Ore-forming mechanism and its relationship with deformational and metamorphic episodes at Haimur gold mine, Nubian Shield, Egypt

Abstract

<jats:title>Abstract</jats:title> <jats:p>The Haimur area represents the central part of the Wadi Allaqi region in the southern block of the Egyptian Eastern Desert near Nasser Lake and the Nile valley. It is made up of ophiolitic assemblage comprising serpentinite and talc carbonate, listwenite, metagabbro/amphibolite and metabasalt and island arc assemblages. The orogenic gold deposits in the Haimur area occur in the form of smoky/white sulphide-bearing quartz / quartz-carbonate veins or lenses cutting through the listwenite zone-related rocks. The NE-trending auriferous veins were formed due to an extensional to transtensional shearing related to NW Najd shear tectonics. Gold was observed in association with late-pyrite and chalcopyrite paragenetically formed in the gold phase (second phase), while the first phase is the sulphide phase including early-pyrite and arsenopyrite. Arsenopyrite was formed during early metamorphic recrystallization at a high-temperature range between 405 and 512 °C. However, gold was formed at lower temperature through retrograde metamorphism. Three types of fluid inclusions have been recognized: aqueous (type-I), mixed aqueous–carbonic (type-II) and hydrocarbonic (type-III). The <jats:italic>P</jats:italic>–<jats:italic>T</jats:italic> conditions of trapping were obtained from the isochore lines of intersection between <jats:italic>T</jats:italic> = 300–320 °C and pressure range of 60–180 MPa. The Haimur gold deposit was supposed to be derived from metamorphic fluids created by dehydration and decarbonation of ophiolitic mélange assemblages and volcano-sedimentary rocks, in which the gold was transported as Au(HS)<jats:sup>2–</jats:sup> complexes and precipitated in reduced environment. The strong linkage between the deformation and metamorphism triggered gold deposition in structurally favourable sites related to the Najd fault system.</jats:p>

Geology, fluid inclusions, mineral and (S-O) isotope chemistry of the Badran orogenic Au deposit, Yana-Kolyma belt, eastern Siberia: implications for ore genesis

“…The obtained parameters are typical for the Phanerozoic orogenic deposits (Wilkinson, 2001;Goldfarb and Groves, 2015). In low-and moderately-saline fluids, the sulfide (HS¯) complex can be the major agent for gold transportation in hydrothermal fluids in the Badran gold deposit (Monsef and Abdelnasser, 2021). The change from the early stages to the late stages of the P-T parameters of the ore fluid, its cooling, pressure reduction, and interaction with surrounding rocks leads to a decrease in the solubility of gold, destabilization of Au(HS) 2 , gold precipitation in association with sulfides Fe, Pb, Zn, and Cu.…”

Origin and Evolution of Ore-Forming Fluids at the Small-Sized Gold Deposits in the Khudolaz Area, Southern Urals

“…We consider intrusions of the Khudolaz and Ulugurtau complexes as the main source of gold. We believe that the gold was transported as bisulfide complexes (e.g., Au(HS) 2 − ), as evidenced by the mesothermal regime of fluids and widespread sulfides in quartz veins [55,59]. Hydrothermally altered rocks of the Khudolaz and Ulugurtau intrusions with sulfide mineralization can be considered the main sulfur sources [25].…”

“…It is often difficult to differentiate magmatic and metamorphic fluids in their composition and PT parameters. The typical metamorphogenic fluid is considered to be rich in CO2 and shows a relatively weak salinity [6,54,55], while quartz veins produced by this fluid commonly display negative Eu-anomalies and low REE values (ΣREE < 0.n ppm) [42,[56][57][58]. Fluids of the studied minor deposits show weak to moderate salinity, low to moderate Coexisting single-phase gas, fluid and more concentrated two-phase inclusions indicate the heterogenization of the fluid [52], which can be a reason for gold precipitation in quartz veins [53].…”