Petrography of host rocks
The Venarch manganese deposit is accommodated by volcanic and plutonic rocks. The volcanic strata mainly consist of basalt, trachybasalt, andesite, and basaltic andesite which are intruded by monzonite, monzodiorite, granodiorite, and syenite. The plutonic rocks are mostly granular in texture; however other textures such as graphic and poikilitic textures are present. The dominant minerals are plagioclase phenocrysts, quartz, K-feldspar, and hornblende and accessory minerals such as biotite, pyroxene, apatite, sphene, and opaque minerals can be seen in some of these rocks. The Venarch volcanic rocks are mostly porphyritic (the main texture in the samples), but other textures such as glomeroporphyritic, microlitic, …show more content…
The basaltic and andesitic volcanic lavas and pyroclastic rocks are deposited in the sedimentary basin in which magmas are enriched in iron and to some extent manganese. Due to mafic magmatism and subsequent heat exchange, high-temperature hydrothermal fluids pass through the volcano-sedimentary rocks in the sedimentary basin, and elements such as Mn, Fe, Ca, and Si are therefore leached from the mafic rocks into the water. These elements are then precipitated as Fe- Mn oxides and hydroxides (such as goethite, hematite, magnetite and manganite), and carbonates during magmatic lull. Iron-manganese precipitation in the shallow depositional environment in the Venarch area has formed the bands of manganese, hematite, silica, and calcium carbonates. The Mn mineralization in Veanrch deposit has occurred as bands, laminates, and manganese layers concurrent with the other volcano sedimentary rocks. The manganese mineralization in the area is easily distinguished by their black color in the field. However, the secondary mobilization of the Fe-Mn oxides, silica, and carbonates is also evident in the area, which might happened during the final stages of Mn mineralization. During the later stages of ore formation, Mn filled veins and veinlets of fractures and joints of the host rocks. The mineralized horizons (laminate and bands) are locally boudinaged and cut by the veins and veinlets, indicating that the role of tectonic activities and fault rupturing during the late stage of Mn mineralization in the area. However, emplacement of Eocene-Oligocene intrusions have also affected the ore bodies in the Venarch mine deposit and produced different alteration minerals such as chlorite, epidote, serecite, and
The Venarch manganese deposit is accommodated by volcanic and plutonic rocks. The volcanic strata mainly consist of basalt, trachybasalt, andesite, and basaltic andesite which are intruded by monzonite, monzodiorite, granodiorite, and syenite. The plutonic rocks are mostly granular in texture; however other textures such as graphic and poikilitic textures are present. The dominant minerals are plagioclase phenocrysts, quartz, K-feldspar, and hornblende and accessory minerals such as biotite, pyroxene, apatite, sphene, and opaque minerals can be seen in some of these rocks. The Venarch volcanic rocks are mostly porphyritic (the main texture in the samples), but other textures such as glomeroporphyritic, microlitic, …show more content…
The basaltic and andesitic volcanic lavas and pyroclastic rocks are deposited in the sedimentary basin in which magmas are enriched in iron and to some extent manganese. Due to mafic magmatism and subsequent heat exchange, high-temperature hydrothermal fluids pass through the volcano-sedimentary rocks in the sedimentary basin, and elements such as Mn, Fe, Ca, and Si are therefore leached from the mafic rocks into the water. These elements are then precipitated as Fe- Mn oxides and hydroxides (such as goethite, hematite, magnetite and manganite), and carbonates during magmatic lull. Iron-manganese precipitation in the shallow depositional environment in the Venarch area has formed the bands of manganese, hematite, silica, and calcium carbonates. The Mn mineralization in Veanrch deposit has occurred as bands, laminates, and manganese layers concurrent with the other volcano sedimentary rocks. The manganese mineralization in the area is easily distinguished by their black color in the field. However, the secondary mobilization of the Fe-Mn oxides, silica, and carbonates is also evident in the area, which might happened during the final stages of Mn mineralization. During the later stages of ore formation, Mn filled veins and veinlets of fractures and joints of the host rocks. The mineralized horizons (laminate and bands) are locally boudinaged and cut by the veins and veinlets, indicating that the role of tectonic activities and fault rupturing during the late stage of Mn mineralization in the area. However, emplacement of Eocene-Oligocene intrusions have also affected the ore bodies in the Venarch mine deposit and produced different alteration minerals such as chlorite, epidote, serecite, and