A number of epithermal gold-silver-lead-zinc rhodochrosite veins of Neogene age are distributed in southwestern Hokkaido, Japan. They are the principal vein-type manganese deposits in Japan and called the In-akuraishi-type manganese deposits. Gold and silver are important by-products in these ore deposits.
In this study electrum from five representative ore deposits of this type, namely, Imaiishizaki, Jokoku, Yakumo, Oe and Inakuraishi, has been analysed by electron microprobe analyzer.
The veins show banded structure, and electrum occurs in sulfide-rich bands alternating with rhodochrosite bands. It associates mainly with pyrite, sphalerite, galena, chalcopyrite, tetrahedrite, acanthite, polybasite, pyrargyrite, rhodochrosite, quartz and barite with a small amount of Ag-Pb-Sb-S minerals, stannite, canfieldite and argyrodite.
Rounded grains of electrum, 10 to 20 microns in diameter, are common. Various kinds of compositional heterogeneity (e.g., irregular, zoned, homogeneous etc.) are found in electrum grains.
Silver content of electrum ranges from 16.70 to 82.35 atomic percent as a whole. However, most electrum contains 55-75 atomic percent Ag. This mode value of Ag content is higher than those of Kuroko and epithermal gold-silver vein deposits in Japan. Both Ag content of electrum and FeS content of sphalerite increase in an order; Kuroko deposits<epithermal gold-silver quartz vein deposits<Inakuraishi-type manganese deposits<epithermal gold-silver bearing lead-zinc vein deposits.

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The Kushikino mine is located at the northeastern part of Kushikino City in Kagoshima Prefecture, Japan. The ore deposit is of representative epithermal Au-Ag quartz vein type developed in Miocene andesite. Two Te-concentrated veins were investigated in the present study: the Arakawa No.5 and Shinpi No.1 veins. The veins are largely composed of quartz, calcite, chlorite/smectite interstratified mineral, apatite, and ore minerals. The following ore minerals were confirmed to occur, as determined with ore microscope and electron microprobe: sphalerite, chalcopyrite, galena-clausthalite solid solution, pyrite, hessite, altaite, calaverite, petzite, electrum, sylvanite, etc. in the order of decreasing abundance.
A tentative low-temperature phase diagram for the Au-Ag-Te system was constructed in the present study on the basis mainly of the observed mineral assemblages and the chemical compositions of the coexisting minerals. The equilibrium temperature for the assemblages, inferred from the experimental studies carried out by previous in-vestigators, is approximately 100°C (at least lower than 120°C). On the other hand, the homogenization tempera-tures, measured on fluid inclusions in quartz and calcite associated with ore minerals, range from 200° to 250°C. If it is the case that the ore minerals precipitated from fluids in this temperature range, there is a significant temperature difference, as large as more than 100°C, between the precipitation temperature and the equilibrium temperature. This may be attributed to the rapid reaction rate during retrograde process and the relatively slow cooling rate in natural environments.

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It is well known that mackinawite-bearing chalcopyrite dots occur commonly in sphalerites from some sulfide deposits. Microscopic examination of many polished sections from various ore deposits in Japan and Korea, reveals that the sphalerite with those dots is found only in pyrrhotite-predominant deposits. On the basis of phase relations in the central portion of the Cu-Fe-S system, it is concluded that the dots have originally been intermediate solid solution (iss), and later they broke down to chalcopyrite and mackinawite during the cooling of deposits without the supply of sulfur from outside of the sphalerite. The presence of the dots (called iss dots) in sphalerite could be regarded as a direct evidence for the presence of iss instead of chalcopyrite in the ore before cooling.

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Sphalerite contained in the Pb-Zn-quartz-calcite ore ("Shiroji-ore") from the Mozumi deposit of the Kamioka mine exhibits complex compositional zoning and includes both chalcopyrite dots and "chalcopyrite disease". The results of microscopic observation and EPMA analysis suggest that the compositional zoning and chalcopyrite dots and "disease" in sphalerite are replacement products by later hydrothermal solution after the crystallization of primary Fe-poor sphalerite. The inferred processes are as follows: (1) Fe enrichment to the margins and along the cracks of the Fe-poor sphalerite by Fe-rich solution. (2) Formation of chalcopyrite dots in the Fe-enriched sphalerite formed at the stage (1) and Fe reduction of sphalerite near the chalcopyrite dots by Cu-bearing solution. (3) Formation of "chalcopyrite disease" penetrating the compositional zoning of sphalerite.

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The relationship of chemical composition to reflectivity and Vickers hardness of fahlore was examined by electron microprobe analyzer, microscope photometer and microhardness tester. 95 specimens of fahlore from ores of Tertiary epithermal gold- and silver-bearing quartz vein, polymetallic sulfide vein and Kuroko, and Silurian stratabound massive sulfide deposits were used for this study.
The maximum amounts of respective constituents of fahlore are 35.9 atom.% Cu, 18.5 atom. % Ag, 8.2 atom. % Zn, 6.4 atom.% Fe, 14.9 atom.% Sb and 13.6 atom.% As. The ranges of reflectivity of fahlore are 26.9-31.5% at 450 nm, 27.7-31.6% at 530 nm and 26.4-31.0% at 600 nm. And the range of Vickers hardness is 276-389.
There are close relationships among Sb/(Sb+As) ratio, reflectivity at 600 nm in air and lattice constant, and between Agcontent and Vickers hardness of fahlore.
The relationship between reflectivity and Vickers hardness of fahlore is useful for identification of tetrahedrite, Ag-tetrahedrite and tennantite.

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Intense Sn-As-Zn-Ag vein mineralization was found at the 26th Level of the Besshi mine, of which deposit is a conformable massive sulfide type (Besshi-type). The mineralization resulted in formation of such rare Sn minerals as rhodostannite, hocartite and a franckeite-like mineral, as well as common stannite and cassiterite. Pyrite, arsenopyrite, sphalerite, tetrahedrite, manganese carbonates, quartz, tourmaline and so on occur in association with these Sn minerals. The prominently polymetallic ores are composed of minerals that were formed at several stages during the mineralization sequence.
The present microprobe analyses, combined with previous chemical data, indicate that the substitution of Ag for Cu is extensive in rhodostannite, whereas that of Zn for Fe is very limited. The substitution relationship of these elements in stannite and hocartite is just the opposite to that found in rhodostannite. Divalent Sn may substitute for Pb in the franckeite-like mineral, which is considered to be mainly responsible for the extensive solid solution observed in this mineral.
The mineralization may have taken place nearly simultaneously with contact metamorphism, which converted the massive pyrite ores and surrounding pelitic schists to massive pyrrhotite ores and biotite hornfels, respec-tively. A granitic intrusion, which is supposed to be hidden in the deeper part of the Besshi mining district, probably caused the vein mineralization and contact metamorphism. The geological situation and mineralogical characteristics of the vein mineralization are quite similar to those observed in the Sn deposits adjacent to Miocene granitic intrusives in the Outer Zone of Southwest Japan at Kyushu. The Miocene Sn metallogenic province in the Outer Zone of Southwest Japan at Kyushu should be extended eastward to the Besshi mining district in Shikoku.

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Various kinds of tin-bearing minerals, such as cassiterite, stannite, kesterite, franckeite, hocartite, teallite, cylindrite, rhodostannite, canfieldite, incaite and potosiite occur from polymetallic deposits in Eastern Cordillera of Bolivian Andes. These deposits, called Bolivian type polymetallic deposits, were formed by xenothermal mineralization related to Miocene igneous activities. The mineralization stages are generally divided into six as follows: I: quartz-tourmaline, II: quartz, III: quartz-pyrite, IV: sulfide, V: sulfosalt and VI: sulfate-phosphate stages. Cassiterite principally occurs in the quartz-tourmaline (I), quartz (II) and quartz-pyrite (III) veins. Stannite and kesterite appear in the sulfide (IV) and sulfosalt (V) veins. Meanwhile, tin-bearing sulfosalt minerals, such as franckeite, hocartite, teallite, cylindrite, rhodostannite and canfieldite are found commonly in the sulfosalt (V) vein in small amount. Homogenization temperature and NaCl equivalent concentration of fluid inclusions in quartz at each stage of the mineralization are I: 260° to 510° and 18.5 to 55.4 wt%, II: 250° to 405°C and 23.4 to 26.0 wt%, III: 250° to 400°C and 4.4 to 19.7 wt%, IV: 230° to 350°C and 1.5 to 10.6 wt%, and V: 190° to 300°C and 0.4 to 5.4 wt%, respectively. The homogenization temperatures, salinities and sulfur fugacities at each stage decrease as a whole with progressing the mineralization stages. Sulfur fugacity values at the III, IV and V stages are 10^-13 to 10^-7 atm., 10^-15 to 10^-9 atm., and 10^-16 to 10^-19 atm., respectively.

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Silician magnetite was found in the copper sulfide ores from the Tengumori ore deposit of the Kamaishi mine, Iwate Prefecture, northeastern Japan. The mineral occurs generally as a zonal intergrowth with normal magnetite and as a narrow rim surrounding normal magnetite sparsely dispersed in chalcopyrite-pyrrhotite-cubanite ores. The optical and compositional aspects of the mineral fairly approximate those of magnetite. In polished section, the mineral is isotropic with brownish gray color and is slightly darker than normal magnetite. The chemical composition of the material, determined using an electron microprobe, is as follows: CaO 0.15, FeO 87.25 (total Fe as FeO), SiO₂ 5.52 wt. percent. Although the crystal structure is not still defined, the optical and compositional data indicate a possibility of a new variety of magnetite with a coupled substitution 2Fe³⁺→←Si⁴⁺+Fe²⁺. In the case, the structural formula is written as Fe²⁺(Fe3+/1.6Si_0.2Fe2/0.2)O₄.

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Dosulite which was named after the Dosu mine by YOSHIMURA (1967) is considered to be a major consti-tuent mineral of "chocolate ore" in the bedded manganese deposits in Japan. However, it is identified as a mixture of gageite and the associated hausmannite, rhodochrosite and Mn-humites based on electron microprobe and X-ray powder diffraction analyses in this study. The Dosu gageite has a composition in good agreement with the ideal chemical formula proposed by FERRARIS et al. (1987) and shows a similar X-ray diffraction pattern to that of MOORE (1968).The gageite is also associated with cymrite and is assumed to be more stable phase compared with Mn-humites such as alleghanyite and sonolite under high PH2O/T ratio conditions. Seven occurrences of gageite have been found in Japan including another two from Nagatani and Manako mines in this study and four by MATSUBARA and KATO (1979) and almost all these are located in the northern Chichibu Belt where the sediments containing the manganese deposits were affected by low temperature metamorphism of Mesozoic age. Hence, it is assumed that primary gageite which ac-cepted more high temperature metamorphic event was decomposed to common assemblages containing Mn-humites and so on.

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The mode of occurrence, mineral assemblage, and chemical composition of welinites from the Taguchi, Fukumaki and the Ioi manganese mines were described.
Welinite from the Taguchi mine in the Ryoke metamorphic belt, occurs in rhodochrosite-tephroite-alabandite ore associated with small amounts of galaxite and pyrophanite. The mineral occurs as fine-grained crystals about 0.3-0.7mm in diameter. Under the microscope, the welinite is weakly pleochroic in shades of yellowih brown to pale yellow. No cleavage is observed. A parting is developed which is similar to that of tephroite. X-ray powder diffraction data for welinite are agreement with those of welinite from the Langban mine.
Welinite from the Fukumaki mine in the Ryoke metamorphic belt, occurs in rhodochrosite-alabandite ore. In thin section, it is associated intimately with tephroite and alabandite. Small amount of rhodochrosite, galaxite and pyrophanite coexist with the welinite. The mineral is rarely, occurs as very fine grains up to 0.2mm in diameter. Under the microscope, it is colorless or has slight yellowish tint, therefore it is difficult to distinguish it from tephroite.
Welinite from the Ioi mine in Paleozoic Chichibu formation, occurs in tephroite-alabandite ore. The mineral is associated with tephroite, rhodochrosite, alabandite and small amounts of galaxite and pyrophanite. The mineral is yellow to yellowish brown in color, and 0.05-0.10mm in diameter.
Microprobe analyses of welinites from the Taguchi, Fukumaki, and Ioi mines yield the empirical formula Mn ₆WSi₂ (O, OH) ₁₄ on the basis of (O, OH)=14. Welinite in the bedded manganese ore deposits is interpreted as a product due to the reaction of manganese ores and hydrothermal solutions cotaining WO₃, H₂O, and CO₂ probably sup-plied from granitic bodies near the ore deposits.

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Tungsten deposits of the Yaguki mine occur as layered, lenticular, massive and amoebic forms in intensely altered clinopyroxene and garnet skarns along the contact with the limestone at hanging wall. The skarns were hydrothermally altered to aggregates of actinolite, epidote, quartz, prehnite, chlorite, sericite, calcite, scheelite. Scheelite occurs as disseminated grains, veinlets and networks in the alteration zone. Under the microscope, it is euhedral to subhedral, and is 0.15 to 2.0 mm in size. This mineral is intimately associated with epidote, quartz and, sometimes, prehnite. Scheelite also occurs with chlorite, sericite and calcite which were crystallized at later stage than that of scheelite.
Ore minerals such as magnetite, pyrrhotite, chalcopyrite, pyrite, sphalerite, bismuthinite and native bismuth appear occasionally with scheelite in the altered skarn. Veinlets of quartz with scheelite sometimes penetrate into magnetite, meanwhile scheelite is surrounded by the sulfide minerals, and cut by veinlets of them.
Temperature and sulfur fugacity of sulfide mineralization obtained from data of ore mineral assemblages and iron contents of sphalerite are 240°to 290°C and 10^-14 to 10^-12 atm., respectively.
Molybdenum content of scheelite is less than 10.1mol% CaMoO₄, commonly less than 3.0mol% CaMoO₄. Zontal structure is usually found in scheelite crystals in term of Mo contents. The central part of the crystal has relatively higher Mo contents than those of outer portion. Crystals are often rimmed with pure scheelite, and sometimes cut by its veinlet.

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