Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland

Matti Poutiainen, Sami Partamies

Research output: Contribution to journalArticleScientificpeer-review

6 Citations (Scopus)

Abstract

The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.
Original languageEnglish
Pages (from-to)196-207
Number of pages12
JournalMineralium Deposita
Volume38
Issue number2
DOIs
Publication statusPublished - 2003
MoE publication typeA1 Journal article-refereed

Fingerprint

Gold deposits
Finland
greenstone belt
fluid inclusion
Archean
gold
deposits
inclusions
Fluids
fluid
fluids
veins
quartz vein
Quartz
Gold
Bearings (structural)
quartz
texture
sulfide
sulfides

Keywords

  • Finland
  • Rämepuro gold deposit
  • Greenstone belt
  • Fluid-inclusion petrography
  • Orogenic gold

Cite this

@article{503b0545b86f4fb9852db860ca3680bc,
title = "Fluid evolution of the late Archaean R{\"a}mepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland",
abstract = "The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The R{\"a}mepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt{\%} NaCl), and (2) H2O–CO2 (≤12 equiv. wt{\%} NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ({"}implosion textures{"}) related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.",
keywords = "Finland, R{\"a}mepuro gold deposit, Greenstone belt, Fluid-inclusion petrography, Orogenic gold",
author = "Matti Poutiainen and Sami Partamies",
year = "2003",
doi = "10.1007/s00126-002-0303-6",
language = "English",
volume = "38",
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journal = "Mineralium Deposita",
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}

Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland. / Poutiainen, Matti; Partamies, Sami.

In: Mineralium Deposita, Vol. 38, No. 2, 2003, p. 196-207.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland

AU - Poutiainen, Matti

AU - Partamies, Sami

PY - 2003

Y1 - 2003

N2 - The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.

AB - The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.

KW - Finland

KW - Rämepuro gold deposit

KW - Greenstone belt

KW - Fluid-inclusion petrography

KW - Orogenic gold

U2 - 10.1007/s00126-002-0303-6

DO - 10.1007/s00126-002-0303-6

M3 - Article

VL - 38

SP - 196

EP - 207

JO - Mineralium Deposita

JF - Mineralium Deposita

SN - 0026-4598

IS - 2

ER -