The Tsumo Cu-Zn-Fe-W deposits consist of various kinds of skarns replacing limestone lenses in the Tsumo formation of Paleozoic age. Intensive felsic igneous activities of Cretaceous age are recognized in the mining area as many dikes and stocks, as well as a thick volcanic pile and some plutonic intrusives. Analyzed were oxygen isotopic compositions of 26 mineral separates from skarns, including clinopyroxene, wollastonite, quartz and magnetite, and six specimens mainly from felsic hypabyssal rocks (Table 1). The estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits, show a wide variation, from the values lower than zero to higher than ten permil (SMOW). Massive main skarns in the two largest Maruyama and Tsumo deposits were formed by the solutions with magmatic isotope compositions, while later tungsten and sulfide mineralizations were brought by the solutions with a little lower values than those of magmatic. The skarns and-associated tungsten ores in the Horai deposit, as well as scheelite-bearing quartz pipes in the Tsumo deposit, were precipitated from the solutions with values of nearly zero permil. Along with the data of hypabyssal rocks, the obtained data indicate a complicated feature of the hydrothermal systems in this area, such as early prevalence of the hydrothermal solutions of magmatic origin with later, gradual replacement by the hydrothermal solutions of meteoric water origin.

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The skarn-type Cu-W orebodies at the Kuga mine are classified in this paper into two groups; orebodies not containing relict limestone and orebodies containing limestone in their inner parts. Mineralogical features are compared between the limestone-absent Umenoki 5 orebody, and limestone-bearing Suho 3-A and 3-D orebodies.
Sulfide minerals and hydrous silicate minerals are present in larger amounts in the Umenoki 5, whereas anhydrous skarn minerals such as clinopyroxene and garnet are present more abundantly in the Suho 3-A and 3-D. Wolframite occurs only in the Umenoki 5. Siderite and ankerite are ubiquitous in the Umenoki 5, whereas these two carbonate minerals are very rare in the Suho 3-A and 3-D. Garnet from the Umenoki 5 contains larger amounts of almandine and spessartine components than that from Suho 3-A and 3-D. FeS contents of sphalerites range from 18.3 to 19.9 mol% in the Umenoki 5 and from 21.3 to 23.9 mol% in the Suho 3-A and 3-D. These markedly different mineralogy between two groups of orebodies may be mainly attributed to the difference in activities of metal ions such as Ca, Fe and Mn, and to variations in pH and f_o2 during the mineralization, which is essentially related to the presence or absence of free CaCO₃.

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Tungsten bearing endoskarns are developed in the Tenpo orebody of the Yaguki W-Cu-Fe mine, northeastern Japan, at the contact between the granodiorite and the slate by replacing both rocks. The endoskarn generally displays a zonal arrangement toward each original rock with successions of pyroxene skam, garnet skarn enriched in andradite component, epidote skarn, garnet skarn enriched in grossular component and plagioclase-pyroxene skam with prehnite veins. The mineral assemblage and mineral composition of each endoskarn is independent of its size and host rock composition, indicating that the same metasomatic process took place in the slate and the granodiorite. The coarse-grained primary hornblende and biotite in the granodiorite are altered into pyroxene, while plagioclases are into anorthite, epidote or garnet, in the endoskarn. The iron content in garnet, pyroxene and epidote decreases toward the host rock. Epidotes also decrease in their iron content with the progress of crystallization. The scheelite mineralization is divided into two stages. The earlier scheelite is characterized by high CaMoO₄ content (0.6-9 mol %) and occurs in association with pyroxenes, while the later scheelite contains low CaMoO₄ component (<0.3 mol %) and occurs in association with epidotes with low pistacite component (<20 mol %), prehnites and/or calcites. In spite of a local development of replacement textures between minerals, textural relations suggesting the prevalence of replacement reactions between skarn zones are not observed. The textural and geochemical data suggest that skarn zones were sequentially formed from the inner zone to the outer zone, in most cases by replacing host rocks directly rather than preexisting zones. It is inferred that the skamization and tungsten mineralization at the Tenpo orebody was primarily related to the decrease in the concentration of Ca and Fe³⁺ in the coexisting fluid.

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Heyrovskyite from the Yakuki mine, Fukushima Prefecture, occurs as aggregates of minute blades in clinopyroxene skarns with two different mineral assemblages. One of them accompanies galena, lillianite solid solution, pyrrhotite, chalcopyrite and magnetite, whereas the other does magnetite, chalcopyrite, sphalerite and galena. The averages of five analyses of them are, respectively: Ag 1.13, 2.17; Cu 0.05, 0.07; Pb 59.33, 56.00; Bi 24.27, 26.72; S 14.83, 15.00; totals 99.61, 99.96%. Their empirical formulae calculated on the basis of S atoms=9 are, respectively: Pb_5.53Ag_0.20Cu_0.02Bi₂.24S₉and Pb_5.15Ag_0.38Bi_2.44S₉. They are Ag-poorer heyrovskyites closer to the ideal formula, Pb₆Bi₂S₉, from which they are derived by the coupled substitution of AgBi for PbPb, though the minor effect of the substitution of 2Bi for 3Pb exists. The average of four analyses of lillianite solid solution is: Ag 1.99, Cu 0.14, Pb 42.30, Bi 39.59, S 15.75, total 99.77%. The range of chemical analyses indicates that this phase demonstrates the substitution of 2Bi for 3Pb. Those of two galena analyses in them are, respectively: Ag 0.37, 0.97; Pb 84.01, 82.16; Bi 1.95, 3.15; S 13.35, 13.29; totals 99.68, 99.56%. In galena the coupled substitution of AgBi for PbPb is less developed than in heyrovskýite, but that of 2Bi for 3Pb is more developed. The cell parameters of two heyrovskýites are, respectively: a=13.719, 13.704; b=31.260, 31.247; c=4.127Å, 4.124Å. Also, the role of Ag is discussed after the reference to the variable Ag contents in this mineral. Probably it serves to prevent the phase from the inversion to its monoclinic derivative aschamalmite, which has real compositions closer to Pb₆Bi₂S₉ and would be stable under lower temperature condition. Ag-free heyrovskyites hitherto described by only chemical analyses needs verification.

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The distribution and behavior of the REE in the zoned skams of the Nippo and Shinyama ore deposits, Kamaishi mine, are described. The zoned skams are developed between dioritic rocks and limestone, and the REE abundances of skarns decrease from the dioritic rock side to the limestone side. All the skarns have lower REE contents than the dioritic rocks, implying that REE of the skams were derived from the dioritic rocks, and no or little REE was added to the skarns from hydrothermal fluids. Clinopyroxenes show negative Eu anomalies on chondrite-normalized REE diagrams, and the magnitude of the Eu anomaly increases from the diorite side to the limestone side. Garnets and garnet skarns exhibit large variations in the extent of Eu anomaly. The oxygen fugacity (fo₂) is the main factor that controls Eu⁺²/Eu⁺³ ratios in the minerals; the negative Eu anomaly of clinopyroxene increases with a decrease of fo₂, and garnet preferentially takes Eu⁺³ relative to Eu⁺². The fo₂ of hydrothermal fluids had declined due to the metasomatic reaction with graphite-bearing limestone. The garnets with positive Eu anomalies were formed by the reaciton between dioritic rocks and initial hydrothermal fluids with higher fo₂. The garnets with negative Eu anomalies were produced by the reaction between limestone and the initial fluids, or between dioritic rocks and the secondary fluids with lower fo₂. The secondary lower fo₂ fluids were originated by the reaction of the initial fluids with limestone.

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Relative concentrations of CaCL_2aq, MgCL_2aq, FeCL_2aq, MnCL_2aq, ZnCL_2aq and CdCL_2aq in the skarn-forming solutions, especially in exoskarns derived from limestones, were estimated from the chemical compositions of minerals and mineral assemblages using experimental data of ion exchange equilibria between aqueous chloride solution and garnet, clinopyroxene, carbonates (calcite, dolomite and magnesite), tungstates (scheelite and wolframite) and sphalerite. The equilibrium temperature is assumed to be 400 to 600°C, and the pressure 1 kbar.
In general, the exoskarns mainly consist of clinopyroxenes and grandite series garnets. The clinopyroxenes have compositions ranging from 0.49 to 0.50 in the Ca/(Ca+Mg+Fe²⁺+Mn²⁺) molar ratio. The content of pyralspite components in the garnets is nomally less than 15 mol.%. The chemical compositions of these minerals indicate that the CaCL_2aq concentration relative to MgCL_2aq, FeCL_2aq and MnCL_2aq in the skarn-forming solution is extremely high. Scheelite is stable in such a solution instead of wolframite. Clinopyroxenes in the exoskarns are poor in a diopside component, which indicates that the MgCL_2aq concentration relative to FeCL_2aq and MnCL_2aq in the skarn-forming solution is very low. The FeCL_2aq/MnCL_2aq ratio in the skarn-forming solution is nearly equal to the Fe/Mn ratio in garnet. The high Fe/Mn ratio in sphalerite can be explained by the preferency of Fe to Mn in sphalerite. The average sphalerite composition of skarn deposits in Japan suggests that relative concentrations of FeCL_2aq, MnCL_2aq, ZnCL_2aq and CdCL_2aq in the skarn-forming solution are in the order of FeCL_2aq+MnCL_2aq≥ZnCL_2aq≥CdCL_2aq.

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The Kamioka deposits are composed of skam type lead-zinc orebodies formed by the replacement of limestone, a member of Hida metamorphic rocks, and there are many variety of dikes and small stocks which occur in and around the deposits. The Kamioka deposits are estimated to have formed from a hydrothermal events related to the Mesozoic magmatism.
In order to clarify the related igneous activity, we carried out K-Ar age determination for representative dikes in the mining area. From the data, the dikes and stocks are roughly divided into two groups, that is late Cretaceous to early Paleogene (55-65Ma) and Cretaceous to some older (90-125Ma). The former age is equivalent to the age of Shiroji(63.8-67.5Ma for sericites, NAGASAWA and SHIBATA, 1985) mineralization of the Kamioka deposits.
Although the igneous rocks clearly related to the mineralization in the Kamioka area have not been identified, it is concluded that the former young dikes belong to a group of late Cretaceous acidic magmatism locating beneath this area that is estimated to be a related magmatism to the mineralization of the Kamioka deposits (SAKAI, 1963; SHIMAZAKI and KUSAKABE, 1990; Among others).

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