International Geologiical Congress - Oslo 2008

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MRD-13 Ore deposits associated with black shales: from their origin to their environmental impacts

 

Gold-sulphide ores in black slates of the Amantaytau deposit (Uzbekistan): Geology, ore composition, micromineralogical features

 

Alexander Jukov, National University of Uzbekistan Named After Mirzo Ulugbek (Uzbekistan)
Marina Zavarzina, National University of Uzbekistan Named After Mirzo Ulugbek (Uzbekistan)
 

 

The Amantaytau gold deposit, which is located 15 km south of the Muruntau deposit, is hosted by rocks of the Auminzabesopan age (O3-S1bs4). Metasomatic change in rocks within the Amantaytau gold ore zone is silicification, carbonatization, albitization, sericitization and chloritization. Silicification is revealed throughout the ore zone along the faults controlling the location of ore bodies shown as veins, stockworks and lenses of quartz with carbonates and albite. The gold deposit consists of two separate sections, which differ in composition and technological properties of ores: the Centralny section presents the secondary ores of oxidation of the deposit and the Severny section containing the primary (sulphide) ores, which are located under Mesozoic to Cenozoic cover rocks. Of principal commercial value are the primary ores, comprising nearly two thirds of the reserves of the deposit.
At the Severny section the primary ores are made up of altered aleurolites and sandstones from dark-grey to black colour with impregnation, veinlets and veins of sulphides. The main minerals are pyrite, arsenopyrite, chalcopyrite, galena, sphalerite, quartz, feldspar, micas, carbonates with rutile, sphene, graphite etc. On the whole gold-bearing capacity of the primary ores is determined by intense development of the gold-pyrite-arsenopyrite association. Of secondary importance is Ag-Sb mineralization.
The study of primary ores has been conducted using the mass-spectrometre technique in the inductive-related plasma (ICP MS ELAN DRC II) and electron-probe microanalyzer Jeol Superprobe JXA 8800R.
The study of ores has revealed a wide occurrence of silver and antimony minerals: acanthite, miargyrite, polybasite, freirbergite, naumannite etc. in the form of microinclusions in antimonite, pyrite and arsenopyrite. Aurostibite was found in silver-antimonite association.
Geochemical series of intensity of element accumulation with respect to clark shows that in the sulphide ores of the Severniy section at the Amantaytau deposit are enriched in As, Te, Sb, Ag, Bi, Hg, along with Au. The dominance of arsenic is due to the fact that the chief minerals of sulphide ore at the deposit are arsenious pyrite and arsenopyrite.
When compared with the Muruntau ores, the studied ores contain less W and Bi, but more Te, Sb, Ag and Se. Mineralogical and geochemical studies show that the ores at the Amantaytau deposit were formed at lower temperatures and are located at a higher crustal level than the Muruntau ores.

 

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