Liquidus phase relations on the join forsterite (Mg₂SiO₄)-anorthite (CaAI₂Si₂O₈)-silica (SiO₂) with 0.3 wt% MgCr₂O₄ were determined in air at 1 atm by ordinary quenching method. Spinel primary field is considerably expanded compared with that in the Cr-free forsterite-anorthite-silica join at the expence of anorthite primary field. As a result, phase assemblages at the points at which 4 phases coexist are completely changed : the assemblages forsterite+spinel+anorth. ite+liquid (piercing point), forsterite+ protoenstatite+ anorthite +liquid (peritectic point), and protoenstatite+anorthite+tridymite+liquid (eutectic point) on the Cr-free join disappear and the assemblages f orsterite +spinel+protoenstatite+liquid and protoenstatite+cristobalite+spinel+ liquid (both are piercing point) are present. However, the phase boundaries between the fields of forsterite and protoenstatite and those of protoenstatite and cristobalite are not affected by the addition of chromium. On the basis of the present data and those of the join forsterite-anorthite-diopside with 0.3% MgCr₂O₄ (Onuma and Tohara, 1983), phase relations of the system forsterite-anorthite-diopside-silica with 0.3% MgCr₂O₄ are inferred and its petrologic significance is briefly discussed.

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Many dikes of various rock types are observed in the central area of the Tamba belt, They intruded into the Tamba Group of age from late Carboniferous to late Jurassic. Whereas basic to intermediate dikes are uniformly distributed in a relative sense, acidic dikes are unevenly spread. Many dikes are distributed around the Shuzan syncline, however, no dikes are found in sandstone area. These observations are suggestive that the dikes were formed under the structural control of the Tamba belt. The rocks from the dikes are classified into seven groups with two subgroups as follows: (1), Granite-porphyry; (2), Felsite; (3), Diorite-porphyry; (4), A, Hornblende-porphyrite with plagioclase phenocryst; B, Hornblende-porphyrite with no plagioclase phenocryst; (5), Clinopyroxene-brown hornblende-porphyrite; (6), Diabase; (7), Diabase-porphyrite. The groups, (1) to (4) A, are acid to intermediate rocks, and the others are intermediate to basic rocks. Petrographic descriptions for these rocks have been carried out.

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Ore deposits of the Koryu mine, which is located near the Shikotsu Lake, Hokkaido, are gold and silver veins of epithermal type. They develop in black hard mudstone of the Miocene age and are composed of mainly quartz associated with some amounts of johannsenite, adularia, chlorite, vermiculite, manganoan calcite, pyrite, chalcopyrite, sphalerite, galena, hematite, electrum and silver minerals such as aguilarite, pearceite, polybasite, pyrargyrite, proustite, miargyrite, unknown Ag-Sb-As sulfosalt mineral and silver bearing tetrahedrite etc. The ore veins show crustified banding structure which consists of bands of quartz, johannsenite, adularia, chlorite, vermiculite, silver minerals and sulfide minerals. Many druses and vugs are found in the central portion of the quartz veins. Many kinds of small crystals of adularia, manganoan calcite, aguilarite, pearceite, pyrargyrite, miargyrite, unknown Ag-Sb-As sulfosalt mineral and tetrahedrite etc. besides quartz occur in the druse.
Electrum is found in intimate association with chalcopyrite, aguilarite, pearceite, sphalerite, galena and pyrite, and its composition is from 38.5 to 70.0 at. % Ag. While that of native silver is 99.9 at. % Ag. The composition of aguilarite has a range from 14 to 41 mole % Ag₂Se. According to Petruk et al. (1974), aguilarite having such compositions as above is not homogeneous and associates with acanthite. However, aguilarite as above from this mine is monophase with monoclinic cell. Pearceite and polybasite series minerals appear as rim of aguilarite or in association with electrum, chalcopyrite and sphalerite. Compositions of pearceite series are from 0 to 100 at. % in Sb/(As+Sb) ratio showing completely continuous solid solution of the series. Also, those of pyrargyrite and proustite series minerals have a wide range from 0 to 98 at. % in Sb/(As+Sb) ratio. It indicates that pyrargyrite-proustite solid solution is stable at low temperatures, although Toulmin (1963) suggested that the solid solution becomes immiscible at temperatures below 300°C. Tetrahedrite assembled with chalcopyrite and pyrargyrite in the druse contains silver from 24.1 to 25.3wt%.
The homogenization temperatures and salinities of fluid inclusions in quartz are from 240° to 270°C and from 0.0 to 1.4wt% NaCl equivalent, respectively. Temperatures and sulfur fugacities of gold-silver mineralization in the Koryu mine are estimated as 175° to 240°C, and -15.5 to -ll.5 in log fs₂ (atm), respectively, from the data of compositions of electrum with aguilarite and FeS contents of sphalerite with pyrite.

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Strontian apatite, about 25% of calcium ion being substituted by strontium ion, has been found in tephroite ore of the Misago ore body, Noda-Tamagawa mine, Iwate Prefecture.
It occurs with baryte, vanadium- and titanium-bearing jacobsite, manganobarian phlogopite, and bementite-like mineral in tephroite ore. Optical properties: uniaxial negative, ω=1.639, ε=1.635. Cell dimensions: a=9.475 (3)Å, c=6.974 (1)Å, V=542.2 (3)ų, c/a=0.7360. Chemical formula: (Ca_7.046Sr_2.574Mn_0.346)_9.966P_6.014O_24.000(F, OH, Cl)_2.000. Infrared spectral data are also given.

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