The exploration of gold by magnetic method in Hired AreaSouth Khorasan, a case study

Hired is a large gold prospecting area which is located in south khorasan province, in theeast of iran. gold mineralization is found in 4 target areas covering about 24 krn. thehost rock s are mainly tertiary volcanics, some jurassic and cretaceous sediments. subvolcanic rocks are of magnetite series (gabbros to diorite) and ilmenite series (granitegranodiorite-monzonite) which have intruded the tertiary and older rocks. importantstyles of mineralization are: stockwork, skarn, vein, and replacement. stockwork goldmineralization has only pyrrhotite and is found within or around the granite-granodioritemonzonite.detail core logging was carried out in 4 target areas with respect to goldcontent, mineral paragenesis, types of veinlets, rock types, and measuring the magneticsusceptibility. within the stockwork mineralization at east of target i , there is goodcorrelation between gold grade, amount of pyrrhotite, and magnetic susceptibility. athired, sub-volcanic rocks of the ilmenite series (granite-granodiorite-monzonite) havesusceptibility less than 40 x 10-5 si. the magnetite series (gabbros to diorite) havesusceptibility of 150 - 900 x 10-5 si. stockwork gold mineralization has susceptibility of200-3500 x 10-5 si. therefore the host rocks, granite-granodiorite-monzonite, have lowmagnetic susceptibility. based on this sharp magnetic contrast ground magnetic wasselected as a suitable geophysical method. the aim was to use the magnetic method fordrill target identification of gold ore east of target 1. the total magnetic field intensity(tmi) was measured in 780 points along 25 line s. measurement spacing was 2 meter.magnetic lines , contour maps , and images revealed large anomalies at east of target irepresenting the magnetic responses of gold ore. the depth of the anomalies is estimatedto be shallow as indicated by their expression on the first vertical derivative map. thisprediction is consistent with mineralogical observation on the surface and the continuedmap . the locations of the anomalies on the reduced to the pole (rtp) map areproposed as suitable points for drilling target.