Petrology and copper geochemistry of the lower part of the tertiary Yemen volcanics, Utma Area, Yemen Republic

الملخص EN

This study concludes that the rocks front the lower sequence of the Tertiary Yemen Volcanics.

in the Utma area are composed of por-phyritic, intergranular, and uncommonly spinifex textured clinopyroxenc (augite and diopside), olivine, ca-plagioclase, and magnetite.

This sequence is interpreted to represent mafic, non-cumulatc effusive volcanite that formed at shallow depth.

Pumpellyite, chlorite, glass, magnetite, spheric, epidote, serpentine, and calcite are among the secondary minerals that were formed by subsequent low-grade metamorphism.

Geochemical analyses and norm calculations of 33 representative samples from the Utma lower sequence suggest that the rocks are undersaturated, high-Mg tholeiites characterized by high MgO, TiO,, Ni, and Cr and by low SiOj, Al,0„ and alkalies contents.

Silica.

MgO, Sr.

Cu, and possibly Ni were remobilized during alteration and low-grade metamorphism, while TiO„ Cr.

Nb, Zr were immobile and very much controlled by fractional crystallization, Geochemical data from Utma were compared with data from various parts of the world and plotted in CaO-MgO-AUO, and A1,0, vs.

FM diagrams.

This study shows that the analyzed rocks resemble those of the Barberton low Al-rock series (Viljoen and Viljoen I%9).

with high TiO, and F/ (F + M) values and possibly they are not komatiites.

Ore microscopy shows the presence of very fine-grained disseminated, veinlets, and amygdale-filled with native copper.

Copper is abundant along fractures and joint surfaces.

Analysis for Cu of separated silicate and iron-oxide fractions show s that the silicate minerals arc the source of syngenetie copper, copper was leached and reconcentrated epigenetically in amyg-dales and fractures, along with hematite.

Pumpellyitization of primary minerals produced metamorphic fluids with favorable gcochcmical conditions for the precipitation of native copper.