Our major objective of resource surveys for polymetallic nodules is to improve the accuracy of resource estimates. To achieve the objective, DORD has been collecting polymetallic nodules by using free fall grab, dredge bucket, and spade-type box corer (BC), obtaining seafloor photographs by using deep-sea cameras, autonomous underwater vehicles (AUV), and finders installed on deep sea cameras (FDC), and obtaining acoustic data by using AUV. Collected samples and data acquired have been used for analysis of physical characteristics and chemical composition and acoustic data by laboratory tests.
BC and multiple corer (MC) were used as our main survey instruments to collect polymetallic nodules and sediments for five resource surveys of polymetallic nodules and environmental baseline studies carried out in 2011, 2012, 2014, 2016, and 2017. As for polymetallic nodules, the shape top, side, and bottom textures, as well as grain size, of collected polymetallic nodules were recorded after measuring the weight and size of each sample. In the laboratory, the density measurement and analysis of chemical composition of samples were conducted. Some of the samples were further examined its internal structure by creating polished sections with a microscope. For sediments, the redox potential measurement and pore water analysis were undertaken. Dating of microfossils and chemical composition analyses were also carried out for some samples.
Three detailed topographic surveys by using AUV and sampling by BC were carried out during a period of 2012 - 2014. A topographic map of 1 m contour for a model area which is likely to be a first-mining site for polymetallic nodules in DORD’s license area was prepared from these surveys. The coverage of polymetallic nodules was also calculated from consecutively photographed seafloor images and the relationship between topography and distribution of polymetallic nodules was examined. Acoustic data acquired by AUV is currently under analysis.
Some of the results of our resource surveys have been published officially (please see Publications). DORD aims to continue conducting environmental baseline studies and resource surveys by incorporating best available technologies.