Wollastonite outcrops at the Palaeozoic terrains of the central haut-atlas (Morocco), as irregular bodies together with garnets, pyroxenes and vesuvianite. Its formation is genetically linked to the intrusion of the Azegour post-Hercynian granite, which cut various rocks (carbonates, schistosed sandstones and volcanic complex) and induced a high-temperature contact metamorphism. Emanations from the intrusive fluid flows, principally consisting of silica and iron, reacted with calcareous rocks for forming calc- and iron-silicates assemblages (wollastonite, garnet and pyroxene). Investigations realized by X-ray diffraction, optical and scanning electron microscopes, and electron microprobe showed that wollastonite is a pure and good crystallized mineral with the chemical formula [Ca(0.96)Mn(0.02)Fe(0.01)P(0.01)]SiO(3), and the aspect- ratio (length to diameter) of the fibers is very high (>20:1). (C) 2011 Elsevier Ltd. All rights reserved.

Koudiat Aicha is a Visean stratiform, volcanogenic massive sulphide (VMS) zinc-copper-lead deposit, situated northwest of Marrakech, within the Central Domain of the Jebilet massif of the Western Moroccan Meseta. The Central Domain is formed mainly of sedimentary (argillite, siltstone, sandstone, carbonate) and magmatic (gabbro and rhyodacite) rocks that host numerous massive sulphide deposits (e.g., Koudiat Aicha, Kettara and Draa Sfar) in a thick grayish argillite sequence (rhythmic metapelite). The deposit is stratabound and consists of highly deformed, sheet-like lenses of massive sulphide located structurally on the eastern flank of a large anticline. Prior to metamorphism, the country rocks were subjected to hydrothermal alteration which is particularly pronounced in the immediate vicinity of the sulphide deposits where chloritization and sericitization are prevalent. Hydrothermal alteration extends into both the stratigraphic footwall and the stratigraphic hanging wall. The footwall lacks an obvious pipe zone (sulphide stringers or vent complex) beneath the sulphide mineralization, but is characterized by an increase in the modal proportion of Mg-chlorite and by the breakdown of feldspar and sericite. Chloritization, the most extensive and readily recognizable alteration useful in mineral exploration, is evident for more than 60 m above the subcropping sulphide deposits. The hanging wall rocks show a pervasive sericitization (over 30 m wide) and a weak chlorite alteration accompanied by disseminated nodules of pyrrhotite stretched parallel to the S(1) foliation. Because chlorite and sericite are metamorphic minerals that also occur in unaltered rocks surrounding the sulphide deposits, abundant Mg-rich chlorite and the absence of feldspar in the footwall are used to distinguish hydrothermal alteration facies from metamorphic facies. The chlorite geothermometer reveals temperatures between 250 and 330 degrees C. Higher temperatures (up to 300 degrees C) are associated with chlorite located in and adjacent to sulphide mineralization, whereas lower temperatures correlate with distal chlorite in both the footwall and hanging wall rocks.Chemical trends in altered footwall rocks are shown by absolute mass gains for Fe(2)O(3total), MnO and MgO, by absolute mass losses for CaO, K(2)O and Na(2)O, and by a moderate loss in SiO(2). Oxygen and hydrogen isotope compositions of Koudiat Aicha lithofacies (6.2-12.4 parts per thousand for oxygen and -51 parts per thousand to -36 parts per thousand for hydrogen) have also been used to determine the temperature and origin of metalliferous fluids. The couple plagioclase-amphibole of gabbros provides equilibrium temperatures between 310 and 380 degrees C and suggests that the heat source for the ore-forming fluid system may have been igneous. On the other hand, oxygen and hydrogen isotope ratios cluster between normal values for sedimentary and magmatic rocks, suggesting a magmatic-metamorphic origin for the ore fluid. (C) 2009 Published by Elsevier Ltd.

The Chouichiat peraluminous structure, located in the northern domain of the Bou Azzer - El Graara (Central Anti-Atlas, Morocco), outcrops as a discontinuous whitish ridge 10 to 60 m wide extending E - W for more than 2 km. This structure coincides with a large reverse-sense steeply dipping shear corridor, marked by penetrative schistosities and folds. The Chouichiat structure displays a strong zoning due to the combined effects of metamorphism, hydrothermal alteration, and deformation of a rhyodacite protolith. It has 1) a central quartz - pyrophyllite zone, surrounded on both sides by 2) a pyrophyllite - quartz - rich proximal zone with small amounts of diaspore, kaolinite and zunyite, and spots of hematite, and 3) a distal pyrophyllite zone with quartz - pyrophyllite in smaller amounts, common hematite and diaspore. The zoning expresses the gradual transformation of rhyodacite to pyrophyllitic rocks, enhanced by the development of the shear zone, which has strongly increased the permeability owing to fluid - rock reaction. Such an interaction is represented by a set of reactions, the most important of which is the hydrolysis of white mica in the rhyodacite to produce pyrophyllite: 2KAl(2)AlSi(3)O(10)(OH)(2) + 6 SiO2 + 2H(+) -> 3Al(2)Si(4)O(10) (OH)(2) + 2K(+). A decrease in temperature and an increase in silica activity led to replacement of early diaspore by pyrophyllite. Zunyite crystallized later, mostly at the interface between proximal and distal zones, together with spectacular rosettes of fibroradial hematite. The main kaolinite - pyrophyllite - quartz assemblage likely was generated around 273 degrees +/- 10 degrees C and 1 kbar. Mass-balance calculations indicate a significant leaching of mobile elements, promoting the residual concentration of Al, and a substantial addition of silica, both due to hydrolysis of aluminum silicates. The pyrophyllite - diaspore - zunyite assemblage is characteristic of hydrothermally altered aluminous felsic volcanic rocks and very similar to rocks altered by acidic fluid associated with gold-bearing epithermal ore deposits.

Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn-Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe7S8, and its absolute magnetic susceptibility is 2.10(-3) SI/g. Ar-Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 +/- 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Star deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile-brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (Pb-206/Pb-204 = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (Pb-206/Pb-204 similar to 18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO(2) conditions and neither a high temperature nor a low aH(2)S (below 10(-3)) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 +/- 10 Ma following a major phase of the Devonian compression. (C) 2007 Elsevier B.V. All rights reserved.

The general geology of the peraluminous rocks of the Bou-Azzer region (Central Anti-Atlas, Morocco) and their firing transformations were investigated by several techniques: optical microscopy, microprobe analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis, scanning electron microscope (SEM), energy dispersive spectrometry (EDS), and by measuring selected physical properties. The results of the geological study show that these rocks consist mainly of a quartz–pyrophyllite assemblage (70–74 wt.% SiO2 and 14–17 wt.% Al2O3), associated with minor amounts of muscovite and nacrite. They formed from a progressive deformation and hydrothermal alteration of felsic volcanic rocks. The principal mineralogical transformations recorded from rhyodacite to peraluminuous rocks are: K-feldspar → muscovite → pyrophyllite. Regarding the firing transformations, it is found that up to about 1100 °C the rock samples are subjected to expansion associated with the destruction of the pyrophyllite hydroxyl framework. The estimated amount of energy associated with this process is 50.226 kJ/mol. Beyond 1100 °C, a marked shrinkage was observed, due to the formation of a glassy phase, and the precipitation of mullite, cristobalite and K-feldspar. The reaction pathways for these phases are proposed and the evolved heat is determined (−160.928 kJ/mol).

Research Article| July 01, 2008 Geology and Mineralogy of the Hercynian Koudiat Aïcha Polymetallic (Zn-Pb-Cu) Massive Sulfide Deposit, Central Jebilet, Morocco F. Lotfi; F. Lotfi 1Faculté des Sciences Semlalia, Marrakech, Morocco. *Present Address: ONHYM, Direction Générale, 5, Av. My-Hassan, BP. 99, Rabat, Morocco; E-mail: lotfi_fouad@yahoo.fr Search for other works by this author on: GSW Google Scholar A Belkabir; A Belkabir † 2Faculté des Sciences et Techniques, Laboratoire Géoressources, BP. 549, Marrakech, Morocco. †Corresponding Author: E-mail: abelkabir@sftg-marrakech.ac.ma Search for other works by this author on: GSW Google Scholar A.C. Brown; A.C. Brown 3Dept. of Civil, Geological and Mining Eng., École Polytechnique de Montréal, 2900 boulevard Édouard-Montpetit, Montréal, Québec, Canada, H3T 1J4. Search for other works by this author on: GSW Google Scholar E. Marcoux; E. Marcoux 4Institut des Sciences de la Terre d’Orléans, Université d’Orléans, Orléans, France. Search for other works by this author on: GSW Google Scholar S Brunet; S Brunet 5Reminex-MANAGEM, Marrakech, Morocco. Search for other works by this author on: GSW Google Scholar L. Maacha L. Maacha 5Reminex-MANAGEM, Marrakech, Morocco. Search for other works by this author on: GSW Google Scholar Exploration and Mining Geology (2008) 17 (3-4): 145–162. https://doi.org/10.2113/gsemg.17.3-4.145 Article history received: 07 May 2007 accepted: 19 Sep 2008 first online: 13 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation F. Lotfi, A Belkabir, A.C. Brown, E. Marcoux, S Brunet, L. Maacha; Geology and Mineralogy of the Hercynian Koudiat Aïcha Polymetallic (Zn-Pb-Cu) Massive Sulfide Deposit, Central Jebilet, Morocco. Exploration and Mining Geology 2008;; 17 (3-4): 145–162. doi: https://doi.org/10.2113/gsemg.17.3-4.145 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyExploration and Mining Geology Search Advanced Search Abstract Koudiat Aïcha is a small Zn-Pb-Cu deposit, enclosed in the Visean Sarhlef volcano-sedimentary series of the Moroccan Hercynian Jebilet massif. Base metal mineralization is located between a basal unit consisting of black argillite with arenite intercalations, and an upper unit composed of black argillite with locally fossiliferous calcareous units towards the top. Paraconcordant gabbro sills are present in both the upper and basal units, and the enclosing strata. Three successive phases of deformation linked to regional deformation overprint the volcano-sedimentary rocks and gabbros, as well as the sulfide mineralization.The mineral deposit includes several lenses of massive to semimassive pyrrhotite, 1 to 20 m thick, with a large halo of disseminated sulfide veinlets and sulfide nodules within a zone of intense chlorite alteration in the footwall. The ore mineralogy consists of massive to semimassive pyrrhotite with lesser amounts of sphalerite, chalcopyrite, arsenopyrite, galena, pyrite, and stannite.Lead isotope results (206Pb/204Pb averaging 18.27) suggest that the metals of the Koudiat Aïcha deposit are derived from the volcano-sedimentary host rocks. Sulfur isotopes also indicate a volcano-sedimentary origin, with bacterial reduction of sulfate (δ34SCDT = −7.5‰ to −10.5‰). The conditions for sulfide metamorphic equilibration range from 250° to 330°C (sphalerite and chlorite geothermometers). The gabbroic sills could have been a local heat source for hydrothermal circulation. Based on these geological and mineralogical features, a Besshi-type model seems appropriate for the genesis of the Koudiat Aïcha mineralization. You do not currently have access to this article.

Draa Sfar is a siliciclastic-fielsic, volcanogenic massive sulphide (VMS) Zn-Pb-Cu deposit located 15 km north of Marrakesh within the Jebilet massif of the western Moroccan Meseta. The Draa Sfar deposit occurs within the Sarhlef series, a volcano-sedimentary succession that hosts other massive sulphide deposits (e.g., Hajar, Kettara) within the dominantly siliciclastic sedimentary succession of the lower Central Jebilet. At Draa Sfar, the footwall lithofacies are dominated by grey to black argillite, carbonaceous argillite and intercalated siltstone with localized rhyodacitic flows and domes, associated in situ and transported autoclastic deposits, and lesser dykes of aphanitic basalt and gabbro. Thin- to thick-beddcd, black carbonaceous argillite, minor intercalated siltstone, and a large gabbro sill dominate the hanging wall lithofacies. The main lithologies strike NNE-SSW, parallel to a pronounced S1 foliation, and have a low-grade, chlorite-muscovite-quartz-albite-oligoclase metamorphic assemblage. The Draa Sfar deposit consists of two stratabound sulphide orebodies, Tazakourt to the south and Sidi M'Barek to the north. Both orebodies are hosted by argillite in the upper part of the lower volcano-sedimentary unit. The Tazakourt and Sidi M'Barek orebodies are highly deformed, sheet-like bodies of massive pyrrhotite (up to 95% pyrrhotite) with lesser sphalerite, galena, chalcopyrite, and pyrite. The Draa Sfar deposit formed within a restricted, sediment-starved, fault-controlled, anoxic, volcano-sedimentary rift basin. The deposit formed at and below the seafloor within anoxic, pelagic muds.The argillaceous sedimentary rocks that surround the Draa Sfar orebodies are characterized by a pronounced zonation of alteration assemblages and geochemical patterns. In the more proximal volcanic area to the south, the abundance of medium to dark green chlorite progressively increases within the argillite toward the base of the Tazakourt orebody. Chlorite alteration is manifested by the replacement of feldspar and a decrease in muscovite abundance related to a net addition of Fe and Mg and a loss of K and Na. In the volcanically distal and northern Sidi M'Barek orebody alteration within the footwall argillite is characterized by a modal increase of sericite relative to chlorite. A calcite-quartz-muscovite assemblage and a pronounced decrease in chlorite characterize argillite within the immediate hanging wall to the entire Draa Sfar deposit. The sympathetic lateral change from predominantly sericite to chlorite alteration within the footwall argillite with increasing volcanic proximity suggests that the higher temperature part of the hydrothermal system is coincident with a volcanic vent defined by localized rhyodacitic flow/domes within the footwall succession. (C) 2007 Elsevier B.V. All rights reserved.

The Mouska mine, in the Bousquet region of the Abitibi greenstone belt, Quebec, exploits a sulfide-rich quartz-vein-type gold deposit hosted by a metavolcanic sequence of basalt and andesite. The ore zones constitute three main structural and lithologic systems, named 07, 08 and 22, comprising both lenses of massive and disseminated sulfides and quartz veins. Gold, varying from microscopic to visible, is hosted by both sulfide and quartz veins. The ore minerals consist of pyrrhotite and chalcopyrite, together with minor amounts of pyrite. Pyrite in particular, consists of two generations. Pyrite I is fine-grained (100 to 200 μm), and encloses micro-inclusions of gold (10 to 12 μm), chalcopyrite and pyrrhotite. Pyrite II is late, coarse-grained and cataclastic, and lacks micro-inclusions of gold. Pyrite I is rare, and partially to completely replaced by chalcopyrite and pyrrhotite. It may well represent a remnant of the first paragenetic assemblage (with chalcopyrite and pyrrhotite inclusions) in the deposit. Gold in the Mouska deposit exhibits a wide range of occurrences and habits. The gold micro-inclusions in pyrite I contain 4 to 6% Ag; gold in any other habit contains up to 25% Ag. Compared to the common Archean auriferous quartz-vein deposits, the Mouska deposit has a higher sulfide content of the veins, and the variably altered and deformed metabasic rocks show both distal and proximal halos of alteration. Such halos result from a complex and progressive interaction between hydrothermal-predeformational (sulfide event) and tectonometamorphic (quartz event) imprints. Mineralogical, geochemical and isotopic studies show that alteration assemblages surrounding the ore zones not only vary with lithology (basalt to andesite), but indicate a complex hydrothermal history, where the mafic protoliths have undergone several transformations during the Au–sulfide and Au–quartz depositions. In the proximal alteration, the mass-balance calculations display a clear addition of K, which may account for the observed enrichment in biotite and white mica toward the ore zones. However, these calculations show substantial addition of SiO2 only in the altered basalts, which can be explained by the massive destruction of ferromagnesian minerals.

The composite Mooshla stock displays clear evidence of variations in style and intensity of strain that are closely related to its internal lithological heterogeneity. Gabbro-diorite, quartz diorite, and tonalite rocks are weakly foliated and characterized by brittle and brittle-ductile small-scale shear zones, whereas leucotonalitic rocks are strongly foliated and transected by numerous wide and extensive ductile shear zones. Increasing degrees of penetrative deformation and marked changes of strain style in the pluton, from the more mafic rocks to the more felsic ones, are interpreted to reflect metamorphism-related rheological contrasts, rather than differences in the physical conditions of deformation. Metamorphism of the stock is characterized by an intensive hydration of the igneous rocks that has greatly enhanced their original heterogeneities. Petrographic, microstructural, and chemical studies show that the least deformed rocks are characterized by abundant albite-oligoclase (65-80%) with a matrix of minor quartz (5-10%) and actinolitic amphibole. The resistant plagioclase laths, although altered and replaced, form a stress-supporting framework that has protected the interstitial weak minerals, such as quartz, chlorite, and biotite, from deformation. However, the least deformed leucotonalites are characterized by low albite (35-45%) and high quartz contents (up to 65%). Extensive metamorphic hydration of these rocks produces quartz and phyllitic minerals that had enhanced significantly the ductility of the leucotonalites. Characterization of the chemical changes and the thermochemical conditions of the fluid, using microstructure and measurement of stable isotopes, indicates that fluid-rock interactions during metamorphism and syntectonic hydrothermal alteration have played an important role in creating the contrasting deformation of the composite granitoid.

The Mouska mine in the Bousquet mining district represents a sulfide-rich gold deposit hosted by the Archean mafic metavolcanites of the Blake River Group, southern Abitibi greenstone belt. Mineralization shows both lithological and structural control and coincides with variably oriented high angle-reverse ductile and brittle-ductile shear zones. Host shear zones are superimposed on the regional foliation, and both appear to have formed from the same bulk stress field.Gold mineralization is composed of sulfide and quartz lodes and is associated with three district ore zones; each differs from the others by its style of veining and the nature of tectono-metamorphic overprint. Sulfide mineralization in this area varies from semimassive to massive sulfide lodes and dissemination. The strain features and age relationships of ore-bearing rocks and vein material throughout the ore zones display evidence of earlier sulfide mineralization with gold. This mineralization is pretectonic (with respect to the development of the foliation) and is interpreted as hydrothernlal-synvolcanic. The auriferous quartz sulfide veins correspond to a multistage syn- to late tectonic mineralization and clearly crosscuts massive sulfide bodies.In the Mouska deposit, strain features and structural setting of gold mineralization show interactions between lithological factors, such as contacts, competence contrast and rock-body geometry, and die presence of pretectonic sulfides. In several parts of the mine volcanic sequence, the shear zone nucleation and development were controlled by both rock heterogeneities and the presence of soft sulfide bodies. The sulfides, in particular, were responsible for the structural instability recorded in some volcanic contacts and their activation as shear zones. In other parts, the sulfides have variably influenced the local slip movement. The shapes of ore shoots throughout the ore zones are variable and interpreted as reflecting the initial geometry of anisotropic interfaces involved in the deformation history.

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.