Uraniferous Leucogranites in the Rössing Area, Namibia: New Insights from Geologic Mapping and Airborne Hyperspectral Imagery

2021 ◽  
Author(s):  
Tim Gray ◽  
Judith Kinnaird ◽  
Justin Laberge ◽  
Alejandro Caballero
Keyword(s):  
Hyperspectral Imagery ◽  
Granulite Facies ◽  
Uranium Mine ◽  
Uranium Deposits ◽  
Geologic Mapping ◽  
Granulite Facies Metamorphism ◽  
Partial Melt ◽  
Host Rocks ◽  
Ore Grade ◽  
Extensional Structures

Abstract This study combines historical exploration data with new mapping, underpinned by airborne hyperspectral imagery, to provide a detailed camp-scale geologic view of the Rössing uranium mine area in the Damara orogen, Namibia. The Neoproterozoic Damaran metasedimentary host rocks to uranium deposits of the Rössing area structurally overlie Paleoproterozoic basement rock. Both units were subjected to polyphase deformation and upper amphibolite to lower granulite facies metamorphism during Pan-African orogenesis. The sequence was voluminously intruded by leucogranites, where younger phases may contain ore-grade uranium as magmatic uraninite and traces of betafite, together with secondary uranium minerals. Early, postdepositional modifications to the Damaran sequence included partial dolomitization of marble units and development of evaporite dissolution and diapiric breccias. Major pre-D3 extensional structures developed in conjunction with recumbent, isoclinal folding and acted to focus the intrusion of early, mostly barren leucogranites generated primarily through anatexis of Damaran metasediments. Syn-D4 leucogranites overprint complex interference fold geometries that resulted from D3 deformation. D4 leucogranites were emplaced under predominantly ductile, transtensional conditions, into NNE-trending zones oriented highly oblique to all preexisting structures. These steeply dipping zones provided the prerequisite conditions for partial melt material to be derived from uraniferous basement lithologies. The concentration of magmatic uranium was promoted where leucogranite melt material interacted with carbonates and sulfide-bearing Damaran metasedimentary units. In the Rössing area these horizons occur at the Khan-Rössing Formation contact zone for the SJ, SK, SH, Z20, and Husab deposits and within and above the Arandis Formation for the Z19 deposit leucogranites.

Mesoproterozoic graphite deposits, New Jersey Highlands: geologic and stable isotopic evidence for possible algal origins

2000 ◽  
Vol 37 (12) ◽  
pp. 1665-1675 ◽  
Author(s):  
Richard A Volkert ◽  
Craig A Johnson ◽  
Albert V Tamashausky
Keyword(s):  
New Jersey ◽  
Country Rock ◽  
Sedimentary Environment ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Stable Isotopic ◽  
Facies Metamorphism ◽  
Anoxic Basin ◽  
C Value ◽  
Host Rocks

Graphite deposits of Mesoproterozoic age are locally abundant in the eastern New Jersey Highlands, where they are hosted by sulphidic biotite–quartz–feldspar gneiss, metaquartzite, and anatectic pegmatite. Gneiss and metaquartzite represent a shallow marine shelf sequence of locally organic-rich sand and mud. Graphite from massive deposits within metaquartzite yielded δ13C values of –26 ± 2‰ (1σ), and graphite from massive deposits within biotite-quartz-feldspar gneiss yielded δ13C values of –23 ± 4‰. Disseminated graphite from biotite–quartz–feldspar gneiss country rock was –22 ± 3‰, indistinguishable from the massive deposits hosted by the same lithology. Anatectic pegmatite is graphitic only where generated from graphite-bearing host rocks; one sample gave a δ13C value of –15‰. The δ34S values of trace pyrrhotite are uniform within individual deposits, but vary from 0 to 9‰ from one deposit to another. Apart from pegmatitic occurrences, evidence is lacking for long-range mobilization of carbon during Grenvillian orogenesis or post-Grenvillian tectonism. The field, petrographic, and isotope data suggest that massive graphite was formed by granulite-facies metamorphism of Proterozoic accumulations of sedimentary organic matter, possibly algal mats. Preservation of these accumulations in the sedimentary environment requires anoxic basin waters or rapid burial. Anoxia would also favour the accumulation of dissolved ferrous iron in basin waters, which may explain some of the metasediment-hosted massive magnetite deposits in the New Jersey Highlands.

In situ LA–ICP–MS dating of monazite from aluminous gneisses: insights on the tectono-metamorphic history of a granulite-facies domain in the central Grenville Province

2014 ◽  
Vol 51 (6) ◽  
pp. 558-572 ◽  
Author(s):  
Stephanie Lasalle ◽  
Greg Dunning ◽  
Aphrodite Indares
Keyword(s):  
Age Distribution ◽  
Granulite Facies ◽  
Melt Crystallization ◽  
Metamorphic Overprint ◽  
Grenville Province ◽  
Granulite Facies Metamorphism ◽  
Metamorphic History ◽  
Fluid Infiltration ◽  
Host Rocks

In situ U–Pb dating of monazite from granulite-facies anatectic aluminous gneisses of the hinterland of the Grenville Province (Manicouagan area) is used to constrain the age of metamorphic events. Matrix grains in these rocks show complex internal textures consistent with extensive corrosion and overgrowths which are attributed to partial dissolution of earlier monazite in anatectic melt followed by new growth during melt crystallization or subsequent fluid infiltration. The new monazite data show the following: (i) inherited “pre-Grevillian” ages up to ca. 1400 Ma in some rocks; (ii) “main Grenvillian” ages in the general range of ca. 1070–1020 Ma, with a variable spread in individual samples and a general cluster at 1070–1050 Ma; and (iii) “late Grenvillian” ages at ca. 1010–990 Ma, mostly restricted to backscatter electron (BSE)-bright rims of matrix grains. The wide age range of the main Grenvillian metamorphism suggests episodic growth of monazite over a wide time span, consistent with protracted residence of the host rocks under high-temperature conditions. The clusters in the age distribution likely represent major episodes of melt crystallization in the respective rocks, following the granulite-facies metamorphism. In contrast, the growth of the late Grenvillian monazite at ca. 1000 Ma is attributed to late fluid infiltration of the host rocks under greenschist-facies conditions, coeval with ultrapotassic magmatism. It is the first report of a late Grenvillian metamorphic overprint on granulite-facies mineral assemblages in the hinterland and is consistent with the model of extensional collapse of the orogen.

A Discussion on global tectonics in Proterozoic times - Late Proterozoic cratonization in southwest Saudi Arabia

1976 ◽  
Vol 280 (1298) ◽  
pp. 517-527 ◽  
Keyword(s):  
Saudi Arabia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Granulite Facies ◽  
Greenschist Facies ◽  
Arabian Shield ◽  
Granulite Facies Metamorphism ◽  
Quartz Monzonite ◽  
Facies Metamorphism ◽  
Global Tectonics

Early cratonal development of the Arabian Shield of southwestern Saudi Arabia began with the deposition of calcic to calc-alkalic, basaltic to dacitic volcanic rocks, and immature sedimentary rocks that subsequently were moderately deformed, metamorphosed, and intruded about 960 Ma ago by dioritic batholiths of mantle derivation (87Sr/86Sr = 0.7029). A thick sequence of calc-alkalic andesitic to rhyodacitic volcanic rocks and volcanoclastic wackes was deposited unconformably on this neocraton. Regional greenschistfacies metamorphism, intensive deformation along north-trending structures, and intrusion of mantle-derived (87Sr/86Sr = 0.7028) dioritic to granodioritic batholiths occurred about 800 Ma. Granodiorite was emplaced as injection gneiss about 785 Ma (87Sr/86Sr = 0.7028- 0.7035) in localized areas of gneiss doming and amphibolite to granulite facies metamorphism. Deposition of clastic and volcanic rocks overlapped in time and followed orogeny at 785 Ma. These deposits, together with the older rocks, were deformed, metamorphosed to greenschist facies, and intruded by calc-alkalic plutons (87Sr/86Sr = 0.7035) between 600 and 650 Ma. Late cratonal development between 570 and 550 Ma involved moderate pulses of volcanism, deformation, metamorphism to greenschist facies, and intrusion of quartz monzonite and granite. Cratonization appears to have evolved in an intraoceanic, island-arc environment of comagmatic volcanism and intrusion.

scholarly journals Exotic garnet–clinopyroxene–K-feldspar granulites from the Chepelare shear zone, Central Rhodope massif, Bulgaria: implications for high-pressure granulite facies metamorphism

2019 ◽  
Vol 48 (3) ◽  
pp. 49-63
Author(s):  
Milena Georgirva ◽  
Tzvetomila Vladinova
Keyword(s):  
Shear Zone ◽  
Thick Layer ◽  
Granulite Facies ◽  
Mineral Association ◽  
Granulite Facies Metamorphism ◽  
Fine Grain ◽  
Fluid Infiltration ◽  
High Pressure Granulite ◽  
The Matrix ◽  
Homogeneous Matrix

Garnet–clinopyroxene–K-feldspar granulite occurs as a thick layer or boudin within the variegated rocks of the Chepelare shear zone in the Central Rhodope massif, Bulgaria. It consists of several domains: mesocratic homogeneous matrix (clinopyroxene–plagioclase–K-feldspar–quartz ± amphibole), porphyroblastic garnet, K-feldspar and clinopyroxene, and strongly foliated fine-grain bands (chloritized biotite–chlorite–prehnite–albite ± epidote). The origin and nature of the matrix mineral association is still unclear. The peak porphyroblast association forms at the expense of plagioclase from the matrix at higher pressure. The fine-grain deformation zones channel the lattermost fluid infiltration. The clinopyroxene-garnet and Zr-in-titanite thermometry give temperatures higher than 790–860 ºC at 2 GPa and, with thermodynamic modeling, suggests crystallization at ~1.8–2.1 GPa and temperature of ~850 ºC in HP granulite field for the porphyroblast granulite association.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

Sign in / Sign up

Export Citation Format

Share Document