資源地質
Online ISSN : 2185-4033
Print ISSN : 0918-2454
ISSN-L : 0918-2454
42 巻, 232 号
選択された号の論文の6件中1~6を表示しています
  • 汐川 雄一, 岡田 和也, 窪田 亮, 川崎 潔
    1992 年 42 巻 232 号 p. 73-84
    発行日: 1992/05/20
    公開日: 2009/06/12
    ジャーナル フリー
    The Hishikari mine, one of the richest epithermal gold-silver deposits, had been wholly concealed except small ruins of old mining. Geophysical surveys have playèd an important role in the exploration throughout the discovery in 1981 and the subsequent mine development. Besides the exploration activity, we also tested various geophysical methods in this area to examine their application to the exploration for this type of gold deposits, including several methods that had never been applied to mineral exploration in Japan, such as the MT (magnetotelluric ) method that is discussed in this paper.
    In the MT method, natural electromagnetic fields set up by lightning and solar activity, are used to investigate the electrical substructure of the earth. The advantages of the method are its unique capability for exploration from shallow depth to very great depth without artificial sources. In the first survey carried out in 1983 using BEICIP MT 5C/7 system, an extremely low resistivity zone was detected at the depth of more than 10 km beneath the major mineralized area. To check the results from the previous survey, we made another survey on the same profile line using the latest PHOENIX V5-16 system in 1991.
    Prior to the analysis, we removed statics effects from the MT data. The statics effects are defined as vertical displacements of apparent resistivity curves, which are considered as results of near-surface resistivity features. The extremely low resistivity block derived from the previous analysis was nullified by this procedure. Two-dimensional analysis provided better understanding of deep resistivity structure that would be useful for discussion about the tectonic model of the deposit.
  • 三箇 智二, 神原 洋, 庄司 敏行, 嶽山 輝夫
    1992 年 42 巻 232 号 p. 85-100
    発行日: 1992/05/20
    公開日: 2009/12/14
    ジャーナル フリー
    The Toyoha mine is one of the largest Ag-Pb-Zn-Cu vein deposits in Japan. Two stages of mineralization, the earlier and the later, are found in the deposits. Polymetallic and polyascendant mineralization of the later stage occurs mainly in the southwestern to southeastern parts of the mining area (Soya, Iwami, Izumo and Shinano veins).
    Two substages (the first and the second) are distinguished in the later stage mineralization based on the detailed study of paragenetic sequence in ore. The former is exclusively emplaced in the E-W fracture system, while the latter mainly in the NW-SE one. Distinct ore zonations are recognized in each fracture system controlling the later stage mineralization. The zoning centers, indicating main path of ore fluids, are located at the eastern lower parts of Izumo vein for the former and the still eastern part of them for the latter, respectively. Junction of both fracture systems might have offered the largest bonanza at the Izumo and the Shinano veins in superimposed mineralizations.
    A great geothermal activity is still continued at the southeastern part of the mining area, nearby the large Shinano vein. Proposed structural model for the active geothermal system deduced the success of the mining operation of the vein. A sericite alteration cap overlying the upwelling zone of the active system might have controlled the top of ore veins.
    It is anticipated the discovery of new ore veins in the southeastern part and the potentiality of further ore reserves in the peripheral zone based on the characteristics of the later stage mineralization at the deposits.
  • コロンビア共和国エルロブルレ鉱山周辺地域の例
    古野 正憲, 市毛 芳克, 堀 昌雄, 岨中 真洋
    1992 年 42 巻 232 号 p. 101-117
    発行日: 1992/05/20
    公開日: 2009/06/12
    ジャーナル フリー
    El Roble Mine is located at Carmen de Atrato in the northwestern province of Colombia. The ore deposits classified as submarine volcanogenic massive sulfide type are situated along the contacts between the basic volocanic rocks and the sedimentary rocks.
    The δ34S values of ore sulfide range from -9.3 to +7.8 per mil with an average value around +3.1 per mil. Moreover, ore sulfides are classified into Type A and Type B based on the occurrence of pyrite. Type A ore is characterized by much amount of pyrite and colloform or framboidal texture, and occurs near the black shales. δ34S values of Type A range from -9.3 to +1.8 per mil. Whereas Type B ore is composed of massive chalcopyrite associated with euhedral to subhedral pyrite crystals. The δ34S values range from +4.3 to +7.8 per mil. Most of sulfurs measured for isopopic compositions are contained in chalcopyrite and pyrite. According to SAKAI(1968) and KAJIWARA and KxousE(1971), if ore is formed from an identical ore solution under an equilibrium condition, pyrite becomes higher in δ34S values than chal-copyrite. But in our research, δ34S values of Type B ore which contains abundant chalcopyrite are higher than those of Type A ore which contains abundant pyrite. Therefore, ore sulfur should have been deribed from two or more sources.
    The δ34S values of basic volcanic rocks close to the ore deposits are similar to those of the ore, while in the other areas basic volcanic rocks have various δ34S values. The δ34S values of the black shales near the deposits show wide ranges, whereas those of the part far from the deposits are relatively constant ranging from -20 to -15 per mil.
    Each rock facies has a given 87Sr/86Srr ratio. The average 87Sr/86Srr ratio of the ore is 0.7063, while those of the basic volcanic rock, the sedimentary rock and andesitic dyke are 0.7055, 0.7081 and 0.7046, respectively. Moreover, the 87Sr/86Srr ratios of the basic volcanic rocks and the black shales close to the ore bodies range from 0.7057 to 0.7068, which are similar to those of the ore.
    The basic volcanic rocks close to the deposits are strongly altered. These rocks have lower Cu content and higher LOI(Loss of Ignition) than the fresh basic volcanic rocks in the other areas:
    For the exploration of massive sulfide deposits we consider that the stable isotopic compositions and the contents of minor elements in the host rocks may be good indicaters. In the near future these analytical methods will be an effective exploration tool.
  • 荻野 厚, 内田 悦生, 角田 康嗣, 今井 直哉
    1992 年 42 巻 232 号 p. 119-129
    発行日: 1992/05/20
    公開日: 2009/06/12
    ジャーナル フリー
    1kbar,600℃の条件下におけるCaSiO3-FeSiO3-MnSiO3系鉱物の安定関係をイオン交換法を用いた実験により求めた.陽イオンCa2+,Fe2+,Mn2+の移動媒体として1mol/lの塩化物水溶液を使用した.実験条件下で安定な鉱物は珪灰石,バスタム石-鉄バスタム石固溶体,ヘデン輝石,パイロクスマンガン石,バラ輝石と鉄カンラン石+石英である.フェロシライトは実験条件下では不安定であり,鉄カンラン石+石英の組み合わせに分解する.バスタム石は,CaSiO3とMnSiO3を結ぶ線に沿って広い安定領域を持ち,また,鉄バスタム石と連続固溶体を形成する.パイロクスマンガン石およびバラ輝石はFeSiO3とMnSiO3を結ぶ線に平行な広い安定領域を持つ.実験条件下では,ヘデン輝石+バスタム石+鉄カンラン石+石英とバスタム石+パイロクスマンガン石+鉄カンラン石+石英の鉱物組み合わせが安定であることが確認された.全体的に見て二価の鉄およびマンガンイオンはカルシウムイオンに比べて固相中に入りやすい傾向を示した.
  • 正路 徹也
    1992 年 42 巻 232 号 p. 131-144
    発行日: 1992/05/20
    公開日: 2009/12/14
    ジャーナル フリー
  • 1992 年 42 巻 232 号 p. 145-146
    発行日: 1992/05/20
    公開日: 2009/06/12
    ジャーナル フリー
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