Document Details
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Document Type |
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Article In Journal |
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Document Title |
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Geochemical Evolution of Rare Metal-Bearing A-Type Granites from the Aja Batholith, Hail Terrain, Saudi Arabia الجيوكيميائية تطور المعادن النادرة ، وإذ تضع الصوان ، ألف نوع ، اراضي حائل ، المملكة العربية السعودية |
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Subject |
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Geochemical Evolution of Rare Metal-Bearing A-Type Granites from the Aja Batholith, Hail Terrain, Saudi Arabia |
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Document Language |
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English |
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Abstract |
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The Aja Batholith, northeastern Arabian Shield, consists of five granite varieties namely: hornblende alkali feldspar granite, granophyre. arfvedsonite-aegirine alkali feldspar granite, porphyritic alkali granite and albite granite. Zircon, sphene, thorite, Samraskite, Ta-selenide, pyrochlore, tluorite, magnetite and hematite are magmatic rare-metal¬bearing accessory minerals. In some rock varieties, hematite is post-magmatic where local metasomatic effects are visible in varying degrees and played a significant role in the genesis of silica-hematite-rich rocks (hematosilconite). The granite varieties in the batholith are highly siliceous (SiOz==68-75%) with high KzO (3.72-5.52%) and Nap (2.52¬6.25%) and low AI20) (8.35-13.5%), MgO (0.07-0.4%), CaO (0.17-1.5%), Ba (20-409 ppm) and Sr (6-134 ppm). The alumina saturation index (A/CNK) for most samples is < I while the agpaitic index is> 1 confirming their alkaline to pera1kaline character. The granites have high and variable contents of Rb (81-495 ppm), Ga (20-52 ppm), Nb (10¬414 ppm), Zr (290-31915 ppm), Y (22-552 ppm), Sn (3-10 I ppm), and total rare earth elements (362-3518 ppm). These data indicate that the Aja batholith represents post-orogenic A-type granites. The generation of their parental magma probably involved partial melting of lower crustal rocks as a result of the decomposition of P-rich biotite. Comparison of the geochemical data with many specialized rare metal-bearing granites show that the Aja granites are enriched in Nb, Ta, Sn, Zr and REE, especially the arfvedsonite-aegirine alkali granite, the albite granite and the hematosilconite. Although the geochemical effects of metasomatism is locally visible; nonetheless, most of the chemical variations in the content of these elements appear to be the result of ill situ fractional crystallization (feldspars, ferrornagnesian minerals and rare metal bearing accessory phases) and fluorine complexing. The strong positive correlation of alkalis (Rb and K) that was mobile during metasomatism with elements that were not (Nb and Ta), argues strongly against metasomatic alteration in the granites. However, the hematosilconite is consistently rich in Fe, Si, Ca, Pb, Zn, Sn and poor in Na, K, Rb relative to the granites suggesting the local effect of metasomatism |
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ISSN |
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1012-8832 |
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Journal Name |
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Earth Sciences Journal |
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Volume |
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70 |
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Issue Number |
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1 |
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Publishing Year |
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1428 AH
2007 AD |
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Article Type |
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Article |
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Added Date |
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Sunday, September 26, 2010 |
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Researchers
| طلال الفاضي | Qadih, talal | Investigator | Doctorate | |
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