Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Dinesh Gupta ¹, Radhe Shyam ¹, A. K. Agarwal ¹, B. B Bhattacharya ², B. Banerjee ³

Affiliations
1 Geological Survey of India, 15-16 Jhalana Doongri, Jaipur-302004, IN
2 Indian School of Mines, Dhanbad-826004, IN
3 Marine Wing, Geological Survey of India, Calcutta -700016, IN

Abstract

In surface geophysical surveys, resistivity contrast between the ore and host rock plays a vital role in the success ratio of the surveys. To overcome the problem of insufficient resistivity contrast, a modified method, Mise-a-la-masse, as tried and found to be very effective in tracing the extensions of polymetallic sulphides intersected in a borehole. The method was applied to Pb-Zn and sulphide hosted gold prospects in Rajasthan and the results obtained indicate that Mise-a-la-masse method can be successfully employed for delineating subsurface extension of polymetallic sulphide deposits.

Keywords

Exploration Geophysics, Electrical Resistivity Contrast, Polymetallic Sulphides, Rajasthan.

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L. N. Singh ¹, D. Gupta ², Ram Gopal ², Radhe Shyam ², S. K. Singh ¹, S. L. Singh ², A. K. Agrawal ³

Affiliations
1 Geological Survey of India, Northern Region, Lucknow - 226 024, IN
2 Geological Survey of India, Western Region, Jaipur - 302 004, IN
3 Geological Survey of India, A M S E Wing, Bangalore - 560 078, IN

Abstract

A small deposit of lead and zinc was established in southern part of Sawar metasedimentary belt during third phase of drilling. The Mise-A-La-Masse survey, a post discovery geophysical method carried out in the boreholes of this belt has yielded significant results. This method has been useful in delineating the subsurface disposition of mineralised zones and their lateral extension. This technique is also successful in the area in establishing correlation between different parts of an ore body with varying sulphide percentage, which are located distantly but are in electrical continuity. Hence the Mise-La-Masse method has been of immense help in planning the boreholes thereby optimizing drilling cost in the Sawar Belt. The composite map of equipotential line and chargeability contour has indicated that the contour pattern and disposition of anomaly axes are similar in both the cases.

Keywords

Mise-A-La-Masse Survey, Pb-Zn Mineralised Zone, Composite Map, Sawar Metasedimentary Belt, Ajmer District, Rajasthan.

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Ram Gopal ¹, Dinesh Gupta ¹, Radhe Shyam ¹

Affiliations
1 Geological Survey of India, WR, 15-16, Jhalana Doongri, Jaipur-302004, IN

Abstract

Downhole wide spacing IP (DHIP), Self-potential (SP), magnetic susceptibility and applied potential observations were made along the boreholes drilled for Pb-Zn-Cu sulphide in mineral belts of Rajasthan The aim was to identify mineralised zones, physical property contrast of the mineral and country rock and presence of mineralisation in the vicmity of the borehole but missed in drilling

Number of boreholes were surveyed in different parts of the mineral belts of Rajasthan and the relationship between apparent resistivity and chargeability, SP and magnetic susceptibility and lithology of the cores has been studied and analyzed Chargeability 'high', resistivity 'low', SP 'low/high' and magnetic susceptibility 'high' characterized the sulphide mineralisation The surveys were successful in detecting the presence of mineralisation in the drill hole, studying the m situ physical properties of barren & mineralised rocks and finding the correct depth of the conductor It helped in conducting raise-a-la-masse surveys and interpretation of surface geophysical data m mineral belts of Rajasthan Applied potential (Mise-a-la-masse), surveys were able to give information on the lateral extension of the mineralised zones intersected in the borehole

Five examples of detection of sulphide mineralisation in boreholes of Kayar, Pindwara-Watera and Danba-Bethumbi mineral belts of Rajasthan are presented The results indicated average appaient resistivity low value of the order of 1 to 10 ohm-m and magnetic susceptibility of order of 600-5000 x 10⁶ c g s units in the sulphide zones, while in the country rocks values recorded were m the range of 3000-24,000 ohm-m and 50-500 x 10⁶c g s units respectively The diagnostic resistivity response is simply related to the percentage, size and disposition of the sulphide mineralisation The association of high magnetic susceptibility is indicative of pyrrhotite mineralisation in these zones The SP 'high' and 'low' could be due to the electrochemical potential developed at the interface of country rock and ore body Detection IP/ resistivity measurements have also improved the prospective search radius of drill-holes and are successful in assessing qualitatively the lateral extent ol intersected mineralisation.

Keywords

Drill-Hole Induced-Polanzation (DHIP), Self-Potential, Magnetic, Geometric Disposition, Rajasthan.

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