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Sekisovskoye, Sekisovka
Main commodities: Au Ag

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The Sekisovskoye or Sekisovka gold deposit is located adjacent to Sekisovka village, 40 km north of Ust Kamenogorsk, on the north-western margin zone of the 40 000 sq. km Palaeozoic Rudny Altai metallogenic province that occupies the eastern border of Kazakhstan and the Altaisky region of Russia.

The deposit was discovered in 1833 and has been mined on an intermittent basis up to 1946. Between 1978 and 1982 the oxidised area of ore body was also exploited via an open pit worked to a depth of 35m to produce a total of 3.4 t of gold and 3.43 t of silver.

The Sekisovskoye deposit is located in the Rudny Altai block and the Charsk Gold belt of the Greater Altaid and Transbaikal-Mongolian Orogenic Collage. The Rudny Altai is essentially a tectonically disrupted segment of one of the continental scale magmatic arcs developed within the Palaeo-Asian ocean during the Lower to Mid Palaeozoic. It was subsequently amalgamated through subduction and collision, accretion and lateral translation into a single Hercynian collage as part of the Central Asian Orogenic Belt. The Rudny Altai block is essentially composed of Devonian to Carboniferous felsic to lesser mafic volcanic, volcano-sedimentary and intrusive rocks overlying a metamorphosed Lower Palaeozoic basement. It trends NW-SE, is ~100 km wide, and is bounded by two major structures, the continental scale transverse Irtysh Fault to the SW, and the NE Shear Zone to the NE (Kruk et al., 2014).

The Sekisovskoye deposit is associated with the Zmeinogorsky Complex, which constitutes the most significant Late Devonian intrusive of the Rudny Altai Block. The complex is subdivided into four phases from earliest to latest: i). gabbro and diorites; ii). melanocratic amphibole-biotite plagiogranites; iii). biotite plagiogranites; and iv). biotite plagioleucogranites. All are represented by sub-alkaline varieties, exhibiting features of volcanic arc granites that are enriched in Rb, Th, Pb and K and strongly depleted in Sr, P and Ti.

The age of the granitoids of the Zmeinogorsky Complex obtained from zircons from 3 plagiogranites by U-Pb isotopic SHRIMP-II are Late Devonian (378±6; 376±3, and 371±2 Ma; Kruk et al., 2014). It is exposed as a series of partially connected bodies over an area of ~200 x 100 km, intruding Siluro-Devonian turbidites, Devonian subduction-related volcanic sequences and other Devonian granitoids, as well as being overlain by Carboniferous continental deposits and intruded by Carboniferous granitoids.

According to Dolgopolova et al. (2016), the ore deposit at Sekisovskoye lies within the Zmeinogorsk Complex, and occurs as hydrothermal gold-telluride-sulphide ore, closely associated with explosive fluid-breccias. These breccias include both hydraulic fracturing and breccia pipes with diorite, gabbro and plagiogranite clasts cemented by a propylitic and beresitic altered (feldspar alteration to a fine altered aplite like mass) groundmass that host the mineralisation. Mineralisation occurs as large tabular orebodies, controlled by NW striking faults and zones of dislocation and extreme deformation characterised by cataclastic to mylonitic rock textures.

U-Pb zircon crystallisation ages for the plagiogranite pluton hosting the Sekisovka gold deposit are 368.4±4.2 Ma, similar to intrusions of the adjacent Zmeinogorsk complex, whereas the age of leucogranite porphyry dykes with abundant pyrite within the deposit area is 304.5±2.6 Ma (Naumov et al. 2013).

Mineralisation within these brecciated tabular orebodies occurs as stock-works, breccia-matrix disseminations, medium sized veins, lenses, small veins, pipes and dykes, and occasionally also in isolated lenses or veins. Individual breccia ore bodies are elongated, with dimensions of ~40 x 100 to 120 m, and locally up to 500 m in plan area, and have been traced to depths of at least 950 m in drilling. The true thickness of the tabular ore zones varies rapidly, both along strike and down dip, with a maximum of 45 m. Most of the ore zones are parallel to sub-parallel to the breccia pipes within which they lie, and dip at between ~65 to 80° to the NE. These tabular zones may be continuous over vertical intervals of up to 700 m and up to 150 m along strike. There are around 245 separate mineralised zones above the 250 m below surface level, with even more below that depth.

Gold is associated with both hydrothermal alteration of the breccia matrix and with hydrothermal sulphide veining. A high percentage of the gold occurs as intergrowths and as free grains, with only a minor amount locked within sulphides. The gold particles can be coarse (up to 0.4 mm), with an erratic grade distribution.

The variability of the hosting magmatic units, the complex morphology of the orebodies and rapid changes in alteration style are interpreted to reflect a turbulent magma-fluid system evolving at a shallow (sub-volcanic) crustal level where pressure fluctuations triggered mineralisation pulses. Gold is irregularly distributed and embedded in the cementing mass of the explosive hydrothermal breccias and tends to concentrate at the geological boundaries between breccias and igneous rocks (Dolgopolova et al., 2016).

JORC compliant ore reserves and mineral resources in 2007 included:
    Total indicated and inferred resource - 29.34 Mt @ 2.7 g/t Au, 3.8 g/t Ag;
    Open pit probable reserve - 4.19 Mt @ 1.6 g/t Au, 0.5 g/t Ag;
    Underground probable reserve - 0.083 Mt @ 5.1 g/t Au, 0.2 g/t Ag.

JORC compliant ore reserves and mineral resources in December 2013 (Goldbridge Resources plc website, 2016) were:
    Total indicated + inferred resource to -800 m at a 2.46 g/t Au cut-off - 33.90 Mt @ 4.72 g/t Au, 6.99 g/t Ag (=159.9 t Au, 109.5 t Ag);
    Probable reserves to -400 m - 17.25 Mt @ 4.09 g/t Au, 5.37 g/t Ag (=70.3 t Au, 92.4 t Ag).

The most recent source geological information used to prepare this decription was dated: 2016.     Record last updated: 23/4/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Dolgopolova, A., Mizerny, A., Mizernayab, M. and Seltmann, R.,  2016 - The Sekisovka gold-telluride deposit in Eastern Kazakhstan: tectonics and magmatism: in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v.125, DOI: 10.1080/03717453.2016.1166623

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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