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Mnogovershinnoe, Mnogovershinnyi |
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Khabarovsk Kray, Russia |
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Au Ag
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Super Porphyry Cu and Au
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The Mnogovershinnoe or Mnogovershinnyi gold deposit is located in the Nikolaevsk district of the Khabarovsk Oblast, <20 km SW of the Sea of Okhotsk coast and 675 km NNE of Khabarovsk, in the far east of Russian (#Location: 53° 56' 9"N, 139° 54' 51"E).
Four NE-SW trending zones of veining are recognised, from SE to NW, namely the Vodorazdelnaya, Glavnaya, Promezhutochnaya and Medvezhya zones, each separated by from 0.6 to 1 km over a 3 km width. Shoots within these zones shoots define at least ten orebodies: Central, Verkhnee, Olene, Middleware, South, Flank, Severnoe, Deep, Quiet and Boulder.
The deposit was discovered in 1959, but was exploited until 1991 when mining commenced. The initial 'reserve' estimates at the commencement of mining was for >80 tonnes of contained gold (Yushmanov, 2014), although this was expected to be well below the expected potential endowment (Khomich , 2018). The mine closed in 1997 as a result of poor technical and financial performance. Following a change of ownership, gold mining and gold extraction restarted in 1999. It is operated as both an openpit and underground mine.
The Mnogovershinnoe deposit lies within the Sikhote-Alin Belt of the Pacific Orogen, just east of where the north-south Sikhote-Alin Fault truncates the east-west trending Mongol-Okhotsk Suture to the west of that structure. The surrounding country rocks in the Mnogovershinnoe district comprise Upper Jurassic to Lower Cretaceous clastic sequences, unconformably overlain by Early Cretaceous and younger andesite to dacite volcanic suites and intrusive necks in local volcanic centres (Seltmann, et al., 2010). The mineralised district lies within the 30 x 30 km Bekchiul volcano-plutonic complex which was developed in two stages during the Senonian of the Upper Cretaceous and the Paleocene-Eocene. The early stage comprises a poorly differentiated andesite and granodiorite association whilst the late stage is marked by sub-alkaline monzodiorite-granite intrusions, overlain by Neogene plateau trachybasalt and trachyandesite, and intruded by syenite porphyry dykes. The early stage of magmatic activity is accompanied by the formation of thick gold-silver mineralised vein-metasomatic zones, crosscut by large dykes of the late stage, whilst the late stage is represented by tourmaline-quartz veins lacking significant precious metals (Khomich et al., 2018), but minor molybdenite, cassiterite and wolframite (Seltmann, et al., 2010).
On the orebody cluster scale, the mineralised system is associated with an east-west elongated 10 to 14 x 5 to 7 km graben-like depression in the western part of the Bekchiul volcano-plutonic complex, bounded in the north by a large, near east-west fault. The southeastern and eastern margins are fault juxtaposed with the Bekchiul granitoid massif, whilst the western boundary is overlain by Neogene to Quaternary cover. The graben is filled with Paleogene volcanic rocks, predominantly of intermediate composition. The sedimentary rocks underlying this volcanic facies fill are deformed into NE striking linear folds, the orientation of which extend into the basement, interpreted to have been inherited from the early tectonic dislocation of the volcanic structure. It is assumed that the mineralised zones are aligned withthe axial zones of these anticlinal folds (Khomich et al., 2018).
Two main fault sets are recognised, representing stress propagation occurring along earlier NE trending structures, parallel to the linear folds, and NW, normal to, and dislocating the former trend with large displacements. The dislocation fractures were almost synchronously healed with quartz-veins.
The Northeast faults are steeply dipping dislocations, with displacements that resulted in a block-faulted step-like structure of the district and an increase in thickness of the volcanic units with distance from the Bekchiul granodiorite to granite massif. Zones up to 100 m wide of extensive vein systems carrying gold-silver mineralisation and flanked by metasomatic halos are restricted to these faults. These zones have strike lengths of as much as 5 to 7 km and occur within volcanic rocks. They extend into the basement to a depth of several hundred metres. Of these, the Vodorazdel'naya Zone, closest to the Bekchiul pluton, has been most deeply eroded, whilst the intermediate Glavnaya zone is partly preserved and the distal Promezhutochnaya zone is little eroded. The Medvezh'ya zone, 3 km to the NW, farthest from the pluton, is largely unaffected by erosion, with a upper lateral extension of the zone preserved as a halo of metasomatic alteration (Khomich et al., 2018).
The Northwest faults are oriented normal to and offset ore zones into several segments at differential erosion levels. The central segments are less eroded, whilst the flanks have been more uplifted and underwent stronger denudation. These faults also control the distribution of late stage tourmaline-quartz veins that do not contain significant precious metal concentrations. Dykes, dyke-like bodies and intrusions that crosscut the volcanic structure are also oriented NW. The largest of these intrusions, represented by 77 to 66 Ma granodiorite-porphyries, divides the mineralised system into two domains, with the bulk of the ore-bearing zones to its NE. Those to its SW are oriented both NE and NW (Khomich et al., 2018).
Mineralisation occurs as complex steeply dipping, thick, tabular quartz veins with lateral extents of up to 100 m, encased within halos of biotite-epidote-albite and biotite-free sericite-chlorite-epidote-albite alteration facies (Khomich et al., 2018).
The alteration halo in the hanging wall, adjacent to the quartz veins, is several tens of metres thick, whilst that in the footwall is composed of light-grey quartz with varying amounts K feldspar and sericite. The upper parts of the quartz veins contain pyrite, chlorite, albite, sericite and K feldspar. The veins are composed of fine-grained quartz with varying adularia, sericite and ore minerals. The adularia and sericite are normally dispersed in the quartz aggregate of the veins, forming either nest-like accumulations or local banding (Khomich et al., 2018).
Ore minerals include sulphides, sulphosalts, tellurides and native gold occupying ≤0.5 to 3 vol.% of the vein, occurring as thin and finely dispersed disseminations, and rarely as streak-like segregations, or nest-like accumulations. The ore mineralisation is characterised by an accompanying wide spectrum of mineral species with low sulphide contents. The sulphides include pyrite, which dominates, together with chalcopyrite, galena and sphalerite, with sporadic pyrrhotite and arsenopyrite. Subordinate sulphosalts form 'grey ore' (pearceite-polybasite) and tellurides (hessite, petzite). Rare tellurobismuthite, altaite, scheelite and the selenides naumannite, telluroselenides of silver and galena-clausthalite are also present (Fatyanov and Sapin, 1988). Irregularly distributed native gold has a fineness varying widely from 650 to 925 (Khomich et al., 2018).
Explosive breccias with cementation of fragments by quartz, adularia-quartz, and in some cases, carbonate-quartz aggregates has been identified. Adularia occurs in two varieties, either as intermediate orthoclase in the areas of brecciation; or as high and intermediate microcline within the aureoles of recrystallised quartz, fringing the brecciated areas (Fatyanov et al., 1989). Carbonate filling is represented by small lens-like carbonate bodies in the veins representing the final stage of hydrothermal activity. In the Glavnaya Zone, they are composed of dolomite, whilst in the Promezhutochnaya Zone they are calcite, usually Mn-bearing. Where cut by subalkaline granitoids intruded within the northwestern faults, veins containing carbonates have been subjected to skarn alteration, now preserved in breccia fragments. Carbonate precipitation may have continued after intrusion, as inferred from the presence of lenses of calcite with pyrite, galena, and sphalerite in the Glavnaya Zone without evidence of skarn formation (Khomich et al., 2018).
Where present skarn-like Mn, Fe and Mg-Fe metasomatic zones represent late-stage hydrothermal activity, usually developed at the contact between quartz veins and altered volcanic wall rocks. The Mn-rich skarns are dominated by wollastonite, bustamite and rare rhodonite, with subordinate spessartite, grossular-andradite, Mn-bearing diopside and axinite, with associated galena, iron-free sphalerite (cleiophane) and locally 820 to 890 fineness gold. The Fe-rich skarns comprise andradite-grossular garnet, diopside-salite pyroxene, and magnetite, with local variable tremolite-actinolite series amphibole, epidote, quartz, calcite and hematite. In addition to the oxides magnetite and hematite, this alteration is also accompanied by sulphides in the form of pyrite and chalcopyrite. The Mg-Fe metasomatic domain includes diopside and diopside-salite pyroxenes, tremolite-actinolite amphiboles, epidote, serpentine and magnetite, and in addition to dominant magnetite and pyrite, high-fineness gold (93.6%) and tellurobismuthite occur (Khomich et al., 2018).
The late stage intrusions have contact-metamorphosed veins within their aureole. Where in contact with monzo-granodiorites, dense fine-grained quartz is transformed into semi-transparent coarse-grained, up to 5 to 7 mm, quartz aggregate containing emulsion-like coatings of K feldspar, gradually transitioning away from the contact to fine-grained sugary quartz aggregates. Within the same zone, the country rock is converted into hornfels with the development of a biotite-amphibole-K feldspar assemblage (Khomich et al., 2018).
Late stage tourmaline-quartz superimposed on the main vein zone occurs as quartz with variable tourmaline and rare feldspar, usually as streaks and veinlets with a NW orientation, orthogonal to the ore zones (Khomich et al., 2018).
The Mnogovershinnoe deposit combines features of epithermal mineralisation overprinted by higher temperature mineralisation. There appears to be a vertical zonation in the distribution of Au and others ore-forming elements, characterised by Mo, Sn and locally W, Cu, Ni and Co at deeper levels, grading upwards to anomalous Pb, Zn, Ag and Au at shallower levels. The individual deposits are characterised by a maximum in the thickness of the quartz veining and alteration halos at deeper and intermediate levels, decreasing to shallower levels, before splitting into several vein-like bodies, and finally into a series of veins. Significant decrease in thickness also occurs downward from the main ore zone (Khomich et al., 2018).
There is also a lateral zonation in alteration halos surrounding the quartz veins, specifically, i). an inner zone composed of quartz with variable quantities of sericite and K feldspar; ii). an outer zone within the country rock comprising sericite, K feldspar, albite, chlorite and pyrite; iii). lateral zoning developed in the Mg-Fe skarn alteration zone developed within dolomite near their contact with the hydrothermally altered andesitic tuffs, with a zonation of serpentine, tremolite, diopside and actinolite-epidote facies as the tuffs are approached. The first three minerals formed in dolomites, whereas the fourth occurs in the andesitic tuffs. As referred to above, at shallower levels along the veins and alteration halo, the carbonate has a marked change in composition from dominantly dolomite at depth, to calcite, usually at shallower levels, usually Mn-rich. This zonation also affects the skarn mineralogy, with Mg-Fe skarn assemblages in dolomites, Mn-skarn forms from Mn-bearing calcites, and Fe skarn in the quartz-rich zones. The mineralisation also vertically zoned, from i). a gold-sulphosalt-sulphide association at depth [Au:Ag = 1:0.5 to 13.6], to ii). gold-sulphide ore at shallower levels [Au:Ag = >1:0.5]; grading upward to iii). a gold-telluride-sulphide association [Au:Ag = 1:0.5 to 3], and finally to iv). telluride-sulphide [Au:Ag = 1:3 to 1:10] (Fatyanov et al., 2007; Khomich et al., 2018).
The bulk of the gold (92 to 96%) and silver (80 to 90%) occurs in a free form, amenable to standard cyanidation leaching (Mining Weekly September, 2014).
Reserves and Resources
• The initial 'reserve' estimates at the commencement of mining was for >80 tonnes of contained gold (Yushmanov, 2014), although this was expected to be well below the expected potential endowment (Khomich , 2018). Seltmann et al. (2010) suggest the potential is >100 tonnes of contained gold.
• Total measured, indicated and inferred mineral resources as at December 31, 2013 (Mining Weekly September, 2014), were estimated as:
16.33 Mt @ 3.4 g/t Au for 55.5 t of contained gold.
• JORC compliant Mineral Resources (Highland Gold Mining Limited website Reserves and Resources report), as at 31 December, 2019, were:
Measured + Indicated Resource - 7.863 Mt @ 3.0 g/t Au;
Inferred Resource - 6.000 Mt @ 3.2 g/t Au;
Total Resource - 13.863 Mt @ 3.1 g/t Au for 43 t of contained gold.
The most recent source geological information used to prepare this decription was dated: 2018.
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.
Mnogovershinnoe
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Selected References:
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Khomich, V.G., Boriskina, N.G., Fatyanov, I.I. and Santosh, M., 2018 - Characteristics and genesis of the Mnogovershinnoe gold-silver deposit, SE Russia: in Ore Geology Reviews v.103, pp. 56-67.
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Seltmann, R., Soloviev, R., Shatov, V., Pirajno, F., Naumov, E. and Cherkasov, S., 2010 - Metallogeny of Siberia: tectonic, geologic and metallogenic settings of selected significant deposits: in Australian J. of Earth Sciences v.57, pp. 655-706.
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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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