14:15 〜 14:30
[HRE12-02] ナミビア共和国オタビマウンテンランドにおける銅鉱化作用の流体包有物研究
キーワード：ナミビア、堆積岩内鉱床、オタビマウンテンランド
The Otavi Mountainland is located in a carbonate platform of northern edge of the Damara orogenic belt in the Republic of Namibia, which was deposited on Grootfontein Basement Complex during late Proterozoic between the Congo Craton and the Kalahari Cratons. The Damara orogenic belt is composed of two arms along the western coastline of Namibia and ENE-WSW trending intercontinental belt. The area is known for its endowment of polymetallic mineralization at the Tsumeb and Kombat deposits, which are classified as Mississippi Valley type, as well as the Tschudi deposit, which is sediment-hosted type especially in arenite (Weatherly Mining Namibia, 2016).. The Damara belt is considered to be an extension of the Lufilian Arc of the Central African Copper Belt in the Republic of Zambia (Gray et al., 2008).
Japan Organization for Metals and Energy Security (JOGMEC) has been conducting Zn-Pb-Cu exploration since 2015 through a joint venture with Nexa Resources S.A. and its subsidiaries including Votorantim Metals Namibia (Pty) Ltd. Multiple exploration targets were extracted by topographic analysis, geochemical survey, and geophysical survey (IP and AMT), and those targets were tested by RAB and diamond drillings.
Based on the exploration results especially at T13, Deblin, and other new targets, the mineralization model in our licenses is interpreted as a structural-controlled hydrothermal system rather than traditional sediment-hosted type of mineralization derived from rift-related basinal brine.
While most of geological features confirmed during field surveys support suitable geological/geodynamic settings for generation of brine, giving a pathway, as well as convection of the generated brine to give a chance of scavenge metals from potential source rocks, the area might lack appropriate trap system of physicochemical boundary between permeable sequence (the Nabis Formation) with reductant layer (the Ombombo Formation).
In this research, ore samples were collected from calcite-quartz and quartz veins intersected by drilling at the T13 and Deblin targets. Bornite, chalcopyrite, and (selenium-bearing) galena are dominant ore minerals in the samples.
There are very tiny liquid-vapor fluid inclusions (generally less than 10 micrometers) observed as primary or pseudosecondary inclusions in calcite and quartz. Fluid inclusion microthermometry shows homogenization temperatures higher than 200 ℃ up to about 300 ℃, while low salinity indicated by measured ice melting temperatures (-1.2 to -2.3 ℃), which are unusual physicochemical conditions for typical sediment-hosted type of mineralization. Mineralization condition of (calcite-)quartz veins might be far different from that of the principal Mississippi Valley type or sediment-hosted type of mineralization. Since the study area experienced complex geological processes, remobilization of primary metals should also be taken into consideration to understand the ore formation process.
Japan Organization for Metals and Energy Security (JOGMEC) has been conducting Zn-Pb-Cu exploration since 2015 through a joint venture with Nexa Resources S.A. and its subsidiaries including Votorantim Metals Namibia (Pty) Ltd. Multiple exploration targets were extracted by topographic analysis, geochemical survey, and geophysical survey (IP and AMT), and those targets were tested by RAB and diamond drillings.
Based on the exploration results especially at T13, Deblin, and other new targets, the mineralization model in our licenses is interpreted as a structural-controlled hydrothermal system rather than traditional sediment-hosted type of mineralization derived from rift-related basinal brine.
While most of geological features confirmed during field surveys support suitable geological/geodynamic settings for generation of brine, giving a pathway, as well as convection of the generated brine to give a chance of scavenge metals from potential source rocks, the area might lack appropriate trap system of physicochemical boundary between permeable sequence (the Nabis Formation) with reductant layer (the Ombombo Formation).
In this research, ore samples were collected from calcite-quartz and quartz veins intersected by drilling at the T13 and Deblin targets. Bornite, chalcopyrite, and (selenium-bearing) galena are dominant ore minerals in the samples.
There are very tiny liquid-vapor fluid inclusions (generally less than 10 micrometers) observed as primary or pseudosecondary inclusions in calcite and quartz. Fluid inclusion microthermometry shows homogenization temperatures higher than 200 ℃ up to about 300 ℃, while low salinity indicated by measured ice melting temperatures (-1.2 to -2.3 ℃), which are unusual physicochemical conditions for typical sediment-hosted type of mineralization. Mineralization condition of (calcite-)quartz veins might be far different from that of the principal Mississippi Valley type or sediment-hosted type of mineralization. Since the study area experienced complex geological processes, remobilization of primary metals should also be taken into consideration to understand the ore formation process.