Field works and methods
A number of laboratory members have participated in research cruises of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) to investigate seafloor mineral resources or submarine volcanism. The cruises take from about a week to a month. So far, the main targets have been around Minamitorishima and Okinawa, and off the coast of Tohoku. We are also participating in international collaborative research expeditions under the International Ocean Discovery Program (IODP) to study global environmental changes in Earth's history.
We are conducting field surveys for sample collection at mines that are currently or were once in operation in Japan. We collect ore samples and rock samples from the surrounding geological units to elucidate the origin of the deposits.
<University of Tokyo>
Inductively coupled plasma quadrupole mass spectrometer (ICP-QMS): Thermo Fisher Scientific iCAP Q
In an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS), a fluctuating magnetic field produced by a high-frequency current generates high-energy argon plasma. A sample solution is introduced into the ICP as an aerosol, which is decomposed immediately in the plasma at temperatures of up to 6,000–10,000 K. The generated ions are then introduced into the quadrupole mass filter where a combination of DC and AC voltage is applied to four electrodes (quadrupole), which enables each element to be separated according to its mass-to-charge ratio for quantitative determination. ICP-QMS is used for high-precision measurements of the content of various critical metals such as gold and rare earth elements.
X-ray fluorescence spectrometer (XRF): Rigaku ZSX Primus II
To use an X-ray fluorescence spectrometer (XRF), a sample powder and flux (usually lithium tetraborate) are mixed well and melted at a temperature of approximately 1200 °C to produce a homogenized glass bead. When the glass bead is irradiated with an X-ray, fluorescent X-rays of different wavelengths and intensities are emitted depending on the elements contained in the sample. The elemental contents are determined by the fluorescent X-ray intensities and calibration curves. XRF is mainly used to determine the major elements in substances in the range of several to tens of percent.
X-ray diffractometer (XRD): Rigaku Ultima IV
When a powder sample is irradiated with X-rays, the X-rays are diffracted depending on the crystal structure of the material. The X-rays are intensified by interference only at angles satisfying Bragg’s equation and are observed as diffracted X-rays. Based on the angles and intensities of the diffraction X-ray peaks, which are unique to each substance, the substances (e.g., minerals) contained in the sample can be identified.
Scanning electron microscope with an energy-dispersive X-ray spectrometer (SEM-EDS): Hitachi Miniscope TM3000
A scanning electron microscope (SEM) is a device for observing surface structures using various signals generated when an electron beam is irradiated onto a sample surface. Surface topography can be observed from the intensity of secondary electrons generated from the sample surface, whereas surface irregularities and composition images can be obtained from reflected electrons (backscattered electrons). An energy-dispersive X-ray spectrometer (EDS) can map the distribution of elements by detecting the characteristic X-rays of elements in a sample excited by an electron beam.
＜Chiba Institute of Technology＞
Multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS): Thermo Scientific Neptune Plus
Isotope ratios of elements provide important information for revealing ore genesis and environmental changes. Multiple detectors are used to accurately detect small differences in the mass of various isotopes in a sample. Unlike ICP-QMS, all target isotope signals are detected simultaneously in a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) without changing the magnetic field to obtain accurate measurements by cancelling out any fluctuations in the detection signal caused by sample introduction and/or plasma instability.
Digital microscope: HIROX HRX-01
Microscopic observation is essential for the description and identification of small particles in geological samples, especially microfossils. We use a sophisticated, high-resolution digital microscope that features focus merging, automatic image merging, and 3D-image synthesizing.
For accurate chemical analyses (especially isotope analysis), the sample must be kept free of impurities. For this purpose, we have an extremely clean working space—a cleanroom—for sample preparation. A special dust-free suit is worn during the work, and an air shower is used to remove fine dust before entering the room.
Independent component analysis
Independent component analysis is a type of multivariate analysis. Unlike classical principal component analysis and factor analysis, independent component analysis extracts new base vectors that maximize the non-Gaussianity inherent in the data structure. That is, we can extract the most characteristic structure of “non-random” data. In the example of chemical composition data of sediments, mixtures of materials with characteristic compositions constitute the independent components.
Machine learning is a technique for automatically extracting systematic information contained in data as knowledge and laws by having computers imitate the process of human learning and recognition. Whereas multivariate analysis is often primarily concerned with describing data, machine learning is often concerned with building predictive general models from data.