Geophysical Methods of Identification of Ore Control Structures of Orogenic Gold Deposits in Low-Contrast Terrigenous Rocks by Petrophysical Characteristics

The paper presents the analysis of characteristics of abnormal geophysical fields of the ore control of the Malo-Tarynskoe orogenic gold deposit in Verkhoyano-Kolymsky folded area, the Northeast of Russia. It is located in terrigenous rocks of the top Triassic, poorly contrast on petrophysical characteristics. Ore bodies of the Malo-Tarynskoe deposit are presented by the mineralized crushing zones with veinlet-disseminated and vein-disseminated mineralization. To identify the features of manifestation the ore control in geophysical fields land geophysical surveys are conducted by the methods of high-precision magnetic exploration and electroinvestigation. Magnetoprospecting works have established the low-amplitude mosaic structure of the magnetic field of the Malo-Tarynskoe deposit. The main magnetorevolting structure is the Samyr granitoid massif which is allocated with a magnetic minimum (-99 nT). Extreme positive values of the magnetic field are connected with hornfelsed ores in the zone of contact metamorphism (170 nT). Various anomalies as low-magnetic, mainly linear ones caused by explosive violations are distinguished (-12 - 20 nT). In the electric field, the abnormal zones have the linear nature of various extent and intensity. Pro-deleting of anomalies changes from sublongitudinal to northwest. The anomalies of low electrical resistance, generally trace zones of crushing and jointing (208-2300 ohm*m). In general, they are grouped in three "regional" abnormal areas of the northwest and North northwest orientation of low electrical resistance and correlated with the situation of the ore control zones of the Malo-Tarynskoe fault (208 - 1600 ohm*m). Sites with frequent alternativeness and alternating electric anomalies indicate lithologic heterogeneity of the environment (2500 - 10000 ohm*m). The study has shown magnetoprospecting to be effective when mapping magmatic formations and explosive violations. They allow delineating intrusive bodies and allocating hornfelsed zones. The electric profiling application by the method of a median gradient solves a wide range of geological tasks. Apart from allocation of the structures controlling gold mineralization in faint terrigenous ores, electro-investigation allows to carry out the lithologic partition of permafrost rocks in the territories blocked by friable deposits of considerable power.