الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 231 |  |  |
| | | from | 231 | | |
Abstract
The present study deals with geology, petrography, geochemistry, alteration zones and their mineralization (barite veins, specularite veins, gold bearing quartz veins and calcite vein mineralizations of Wadi Makhrag El Ebl area, North Eastern Desert, Egypt. Makhrag El-Ebl area is located in the north Eastern Desert of Egypt between Latitudes 27° 49’ 20’’ - 27° 48’ N and longitudes 33° 03’ - 33° 05’ 30” E. The basement rocks of Wadi Makhrag El Ebl area are composed essentially of Pan-African island arc granodiorite rocks, Dokhan volcanics, younger granites (syenogranites, alkali granites) and post granitic dykes and veins. Granodiorite are the oldest rock unit in the study area. It is extruded by Dokhan volcanics with clear intrusive contact. Petrographically, granodiorites showing equigranular, hypidiomorphic, perthitic, graphic and piokilitic textures. It is composed mainly of plagioclase, alkali feldspar and quartz associated with minor biotite and hornblende. The Dokhan volcanics in the study area composed entirely of dacite. The Dokhan volcanics extrude the older granits and intruded by younger granits with sharp contact. Petrographically, Dokhan volcanic is unequigranular, displaying several amygdaloidal and porphyritic textures. Dacite is composed mainly of phenocrysts of plagioclase and quartz embedded in groundmass composed of very fine-grained aggregates of plagioclase, quartz, alkali feldspar, and biotite associated with minor amount of muscovite in addition to rare opaque minerals and iron oxides. Amygdales are filled with chlorite, carbonates (mainly calcite), secondary quartz and epidote. Younger granites are composed mainly of syenogranites and alkaligranites. The syenogranite rocks occupy the south western and eastern parts of the mapped area. They are massive, equigranular,medium to coarse grained. Petrographically, syenogranites is equigranular hypidiomorphic texture. It is composed mainly of quartz, alkali-feldspar, plagioclase and rare biotite. Alkali granites are characterized by equigranular hypidiomorphic texture. It is essentially composed of plagioclase, alkali feldspar, quartz, hornblende and biotite.
Auriferous quartz veins cut through the granitic and dacitic rocks with development of alteration zones. The quartz veins display two main trends, NW-SE. and NE-SW. They vary in length from few meters to more than 100 m and in thickness from very thin veinlets to more than 20 cm. The mineralogical studies accompanied by geochemical analyses for the different alteration zones revealed the existence of eight main facies include: silicification, ferrugination, chloritization, sericitization, argellic, propylitic, carbonatization and muscovite alteration. The quartz veins are massive, white and occasionally stained by iron and copper minerals. They consist mainly of quartz which carries variable amounts of gold, pyrite, native silver, hematite, goethite and barite. The altered granitic and dacitic rocks in the study area were examined using microscopic investigations, XRD, SEM-EDX analyses and whole chemical analyses of major and trace elements Two main stages of ore mineralization in Makhrag El Ebl gold deposit can identified. The early stage caused the formation of oxide (hematite), sulphide (pyrite) and barite minerals. The late stage of hydrothermal phase caused the formation of gold and silver native minerals. This paragenetic sequence minerals originated from the hydrothermal signals that produce the epigenetic ore- filled veins and fissures to the supergene enrichment processes that occurred under the surface weathering conditions. Barite veins cut the dacite and alkali granite rocks. The mineralized veins vary in length from a few centimeters to more than 300 m long. The thickness also varies from a few centimeters up to 2 m. They trend in ENE – WSW and dip steeply (65°-80°) to the southeast and usually developed along the regional fracture at Wadi Makhrag El Ebl. The barite veins are composed mainly of barite and quartz associated with subordinate amount of chalcopyrite and magnetite. Gold grade in the auriferous quartz veins pertaining to low grade (av. 2.51 g/t.) while the gold grade in the altered rocks pertaining to extremely low grade (av. 0.53 g/t.) The specularite occurs as thin vein cutting the granodiorite rocks. Ferrugination alteration zone occurs around the contact between the vein and the surrounding granodioritic rocks. Calcite vein occurs in the south western part of the study area and cutting across the granitic rocks. The calcite veins are composed mainly of calcite, barite, gold, pyrite, goethite and quartz.