Hydrothermal coprecipitation experiments were performed at 350 and 300°C, in order to reproduce the “chalcopyrite disease” texture involving Fe-bearing sphalerite. Sector-zoned chalcopyrite disease textures were obtained in some runs using a hydrothermal transporting method, and this shows that coprecipitation is responsible for formation of the texture in Fe-bearing sphalerite. These chalcopyrite disease textures with compositions similar to the run products occur in Fe-bearing sphalerite ores from the modern seafloor deposits at the Okinawa Trough and North Fiji Basin, suggesting a possibility that the chalcopyrite disease textures in the deposits were caused by the process of coprecipitation in short spans of time.

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The Ezuri Kuroko deposits are located approximately at 140°36'of east longitude and 40°15' of north latitude in the Hokuroku district of Akita Prefecture. The ore deposits are hosted by basaltic tuff and dacitic rocks of the Miocene age, and they are composed mainly of stratiform black ores.
   In this paper, the features of Au- and Ag-bearing ores and minerals are described, and the environment of the mineralization is estimated from the FeS content of sphalerite and the data of fluid inclusions in sphalerite.
   Gold- and/or silver-bearing minerals identified by microscopic examination and electron microprobe analysis are electrum, stromeyerite, pearceite, mckinstryite, argyrodite and fahlore (up to 7.8 atomic % Ag). These minerals are particularly found in fine-grained massive black ore. Most of electrum contains 30-40 atomic % Ag, and Ag distribution of an individual grain is comparatively homogeneous. Silver content of black ore (20-1, 260 ppm) is dependent on the amount of fahlore as well as of other silver minerals.
   The ranges of homogenization temperatures of fluid inclusions in sphalerite are 236°-283°C (breccia-like black ore), 210°-279°C (massive black ore) and 165°-230°C (coarse-grained sphalerite filling cavities in massive black ore), respectively. The FeS content of sphalerite coexisting with electrum is less than 0.2 mole%. Taking account of the effect of pressure, it is deduced from these data that Au- and Ag-bearing ores were formed in a range of ca. 240°-290°C under the condition of a high activity of sulfur. Furthermore, it appears that gold was precipitated from Au(HS)₂⁻ complex mainly owing to cooling and a decrease in H₂S concentration of ore-forming fluids caused by mixing with seawater and/or by precipitation of metal sulfides.

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The occurrence of nsutite and manganoan nsutite is reported for the first time from Goriajhar manganese deposit in Gangpur group of rocks, India. Detailed mineralogic and geochemical characteristics of these phases are described. Mn³⁺ rather than Mn²⁺ is found to coexist with Mn⁴⁺ ion, the general formula being (Mn³⁺, Mn⁴⁺) (O, OH)₂. These are formed from the host gonditic rocks through oxidation and precipitation processes under supergene enrichment condition.

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Strontianite was found as authigenic mineral in cavities in Torinosu limestone, Sakawa-cho, Kochi Prefecture, forming fibrous and needle forms up to 5 mm in length, often radial globular aggregates on calcite. It is closely associated with dolomite, fluorite, barite and rarely celestine, colorless to pale yellow with vitreous luster. The refractive indices are α=1.520, γ=1.666, γ−α=0.146. Unit cell parameters are a=5.088 (5), b=8.340 (9), C=5.966 (7) Å, V=253.1 (8) ų. The chemical compositions by EPMA analyses varies from SrCO₃ 79 mol%, CaCO₃ 20 mol%, FeCO₃ 1 mol% to SrCO₃ 80 mol%, CaCO₃ 19 mol%, FeCO₃+MnCO₃ 1 mol%. Consequently, it was identified as calcian strontianite.

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