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TitreCompositional data analysis to constrain the geochemical footprint of iron oxide copper-gold deposits, Great Bear Magmatic Zone, Northwest Territories, Canada
AuteurMontreuil, J -F; Corriveau, L
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 36, 2011 p. 144-145; 1 CD-ROM
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120009
RéunionGAC/AGC - MAC/AMC - SEG - SGA; Ottawa; CA; mai 25-27, 2011
Documentpublication en série
Mediapapier; CD-ROM
ProvinceTerritoires du Nord-Ouest
Lat/Long OENS-117.0000 -116.5000 63.7500 63.5000
Sujetsanalyses géochimiques; interprétations géochimiques; altération hydrothermale; altération; gîtes minéralogiques; gisements minéraux; oxydes de fer; cuivre; or; uranium; Zone de Great Bear Magmatic ; géologie économique; géochimie
ProgrammeUranium, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Iron oxide copper-gold (IOCG) systems are characterized by a wide range of hydrothermal alteration types that indiscriminately and intensively replace their host rocks over several kilometres. The resulting alteration imprint can be reproduced irrespective of the nature of the original host and intense alteration is usually the norm over areas of >100 km2. Consequently, mass-balance systems analysis (e.g. Gresen's equations) cannot be used systematically for lithogeochemical characterization of geochemical zonation and partitioning within the alteration zones of IOCG systems. For effective geochemical evaluation of these rocks, the use of log-ratio transforms has been applied as they overcomes the closure constraint inherent with geochemical data and permits the use of multivariate statistical tools for geochemical process identification. To provide robust discrimination parameters for IOCG hydrothermal alteration with multivariate statistical methods, the geochemical data must have accompanying reliable and carefully documented field observations. Cataloguing this additional information provides useful qualifications for understanding the para-genesis of the host hydrothermal system and associated mineralization. The numerous IOCG hydrothermal systems of the Great Bear magmatic zone in the north-western Canadian Shield are good candidates to undertake such multivariate statistical studies using the log-ratio approach. These systems encompass a wide range of hydrothermal alteration emplaced in different protoliths and are sufficiently intense to have completely replaced the original rock. Their evolution history is well constrained within an alteration to mineralization zoning model. A database of fully documented geochemical analysis is available. Principal component analysis (PCA) was done on the lithogeochemistry of 458 hydrothermally altered and mineralized rocks from the Port Radium-Echo Bay IOCG district and various IOCG systems within the Southern Great Bear magmatic zone (including the NICO and Sue Diane deposits). PCA analysis records strong partitioning between LREE and HREE in most alteration zones. Decoupling of typical element association (e.g. Ca and Sr) is commonly observed. Calcium and K-Na are either decoupled or negatively correlated, whereas K and Na are sometime positively correlated. PCA analysis also indicates that the influence of protolith
composition on resulting alteration signature is only weak to moderate as very distinctive signatures are not observed, indicating that the alteration signature dominates over the protolith signature. A linear discriminant analysis confirms the difference between the various alteration types of the IOCG model. Current modelling is unable to retrace significant chemical modification of high-temperature alteration from the low temperature alteration overprints in the IOCG systems that have been studied.