips in Section A-A´ of Fig. 5 show that all the dips on the southern limb of the anticline are steep.
- Should the sub-horizontal cluster of bedding data (see previous point) be including in defining the statistical fold axis (β)? This question relates to understanding the geometry of the anticline:
- The southern limb of the anticline appears to be separated from the hinge and northern limb by a fault. Should the geometry of these domains be treated separately instead plotting a common β -axis for all the bedding data?
- What causes the) is “flat-topped” character of the anticline (Section A-A´ in Fig. 5)? Flattening of the fold hinge along Section A-A´from SE to NW is not justified as shown above.
- Is there sedimentary way-up data? Should the “anticline” be “antiform”?
Fig. 4:
- Orientations and sampling sites are largely missing and should be included.
- The figures are jumping back and forth from topic to another; please restructure to explain the geometries of the structural elements and their (cross-cutting) relationships, then proceed to the evidence about localized deformation (shearing, faulting), including the shear sense criteria
- The character of the highlighted clasts in Fig. d are not discernible from the figure
- Add reference to the orientation of the thin section, and the interpreted sense of shear for figs. e) + f). Moreover, show the spatial context of section by indicating their occurrence on a map / cross-section. Within these, the microphotographs are not useful.
Fig. 5:
- This is a nice 3D-illustration
- The moderately SE-dipping fault in Section A-A´ doesn’t intersect the section in the 3D-model. Please revise /extend.
- What is the character of the discordant bottom contact of the pillow basalt; tectonic or depositional unconformity? Please explain and annotate in the figure accordingly.
Fig. 6:
- This tectonic sketch should cover the same area as Fig. 7 as the latter encloses also the major IOA deposits, which are not presented here. For this reason, this figure is not motivated in providing improved understanding about the relationship between the different deposits types (Pahtohavare & IOAs), which in the beginning of the abstract is stated to be one of the major unknowns of the area, and as such, main aims of the study.
The same scale problem applies to correlation with Fig. 1: Which of the WNW-ESE faults in Fig. 1 corresponds to the northern WNE-ESE fault in Fig. 7?
>>> This is in fact a critical point for understanding the primary (syn-depositional) fault network and their potential control over the deposition of the supracrustal rocks:
- The northern WNW-ESE fault constrains the lateral extent of the Hauki, Matojärvi and Luossavaara FMs so that they occur only to the north of the fault
- By contrast, the depositional basin defined by the two opposingly dipping, WNW-ESE trending normal faults in Fig. 6a would suggest that the above FMs should have been deposited to the south of the northern WNW-ESE fault in Fig. 6. Northerly dip for both WNW-ESES trending normal faults in Fig. 6a could be more compatible with respect to the spatial distribution and thickness of the presented stratigraphic units.
- a): The age should be max. 1.89 Ga = age of the oldest supracrustals
- Please clarify the timing relationship between the 1.87 Ga deformation event (Gig. 6b) and the deposition of the 1.89-1.85 Ga rocks; is there ongoing deposition at the time of this deformation event? In particular one would expect deposition of syn-faulting (1.87Ga) strata into the releasing bend of the N-S strike-slip fault (presently just teh Rakkurijärvi deposit is localized into this site).
- Please replace symbols for the deposits so that the symbol better illustrates the location, shape and orientation of each deposit, as far as possible, in the given scale. This needs to be in line with the information presented in Fig. 7.
Citation: https://doi.org/10.5194/egusphere-2022-1475-RC1 -
AC1: 'Reply on RC1', Leslie Logan, 27 Feb 2023
Dear Dr. Skyttä,
On behalf of all co-authors, I would like to thank you for your comments and review. We will respond to you as soon as we have received comments from the second reviewer and editor regarding the manuscript. Thank you for your consideration.
Kind regards,
Leslie Logan
Citation: https://doi.org/10.5194/egusphere-2022-1475-AC1 - AC3: 'Reply on RC1', Leslie Logan, 22 May 2023
-
RC2: 'Comment on egusphere-2022-1475', Giovanni Musumeci, 05 Apr 2023
General comments
The subject of manuscript is interesting and potentially of wide audience.
However, in the present form the manuscript is not suitable for publication for the following reasons:
- the text is difficult to understand, and some sections are very confusing;
- tectonic structures are poorly described. In particular faults and shear zones are not adequately described;
- the interpretation of the stereonets (fig 3A-C) does not seem exact; It should be revised and discussed in more detail, (see comments in the annotated text, figure 3);
- some structural terms are cited inappropriately or not proven (e.g. mylonitic);
- a clear and exhaustive description of relationships between mineralizations and stuctures is completely lacking;
- several statements in the “Discussion section” seem speculative;
- some figures (Figure 1 - 3) are poorly mentioned in the text and some localities and/or mineralizations are not reported in these figures;
- the photos in figure 4 illustrating the meso and microstructures are of very low quality. This makes comparison with the text very difficult.
Specific comments
Given the subject of the manuscript (structures and mineralization), I suggest that the authors review the organization of the text in the following way and order:
1) detailed description of the tectonic structures (foliations, faults, fractures) at the meso and microscale. Interpretation of structural data should be revised, in particular as regard relations between bedding and cleavage;
2) detailed description of the mineralizations (mineralogical association, host rocks, style of deposit, type of veins, deformation) with high quality meso and microphotos;
3) exhaustive description of the geometric and spatial relationships between mineralizations and tectonic structures;
4) the “Discussion section” should be re-organized on the basis of these data.
This order of presentation of analytical data would allows
(i) the authors a better formulation of the "Discussion section" and
(ii) a clear understanding for the reader
Other comments and technical correction are reported in the annotated text.
- AC4: 'Reply on RC2', Leslie Logan, 22 May 2023
-
AC2: 'Comment on egusphere-2022-1475', Leslie Logan, 14 Apr 2023
Dear Dr. Skyttä and Dr. Musumeci,
Thank you both for your comments on the manuscript. Overall, both reviews indicated a lack of clarity in the organization and language of the manuscript. We will edit the manuscript according to your input to improve the content, flow, and structure of the writing. Additionally, an important point was brought up that the research question was unclear and unmotivated. Below is a revised statement that we will incorporate into the introduction section to improve on this point.
Research Question:
The main purpose of this study is to determine the relative timing of the formation of the Pahtohavare Cu ± Au deposits (which is currently unknown) by a structural investigation of the area and contextualizing the structural results within the district and regional tectonic evolution. This is significant to the local scientific community because there is limited structural information published from the Pahtohavare area (Martinsson et al., 1993), while several studies have been carried out around the Kiirunavaara deposit and the region between Kiruna town and Kurravaara (Vollmer et al., 1984, Wright 1988, Grigull et al., 2018, Andersson et al., 2021). It also is significant to the broader scientific community because there are currently no studies from the Kiruna mining district (which contains the type locality for Kiruna-type IOA deposits) that assess the timing of IOA versus IOCG mineralization within the context of the Svecokarelian orogeny. The results from this work add important data to the debate about the genesis of IOA and IOCG deposits and whether they necessarily form coevally and under the same tectonic conditions. This study has important implications for exploration by providing insight into the structural vectors to Cu ± Au ore in Norrbotten and in districts that host both IOA and IOCG deposits.
In addition, both reviews highlighted shortcomings in the descriptions of the structural features in the area. We will work to improve the presentation of the structural features in Figure 4 by bettering the resolution (where possible), description, georeferencing, and adding more content where needed. Furthermore, it was indicated that the stereonets and map in Figure 3 need more discussion and transparency. For this we have two initial comments. First of all, the authors chose originally to simplify the reporting of the structural measurements on the geologic map to avoid confusion and keep a clean appearance. However, we will work to incorporate more spatial data to the map so that the stereonet data, spatial data, and supporting descriptions can be more easily matched. Secondly, it should be noted that the overall outcrop coverage is quite low, averaging less than ca. 5%. As a result, the representation of bedding in the southwestern limb of the anticline is restricted to the outcrops exposed at the Southern Pahtohavare open pit, while the northeastern limb bedding measurements come from minor tuffitic and chemical sediment interlayers within the Peuravaara formation (composed mainly of basaltic lava). Attached you can find two additional subfigures that will be added to the manuscript. A) An aeromagnetic anomaly map showing the enhanced vertical component (dzdz) of the total magnetic intensity. The shear zones, faults, and ore deposit localities from Fig. 3 have been added for easier correlation between figures. Data source: Geological Survey of Sweden. Data processing by T. Rasmussen, and B) the geologic map from Fig. 3 showing all bedding and cleavage measurement localities, observation points, and outcrop exposure (occasionally boulders, data from the Geological Survey of Sweden) in the Pahtohavare-Rakkurijärvi area.
The authors will continue to work to revise the manuscript according to the reviewer comments. Thank you for your input.
Kind regards,
Leslie Logan
Peer review completion
Journal article(s) based on this preprint
Leslie Logan et al.
Leslie Logan et al.
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 309 | 103 | 23 | 435 | 6 | 5 |
- HTML: 309
- PDF: 103
- XML: 23
- Total: 435
- BibTeX: 6
- EndNote: 5
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2947 KB) - Metadata XML