Three‐dimensional probability tomography of self‐potential anomalies of graphite and sulphide mineralization in Orissa and Rajasthan, India

Abstract

International audienceCharge occurrence probability (COP) and dipole occurrence probability (DOP) tomographic imaging of graphite and sulphide orebodies, which were earlier detected by a self-potential (SP) survey, were carried out. Three typical examples, two shallower graphite lenses in Bender and Berni, Orissa State, and one relatively deeper sulphide deposit in Kayar, Rajasthan State, are presented. An exploratory test hole, drilled on the basis of the SP results in Bender and Berni, struck graphite. A mise-à-la-masse survey was also carried out on these two deposits to delineate the orebody. The graphite deposits have subsequently been mined. The shapes of the graphite bodies, especially the upper parts, are now known. The Bender deposit is a single graphite lens, whereas the graphite occurrences in Berni are complex multilens-type deposits. Both the COP and DOP techniques clearly imaged the single lens at Bender, as well as the multilens deposits at Berni. The Kayar sulphide deposit, unlike the graphite deposits, has not yet been mined, and therefore it is not delineated as precisely as the graphite orebodies. However, its outline is known from the drilling data. The imaging results of COP and DOP show good agreement with the drilling results of the sulphide deposits

Interpretation of self-potential anomalies by Enhanced Local Wave number technique

“…Revil et al (2001) and Iuliano et al (2002) further extended the concept of COP to account for the dipolar sources, i.e., dipolar occurrence probability (DOP) function to interpret potential field data. Bhattacharya et al (2007) compared the COP and DOP responses over the graphite and sulfide ore deposits in India. It may be worth mentioning that the COP/DOP techniques do not provide any information on the shape of the causative source.…”

A fast interpretation of self-potential data using the depth from extreme points method

“…Here we interpret the Bender anomaly (Figure 9), Balangir, Orissa, India (Bhattacharya et al, 1984(Bhattacharya et al, , 2007. The rock units in the area are mainly of the Archaean crystalline complex; garnetiferous sillamanite schists, gneisses, and garnetiferous quartzites traversed by quartzite and pegmatite veins.…”

“…The correlation method has an inherent lack of criteria to assess a priori the best type of scanning source (Gilbert and Sailhac, 2008). In fact, Bhattacharya et al (2007) compare the crosscorrelation results for dipole and pole sources of SP data over graphite and sulfide ore deposits in India, but they are not able to indicate the best result.…”

“…The deposits are shallow, and the ore was extracted by open cast mining and the actual depth to the top was 5 m. The open cast mine stopped due to flooding by groundwater but the presence of the ore is still seen at the bottom of the abandoned mine (Bhattacharya et al, 1984). Bhattacharya et al (2007) interpret this anomaly and compute COP and DOP maps from SP crosscorrelation. However, they obtain inconsistent results, yielding a much deeper result in the DOP case (their Figure 3).…”

Reply to comment by D. Gibert and P. Sailhac on “Self‐potential signals associated with preferential groundwater flow pathways in sinkholes”

“…We discuss below the validity of this approach to self-potential data. Note that this approach was also used very successfully by Revil et al [2001], Iuliano et al [2002], and Revil et al [2003aRevil et al [ , 2003b and recently by Jardani et al [2006b] and Bhattacharyal et al [2007] to localize the causative source of self-potential anomalies. Finally, we will discuss briefly future exciting trends in the inversion of self-potential signals.…”