Publication Type:Journal Article
Source:Mineralium DepositaMineralium Deposita, Volume 46, Number 3, p.289-304 (2011)
Keywords:Dufferin, Meguma terrane, Nova Scotia, Orogenic gold deposits, Oxygen isotopes, The Ovens
Sampling of quartz vein material from two gold deposits of similar geological setting but different ages (The Ovens, 408 Ma; Dufferin, 380 Ma) in the Meguma Terrane of Nova Scotia has been done to compare and contrast their delta(18)O(quartz) signatures. Despite different ages of formation, quartz from all vein types in each of the deposits (i.e. saddle-reef, bedding-concordant leg reefs, en echelon, discordant) shows limited intra-deposit variation with similar average delta(18)O values of +15.2 +/- 0.9aEuro degrees (n = 16) for The Ovens and +15.7 +/- 0.6aEuro degrees (n = 12) for Dufferin. Using an average delta(18)O value of +15.4aEuro degrees for the two deposits, the corresponding delta(18)O(H2O) values, calculated for 400A degrees C and 350A degrees C based on constraints from mineral assemblages and fluid inclusion studies, indicate averages of 11.4 A +/- 0.2aEuro degrees and +10.2 A +/- 0.2aEuro degrees, respectively. The isotopic data indicate that: (1) the vein-forming fluids have a metamorphic signature, (2) all vein types in the two deposits represent formation from a single, isotopically homogeneous fluid, and (3) a fluid of similar isotopic signature was generated by two contrasting tectono-thermal events in the Meguma Terrane that were separated by 30 Ma. Integration of these results with previously published data for 14 Meguma gold deposits indicate a general stratigaphic dependence in delta(18)O(H2O) values for deposits when arranged in their relative stratigraphic position such that delta(18)O(H2O) values increase upwards in the stratigraphy. This apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein-forming fluids, but instead is modelled using fluid/rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy.