Magnetic mapping of Majhgawan diamond pipe of central India

Abstract

Magnetic response over kimberlite/lamproite pipes can be used to map their horizontal and vertical cross‐sections. A published ground magnetic vertical intensity contour map is used to map the Majhgawan kimberlite pipe near Panna in central India. Using Barnett’s (1976) method, we obtained a reasonable match between the computed and observed fields with three separate bodies. The model suggests a possible later intrusion into the main pipe. Geological studies (using drill‐hole data) imply a nearly concentric vertical lithological zoning within the pipe and thus support the hypothesis of multiple intrusions, indicated by magnetic data. The multiple intrusion hypothesis is of interest to exploration because specific intrusions within one composite pipe may differ markedly in the incidence of diamonds. The higher incidence of diamonds reported in the central part of the Majhgawan pipe, as compared to the outer part, also supports the possibility of a later intrusion into the main pipe.