The Aleksandriusk polymetallic massive sulfide deposit (the Urals, Russia)

Ores and wall rocks were studied by various modern mineralogical and geoche mical techniques using the open pit exploration data from the Aleksandrinsk deposit. Formation conditions were estimated. Rocks and ores of the deposi t are weakly metamorphosed, and preserve their primary fabrics and textures . Brecciated fabrics indicating the continuous development of an ore-formin g system, are widespread in ores. The deposition of major volume of ores oc curred at T = 160 to 340 degrees C and higher sulfur activity in a hydrothe rmal fluid (a(Sa) similar to 10(-8)...10(-12)). Abundant barite suggests a high oxidation degree of the fluid (a(O2) similar to 10(-28)...10(-35)). Sp halerite (<0.02 to 0.12 wt % Ag) (<0.02 to 0.24 wt % Ag), bornite (0.10 to 0.27 wt % Ag), as well chalcopyrite (<0.02 to 0.09 wt % Au and 0.001 to 0.0 9 wt % Ag) are principal commercial minerals as carriers of precious metals . Particles of native gold of low fineness are rather rare. Major gold loss es at a treatment of ores are related to pyrite (<0.005 to 0.022 wt % Au).