Abstract

Laboratory velocity measurements on nickel-sulphide samples show that the velocity contrast between a sulphide body and rocks typical of the Canadian Shield can be fairly large. In view of this, the feasibility of delineating the sulphide body by means of a combination of fan shooting and least-squares analysis was examined by both computer model simulation and field experimentation. The method consists, essentially, of shooting several fans emanating from the perimeter of a rectangle around the suspected location of a deposit, and measuring the corresponding first arrival times. The rectangle is then divided into grid units, and the apparent velocity in each grid unit is found by least-squares solutions of an overdetermined system of linear equations.The computer model tests indicate that in cases where the velocity contrast between the surrounding medium and the anomalous zone is good, and each medium homogeneous, the method is a potentially useful auxiliary technique for mining exploration. However, field tests show that these requirements (i.e., good velocity contrast and homogeneity of each medium) may constitute a serious limitation of the method.

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