Two stage model for the Muruntau (Uzbekistan) high grade ore structures based on characteristics of gold, host quartz and related fluids
Graupner, Torsten; Kempe, Ulf; Klemd, Reiner; Schüssler, Ullrich; Spooner, Edward T.C.; Götze, Jens; Wolf, Dieter
published: Jan 21, 2005
ArtNo. ESP154018101007, Price: 29.00 €
Two types of native gold, characterized by significant differences in their distributions, mineral associations, habits and chemical compositions, have been identified in a high-grade quartz vein zone (Central veins) and in adjacent altered wall rocks in the giant Muruntau gold deposit, Uzbekistan. Scanning electron microscopy and electron microprobe analysis show that Au I occurs as isolated euhedral crystals with a narrow size range (10 to 40μm across) and limited variations in Ag contents (8.5 to 13.0 wt.%). In contrast, Au II appears as anhedral grains with a wide size range (<10 to 250μm), and is Ag-poorer in most cases (6.0 to ~ 11.0 wt.%). Two similar types of gold have been identified in the wall rocks. Within the veins, Au I precipitated simultaneously with the growth of primary quartz in dilational sites during early stages of Central vein formation. Au I precipitation occurred during microclinization of the wall rocks. A reduced ore fluid and temperatures of ~400°C are derived for this stage. High grade Au II ore shoots formed subsequently during intense deformation. Near-neutral pH values, fluid unmixing and temperatures of ~ 230° 330 °C are derived for Au II formation.