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The Samarchuk gold deposit is located in the south-western spur of the Chatkal ridge (Uzbekistan) and constitutes one of the ore occurrences within the Kyzylalmasai orefield. The ores are hosted within rocks that are strongly altered (here called metasomatites). Within and enclosing the orebody there are a large group of genetically heterogeneous metasomatites which were the result of hydrothermal-pneumatolytic and hydrothermal processes manifested at different times during the ore-forming process and at different scales. The oldest metasomatites within the orefield relate to hydrothermal pneumatolytic processes associated with formation of a granitoid massif. They are commonly pegmatoid in character and consist of muscovite-quartz - feldspar and have an irregular lens or vein-shaped form. They are coarse-grained, are not zoned and do not contain ore minerals. The periore metasomatites are related to processes of hydrothermal ore formation and are mainly observed in the basement rocks. Their distribution shows control by the Kyzylalmasay and Karabau faults and associated feather jointing; these zones display evidence of multiple deformation. They are variegated and often contrast with the rocks away from the fault zones in terms of their physicochemical and mechanical properties. In addition, granitoids, the products of dislocation metamorphism, associated with dikes of varied composition, and fault breccias are observed. All of these have contributed to the complex structure of the periore metasomatites. The Samarchuk ore deposits contain two distinct mineral associations: 1.Quartz-gold-pyrite 2.Quartz-carbonate-gold-telluride-base metal sulphides. The proportion of ore minerals in ores of the Samarchuk deposit varies greatly, from fractions of a percent up to tens of % within individual ore pockets. The major ore minerals (sulphides) appear to have been significant concentrators of gold and are often the matrix for inclusions of rare microminerals. Pyrite, one of the key ore minerals, is recognized in the form of impregnations and pockets. Along with other sulphides, it is also recognized in the form of colloform-banded formations within explosive breccias. Spectral, chemical and neutron-activation analyses of pyrite concentrate have been performed. It should be noted that there are very high contents of gold with the Au:Ag ratio as high as 13.3:1. There are also increased concentrations of Se and Te (Se/Te = 1:3.6). The pyrite always contains significant admixtures of Cu, Pb, Zn, and to a lesser extent, As, as well as increased Bi and Sb and a Co:Ni ratio of 1:3.2. Mo, W and Sn are rarely present in significant concentrations. Sphalerite is also an abundant ore mineral and displays no unusual physical properties: it can be considered as typical ?marmatite'. Admixtures of importance include Cd, rarely In, Mn, Sn, Ge, Sphalerite is Fe-rich and consistently is black in colour.
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