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Resolving temporal links between the Högberget granite and the Wigström tungsten skarn deposit in Bergslagen (Sweden) using trace elements and U-Pb LA-ICPMS on complex zircons

Plan, Anders LU (2020) In Dissertations in Geology at Lund University GEOR02 20182
Department of Geology
Abstract
Combined U-Pb and REE trace element LA-ICPMS analyses were performed on zircons, from the scheelite-bearing Wigström skarn, associated micro-granitic dykes and the highly evolved parental Högberget (sensu stricto) granite. Combined systematic of zircon typology and microtextures, trace elements and isotopic chemistry suggest the presence of several diverse zircon types, spanning from early- to late- magmatic stage into a hydrothermal stage. Early stage magmatic zircons (type M1 and M2-S) have high concentrations of U (3300–11500 ppm), Th (1500–7300 ppm), REEs (average ΣREEn: 11500) and Pb-C signatures and yield highly discordant data. Typological features are varying, but the majority consists of prismatic crystals with oscillatory... (More)
Combined U-Pb and REE trace element LA-ICPMS analyses were performed on zircons, from the scheelite-bearing Wigström skarn, associated micro-granitic dykes and the highly evolved parental Högberget (sensu stricto) granite. Combined systematic of zircon typology and microtextures, trace elements and isotopic chemistry suggest the presence of several diverse zircon types, spanning from early- to late- magmatic stage into a hydrothermal stage. Early stage magmatic zircons (type M1 and M2-S) have high concentrations of U (3300–11500 ppm), Th (1500–7300 ppm), REEs (average ΣREEn: 11500) and Pb-C signatures and yield highly discordant data. Typological features are varying, but the majority consists of prismatic crystals with oscillatory zonations. In comparison, late stage magmatic zircons (type M2) have lower concentrations of U (200–3000 ppm), Th (100–1900 ppm), REEs (average ΣREEn: 7600) and Pb-C signatures (e.g. average 204Pb CPS: 300). Typological features include irregular, quasi-smooth forms which lack internal zonations. Geochronological analyses yield concordant data, after interpretation an 207Pb/206Pb weighted mean age of ~1.8 Ga is achieved. Hydrothermal zircon (skarn hosted, type H) associates with hydrothermal quartz, calcite, fluorite and scheelite within the skarn. Type H zircons shares similarities with type M2, yielding low concentrations of U (100–6200 ppm), Th (1–1500 ppm), and Pb-C signatures (e.g. average 204Pb CPS: 300), but slightly higher concentrations of REEs (average ΣREEn: 17800). Typological features display various forms, i.e. skeletal, irregular, oblong, and typically lacks prisms. Internal textures vary from zoned to homogenous, and spongy textures are common. Geochronological data are scattered, but display a concordant cluster around 1.8 Ga, calculated as 207Pb/206Pb weighted mean age of 1795±20 Ma (2.0 MSWD). The achieved ages further fortify a ~1.8 Ga for the tungsten metallogenesis in Bergslagen. Magmatic (early- and late types) and hydrothermal zircon can be distinguished via trace elemental discrimination diagram and in CI-chondrite normalized spidergrams. For discrimination diagram, Th versus Th/U, U versus Th, and ΣREEn versus Th diagrams clearly displays evolutionary transitional trend between the different zircon types. In spidergrams, Magmatic zircons have typical patterns for magmatic zircons (but shows LREE enrichments), whereas hydrothermal zircons display a convex pattern, which clearly distinguish the zircon populations apart. (Less)
Popular Abstract (Swedish)
I Bergslagen, Sverige, finns Skandinaviens största tungstenstillgångar, och här har man i årtionden brutit denna värdefulla metall. Brytningen fick dock ett abrupt slut runt 80-talet, men i dagsläget finns planer från prospekterare att återuppta industrin. Bildningsmodellerna för tungstensmineraliseringarna har sedan länge varit omdebatterad, men brett accepterat är att värme från närliggande graniter genererade under sin bildning ett hydrotermalt system där metalliska element kunde utlösa, vilket vidare påverkade kringliggande bergarter och slutligen ansamlades malmen i en hydrotermal omvandlad bergart kallat skarn.
I detta arbete har zirkoner används för att tidsmässigt knyta samman en tungstensmineralisering till en närliggande... (More)
I Bergslagen, Sverige, finns Skandinaviens största tungstenstillgångar, och här har man i årtionden brutit denna värdefulla metall. Brytningen fick dock ett abrupt slut runt 80-talet, men i dagsläget finns planer från prospekterare att återuppta industrin. Bildningsmodellerna för tungstensmineraliseringarna har sedan länge varit omdebatterad, men brett accepterat är att värme från närliggande graniter genererade under sin bildning ett hydrotermalt system där metalliska element kunde utlösa, vilket vidare påverkade kringliggande bergarter och slutligen ansamlades malmen i en hydrotermal omvandlad bergart kallat skarn.
I detta arbete har zirkoner används för att tidsmässigt knyta samman en tungstensmineralisering till en närliggande granit. Efter tolkning utav zirkon analyser kan en ålder runt 1.8 miljarder år för graniten och mineraliseringen härledas. Med de båda likvärdiga åldrarna stärks den nuvarande accepterade granitiska modellen för tungstensbildning i Bergslagen. För prospekterare medför detta att man bör fokusera och bedriva tungstensprospektering kring liknande graniter då dessa verkar ha en direkt koppling till höga malmkoncentrationer utav tungsten. (Less)
Please use this url to cite or link to this publication:
author
Plan, Anders LU
supervisor
organization
alternative title
Undersökning av den tidsmässiga relationen mellan Högberget-graniten och Wigström-tungstensmineraliseringen i Bergslagen (Sverige) med hjälp av spårelement och U-Pb LA-ICPMS på komplexa zirkoner
course
GEOR02 20182
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Bergslagen, Wigström, Högberget, geochronology, geochemistry, U-Pb, REE, trace element, zircon, hydrothermal zircon, LA-ICPMS, SEM, skarn, tungsten, wolfram, scheelite, deposit, ore, critical raw material
publication/series
Dissertations in Geology at Lund University
report number
580
language
English
additional info
External supervisor: Edward Lynch, Sveriges Geologiska Undersökning
id
9000072
date added to LUP
2020-01-08 15:32:17
date last changed
2020-01-08 15:32:17
@misc{9000072,
  abstract     = {Combined U-Pb and REE trace element LA-ICPMS analyses were performed on zircons, from the scheelite-bearing Wigström skarn, associated micro-granitic dykes and the highly evolved parental Högberget (sensu stricto) granite. Combined systematic of zircon typology and microtextures, trace elements and isotopic chemistry suggest the presence of several diverse zircon types, spanning from early- to late- magmatic stage into a hydrothermal stage. Early stage magmatic zircons (type M1 and M2-S) have high concentrations of U (3300–11500 ppm), Th (1500–7300 ppm), REEs (average ΣREEn: 11500) and Pb-C signatures and yield highly discordant data. Typological features are varying, but the majority consists of prismatic crystals with oscillatory zonations. In comparison, late stage magmatic zircons (type M2) have lower concentrations of U (200–3000 ppm), Th (100–1900 ppm), REEs (average ΣREEn: 7600) and Pb-C signatures (e.g. average 204Pb CPS: 300). Typological features include irregular, quasi-smooth forms which lack internal zonations. Geochronological analyses yield concordant data, after interpretation an 207Pb/206Pb weighted mean age of ~1.8 Ga is achieved. Hydrothermal zircon (skarn hosted, type H) associates with hydrothermal quartz, calcite, fluorite and scheelite within the skarn. Type H zircons shares similarities with type M2, yielding low concentrations of U (100–6200 ppm), Th (1–1500 ppm), and Pb-C signatures (e.g. average 204Pb CPS: 300), but slightly higher concentrations of REEs (average ΣREEn: 17800). Typological features display various forms, i.e. skeletal, irregular, oblong, and typically lacks prisms. Internal textures vary from zoned to homogenous, and spongy textures are common. Geochronological data are scattered, but display a concordant cluster around 1.8 Ga, calculated as 207Pb/206Pb weighted mean age of 1795±20 Ma (2.0 MSWD). The achieved ages further fortify a ~1.8 Ga for the tungsten metallogenesis in Bergslagen. Magmatic (early- and late types) and hydrothermal zircon can be distinguished via trace elemental discrimination diagram and in CI-chondrite normalized spidergrams. For discrimination diagram, Th versus Th/U, U versus Th, and ΣREEn versus Th diagrams clearly displays evolutionary transitional trend between the different zircon types. In spidergrams, Magmatic zircons have typical patterns for magmatic zircons (but shows LREE enrichments), whereas hydrothermal zircons display a convex pattern, which clearly distinguish the zircon populations apart.},
  author       = {Plan, Anders},
  keyword      = {Bergslagen,Wigström,Högberget,geochronology,geochemistry,U-Pb,REE,trace element,zircon,hydrothermal zircon,LA-ICPMS,SEM,skarn,tungsten,wolfram,scheelite,deposit,ore,critical raw material},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Resolving temporal links between the Högberget granite and the Wigström tungsten skarn deposit in Bergslagen (Sweden) using trace elements and U-Pb LA-ICPMS on complex zircons},
  year         = {2020},
}