Petrology, geochemistry and uranium mineralisation of post-collisional magmatism around Goanikontes, southern Central Zone, Damaran Orogen, Namibia

The Goanikontes area lies within the southern Central Zone of the northeast trending branch of the Damara Orogen. The cover succession around Goanikontes, which comprises Etusis to Chaos Formation metasediments, is in tectonic contact with older pre-Damaran basement rocks. The area can be divided into three structural domains with basement in the east, a northeast-plunging anticline of Damaran metasediments to the west and a high strain zone up to I km wide that separates them and truncates the anticline. The high strain zone has provided an important focus for the emplacement of sheeted granites adjacent to the basement-cover contact. Goanikontes is also one of several significant uranium anomalies within the Damaran Orogen, and the excellent 3D exposure of the Swakop river has provided evidence for an interpretation of the tectono-metamorphic setting of magmatism and mineralisation. The granitoids have been divided into equigranular granites and sheeted leucogranites. The sequence of emplacement of the equigranular granites is from red syenogranite (534 +/- 7 Ma) to later grey monzogranite (517 +/- 7 Ma) with foliated basement-hosted granite of probable time equivalence to the syenogranites, Each type can be distinguished on major- and trace-element geochemistry. The later sheeted leucogranites, which are volumetrically the most important. intrude both basement and cover rocks. These have been divided into six distinct types based on field characteristics and structural setting backed by geochemical data and fluid extraction analyses. The earliest type A are irregular in form, boudinaged and folded by D-3, and geochemically distinct with notably low HFSE: type B's are white, weakly foliated, folded by D-3. garnetiferous and highly peraluminous; type C are tourmaline-bearing, occasionally boudinaged and exhibit the typical sheet-form within the cover rocks. Of the post-D-3 sheets, type D, which is restricted to the high strain zone is characterised by smoky quartz. high radioactivity and often by visible betafite or beta-uranophane; type E, the dominant type within the high strain zone contains prominent oxidation haloes and type F is red in colour. coarsely pegmatitic and has the highest concentration of alkalis. The uranium-mineralised type D sheets have consistently higher fluid and CO2 content than other sheeted leucogranites. The close correlation between sheet type and uranium abundance, supported by linear trends on LIL plots suggests that the distribution of radiogenic elements is primarily magmatic with more recent meteoric re-distribution, rather than due to substantial hydrothermal modification (C) 2002 Elsevier Science Ltd. All rights reserved.</p

Spinel-bearing assemblages adn their metamorphic significance from the Central Zone of the Damara Orogen, Namibia.

The Central Zone of the Damara Orogen in Namibia is dominated by intrusive granitoids and upper amphibolite to granulite-facies metasediments. High-temperature low-pressure mineral assemblages near the Atlantic Coast have not been previously described with spinel symplectites. In semi-pelitic gneisses, the symplectites are composed of hercynitic spinel and Fe-Ti oxides occurring within the cores of zoned porphyroblasts of antiperthite + sillimanite. In pelitic schists, hercynite-sillimanite symplectites occur together with minor quartz in the core of Mg-cordierite porphyroblasts (X-Mg = 0.66-0.72). Thermobarometry determines the P-T conditions of spine] symplectites to be 527 +/- 112 degreesC and 4 +/- 1 kbar. Textural relationships indicate that the symplectite post-dates the metamorphic peak conditions dated by syn-metamorphic granite at 534 +/- 7 Me (published U-Pb zircon age) but are still relatively early within the metamorphic history. Subsequent isobaric regional heating and partial melting occurred in association with biotite breakdown and garnet growth. Thermobarometry gives 700 +/- 50 degreesC and 4 +/- 1 kbar for this episode. This regional isobaric heating is equated with the emplacement of voluminous granitoid magmas, dated at post-534 +/- 7Ma and pre-508 +/- 2 Ma (published U-Pb zircon and monazite ages) and generated during decompression caused by the exhumation of the Central Zone. The system then cooled through 550 +/- 25 degreesC and 2 +/- 1 kbar at 465 +/- 5 Ma (published Rb-Sr and Ar-40/Ar-39 biotite-muscovite ages) on its way to the surface. The occurrence of a later separate thermal overprint as evidenced by spinal symplectites and garnet growth argues in favour of a two-stage metamorphic model. This study confirms the clockwise P-T path for the Central Zone of the Damara Orogen. (C) 2001 Elsevier Science Limited. All rights reserved.</p

Lamprophyric dykes in the Bushveld Complex: the lithospheric mantle and its metallogenic bearing on the Bushveld large igneous province

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Abstract from the winter meeting of the Geological Society's Mineral Deposits Studies Group, held on 4–6 January 2016 at University College Dublin, Irelan