Seismic depth imaging of iron‐oxide deposits and their host rocks in the Ludvika mining area of central Sweden

Abstract Iron oxide copper-gold (IOCG) deposits form in spatial and genetic relation to hydrothermal iron oxide-alkali-calcic-hydrolytic alteration and thus show a mappable zonation of mineral assemblages toward the orebody. The mineral zonation of a breccia matrix-hosted orebody is efficiently mapped by regularly spaced samples analyzed by the scanning electron microscopy-integrated mineral analyzer technique. The method results in quantitative estimates of the mineralogy and allows the reliable recognition of characteristic alteration as well as mineralization-related mineral assemblages from detailed mineral maps. The Ernest Henry deposit is located in the Cloncurry district of Queensland and is one of Australia’s significant IOCG deposits. It is known for its association of K-feldspar altered clasts with iron oxides and chalcopyrite in the breccia matrix. Our mineral mapping approach shows that the hydrothermal alteration resulted in a characteristic zonation of minerals radiating outward from the pipe-shaped orebody. The mineral zonation is the result of a sequence of sodic alteration followed by potassic alteration, brecciation, and, finally, by hydrolytic (acid) alteration. The hydrolytic alteration primarily affected the breccia matrix and was related to economic mineralization. Alteration halos of individual minerals such as pyrite and apatite extend dozens to hundreds of meters beyond the limits of the orebody into the host rocks. Likewise, the Fe-Mg ratio in hydrothermal chlorites changes systematically with respect to their distance from the orebody. Geochemical data obtained from portable X-ray fluorescence (p-XRF) and petrophysical data acquired from a magnetic susceptibility meter and a gamma-ray spectrometer support the mineralogical data and help to accurately identify mineral halos in rocks surrounding the ore zone. Specifically, the combination of mineralogical data with multielement data such as P, Mn, As, P, and U obtained from p-XRF and positive U anomalies from radiometric measurements has potential to direct an exploration program toward higher Cu-Au grades.

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Deep reflection seismic imaging of iron‐oxide deposits in the Ludvika mining area of central Sweden

Geophysical Prospecting ◽

10.1111/1365-2478.12855 ◽

2019 ◽

Vol 68 (1) ◽

pp. 7-23 ◽

Cited By ~ 8

Author(s):

Magdalena Markovic ◽

Georgiana Maries ◽

Alireza Malehmir ◽

Julius Ketelhodt ◽

Emma Bäckström ◽

...

Keyword(s):

Iron Oxide ◽

Seismic Imaging ◽

Mining Area ◽

Reflection Seismic

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Mineralization, alteration and geochemical characteristics of host rocks in the Rangraz iron oxide-copper mineralization area, north Saveh, central part of Urumieh–Dokhtar magmatic arc

Iranian Journal of Crystallography and Mineralogy ◽

10.29252/ijcm.27.4.821 ◽

2019 ◽

Vol 27 (4) ◽

pp. 821-838

Author(s):

Somayeh Dolatshahi ◽

hasan Zamanian ◽

Alireza Karimzadeh Somarin ◽

◽

...

Keyword(s):

Iron Oxide ◽

Geochemical Characteristics ◽

Magmatic Arc ◽

Copper Mineralization ◽

Area North ◽

Host Rocks

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3D reflection seismic imaging of the iron-oxide deposits in the Ludvika mining area (Sweden) using a focusing pre-stack depth migration approach

10.5194/se-2021-101 ◽

2021 ◽

Author(s):

Felix Hloušek ◽

Michal Malinowski ◽

Lena Bräunig ◽

Stefan Buske ◽

Alireza Malehmir ◽

...

Keyword(s):

Iron Oxide ◽

Seismic Imaging ◽

Mine Planning ◽

Seismic Exploration ◽

Depth Imaging ◽

Mining Site ◽

Depth Migration ◽

Reflection Seismic ◽

Imaging Results

Abstract. We present the pre-stack depth imaging results for a case study of 3D reflection seismic exploration at the Blötberget iron-oxide mining site belonging to the Bergslagen mineral district in central Sweden. The goal of this case study is to directly image the ore-bearing units and to map its possible extension down to greater depths than known from existing boreholes. Therefore, we applied a tailored pre-processing workflow as well as two different seismic imaging approaches, Kirchhoff pre-stack depth migration and Fresnel Volume Migration (FVM). Both imaging techniques deliver a well resolved 3D image of the deposit and its host rock, where the FVM image yields a significantly better image quality compared to the KPSDM image. We were able to unravel distinct reflection horizons, which are linked to known mineralisation and provide insights on lateral and depth extent of the deposits beyond their known extension from borehole data. A comparison of the known mineralization and the image show a good agreement of the position and the shape of the imaged reflectors caused by the mineralization. Furthermore, the images show a reflector, which is interpreted to be a fault intersecting the mineralisation and which can be linked to the surface geology. The depth imaging results can serve as the basis for further investigations, drillings and follow-up mine planning at the Blötberget mining site.

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Absence of hydrothermal oxygen isotope variations in host rocks supports magmatic origin of the giant Grängesberg iron oxide–apatite (IOA) deposit, Central Sweden

International Journal of Earth Sciences ◽

10.1007/s00531-021-02122-9 ◽

2021 ◽

Author(s):

Franz Weis ◽

Valentin R. Troll ◽

Erik Jonsson ◽

Karin Högdahl ◽

Chris Harris ◽

...

Keyword(s):

Iron Oxide ◽

Oxygen Isotope ◽

Large Scale ◽

Country Rock ◽

Isotope Composition ◽

Northwestern Part ◽

Magmatic Origin ◽

Ore Body ◽

Two Samples ◽

Host Rocks

AbstractThe origin of Kiruna-type iron oxide–apatite ores is controversial, and debate presently centres on a ‘magmatic’ versus a ‘hydrothermal’ mode of formation. To complement recent investigations on the Grängesberg iron oxide–apatite ore deposit in the northwestern part of the Palaeoproterozoic Bergslagen ore province in central Sweden, we investigated the oxygen isotope composition of the host rocks of this large iron oxide–apatite ore body. As the metavolcanic and metagranitoid country rocks around the Grängesberg ore body either pre-date or are coeval with ore formation, they would be expected to record an extensive isotopic imprint if the ore body had formed by large-scale hydrothermal processes involving an externally sourced fluid. A direct magmatic formation process, in turn, would have produced localized alteration only, concentrated on the immediate vicinity of the ore body. Here, we test these two hypotheses by assessing the oxygen isotope variations in the host rocks around the main Grängesberg iron oxide–apatite ore body. We analysed oxygen isotopes in quartz from metavolcanic (n = 17) and metagranitoid host rocks (n = 14) from the vicinity of the ore body, and up to 2 km distance along and across the strike of the ore body. Remarkably, we find no significant variation in δ18O values with distance from the ore body, or any deviations in country rock δ18O from common magmatic and/or regional values. Only two samples show shifts to values more negative than the common magmatic range, indicating highly localized hydrothermal overprint only. As a large-scale, low-temperature hydrothermal origin of the ore body through voluminous fluid percolation would be expected to have left a distinct imprint on the oxygen isotope values of the country rocks, our results are more consistent with an ortho-magmatic origin for the Grängesberg iron oxide–apatite ore.

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