17:15 〜 18:45
[HRE13-P03] The characterization and paragenesis of the gold mineralization in gold deposits of the Vumba Greenstone Belt of northeastern Botswana.
キーワード：Vumba Greenstone Belt, Arab deposit, White Pidgeon deposit, garnet
The 2.7 Ga Vumba Greenstone Belt (VGB), located in the southwestern part of Zimbabwe Craton in northeastern Botswana, hosts various types of deposits, such as Au and base metals represented by the Somerset, White Pidgeon, Eldorado, Arab, New Rush and Sheba deposits. The VGB is composed of metavolcanic and metasedimentary rocks that have been affected by several episodes of metamorphism at conditions spanning from greenschist to upper amphibolite and granulite facies. The limited geological and geochronological studies that have been conducted so far in the VGB, have not revealed the characteristics of mineralization, ages of deposits, and relationships among all the above-mentioned deposits. The objectives of the study are to identify ore minerals, assess textures and investigate the genetic relationship of mineralization from White Pidgeon, Somerset, Eldorado, and Arab gold deposits. Optical microscopy and SEM-EDS were used to analyze mineralized biotite schist, garnet-biotite shist, garnet-mica schist, amphibolite, and garnet amphibolite.
In the White Pidgeon deposit, pyrrhotite, arsenopyrite, chalcopyrite and pyrite occur as disseminations along the foliation or post-foliation in the biotite schist, amphibolite, and quartz veins. Gold occurs as inclusions of electrum in arsenopyrite and native gold in quartz-siderite veins. At the Somerset deposit, sulfides occur as disseminations in the biotite-garnet schist, garnet-mica schist, and garnet amphibolite and occasionally filling fractures and as inclusions in the garnets. Gold occurs as inclusions of native gold in arsenopyrite. The Eldorado deposit is characterized by gold-bearing sulfides disseminated in the amphibolite, along the foliation and in quartz veins. Pyrrhotite is intergrown with chalcopyrite and arsenopyrite and has inclusions of one another. Native gold and bismuth telluride occur as inclusions in arsenopyrite. The mineralization at the Arab deposit is disseminated, along the foliation and vein-hosted. Gold occurs as inclusions of electrum in arsenopyrite and bounded to pyrrhotite and chalcopyrite. Oxides such as rutile, and ilmenite with probably hydrothermal origin are common in the White Pidgeon, Arab and Eldorado deposits, which are intergrown with sulfides or included in both pyrrhotite and arsenopyrite.
In the White Pidgeon deposit, pyrrhotite, arsenopyrite, chalcopyrite and pyrite occur as disseminations along the foliation or post-foliation in the biotite schist, amphibolite, and quartz veins. Gold occurs as inclusions of electrum in arsenopyrite and native gold in quartz-siderite veins. At the Somerset deposit, sulfides occur as disseminations in the biotite-garnet schist, garnet-mica schist, and garnet amphibolite and occasionally filling fractures and as inclusions in the garnets. Gold occurs as inclusions of native gold in arsenopyrite. The Eldorado deposit is characterized by gold-bearing sulfides disseminated in the amphibolite, along the foliation and in quartz veins. Pyrrhotite is intergrown with chalcopyrite and arsenopyrite and has inclusions of one another. Native gold and bismuth telluride occur as inclusions in arsenopyrite. The mineralization at the Arab deposit is disseminated, along the foliation and vein-hosted. Gold occurs as inclusions of electrum in arsenopyrite and bounded to pyrrhotite and chalcopyrite. Oxides such as rutile, and ilmenite with probably hydrothermal origin are common in the White Pidgeon, Arab and Eldorado deposits, which are intergrown with sulfides or included in both pyrrhotite and arsenopyrite.