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TitreEvaporate mound analysis of quartz-hosted fluid inclusions by SEM/EDS: evaluation and application of method to assess granitoid metal fertility
AuteurTweedale, F M; Kontak, D; Hanley, J; Rogers, N
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 36, 2013 p. 191
LiensOnline - En ligne (PDF 36.1 MB)
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130605
RéunionGAC-MAC Joint annual meeting; Winnpeg, MB; CA; mai 2013
Documentpublication en série
Mediaen ligne; numérique
SNRC11D; 11E; 21A
Lat/Long OENS -66.0000 -61.5000 45.7500 44.0000
Sujetsroches intrusives; roches granitiques; inclusions fluides; quartz; métallogénie; minéralisation; analyses pétrographiques; altération; gîtes magmatiques; gisements minéraux hydrothermaux; Batholite de South Mountain ; pétrologie ignée et métamorphique; géochimie; Dévonien
ProgrammeÉtude des gîtes porphyriques, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
A cost-effective, simple, and time-efficient method to determine the bulk composition of fluid inclusions is evaporate mound analysis. This
method is semi-quantitative and determines inclusion composition by integrating SEM imaging with energy-dispersive analysis of precipitates, or mounds, produced by thermal decrepitation of fluidinclusions. The method is applicable to magmatic-hydrothermal systems where fluid inclusions contain solute ions (e.g., Na, K, Ca, Cl, F). In order to assess the application of this method for evaluating hydrothermal evolution and metal fertility with regards to intrusionrelated mineralisation, a test study is being conducted on the large (7800 km2) and variably mineralized (e.g., Sn, W, Cu, U, Mo, Ta) South Mountain Batholith (SMB) of Nova Scotia.
Decrepitate mounds were analyzed using a LEO 1450VP (SEM) imaging system linked to an Oxford X-Max 80 mm2 SDD detector energy-dispersive detector. Based on decrepitating over a range of temperatures, from 325° to 500°C, it appears that T = 500°C is optimal to produce large, well-shaped, and readily identifiable mounds. To optimize analysis time and, hence, increase research efficiency while maintaining result accuracy, data were collected with 5-, 10-, and 30-second acquisition times. A comparison of results is discussed herein. The number of analyses required to produce a representative result is also discussed by comparison of results for 4, 8, 16, 32, and 64 analyses of mounds for individual samples. Multiple (N = 12) point-mode analyses on individual decrepitate mounds substantiate mound heterogeneity. Results that accurately reflect in-situ fractionation are shown to be achievable with single, 10-second raster-mode analysis.
The results of the aforementioned analytical conditions are utilised to define optimal operational protocols for efficient (i.e., cost effective) analysis for a regional study of the SMB. This test case is the first of its kind conducted on a batholithic scale, with the resulting methodological protocols being readily exportable for the mineral fertility assessment of other regions. In addition to presenting the method protocol, the initial results of this work will be shown. The latter integrates a petrographic alteration index designed for granitic samples, fluid inclusion types and density, and evaporate mound chemistry for 100 samples. Samples are chosen such that the entire batholith may be assessed, and all mapped lithologies represented. Fluid compositions determined thus far include brines with 5- 15 % fluorine, which are quantitatively indeterminable using other methods.