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COPYRIGHT 2007 The Mineralogical, Inc.
Bou Azzer has produced the world's finest specimens of erythrite, roselite, roselite-beta, talmessite, wendwilsonite, skutterudite and gersdorffite. About 215 mineral species have been identified from the district, of which six were new to science: irhtemite, arhbarite, nickelaustinite, wendwilsonite, bouazzerite and maghrebite. Bou Azzer is also considered to be the world's best (or at least second best) locality for the very rare species cobaltarthurite, cobaltaustinite, cobaltlotharmeyerite, karibibite and guanacoite.
INTRODUCTION
Bou Azzer might be translated as "where the fig tree stands." In a little gorge to the left of the road out of Tazenahkt a tiny garden lies hidden, not far from a spring inhabited by many frogs--a rare thing in the barren Anti-Atlas Mountains. An old, stunted fig tree seems to watch over the garden, and it is this diminutive tree which has given a name to the whole, very well-mineralized region thereabouts.
The Bou Azzer mining district encompasses many distinct mines, of which the most famous--from west to east--are Bou Azzer proper, Aghbar (Arhbar), (12) Ightem (Irhtem), Tamdrost and Ait Ahmane. These classic localities have produced the world's finest specimens of erythrite, roselite, roselite-beta, talmessite, wendwilsonite, skutterudite and gersdorffite. As of the end of 2006 the Bou Azzer district had produced about 215 mineral species altogether, and was the type locality for four of them: irhtemite (Pierrot and Schubnel, 1972), arhbarite (Schmetzer et al., 1982), nickelaustinite (Cesbron et al., 1987), and wendwilsonite (Dunn et al., 1987). Two more new species have just been described from the district: bouazzerite and maghrebite (Meisser and Brugger, 2006). Bou Azzer is also considered to be the world's best (or second best) locality for the rare minerals cobaltarthurite, cobaltaustinite, cobaltlotharmeyerite, karibibite and guanacoite.
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Since the early 1930's there have been numerous publications about the Bou Azzer mining district--chiefly geological and economic studies concerning extraction of cobalt and nickel arsenide ores. By contrast, descriptions of the district's other minerals, especially the secondary mineralogy, are dispersed among various specialized treatises. Most published works on the descriptive mineralogy of Bou Azzer are products of the Service Geologique du Maroc: windows to a "golden age" in the time of French geolo-gists like Christophe Gaudefroy (1888-1971), Georges Jouravsky (1896-1964) and Francois Permingeat (1917-1988). These original works are highly interesting, and remain pertinent even now. The same remarks apply to the excellent works on arhbarite, schneider-hohnite and karibibite by German scientists.
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Although the region's deposits are world-famous and although two of us (GF and JED) have visited them many times, we have had to recognize that the extant listings of Bou Azzer's known secondary minerals and their varieties are radically incomplete. The fact has moved us to conduct many new investigations, particularly for the microcrystalline minerals. The result has been the identification of 46 Bou Azzer mineral species not previously known from there. These include arseniosiderite, bromargyrite, cabalzarite, chalcophyllite, clinoclase, clinotyrolite, cobaltkoritnigite, cornubite, fornacite, geminite, litharge, mottramite, nickellotharmeyerite, novacekite, parnauite, powellite, uvarovite, walentaite, wulfenite, yukonite and zalesiite.
HISTORY
For a long time the tribal Berbers of the region around Bou Azzer had known of the outcropping arsenic-rich ore veins and of their cobalt arsenate minerals, especially erythrite, whose beautiful violet-red color seized their attention. The local populations knew of the toxic properties of these substances, and used them to fight insects. Contracts for their use existed between the Pasha of Mar-rakech and the Ait-Hammou tribe, and they are said to have been sold in the Marakech "souks" (markets) as rat poison.
The economic potential of the cobalt ore occurrences was first recognized near the end of the First World War. The area in which the veins appeared was fairly small, difficult of access, and--during the first years of the French protectorate--politically unsettled. The first mining facilities (still visible today) took the form of small fortresses--"Bordj," in Arabic.
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1928: BOU AZZER IS "DISCOVERED"
In 1927, His Excellency Si Hadj Thami el Glaoui, Pasha of Marrakech, concluded contracts with the local tribes who controlled the ore deposits. These contracts permitted exploration work by French prospectors which led, in 1928, to the true "discovery" of the deposits. With the intensification of prospecting after 1929, the most important occurrences--Veins 7, 5 and 2, Aghbar and Ightem--were located. Mining began in 1932, and several hundred tons of hand-sorted ore were produced. In 1934 the Bou Azzer-El Graara Mining Company began industrial mining of Veins 7, 5 and 2, all in the mining center of Bou Azzer, and of the deposits at Ightem.
Until 1950 the ore was processed through simple sorting and washing in basins--bacs sardes. During the Second World War production ceased for four years (1940-1944). In 1944 the installation of pneumatic tables and a hydraulic ore-washing system for ore concentration was completed. At that time, development of the deposits at Aghbar was also initiated.
In the period 1953-1958, mining activity was reinvigorated by the Penarroya mining company. A new ore-concentration facility was constructed, and in May of 1957 a flotation plant came on line. Thanks to these new facilities, 8,000 tons of raw ore from Bou Azzer and 4,000 tons from Aghbar were processed into 700-900 tons of ore concentrate each month. During this time about 2,000 people, of whom 800 to 900 were Moroccan workers and 120 were Europeans, lived in the mining district.
Because the hydrothermal cobalt-nickel mineralization is linked to serpentinite bodies (at the intersections between southwest-striking faults and the main fault zone of the Anti-Atlas Mountains), geophysical investigations (magnetometry and electrical conductivity measurements) were undertaken in 1956, in order to determine the size and shape of the serpentinite bodies beneath the sedimentary cover.
During the 1960's the cobalt ore concentrates were shipped to Europe out of the harbors of Casablanca and Agadir. The transport of the material over 520 km to Casablanca made for an arduous expedition: 15-ton trucks had to surmount the 2,270 meter-high Tichka Pass over the High Atlas Mountains, and then, in Marrakech, the ore concentrate had to be transferred to railroad cars to be taken to Casablanca. The route to Agadir was somewhat less perilous: the concentrate was carried by trucks with capacities of up to 20 tons.
Since 1958 the mining rights have belonged to the Moroccan holding company Omnium Nord-Africain (ONA), headquartered in Casablanca. This company is represented by the Compagnie de Tifnout-Tiranimine (CTT), which currently conducts mining operations.
1967: WAS BOU AZZER "EXHAUSTED"?
In September 1967, the workings on Veins 7 and 5 were closed, the ore zone there having been declared exhausted. A little mining in the Aghbar deposits continued, but by 1970 the reserves there were also thought to be exhausted. Accordingly the ONA hired a team of Soviet experts who specialized in exploring for ore mineralization in greenstones. Between 1969 and 1971 this team investigated the area's geochemistry and geophysics through mapping, drilling, and prospecting; the team found evidence of a large Co-As-Bi-Ag-Ni-Cu-Zn-Mo anomaly, with rich ore occurrences in Taghouni, Tamdrost and Bou Azzer-East.
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CTT began mining for ore in Bou Azzer-East in 1971, and in Tamdrost (with estimated reserves of 350,000 tons of ungraded cobalt ore) in 1974. After 1976 there was ore production also from a series of small to medium-size deposits including Taghouni (or Tarouni, 1976), Oumlil Centre (1977), Ait Ahmane (Vein 61, 1980) and Bouismas (1981), as well as from the small ST1 and ST2 Veins in the mining center of Bou Azzer. However, mining ceased again in 1983.
In 1987, geologists employed by CTT discovered the cobalt deposits of Mechoui, and mining there was begun in the same year, followed in 1990 by Vein 53, Ait Ahmane. Work stopped at Mechoui in 1994 after a short period of operation.
At this time the deposit at Aghbar, from which have come the most beautiful minerals of the region, was still slumbering, its specimen riches only partially known. Revival of mining there began with the dewatering of the shafts in 1997-1998. In 1999-2000, new workings were initiated in the oxidation zone near the top of the deposit, where exceptionally rich areas were found. New open-cut diggings there intersected old workings, and a few spectacular secondary mineral specimens were found.
By the end of 2002 short-lived mining had brought to light some very interesting, rare secondary minerals (iron and arsenic-bearing minerals like karibibite and schneiderhohnite), both from the small Mechoui I and Khder mines and from large mines at Oumlil-East and Tamdrost.
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As of November 2005, of the 20 deposits mentioned above and about 60 prospect pits, five mines remain in operation; since 2002-2003, all serious mining activity has taken place underground in these mines. The westernmost of these mines is Taghouni. At the mining center of Bou Azzer, Shaft 3, with Veins 7 and 5, is temporarily dormant, as is Bou Azzer East. The other currently active mines, from west to east, are Aghbar, Bouismas, Oumlil-Centre and Agoudal. Currently the workings exploit primary arsenide ores. The mining of oxide ores is not considered economically feasible.
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GEOLOGY
Setting and Landscape
Bou Azzer lies in the central part of the Anti-Atlas Mountains of southern Morocco and within a distinctive geological feature, the saddle-shaped ridge of Bou Azzer-El Graara. This boutonniere (13) stretches in an east-southeast direction for about 50 km; its western edge lies about 60 air-kilometers southwest of Ouarzazate and about 30 km east of Tazenahkt.
The landscape resembles that of the southwestern United States; American Westerns have been filmed in the vicinity of Ouarzazate. The dominant prospect is one of brown steppelands where innumerable gray-green St. John's wort bushes (Izri in the Berber language) flourish. Small life forms, mostly concealed, are everywhere. Immediately after sunset, or in shaded hollows where water collects, one can observe the region's fauna, including some dangerous species such as biting spiders and horned vipers.
On a large-scale geological map the Bou Azzer-El Graara boutonniere is easy to see: in the midst of a homogenous geological prospect the ridge of the boutonniere is entirely distinctive. Its surroundings consist of a series of Precambrian volcanic rocks, including a carbonaceous unit (the Adoudounian Formation), resting on a still older basement. These basement rocks, about 2 billion years old, consist predominantly of leucocratic (felsic) granites, noticeable as paler rocks cropping out among the green (brown, when weathered) serpentinites which stretch between Aghbar and Tamdrost.
IN THE PRECAMBRIAN HIGHLANDS
The geology of the region is extremely complex; the Precambrian rocks have undergone multiple episodes of deformation since their formation, resulting in overthrusts, horizontal and vertical fracturing, brecciation, and the creation of cavity-rich permeable zones in which hydrothermal solutions could circulate. Profound chemical transformations resulted, including the serpentinization of rocks and the deposition of metallic vein deposits.
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The Anti-Atlas Mountains consist of two clearly distinct structural blocks separated by a prominent fault zone running west-southwest to east-northeast, called the "AMAA," or "Accident Majeur de l'Anti-Atlas." This fault zone, which runs through the middle of the Bou Azzer-El Graara ore district, lies on the northern margin of an Achean-age craton which is the West African part of the earth's primordial crust. The stable craton is ringed by major tectonic boundary zones characterized by thick, weakly deformed sedimentary sequences (e.g. the Tindouf Basin and the Taoudemni Depression).
The Bou Azzer-El Graara ore district is elongated, stretching along the strike of the "AMAA" fault zone within the Precambrian boutonniere. The central ore-rich region is demarcated in the west by Bou Azzer (veins 7 and 5) and in the east by El Graara, with Aghbar, Ightem and Ambed among the intermediate mining areas.
In general the most important orebodies seem to lie in the vicinity of Middle Precambrian serpentinites. These orebodies are elongated east-northeast to west-southwest along the fault zone and are displaced to varying degrees by northeast-southwest transverse faulting.
Probably the cobalt-nickel ores were already being formed during the Precambrian by serpentinization and by weathering processes (leading in part to a layering of the deposits), then later by hydrothermal mobilization related to volcanic emplacement of alkaline andesite-trachytes (600 to 565 million years ago). Thus, deposition of primary ores in the Bou Azzer-El Graara region began in the Precambrian (more than 800 million years ago) in ophiolitic greenschists; ore vein formation reached its maximum during the late phases of a pan-African mountain-building orogeny (about 550 million years ago), and the process finally ended during the so-called "Saalian phase" of the Hercynian orogeny (250 to 240 million years ago).
ORES CONTACTING SERPENTINITES
A general rule for the Bou Azzer district is that all Co-Ni-Fe arsenide ore mineralization occurs at contacts with serpentinite. Three broad types of ore mineralization are distinguishable:
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[1] Strata-bound mineralization of the Ambed type. The Upper Precambrian Ambed Formation (El Graara) is a result of the serpentinization of ophiolitic greenstones and the later weathering effects of meteoric (surface) water. It was later deformed and eventually covered over by felsic volcanic rocks (rhyolite). This sedimentary formation seems to have served as an essential source of the Co-Ni-Fe in the ore deposits.
[2] Complex capping mineralization of the Aghbar type. The rather strongly weathered Aghbar serpentinite body was covered over by chloritized rhyolite, and the mostly flat-lying contact zones between the two rock types were brecciated by tectonic movements. Parts of the underlying serpentinite were pushed up as horst-like tongues or "pseudoplutons" into the rhyolite layers above, creating structures resembling salt diapirs. Carbonate rock layers, especially on the northern side of the boutonniere, were heavily faulted, with local overthrusting. The mineralization is probably related to a late Variscan tectonic phase during which elements already present in the weathered serpentinite were remobilized and concentrated.
[3] Vein mineralization of the Bou Azzer type. In the area of the Bou Azzer (proper) deposit an extensive, steeply dipping fault running east-northeast/west-southwest separates serpentinite from Precambrian quartz diorite. In this fault zone the #7 ore vein is found at a depth of more than 300 meters; it is, however, mineralized only at the point where it contacts serpentinite. The strongly brecciated Vein #7 carries quartz and carbonate gangue in which the minable ore occurs as lenses dipping about 60[degree] to the west. Probably this indicates either a boudin-like structure formed when tension pressure tore the vein into discrete elliptical pieces, or a large-scale pattern of thin fissures in the vein.
Farther to the north, Vein #7 crosses Vein #5 in the region of quartz diorite. Here the presence of erythrite gives the first sign of cobalt mineralization. Probably these veins, with their accompanying systems of smaller veins, were emplaced during the earlier formation phases (about 600 million years ago).
As Leblanc (1980) has suggested, it seems clear that the "Bou Azzer" type of deposit can be defined as: "Cobalt arsenide deposits in serpentinite with overlying silicate-carbonate sedimentary rocks, the ore concentration resulting from tectonic remobilization and surficial weathering." Of all the rocks of the region, the serpentinites are the richest in cobalt and nickel content which could be leached out and concentrated (Jouravsky, 1952). Serpentinites are not found at the surface in other parts of the Anti-Atlas Mountains or the Tafilalt. Thus the Bou Azzer district is quite remarkable, because of its great age and because of the practically uninterrupted period of formation from the middle Precambrian to the Permian/Triassic boundary (about 240 million years ago).
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The physical form of the orebodies is highly variable--veins, seams, chimneys, lenses and stockworks in breccia. The form of the deposits depends on the intensity of fracturing in the rock and on the properties of the rock, since these two factors affect the circulation of mineralizing fluids and therefore the deposition of minerals. In general we distinguish two types of ore deposits:
[1] Ore masses with strong ore enrichment ("amas"-type) are concentrated along irregular contacts between serpentinites and Precambrian volcanics (Tamdrost) or quartz diorites (Bou Azzer-east, Bouismas). The ore masses, with thicknesses measured in meters, run extensively along the irregular contacts with serpentinite.
[2] Ore veins which are aligned obliquely ("transverse" type) to serpentinite contacts. The rock units on the other side of the contacts may be quartz diorites (Veins 5 and 7), greenstones (Vein 2) or Precambrian volcanics (Tamdrost).
Ore Mineralogy
Most of the ore deposits are bound either in Precambrian structures or in the younger fault zones of the Variscan Orogeny (late Paleozoic). The richest orebodies are always found where deformation was most intense (a fact which often poses problems in mining), particularly in the west-northwest/east-southeast striking zone of contact between quartz diorite and serpertinite, cut in turn by faults striking northeast-southwest.
Co-Ni-Fe arsenides are found ubiquitously in such structures in both the western and eastern parts of the boutonniere; the most common species are skutterudite, lollingite and nickeline. Nickel is more common in the central part of the boutonniere and to the east, at Ait Ahmane. The sulfides linneite, millerite and pyrite seem merely subordinate, and sphalerite and galena can be considered rare. Chalcocite and molybdenite have been noted at both Bou Azzer and Aghbar. Chalcopyrite and bornite are found in most of the deposits, in some cases in considerable quantity. Co-Ni-Fe sulfarsenides such as gersdorffite, glaucodot, arsenopyrite and cobaltite are found generally in the eastern part of the district, around Ait Ahmane.
Gold and silver are the predominant native elements (Ennaciri, 1995). In the western part of the boutonniere (Veins 5, 7, II, ST2, ST1), the average gold content of the ore--more than 8 grams per ton--is higher than in the eastern part. On the other hand, the distribution of silver throughout the district is fairly homogenous at 13-37 grams per ton. The gold-poor sectors in particular (Bouismas, Oumlil, Tamdrost) tend to carry a higher silver content.
Chromite and magnetite, typical minerals in ophiolites, occur throughout the boutonniere and are regarded as relict products of serpentinization. There is a possibly mineable chromite body in the eastern part of the boutonniere. The chromite ore carries 0.2 grams per ton of platinum-group metals, occurring as microscopic inclusions of laurite, native osmium, native iridium, kashinite and heazlewoodite (Ghorfi et al., 2005).
The gangue minerals in the veins are quartz, various carbonates, asbestiform and talcose silicates, and much more rarely pyrophyllite and the finely acicular borate szaibelyite.
MINING AND ORE PRODUCTION
In the Bou Azzer mines the ore is extracted by overhead stoping in the veins, then backfilling the mined-out areas with waste rock. In the Bouismas mine and in Veins 7 and 5, chamber-mining has been employed experimentally. The method of reinforcing the floor of the mine with concrete platforms, as used in other places (for instance, in mining the rich ore of Tamdrost) was given up as too costly and risky. Mining proceeds by following an overhead vein upward, letting the ore fall to the floor to be scooped up by a diesel loader or an electric-powered excavator. The ore is then crushed and concentrated by gravimetric separation of the minerals based on the differing densities of ore, gangue and country rock.
To increase production in the future, extraction of ore in Veins 7 and 5 will be further mechanized, with mining activity focused on the most productive areas, including Taghouni and Bou Azzer-East (Veins 7 and 5), Bouismas/Oumlil and Agoudal.
Ennacri (1995) and Ghorfi et al. (2005) estimate the minimum production of the Bou Azzer district between 1933 and 1995 as follows:
50,000 to 60,000 tons of cobalt
5,000 tons of nickel
150,000 tons of arsenic
3,500 tons of chromite
9-10 tons of silver
2-5 tons of gold
To have obtained these quantities of metals, a total of 1,150,000 tons of raw ore (with 2-2.4% Co) must have been mined in Aghbar and 1,350,000 tons must have been mined from Veins 7, 5 and 2 in the center of the Bou Azzer district. Since 2001 the yearly production has increased to 140,000 tons of cobalt ore, with 1.2% Co (Barakate, 2005) and showing a gold content between 1 gram and 49 grams (!) per ton (Ghorfi et al., 2005).
Here are a few final statistics from the years 1992-1995:...
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