Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn–Pb–Ag–(Cu)+magnetite deposit, Bergslagen, Sweden

Jansson, Nils; Allen, Rodney L.

doi:10.1016/j.oregeorev.2015.02.018

Cited by 21 publications

(11 citation statements)

References 22 publications

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“…However, the occurrence of large volumes of pyritic massive sulphides and disseminated Cu-Au mineralisation in quartz-rich altered rocks at Falun, the extent of the intrusive magmatic activity around this deposit, and the more extensive evidence for mineralisation associated with the replacement of carbonate rock at Garpenberg (Allen et al, 1996(Allen et al, , 2003Jansson and Allen, 2015) are three components that distinguish these two deposits.…”

Section: Timing Of Hydrothermal Alteration and Mineralisation At The mentioning

confidence: 99%

“…Both the Falun and Garpenberg deposits are considered to be type examples of the so-called 'Falun' (Magnusson, 1950(Magnusson, , 1953 or stratabound volcanic-associated limestone-skarn-hosted (SVALS) deposit type (Allen et al, 1996;Jansson and Allen, 2015), which is one of two major types of polymetallic sulphide deposits in the Bergslagen ore district. However, the occurrence of large volumes of pyritic massive sulphides and disseminated Cu-Au mineralisation in quartz-rich altered rocks at Falun, the extent of the intrusive magmatic activity around this deposit, and the more extensive evidence for mineralisation associated with the replacement of carbonate rock at Garpenberg (Allen et al, 1996(Allen et al, , 2003Jansson and Allen, 2015) are three components that distinguish these two deposits.…”

Section: Timing Of Hydrothermal Alteration and Mineralisation At The mentioning

confidence: 99%

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Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Kampmann

Stephens

Ripa

et al. 2016

Precambrian Research

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a b s t r a c t U-Th-Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207 Pb/ 206 Pb weighted average age of 1894 ± 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207 Pb/ 206 Pb weighted average age of 1891 ± 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 ± 3, 1894 ± 2 Ma and 1893 ± 3 Ma. The felsic sub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks. Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207 Pb/ 206 Pb weighted average ages of 1831 ± 8 Ma and 1822 ± 5 Ma, respectively. These ages fall well within the temporal range of a younger 1.84-1.81 Ga (M 2 ) metamorphic episode during the 2.0-1.8 Ga Svecokarelian orogeny, with the older episode (M 1 ) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M 2 event in the north-western part of this unit, leading to a complete resetting of the U-Th-Pb isotope system in monazite.

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Section: Timing Of Hydrothermal Alteration and Mineralisation At The mentioning

confidence: 99%

Section: Timing Of Hydrothermal Alteration and Mineralisation At The mentioning

confidence: 99%

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Kampmann

Stephens

Ripa

et al. 2016

Precambrian Research

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“…Textural relations ( Figures 5, 8 and 9) indicate that pyroxenes were replaced by mixtures of hydrous silicates, carbonates, quartz and magnetite, reflecting an increase in water activity and oxygen and/or CO2 fugacities: 5 CaFeSi2O6 (hedenbergite) + H2O + 3 CO2 (g) ↔ Ca2Fe5Si8O22(OH)2 (ferroactinolite) + 3 CaCO3 (calcite)+ 2 SiO2 (quartz) associated with the Sasa deposit are a product of the calc-alkaline to shoshonitic post-collisional magmatism that affected the Balkan Peninsula during the Oligocene-Miocene period [21,23,[38][39][40][41]53], resulting in the formation of numerous magmatic-hydrothermal ore deposits along the Vardar Zone and the Serbo-Macedonian Massif (Figure 1; [25][26][27][28][29][30][31][32][33][34][35]54]). The paragenetic sequence (Figure 4) indicates that, during its formation, the Sasa Pb-Zn-Ag deposit underwent three main stages similar to other known skarn deposits worldwide: (1) a stage of isochemical metamorphism; (2) an anhydrous prograde stage and (3) a retrograde/hydrothermal stage [1,55,56]. As the deposit is hosted by a highly metamorphosed terrain, it is difficult to distinguish the regional metamorphic signature from the metamorphism associated with the emplacement of Tertiary magmatic bodies.…”

Section: Discussionmentioning

confidence: 90%

The Role of Magmatic and Hydrothermal Fluids in the Formation of the Sasa Pb-Zn-Ag Skarn Deposit, Republic of Macedonia

Palinkaš

Peltekovski²,

Tasev

et al. 2018

Geosciences

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The Sasa Pb-Zn-Ag deposit belongs to the group of distal base metal skarn deposits. The deposit is located within the Serbo-Macedonian massif, a metamorphosed crystalline terrain of Precambrian to Paleozoic age. The mineralization, hosted by Paleozoic marbles, shows a strong lithological control. It is spatially and temporally associated with the calc-alkaline to shoshonitic post-collisional magmatism that affected the Balkan Peninsula during the Oligocene–Miocene time period and resulted in the formation of numerous magmatic–hydrothermal ore deposits. The mineralization at the Sasa Pb-Zn-Ag deposit shows many distinctive features typical for base metal skarn deposits including: (1) a carbonate lithology as the main immediate host of the mineralization; (2) a close spatial relation between the mineralization and magmatic bodies of an intermediate composition; (3) a presence of the prograde anhydrous Ca-Fe-Mg-Mn-silicate and the retrograde hydrous Ca-Fe-Mg-Mn ± Al-silicate mineral assemblages; (4) a deposition of base metal sulfides, predominately galena and sphalerite, during the hydrothermal stage; and (5) a post-ore stage characterized by the deposition of a large quantity of carbonates. The relatively simple, pyroxene-dominated, prograde mineralization at the Sasa Pb-Zn-Ag skarn deposit represents a product of the infiltration-driven metasomatism which resulted from an interaction of magmatic fluids with the host marble. The prograde stage occurred under conditions of a low water activity, low oxygen, sulfur and CO2 fugacities and a high K+/H+ molar ratio. The minimum pressure–temperature (P–T) conditions were estimated at 30 MPa and 405 °C. Mineralizing fluids were moderately saline and low density Ca-Na-chloride bearing aqueous solutions. The transition from the prograde to the retrograde stage was triggered by cooling of the system below 400 °C and the resulting ductile-to-brittle transition. The brittle conditions promoted reactivation of old (pre-Tertiary) faults and allowed progressive infiltration of ground waters and therefore increased the water activity and oxygen fugacity. At the same time, the lithostatic to hydrostatic transition decreased the pressure and enabled a more efficient degassing of magmatic volatiles. The progressive contribution of magmatic CO2 has been recognized from the retrograde mineral paragenesis as well as from the isotopic composition of associated carbonates. The retrograde mineral assemblages, represented by amphiboles, epidote, chlorites, magnetite, pyrrhotite, quartz and carbonates, reflect conditions of high water activity, high oxygen and CO2 fugacities, a gradual increase in the sulfur fugacity and a low K+/H+ molar ratio. Infiltration fluids carried MgCl2 and had a slightly higher salinity compared to the prograde fluids. The maximum formation conditions for the retrograde stage are set at 375 °C and 200 MPa. The deposition of ore minerals, predominantly galena and sphalerite, occurred during the hydrothermal phase under a diminishing influence of magmatic CO2. The mixing of ore-bearing, Mg-Na-chloride or Fe2+-chloride, aqueous solutions with cold and diluted ground waters is the most plausible reason for the destabilization of metal–chloride complexes. However, neutralization of relatively acidic ore-bearing fluids during the interaction with the host lithology could have significantly contributed to the deposition. The post-ore, carbonate-dominated mineralization was deposited from diluted Ca-Na-Cl-bearing fluids of a near-neutral pH composition. The corresponding depositional temperature is estimated at below 300 °C.

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“…The Blötberget mining district forms part of the Svecokarelian orogen in the Fennoscandian Shield (Jansson and Allen, 2015). The geological map, which has been published by SGU shown in Figure 2.1 is at scale of 1:50,000 and illustrates the main geologic features and bedrock types formed by the paleoproterozoic volcano-sedimentary and intrusive rocks formed in extensional contenental margin (Allen et al, 1996;Place et al, 2015).…”

Section: Geology Of the Blötberget Mining Areamentioning

confidence: 99%

“…Near the mineralization these host rocks constitute phyllosilicate and amphibole rich assemblages as a result of hydrothermal alteration (Jonsson et al, 2011;Place et al, 2015). The host rocks also comprise lapatite formation i.e., mainly felsic to intermediate regionally metamorphosed (Jansson and Allen, 2015;Jonsson et al, 2016).…”

Section: Geology Of the Blötberget Mining Areamentioning

confidence: 99%

Gravity and magnetic survey, modeling and interpretation in the Blötberget iron-oxide mining area of central Sweden

Yehuwalashet

Malehmir

2018

SEG Technical Program Expanded Abstracts 2018

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Gravity and Magnetic Survey, Modelling and Interpretation in the Blötberget Iron-Oxide Mining Area, Bergslagen, Sweden Ezra YehuwalashetThe Blötberget mining area, the focus of this MSc project, is located about 230 km northwest of Stockholm and 12 km southwest of the city of Ludvika (central Sweden). The mining area has been known since 1600 for its various types of mineralization particularly iron-oxide deposits (magnetite and hematite) with the mining commenced in 1944. Previous geoscientific research in the area provides detailed information about lithological variations and structure of the bedrock near the surface. However, knowledge of the depth extent of the mineral deposits and their host rocks is limited. To shed lights on these issues and support deep mineral exploration potential in the study area, within the recently launched StartGeoDelineation project, new ground gravity data, 180 data points on average 150 m apart, were collected during two field campaigns in 2015 and 2016. Aeromagnetic data were obtained from the Geological Survey of Sweden (SGU) to complement the ground gravity measurement interpretations and modelling. After a careful inspection of the field gravity data, they were reduced to complete Bouguer anomaly with a maximum error estimate of about 0.6 mGal due to uncertainty in the instrumental drift, slab density, geodetic surveying, diurnal variations and terrain (or topography) correction. The Bouguer gravity data after separation of regional field (second order polynomial at the end was used) were used (~ 8 mGal range) for interpretation and 3D inverse modelling. Clear anomalous zones are noticeable in the gravity data particularly due to mineralization and a major boundary separating a gravity low from gravity high in the southern part of the study area likely representing a fault boundary separating two different lithological units. In my study, both forward and inverse modelling using rudimentary objects/shapes and voxel-type (mesh) approach were carried out. Effect of initial and reference models were tested on both gravity and magnetic datasets. While the constrained models have still significant ambiguity, they help to suggest structural control on the location of mineralization and may allow estimating an excess tonnage due to the presence of mineralization in the study area. Due to access limitations (e.g., unable to measure on the water-filled pit) the gravity model is sensitive to the measuring positions and constraints using known shape of mineralization was not at the end successful to overcome this. Collecting more gravity data on the target area and repeated test of 3D inversion by adjusting the inversion parameters might help to improve the final result.

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Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn–Pb–Ag–(Cu)+magnetite deposit, Bergslagen, Sweden

Cited by 21 publications

References 22 publications

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

The Role of Magmatic and Hydrothermal Fluids in the Formation of the Sasa Pb-Zn-Ag Skarn Deposit, Republic of Macedonia

Gravity and magnetic survey, modeling and interpretation in the Blötberget iron-oxide mining area of central Sweden

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