New Petro-Mineralogical Results on the Magmatic Surrounding Rocks of Cu-Ag Mineralization in Tagmout (Eastern Anti -Atlas, Morocco)

Tagmout deposit is located in the Eastern Anti-Atlas, about 30 km south of the city of Qalâat Mgouna. It contains Cu-Ag mineralization which is embedded in magmatic rocks that are essentially intrusive of various facies. Detailed mapping (1/1200) and petro-mineralogical observation of these facies allow us to distinguish: 1) Olivine gabronorite, it is composed mainly of pyroxenes (CPX and OPX), olivine and biotite; 2) Quartz monzogabbro, it is characterized by the presence of pyroxenes, amphiboles, plagioclases, FK and quartz; 3) Quartz monzodiorite, which is a porphyric facies. It occupies the center of the Tagmout sector which is rich in FK, plagioclase, quartz, amphibole and pyroxene; 4) Granodiorite, it is a facies associated with quartz monzodiorite. It shows a paragenesis composed of FK, quartz and plagioclase; 5) Pink microgranite, metric dykes developing in different directions (N10° to N15°, N70° to N90°, N120° to N130 °). It is a facies rich in quartz, FK and plagioclase; 6) Dolerite, It is a dark-colored facies with a typical doleritic texture. It is rich in plagioclase and relics of pyroxenes and amphiboles. This facies occupies the eastern part of Tagmout complex; 7) Volcano-sedimentary facies with rhyolite appearance of brick red color. It is a vitreous fine matrix and conglomerate elements which is rich in quartz and FK. These are conglomerates that are affected by the terminal neoproterozoic rhyolitic lavas. They are also affected to different degrees by several phases of hydrothermal alterations of potassic, phyllitic, clayey, and propylitic types. The effect of these alterations on the rock at the surface is very variable. The granodiorite is highly affected while olivine gabbronorite is not very sensitive and retains a remarkable state of freshness. This raises an interrogation on the chronological place and the advanced age for these facies (557 ± 5 Ma, Benziane and al. 2008).With the exception of recent formations (microgranite, dolerite and volcano-sedimentary facies), the contact between the plutonic rocks of Tagmout (olivine gabbronorite, quartz monzogabbro, quartz monzodiorite, granodiorite and granite) never takes major structural discontinuity nor contact metamorphism. But the localization of some enclaves on both sides of the neighboring facies with an intense brecciation marked the contact of these facies. This configuration suggests that the plutonic formations of Tagmout massive that the setting up was done in a contemporary way and is derived from the same magma by fractional crystallization in a magmatic chamber.

The Jurassic gabbroic intrusions of Utpostane and Muren: insights into Karoo-related plutonism in Dronning Maud Land, Antarctica

Middle Jurassic continental flood basalts of Vestfjella, western Dronning Maud Land are cut by gabbroic intrusions that represent rare exposures of Karoo-related mafic plutons in Antarctica. The gabbros and numerous associated dolerites indicate high magmatic activity along the continental margin of Dronning Maud Land during the break-up of Gondwana. The scattered nunataks of Utpostane (∼25 km2) are dominated by olivine gabbronorite and olivine mela-gabbronorite, which can be grouped into four zones. The Utpostane intrusion exhibits inclined sheet-like geometry, is at least ∼3 km thick and shows moderate enrichment of incompatible element contents from its base towards the exposed roof contact (e.g. Zr from ∼15 to ∼60 ppm). High MgO contents (∼8–36 wt%) indicate that the parental magma of Utpostane was more primitive than a typical Karoo tholeiite (MgO ∼6 wt%). At Muren, gabbroic outcrops record a cross section of a ∼1.3 km thick inclined sheet-like intrusion. The intrusion can be divided to two main units, the upper and lower zones, which are dominated by olivine gabbro and gabbronorite, respectively. Parental melts of the geochemically differentiated upper zone and the homogeneous lower zone of Muren were typical low-MgO Karoo tholeiites, but they were chemically distinct and were emplaced as separate magma pulses.

Petrology and age of the Mechanic Settlement Pluton, Avalon terrane, southern New Brunswick

The Mechanic Settlement Pluton, located at the northern margin of the Caledonian Highlands in southern New Brunswick, is composed of rocks ranging from ultramafic (lherzolite, plagioclase-bearing lherzolite) through mafic (mainly olivine gabbronorite and gabbro) to intermediate (quartz diorite and monzodiorite). Spatial distribution of these lithologies, textural features, and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes, with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas. The dioritic rocks form most of the southwestern (upper?) part of the pluton, whereas the varied gabbroic rocks with ultramafic layers form the northeastern part. U–Pb (zircon) dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 ± 3 Ma. Amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40Ar/39Ar dates of 550 ± 5 and 539 ± 5 Ma, respectively, indicating that the pluton cooled rapidly through the closure temperature for amphibole, with subsequent slower cooling to the time of phlogopite closure. The pluton is interpreted to be the intrusive equivalent of basaltic units in the host Coldbrook Group, analogous to granitic plutons elsewhere in the Caledonian Highlands which appear to be the intrusive equivalents of felsic volcanic rocks in the group. These plutonic and volcanic rocks represent a major, short-lived (ca. 560–550 Ma), dominantly bimodal igneous event, apparently related to late Precambrian extension within the Avalon terrane of southern New Brunswick.