ISBN:

0169-1368

Keywords:

absolute age, Arctic region, Canada, carbonate rocks, chemical composition, dates, diagenesis, early diagenesis, Fluid inclusions, fluid phase, geologic thermometry, Grenvillian Orogeny, homogenization, host rocks, inclusions, isotope ratios, Isotopes, lead ores, lead-zinc deposits, low temperature, mesoproterozoic, metal ores, neoproterozoic, Nunavut, Ordovician, P-T conditions, Paleozoic, Precambrian, proterozoic, pyrite, Re/Os, Rodinia, S-34/S-32, Sedimentary rocks, Stable isotopes, stress fields, sulfides, sulfur, supercontinents, Temperature, upper Precambrian, zinc ores

Abstract:

The age and origin of the past-producing Nanisivik carbonate-hosted Zn-Pb deposit in Nunavut, Canada, have been controversial for decades. Various direct and indirect dating methods have produced results ranging from Mesoproterozoic to Ordovician in age, and previous studies of the mineralising fluids have suggested that the fluids were anomalously hot (> 150 degrees C). This study combines Re-Os (pyrite) geochronology, in-situ sulphur isotope analysis, and fluid inclusion analysis to refine both the timing of mineralisation and the nature of mineralising fluids. Re-Os pyrite analysis shows that the Nanisivik deposit formed ca. 1.1 Ga, broadly similar to the depositional age of the host rock and with the Grenville orogeny, making it one of few known Precambrian carbonate-hosted Zn-Pb deposits. In-situ sulphur isotope measurements from Nanisivik show a narrow delta (super 34) S range of 27.54 + or - 0.72, very similar to what has been reported before in bulk sample analyses. New fluid inclusion data show that the mineralising fluids were nearly equal 100 degrees C, which is not anomalous in the context of carbonate-hosted base-metal deposits. The fluids exhibit no significant spatial variation in homogenisation temperature in the 2-km-long "upper lens" of the ore deposit, but recrystallisation and modification of fluid inclusions took place in the immediate vicinity of the cross-cutting nearly equal 720 Ma "mine dyke". The deposit is broadly inferred to have formed during late Mesoproterozoic assembly of supercontinent Rodinia, when regional hydrostatic head developed under the influence of far-field stresses originating in the developing Grenville orogen. The Nanisivik deposit remains anomalous only in its age; most other aspects of this ore deposit are now shown to be quite typical for carbonate-hosted ore deposits.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2017-074030<br/>Nanisivik Deposit