Fluid inclusions and mineral chemistry of some detrital heavy minerals of alluvium sediments from Meluli- Namuhuca area, Mozambique

Geochemistry and fluid inclusions studies were carried out on garnet and beryl from Quaternary alluvium deposits of Meluli-Namuhuca area, Mozambique. Garnet occurs as euhedral large crystals and is commonly brownish red, with a moderate brown hue in transmitted light. Apatite and ilmenite are the common inclusions. Geochemically, garnet is characterized by nearly homogenous chemical composition with Pyr (46.72-48.35), Alm (39.77-48.35), Gr (10.03-10.56) and Sps (1.14-1.31) mol %. This garnet is referred to as iron-rich pyrope or pyrope – almandine. Chemical compositions reflect their crystallization from magma (Mg-Fe isomorphism).The high-Mg, and low Na of the studied garnet are consistent with high temperature eclogitic garnet associated with diamond. Fluid inclusions study indicates that garnet was deposited from high saline and high temperature fluids. Beryl is present as euhedral hexagonal crystals with different color (green emerald, blue aquamarine, and yellow heliodors). It enclosed cassiterite, wolframite and barite micro-inclusions, which support that the studied beryl is connected to hydrothermal ore-bearing fluids. Fluid inclusions study reveal that beryl was deposited due to boiling process of medium salinity (9-12 wt.% NaCl eq.), and medium temperature (180-240 °C) fluids. Pressure of trapping was estimated between 400 and 700 bars.