Structural Control, Metamorphic Evolution and Genesis of the Gold Mineralization of Abu Khalag area, Central Bayuda Desert, River Nile State, Sudan.

Abstract

The study area constitutes part of east central Bayuda Desert; it lies about 400 Km North of Khartoum. It is composed of gneisses, schists, quartzites, calcsilicate rocks, marbles and amphibolites, which are metamorphosed under greenschist facies of regional metamorphism. These rocks were subjected to folding, shearing and fracturing accompanying metamorphism. The results of Abu Khalag rocks geochemical data show tholeiitic trends of high- grade amphibolites which indicate oceanic environment. The low-grade metavolcanosedimentary rocks show a calc-alkaline affinity, which suggests an island arc paleotectonic environment. The syn-tectonic intrusions have calc-alkaline affinity indicating a subduction related emplacement setting. The low-grade metasediments show a shelf environment of deposition. i Syn to late-granitoid intrusions were emplaced in weak planes of the above- mentioned units and have local thermal and metasomatic aureoles. Field observations have indicated that most of Au mineralized quartz veins in the study area are structurally and lithologically controlled. The auriferous quartz veins can be sub-divided into two phases, occupying fault planes, schistosity, bedding and traces of axial fold planes in permeable and reactive amphibolites and calcsilicate host rocks. The structural, mineralogical and geochemical characteristics together with the style of wall rock alteration of the investigated auriferous quartz veins suggest that they belong to the mesothermal type of gold mineralization. The study involves collecting samples of quartz veins and stream sediments. The background and threshold values are proposed for quartz veins as 0.2 ppm and 0.57 ppm respectively, and for stream sediments as 0.041 ppm, 0.3 ppm respectively. This study indicates that the trace elements Cu, Pb and Zn have greatest potential as indicator of gold mineralization and pathfinders.