Shigen-Chishitsu
Online ISSN : 2185-4033
Print ISSN : 0918-2454
ISSN-L : 0918-2454
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Displaying 1-5 of 5 articles from this issue
Articles for Annual Meeting for Prospecting of Ore Deposits
  • Akira HARA, Michitaka ARUGA, Tomoyuki SASAI, Akira IMAI, Yoshinori OKA ...
    Article type: Articles for Annual Meeting for Prospecting of Ore Deposits
    2024 Volume 74 Issue 1 Pages 1-8
    Published: May 22, 2024
    Released on J-STAGE: June 23, 2024
    JOURNAL FREE ACCESS

    The Hishikari low-sulfidation epithermal gold-silver deposits, located in northern Kagoshima, Japan, consist of the Honko and Sanjin deposits hosted in the Cretaceous Shimanto Supergroup and the Quaternary Hishikari Lower Andesite, and the Yamada deposit hosted in the Hishikari Lower Andesite. Fluid inclusion microthermometry on the Zuisen-6 vein was conducted for understanding gold mineralization in the deeper part of the deposit. Homogenization temperatures of fluid inclusions in the Zuisen-6 vein do not change with depth, suggesting that the hydrothermal fluid moved to the shallower part of the vein without cooling. The increased salinity in the shallow part and the presence of truscottite and bladed quartz in the deeper part suggest that the hydrothermal fluid may have been continuously boiling, and the deepest depth of gold mineralization can be estimated by determining the deepest boiling depth. The estimated deepest depth limit of gold mineralization of the Zuisen-6 vein is -105 to -150ML, which is consistent with the results of drilling data in the surrounding area. This suggests a relationship between hydrothermal boiling and gold mineralization at the depth of the gold deposit such as the Hishikari low-sulfidation epithermal gold-silver deposits, providing new insights into estimating the lower limit of gold mineralization depth using the boiling depth. This indicator might be effective in the exploration at the deeper part of the deposit.

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  • Ryunosuke YANO, Nobuhiko SHIGA, Yoshiharu TAKIGAWA, Kazuhiko YAMANAKA
    Article type: Articles for Annual Meeting for Prospecting of Ore Deposits
    2024 Volume 74 Issue 1 Pages 9-13
    Published: May 22, 2024
    Released on J-STAGE: June 23, 2024
    JOURNAL FREE ACCESS

    Currently, the use of drones is progressing in various areas of society. In Japan, since the late 2010s, the necessary technological development for social implementation of environmental improvement and operation management systems has been underway aiming non-line-of-sight flight in manned areas. MINDECO has been using drones since around 2016, starting with topographic surveying at tailings dam and open-pit mining sites, and has been engaged in aeromagnetic surveys, ground temperature monitoring, and the movement of equipment and supplies, accumulating a track record of achievements. In drone geophysical survey, lightweight, non-contact sensors such as optical sensors (visible-light, thermal infrared, and hyperspectral cameras), LiDAR, and magnetic sensors are used for the sensors mounted on the drones. Multicopter drones can also hover and operate automatically/autonomously. It can reproduce planned flight paths precisely. Fixed-wing drones can glide and have a range of 90 minutes, and surveys using relatively lightweight optical sensors can survey a wider area. Aeromagnetic drone surveys use a multicopter drone, an onboard optical pumping magnetometer, and a magnetometer at a fixed point for daily change compensation. If conditions are favorable, the drone will fly 25 to 40 km per day, repeating 20-minute flights 6 to 10 times. The ground altitude is about 40 to 80 meters and the line spacing is about 100 meters. Except for drone takeoffs and landings, measurements are made according to a flight plan prepared in advance, with automatic flight along the terrain surface. Due to range limitations, flight plans are created to cover the entire survey area from multiple takeoff/landing points. More than 900 km have been measured by drone aeromagnetic surveys over the seven years since 2017. The objectives are mineral exploration and civil engineering exploration. The results of the magnetic survey for the mineral exploration showed that a low magnetic anomaly zone, which is thought to be caused by the dissolution of magnetic minerals due to hydrothermal alteration, was detected. The civil engineering survey was used to identify the serpentinite distribution area in the mountainous area, which is difficult to access by geological survey. It is known that the higher the amount of magnetite produced in the process of serpentinization of peridotite, the higher the magnetic susceptibility of serpentinite, and the drone survey helped to detect such serpentinite distribution areas. Aeromagnetic survey by drone demonstrates its measurement efficiency and resolution in surveys of several km2. In the future, the scope of application will be further expanded compared to the past due to the evolution of batteries and motors and the downsizing and weight reduction of onboard equipment. On the other hand, when drones are used overseas, there may be problems due to differences in legal systems for use of drone, and/or the issue related to the import/export of equipment, so it is necessary to carefully gather information on the local legal system before using drones overseas, or to hedge risks by using local contractors for the procurement and operation of drones.

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  • Shohta SHIMIZU, Takuya SAKAI, Norifumi TODAKA, Makoto TANAKA
    2024 Volume 74 Issue 1 Pages 15-24
    Published: May 22, 2024
    Released on J-STAGE: June 23, 2024
    JOURNAL FREE ACCESS

    Acidic geothermal fluids (pH≤5) are estimated to constitute 30% of the total geothermal resources in Japan (NEDO, 1993). The objective of this project is to understand the chemical properties and distribution of acidic fluids for the power generation. Acidic fluids are classified into two major types, the Onikobe geothermal field as Cl-type and Shiramizugoe geothermal field as SO4-type were selected for this project fields. In this paper, we describe the SO4-type at the Shiramizugoe geothermal field. The geothermal conceptual model of the acidic fluid system was reasonably developed by various data. Based on the conceptual model, a coupled thermal, hydrological, and chemical (THC) simulation for the Shiramizugoe geothermal fields was performed using the TOUGHREACT code (v4) to understand the chemical properties and distribution of acidic fluids.

    The geothermal conceptual model was reproduced by the THC simulation, and the distribution of acidic fluid was estimated by the THC model in good matching with measured data of chemical characteristics and alteration minerals as well as temperatures and pressures of the existing wells. At the Shiramizugoe geothermal field, the acidic fluid is neutralized during lateral flow from the east to the west, reproducing the conceptual model in which acidic and neutral fluids exist in the same reservoir. Such an estimation of the acidic fluid distribution will contribute to the effective utilization of acidic fluids in the future.

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Original Articles
  • −The Magnetite Ore Deposit of the Nakaosaka Iron Mine in the Shimonita Geopark, Gunma Prefecture−
    Atsushi MIYASHITA, Hiroyasu MURAKAMI, Masakazu RIKITA, Takashi ICHIKAW ...
    2024 Volume 74 Issue 1 Pages 25-36
    Published: May 22, 2024
    Released on J-STAGE: June 23, 2024
    JOURNAL FREE ACCESS

    The Nakaosaka iron ore mine in Shimonita, Gunma Prefecture, Japan, is a geosite in the Shimonita Geopark and an industrial heritage site where iron ore (high-grade magnetite) was produced during the early Meiji era in Japan. The Nakaosaka iron ore mine is located to the north of the Oogitano–Iwayama tectonic line (the Median Tectonic Line of Japan). The iron ore deposit is composed of small but high-grade magnetite ore bodies, which are embedded in the Nanjai Formation and the Name granite. The Nanjai Formation can be correlated with the Jurassic Tanba–Mino accretionary complex, and the 70 Ma Name granite can be correlated with the Cretaceous Ryoke I-type granite.

    The magnetite ore bodies are lenticular or vein shaped with wide alteration zones composed of actinolite or hydrobiotite + chlorite with carbonate stockwork veinlets. The magnetite has Si contents of <3 wt.% and often contains euhedral Clapatite micro inclusions. Only minor sulfides (mainly pyrrhotite) are associated with the magnetite ore suggesting a low sulfidation state. Composite löllingite and arsenopyrite grains occur alongside the magnetite, and the arsenopyrite has high As contents (~36 mol.%). This suggests a higher temperature than typical hydrothermal deposits. Furthermore, the magnetite geothermometer yields temperatures of >500 ˚C. Apatite and chlorite associated with the magnetite have Cl contents of <1 wt.%. The altered zones are not associated with acidic alteration index minerals such as alunite or kaolinite.

    Around the Nakaosaka iron ore mine, magnetite with apatite occurs in a neutral to alkaline alteration zone that experienced high temperatures (>500 ˚C) close to a large-scale tectonic line. These features strongly suggest that the magnetite ore deposit is an iron oxide-apatite (IOA, Kiruna)-type deposit.

    Key words: Iron-oxide type ore deposit, IOA-IOCG type ore deposit, Kiruna type ore deposit, Magnetite, Apatite, Nakaosaka iron ore mine, Shimonita Geopark

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Resource News
  • Yasuyuki FUKUSHIMA, Taiji SAKAI, Katsumi TAKAHASHI, Haruna KADOWAKI, T ...
    Article type: Resource News
    2024 Volume 74 Issue 1 Pages 37-48
    Published: May 22, 2024
    Released on J-STAGE: June 23, 2024
    JOURNAL FREE ACCESS

    This paper introduces biosorption technology using a metal recovery material made from cyanobacteria as an environmentally friendly. This metal recovery material is characterized by its ability to selectively recover precious metals dissolved in water, with a recovery rate of over 95%. In the case of gold recovery from hydrogen tetrachloroaurate (III) tetrahydrate solution, the reaction proceeds at a rate of less than a few minute, and the high recovery performance at low pH level is demonstrated. The main component of the metal recovery material is a photosynthetic dye, pheophytin a, which was found to be an important molecule for the recovery of precious metals.

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