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TitlePetrographic observations and evaporate mound analysis of quartz-hosted fluid inclusions: Applications to assess metal fertility in granites
AuthorTweedale, F; Hanley, J; Kontak, D; Rogers, N
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 275-276 Open Access logo Open Access
LinksOnline - En ligne (PDF 8.75 MB)
Alt SeriesEarth Sciences Sector, Contribution Series 20130604
PublisherGeological Association of Canada
PublisherMineralogical Association of Canada
MeetingGAC-MAC Joint annual meeting; Fredericton, NB; CA; May 2014
Mediaon-line; digital
RelatedThis publication is related to Petrographic observations and evaporate mound analysis of quartz-hosted fluid inclusions: applications to assess metal fertility in granites
File formatpdf
ProvinceNova Scotia
NTS11D; 11E; 21A
Lat/Long WENS -66.0000 -61.5000 45.7500 44.0000
Subjectsigneous and metamorphic petrology; geochemistry; intrusive rocks; granitic rocks; fluid inclusions; quartz; metallogeny; mineralization; petrographic analyses; alteration; South Mountain Batholith; Devonian
ProgramTargeted Geoscience Initiative (TGI-4) Intrusion/Porphyry Ore Systems
Released2014 01 01
AbstractThe 380 Ma South Mountain Batholith (SMB), Nova Scotia, is a large (~7300 km2), contiguous, mesozonal granitoid intrusion consisting of 13 coalesced plutons hosting a variety of mineralized zones (e.g., Sn-Zn-Cu-Ag, Mn-Fe-P, U, Cu-Ag). Given the hydrothermal nature of this mineralization, it is expected that a geochemical fingerprint of the mineralizing fluids might be preserved both petrographically and as secondary fluid inclusions (FIs) in the granites on a scale equal to or larger than the mineralized zones. In this unique study, we investigate the possibility of integrating petrographic observations that reflect fluid:rock interaction and the chemistry of secondary, quartz-hosted FIs in samples from the SMB to assess granite fertility and also the scale of this potential vectoring tool. The protocol involved: (1) detailed petrographic study of >500 archived samples and focused on the extent and degree of alteration (e.g., perthite textures, chlorite alteration of biotite, plagioclase alteration, percent of secondary muscovite, abundance of FI in quartz); and (2) determining fluid chemistry of quartzhosted FIs in >100 samples collected from a 10 × 10 km grid superimposed on the SMB. The petrographic data record highly variable degrees of alteration and the results are being used to design an alteration algorithm that can be used to map the extent of fluid:rock interaction throughout the batholith. The chemistry of FIs, determined using the evaporate mound method, is being used as a proxy for both the mineralizing and altering fluids. At present, results for >600 mounds determined for 68 samples indicate the fluids are dominated by Na-K-Ca-Cl-F, with traces of Fe, Mn, and S, and that two distinct types are present, one Na-rich and the other Ca-rich. Two intriguing results to date include: (1) the pervasive occurrence of F in the mound analysis with up to 40 wt. % when normalized to 100%, even in samples distal to known mineralization; and (2) elevated Ca in many samples, including those from chemically evolved, hence Ca-depleted rocks. This latter feature may reflect extensive albitization of plagioclase, hence liberation of Ca, during fluid-mediated alteration. Thus, our preliminary findings clearly indicate that mappable variation in the degree and extent of alteration is retained in the main mineral phases of the granites and that fluid chemistry, preserved as secondary FIs in quartz, is a potential proxy for fluid:rock interaction and hence a measure of metal fertility.

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