GSINET | Geological Survey of Iran , North - East Territory

Writers : Monazami Bagherzadeh; Reza
Refference : The 26th Symposium on Geoscieences;Tehran
Publishing Year : 1386

Abstract :
In this article , several listweanitic events (carbonatized ultramafic rocks) are described for description of accompaniment gold mineralization with mantle pridotites from ophiolitic complexes consequently of serpentinite hydrothermaly alteration in the Morocco ,Italy ,Arabia ,Turkey and Iran(northwest Nehbandan).�� The most of the alterations is related to late cretaceous and in the ophiolitic colored mélange. The most of listweanitization concentration has evented in along major thrust faults.
The listweanites on the base of petrology are divided to types of carbonate listweanite, silica-carbonate listweanite, breccia silicic listweanite bearing sulfide- arsenic and limonitic- hematitic oxidan zones that type of breccia silicic listweanite bearing sulfide – arsenic has high density of Au.
Mineralogy of listweanites consist of cryptocrystalline quartz, white crystalline quartz, calcite,� dolomite, ankerite, magnesite, siderite, serpentine, chlorite as major minerals, and pyroxene, chromite, magnetite, cinnabar, chalcopyrite, pyrite, bornite, arsenopyrite, Fe – oxide and secondry hydroxide as minor minerals.
Au grade in the listweanites usually is 5 to 20 time more than ultramafic host rock that has 5 ppb Au, however enrichment zones bearing sulfide- arsenic specially pyrite and arsenopyrite accompaniment to the most late quartz veins grey colore have one to 10 ppm Au and even�� more over to open space filling texture and contemporaneous with deposition of cryptocrystalline silica, and with due attention to operation of carbonatic part as geochemical bar has mineralized.
Listweanitization is resulting of hydrothermal alteration at medium temperature (150- 300oc) by hydrothermal fluids bearing Na and Cl derived from mantle material and contact to sea water.
The hydrothermal fluids forming of silicic listweanite is been enriched from SiO2, CO2, Ca, and H2O, However the type of carbonatic is poor SiO2.
The source of gold and another base and precious elements has origined serpentinized ultramafic rocks. To progress of regional metamorphic, enriched fluids CO32-, SO42-, S, Cl, As, Na, k, and B have formed complexes to metal and precious elements and consequently ascension to upper parts and near of surface (decrease of temperature and pressure and Eh and PH variation) have been deposited in the breccia zones and accompanied by deposition of silica along tectonic contact when was entered to alkaline medium of carbonatized rocks.
Preliminary isotope investigations (Buisson and Leblanc, 1985) on Moroccan�� carbonate material indicate a marked concentration of δ13C at -3 to -5 ‰ which is�� consistent with mantle derived material. 87Sr/86Sr ratios for age determination from 0.709 to 0.711 and the large range of δ18O from +10 to +25 ‰ is correspond to a complexe hydrothermal evolution and interactions with crustal material or sea water.��
Geophysical exploration research to method IP-RS on the listweanitic outcrops indicated that IP high intensity on the breccia silicic listweanites veins bearing sulfide- arsenic as compared with ultramafic host rock. Maximum anomaly extent has followed to depth of 80 m.
The study of exploration cores indicate accurate corrolate to IP-RS profiles as separation of carbonate- oxidan zone is well noteworthy lower of the upper parts of sulfide zone.
Subject List : Listwaenite, gold

Articles

Comparison of Northwest Nehbandan listwaenite with Turkey, Arabia Morocco and Italy and study of gold genesses and mineralization of Nehbandan listwaenite based on geochemistry, mineralogy, geophysices and drilling core study