264 Economic Geology

Wednesday, 12 October 2011
1:30 PM - 5:30 PM
Room 101H-J

RE-OS AND FLUID INCLUSION CONSTRAINTS ON THE TIMING AND NATURE OF SULFIDE MINERALIZATION AT NANISIVIK AND HAWKER CREEK, BAFFIN ISLAND, NUNAVUT

Paper number: 264-3
Program: Technical Sessions
Time: 2:00 PM – 2:15 PM

Authors

Abstract

The world class Nanisivik Zn-Pb(Ag) deposit is hosted by carbonate rocks of the Proterozoic Nanisivik Formation on Baffin Island, Nunavut . MVT deposits like Nanisivik contain few datable minerals and as such, the timing of fluid flow and related sulfide mineralization is not well constrained. At Nanisivik, a variety of possible ages have been proposed including: ca. 1095 Ma based on paleomagnetism of the host rock, assumed to record the hydrothermal activity associated with mineralization (Symons et al., 2000), and ca. 460 Ma based on Ar-Ar dating of adularia alteration (Sherlock et al., 2004). We applied Re-Os geochronology using pyrite to constrain the timing of sulfide mineralization at Nanisivik and similar mineralization at Hawker Creek, 30 km to the SE. Ten pyrite analyses at Nanisivik yield an age of 1114 ± 120 Ma, but with considerable scatter in the data. New fluid inclusion data for sphalerite using IR microscopy from the main ore zones indicate the dominant fluid inclusion assemblage (L-V type) has Th values of <100oC (with a maximum P correction of 25-30oC). Fluid salinity is mainly 20-28wt% eq. NaCl and SEM/EDS of evaporate mounds reflects a compositional range in Na-Ca-Mg-K space due to F:R interaction. In two locations (near the mine dyke, and east zone) much higher Th values of >300oC and 200-275oC occur and may reflect post entrapment heating by Franklinian-aged dykes (ca 720 Ma) and local methane production, respectively. At Hawker Creek highly radiogenic pyrites were used for age constraints. These Model Ages show a large range from > 900 Ma to ca. 400 Ma. We interpret these Re-Os pyrite and fluid inclusion data to indicate primary mineralization at Nanisivik from a low T (<130oC) Na-rich fluid at ca. 1100 Ma, with younger heating events possibly contributing to scatter in the Re-Os data. At Hawker Creek, primary mineralization is constrained to be > 900 Ma, but with evidence for much younger (ca 400 Ma) pyrite formation within the Nanisivik Fm.

References

Sherlock, RL, et al., 2004, Geologic and geochronologic constraints on the timing of mineralization at the Nanisivik zinc-lead MVT deposit, northern Baffin Island, Nunavut, Canada. Econ.Geol. 99, 279-293

Symons, DTA., et al., 2000, Paleomagnetism of the Society Cliffs dolostone and the age of the Nanisivik zinc deposits, Baffin Island, Canada: Min Dep , 35 , 672–682