資源地質
Online ISSN : 2185-4033
Print ISSN : 0918-2454
ISSN-L : 0918-2454
49 巻, 3 号
選択された号の論文の6件中1~6を表示しています
  • 蘆花鉱山第1鉱床について
    内藤 一樹, 金 ブン榮, 高木 哲一, 高尚 模, 樋田 忠孝, 須藤 定久
    1999 年 49 巻 3 号 p. 165-173
    発行日: 1999/12/31
    公開日: 2009/12/14
    ジャーナル フリー
    In the southern part of the Korean peninsula, hydrothermal clay deposits are mainly associated with the late Cretaceous Yuchon group of the upper Gyongsang system, which principally comprises rhyolitic to andesitic lavas and pyroclastic rocks. In particular, the pyrophyllite/kaolin deposits in the southern Chollanamdo province tend to occur as a largescale sheet in pyroclastic rocks of rhyolitic composition. The pyrophyllite deposits of Nohwado Island at the southwestern extremity of Korea are a representative example in the province. To examine the typical field occurrence and ore mineralogy of hydrothermal clay deposits in Korea, this study has focused the No. 1 deposit of the Nohwa mine of the Minkyung Industry Co., Ltd. (under ground exploitation) on the island.
    The pyrophyllite deposit was formed by intensive hydrothermal alteration of rhyolitic lapilli tuff and interbeds of tuffaceous sandstone and shale. The ore body occurs as, a sheet of 700 m (major axis)×250m (minor axis)×65m (max. thickness), that is almost concordant with the host strata. It is divided into a pyrophyllite and a diaspore zone on the basis of mineral assemblages.
    Diaspore zone: This zone has an elongated shape and occurs in the central part of the ore body. Its mineral assem-blage is pyrophyllite+quartz+diaspore+kaolinite with subordinate alunite and rutile. Diaspore occurs as an aggregate of, 0.2-1.5 mm diameter grains; its content is usually 1-2 vol% (partly>20 vol.%). Pyrophyllite, alunite, and kaolinite com-monly replace diaspore along rims and cleavage.
    Pyrophyllite zone: This zone is characterized by the mineral assemblage pyrophyllite+quartz, and constitutes a main part of the ore body. Alunite and rutile occur as accessory phases.
    Both zones are partly silicified (SiO2>80wt%). The irregular shaped silicified parts tend to occur in and around the boundaries between the two zones and in the marginal parts of the ore body. A weakly altered zone, which is composed of quartz and illite with subordinate albite, kaolinite, chlorite, and biotite, occurs in the periphery of the ore body. Although the ore mineral assemblages of the zones are different, their chemical composition is similar.
    Ore texture and thermodynamic considerations suggest that the diaspore zone may have been secondarily formed by the alteration of the central pyrophyllite zone due to the ascent of steam. The high permeability of the sedimentary host rocks enabled the passage of the hydrothermal fluid, leading to the formation of the large sheet pyrophyllite deposit.
    Several illite veins are observed along fractures in the ore body. One illite sample from such a vein yielded a K-Ar age of 71.8±3.6 Ma.
  • その起源と低微量元素濃度の示唆
    加藤 泰浩, 木村 進一
    1999 年 49 巻 3 号 p. 175-189
    発行日: 1999/12/31
    公開日: 2009/06/12
    ジャーナル フリー
    Major, minor, and rare earth element abundances are reported for the Boolgeeda Iron Formation of the Hamersley Group, Western Australia. The banded iron formations (BIFs) of the present study are divided into five types based on their color; black, gray, yellow, red, and white layers. Black, red, and white layers are exclusively composed of SiO2 and Fe2O3*, while gray and yellow ones contain significant amounts of lithogenous components such as AL2O3, TiO2, MgO, K2O, and Na2O. There are excellent positive correlations among these lithogenous major elements and minor elements including Sc, Cr, Ni, Zr, Hf, and Th. These elements were supplied from the exposed continental crust as clastic materials. High Th/Sc and (La/Yb)cn ratios and negative Eu anomalies of the gray and yellow layers indicate a significant contribution of granitic clastics.
    Most of red and white layers with a minor terrigenous component generally exhibit no Eu anomaly when normalized to chondrite. This implies that these layers were genetically related to a submarine hydrothermal solution, taking it into consideration that river waters with a significant negative Eu anomaly should have drained considerably into the ocean. A positive corre-lation between Fe and minor elements such as P, V, Ni, Y, U, and REEs is analogous to that of modern hydrothermal sediments at mid-ocean ridge, indicating that iron-rich suspended particulates, precursors of BIFs, scavenged these minor elements as like today. However, their metal/Fe ratios of the BIFs are generally lower than those of modern hydrothermal sediments by one order of magnitude. It is likely that much more abundant iron-rich suspended particulates were formed in the 2.5 Gyr ocean due to much higher Fe contents in the hydrothermal solution than today. Large quantities of iron-rich suspended particulates scavenged competitively the minor elements, resulting in very low contents of them in the BIFs.
  • 八幡 正弘, 久保田 喜裕, 黒沢 邦彦, 山本 邦仁
    1999 年 49 巻 3 号 p. 191-202
    発行日: 1999/12/31
    公開日: 2010/03/04
    ジャーナル フリー
    Many epithermal Au-Ag, Cu-Pb-Zn and Hg deposits are distributed in the Northeast Hokkaido Metallogenic Province (NHMP). Thirteen K-Ar ages for hydrothermally altered rocks and quartz-adularia veins from Au-Ag deposits and Cu-Pb-Zn deposits, were determined to estimate thier mineralization ages. The newly-obtained age data and reported ones show that mineralization ages vary from approximately 14.4 Ma to 0.3 Ma, and tend to young southward in the NHMP. Based on the distribution of epithermal deposits and mineralization ages, this metallogenic province is divided into Ohmu-Monbetsu (14.4-11.2 Ma), Ikutahara-Rubeshibe (8.1-2.9 Ma) and Kamishihoro-Akan (3.8-0.3 Ma) areas, lying in an E-W trending parrallel arrangment along to Kuril Arc. Temporal and spatial evolution of mineralization is in accordance with the feature of terrestrial Miocene-Pleistocene volcanism which was initially widespread, but gradually became spatially restrict-ed towards the south in the NHMP.
  • 金沢 康夫, 中嶋 輝允, 高木 哲一
    1999 年 49 巻 3 号 p. 203-216
    発行日: 1999/12/31
    公開日: 2009/06/12
    ジャーナル フリー
    Recent geoscientific data and models for ore geneses of the Bayan Obo REE-Nb-Fe deposits, Inner Mongolia, China were reviewed. The rift system developed in the northern margin of the Sino-Korean massif during the Early-Middle Proterozoic era made a favorite tectonic setting for the depositions of Bayan Obo Group and the ore deposits. A variety of veins and dykes around the deposits occur in the footwall clastic rocks and the basement of migmatites. K-metasomatism and brecciation of hanging H9 shale indicate that the shale could serve as a sealing cap-rock for the deposits (DREW et al., 1992). Data of isotope ages from Sm-Nd, La-Ba, Rb-Sr, Th-Pb, Ar-Ar, and Re-Os methods suggest that there are at least three metallogenic periods: (1) 1, 700 - 1, 260 Ma (Middle Proterozoic); (2) 555 - 370 Ma (Caledonian); and (3) 343 - 298 Ma (Hercynian). In the three periods the first one is of the most important (BAI et al., 1996). C, O and S isotopic compositions together with mineral chemistry and field observations of the H8 dolostone and ore minerals indicate the following possibilities: (1) The dolostone belongs to normal sedimentary carbonate rocks and is not a magmatic carbonatite. (2) The original iron (hematite) ore bodies were formed syngenetically before REE-Nb mineralization. (3) The hydrothermal fluids with an alkaline-carbonatite chemistry were derived from the upper mantle, and printed the REE-Nb mineralization over the original iron bodies. The process of the above (2) and (3) is considered as a composite process of both crustal and mantle source mineralization (CAO et al., 1995). Many geochemical data and field observations are consistent with the composite model for the origins of the Bayan Obo deposit.
  • 両角 春寿, 目次 英哉, 北 良行
    1999 年 49 巻 3 号 p. 217-225
    発行日: 1999/12/31
    公開日: 2009/06/12
    ジャーナル フリー
    Geochemical exploration technique using oxygen isotope geochemistry has been conducted by Ministry of International Trade and Industry (MITI, 1999) with entrustment to Metal Mining Agency of Japan since 1994. Intention of this paper is to introduce the main results of the studies for epithermal Au deposits of the Koryu, Okuzu, Kushikino and Iwato mines.
    In addition to oxygen isotope compositions, we introduced the following indexes to evaluate the degree of hydrother-mal alteration.
    K2O#=(K2O)/(CaO+K2O+MgO+Na2O)(wt%)
    T/A=log10{(Total)/(CaO+MgO+Na2O)}(wt%)
    K2O#express the degree of K2O enrichment in low sulfidation system, and T/A express the degree of hydrothermal leaching in both low and high sulfidation systems. Different alteration patterns between low and high sulfidation systems can be successfully distinguished using K2O#and T/A values and Au contents.
    In the Koryu area, the combined indicator of oxygen isotopic compositions, Ag contents and T/A values is more useful for focusing the mineralized area than a single indicator.
  • 島田 允堯
    1999 年 49 巻 3 号 p. 227-228
    発行日: 1999/12/31
    公開日: 2009/12/14
    ジャーナル フリー
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