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 Chikyukagaku (Geochemistry) 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. This collaborative special volume is followed by volume 2 in the next year.

The relation between grade x and-tonnage T (x), which is cumulated from high grade side, is approximated by an exponetial function in each case of nickel and zinc deposits. If the approximation T (x) = T₀ exp(-x/x_C) is assumed, diferrential metal tonnage m(x) = x・dT(x)/dx has a local maximum at x_C (craitical grade). We can expect, therefore, more metal with decreasing grade at x > x_C, while less metal at x < x_C, and hence resoureces being the former condion is optimistic, and those being the latter are pessimistic. Nickel resources are optimistic because of x_C = 0.31 %, while zinc resources are pessimistic (4.3 %). The grade-tonnage relation of gold deposits is convex downwards, and hence approximated by combination of three exponential functions. The function applied in the low-grade part gives the critical grade of 1 g/t suggesting optimistic. Polymetallic deposits are treated as low grade, because the independent variable of grade-tonnage diagram is grade of a single metal. In contrast, ore value (OV), which is sum of product of grade and price of each metal, can evaluate polymetallic deposits and monometallic ones equally. The OV-tonnage diagram of all deposits consists of three parts: high, middle and low value classes. Since metal prices vary in time, however, the ore value is not universal. For solving this problem, the enrichment ratio (ER), which is sum of enrichment ratio of each metal given as grade normalized by the custal abundance of the metal, is introduced. The ER-tonnage diagram of all deposits also consists of three parts: high, middle and low ratio classes. The correlation coefficient between ER and OV is not so high as 0.76 in antilogarithm and 0.63 in logarithms. This implies that human desire for metal resources deviates from the complexity of formation of metallic deposits. Enrichment ratios of platimum group metals (PGM) are high as compared with those of gold, silver and base matals. Two causes are considered for this phenomenon: 1) geological characteristics of PGM deposits assicating with ultrabasic rocks, and 2) too low crustal abundance of PGM. We need future study for the problem.

Kuroko deposits have been traditionally defined by volcanogenic, strata-bound， massive sulfide and sulfate deposits in submarine environment. Recently, it is suggested to include the following term in the definition: relating to bi-modal volcanism in back-arc tectonic setting. The deposits are essentially composed of zonal massive sulfide layers underlain by massive gypsum and disseminated or stockwork sulfides in the footwall unit. On the other hand, varieties exist in forms of deposits such as single unit stratiform ore, stockwork sulfide without significant massive sulfides and dominance of sulfate minerals, and so on. In the present paper, the following geological aspects related to Kuroko deposits are reviewed; geologic setting in the Hokuroku district as a representative Kuroko cluster, tectonic background and magmatic process relating to the Kuroko deposits based on previous studies. The primary ore textures are also discussed followed by discussion of deep marine environments during ore formations based on recently accumulated knowledges. Lastly, several exploration methods, which have been accumulated in a mining company for a long time, are introduced including low magnetic susceptibility, low Na₂O anomalies in the footwall rocks, and alteration mineral zoning around ore deposits.

The types of metallic ore deposits vary from porphyry copper to strata-bound deposit, which have been developed in many countries of the world. These economic ore deposits are especially concentrated in the convergent plate boundaries. However, the copper reserves are different from place to place, even in the Circum-Pacific subduction zone. The amount of copper reserves is excellent in the western coastal region of South America, and particularly the northern Chile (central Andes) is famous to occupy about 30% of world copper reserves. It is also noteworthy that the ages of N-S trending porphyry copper belts get younger to the East (inland Chile), indicating an inland migration of volcanic front. What factors control such process to concentrate copper? The original supplier of copper is a mid-oceanic ridge where metallic elements including copper, are fixed as massive sulfide ore deposits through the formation and sedimentation of chimneys. Later they move further from the midoceanic ridge through oceanic plate spreading and are fixed in a subduction zone. The mechanism to accumulate copper can be explained by “tectonic erosion”, which destroys the hanging wall of an older subduction complex or even the basement of the overriding continental plate. Accumulation of copper is driven by dehydration of subducting materials, consisting of both oceanic plate and eroded continental material, which could release metallic elements to forearc region with volatiles through hydrothermal circulation. This mechanism constrains subduction of metallic elements into deep mantle, resulting in storage of metallic elements within forearc region, since tectonic erosion emerged along the western coast of South America. In addition, ridge subduction causes partial melting of both oceanic plate and eroded continental material, resulting in formation of enormous porphyry copper deposits coupled with the inland migration of volcanic front. The tectonic erosion has been ongoing in the western coastal region of South America over 600 million years and will be a key mechanism to unravel the Andean metallogenesis through extensive future research. To emphasize the significance of this mechanism, we name it“ Metallogenic Copper Accumulation Mechanism (MCAM)”. And, the place to accumulate copper through tectonic erosion is named “Copper Bank”.

This annual review presents many topics from September 2017 to August 2018. North Korea conducted its sixth nuclear test on September 3, 2017, and the world was hitted by an etreme heat wave in July and August 2018. In contrast, topics of mineral and energy exploration are not so sensational. However, we had several remarkable topics as follows: 1) initiation of the development of Los Gatos Ag-Zn-Pb Project in Mexico, 2) commencement of crude oil production from Western Isles Development Project, U.K. North Sea, and first oil delivery for the Kaikias deep-water project in the Gulf of Mexico, 3) commencement of LNG Production at Australia's Wheatstone LNG, and Ichthys LNG Project, 4) world’s first success in continuous ore lifting test for seafloor polymetallic sulphides conducted by JOGMEC.