INTEGRATED GEOPHYSICAL INVESTIGATIONS OF METALLIC MINERALS IN PRE-CAMBRIAN SHIELD ROCKS OF WAD SAYYIDAN AREA CHINIOT PUNJAB (TOPOSHEET NO.44-A/13)

Abstract

Pre-Cambrian Shield Rocks have always been attractive target for valuable metallic minerals exploration all over the world. In Pakistan these rocks are exposed in Sargodha, Shah Kot, Sangla Hill (Punjab), and Nagar Parker area of Sindh Province. Geological Survey of Pakistan and Mines and Mineral Department, Government of Punjab, initiated a joint venture project in 2013 for the exploration of metallic minerals. The project includes the coverage of 28 toposheets by semi-detailed magnetic survey and followed by three promising zones with detailed integrated geophysical surveys. Gravity, magnetic and IP/Resistivity surveys were included in the detailed integrated survey. In 28 toposheets the areas of Sargodha, Faisalabad, Chiniot, Hafizabad, Shahkot, Sangla hill, Nankana Sahib, Sheikhupura, Lahore, Kot Radha Kishan, some part of Changa Manga Forest etc. are included by covering an area of about 18000 Square kilometers. The Topo Sheets included are 44-A/9, 44-A/13, 44-A/14, 44-A/15, 43-D/12, 43-D/16, 44-E/1, 44-E/2, 44-E/3, 44-E/6, 44-E/7, 43-H/4, 43-H/8, 43-H/12, 43-H/16, 44-E/5, 44-E/9, 44-E/13, 44-I/1, 44-E/10, 44-E/11, 44-E/12, 44-E/14, 44-E/15, 44- E/16, 44-I/2, 44-I/3 & 44-I/4. The data acquisition started in August, 2013 and continued till December, 2015. The Semi-detailed magnetic stations were observed along all the mattled and un-mattled accessible tracks present in the area at approximately 500 meters interval. The semi-detailed magnetic map of the area shows two parallel NW-SE trending faults. The majority of the demarcated 32 magnetic anomalies lie on the same inferred faults. Based on the semi-detailed magnetic survey, three areas Wad Sayyidan, Ghutti Sayyidan and Chak Jhumra were selected for detailed integrated geophysical survey. The areas are in close proximity of already discovered Chiniot and Rajoa Iron ores. A grid spacing of 50 x 50 meters in Wad Sayyidan was laid. About 9600 gravity and same number of magnetic stations were observed in Wad Sayyidan area. Similarly, 55 IP/Resistivity points were observed down to the depth of 1000 meters in Wad Sayyidan area, respectively. The gravity signature of the anomalies is also supporting the presence of concealed subsurface fault in the areas of investigation and magnetically susceptible DRSML QAU material has most probably been emplaced along the fractured weak zone. In general, in Punjab plains, bouguer gravity effects are closely correlated with the subsurface topography of basement rocks. However, the magnetic signature in shallow basement rocks as inferred from Vertical Electrical Soundings with high gravity show the presence of magnetically susceptible minerals like magnetite. The IP signal in Wad Sayyidan area has quite a large variable range as compared to the other two areas (Ghutti Sayyidan & Chak Jhumra) where the detailed studies were carried out. The large values of chargeability are observed at the edges of the positive gravity closures. These large values of chargeability normally correspond to the sulphide mineralization like copper, gold, zinc, lead etc. Test drilling is recommended based on the results of the integrated geophysical surveys for the confirmation of subsurface picture of geology and the causative source generating the anomalous gravity, magnetic and IP effect