Through the 4.6 Gyr of Earth’s history, ore deposit has been formed via close linkage with the evolution of this planet. Ore deposit is an abnormally enriched material of targeted elements and its enrichment mechanism mac-roscopically controlled by “Geology” and microscopically controlled by “Geochemistry”. “Front line of economic geology” is the first collaborative special volume by two Japanese academic journals of Chikyukagaku（Geochemis- try）and Shigen-Chishitsu, aiming to review the metallogenesis, recent progresses and unsolved questions in each type of ore deposit for future researches on economic geology and geochemistry. This collaborative special volume will be followed by volume 3 in the next year.

Deep-sea environments are faced with cumulative effects of many human activities, e.g. accumulation of plastics, overwhelming fishing and resource exploitation, heavy maritime transportation, and effects from climate change. Recently, growing interest in deep-sea mining enhances the activities of engineering development on seabed mining and environmental monitoring, and exploration of mining sites within States Exclusive Economic Zones (EEZ) or in areas beyond the limits of national jurisdiction. Since 2010, attention paid to potential environmental impacts caused by deep-sea mining has been increased, and many workshops and research conferences have been held. In the Western Pacific Ocean, the Nautilus Minerals Ltd. has announced that the sea mound located in Papua New Guinea will be a first site likely to be commercially exploited polymetallic sulfide deposit. The Japan Oil, Gas and Metals National Corporation (JOGMEC) conducts a feasibility project for seabed mining in the Okinawa Trough. In 2015, the leaders’ declaration from the G7 summit in Germany identified the conducting of Environmental Impact Assessment (EIA) and scientific research as a priority issue for sustainable development of deep-sea mining. The EIA protocol developed for deep-sea mining is recognized that it will be a practical component for ensuring effective management and protection of ocean ecosystems. The development of EIA protocols is started in Japan as a national project. This paper describes the current situation of technologies concerning deep-sea environmental assessment and monitoring on seabed mining, and technical background of multidisciplinary approaches for deep-sea environmental survey.

Recent progresses on the iron oxide-copper-gold (IOCG) deposits, especially on principal Chilean deposits, are summarized to clarify metallogenesis and exploration of the type of deposits in Mesozoic extensional subduction regime. The principal composite-mode deposits (Candelaria, Punta del Cobre, Mantoverde) are closely associated with Cretaceous Atacama fault system, and are characterized by the typical Na-Ca-K alteration with the early-stage magnetite (or hematite) and the following Mg alteration with copper-sulfide and gold mineralizations. Fluid inclusion and stable isotope studies suggest that the IOCG deposits were formed by high-temperature hypersaline magmatic-hydrothermal fluids. If the IOCG deposits are generated from FeCl₂-bearing magmatic fluids, the spatial-temporal relation between the IOCG and iron oxide-apatite (IOA) deposits is well explained by the magmatic magnetite-bubble segregation model (Knipping et al., 2015b; Simon et al., 2018). Nevertheless, a few problems still remain unsolved in the genetic model including contribution of basinal brines.

Commercial gas production was commenced from the Culzean gas field in UK North Sea, the Beryl gas field offshore Sarawak, Malaysia, the Sirasun and Batur gas fields in the Republic of Indonesia, and the Prelude floating liquefied natural gas facility offshore Western Australia in this year from September, 2018 to August, 2019. The Ichthys LNG project, which commenced production of gas on July 2018, commenced sequentially shipping of condensate, LNG, and LPG. Many LPG carriers were built to transport natural gas from the Cove Point project in Maryland, the Freeport LNG project in Texas, and the Camero LNG project in Louisiana. Geothermal power stations commenced commercial operation at Wasabizawa (46 MW) in Akita and at Matuso-Hachimantai (7.5 MW) in Iwate.