Sa ad Zeki A.kade AL-MASHAIKIE

MA’RIB BÖLGESİ’NDE (ARABİSTAN YARIMADASI GB’SI) İLK KEŞFEDİLEN MANYEZİTDOLOMİT KUŞAĞININ KÖKENİ, SEDİMANTOLOJİSİ VE MİNERALOJİSİ

Bu makalede, KB Yemen’de, Rub’Al-Khali sektörünün Al-Thanyiah bölgesinde yer alan metamorfik kıvrım kuşağında ilk kez keşfedilen ve tanımlanan yüksek saflık derecesindeki manyezit mineralizasyonu ele alınmıştır. Prekambriyen-Neoproterozoyik (?) yaşlı manyezitli metamorfik kuşağı, genel olarak K-G uzanımlı bir bindirme kuşağı halindedir.Manyezit mineralizasyonu, onlarca km boyunca uzanan (yaklaşık 31 km) karbonat-metamorfik kuşağı içinde keşfedilmiş olup sekiz ayrı stratigrafik seviye ile ilişkilidir. Saf manyezit içeren seviyelerin net kalınlıkları 20 ila 60 metre arasında olup büyük ultrabazik sokulumlar ile kesilen koyu yeşil klorit-şist düzeyleri ile ilişkilidir. Jeokimyasal, mineralojikve petrografik analizler, söz konusu stratigrafik düzeylerdeki manyezit zenginleşmesinin % 78 ile % 99.6 arasında, MgOoranının ise % 35 ile % 48.9 arasında değiştiğini, az miktarda da dolomit ve kalsit bulunduğunu göstermiştir. Bunlarınyanı sıra, eser miktarda talk ve brusit mineralleri de saptanmıştır. Bunlardan, MgCO3 içerikleri %95’in üzerinde olan vekalınlıkları 40 ve 60 metre olan iki adet manyezit yatağının, ekonomik olduğu anlaşılmıştır. Manyezitin kaynağı olarak,ultramafik sokulumlar ile ilişkili amfibolit ve harzburjit gibi kayaçların bölgesel metamorfizma sırasında sokulumuntermal etkisiyle Mg2+ açısından zenginleşen diyajenetik çözeltiler gösterilebilir. Dolomitin manyezite alterasyonu, kalsitya da dolomitin çok fazlı olarak manyezite dönüşümü şeklinde gelişmiştir.

SEDIMENTOLOGY, MINERALOGY AND ORIGIN OF THE FIRST DISCOVER MAGNESITEDOLOMITE BELT IN MA’RIB DISTRICT, SW ARABIAN PENINSULA

Magnesite mineralization of high purity was discovered and described herein for the first time from metamorphosed folded belt from Al-Thanyiah locality in Rub’Al-Khali sector, 360 km east of Sana’a City, northwest Yemen. The magnesite-metamorphic belt, belonging to the Precambrian/Neoproterozoic age? comprises thrust belt, which trends generally N-S direction. Magnesite mineralization was identified in an extended carbonate-metamorphic belt for several tens of kilometers cf. 31 km and occurred in association with 8 stratigraphic units. The thicknesses of pure magnesite bearing units are variable and ranges from 20 to 60 m, associated with dark green chlorite-schist with intersecting huge ultrabasic intrusions. Geochemical, mineralogical and petrographic analyses show that the magnesite concentrations in the stratigraphic units are ranging from 78% up to high purity of 99.6% cf. 35 to 48.9% MgO, with minor dolomite and calcite respectively. Little to rare content of talc and brucite were also recognized. Two thick, productive and high purity magnesite beds, the first is of 40 m thick and the second is 60 m in thickness, which reveals more than 95% MgCO3 and considered to be economic. The suggested origin of the magnesite mineralization is coming from high stress of regional metamorphism associated with ultramafic intrusions cf. amphibolite and harzburgite associated with diagenetic solutions rich in Mg2+, associated with the heat of magma. The alteration of dolomite to magnesite was formed by multiple phases to transform calcite and/or dolomite to magnesite.

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