Examination of grades, tonnages, and basement rocks for 88 epithermal precious- and base-metal quartz-adularia-type districts in North, Central, and South America, and Japan reveals that the type of basement rock below the mineralized veins is useful for predicting grade and size of deposits. Epithermal districts overlying basement with salt and evaporites, or rocks with trapped sea water, have a median tonnage (production and reserves) of 1.4 million metric tons and median grades of 1.5g/t Au, 130g/t Ag, 2.5%Pb, 1.7%Zn, and 0.16%Cu. Districts overlying sedimentary basements have a median tonnage of 0.77 million metric tons and median grades of 7.5g/t Au, 110g/t Ag, <0.025%Zn, <0.005%Cu, and <0.001%Pb. Districts overlying igneous basements have a median tonnage of 0.3 million metric tons and median grades of 5.9g/t Au, 38g/t Ag, <0.25%Zn, <0.002%Cu, and <0.003%Pb. This investigation suggests that basement rocks affect vein components in epithermal precious- and base-metal quartz-adularia-type deposits.

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K-Ar age determinations were carried out on ten specimens from seven representative gold deposits in South Korea. Microclines separated from pegmatites, which are associated with gold alaskite vein in the Geumjeong mine, yield ages of late Proterozoic. White micas in ores and associated pegmatites from the Homi, Cheonbo and Namchang mines in the Cheonan district, give ages of 130-160Ma, and confirm the middle to latest Jurassic gold mineralization in this district. The results for sericites from the Mugug, Imcheon and Geochang mines are around 100Ma. The present results together with data available in the literature reveal that majority of precious, base and heavy metal deposits at the present erosional levels in South Korea were formed in Cretaceous time with a genetic relationship to the Bulgugsa felsic igneous activity.

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The Toyoha zinc-lead-silver ore deposit of vein-type is located in the Green Tuff Region of Southwest Hokkaido. In the eastern area of the Toyoha mine, ore veins are unrecognizable at the surface, but sulfide veins have been confirmed by some drilling cores at 600-1000 meters from the surface. All the rocks in the studied area composed of andesite, dacite, acidic tuff, sandstone, mudstone and conglomerate of Miocene age have been converted into various types of altered rock. The alteration intricately duplicated may be ascribed to the composite alteration of different origin. This conception was obtained by the altered mineral assemblage and the distribution, from which the diagenetic and the hydrothermal alterations were distinguished. Followings are evidences and conclusions.
(1) Alteration in the studied area is divided into four alteration zones, A, B, C and F. Moreover facies A is subdivided into subfacies A-1, A-2 and A-3. Characteristic mineral assemblage of each alteration zone is as follows. A-1: Smectite, A-2: Chlorite/smectite mixed-layer mineral-sericite/smectite mixed-layer mineral, A-3: Chlorite-sericite-quartz-calcite, B: Quartz-chlorite-albite-calcite, C: Quartz-chlorite-sericite-pyrite, F: Quartz-kaolinite-sericite.
(2) Alteration zone A is widely distributed and shows zonal distribution of subfacies A-1, A-2, A-3 downward. Alteration zones B-C and F are locally distributed around the ore veins and the junction of the Shirai and Yunosawa rivers, respectively.
(3) Alteration zones B and C are inferred to be formed by a solution associated with mineralization. Alteration zone F is a product by an acidic solution. Various hydrothermal solutions, ore solution, acidic one and so on, was very active.
(4) As alteration zone A is affected strongly by the geothermy, the terrestrial heat flow reaches 27.5 HFU, and activity of various hydrothermal solutions, it may be generated by the diagentic process at the highest geothermal gradient area.
(5) The mineral assemblage and character of clay minerals of the alteration associated with the mineralization at the studied area are similar to those at the Motoyama deposits. Nevertheless the distribution of alteration zone B is narrower and the degree of silification or pyritization is lower than that of the Motoyama deposits.

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