Epithermal gold mineralization in the Minamikayabe area located on the Kameda peninsula, southwestern Hokkaido, includes the Mitsumoriyama high-sulfidation and Hokko-Minami low-sulfidation systems. The Mitsumoriyama high-sulfidation system consists of advanced argillic alteration which is sub-divided into alunite and kaolinite zones. This advanced argillic alteration grades into propylitic alteration laterally, and with a sericite alteration overprint in, and near to the advanced argillic alteration. The Hokko-Minami low-sulfidation system consists of adularia-bearing quartz veins with adularia alteration envelops. K-Ar ages of alunite, sericite and adularia indicate that the Mitsumoriyama high-sulfidation system was formed at approximately 6.5 Ma, and that the sericite alteration followed on from the advanced argillic alteration at 6.0 Ma, possibly due to an evolving hydrothermal system caused by an intrusion of quartz porphyry beneath the advanced argillic alteration zone. The Hokko-Minami low-sulfidation quartz veins formed at 3.9 Ma, which suggests no direct, genetic relation with the Mitsumoriyama high-sulfidation system. The high-and low-sulfidation epithermal systems in the Minamikayabe area occurred during periods of normal and oblique subduction of the Pacific plate beneath the Northeast Japan arc, respectively. Thus, the change in style of the epithermal gold mineralization in the Minamikayabe area from high-sulfidation to low-sulfidation may have been related to a change in the subduction mode of the Pacific plate.

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Various types of hydrothermal ore deposits; copper-lead-zinc vein, manganese vein, manganese strata-bound, barite vein, pyrite vein and Kuroko, are distributed in the Shakotan Peninsula, southwest Hokkaido. K-Ar ages for sericite separated from hydrothermally altered rocks collected from the individual types of ore deposits are as follows; copper-lead-zinc vein (10.22 to 1.99 Ma), manganese vein (6.29 to 3.14 Ma), pyrite vein (2.39 Ma) and barite vein (4.85 Ma). A Kuroko deposit yields 12.27 Ma and a manganese strata-bound deposit, 6.53 Ma.
Newly and previously obtained K-Ar age data, and geological information for the hydrothermal ore deposits in the Shakotan-Shikotsu district suggest that the major ore mineralization are grouped into three epochs; Middle Miocene Kuroko, Late Miocene vein (copper-lead-zinc) and Plio-Pleistocene vein (gold-silver, copper-lead-zinc and manganese). The Late Miocene mineralization is related to the activity of acidic intrusive rocks. The Plio-Pleistocene mineralization age is coincident with that of andesite lavas overlying the vein-type deposits.

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The Mozumi skarn-type Zn-Pb-Ag deposit of the Kamioka mine occurs in crystalline limestone of the Hida gneisses. The ore formation processes are divided into five periods: clinopyroxene-Zn-Pb, calcite-quartz-Pb-Zn, actinolite-Cu, quartze-calcite-Cu and quartz-Ag periods, in order of formation. The clinopyroxene-Zn-Pb period began with the formation of huge amounts of clinopyroxene (Di_10-35Hd_43-75Jo_11-35) at 400-330°C, associated with minor amounts of grandite garnet (Ad_16-78), calcite, quartz, Ag-and Bi-bearing galena, native bismuth, bismuthinite, Ag-Pb-Bi-S minerals and Fe-poor sphalerite(3-8 FeS mole%). The second stage (240-12°C) of the first period was the main sulfidation stage. The sulfide minerals, which had already begun to crystallize during the first stage, vigorously formed in this second stage and replaced earlier-formed pyroxene and garnet. During the late second stage, the ore fluid increased in Fe content and produced hedenbergetic pyroxene (Hd_53-88) and Fe-rich sphalerite (9-14 FeS mole%), which replaced portions of earlier-formed pyroxene and sphalerite, respectively. During the first stage of the calcite-quartz-Pb-Zn period, early calcite(400-270°C), quartz (360-310°C) and Fe-poor sphalerite (400-270°C; 3-7 FeS mole%) associated with Ag-and Bi-bearing galena, native bismuth, bismuthinite and Ag-Pb-Bi-S minerals were formed by replacing limestone and a part of the clinopyroxene-Zn-Pb ore. In the second stage (300-230°C), infiltrated Fe-rich ore fluid produced Fe-rich sphalerite (7-21 FeS mole%) which replaced early sphalerite and minor amounts of chalcopyrite, pyrite, pyrrhotite, arsenopyrite and magnetite. Ag-and Bi-bearing galena, native bismuth, bismuthinite and Ag-Pb-Bi-S minerals continued to precipitate at this stage. During the succeeding third stage (230-150°C), late galena (Ag-poor), freibergite and Fe-rich sphalerite (10-14 FeS mole%) were formed. At the end of this stage, a minor amount of hematite crystallized in association with late calcite, quartz and epidote. The actinolite-Cu period was characterized by hydration and Fe and Cu metasomatism of the early-formed barren clinopyroxene skarn and clinopyroxene-Zn-Pb ore. During this period, clinopyroxene was extensively replaced by actinolite in the lower levels of the deposit, associated with quartz, arsenopyrite, magnetite, pyrite, pyrrhotite, chalcopyrite, Fe-rich sphalerite and other sulfide minerals. Ore formation during the quartz-calcite-Cu and quartz-Ag periods was local. Ores produced during these five periods are thought to have been formed by different hydrothermal circulation systems that were controlled by a common igneous heat source.

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The Otoge mine is located near the southern border of Yamagata Prefecture. Since the discovery of Au-Ag mineralization near the mine, the area has become an active target of exploration for gold. Pyroclastic rocks in the area, which are mostly dacitic to rhyolitic compositions, were subjected to intense hydrothermal alteration.
Based on mineral assemblages, six alteration zones: the propylitic, smectite, interstratified I/S, sericite, kaolin and pyrophyllite zones, were defined. Micaceous minerals are the most common hydrothermal products except the smectite zone. Expandability in the micaceous minerals becomes higher with the elevation increase. Polytypes of micaceous minerals are 2M₁, 1M, lMd and 2M₂. The 1M type is the dominant polytype. 1M sericite (≤10%S) is close to muscovite and phengite in chemical composition, and shows close genetic relationship with Au-Ag mineralization.
Chemical and mineralogical data suggest that the pyrophyllite and kaolin zones formed by acid hydrothermal fluids, and the sericite zone associated with Au-Ag bearing quartz veins resulted from a near neutral pH hydrothermal activity. The crosscutting relationship and age data indicate that the acid hydrothermal alteration was followed by the near neutral pH sericitization and Au-Ag mineralization. All these hydrothermal activities occurred during 4.7-4.0 Ma.

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Skarn gold deposits account for about 14.8% of the gold resources in China. Thus great importance is attached to the study and prospecting of skarn gold deposits. A favourable ore-forming environment for skarn gold deposits is developed in East China (particularly the mid-lower Yangtze river district), Tianshan-Mongolia-Xing'anling, Kunlun-Qilian-Qinling-Dabie and Qinghai-Tibet-Sanjiang subduction-collision orogens, and those areas should be the key areas for search of skarn gold deposits. The following characteristics of skarn gold deposits in China can be taken as geological and geochemical indicators for ore prospecting: carbonate rock areas which have experienced extensive Yanshanian intermediate-felsic magmatism (particularly with volcanic-subvolcanic rocks), areas associated with intensive nonferrous and precious metallic mineralization (especially with porphyry and skarn copper or pyrite mineralization), the outer rims of disseminated molybdenum orebodies around porphyries, intensive alterations such as pyritization-silicification-sericitization and polymetallic sulfidization, poorly crystallized metasomatic minerals such as fine pentagonal pyrite, positive anomalies of S, As, Sb, Bi, Pb, Zn, Cu, Ag and Fe, and strongly broken rocks with extensive microfractures.

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