Boron, sulphur and copper isotope systematics in the orogenic gold deposits of the Archaean Hattu schist belt, eastern Finland

Boron, sulphur and copper isotope systematics in the orogenic gold deposits of the Archaean Hattu... The Hattu schist belt is located in the western part of the Archaean Karelian domain of the Fennoscandian Shield. The orogenic gold deposits with Au–Bi–Te geochemical signatures are hosted by NE–SW, N–S and NW–SE oriented shear zones that deform 2.76–2.73Ga volcanic and sedimentary sequences, as well as 2.75–2.72Ga tonalite–granodiorite intrusions and diverse felsic porphyry dykes. Mo–W mineralization is also present in some tonalite intrusions, both separate from, and associated with Au mineralization. Somewhat younger, unmineralized leucogranite intrusions (2.70Ga) also intrude the belt. Lower amphibolite facies peak metamorphism at 3–5kbar pressures and at 500–600°C temperatures affected the belt at around 2.70Ga and post-date hydrothermal alteration and ore formation. In this study, we investigated the potential influence of magmatic-hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope (B, S, Cu) studies of tourmaline and sulphide minerals by application of in situ SIMS and LA ICP MS analytical techniques.Crystal chemistry of tourmaline from a Mo–W mineralization hosted by a tonalite intrusion in the Hattu schist belt is characterized by Fe3+–Al3+-substitution indicating relatively oxidizing conditions of hydrothermal processes. The range of δ11B data for this kind of tourmaline is from −17.2‰ to −12.2‰. The hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry (e.g. dravite–povondraite compositional trend with Fe3+–Al3+ substitution) and δ11B values between −19.0‰ and −9.6‰. The uvite–foitite compositional trend and δ11B ‰ values between −24.1% and −13.6% characterize metasomatic–hydrothermal tourmaline from the metasediment-hosted gold deposits. Composition of hydrothermal vein-filling and disseminated tourmaline from the gold-bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment-hosted tourmaline. Rock-forming (magmatic) tourmaline from leucogranite has δ11B values between −14.5‰ and −10.8‰ and the major element composition is similar to that of the metasediment-hosted tourmaline.The range of δ34SVCDT values measured in pyrite, chalcopyrite and pyrrhotite is from −9.1 to +8.5‰, which falls within the typical range of sulphur isotope data for Archaean orogenic gold deposits. In the Hattu schist belt, positive δ34SVCDT values characterize metasediment-hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite. The δ34SVCDT values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite. Purely negative values were only recorded from the pyrite-dominated gold mineralization within metavolcanic units. Therefore the shift of δ34SVCDT values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids. The range of measured δ65CuNBS978 values from chalcopyrite is from −1.11 to 1.19‰. Positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks. Positive and negative δ65CuNBS978 values occur in the ores hosted by metavolcanic rocks. There is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains.Evaluation of sulphur and boron isotope data together and comparisons with other Archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the Hattu schist belt. Variations in major element and boron isotope compositions in tourmaline, as well as in the δ34SVCDT values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes. The results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original, distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ore Geology Reviews Elsevier

Boron, sulphur and copper isotope systematics in the orogenic gold deposits of the Archaean Hattu schist belt, eastern Finland

Loading next page...
 
/lp/elsevier/boron-sulphur-and-copper-isotope-systematics-in-the-orogenic-gold-PPPBoGzY0k
Publisher
Elsevier
Copyright
Copyright © 2016 Elsevier B.V.
ISSN
0169-1368
eISSN
1872-7360
D.O.I.
10.1016/j.oregeorev.2016.02.012
Publisher site
See Article on Publisher Site

Abstract

The Hattu schist belt is located in the western part of the Archaean Karelian domain of the Fennoscandian Shield. The orogenic gold deposits with Au–Bi–Te geochemical signatures are hosted by NE–SW, N–S and NW–SE oriented shear zones that deform 2.76–2.73Ga volcanic and sedimentary sequences, as well as 2.75–2.72Ga tonalite–granodiorite intrusions and diverse felsic porphyry dykes. Mo–W mineralization is also present in some tonalite intrusions, both separate from, and associated with Au mineralization. Somewhat younger, unmineralized leucogranite intrusions (2.70Ga) also intrude the belt. Lower amphibolite facies peak metamorphism at 3–5kbar pressures and at 500–600°C temperatures affected the belt at around 2.70Ga and post-date hydrothermal alteration and ore formation. In this study, we investigated the potential influence of magmatic-hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope (B, S, Cu) studies of tourmaline and sulphide minerals by application of in situ SIMS and LA ICP MS analytical techniques.Crystal chemistry of tourmaline from a Mo–W mineralization hosted by a tonalite intrusion in the Hattu schist belt is characterized by Fe3+–Al3+-substitution indicating relatively oxidizing conditions of hydrothermal processes. The range of δ11B data for this kind of tourmaline is from −17.2‰ to −12.2‰. The hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry (e.g. dravite–povondraite compositional trend with Fe3+–Al3+ substitution) and δ11B values between −19.0‰ and −9.6‰. The uvite–foitite compositional trend and δ11B ‰ values between −24.1% and −13.6% characterize metasomatic–hydrothermal tourmaline from the metasediment-hosted gold deposits. Composition of hydrothermal vein-filling and disseminated tourmaline from the gold-bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment-hosted tourmaline. Rock-forming (magmatic) tourmaline from leucogranite has δ11B values between −14.5‰ and −10.8‰ and the major element composition is similar to that of the metasediment-hosted tourmaline.The range of δ34SVCDT values measured in pyrite, chalcopyrite and pyrrhotite is from −9.1 to +8.5‰, which falls within the typical range of sulphur isotope data for Archaean orogenic gold deposits. In the Hattu schist belt, positive δ34SVCDT values characterize metasediment-hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite. The δ34SVCDT values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite. Purely negative values were only recorded from the pyrite-dominated gold mineralization within metavolcanic units. Therefore the shift of δ34SVCDT values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids. The range of measured δ65CuNBS978 values from chalcopyrite is from −1.11 to 1.19‰. Positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks. Positive and negative δ65CuNBS978 values occur in the ores hosted by metavolcanic rocks. There is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains.Evaluation of sulphur and boron isotope data together and comparisons with other Archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the Hattu schist belt. Variations in major element and boron isotope compositions in tourmaline, as well as in the δ34SVCDT values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes. The results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original, distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes.

Journal

Ore Geology ReviewsElsevier

Published: Sep 1, 2016

References

  • Fluid speciation controls of low temperature copper isotope fractionation applied to the Kupferschiefer and Timna ore deposits
    Asael, D.; Matthews, A.; Oszczepalski, S.; Bar-Matthews, M.; Halicz, L.
  • Sulphur isotope characteristics of metamorphosed Cu–(Zn) volcanogenic massive sulphide deposits of the Norwegian Caledonides
    Cook, N.J.; Hoefs, J.
  • Copper isotope ratios in magmatic and hydrothermal ore-forming environments
    Larson, P.B.; Maher, K.; Ramos, F.C.; Chang, Z.; Gaspar, M.; Meinert, L.D.
  • Copper isotopic zonation in the Northparkes porphyry Cu–Au deposit, SE Australia
    Li, W.; Jackson, S.E.; Pearson, N.J.; Graham, S.
  • Boron isotopic composition of tourmaline, prismatine, and grandidierite from granulite facies paragneisses in the Larsemann Hills, Prydz Bay, East Antarctica: evidence for a non-marine evaporite source
    MacGregor, J.R.; Grew, E.S.; De Hoog, J.C.M.; Harley, S.L.; Kowalski, P.M.; Yates, M.G.; Carson, C.J.
  • P–T–t–deformation–fluid characteristics of lode gold deposits: evidence from alteration systematics
    McCuaig, T.C.; Kerrich, R.
  • Translating the mineral systems approach into an effective exploration targeting system
    McCuaig, T.C.; Beresford, S.; Hronsky, J.
  • Matrix effects during laser ablation MC ICP-MS analysis of boron isotopes in tourmaline
    Miková, J.; Košler, J.; Wiedenbeck, M.
  • Formation of gold deposits: review and evaluation of the continuum model
    Phillips, G.N.; Powell, R.
  • Formation of gold deposits: a metamorphic devolatilization model
    Phillips, G.N.; Powell, R.
  • Quantum chemical calculations of equilibrium copper (I) isotope fractionation in ore-forming fluids
    Seo, J.H.; Lee, S.K.; Lee, I.
  • Windows of metamorphic sulfur liberation in the crust: implications for gold deposit genesis
    Tomkins, A.G.
  • The diversity of B-isotope variations in tourmaline from rare-element pegmatites in the Borborema Province of Brazil
    Trumbull, R.B.; Beurlen, H.; Wiedenbeck, M.; Soares, D.R.
  • Boron isotope and light element sector zoning in tourmaline: implications for the formation of B-isotopic signatures
    van Hinsberg, V.J.; Marschall, H.R.
  • Laser microprobe sulphur isotope analysis of arsenopyrite: experimental calibration and application to the Boliden Au–Cu–As massive sulphide deposit
    Wagner, T.; Boyce, A.J.; Jonsson, E.; Fallick, A.E.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches

$49/month

Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.

$588

$360/year

billed annually
Start Free Trial

14-day Free Trial