The Djilouet granite suite (Djanet terrane, eastern Hoggar, Algeria): petrography, mineralogy, geochemistry, and relations with quartz-cassiterite-wolframite vein systems

Abstract The Grobgneis complex, located in the eastern Austroalpine unit of the Eastern Alps, exposes large volumes of pre-Alpine porphyric metagranites, sometimes associated with small gabbroic bodies. To better understand tectonic setting of the metagranites, we carried out detailed geochronological and geochemical investigations on the major part of the porphyric metagranites. LA–ICP–MS zircon U–Pb dating of three metagranites sampled from the Grobgneis complex provides the first reliable evidence for large volumes of Permian plutonism within the pre-Alpine basement of the Lower Austroalpine units. Concordant zircons from three samples yield ages at 272.2 ± 1.2 Ma, 268.6 ± 2.3 Ma and 267.6 ± 2.9 Ma interpreted to date the emplacement of the granite suite. In combination with published ages for other Permian Alpine magmatic bodies, the new U–Pb ages provide evidence of a temporally restricted period of plutonism (“Grobgneis”) in the Raabalpen basement Complex during the Middle Permian. Comparing the investigated basement with that of the West Carpathian basement, we argue that widespread Permian granite magmatism occurred in the Lower Austroalpine units. They belong to the high-K calc-alkaline to shoshonitic S-type series on the base of geochemical data. Zircon Hf isotopic compositions of the Grobgneis metagranites show εHf(t) values of − 4.37 to − 0.6, with TDM2 model ages of 1.31–1.55 Ga, indicating that their protoliths were derived by the recycling of older continental crust. We suggest that the Permian granitic and gabbroic rocks are considered as rifted-related rocks in the Lower Austroalpine units and are contemporaneous with cover sediments.

Download Full-text

Nature and longevity of hydrothermal fluid flow and mineralisation in granites of the Bushveld Complex, South Africa

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300007434 ◽

2000 ◽

Vol 91 (1-2) ◽

pp. 269-281 ◽

Cited By ~ 4

Author(s):

L. J. Robb ◽

L. A. Freeman ◽

R. A. Armstrong

Keyword(s):

Fluid Flow ◽

Bushveld Complex ◽

Hydrothermal Activity ◽

Incompatible Trace Element ◽

Ore Deposits ◽

Fluid Saturation ◽

Fracture Systems ◽

Sulphide Ores ◽

Tin Deposit ◽

Granite Suite

The Lebowa Granite Suite of the Bushveld Complex is a large, 2054 Ma old, A-type batholith, characterised by numerous relatively small magmato-hydrothermal, polymetallic ore deposits. The mineralisation is represented by a three-stage paragenetic sequence: early magmatic Sn-W-Mo-F ores (600°C > T > 400°C), followed by a Cu-Pb-Zn-As-Ag-Au paragenesis (400°C > T > 200°C) and then late-stage Fe-F-U mineralisation (< 200°C). The first stage of mineralisation (typified by the endogranitic Zaaiplaats tin deposit) is related to incompatible trace element concentration during crystal fractionation and subsequent fluid saturation of the magma. Evolution of the late magmatic fluids as they were channelled along fractures, as well as mingling with externally derived connate or meteoric fluids, resulted in the deposition of the second stage of mineralisation (typified by the fracture-related, endogranitic Spoedwel and Albert deposits and the exogranitic, sediment-hosted Rooiberg mine) which is dominated by polymetallic sulphide ores. As the externally derived fluid component became progressively more dominant, oxidation of the polymetallic sulphide assemblage and precipitation of hematite, pitchblende and fluorite occurred generally along the same fracture systems that hosted the earlier sulphide paragenesis.Small hydrothermal zircons trapped along quartz growth zones from the Spoedwel deposit yield a U-Pb concordia age of 1957 ± 15 Ma. Whole-rock Rb-Sr age determinations from the Lebowa Granite Suite fall in the range 1790 ± 114 Ma to 1604 ± 70 Ma and are interpreted to reflect alkali element mobility and isotopic resetting during exhumation of the Bushveld granite. In contrast to thermal modelling which indicates that hydrothermal activity should have ceased within 4 my of emplacement, isotopic evidence suggests that mineralisation was long-lived, but episodic, and that fluid flow events were linked to major periods of Palaeo- and Mesoproterozoic orogenic activity along the margins of the Kaapvaal Craton. During these orogenic episodes, fluid flow was enhanced by tectonically induced fluid over-pressuring and/or exhumation of the Bushveld Complex.

Download Full-text

THE ORIGIN OF FERROAN-POTASSIC A-TYPE GRANITOIDS: THE CASE OF THE HORNBLENDE-BIOTITE GRANITE SUITE OF THE MESOPROTEROZOIC MAZURY COMPLEX, NORTHEASTERN POLAND

The Canadian Mineralogist ◽

10.3749/canmin.48.4.947 ◽

2010 ◽

Vol 48 (4) ◽

pp. 947-968 ◽

Cited By ~ 17

Author(s):

J.-C. Duchesne ◽

H. Martin ◽

B. Baginski ◽

J. Wiszniewska ◽

J. Vander Auwera

Keyword(s):

Biotite Granite ◽

Northeastern Poland ◽

Granite Suite

Download Full-text

The distribution of surface magnetization in the English River and Kenora subprovinces of the Archean shield in Manitoba and Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e79-162 ◽

1979 ◽

Vol 16 (9) ◽

pp. 1764-1777 ◽

Cited By ~ 14

Author(s):

D. H. Hall ◽

R. L. Coles ◽

J. M. Hall

Keyword(s):

High Surface ◽

Magnetic Anomalies ◽

Ambient Temperatures ◽

Long Wavelength ◽

Red Lake ◽

Surface Magnetization ◽

The Vertical Distribution ◽

Granite Suite ◽

Opaque Minerals ◽

Distribution Of Magnetization

Surface magnetizations (induced and remanent) have been measured from almost 600 oriented cores collected over an area of 50 000 km2 covering portions of the Kenora, English River, and Red Lake subprovinces of the western Archean shield, between latitudes 49 and 51 °and longitudes 93 and 96°. These surface magnetizations reflect major geological provinces in the area, and throw light on the vertical distribution of magnetization and on the associated long wavelength magnetic anomalies. A major belt of high surface magnetization lies over the granodiorite–granite suite in the southern part of the English River subprovince and a major belt of low magnetization over the metasedimentary gneiss belt in the northern part of the subprovince. Remanent magnetization is prevalent, but is very unstable, apparently due to viscous remanence, and subparallel to the present-day geomagnetic field. This fact is of importance because rocks of this type, if deeply buried and at ambient temperatures above surface values, may lead to rather large intensities of magnetization. The magnetization is almost entirely due to magnetite, and titanomagnetite is only rarely encountered. The prevalent opaque minerals are magnetite, ilmenite, pyrite, pyrrhotite, and hematite.

Download Full-text