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Temporal and genetical constraints of the Cu-Co Vena-Dampetorp deposit, Bergslagen, Sweden

Leopardi, Dino LU (2020) In Dissertations in Geology at Lund University GEOR02 20192
Department of Geology
Abstract
The Bergslagen Province is known for containing major Zn-Pb-Ag and Zn-Pb-Cu-Ag sulphide mineralizations with associated iron-oxide skarns and a lot of research have focused on understanding them. However, Cu-Co deposits like the Vena-Dampetorp deposit have received less attention. The Vena-Dampetorp deposit is a disseminated and vein Cu-Co mineralization hosted primarily in a 1.89 Ga rhyolitic to dacitic volcanoclastic sequence with thin interbedded calcareous horizons and associated mafic and granodioritic intrusions. Two stages of deformation and regional high-temperature and low-pressure metamorphism affected this shallow subaqueous back-arc assemblage. The aim of this study is to constrain the spatial, temporal and genetical... (More)
The Bergslagen Province is known for containing major Zn-Pb-Ag and Zn-Pb-Cu-Ag sulphide mineralizations with associated iron-oxide skarns and a lot of research have focused on understanding them. However, Cu-Co deposits like the Vena-Dampetorp deposit have received less attention. The Vena-Dampetorp deposit is a disseminated and vein Cu-Co mineralization hosted primarily in a 1.89 Ga rhyolitic to dacitic volcanoclastic sequence with thin interbedded calcareous horizons and associated mafic and granodioritic intrusions. Two stages of deformation and regional high-temperature and low-pressure metamorphism affected this shallow subaqueous back-arc assemblage. The aim of this study is to constrain the spatial, temporal and genetical relationships of ore minerals and the effects of metamorphism on the host rocks and their assemblages. Building on existing work, it aims to explore the origin and processes responsible for the concentration of Co and genesis of Cu-Co deposits in the Bergslagen area.

Textural relationships and geochemical data of drill cores show that the mineralization is zoned from pyrite-pyrrhotite zones to chalcopyrite-sphalerite richer zones, with localized Cu-Co areas. At the deposit scale, Co rich zones occur in the SE while Pb-Sb enriched zones concentrate in the NW. The U-Pb dating of metamorphic titanite with LA-ICP-MS gave a mean concordant 207Pb/206Pb date of 1882±16 Ma for a skarn sample. This age is interpreted as the onset of regional metamorphism. In contrast, the lower intercept age of 1882±16 Ma obtained for titanite in one metavolcanic sample could either represent the onset of metamorphism or a cooling age. Sulphide thermobarometric estimates, EDS-SEM mapping, and the presence of sulphosalt-rich associations together with deformational features in the ore minerals, indicate that the Fe-oxide mineralization at the Vena-Dampetorp deposit occurred as a Bastnäs-type deposit due to the interaction of magmatic fluid with carbonate horizons. In comparison, the sulphide Cu-Co-rich mineralization was deposited in a sub-seafloor hydrothermal exhalative system, where the higher Cu-Co concentrations are related to high temperature stringers near the feeder zone. Later mechanical, hydrothermal and melt-assisted re-mobilization during metamorphism concentrated certain metals like Co in secondary veins and assemblages. (Less)
Abstract (Swedish)
Bergslagens malmprovins är känd för att innehålla stora Zn-Pb-Ag- och Zn-Pb-Cu-Ag-sulfidförekomster med tillhörande järnoxidskarn och många studier har fokuserat på att förstå dessa förekomster. Cu-Co-förekomster som Vena-Dampetorp-förekomsten har emellertid fått mindre uppmärksamhet. Vena-Dampetorp-förekomsten är en disseminerad och åderstödd Cu-Co-mineralisering som förekommer i en 1,89 Ga ryolitisk till dacitisk vulkaniklastisk sekvens med tunna inbäddade kalkhaltiga horisonter och tillhörande mafiska och granodioritiska intrusioner. Två deformationsstadier med regional högtemperatur- och lågtrycksmetamorfos har påverkat denna sekvens som avsattes i grund, subakvatisk miljö i en sedimentär bassäng i en öbågemiljö. Syftet med denna... (More)
Bergslagens malmprovins är känd för att innehålla stora Zn-Pb-Ag- och Zn-Pb-Cu-Ag-sulfidförekomster med tillhörande järnoxidskarn och många studier har fokuserat på att förstå dessa förekomster. Cu-Co-förekomster som Vena-Dampetorp-förekomsten har emellertid fått mindre uppmärksamhet. Vena-Dampetorp-förekomsten är en disseminerad och åderstödd Cu-Co-mineralisering som förekommer i en 1,89 Ga ryolitisk till dacitisk vulkaniklastisk sekvens med tunna inbäddade kalkhaltiga horisonter och tillhörande mafiska och granodioritiska intrusioner. Två deformationsstadier med regional högtemperatur- och lågtrycksmetamorfos har påverkat denna sekvens som avsattes i grund, subakvatisk miljö i en sedimentär bassäng i en öbågemiljö. Syftet med denna studie är att begränsa de rumsliga, temporala och genetiska förhållandena mellan malmmineral och effekterna av metamorfos på värdbergarterna och deras sammansättningar. Utifrån befintligt Målet är att utifrån befintlig forskning utforska ursprung och processer som givit upphov till koncentrationen av Co och uppkomsten av Cu-Co-avlagringar i Bergslagen.

Texturella förhållanden och geokemiska data från borrkärnor visar att mineraliseringen är zonerad från pyrit-magnetkiszoner till kopparkis-zinkblände-rikare zoner, med lokala Cu-Co-områden. På avlagringskala förekommer Co-rika zoner i SO medan Pb-Sb-anrikade zoner koncentreras i NV. U-Pb-datering av metamorf titanit med LA-ICP-MS gav ett 207Pb / 206Pb medelvärde datum av1882 ± 16 Ma för ett skarnprov. Denna ålder tolkas som början av den regionala metamorfosen. Däremot kan den lägre avlyssningsåldern 1882 ± 16 Ma erhållen för titanit i ett metavulkaniskt prov antingen representera början av metamorfosen eller en kylningsålder. Sulfidtermobarometriska uppskattningar, EDS-SEM-kartläggning och närvaron av sulfosalt rika föreningar tillsammans med deformationstexturer i malmmineralen indikerar att Fe-oxidmineraliseringen vid Vena-Dampetorp bildades som en Bastnäsavlagring på grund av interaktionen mellan magmatiska/hydrotermala vätskor och karbonathorisonter. Som jämförelse avsattes den sulfidiska Cu-Co-rika mineraliseringen i ett hydrotermalt system på havsbotten, där de högre Cu-Co-koncentrationerna är relaterade till högtemperatursträngar nära matarzonen. Senare mekanisk, hydrotermal och smältmedierad återmobilisering under metamorfos koncentrerade vissa metaller som Co i sekundära ådror och parageneser. (Less)
Popular Abstract
Why and when does cobalt form and why does it matter?

Cobalt and all the nasty problems associated with it, prominently featured in the news during the past few years, but what is it exactly? Cobalt is a relatively rare metal that is used, among other things, in batteries for cellphones, cars and other electronics. With more and more electric cars being used worldwide, cobalt has become the new popular metal in town, together with lithium. Unfortunately, the ugly truth is that cobalt is mostly extracted in countries of conflict, such as the Democratic Republic of Congo, where either child or forced labor is used for their extraction. The good news, on the other hand, is that cobalt can be found in other places around the world, even... (More)
Why and when does cobalt form and why does it matter?

Cobalt and all the nasty problems associated with it, prominently featured in the news during the past few years, but what is it exactly? Cobalt is a relatively rare metal that is used, among other things, in batteries for cellphones, cars and other electronics. With more and more electric cars being used worldwide, cobalt has become the new popular metal in town, together with lithium. Unfortunately, the ugly truth is that cobalt is mostly extracted in countries of conflict, such as the Democratic Republic of Congo, where either child or forced labor is used for their extraction. The good news, on the other hand, is that cobalt can be found in other places around the world, even here in Sweden!
So how do we find this elusive metal? Well, it is key to understand at what time of the Earth’s history and how cobalt formed. To find this out we can study known deposits. The Vena-Dampetorp deposit is a small group of mining pits, located within the Bergslagen mining region, where copper and cobalt were mined up to the XIX century. The rocks in this area represent ash and lava which erupted from volcanoes in an ancient sea around 1,890 million years ago. From those times till today they experienced a though road where the rocks were pushed in different directions and cooked at very high temperatures, changing the minerals and the structures in them.

Using detailed observations of the rocks under the microscope together with chemical analyses, the origin, location and evolution of cobalt can be investigated. Similarly, one can discover when this happened through analysis of individual crystals of a mineral called titanite . This mineral is special as it contains uranium, a radioactive element that through time transforms into lead, a non-radioactive element, due to its radioactive decomposition. This acts as an hourglass where on the top we have “grains” of uranium that over time turns into lead “grains” in the bottom of the hourglass. By counting the “grains” of each element in individual grains it is possible to know how much time has passed these crystals formed.

Where does cobalt come from?
The results suggest that the mineral deposit formed in the bottom of an ancient sea in a similar way as modern sea-floor chimneys operate. In these chimneys hot fluids carry metals from the rocks underneath through these chimneys and deposit them on the seabed or in the rocks immediately beneath it. In addition, it was also found that the cobalt, which probably comes from a magma source, was transported and concentrated during the high temperature cooking of these rocks. Cobalt was either squeezed, dissolved or melted and migrated to other parts of the deposit. So, when did this happened? The mineral clocks analysed tell us that these crystals formed around 1,882 million years ago. This means that the first appearance of cobalt in this area of Sweden happened before this date and that it was transported later.
In summary, cobalt in the Bergslagen region is associated to ancient underwater chimneys. By finding rocks that share similar geological characteristics and age in the region, while considering the effects that high temperatures have in the transport that late, it is possible to find more cobalt deposits in the region.
Master’s Degree Project in Geology 45 credits 2020
Department of Geology, Lund University
Supervisors: Charlotte Möller (LU), Alex Lewerentz (SGU) (Less)
Please use this url to cite or link to this publication:
author
Leopardi, Dino LU
supervisor
organization
course
GEOR02 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Bergslagen, Vena, Dampetorp, Cu-Co, sulphide melting, Bastnäs-type, cobaltite, arsenopyrite, titanite dating, sulphide mineralization, sulphide re-mobilisation.
publication/series
Dissertations in Geology at Lund University
report number
582
language
English
additional info
External supervisor: Alexander Lewerentz, Sveriges Geologiska Undersökning
id
9008261
date added to LUP
2020-04-24 11:52:19
date last changed
2020-04-24 11:52:19
@misc{9008261,
  abstract     = {The Bergslagen Province is known for containing major Zn-Pb-Ag and Zn-Pb-Cu-Ag sulphide mineralizations with associated iron-oxide skarns and a lot of research have focused on understanding them. However, Cu-Co deposits like the Vena-Dampetorp deposit have received less attention. The Vena-Dampetorp deposit is a disseminated and vein Cu-Co mineralization hosted primarily in a 1.89 Ga rhyolitic to dacitic volcanoclastic sequence with thin interbedded calcareous horizons and associated mafic and granodioritic intrusions. Two stages of deformation and regional high-temperature and low-pressure metamorphism affected this shallow subaqueous back-arc assemblage. The aim of this study is to constrain the spatial, temporal and genetical relationships of ore minerals and the effects of metamorphism on the host rocks and their assemblages. Building on existing work, it aims to explore the origin and processes responsible for the concentration of Co and genesis of Cu-Co deposits in the Bergslagen area. 

Textural relationships and geochemical data of drill cores show that the mineralization is zoned from pyrite-pyrrhotite zones to chalcopyrite-sphalerite richer zones, with localized Cu-Co areas. At the deposit scale, Co rich zones occur in the SE while Pb-Sb enriched zones concentrate in the NW. The U-Pb dating of metamorphic titanite with LA-ICP-MS gave a mean concordant 207Pb/206Pb date of 1882±16 Ma for a skarn sample. This age is interpreted as the onset of regional metamorphism. In contrast, the lower intercept age of 1882±16 Ma obtained for titanite in one metavolcanic sample could either represent the onset of metamorphism or a cooling age. Sulphide thermobarometric estimates, EDS-SEM mapping, and the presence of sulphosalt-rich associations together with deformational features in the ore minerals, indicate that the Fe-oxide mineralization at the Vena-Dampetorp deposit occurred as a Bastnäs-type deposit due to the interaction of magmatic fluid with carbonate horizons. In comparison, the sulphide Cu-Co-rich mineralization was deposited in a sub-seafloor hydrothermal exhalative system, where the higher Cu-Co concentrations are related to high temperature stringers near the feeder zone. Later mechanical, hydrothermal and melt-assisted re-mobilization during metamorphism concentrated certain metals like Co in secondary veins and assemblages.},
  author       = {Leopardi, Dino},
  keyword      = {Bergslagen,Vena,Dampetorp,Cu-Co,sulphide melting,Bastnäs-type,cobaltite,arsenopyrite,titanite dating,sulphide mineralization,sulphide re-mobilisation.},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Temporal and genetical constraints of the Cu-Co Vena-Dampetorp deposit, Bergslagen, Sweden},
  year         = {2020},
}