Document Details
|
Document Type |
: |
Thesis |
|
Document Title |
: |
GEOLOGY AND MINERALIZATION OF WADI AL HWANET AREA, NORTH-WESTERN SAUDI ARABIA: WITH SPECIAL REFERENCE TO ULTRAMAFIC ROCKS جيولوجية وتمعدنات منطقة وادي الحوانيت، شمال غرب المملكة العربية السعودية : دراسة خاصة عن الصخور فوق المافية |
|
Subject |
: |
Faculty of Earth Sciences - mineral and rock |
|
Document Language |
: |
Arabic |
|
Abstract |
: |
Wadi Al Hwanet and Jabal Al Wasq, parts of Al’Ays belt, represent one of the most important ophiolitic rocks of Proterozoic age in the Arabian Sheild. The mantle section is dominated by harzburgite with abundant dunite. Most of the primary silicates in the Proterozoic ophiolitic mantle rocks were converted into secondary minerals. Although intense alteration and serpentinization, primary silicate minerals like olivine, orthopyroxene and clinopyroxene are still preserved, especially in Wadi Al Hwanet area. Primary chromian spinel in the studied areas is also survived alteration and is used as a petrogenetic indicator of the tectonic setting at which the podiform chromitites are formed.
The podiform chromitite deposits in Wadi Al Hwanet are common as lenses and micropods. The lenses differ in shape from elliptical to lenticular, but some occur as elongated discontinuous bodies of chromite lenses. The lenses are 1to more than 20 m long and up to 2m wide and consist of fine- to medium–grained, massive and fractured chromite with few interstitial serpentine gangue minerals. The Cr# (Cr# = Cr/(Cr + Al) atomic ratios) exhibits a wide compositional variation from lens to lens.It varies from intermediate 0.62 to high 0.81 in chromitites, from 0.56 to 0.60 in dunite envelope, from 0.54 to 0.57 in dunite mass and from 0.46 to 0.57 in harzburgites.
The podiform chromitite deposits in Jabal Al Wasq occur mainly as lensoidal bodies; the size of the studied lens is about 30 m in dimensions. It is massive to sub-massive and surrounded by a thin veneer of in¬tensely altered and sheared serpentinitized dunite envelope. The chromian spinel of Jabal Al Wasq chromitite usually has high and restricted Cr#, usually ≥ 0.80. The Cr# of the spinel in dunites and harzburgites of Jabal Al Wasq are also very high; it varies from 0.75 to 0.80 in dunites, and from 0.77 to 0.80 in harzburgites. The total PGE content of Wadi Al Hwanet chromitites ranges from 351 to 967 ppb, and display two distribution patterns: (1) negatively sloped PGE patterns where the IPGE is highely enriched compared with PPGE (Pd/Ir ratio = 0.21 on average), (2) positively sloped PGE patterns where the PPGE is much more enriched compared with IPGE (Pd/Ir ratio = 5 on average). In Jabal Al Wasq chromitites, almost all samples show a negatively sloped PGE patterns, but some samples show relative enrichment in both IPGE and PPGE contents. The total PGE contents of Jabal Al Wasq chromitites ranges from 139 to 355 ppb. The most common platinum- group minerals (PGE) in Wadi Al Hwanet chromitites are Ir –rich laurite (RuS2) as solitary inclusions within chromian spinel, while in Jabal Al Wasq chromitites the most common PGM species are the Os- Ir- Ru alloys.
The intermediate Cr# (~ 0.6) and PPGE- enrichment in Wadi Al Hwanet area, may suggest partly, low to intermediate degrees of partial melting for these chromitite deposits during the first stage melting at a MORB setting. The high Cr# of spinel ( ≥0.8) and IPGE in Wadi Al Hwanet area enrichment and some extent, in Jabal Al Wasq area with low TiO2 content of chromite (0.01- 0.35 wt%) suggest second stage melting in a supra-subduction zone setting, and involvement of boninite or high-Mg arc tholeiitic magma in the formation of these high Cr- chromitites.
The primary compositions of chromian spinel have been used to calculate the composition of parental melt involved in formation of the podiform chromitites of the studied areas. The parental melt calculations indicate derivation from a high- Mg tholeiites or boninitic magmas that is similar to the composition of parental melts in equilibrium with Proterozoic chromitites of other complexes such as those of Eastern Desert of Egypt, and Bou Azzer, Morocco, and slightly different from those of Phanerozoic ophiolites, e.g. Oman ophiolite. Tectonic discrimination diagrams using the spinel primary composition indicate a supra- subduction zone setting that modify the intial MORB setting. |
|
Supervisor |
: |
Dr. Ahmed Hassan Ahmed |
|
Thesis Type |
: |
Master Thesis |
|
Publishing Year |
: |
1433 AH
2011 AD |
|
Co-Supervisor |
: |
Dr. Hisham Mohammed Harbi |
|
Added Date |
: |
Saturday, December 31, 2011 |
|
Researchers
| عبدالمنعم مرصاص حبتور | Habtoor, Abdelmonem Marsas | Researcher | Master | |
|
Back To Researches Page
|