A better understanding of glacial transport and depositional environments has resulted from micromorphological studies of glacial sediments over the last several decades. The past-producing Pb-Zn mine at Pine Point, Northwest Territories, has >20 m of continuous diamicton overlying low-relief Paleozoic bedrock, which provides a unique opportunity to further the investigation of micromorphology in the study of glacial sediments, in particular the sustained depositional record versus the erosional records of various ice-flow trajectories and how that information can help document indicator mineral dispersal. Pit-K62 at Pine Point has a ~23 m section of diamicton from which 19 samples were collected and thin sections prepared. This report describes sample collection, thin section production and analysis, and microstructure identification of each of these 19 samples. These results will be combined with glacial stratigraphy and indicator-mineral work previously completed for the area to refine exploration techniques for Mississippi Valley-type Pb-Zn deposits utilizing the transportation history of their indicator minerals.
With increased focus on the practical applications of glacial-drift prospecting, especially in northern Canadian regions, a firm understanding of the glacial history of the region is becoming increasingly important. The past-producing Pine Point mine, Northwest Territories, offers an ideal location to further this understanding as it provides large sections of unaltered till facies, which overlie low-relief bedrock. Field research in the area has used visual observations, clast fabrics, grain-size analysis, geochemical analysis, heavy-mineral concentrates, striation measurements, and pebble lithologies to determine the glacial history of the region. This information will then be used in conjunction with indicator-mineral work in the area to develop a better understanding of how to explore for Mississippi Valley-type Pb-Zn deposits and the transportation history of their indicator minerals.
The glacial records of the inner-core regions of the Laurentide Ice Sheet (LIS) document complex yet coherent patterns reflecting ice-sheet change (e.g. ice-divide migration), providing unique insights into past glacial conditions. This study develops a conceptual model of subglacial dynamics evolution within a major ice-dispersal centre of the LIS in northeastern Quebec, Canada using a GIS-based analysis of the surficial geologic record. Multiple proxies of subglacial conditions (subglacial streamlined landforms, lake density and lake area over thin drift/bedrock) were analysed through grid-overlay techniques and then classified based on different proxy variables ranging from highly mobile warm-based to immobile cold-based conditions. An additional proxy (till blanket) was used to identify areas of thick till deposition, but with few proxies (few lake or landform metrics). Based on local ice-flow reconstructions, the most 'relict' glacial terrain zone (GTZ1) has warm-based conditions over 66% of its area and is remarkably well preserved, suggesting laterally extensive warm-based conditions during the oldest identified ice-flow phase. This relict glacial terrain is partially overprinted by two subsequent ice-flow phases in spatially restricted zones in the northeast (73% warmbased), east-central (41% warm-based), and northwest (33% warm-based) of the study area. A zone of more sluggish conditions (only 3% warm-based) was identified in the highlands at the centre of the study area, characterized by thin till cover, few landforms, yet with large patches of relatively abundant small lakes, indicative of areal scouring. No clear evidence of sustained cold-based conditions (i.e. high chemical index of alteration values or high 10 Be abundances) was found in the study area. These results suggest that warm-based conditions (active erosion and/or deposition) were uniformly widespread during the earliest ice-flow phase, later becoming more spatially restricted with broader sluggish ice conditions. These spatially restricted regions of warm-based subglacial regimes were likely controlled by surrounding and down-flow ice streaming.
The Rivière De Pas area is of moderate relief, characterized by extensive till blanket units in lowlands and till veneer units and bedrock outcrops at higher elevations. The region was differentially eroded by the Laurentide Ice Sheet throughout Wisconsin time, largely influenced by the migration of the Ancestral Labrador Ice Divide, originally from east of the De Pas batholith to west of the map area. Phases of radial ice flow from the migrating ice divide imparted discordant erosional ice-flow landforms and flow indicators on the landscape. Significant regions of bedrock at higher elevations have been washed of till from late-phase ablation of the ice sheet during deglaciation, with associated small meltwater channels. Below 425 m elevation, the region was inundated by glacial Lake McLean, a proglacial lake that occupied the lowlands in the northwest. Sediments from glacial Lake McLean are limited to littoral beach deposits and winnowed till surfaces.
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