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Borehole magnetics navigation

An example from the Stratmat Deposit, Bathurst, New Brunswick

McMaster University, Hamilton, Ontario, Canada

J. Mwenifumbo

Geological Survey of Canada, Ottawa

Corresponding author: morriswa{at}mcmaster.ca

Information acquired from studies of borehole core or from borehole geophysical logs form an integral part of all mineral and oil exploration programs. Yet, as is the case of any survey, the value of that information is dependent upon how well the location of each observation point is known. Location information becomes especially critical when the resource target has limited depth extent. For example, a location error of 10 m when evaluating a 5-m thick gold vein can make the difference between an economic and noneconomic deposit. The trajectory of a borehole is commonly computed using an array of data points that are acquired progressively with increasing distance along the borehole. Depending on the type of survey employed, observation points may be sparse (static readings at a limited number of points) or redundant (dynamic surveys where the distance between observation points is less than the length of the rigid probe). At each observation point, three parameters are normally acquired: (a) inclination, dip of the borehole relative to horizontal; (b) dip direction, the orientation of the maximum dip direction relative to geographic north; and (c) depth, usually measured as distance along the borehole.