| 講演要旨(和文) | | 海洋調査協会では，一部既知鉱床が明らかとなっている久米島西方沖にて，深海曳航体による電気探査を行うとともに，ROVによる海底重力探査を実施した．電気探査では明瞭な自然電位異常も観測され，負の電位異常を示す範囲は同時に海水よりも低比抵抗であるという結果を得た．この結果と反射法地震探査の結果から，5点は負の電位異常・低比抵抗を示す地点を，1点はこれらの異常域に近接するが異常が認められない地点を選定し，ボーリングを実施した．その結果，先の5点では量の多少はあるが硫化物層が確認され，また後の1点では硫化物層が存在しなかった．またこれらのボーリング地点を東西に横切る2測線について海底重力探査を実施した．その結果，硫化物層が最も厚く存在するボーリング地点付近を中心に高重力異常を示し，高密度物体が埋もれているモデルで説明することができる．これは硫化物鉱床の規模を示していると考えられる． |
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| | 講演要旨(英文) | | The electrical prospecting methods were conducted by a deep-tow off the west of Kumejima where the existence of the hydrothermal ore deposit was partially known, and ocean bottom gravity survey was also conducted by a ROV. In the electric survey, clear SP anomalies were observed, and the results that the areas showing the negative SP anomaly were simultaneously lower resistivity than the seawater were obtained. Based on this result and the result of the seismic reflection survey, six bowling points were selected. Five of them were points where negative SP anomaly and low resistivity were shown, and one was close to these anomalies, but no anomaly was observed. As a result, in the previous five points, the sulfide layer was confirmed although there was some amount, and at the later point there was not found sulfide layer. The ocean bottom gravity survey was also conducted on two lines crossing these bowling points in the east-west direction. As a result, high gravity anomaly was observed around the point where the sulfide layer was the thickest, which indicates that the high density materials are buried. This is considered to indicate the scale of the sulfide deposit. |
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