Base de données de recherche des TNO

Régions: North Slave Region

étiquettes: geology, sedimentary rocks

Objectif(s): To collect several kg rock samples of 2.85 billion year old sedimentary rocks from 3-4 areas of the Slave province, extending Point Lake west to Exmouth Lake for diamond separation, after which mineral analyses will be conducted.

Description du projet: This licence has been issued for the scientific research application No.5325. The aim of this project is to collect several kg rock samples of 2.85 billion year old sedimentary rocks from 3-4 areas of the Slave province in the NWT, extending Point Lake west to Exmouth Lake. These samples will be collected during summer 2022 and then the research team will spend ~2 years studying these samples in our laboratories in Canada and the United State. The samples will be processed for diamond separation at the Saskatchewan Research Council, after which mineral analyses will be conducted at both the University of Alberta and Penn State University in the United States. Outputs from this project will include research presentations (one at the Yellowknife Geoscience Forum if funding allows), as well as peer-reviewed research papers. These outputs will be shared with the interested communities and agencies as the work progresses. There will be three to five geologists and one float plane pilot staying at the Peterson's Lodge on Point Lake. The research team will take day trips with a Bush Hawk float plane to nearby lakes where the geologists will use small rock hammers to take ~1kg rock samples for scientific research. The team will conduct field sampling of ancient basement rocks exposed on the surface. The team will be residing at Peterson's Lodge for the duration of our project and will be flying a Bush Hawk float plane up to 100 km from this location during the day. The team will land the Bush Hawk on small lakes, and hike to outcrops near the lakes. Once at outcrops of scientific interest, the team will use small hand hammers to take geological samples for research (~1 kg samples) of the rocks of scientific interest. First, the team will analyze the U-Pb ages of detrital minerals found within the Slave craton metasediments. The extent of previous data from the Slave craton cover group samples is limited to single zircon grain Thermal Ionization Mass Spectrometry (TIMS) analyses and laser-ablation Uranium-Lead (U-Pb) zircon ages from samples in the south-central Slave followed by hafnium isotopic analysis. We will vastly expand this dataset by analyzing U-Pb ages of detrital zircons from samples collected along strike and vertically through these sedimentary sequences. These analyses will be conducted in the newly established PSUchron LA-ICPMS laboratory, which is co-directed by Principal Investigator (PI) Reimink. This laboratory contains an Analyte G2 laser ablation system coupled to two mass spectrometers (a Thermo ElementXR magnetic sector mass spectrometer and a Thermo iCapRQ quadrupole mass spectrometer). Several hundred zircon grains from each sample will be analyzed (the number of analyses per sample will vary depending on factors such as zircon recovery and sample importance), with the bulk of analyses being conducted by the PhD and undergraduate students, providing them with experience and expertise in cutting-edge analytical techniques. This data will provide information on maximum depositional ages, an estimate of the bulk age of the felsic crust eroded into the sedimentary unit, and allow us to identify very ancient (>3.6 Ga) crustal sources in the Mesoarchean. Additionally, comparisons of the U-Pb age spectra of individual samples from the same units will allow the team to determine the amount of source heterogeneity that is primarily a function of catchment size and transport distance. Finally, U-Pb zircon ages will be integrated with whole-rock isotopic data to evaluate the mechanisms of formation of the Mesoarchean Slave craton, be it internal reprocessing or juvenile addition. Specific samples collected during the fieldwork will be analyzed for their chemical compositions. The whole-rock elemental chemistry of ancient sediments has been used to evaluate both the degree of chemical alteration and defining chemical groupings of ancient sediments. The research team analyze many of the same samples for their Samarium-Neodymium (Sm-Nd) isotopic compositions. The Nd-isotope system can be used to estimate the crustal model age for the bulk source to the sediments and is particularly important in concert with detrital zircon U-Pb analyses, as has been shown with previous analyses of Slave craton sediments. The team will test models for the source composition, ages, and crustal sources, by integrating the U-Pb ages of Mesoarchean sediments with their whole-rock Nd-isotope compositions. The whole-rock Sm-Nd isotopic compositions will be analyzed at The Pennsylvania State University using the Thermo Triton Plus mass spectrometer in the Laboratory for Isotopes and Metals in the Environment (LIME). PI Reimink has extensive expertise in using the Sm-Nd system and is currently setting up his own Sm-Nd analytical protocols. Whole-rock Sm-Nd analyses will be conducted by dissolution of whole-rock powders, using a calibrated mixed 149Sm-150Nd spike, with both Sm and Nd isotopic analyses being measured on the Thermo Triton Plus TIMS instrument. Diamond separation will first be conducted in the Saskatchewan Research Council’s (SRC) accredited diamond separation facility¬—the world-leaders in micro diamond recovery. Yields will be enhanced by using the University of Alberta Sel-Frag disintegration facility which has been shown to increase micro-diamond yield from some rocks. The team will use SRC’s services for two reasons. First, they are an accredited diamond separation facility, meaning there will be no doubt as to the veracity of the diamond discoveries. Second, they have a more industrial-scale process that can both intake large (>20 kg) samples efficiently, and be able to thoroughly extract all valuable (and potentially limited) diamonds from these samples, along with any diamond/kimberlite indicator minerals that may be present (e.g., high-Cr garnets, chromites, Cr-diopsides) plus possible gold. Depending on diamond abundance, additional diamond separations will be conducted in the PSUchron’s sample preparation facilities (following Sel-Frag disaggregation) under the direction of PI Reimink by standard heavy mineral separation procedures, and additional techniques derived from SRC procedures. This proposal provides a chance to create an unprecedented archive of Archean diamonds that have uniquely modest mantle residence times (i.e., have resided near the surface for ~2.8 Ga). The team anticipate the recovery of many more stones, which will provide us with an unparalleled opportunity to trace diamond paragenesis in the Archean, and such a diamond sample set will provide ample opportunities for future analyses to be conducted by the geochemical community. Once separated, diamonds will be first analyzed by Fourier-transform infrared spectroscopy (FTIR) to both confirm the diamond composition and determine the aggregation state (B-centers) of nitrogen within the diamond lattice. This information will help determine the time-temperatures of mantle residence for these diamonds and place minimum constraints on their ages. Select diamonds will be mounted, polished and analyzed for their carbon and nitrogen isotopic compositions by ion microprobe at the University of Alberta’s Cameca 1280 ion microprobe. The research team plan to present ongoing research at the NWT Geoscience Forum, and will pass along all publications and research outputs to the interested NWT stakeholders, including the Northwest Territories Geological Survey. If other communities and stakeholders are interested, the team are very happy to share final research outputs with them. All data collected during this research will be uploaded to free, open-access geoscience data libraries (EarthChem, Geochron.org, etc) so that the broader geoscience community, and any interested persons can access the data. The fieldwork for this study will be conducted from August 7, 2022 to August 12, 2022