Metallic Minerals in Yemen

1. Introduction:
The available information from previous projects and the results of the mineral exploration and prospecting activities point out to the occurrence of significant gold, lead, zinc, copper, silver, nickel, iron and titanium mineralization. Previous studies have shown that the geological conditions in Yemen and other factors are favourable for many types of commercial mineral deposits based on comparisons with the geology of major mineral deposits seen elsewhere in the world. Based on the current knowledge of geology, the investment opportunities for metallic minerals in Yemen have been pinpointed to several fields such as gold, copper, nickel, platinum, zinc, lead, iron, titanium, rare earth metals, tungsten, tin and radioactive elements.
2. The metallic minerals discovered in Yemen:

2-1 Gold:

Over 50 sites of gold and silver mineralization have been detected in Yemen, the most important of which are located in the basement rocks of the Precambrian period. The regional geological condition of the Arabian-Nubian Shield constitutes a good opportunity for gold occurrence in Yemen. This has been confirmed by the exploration studies. Gold occurrence has also been detected in YVG of the Triassic age. Historically, the people of Sheba were famous for their exploitation of gold and it was said that they were the richest people in the region due to the abundance of gold mines in their territory; the gates to their palaces, temples, walls and ceilings were decorated with gold, ivory, silver and precious stones. Gold mineralization in Yemen can be summed up as follows:

2-1-1 Gold in the Basement Rocks:

 There is significant gold mineralization in the basement rocks of Precambrian age where it is hosted by metamorphosed volcanic and sedimentary rocks and by the intruded granite rocks. Gold and associated gold bearing minerals occur in the metamorphic volcanic and sedimentary rocks and within the quartz veins and shear zones. Vein and shear zone gold were formed due to the migration of fluids during the metamorphic and regional deformation during the tectonic movements such as in Madan area in Hadramawt, Al-Hariqah, A'ahim, Qishr, Haradh, Ba'alan, Al-Harirah and Shars in Hajja along with Al-Feidh, Wadi marwan and Wadi Al-Aradh in Sa'ada and the areas of Sabryn, Lawth and Wadi Al-Kuhail in AlJawf and Najd Al-Malaji in Shabwa.

There are disseminated gold sites and gold stockwork occurrences in granitic igneous that were formed in the post-tectonic era such as in Falhan, Wadi A'atif and Namasah in AlJawf and granite rocks that were syn-tectonic in areas like Bharah in Sana'a. It is noteworthy that the gold mineralization in the northwestern areas (Sa'ada and Hajja) occurs within Nabitah belt which extends from the center of Saudi Arabia across Yemen's north western sides to the north eastern side of Ethiopia.

2-1-2 Gold in the Volcanic Rocks:

Gold3New exploration studies have been conducted on the volcanic rocks which are of Triassic or younger ages and which are forming the western plateau of Yemen. Such studies have led to obtaining encouraging results for initial geochemical studies in the faults sites and fault extensions. Gold mineralization occurs within volcanic deposits accompanied by acidic rock lava and volcanic craters such as Shahara, Manakha and A'athyin. There is another type of gold mineralization within the volcanic rocks influenced by hydro-thermal alterations caused by water and hot vapor in areas like Waraqah, Ottma and Waziayah. The predicted model of gold occurrence is epithermal.

2-1-3 gold in the sedimentary rocks

The Sabatayn rift area and the similar structures of high heat flow represent  favourable environments for gold mineralization. Rock lava and the magmatic activities represent the heat engine while a group of fractures related to the Sabatayn  and Al-Dhalie grabens represent are the conduits for hydrothermal fluids carrying gold in solution.  Gold from these solutions is deposited in zones of dilation in brittle host rocks and other favourable environments.  When gold is eroded from such occurrences is may form placer deposits or be deposited as part of the sedimentary pile.

2-2 Zinc, Lead and Silver

Yemen posses several sites with known occurrences of of zinc, lead and silver, most of which are related to the Sabatayn rift zone (Jurassic- Paleocene) Mineralization occurs in fractures and pockets in the carbonate rocks and along with volcanic massive sulphides. Jabal Salab near Sana'a is one of the major zinc, lead and silver mineralization in Yemen.

Jabal Salab is 110 km to the north east of Sana'a. The area can be accessed by an asphalted road from Sana'a- to Marib for 92 km and then by taking a turn to the right along a paved road for 18 km to the site. The area is 2000 m above the sea level. zinc, lead and silver mineralization occur within the sedimentary limestone dolomite rocks (Amran Group) especially near the basins' edges. The Jabali deposit is believed to have formed by a combination of processes, involving features of both Mississippi Valley type and Carbonate replacement models. Mineralisation is generally stratiform (manto type) and particularly well developed along fault structures. The fault directions have a major influence on the vertical extension of stronger mineralisation in keels and chimneys. Mineralisation occurs within an envelope of relatively coarse grained ferruginous dolomite and is almost completely oxidised. Oxidation of the original primary sulphide orebody has occurred in-situ. The principal minerals are smithsonite (zinc carbonate), cerrusite (lead carbonate) and argentite (native silver).

Jabal Salab is an ancient mine itself. The Yemeni geographic historian Abi Al-Hassan Al-Hamadani indicated in his book (the Two Ancient Jewels) that the area Jabal Salab is a historical mining zone that used to be known as Al-Redhradh and was considered in the tenth century a major mine in the Islamic world for the extraction of silver.

The artisanal workings at Jabali are thought to be up to 2,000 years old. The galleried workings followed cavities filled by the softer oxidised ore, locally rich in silver. The ore was hand crushed on site and then probably processed using gravity techniques. It is estimated that about 300,000 -400,000 tonnes of ore were mined.

Over the period 1980-1986, the area was rediscovered by a Yemeni team in cooperation with the French Company BRGM. Exploration studies have been conducted including the preparation of detailed geological maps, geochemical and geophysical surveys. 57 exploratory bore holes were drilled in a total depth of 7974 m, mineralogical studies were conducted and mineral separation testwork carried out along with a primary study to economically assess the ores. In light of these studies, the ores reserves were estimated at 3.8 million tonnes at 16% zinc, 2% lead and 132 gm/ton of silver. In 1991-1992, YGSMRB and the Canadian Company WGM carried out a pre-feasibility study; 12 exploratory bore holes were drilled for a total depth of 1050 m to follow up the extension and depth of the ores and estimate the reserves, 16 trenches were also drilled in addition to mineral separation tests. In light of all these studies, the reserves were estimated at 3.7 million ton at 15.33% zinc, 1.66% lead and 113 gm/ton of silver.

In 1996, the American company Minorco entered in a coalition partnership with the Yemeni company Ansan and it expressed an interest in the possibility of exploring sulfide sediments in large quantities beneath the oxidation zone. Two holes of a total depth 281 m were drilled without detecting any sulfides. During the period 1998-2003, the British Company ZincOx executed exploratory studies including the drilling of 49 exploratory boreholes for a total depth of 4358 m, metal separation tests and a pre-feasibility study. By the end of 2004, the Company completed the feasibility study of the ores which showed that the ore reserves are estimated at 12.6 million ton in 8.86% zinc, 1.16% lead and 69.3 gm/ ton of silver. It was revealed that Jabal Salab sediment contains an extractable reserve by open-pit mining method (open mine) of 5.9 million ton containing 11% of zinc using  a lower cut of 5% zinc and a stripping rations of 1:6 (ton of wastes against ton of ores). The study forecast the production of 59,000 ton per year of the zinc metal in site. During the extraction and mineral separation experiments, the high percentage of dolomite and the problems associated to the release of zinc proved to be a significant challenge.

Unlike the most common treatment of zinc sulfide mineralization (sphalerite) which is amenable to extraction by floatation, the zinc oxides at Jabal Salab are not amenable to concentration using floatation Several attempts have been made to separate Jabal Salab's zinc in an economic manner, however; the product was featured by low zinc percentage. In 2004, an alternative method for fluid treatment invented by the British Company ZincOx was determined using the chemical laundry technology (LTC) which allowed for the extraction of zinc at about 80% recovery. The feasibility study showed that the factory will treat 800 thousand tons of the ore in an average of 9.7% zinc.

2-3 Copper, Nickel and Platinum

Copper, Nickel, Cobalt and Platinum mineralization in Yemen occur in basement rocks of the Precambrian age. Despite the fact that mineral explorations in Yemen were limited to a large-scale exploratory works that were confined to the Precambrian rocks (metamorphic and intrusions), the results of these studies have revealed the occurrence of several island arcs composed of the volcanic sediments belts which show signs of a prospective environment for copper, nickel and cobalt. Ancient mines were discovered there as old as 300 years when copper was mainly extracted from the quartz lodes in the copper occurrence areas; Al-Ma'adan and Al-Fadhiha. Suwar area in Amran is one of the most important sites for copper, nickel and platinum in Yemen.

Suwar is 80 km to the north west of Sana'a. Copper, nickel, cobalt and Platinum mineralization occur within the basic and ultrabasic rocks. This mineralization was only discovered in 1998 by Canadian Mountain Minerals (Presently Cantex). This company implemented exploration studies covering an area of 100 km2 from 1998 to 2008 including detailed geological surveys, semi detailed geochemical surveys, semi detailed geophysical surveys and geochemical analysis of a large amount of surface and subsurface samples in addition to the drilling of 56 exploration boreholes to a total depth 8433 meter until the end of 2009 focused on the main part of the mineralization in Suwar hill as well as the northern and southern parts of the mineralization which occurs over a 2.7 km  long belt in order to locate any extensions to the known mineralization and complete the collection of the necessary data to prepare the pre-feasibility study if results are sufficiently positive.  

These works have produced encouraging results with percentages ranging between 0.46 and 0.89% for copper and 0.86-1.40% for nickel in addition to good percentages of Cobalt, with traces of Palladium and Platinum. The exploration drilling works implemented in 2008 and 2009 indicated that the mineralization scope contains sulfides of 1-5% and are 0.12-5.02 meter thick. The highest percentage of sulfides was 10-60% of 2-8 meter thickness.

2-4 Rare Earth Elements

Significant mineralization of the Rare Earth Elements occur in carbonatite and pegmatite rocks within the basement rocks of the Precambrian age in Lawdar, Al-Beidha, Nisab and Marboun in Shabwa, Sabab and Burha in Abyan and in the granite intrusions of the Triassic age in Malhan, Al-Mahweet. Lawdar area in Al-Beidha is one of the most important rare elements mineralization sites in Yemen.

Rare elements mineralization sites are located near Lawdar in Al-Beidha, 160 km to the north east of Aden. The rare elements occur with the Monazite metal in the Carbonatite rocks within metamorphic rocks of the late Proterozoic era such as amphibolites, gneiss and pegmatite. Tantalum, niobium, Yttrium and uranium are all amongst the rare elements discovered in the region. Geological, geochemical, geophysical studies and drilling works were implemented and they revealed that the thickness of the carbonatite masses is up to 3 meters while their length is 50-60 meters outcropping over an area of 2 square km (Veselov, 1990). The possible resource to 100 meters were estimated at 5.1 million tons with 4% monazite (Strojexport 1988). The geological resource to 350 meters depth were estimated at 27.7 thousand tons in a concentration of 3.8% (Tr2O3) and 14.5% (Abeulov et al 1981), in addition to 100-120 thousand tons of Tr2O3 and 10 thousand tons of Nb2O5 and 100-250 ton of Ba.

2-5 Iron and Iron-Titaniume:

2-5-1 Iron
The deposition of iron in Yemen is related to the intercalated marble beds in the meta-andesites or the intrusion of the diorites. Each individual iron mineralization zone generally ranges in length from 100-600 m, and may attain up to 900 m at most; the length of each individual ore body is generally 50-100 m, with a maximum of 222 m ; the thickness of the ore bodies is generally 1-5 m, reaching a maximum of 20.44 m ; the total iron content generally ranges from 40-55%, with a maximum of 77.30%, and the great majority of the contents of sulphur and phosphorus are below 0.1%. So the iron deposits and occurrences are of the low-impurity, small and rich type. The ore consists mainly of magnetite, partly with martite and small quantities of siderite and limonite..

The iron mineralization occurs in Yemen in a number of sites within four major belts; Al-Beidha, Sa'ada, Marib along with Al-Thanyia area which is one of the most important ferrite sites in Yemen.

Iron1Iron mineralization occurs in Al-Thanyia area to the northeast of Marib city 150 km to the north east of it. The site is 30 km away from the asphalted road Marib- Shabwa. Magnetite and martite mineralization occurs in the form of a body extending towards the north east- south west within the green schist rocks which are spread out in the region covered by sand dunes. A ground magnetic survey which was implemented by YGSMRB showed that the body extends to about 2.2 km affected by the faults of north west- south east directions and it is 600 m wide and strikes? towards the southwest. It was revealed that a number of hierarchical faults occur causing side- displacements towards the southeast and the northwest. An exploratory borehole was drilled to 105 m deep and it indicated that there are many layers of magnetite/martite reaching a maximum thickness of 4.3 meter at 19.7 meter deep. The results of the analyses gave encouraging percentages of Fe3O4 reaching 96.20% in the surface samples and 90.90% in the holes' core samples (subsurface).

2-5-2 Iron and Titanium

Iron and titanium mineralization occurs within the fine-grain lens-shaped diorite rocks in addition to the occurrence of iron and titanium accumulations and segregations within the basic and ultrabasic intrusions. Mekiras area in Al-Beidha is one of the most important iron mineralization sites in Yemen.

Mekiras (Al-Beidha) is located 20 km to the southeast of Lawdar. There are disseminated mineralizations of apatite, ilmenite, vanadium-titano magnetite within gabbro intruded in the basement rocks of the Precambrian age. The area has had several geological, geochemical studies, exploration trenches and 18 exploration wells of 3400 meters deep, geological surveys, mineral, rock and drilling works. The reserves of these mineralization is estimated at 860 million tonnes distributed as follows; 130 million tonnes of iron mineralization, 46 million tonnes of TiO2, 27 million tonnes of phosphates, 0.15 million tonnes vanadium oxide with a mineral content of 15.5% Fe, 5.3% TiO2, 3.14% P2O5 and 0.02% V2O5.

2-6 Radioactive elements:

Uranium occurrences have been recorded at Ahwar, Abyan within the Cretaceous sandstone in the form of lenses of ferruginous sandstone amounting to 6 lenses of an average thickness of 1.43 m and length of 150-800m. The results of studies have shown that the uranium percentage is 0.042 to 0.343%. Uranium and traces of thorium mineralization occurs in the ferruginous conglomerates within Wajid sandstone in Wadi Marwan, Wadi Al-Nushour and Wadi Aquan in Sa'ada. The radioactive readings ranged between 100 cps and 1,600 cps in conglomerates with Uranium reaching 0.076 to 0.1% therein. This is in addition to the encouraging indicators specified for Uranium and Thorium within Pegmatite rocks in Juban, Al-Dhalie where the chemical analyses showed percentages of 1300 ppm of uranium and 1800 ppm of thorium. There are good signs of uranium and thorium within the pegmatite rocks of Al-Shuwaifah area in Haifan (Taiz) with chemical analyses showing results of up to 2700 ppm of uranium and 16000  ppm of thorium and good signs of thorium reaching 2730 ppm.

2-7 Tin and Tungsten:

Tin and tungsten mineralization occurs in the granite rocks of the post-tectonic movements within the basement rocks (Precambrian) in Qahilla Mount in Sa'ada; Tungsten concentrations ranged between 400 and 1035 g/ton with 690 ppm of tin and 1100 ppm of niobium and 600 ppm of tantalum. Tungsten and tin mineralization also occurs within the Tertiary granitic rocks in Al-Sa'adi Mount in Nahm, Sana'a with Tungsten reaching 268 g/t and tin 694 ppm.
Mineral Res. Metallic minerals in Yemen