Epithermal vein-type gold-silver mineralization from the Akan-Taiho-Tobetsu mine area in the Kitami metallogenic province is characterized by Pliocene (ca.3.8-2.2Ma) based on the K-Ar ages for the vein quartz and adularia mixtures and hydrothermally silicified and illitized or alunitized rock.
The epithermal gold-silver mineralization of ca.3.8-3.2 Ma is representative of the Motoyama and No.1 veins of the Akan deposit and the Motoyama and Takinosawa veins of the Taiho deposit in the northern part of this area, and is accompanied by a near-neutral hydrothermal alteration. On the other hand, that of ca.2.4-2.2 Ma consists of the Kanehana, Kinshu, and Zuiho veins (ca.2.2 Ma) of the Taiho deposit in the northern part of this area, and the Tobetsu vein deposit (ca.2.4 Ma) in the southern part of this area, and is accompanied by the vein-related illitization and/or adularization. The Shikerepeyama acid alteration halo with alunite (ca.2.3 Ma) in the southern part of this area also formed at approximately the same time as the low-sulfidation epithermal gold-silver deposits (ca.2.4-2.2 Ma).

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K-Ar mineral ages were determined on 22 specimens collected from seven tin and three gold deposits in the southern part of the Russian Far East. Average values obtained in the individual ore deposits are as follows: Sn; Khinganskoe 91.8 Ma, Merekskoe 85.9 Ma, Solnechnoe 86.2 Ma, Pravourmiskoe 91.8 Ma, Vostochnoe 90.3 Ma, Chalba 84.4 Ma, and Tigrinoe 79.4 Ma; and Au; Krinichnoe 79.4 Ma (pre-ore dike), 76.2 Ma (post-ore dike), Askold 83.2 Ma and Maiskoe 57.1 Ma. Thus the tin mineralizations occurred related to late Cretaceous granitic activities and are similar to the tin-bearing tungsten mineralization epoch of Southwest Japan. The gold mineralizations are slightly younger than the tin mineralizations in time, and also similar in age to those of Southwest Japan.

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Advanced argillic alteration in the Kobui area, southwestern Hokkaido, is distributed over 5.3 km2 within the Pliocene Kobui andesite lavas, and overlain by Late Pleistocene Maruyama andesite lavas. The advanced argillic alteration consists of acid-leached andesite (including vuggy silica), hydrothermal breccia and massively silicified rocks, and is surrounded by argillic alteration characterized by smectite and pyrite.
The alteration is divided into western Kobui (KAA) and eastern Tokiwamatsu-Furube advanced argillic alteration areas (TFAA) in distribution. KAA formed during the period from 2.9 to 1.8 Ma and TFAA from 1.3 to 0.2 Ma, based on K-Ar ages on alunites. KAA is composed of a relatively large mass with several small exposures, which includes a hydrothermal breccia with strikes of N50°W and N70°E. TFAA consists of four isolated sub-areas aligning in a N10°E direction, with hydrothermal breccia subparallel to the alignment (N5°E, N20°E). In both areas, advanced argillic alteration commonly yield alunite- and kaolinite-group minerals, and KAA is characterized by the presence of pyrophyllite, diaspore, topaz and zunyite, whereas TFAA lacks in these minerals and contains tridymite and cristobalite. The mineral assemblage and sequence, and sulfur isotopic temperatures suggest that the temperature of the hydrothermal fluids during the main alteration in KAA was higher (200°C-320°C) than that in TFAA (-200°C). Crater-forming explosions followed the advanced argillic alteration at both KAA and TFAA, and lacustrine sediments accumulated within the craters. Successive hydrothermal activity occurred after the crater formation is characterized by H2S-dominant, more reduced fluids. This activity disseminated sulfur, arsenic, antimony and mercury in the lacustrine sediments. The loci of the activity has shifted to the east since 2.9 Ma.

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Fluid inclusions in hydrothermal quartz and anhydrite samples from the Mori geothermal field, southwestern Hokkaido, Japan, have been studied microthermometrically and geochemically, using a heating/freezing stage and a quadrupole mass spectrometer (QMS). The samples were selected from cuttings and a boring core from geothermal wells in the field. Based on the results and previous geochemical data (YOSHIDA, 1991), we discuss gas evolution of geothermal fluids from the early stage of geothermal activity to the initial stage of exploitation in the Mori geothermal reservoir.
Fluid inclusions are divided into the following four types; liquid-rich two-phase, vapor-rich two-phase, CO₂-bearing, and polyphase inclusions which contain large halite as a daughter mineral. The liquid-rich inclusions coexist with vapor-rich inclusions in many samples, indicating that the inclusion fluids were trapped in these samples under boiling condition. The minimum values of homogenization temperatures (Th) of liquid-rich inclusions are in general agreement with the measured static borehole temperatures, and it suggests that the inclusions which has minimum Th value were formed at the recent stage of geothermal activity.
Bulk gas contents of liquid-rich inclusions in quartz and anhydrite analyzed by the QMS method are as follows; 91.5 to 99.3 mol% H₂O, 0.56 to 2.4 mol% CO₂, 0.029 to 5.8 mol% N₂, 0.00043 to 0.063 mol% CH₄ and less than 0.001 mol% Ar. The CO₂/N₂ ratios generally increase with increasing the CO₂/CH₄ ratios. This tendency and the variation of CO₂ contents with the minimum Th values reveals that CO₂, N₂ and CH₄ contents in the inclusion fluids are controlled by degassing from initial fluid due to boiling and dilution with groundwater. On the other hand, these gas contents of the inclusion fluids are nearly equal to or higher than those of geothermal fluids at the initial stage of exploitation (YOSHIDA, 1991): From the results and the boiling evidence of the fluid inclusions as mentioned above, it is inferred that CO₂, N₂ and CH₄ degassing of geothermal fluids have proceeded from the early stage of geothermal activity to the initial stage of exploitation in the Mori geothermal reservoir.

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Systematic isotopic age-datings on Wunugetushan porphyry Cu-Mo deposit in NE-Inner Mongolia by several methods were reported by this paper as: the single grain zircon U-Pb age of 188.3±0.6 Ma; the whole rock Rb-Sr age of 183.9±1.03 Ma, and the altered sericite K-Ar age of 182.3-184.7 Ma. They represent the ages of beginning crystallization after magma emplacement, magma cooling, and hydrothermal alteration, respectively. So it is fully approved that the intrusive and metallogenic epoch of the Wunugetushan Cu-Mo deposit is in early Yanshanian (Early Jurassic) rather than late Yanshanian epoch as suggested before. The K-Ar ages (138 Ma) determined formerly perhaps reflect the later volcano-intrusive thermal events after mineralization.

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