The Arba'at Granite, Sudan: a mineralised, Pan-African intrusion enhanced by hydrothermal metasomatism

摘要: Abstract The granite at Arba'at shows many of the chemical features a metallogenetically specialised A-type granite, although no economic mineralisation has yet been found there. character is, however, only strong within aphyric granites low density forming interior intrusion. exterior is composed sparsely feldspar-phyric biotite monzogranite and there are sharp contacts between two types. petrography reveals that transition igneous mineralogy fabric was due to pervasive metasomatism, which modified all minerals textures. An early alteration stage distinguished, characterised by albitisation leaching primary micas, from later ‘oxidative hydration’, caused hematisation, clouding K-feldspar growth strongly birefringent white micas. Fluorite common minor constituent altered rocks. Chemical data show losses Ca, Fe, Mg Ti during with consequent increases in Si but significant additions alkalis. Of trace elements were overall Ba, Sr, P, Zr, Ti, V, Cu, Zn, W LREE, gains F, Rb, Th, U, Nb, Ta Y. Among ratios large Rb/Sr Rb/Ba, while chondrite normalised REE profiles developed ‘gull-wing’ pattern F-rich rich granites, severe LREE large, negative, Eu anomalies. Leaching redistribution dominated over elemental probably mass transfer into country metasomatizing agents likely have high temperature, hydrothermal solutions rendered effective F Cl. Textural relations chlorite mica suggest an interval temperature preceded onset metasomatism. Intrusion metasomatism occurred limits Pan-African thermotectonic episode (550 ± 100 Ma) time when magmatism Arabian-Nubian Shield changing orogenic calcalkaline anorogenic alkaline.