鉱物資源探査における空中物理探査の現状と将来

Abstract

Airborne geophysical survey methods, such as magnetics, electromagntics, and radiometrics, are well known, have numerous applications, and are regularly employed in regional surveys around the world by both governments and private organizations. Technology regarding each of these methods has gradually improved and along with it, the introduction and necessary accuracy in Global Positioning Systems (GPS), the introduction of image processing techniques allowing a greater range in data display compared with conventional contouring, and the availability of multi-client data sets resulting in significant cost reduction. Airborne geophysical methods have long been recognized as a valuable geological survey tool since the first airborne magnetic survey was flown in 1936 as part of a mineral exploration program. The Metal Mining Agency of Japan (MMAJ) has for more than three decades employed airborne geophysical methods in both its domestic and overseas mineral exploration programs. In general, the surveys provide a wide range of data concerning lithological variation, structure, and features peculiar to mineralization. Domestically, the MMAJ has employed airborne magnetic surveys since 1969 as part of their regional exploration program, and airborne electomagnetic and magnetic surveys since 1975, initially as part of their research into the application of these methods in the search for Kuroko and epithermal style mineralization. A direct result of this work was the discovery of the Hishikari deposit, Japan's premier gold mine. In 1996, the MMAJ embarked on a new program of high-resolution airborne magnetic and radiometric surveys, beginning in the Hokusatsu region of southwest Kyushu. The results confirmed the importance and application of these sensors in the search for low sulphidation epithermal style gold mineralization. High-resolution geophysical surveys remain an integral part of the domestic survey departments current activities. Overseas, the MMAJ began its history of airborne surveys in Zaire in 1968 with a fixed-wing magnetic survey. Since that time a range of sensors have been employed around the world for various styles of mineralization, the most recent being a helicopter survey this year in the Bicol region of the Philippines targeting porphyry and epithermal copper-gold deposits. Although the above mentioned methods have been successfully employed in the search for mineral deposits, they are equally important in other fields. The identification and surveying of faults, slope stability, dam site identification, transport and land-use planning, electric power line construction, underground surveying, and the monitoring of radioactive elements, are just a few of the applications currently employed by both government and private organizations. Airborne geophysical surveys provide an important and essential data source which should be undertaken as part of Japan National Mapping Program with both current and future multipurpose users in mind. Additionally, it is critical that the government continue to develop the necessary technology concerning data acquisition, processing, analysis, and interpretation, and build upon the high standards, already established within the MMAJ. Such a program is believed to be a matter of national importance.