Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology
, Joel B. H. Andersson 1, Martin J. Whitehouse 2, Olof Martinsson 1 and Tobias E. Bauer 1
Rodney Allen
Round 1
Reviewer 1 Report
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Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Reviews of the manuscript #1754823 entitled ‘Energy drive for the Kiruna mining district mineral system(s)’ that was recently submitted to Minerals by Leslie Logan, Joel Andersson, Martin Whitehouse, and other co-authors.
The authors present new zircon U-Pb dating results for igneous rocks from the Kiruna mining district, Sweden, to constrain the ‘energy’ drive for the iron oxide-apatite deposit formation. Most of the samples they dated formed at ~1.88 Ga, with an exception in the Archean. No late orogenic intrusions consistent with previously published geochronological results for mineralization have been constrained. Based on these results, the authors claimed that controls of the late-Cu mineralization/remobilization remain unclear.
In my opinion, the geochronological results are of high quality, the writing is fine, and the main conclusions are conservative. The main drawback is the failure to identify the late orogenic intrusion, which should be of broader interest. Considering the overall quality of the manuscript, I think it fits the journal of minerals and recommend publication after revision.
The main comments are as follows:
(1) Please clarify the ‘energy drive’. The words sound like the intrusions are not providing metals (e.g., Fe) but were just heat sources that drive the circulation of hydrothermal fluids that remobilize the metals from surrounding rocks. Many studies have precluded the remobilization model; the Fe should be from the magmas. I suggest modifying the title.
(2) The authors may want to reconsider the tectonic interpretation they get from the whole-rock geochemistry. Most of the samples are plotted in arc-related settings, which are not consistent with their interpretation that the rocks from during the transitional period from continental margin to within-plate environments.
Some minor comments:
Line 10: What’s the type of Cu mineralization?
Line 19: It is better to compare the dating results previously published and yours.
Line 58-59: Please suggest the type of Cu-Au mineralization here.
Line 184: I do not see the younging sequence to the east. Please clarify.
Line 217-218: I suggest compiling previously published and the new reliable geochronological results in a table.
Line 261-262: Need references here.
Line 353: I suggest that you separate the description of the samples apart. Comparing the difference in zircon grains among the different samples is better.
Line 385-388: The description requires photographs.
Line 403: ‘often truncated by breakage’ to ‘broken’.
Line 417: I would suggest keeping consistent using 2σ.
Line 489-494: I would delete the geochemical interpretation of the tectonic settings. It seems to be dubious and has not been discussed after.
Line 510: It seems you have lost some words here. What’s the meaning of ‘internal 2σ a priori errors’?
Line 515: It seems not ‘always’ here. Sample 005 yielded a very high MSWD value of 5.2.
Line 527: What’s the meaning of ‘texturally correlated’?
Line 529-534: This part should belong to Discussion, not Results here.
Line 591-593: Why this sentence follows here?
Line 619: Readers probably do not know the age of the Kiirunavaara group volcanic rocks. Please compile these results in a table.
Line 674-677: Most samples are located in the arc settings, not in the within-plate environment. I am also not convinced by the geochemical interpretation of the tectonic settings.
Line 686: It is unclear why the sodic alteration bracket the timing of the metasomatism to syn-post magmatic activity.
Line 688-689: The metal can be mobilized by hydrothermal fluids instead of alteration.
Line 692-693: Please clarify the meaning of ‘hydrothermal alteration around the ore deposits’? Is it ‘proximal to’ the ore deposits?
Line 692-695: Are there any differences in the two types of K-alteration?
Line 701-702: You need references to support these rocks formed ‘at the transition from extension to early-D1 compression stage of the tectonic evolution.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is a well written manuscript and should be of interest to geologists interested in the origin of IOA and IOCG ore deposits.
I have made many small suggestions and corrections direct on a microsoft word file in microsoft word review mode.
I have three main comments that I would like the authors to address:
1. In the introduction: The authors should state here that they have made the assumption (?hypothesis) that the energy drive of all these mineral deposits is related to intrusions and that representatives of these intrusions occur at the present surface in the Kiruna region, and hence are available in outcrop for sampling. Discuss also whether there could be alternative “energy drives”, and whether intrusions related to mineralization could be deeper or more ore-distal and therefore missed by the sampling.
2. Also in the introduction: The authors need to provide better evidence or reasoning as to why a study on this relatively small area is considered representative of the whole Kiruna mineral system. Alternatively, you could state that this is a contribution to understanding IOA and IOCG deposits in the Kiruna mining district. It is based on samples from the southern part of the district and results might apply to the district as a whole.
3. In the discussion /conclusions point 2 above should also be made clear: That the samples collected for this study cover just a part of the Kiruna mining district and consequently, the results may not apply completely to all parts of the district.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
