2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 61-6
Presentation Time: 2:15 PM

FURTHER RE-OS ARSENOPYRITE GEOCHRONOLOGY FROM SELECTED MEGUMA AU DEPOSITS, MEGUMA TERRANE, NOVA SCOTIA: POSSIBLE EVIDENCE FOR A PROTRACTED GOLD-FORMING SYSTEM


CHEN, Lin, Earth and Atmospheric Sciences, University of Alberta, 501-8210 111St NW, Edmonton, AB T6G 2C7, Canada, CREASER, Robert A., Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2R3, Canada and KONTAK, Daniel, Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada, lchen2@ualberta.ca

The Meguma terrane is dominated by two rock types, regionally deformed and metamorphosed Cambro-Ordovician metasedimentary rocks and ca. 380-370 Ma meta- to peraluminous granites. The metasedimentary rocks contain numerous orogenic-type, vein-hosted gold deposits which occur throughout the sandstone-dominated Goldenville Group rather than the overlying siltstone- and mudrock-dominated Halifax Group. These mineralized veins are dominated by quartz-carbonate-sulfide assemblages and occupy structures consistent with emplacement during late-stage fold tightening of the regional, northeast-trending, upright folds formed during Neoacadian deformation at ca. 410-385 Ma. Our previous work suggests vein formation, hence gold mineralization, spanned 30-40 Ma, as constrained from field observations and radiometric dating. The former indicates veins post-date cleavage formation given that cleaved wall-rock fragments occur in some veins and that rarely veins post-date hornfels related to 380 Ma granites. Existing absolute age dates indicates two events at 408 Ma (Re-Os Aspy, 40Ar/39Ar wr) and 380-362 Ma (Re-Os Aspy; 40Ar/39Ar am, ms, bi, wr). Here we report new Re-Os geochronological data generated from arsenopyrite in gold-rich veins for two deposits sampled, both of which lie in the same stratigraphic-structural position in the lower part of the Goldenville Group. The Re-Os analysis of arsenopyrite from three veins from the Beaver Dam deposit, which is dominated by bedding-concordant type veins, yielded isochron ages of ca. 461 Ma, 459 Ma and 440 Ma. In contrast, Re-Os analysis of one vein-hosted arsenopyrite sample from the Touquoy deposit of the Moose River gold district, where mineralization occurs in a vein-poor sequence of carbonate-rich metasiltstone rocks, yielded two isochron ages of ca. 380 Ma and 438 Ma; one other sample from the same deposit provided Re-Os model ages from ca. 400 Ma to 440 Ma. In addition, obvious zoning of the arsenopyrite is noted from both SEM and LA ICP-MS trace element mapping, which also indicates multiple generations for this mineral. This new data suggests that in the Meguma terrane several stages of gold mineralization exist, the first pre-dating the Neoacadian deformation and metamorphism of the host rocks.
Handouts
  • Re-Os, Meguma gold deposit, Lin Chen.pdf (1.7 MB)