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- Jonsson, Erik, 1967-, et al.
(författare)
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Fluorapatite-monazite-allanite relations in the Grängesberg apatite-iron oxide ore district, Bergslagen, Sweden
- 2016
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X. ; 101:7-8, s. 1769-1782
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Tidskriftsartikel (refereegranskat)abstract
- Fluorapatite-monazite-xenotime-allanite mineralogy, petrology, and textures are described for a suite of Kiruna-type apatite-iron oxide ore bodies from the Grangesberg Mining District in the Bergslagen ore province, south central Sweden. Fluorapatite occurs in three main lithological assemblages. These include: (1) the apatite-iron oxide ore bodies, (2) breccias associated with the ore bodies, which contain fragmented fluorapatite crystals, and (3) the variably altered host rocks, which contain sporadic, isolated fluorapatite grains or aggregates that are occasionally associated with magnetite in the silicate mineral matrix. Fluorapatite associated with the ore bodies is often zoned, with the outer rim enriched in Y+REE compared to the inner core. It contains sparse monazite inclusions. In the breccia, fluorapatite is rich in monazite-(Ce) xenotime-(Y) inclusions, especially in its cores, along with reworked, larger monazite grains along fluorapatite and other mineral grain rims. In the host rocks, a small subset of the fluorapatite grains contain monazite xenotime inclusions, while the large majority are devoid of inclusions. Overall, these monazites are relatively poor in Th and U. Allanite-(Ce) is found as inclusions and crack fillings in the fluorapatite from all three assemblage types as well as in the form of independent grains in the surrounding silicate mineral matrix in the host rocks. The apatite-iron oxide ore bodies are proposed to have an igneous, sub-volcanic origin, potentially accompanied by explosive eruptions, which were responsible for the accompanying fluorapatite-rich breccias. Metasomatic alteration of the ore bodies probably began during the later stages of crystallization from residual, magmatically derived HCl- and H2SO4-bearing fluids present along grain boundaries. This was most likely followed by fluid exchange between the ore and its host rocks, both immediately after emplacement of the apatite-iron oxide body, and during subsequent phases of regional metamorphism and deformation.
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| 2. |
- Jonsson, Erik, et al.
(författare)
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Apatite-iron oxide-hosted REE mineralisation at Kopslahyttan, NW Bergslagen, Sweden
- 2015
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Ingår i: Mineral Resources In A Sustainable World. - 9782855550664 ; , s. 781-784
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Konferensbidrag (refereegranskat)abstract
- Of the different types of REE mineralisation known from the Fennoscandian shield, the Palaeoproterozoic apatite-iron oxide ores of Kiruna type represent one resource type with significant potential. Here we describe an REE-rich apatite-magnetite mineralisation from the classic Bergslagen ore province in south central Sweden. Associated with moderately to weakly REE-enriched magnetite mineralisation of banded and vein types, the most apatite-rich occurrence at Kopslahyttan shows REE enrichment that is similar in both magnitude and pattern to other Kiruna type deposits. Yet, the present REE mineralogy is wholly dominated by monazite-(Ce), allanite-(Ce) and LREE-enriched epidote, the latter two often occurring as zoned crystals or aggregates. Minor xenotime-(Y) also occurs, and titanite locally hosts minor Y+HREE. The abundant fluorapatite is suggested to have been an additional, original host for REE, prior to fluid-mediated alteration leading to wholesale remobilisation of REE from the apatite. This remobilisation included dissolution-reprecipitation processes that lead to the nucleation of monazite in fluorapatite, but probably also further transport and precipitation as e.g. allanite/REE-epidote, through reactions with locally common silicates. In addition, we suggest that very coarse grained, variably Th-bearing monazite present in the mineralisation may have been a primary REE phase, in marked contrast to most other deposits of this type.
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| 3. |
- Place, Joachim, et al.
(författare)
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Seismic characterization of the Grangesberg iron deposit and its mining-induced structures, central Sweden
- 2015
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Ingår i: Interpretation. - 2324-8858 .- 2324-8866. ; 3:3, s. SY41-SY56
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Tidskriftsartikel (refereegranskat)abstract
- We have conducted a reflection seismic investigation over the apatite-iron deposit at Grangesberg in central Sweden. At the time of closure in 1989, the mine was operated using the sublevel caving method down to approximately a 650-m depth. This mining technique caused subsidence and generated a network of faults that propagated from excavated zones at depth up to the surface. The Grangesberg deposit is the largest iron oxide mineralization in central Sweden and is planned to be mined again in the coming years. It is therefore imperative to have a better understanding of the ore geometry and the fault network. A reconnaissance survey consisting of two seismic lines with a total length of 3.5 km was carried out to address these issues. The profiles intersect the Grangesberg deposit and open pit, as well as the major mining-induced fracture zone present in this area. A drop-hammer source mounted on a hydraulic truck was used to generate seismic signals; cabled and wireless receivers were used for the data recording. Preprocessing of the data first required the cable-and wirelessrecorded data sets to be merged before stacking all data available at each shot point. Source gathers exhibit reflections from the near surface, probably generated at lithological boundaries hosting the iron mineralization and other geologic structures. Deeper reflections were also observed. The metavolcanic assemblage hosting the mineralization and the anthropogenic fault network were depicted in the stacked sections, bringing in new elements to refine the geologic model of the area. This study also illustrated the ability of reflection seismic methods to delineate mining-induced structures in hard-rock environments. Low-velocity anomalies from the open pit and adjacent structures were depicted in tomographic sections along the two lines, which showed good agreement with known geologic features and the reflection seismic results.
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| 4. |
- Place, Joachim, et al.
(författare)
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Reflection seismic characterization of the Grängesberg iron deposit and its mining-induced structures, central Sweden
- 2014
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Konferensbidrag (refereegranskat)abstract
- Reflection seismic investigation has been conducted on the Grängesberg apatite iron deposit. At the timeof closure in 1989, the mine was operated at about 650 m below the surface. Mining activities might beresumed in the next years, which require better understanding of (1) the ore geometry and (2) the faultnetwork which has developed up to the surface from excavated zones at depth. Two E-W orientedreflection lines with a total length of 3.5 km were acquired. The seismic lines intersect the Grängesbergore body and open pit, as well as several of the mining-induced faults. A weight drop mounted on anhydraulic bobcat truck was used as a seismic source; both cabled and wireless receivers were used for thedata recording. Preprocessing of the data first required the cable- and wireless- recorded datasets to bemerged before stacking all data available at each shot point. The dataset exhibits several shallowreflections which are likely to occur on steep lithologic or tectonic structures. Other deeper reflections arerecorded; careful processing will be carried out in order to preserve such events in final stacked sectionsand help with refining the geological model of the area.
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| 5. |
- Högdahl, Karin, et al.
(författare)
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Reactive monazite and robust zircon growth in diatexitesand leucogranites from a hot, slowly cooled orogen : implicationsfor the Palaeoproterozoic tectonic evolution of the central Fennoscandian Shield, Sweden
- 2012
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 163:1, s. 167-188
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Tidskriftsartikel (refereegranskat)abstract
- Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens, small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites and leucogranites from two Svecofennian domains yields older, coeval and younger U–Pb SIMS and EMP ages than zircon from the same rock. As zircon precipitated during the melt-bearing stage, its U–Pb ages reflect the timing of peak metamorphism, which is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87–1.86 and 1.82–1.80 Ga. The younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred at 1.83–1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening accommodated by major thrusting.
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