Vite-Sánchez, Octavio; Ross, Pierre-Simon 
ORCID: https://orcid.org/0000-0002-5302-698X et Mercier-Langevin, Patrick
(2024).
Mafic to intermediate volcanic rocks of the Blake River Group, Abitibi greenstone belt, Canada: Geochemistry, petrogenesis and relation with VMS deposits.
Precambrian Research
, vol. 404
.
p. 107331.
DOI: 10.1016/j.precamres.2024.107331.
Résumé
Volcanogenic massive sulfide (VMS) deposits, prevalent since the Archean, constitute a well-explored ore deposit type. Nonetheless, the factors contributing to variations in fertility among volcanic centers, assemblages within greenstone belts, or entire greenstone belts remain unclear. For instance, the Blake River Group (BRG) of Ontario and Quebec, Canada, hosts almost half of the total VMS tonnage of the entire Abitibi greenstone belt, yet represents less than 10 % of its map surface. This study utilizes a large dataset (n = 2271) of whole-rock geochemistry for mafic to intermediate volcanic rocks to understand the BRG petrogenesis, and its implications for VMS endowment in the Abitibi.
Principal Component Analysis shows that Ti, Th, and Yb are the primary contributors to the dataset's variation. This yields a two-ratio diagram (Th/Yb versus Zr/Ti) revealing seven geochemical groups with coherent map patterns referenced as tholeiitic basalts, tholeiitic intermediate rocks, medium-Th basalts, transitional intermediate rocks, high-Th basalts, calc-alkaline intermediate rocks and low-Zr basalts.
A least altered subset of the data is used to analyze major element patterns. BRG mafic to intermediate magmas show variable degrees of Fe-Ti enrichment/depletion during their evolution, with simultaneous Al2O3 depletion or lack thereof. Utilizing a single parental mafic tholeiitic magma, the Magma Chamber Simulator enables the modeling of major and trace element compositions for each geochemical group. Fractional crystallization (FC) models with variable initial water contents can explain the range of the tholeiitic basalt and tholeiitic intermediate compositions. Assimilation fractional crystallization (AFC) models successfully replicate most of the geochemical groups using a TTG average composition for the assimilant.
While mafic-intermediate host rock geochemical signatures are not the sole factor influencing VMS endowment in volcanic belts, regional analysis reveals that the vast majority of volcanic rocks in geological formations bearing VMS deposits in the BRG are crustally contaminated lacking tholeiitic geochemical groups. Conversely, poorly endowed formation consistently contain samples from these groups. Moreover, the Bousquet formation, which hosts several world-class gold-rich VMS deposits, displays the highest rates of crustal assimilation, further suggesting that petrogenesis of mafic-intermediate volcanic rocks is linked to VMS metallogenesis in the BRG.
| Type de document: | Article |
|---|---|
| Mots-clés libres: | basalt; andesite; crustal assimilation; Archean greenstone belt; VMS fertility |
| Centre: | Centre Eau Terre Environnement |
| Date de dépôt: | 31 juill. 2024 20:19 |
| Dernière modification: | 31 juill. 2024 20:19 |
| URI: | https://espace.inrs.ca/id/eprint/15501 |
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