Niue - Deepsea Mineral Resources Survey (Atlas &Report)

The Cooperative Study on the Deepsea Mineral Resources in Selected Offshore Areas of the SOPAC Region, 2003
-Sea Area of Niue-
The survey area of the SOPAC project for fiscal year 2003 is a quadrilateral sea area (approximately 605,000 km2) within the EEZ of Niue, enclosed by geodesic lines connecting the following coordinates (Fig. 1-1). The area was selected in accordance with the joint study program for deepsea mineral resources in the EEZ of the SOPAC member countries agreed upon by the Japanese executing agency and South Pacific Applied Geoscience Commission (SOPAC) on February 27, 2003.The survey aims to assess the potential of manganese nodules by conducting deep seafloor mineral resources survey within the Exclusive Economic Zone (EEZ) of Niue, a member country of SOPAC. The survey comprises ship survey and data analysis for assessment of mineral resources and understanding of environmental characteristics within the sea area.Latitude Longitude a. 16°00′S 173°00′Wb. 16°00′S 166°00′Wc. 23°00′S 166°00′Wd. 23°00′S 173°00′W The water depth of the survey area is about 5,000m deep. In the north part of the area the SBP type with acoustically opaque layer on the uppermost horizon is predominant, suggesting scarce distribution of unconsolidated sediments. The south of the area, on the other hand, is dominated by the SBP type consisting of thin acoustically opaque top layer underlain by transparent layer, and the uppermost acoustically opaque layer is suggested to indicate compact unconsolidated sediments of several tens of meters thick. In accordance with SBP survey, the results of MBES survey show that the north area is dominantly represented by dark color on the MBES image, suggesting that the seafloor surface is occupied by hard material.All of the bottom sediments samples collected by FG and SC are insoluble brown clay with comparatively abundant volcaniclastics grains. According to microfossil study of the sediments, the deposition of the sediments is assumed to have started before Miocene time and continues up to present. The area is assumed to have been lain under tropical to subtropical climatic condition, same as present, since 500,000 years ago.Among the FG sampling at twelve stations, manganese nodule was collected only at one station (03506 station, 3 FG sampling points), and the abundance of manganese nodules was calculated to be 1.02kg/m2 as the average of 3 sampling points (sampling point FG01: 1.25 kg/m2, FG02: 0.69 kg/m2, FG03: 1.13 kg/m2). At the 03504 station, manganese nodules were not collected by FG but the existence of them was confirmed by the sea-bottom photographs and the abundance was estimated from the photographs to be 8 to 10 kg/m2. An additional sampling by Arm Dredge (AD) (03509), conducted at the same location as 03504 to confirm the manganese nodules revealed by the sea-bottom photograph, resulted in collecting 157.7kg of pebbly manganese nodules of 2 to 4cm across and 2.4kg of manganese crust. Manganese crust of approximately 9kg was collected by another AD sampling (03511) conducted at the slope of seamount in the south of the area.The chemical compositions of manganese nodules are slightly different between the Plain Province (average abundance, Co: 0.36%; Ni: 0.41%; Cu: 0.24%) and the Hilly Province (Co: 0.69%; Ni: 0.25%; Cu: 0.07%). The former resembles the chemical composition of hydrogenous manganese nodule (s-type) reported from the Central Pacific Basin. The latter, on the other hand, resembles that of manganese crust collected on the slop of the sea mountain in the south part, further similar to that of typical cobalt-rich manganese crust of the Northwest Pacific, and this suggests a close genetic relation between manganese nodules of the Hilly Province and cobalt-rich manganese crust.