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TitreA new geochemical tool to assist VMS exploration in the Matagami Mining Camp: the positive europium anomaly
AuteurGenna, D
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 34, 2011 p. 72-73
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130568
RéunionGAC-MAC-SEG-SGA Joint Annual Meeting 2011; Ottawa; CA; mai 25-27, 2011
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC32F/12; 32F/13
Lat/Long OENS-78.0000 -77.5000 50.0000 49.5000
Sujetsgîtes minéralogiques; gisements minéraux; minéralisation; or; cuivre; argent; gîtes volcanogènes; géologie économique; géochimie; minéraux métalliques
ProgrammeÉtude des gîtes d'or, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The Key Tuffite (KT) is the main guide used for VMS exploration in the Matagami camp (Abitibi) for the last 50 years. All the major exploited deposits are located along this continuous and extensive tuffaceous and locally cherty unit. Despite the importance of this horizon and the numerous studies on it, attempts to develop geochemical vectoring tools to assist exploration were inconclusive. Exploration drilling related to the Bracemac-McLeod VMS deposits provided an exceptional opportunity to sample the KT around and away from the mineralization. Twenty three drill-cores where selected from more than 400 holes in an area of 1.4 by 2.6 km. Macroscopic observations revealed that the complex nature of the KT results at least from the mixing of 2 components in varying proportions: a tuffaceous component, represented by chlorite, and a chemical component represented by silica and sulfides. This last component is proximal to the lenses. Whole-rock lithogeochemistry was carried out on 42 samples. Chemically, the bimodal component of the KT is well illustrated by a linear regression (R2=0.81) between SiO2 and Fe2O3, where SiO2 represents the silica, and Fe2O3 can represent chlorite and/or sulfides. Single element and ratio element plots proved to be useless in an attempt to decipher any increase of elements relative to the spatial position of the sulphide lenses. However, europium anomalies showed a systematic increase towards the deposit. This anomaly is defined as Eu/Eu* = Eu/[(0.67Sm + 0.33Tb)]MUQ, where MUQ (Mud of Queensland) is the normalization value. Away from the deposit, the anomaly is around 0.6 and reaches a maximum of 3.0 in the lens. This positive Eu signature is persistent up 200 m from the deposit. Europium enrichment in VMS settings is a well known process induced by hydrothermal fluid flow. Because of the double valence of this element, Eu2+ is leached by hot and reducing fluids in the alteration area and then redeposited at the hydrothermal vent sites. In the KT, this enrichment may be related to hydrothermal alteration or seafloor precipitation. Even if the Eu anomaly acts as a proxy for VMS mineralization, there is no apparent relationship with the bimodal components of the KT. Specifically, europium- bearing phases remain to be established as well as the enrichment process. However a third component related to late hydrothermal influx along the KT following the capping of the hydrothermal system appears to be the best explanation for Eu enrichment.