DEFORMATIONAL QUARTZ TEXTURES AND MINERALOGY OF HYDROTHERMAL ALTERATION ASSOCIATED WITH INTRUSION-RELATED GOLD DEPOSITS: A CASE STUDY FROM THE ATUD AREA, CENTRAL EASTERN DESERT, EGYPT

Gold mineralization in the Atud gold deposit is mainly associated with quartz and hydrothermal veins that occupy pre-existing fractures (open-space filling). The source of the mineralized fluids is late hydrothermal solutions that resulted from intermediate magma that formed diorites. Here, we study the nature and origin of the hydrothermal fluids as well as the forms of the veins by defining the deformational textures of quartz from mesothermal quartz veins and hydrothermal alteration minerals. There are two generations of auriferous quartz in the Atud gold mine. The older generation, the mineralized one, cuts the metagabbro-diorite rocks, and some of them pinch out, trending NW-SE and dipping around 45°. It is mainly composed of bluish, coarse, or medium-grained and brecciated quartz containing an appreciable quantity of opaque minerals. On the other hand, the younger generation that crystallized later is poorly mineralized or even barren and is localized far away from metagabbro-diorite rocks; it is directed NE-SW and dips around 15° NW. It is largely composed of milky white, fine-grained, and compact quartz containing a few opaque minerals.

The mineralized veins largely exhibit bulging recrystallization (BLG) deformation with bulged and recrystallized grains at the quartz grain boundaries that occurred at temperatures of around 280 to 400°C. The quartz porphyroclastsare characterized by undulose and patchy extinctions with serrated grain boundaries and recrystallized bulges along the grain boundaries and cracks. X-ray Diffraction (XRD) data revealed that the hydrothermal alteration minerals associated with gold mineralization are mostly quartz, pyrite, sericite, Kaolinite, and dolomite with selective ankerite, chlorite, and albite.