Chemical composition of Fe-Ni metal and phosphate minerals in Yamato-82094 carbonaceous chondrite

The mineralogy of Fe-Ni metal and associated minerals in the Yamato (Y)-82094 carbonaceous chondrite (CO) have been studied by optical, scanning electron microscope and electron microprobe techniques. There are some characteristic features for the Fe-Ni metal in the Y-82094 : (1) Ni contents in taenite grains are divided into two groups consisting of low-and high-Ni taenite. (2) Partition of Co between coexisting kamacite and taenite shows relatively higher temperatures (approximately 800℃), and their temperature ranges are wide. (3) polycrystalline taenite exists. (4) Fe-Ni metal and troilite form micron-sized intergrowths. (5) The Ni-Co trend of kamacite in chondrule is positive. The high-Ni taenite could have formed through thermal metamorphism on the parent body, while low-Ni taenite might have formed due to reheating caused by shock metamorphism on the parent body or during the colling process of chondrule formation. The positive Ni-Co trend of kamacite in Y-82094 is similar to that of the metal in CR chondrites. This trend may suggest that kamacite in Y-82094 preserves the primitive chemical composition indicating nebula condensation origin. The Fe-Ni metal grains have many phosphate mineral inclusions (whitlockite, brianite and panethite). The mode of occurrence of brianite and panethite indicates that they might have formed simultaneously with the Fe-Ni metal in the nebula

Diagnostic Genesis Features of Au-Ag Selenide-Telluride Mineralization of Western Java Deposits

DOI: 10.17014/ijog.3.1.67-76The ore mineralogy of the westernmost part of West Java such as Pongkor, Cibaliung, Cikidang, Cikotok, and Cirotan are characterized by the dominance of silver-arsenic-antimony sulfosalt with silver selenides and rarely tellurides over the argentite, whereas the eastern part of West Java including Arinem and Cineam deposits are dominated by silver-gold tellurides. Mineralogy of Se-type deposits at Pongkor, Cikidang, Cibaliung, Cisungsang, and Cirotan and Te-type deposits at Arinem and Cineam shows their different geochemical characteristics. Mineralogical and geochemical differences can be explained by variation of physico-chemical conditions that existed during gold-silver deposition by applying the phase relation among sulfide, telluride, and selenide mineral association in the deposits. The relative values of ƒSe2(g), ƒTe(g), and ƒS2(g) control the actual presence of selenide or telluride minerals within the West Java deposits, which also depend on their concentrations in the hydrothermal fluid. Even though the concentration of selenium in the hydrothermal fluid of Te-type deposits might have been similar or even higher than that in the Se-type, early substitution of selenium in the sulfide minerals prevents its concentration in the hydrothermal fluid to the levels for precipitating selenide minerals. Therefore, early sulfide mineral deposition from reduction fluids will not increase the ƒSe2(g)/ƒS2(g) ratio to form selenide minerals in Te-type deposits of Arinem and Cineam, other than selenium-bearing sulfide mineral such as Se-bearing galena or Se-bearing pyrargyrite-proustite

Epithermal Gold-Silver Deposits in Western Java, Indonesia: Gold-Silver Selenide-Telluride Mineralization

DOI: 10.17014/ijog.v1i2.180The gold-silver ores of western Java reflect a major metallogenic event during the Miocene-Pliocene and Pliocene ages. Mineralogically, the deposits can be divided into two types i.e. Se- and Te-type deposits with some different characteristic features. The objective of the present research is to summarize the mineralogical and geochemical characteristics of Se- and Te-type epithermal mineralization in western Java. Ore and alteration mineral assemblage, fluid inclusions, and radiogenic isotope studies were undertaken in some deposits in western Java combined with literature studies from previous authors. Ore mineralogy of some deposits from western Java such as Pongkor, Cibaliung, Cikidang, Cisungsang, Cirotan, Arinem, and Cineam shows slightly different characteristics as those are divided into Se- and Te-types deposits. The ore mineralogy of the westernmost of west Java region such as Pongkor, Cibaliung, Cikidang, Cisungsang, and Cirotan is characterized by the dominance of silver-arsenic-antimony sulfosalt with silver selenides and rarely tellurides over the argentite, while to the eastern part of West Java such as Arinem and Cineam deposits are dominated by silver-gold tellurides. The average formation temperatures measured from fluid inclusions of quartz associated with ore are in the range of 170 – 220°C with average salinity of less than 1 wt% NaClequiv for Se-type and 190 – 270°C with average salinity of ~2 wt% NaClequiv for Te-type

Epithermal Gold-Silver Deposits in Western Java, Indonesia: Gold-Silver Selenide-Telluride Mineralization

DOI: 10.17014/ijog.v1i2.180The gold-silver ores of western Java reflect a major metallogenic event during the Miocene-Pliocene and Pliocene ages. Mineralogically, the deposits can be divided into two types i.e. Se- and Te-type deposits with some different characteristic features. The objective of the present research is to summarize the mineralogical and geochemical characteristics of Se- and Te-type epithermal mineralization in western Java. Ore and alteration mineral assemblage, fluid inclusions, and radiogenic isotope studies were undertaken in some deposits in western Java combined with literature studies from previous authors. Ore mineralogy of some deposits from western Java such as Pongkor, Cibaliung, Cikidang, Cisungsang, Cirotan, Arinem, and Cineam shows slightly different characteristics as those are divided into Se- and Te-types deposits. The ore mineralogy of the westernmost of west Java region such as Pongkor, Cibaliung, Cikidang, Cisungsang, and Cirotan is characterized by the dominance of silver-arsenic-antimony sulfosalt with silver selenides and rarely tellurides over the argentite, while to the eastern part of West Java such as Arinem and Cineam deposits are dominated by silver-gold tellurides. The average formation temperatures measured from fluid inclusions of quartz associated with ore are in the range of 170 – 220°C with average salinity of less than 1 wt% NaClequiv for Se-type and 190 – 270°C with average salinity of ~2 wt% NaClequiv for Te-type.</div

Petrological Characteristics of the Granitoids Around the Yaguki Mine, Fukushima Prefecture, Japan : With Special Reference to the Relationships between the Yaguki-type Granodiorite and Ore Mineralization

Granodiorite bodies of the Yaguki-, the Ohbisagawa-, and the Yokokawa-types are distributed around the Yaguki contact metasomatic copper-iron and tungsten ore deposits. The tungsten mineralization might have occurred later than the copper-iron ore mineralization in the Yaguki ore deposit on the basis of field evidence. The Yaguki-type granodiorite (GD), lying beneath the ore bodies, is considered to be closely related to both of the ore mineralizations at the deposit. Based on the magnetic susceptibility and the mode of occurrences of Fe-Ti oxide minerals, the Ohbisagawa- and the Yokokawa-type granodiorites belong to the magnetite-series granitoids, while the Yaguki-type GD belongs to the ilmenite-series granitoids. The upper intrusion surface of the Yaguki-type GD body dips gently to the northeast and shows local dome structures. The ore bodies are mostly distributed around these domes. Based on bulk chemical compositions, the distribution of alkali contents of the Yaguki-type GD is in accord with that of the ore bodies such as No.1, No.2, and the Nambu-Hinokiyama ore bodies. MnO content in ilmenite within the Yaguki-type GD body tends to increase toward the west as a whole and is not correlated to the D. I. of the host rocks. Although fluorine contents of apatite in the Yaguki-type GD do not greatly change with the increase in D. I., chlorine contents slightly increase with increasing D. I. in the early stage of magmatic differentiation (D. I.=64-68) and then decrease in the later stage (D. I. >68). Three-phase fluid inclusions, consisting of liquid, vapor, and halite, are observed in the Yaguki-type GD. On the basis of several assumptions, magma of the Yaguki-type GD might be initially unsaturated with water, but it became saturated with water during magma crystallization. The differentiated magma of the Yaguki-type GD might be coexisted with an aqueous fluid containing chlorine and base metals. The aqueous fluids moved up to the sedimentary rocks above the granodiorite along the fissure zone. Mineralization occurred at the boundary between slate and limestone beds. Namely, not only the geologic structure but also the nature of magma might control the distribution of ore bodies in the Yaguki ore deposit

Texture, Chemical Composition and Genesis of Schreibersite in Iron Meteorite

Thirteen iron meteorites composed of Hexahedrite, Octahedrite and Ataxite were investigated to estimate their cooling history and origin. They are mainly composed of Fe-Ni metals (kamacite and taenite) with smaller amounts of schreibersite (Fe, Ni)3P and sulfides (troilite and sphalerite). Schreibersite occurs an idiomorphic and xenomorphic crystals and its mode of occurrence is variable in iron meteorites. Xenomorphic schreibersite is subdivided into 6 types on the basis of their textures and relationships with coexisting minerals. Chemical composition of schreibersite varies from 20 to 40 atom. % Ni with textural types among some iron meteorites with different bulk chemical compositions and even in the same meteorite (e.g. Canyon Diablo), while it does not vary so clear with textural types in ALH-77263. Schreibersite seems to maintain a local equilibrium with coexisting metal phases. Based on the Fe-Ni-P phase diagram, it is estimated that xenomorphic and coarse-grained schreibersite in Y-75031 and in DRPA 78007 were crystallized from stability field of taenite and schreibersite at about 800℃ under rapid diffusion conditions. Cooling rates within the parent bodies are calculated by using the diffusion rate of Ni between schreibersite and kamacite as follows; Canyon Diablo: 1.1×10^6, Odessa: 1.7×10^6, North Chile: 2.3×10^6, ALH-77263: 8.7×10^7 (year/℃). It is considered that ALH -77263 had been cooled keeping more equilibrated state with slower cooling rate than Canyon Diablo. Variable textures and chemical compositions of schreibersite suggest that it had been maintained a local equilibrium with kamacite. Estimated temperatures at which the reaction mostly completed among metals and sulfide tend to show higher value in unequilibrated iron meteorites than equilibrated ones. It is inferred that unequilibrated iron meteorites had been rapidly cooled, but equilibrated ones slowly to maintain diffusion under the lower temperatures

Study of Macroscopic and Microscopic Reaction Textures Associated with Corundum of Balangoda Region, Sri Lanka

Corundum is the most sought after gem variety among Sri Lankan gem minerals. Locations of most of the gem quality stones were identified as alluvial. The in-situ corundums rarely show a gem quality and are mostly associated with macroscopic and microscopic reaction textures. Studies of these textures, associated reactants and the intrusion of corundum by reaction products using electron probe microanalysis and energy dispersive x-ray analysis reveal that hydrous minerals such as phlogopite mica play an important role in promoting such reactions. Because of these reactions corundum is likely to be fractured and the fractures are often filled with reaction products. Hence the gem quality is not retained in most corundum after their formation. Also the natural shielding effect, called plagioclase shielding that protects corundum against the retrograde reactions, is found to be responsible for the production of valuable gem quality stones.International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan