Plio–Pleistocene Hydrothermal Activity Related to Gold Mineralization in the Seta Area, Northeastern Hokkaido, Japan

Abstract: Plio–Pleistocene hydrothermal activity resulted in high grade low sulfidation epithermal gold mineralization in the Seta area, the southern end of the Monbetsu-Kamishihoro Graben of northeastern Hokkaido, Japan. Hydrothermal activity and accompanying hydrothermal eruptions began at approximately 2 Ma along NNW-SSE trending faults, the Tohbu-ko fault I and II. This activity resulted in two main zones of gold mineralization, the west quartz-adularia veins(QAV) and east stock-work zone(STZ), formed between 1. 8 and 1. 2 Ma. A smectite-chlorite alteration zone is observed at deeper levels, while kaolinite and kaolinite-smectite zones occur at shallower levels with an acid-leached zone present near the surface. The kaoli-nite and kaolinite-smectite zones are also distributed along faults and the STZ, to depths of several hundred meters. δ³⁴S values of pyrite and alunite from the kaolinite and silicified zones indicate alunite formed by the oxidation of sulfide, either H₂S(vapor) or mineral.
Formation of the STZ and the southern part of the QAV took place during lacustrine sedimentation, while formation of the northern part of the QAV took place after eruption of andesitic lava; the latter being associated with widespread alteration formed under neutral-pH conditions. δ¹⁸O values of quartz veins and silicified rocks indicate that the paleo-hydrothermal waters have a large meteoric component, increasing with decreasing depth in the STZ. Acid hydrothermal waters, resulting from near surface oxidation of H₂S were responsible for acid-leaching and kaolinization of surrounding rocks. Between 1. 4 and 0. 3 Ma, the acid hot waters drained back along the STZ to depths of at least 500m, as a result of a fall in the paleo-water table level.     

新疆西滩低温浅成热液金矿床

西滩金矿床是近年西安工程学院发现的重要金矿床之一。该矿床是以含金玉髓质石英为基本矿石建造的脉状热液矿床,成矿物质来源于幔源火山岩（ 石炭系安山岩）,成矿流体中Ｈ２Ｏ 主要为大气降水,岩浆活动是成矿流体起源及演化成矿的热动力;成矿温压条件均较低,从矿物组合及成矿学特点,把该矿床归为火山岩区冰长石绢云母型低温浅成热液矿床;但特殊之处是成矿作用发生在碰撞造山过程中,与岛弧安山岩的成岩年龄有较大差别。     

Characteristics and Mineralization Age of the Fukusen No. 1 Vein,Hishikari Epithermal Gold Deposits,Southern Kyushu,Japan

The Fukusen No. 1 vein is located in the southeastern part of the Yamada deposit, Hishikari epithermal gold deposits, southern Kyushu, Japan. ⁴⁰Ar/³⁹Ar plateau ages of adularia from the margin and the center of the Fukusen vein are determined to be 0.617 ± 0.024 Ma and 0.606 ± 0.009 Ma, respectively. The Fukusen No. 1 vein shows banding structure composed mainly of quartz, adularia and clay minerals. Colloform texture is displayed by cryptocrystalline to amorphous silica material that is associated with fine-grained electrum and sulfides near the center of the vein. Pyrite in the Fukusen No. 1 vein often shows acicular shape resulting from inversion from marcasite. Near the center of the vein, primary marcasite occurs associated with colloform texture of silica. The Fukusen No.1 vein preserves primary texture and materials which were deposited from the ore-forming hydrothermal solution. The Fukusen No. 1 vein was formed in a short period and is one of the youngest veins in the Hishikari deposits.     

Potassium–Argon Ages of the Epithermal Gold–Silver Mineralization in the Haenam–Jindo Area,Southwestern Korea

The Haenam–Jindo area, located on the southwestern margin of the Korean Peninsula, was the site of vigorous volcanic activity during the Late Cretaceous and Early Tertiary periods. Large parts of the area record strong hydrothermal alteration, and there exist many clay–alunite and gold–silver deposits. We undertook potassium–argon (K–Ar) age dating of five mineral samples (including adularia, sericite and alunite) from the Eunsan, Moisan and Gasado epithermal gold–silver deposits in this area. The purities of the samples were confirmed by X‐ray diffraction analysis. The K–Ar ages of adularia from the Eunsan deposit and adularia and sericite from the Moisan deposit (related to gold–silver mineralization) are 75.0 ± 1.6, 74.7 ± 1.6 and 75.1 ± 1.6 Ma, respectively. The similarity of these ages, combined with the close proximity and similar geochemical characteristics of the deposits, indicates that the mineralization occurred as part of a single hydrothermal system. The K–Ar ages of alunite at the surface and adularia at depth within the Gasado deposit are 82.2 ± 1.9 and 70.7 ± 1.9 Ma, respectively, revealing that the clay–alunite and gold–silver mineralization formed at different ages. K–Ar age data indicate that the gold–silver mineralization in this area occurred mainly at 75–70 Ma, resulting from hydrothermal activity in the Haenam–Jindo area (82–70 Ma). This is the first time that the mineralization of precious metals in Korea has been identified during this period.     

福建碧田金矿床冰长石特征及其意义

电子探针、扫描电子显微镜、Ｘ射线衍射等测试方法的应用,揭示了碧田金矿床冰长石的存在及其矿物学特征。冰长石的存在及其它地质证据,说明碧田金床属于冰长石－绢云母型浅成低温热液贵金属矿床,与附近产出的紫金山酸性－硫酸盐型铜金矿床成因类型不同。