Characteristic mineralizations and alterations of the Kuroko- and Vein types deposits.

Ezuri Kuroko矿床，位于秋田县北崎地区的中心部分。本区寄主火山岩在黑子成矿期和脉状成矿期经历了热液蚀变。在火山岩中可识别出以下两种热液蚀变包壳。(1)早期热液蚀变与黑子矿化有关。矿床中部以绢云母和钾长石组合为特征。蚀变带与地层边界呈轻微交叉关系，呈似沼泽状。(2)后期与脉状矿化有关的热液蚀变。矿床中部以叶蜡岩为特征，石英斑岩侵入体周围存在镁绿泥石。蚀变带与地层边界呈明显的横切关系，呈漏斗状。后者叠置于前者之上，特别是在岩上脉型矿床周围。上述事实表明，岩上脉型矿床的叶岩化成矿作用发生在晚中新世石英斑岩侵入的近地表热液活动中。镁绿泥石主要分布在石英斑岩周围，表明后期镁离子活性高的热液促进了镁的固定。

The Ezuri Kuroko deposit, located nearly at the central part of the Hokuroku district, Akita Prefecture. In the area host volcanic rocks were hydrothermally altered during Kuroko mineralization and vein-type mineralization of the younger stage.The following two kind of hydrothermal alteration envelopes are reconginized in the volcanic rocks. (1) Hydrothermal alteration related to the kuroko mineralization at the earlier stage. The cenrtal part of the deposit is characterized by the sericite and K-feldspar assemblage. The alteration zones show gently crossed relationships to the formation boundaries with marshroom-like shape. (2) Hydrothermal alteration related to the vein-type mineralization at the later stage. The central part of the deposit is characterized by the pyrophyllite and Mg-chlorite is present around the quratz porphyry intrusion. The alteration zones show steeply cross cutting relationships to the formation boundaries with funnel-like shape.The latter is superposing upon the former, especially around the Iwagami vein-type deposit. These facts mentioned above suggest that the pyrophyllitization and mineralization of the Iwagami vein-type deposit took place at the near surface of land during the late Miocene hydrothrmal activity with quratz porphyry intrusion. Predominated distribution of the Mg-chlorite is around the quratz porphyry may indicate that the magnesium fixation have been promoted by the hydrothrmal solutions with high ionic activity of magunesium at the later stage.