SP 44 Chapter 18: Bedrock Topography and Drift Thickness Models from the Timmins Area, Northeastern Ontario An Application of GIS to the Timmins Over
by Roger C. Paulen, M.B. McClenaghan and J.R. Harris.
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This chapter is from GAC's Special Paper 44: "GIS For the Earth Sciences" editted by Dr. Jeff Harris. To purchase the entire book in hardcopy or disc formats, please see the Special Papers section of our bookstore.
ABSTRACT: Mineral exploration in thick, drift-covered glaciated terrain, such as northeastern Ontario, is often difficult. Exploration geologists require a regional-scale overburden geological framework, suitable media for geochemical sampling (till) and an accurate map of bedrock topography. Quaternary glacial sediment can exceed 100 m thickness over the highly mineralized Abitibi Greenstone Belt, which hosts multiple lode gold and polymetallic volcanogenic massive sulfide (VMS) deposits.
As part of the Canada-Ontario Mineral Development Agreement (NODA), the Geological Survey of Canada compiled information from exploration and government overburden drillhole records from the Timmins area. The compilation includes information from over 5400 overburden boreholes and over 1400 diamond drillhole logs and was released digitally in 1995.
A digital elevation model (DEM) of bedrock topography based on bedrock depths recorded in the Timmins Overburden Drillhole Database was created in a Geographic Information System (GIS) using various interpolation methods. Borehole records that have surficial geological data were integrated, to provide additional control for the bedrock DEM and associated drift thickness (isopach) map. Utilizing a GIS to integrate a borehole database with surficial mapping to facilitate drift prospecting is new to the Timmins region. This 3-D structural model may lead to a better understanding of the geometry and depositional environments of the Quaternary units. It can be a key tool for delineating till units suitable for mineral exploration sampling, predicting overburden thickness and inferred drilling costs, providing information pertaining to the aggregate industry, aquifer delineation, and supporting geophysical interpretations. The results of this GIS study indicate that the general trends in subsurface topography, such as preglacial differential weathering and former basins, are closely related to bedrock lithology.
Geological Association of Canada
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