|
Document Type |
: |
Article In Journal |
|
Document Title |
: |
Petrology and Copper Geochemistry of the Lower Part of the Tertiary Yemen Volcanics, Utma Area, Yemen Republic بترولوجية وجيوكيميائية النحاس لصخور الجزء الأسفل من بركانيات اليمن منطقة عمتة ـ الجمهورية اليمنية |
|
Subject |
: |
Earth Sciences |
|
Document Language |
: |
English |
|
Abstract |
: |
This study concludes that the rocks from the lower sequence
.of the Tertiary Yemen Volcanics, in the Utma area are composed of porphyritic,
intergranular, and uncommonly spinifex textured clinopyroxene
(augite and diopside), olivine, ca-plagioclase, and magnetite. This sequence
is interpreted to represent mafic, non-cumulate effusive volcanite that
formed at shallow depth. Pumpellyite, chlorite, glass, magnetite, sphene,
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, TiO2, Ni, and Cr and
by low SiO2, A12O3' and alkalies contents. Silica, MgO, Sr, Cu, and possibly
Ni were remobilized during alteration and low-grade metamorphism, while
TiOvCr, 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-AI2O3 and Al2O3 vs. FM diagrams.
This study shows that the analyzed rocks resemble those of the Barberton
low AI-rock series (Viljoen and Viljoen 1969), with high TiO2 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 ironoxide
fractions shows that the silicate minerals are the source of syngenetic
copper, copper was leached and reconcentrated epigeneticallyin amygdales
and fractures, along with hematite. Pumpellyitization of primary minerals
produced metamorphic fluids with favorable geochemical conditions
for the precipitation of native copper. |
|
ISSN |
: |
1012-8832 |
|
Journal Name |
: |
Earth Sciences Journal |
|
Volume |
: |
5 |
|
Issue Number |
: |
1 |
|
Publishing Year |
: |
1412 AH
1992 AD |
|
Number Of Pages |
: |
30 |
|
Article Type |
: |
Article |
|
Added Date |
: |
Sunday, October 11, 2009 |
|