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Imiter |
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Morocco |
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Ag
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Super Porphyry Cu and Au
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The Imiter Neoproterozoic epithermal silver deposit is genetically associated with a felsic volcanic event formed within a regional extensional tectonic regime. It is located in the Anti-Atlas mountains of Morocco in north Africa, some 280 km east of Marrakech.
The deposit is located on the northern side of the Saghro massif, one of a series of Proterozoic inliers within Palaeozoic rocks which constitute the Pan-African Anti-Atlas orogenic belt of Morocco. The oldest rocks in the Imiter area are a sequence of Neoproterozoic pyritic black shales which were deposited on an oceanic crust basement and have been folded and metamorphosed to greenschist facies during the Neoproterozoic, along with ophiolites in the neighbouring Sirwa massif to the WSW. This orogenic event on an active margin included the subsequent emplacement of considerable calc-alkaline magmatism and the development of a foreland basin. In the Imiter area the black shales were unconformably overlain by immature basal conglomerates and late Neoproterozoic volcanics and volcaniclastics (andesites at the base and ignimbrites at the top) dated at 580 to 560 Ma, with associated emplacement of granodioritic and granophyric intrusives. During the Cambrian the belt became a passive margin with the emplacement of rift clastics, carbonaceous rocks and volcanic and sub-volcanic activity.
At Imiter three phases of intrusion are recorded: i). granodiorite cutting the Neoproterozoic black shales, prior to the immature late Neoproterozoic basal conglomerates, ii). a granodioritic massif cut the black shales and the conglomerate and overlying volcanics, and iii). a major felsic magmatic event occurred at Imiter represented by various dykes in the mineralised area. A strong connection between this third phase and the silver mineralisation is implied. It is characterised by a well developed concentric magmatic structure suggesting a hypabyssal body emplaced under subaerial conditions. The main intrusive is the Tachkakacht rhyolite dyke which cuts trachyandesite dykes in the same area. The mineralised rocks are overlain by un-mineralised middle Cambrian sediments.
Two successive paragenetic associations are recognised at Imiter.
1). The first comprises an early quartz vein network with abundant chlorite, muscovite and base metals (pyrite, chalcopyrite, sphalerite and galena).
2). The second silver rich stage is subdivided into, a). Another quartz phase with minor muscovite developed on the first stage chlorite, further base metals and silver, and b). A late phase characterised by pink dolomite gangue and increasing amounts of Co, Ni and Hg bearing sulphides.
Ore occurs in metre wide faults, stockworks and hydraulic breccias, as well as disseminations of silver bearing minerals in the Neoproterozoic pyritic black shales and volcanics, all distributed along the Imiter Fault as a series of shoots approximately 10 m thick, 100 m long and 100 m down dip. Supergene modification has limited the upper levels of the deposit which is characterised by iron hydroxides at the expense of sulphides, while cerussite rims galena crystals, with no supergene sulphide enrichment. Mineralisation has been dated at 572 ±5 Ma.
The total identified resource at Imiter is 8000 tonnes of recoverable silver (2002).
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2002.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Cheilletz A, Levresse G, Gasquet D, Azizi-Samir M R, Zyadi R, Archibald D A, Farrar E 2002 - The giant Imiter Silver deposit: Neoproterozoic Epithermal mineralization in the Anti-Atlas, Morocco: in Mineralium Deposita v37 pp 772-781
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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