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Industrial minerals in Yemen

1. Introduction

There are many industrial ores of metals and rocks in Yemen in large quantities and good quality. The majority of these rocks occur in populated areas with available infrastructure and facilities easing the process of investment and exploitation of these ores and lowering their costs. The exploration works conducted by YGSMRB in cooperation with foreign expeditions have led to determining the sites of these ores such as limestone, gypsum, perlite, pumice, saltpeter, mineral clay, silica sandstone, scoria, zeolite, feldspar, quartz, silica sand. Yemen has abundance of the construction and decoration stones in high specifications such as granite, gabbro, marble, basalt, tuff and ignimbrite.

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2. Industrial metals discovered in Yemen.

2-1 Natural Zeolite:

Natural zeolite of good quality has been found in several areas of Yemen. The reserves of natural zeolite deposits in Yemen are estimated to be about 200 million m3. Natural zeolite occurs in altered volcanic tuffs. Parts of Yemen have experienced violent and long-lasting volcanic activity which has covered large areas (> 60,000 km2) with volcanic ashes. These fields provide excellent targets for zeolite exploration and exploitation. The zeolitic tuff deposits are found in three governorates, Ta’iz, Ibb and Dhamar, and they appear to be holding interesting resources. The deposits are characterised by white, grey, green and yellowish colours with fine grained textures. Pumice and perlite fragments are often present within the zeolitic tuffs deposits. The zeolite was presumably formed by hydrothermal alteration of volcanic glass in the tuffaceous rocks.

2-2 Magnesite:

Magnesite and dolomite rocks are one of the most important industrial minerals in Yemen. They have a high quality, which permits to use it in industrial applications. Compositionally the Yemeni magnesite and dolomite is comparable to magnesite deposits exploited in other countries. Yemen hosts large and pure magnesite and dolomite rocks of Precambrian Jurassic and Tertiary age. 
Magnesite and dolomite rocks in Marib zone are exposed at Al-Thanyyah area on the surface with variable of thickness and degree of purity. They were discovered in 1983 by Geomin. At Al-Thanyyah area, the magnesite deposit located at 120 km northeast of Marib city. The Al-Thanyyah belt attains 13 km long, 1.36 km wide and 90-135 m height, which appears to be surrounded by recent sandy dunes. The belts are made up of magnesite, dolomite, and marble with various colours of white, white-grey, grey-yellow and brick with intermediate hues. These rocks have crystalline, and granular, granoblastic structure with compact texture, sometimes with vacuoles and irregular break. The whitish zones are less hard than the intensively colored ones. The results of the chemical analysis showed that the magnesium oxide percentage is 43.76- 47.65%. The reserves of magnesite and dolomite at Al-Thanyyah are estimated to be about 58 million cubic meters.
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2-3 Dolomite:

Dolomite deposits occur in Yemen in huge quantity and high quality. The reserves are estimated at about 3.4 billion m3. The results of the chemical analysis showed that the magnesium oxide percentage is 11-23%.

At Rayyan area in Al Jawf, the dolomite deposits are of extreme purity of 98-100%. The chemical analysis showed that the magnesium oxide percentage ranges between 19.84 and 23.05% which confirm the purity of the raw materials and the possibility of diversifying the applications to involve industrial, construction and agricultural applications such as; the manufacturing of creams and toothpastes, especially crystallized dolomite, the production of dolomite fractions for mosaic tiles and limestone bricks, soil amendments and carriers of pesticides as well as in the production of decoration stones.

2-4 Pure Limestone:

Limestone deposits are widespread in Yemen, and a number of pure limestone deposits are found in different areas specially, the eastern part of Yemen. Pure Limestone occurs within Amran, Hadramawt and Shihr groups of Jurassic to Pleistocene age. The pure limestone deposits are almost exposed on the surface with variable of thickness and degree of purity. The results of the chemical analysis showed the purity of the limestone; CaO percentage ranges between 51.50 and 55.60%, SiO2 0.03 and 4.28% and Fe2O3 0.02 and 0.72%. Physical experiments have shown that the density of the limestone is 2.4-2.7 gm/ cm3, whiteness degree is 81.70 to 95.15% and the surface area is 2685 to 4488 m2/gm which confirms the high purity of limestone in Yemen and the possibility of diversifying the applications such as production of pure calcium carbonate, white cement, iron and steel, glass, paper and agricultural uses. There are 44 reported pure limestone occurrences in Yemen. The reserves are estimated to be about 3.6 billion m3.

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2-5 Rock Salt:

Rock salt deposits are common in both Mesozoic and Cenozoic rocks. Open pit mining operations date back at least to the Turkish occupation of 1538. There are some 11 reported rock salt deposits in Yemen. The reserves of rock salt deposits in Yemen are estimated to be about 390 million m3. ¬¬¬¬¬¬¬¬Rock salt occurs as salt domes within the Sab’atayn Formation (Amran Group) of upper Jurassic age, and within the Salif Formation (Tihamah Group) of Late Tertiary age. The rock salt alternates with gypsum, anhydrite and clay. It is white and grey in colour, massive and overlain by bituminous shale's and gypsum.

2-6 Gypsum

Gypsum is found in abundance in Yemen. A large part of the mined gypsum is used as retardant in cement. Gypsum is also mined from a series of small quarries near Sana’a for local production of building plaster. The reserves are estimated to be about 390 million m3.
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Gypsum occurs in the Upper Jurassic in the Shabwah governorate and in the Upper Jurassic and the Lower Cretaceous north-east of Sana’a as well as in Marib. Huge deposits of gypsum of Lower Eocene age as well as Oligocene age are found in Al-Maharah, Abyan, Shabwah, and Hadramaut. In Middle-upper Miocene deposits gypsum alternate with salt and clay beds in Al-Hudaidah. There are some 25 reported gypsum deposits in Yemen. The gypsum sediments are of good specifications; SO3 rates range between 32.40 and 51.90%, insoluble materials are between 0.60 and 1.20% with the purity of gypsum ranging between 65.40 and 98.00%.

2-7 Pumice

Pumice deposits are common in the Cenozoic volcanic of Yemen. The porosity and low density of these rocks make them useful in the production of lightweight concrete blocks. They are widespread in various areas, among others Dhamar, Taiz and Ibb. Pumice shows as thin beds within volcanic ash beds (pumicite) or as blocks mixed with ash. The reserves of pumic deposits in Yemen are estimated to be about 1 billion m3. The Pumice deposits are characterized by good quality with silicon oxide ranging between 58.40 and 74.21%, aluminum oxide 7.59 and 10.83%, Magnesium oxide between 0.01 and 0.23%, sodium oxide between 3.62 and 7.06% and Potassium oxide 3.28 to 4.72%.

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2-8 Heavy metals:

There are 15 known deposits and occurrences of minerals-bearing beach sands in Yemen, containing ilmenite, rutile, zircon, magnetite, monazite, leueoxene. They are found along the coastal plains of Arabian Sea and Red Sea. Generally, heavy minerals are placer deposits formed usually in beach environments by concentration due to the specific gravity of the mineral grains. Heavy minerals in Yemen occur as Quaternary sand layers within beach sand and occasionally within stream beds, but most are of low grade and relatively small. Heavy minerals -bearing sands are characterized by gray, dark grey, black to yellow sands and silty sand lenses, intermingled with dark grey and buff colour clayey sediments. The reserves are estimated to be about 500 million m3.

2-9 Feldspar

The potentially exploitable feldspar-bearing pegmatite lenses occur at several localities within Precambrian basement rocks. There are 17 reported feldspar occurrences in Yemen. The reserves are estimated to be about 44 million m3. Lenses of feldspar-bearing pegmatite of significant sizes and economic importance were identified in Yemen within Precambrian basement rocks such as granite, granitic gneiss, amphibolite and schist. They are mainly consist of potash feldspar and sodium feldspar, subordinately of quartz, muscovite, biotite, garnet and opaque iron minerals.
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2-10 Pure sandstone and Quartz

Pure sandstone and quartzite (high silica) potentially suitable as a raw material for glass manufacture occur in several places in Yemen such as Sana’a, Shabwah, Sadah and Taiz. There are 25 reported feldspar occurrences in Yemen. The pure sandstone deposits occur within the Wajid Formation of Paleozoic age, the Kohlan Group of lower Jurassic age and the Tawilah Group of cretaceous age. Generally they are friable, white-grey, and fine to medium grained with minor kaolinite in the matrix in some places. The pure sandstone deposits are almost exposed on the surface with variable of thickness and degree of purity. The reserves are estimated to be about 2 billion cubic meters. These deposits are characterized with the high silica rates reaching 99.4% in some areas and the homogeneity and low impurities.

2-11 Scoria
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Most of the scoria deposits in Yemen are characterised by high porosity, low specific gravity and great strength. The reserves of scoria deposits in Yemen are estimated to be about 1.8 billion m3. According to the chemical composition of scoria in Yemen is analogous to the volcanic rock, used by the construction industry as active mineral additives in Portland- pozzolan cement production. As to its physical and mechanical properties scoria meets the requirements of industry to aggregates of lightweight construction concretes. Strombolian type explosions have formed numerous scoria pyroclastic cones within the basaltic lava in the Quaternary volcanics. The Quaternary volcanic activity occurred in discrete volcanic fields all over Yemen. The scoria deposits are found at five volcanic fields: Sana’a-Amran, Dhamar-Rada’, Marib-Sirwah, Shuqra and Balhaf-Bir Ali.

2-12 basalt

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Tertiary basalts volcanic rocks are developed as dykes crossing basement rocks, the Jurassic and Cretaceous deposits and as interstratified flows with tuffs and ignimbrites in equal shares. Quaternary basalts appear as flows and volcanic cones. In Yemen there were identified many occurrences of compact and vesicular basalts. Basalt stone is used for framing doors and windows as well as external decoration. There are good investment opportunities in the field of Basalt fibers industry (wool rock and basalt pipes) in Yemen due to the availability of tremendous reserves of Basalt and their occurrence in sites where infrastructure is available. The chemical analysis of basalt showed that the SiO2 is 47.80 to 49.15%, Al2O3 is 12.70 to 15.80% and Fe2O3 is 11.20 to 15.44%. The viscosity coefficient value varied between 1.2 and 1.8 while the standard acidity reported 1.66 to 2.50%.

13-2 Clay Minerals:
clay1Several occurrences of kaolinite with quartz are reported in Sadah, these occurrences consist of altered or weathered Precambrian granite. Also it occurs as cement material in sandstone of Cretaceous Tawella Group. The clays and marls are found as interbeded in Jurassic Akbara and Kohlan Formation, Amran and Tawella Group. Extensive clay (montmorillonite, attapulgite and sepiolite) occurs in the Oligocene- Miocene Shihr Group. Clay also occurs within Yemen volcanic rocks, resulted by weathering of volcanic rocks. Loess and loam deposits (montmorillonite) of Quaternary period cover the plains around the towns of Sana’a, Sadah, Ibb, Hudaidah, Lahj, Abyan and Hadramawt. The total reserves are estimated at about 120 million m3.
Mineral Res. Industrial minerals in Yemen