Summary:
The Raygorodok Project comprises of two open pits: South Raygorodok (SRG) and North Raygorodok (NRG).
The Raygorodok gold deposits are a type of porphyry-epithermal ore-magmatic system in the accretion continental margin.
The relation of the NRG and SRG gold deposits and association with the Raygorodok dioritegabbro-dolerite-monzonite/monzo-diorite intrusive complex is well understood on a broad scale based on geophysical studies of gravity and magnetic anomalies.
The stratigraphy and mineralization of both deposits appears to be steep north dipping. Locally, both deposits are affected by cross-cutting fault or thrust fault features that are generally not well defined by drilling.
Mineralization is not well structured. Veins are fine (cm scale), have variable orientations, and are unlikely to be through-going on the scale of the drilling. Mineralization is spatially associated with some (not all) portions of interpreted intrusive rock types and the adjacent country rock.
Both intrusive and host rock types can be mineralized. Structural controls on the berezitic alteration appear to be spatial association with the intrusive rock types, their apices, and the volcaniclastic layering.
The Raygorodok deposit is classified as an orogenic gold deposit, commonly formed in accretionary volcanogenic-sedimentary complexes. In this case, the deposit is localized within a volcanic-tectonic structure and linked to small to medium-sized intrusive bodies (e.g., diorites, monzonites).
Gold mineralization occurs in zones of berezitization with stockwork-style quartz veinlets and disseminated pyrite. Multiple generations of pyrite are associated with gold, forming fine-grained, non-persistent veinlets up to 2–3 mm thick. Sulphide assemblages include pyrite, chalcopyrite, molybdenite, and rare sphalerite and galena. Gold typically occurs as free-milling particles within quartz veins and fractures or encapsulated in pyrite grains.
Volcaniclastic host lithologies
A complex package of volcaniclastic rocks are present throughout both deposits, hosting both the intrusive rock types and mineralization. The volcaniclastic rocks (tuffites, tuffs, lithoclastic variations (volcanic breccias, tuff-sandstones, tuff conglomerates. Volcanic rocks (andesites, basaltic-andesites, and basalts) are occasionally interlayered as thin beds amongst the volcaniclastic rocks. Sedimentary rock types (conglomerates, gritstone, sandstones) are also interlayered with the volcaniclastic rocks. A typical feature of the volcanoclastic and volcanic units lies in their variability and heterogeneity, as well as strong secondary alterations. There have not been any distinct boundaries accurately established between the volcanic sequences. The complex sequence of volcanic environment rock types makes it equally difficult to interpret the complex contact metamorphic variant rock types caused by ‘‘skarnification’’ and ‘‘dioritization’’ of the rocks.
Intrusives and intrusive host lithologies
The dolerite-gabbro-diorite intrusive body of SRG consists of complex mass of several rod-shaped bodies and dykes. At SRG, thrust faulting adds additional complexity to the overall intrusive geometry.
The gabbro-diorite-monzonite intrusive body of NRG is similarly complex, but with a more definite mass to the west and dykes to the east. At NRG, some poorly drill-defined steep cross-faulting is responsible for some apparent offsets in the overall intrusive geometry.
The contours of the main SRG intrusive body are mostly uneven, sinuous, with numerous small protrusions and apophyses. The central main massif is characterized by internal heterogeneity and the presence of xenoliths and blocks of enclosing tuffites and tuff-conglomerates. Contacts with the host most of the intrusive with the contact zones (up to 3 m) of plastic deformation and flaring. The intrusives have a contact metamorphic impact on host rocks. Overprinting skarnification processes associated with dioritization (granitization) are also present.
Dolerites are the dominant varieties of intrusive rocks. A characteristic feature is an indistinct banding oriented at 40° to 45° to core axis, which is generally characteristic of the entire massif, and is retained in gabbro, gabbro-diorite and even in diorite.
Gabbro and gabbro-diorite are also widely distributed. These are regularly dyscrystalline units with fine and coarse-grained gabbro texture, containing approximately 50% of dark-coloured minerals. Porphyritic textures are far less common in the units.
Leucodiorites. This unit includes shallow vein-like, and dike-like bodies, with very rare bulges, which can be viewed as small intrusive bodies, composed of light, leucocratic, fine-grained, with fuzzy (veiled) decrystallization of rock.
Dykes of leuco-diorites and accompanying sericite-silica metasomatites are accompanied by zones of berezites. The dykes can be subject to berezitization and pyritization, and therefore can also be mineralized.
Monzonites and monzodiorites form dykes and vein-like injection bodies. These have variable thicknesses and are difficult to correlate within the succession.
Mineralization
Gold mineralization occurs in zones of berezitization with stockwork-style quartz veinlets and disseminated pyrite. Multiple generations of pyrite are associated with gold, forming fine-grained, non-persistent veinlets up to 2–3 mm thick. Sulphide assemblages include pyrite, chalcopyrite, molybdenite, and rare sphalerite and galena. Gold typically occurs as free-milling particles within quartz veins and fractures or encapsulated in pyrite grains.
Gold mineralization is predominantly composed of zones of berezitization with widely developed thin quartz veinlets, fine stringers or pockets of pyrite-quartz and disseminated pyrite. It is described in documentation as a stockwork-style of mineralization, but veinlets are relatively fine (generally up to centimetre thickness), low density, and very unlikely to be continuous on the scale of drilling. NRG mineralization seems to have less associated veining than SRG.
The zones of berezitization are more likely to define coherent zones of mineralization. Alternatively, a minor part of the gold mineralization is comprised of simple disseminated pyrite and little or no berezitic alteration. This ore type is localized in some of the sedimentary conglomerates. It is possible that this is a function of zonation of the mineralization, as the sedimentary sequences tend to overlap with the volcaniclastic rock types.
Sulphide minerals are commonly present throughout the ore zones, and form a relatively low percentage of the overall rock mass. The sulphide minerals are mainly represented by pyrite and lesser chalcopyrite. Rare sulphide minerals are documented as being pyrrhotite, marcasite, molybdenite, arsenopyrite, sphalerite, galena, fahlore, antimonite, bornite, chalcocite and covellite.
Pyrite is the most common sulphide mineral associated with gold. Several generations of pyrite occur. The latest generation of pyrite is related to the gold mineralization and forms short nonpersistent veinlets usually up to 2 mm to 3 mm thick, more rarely up to approximately 1 cm. Veinlets often form a weak stockwork system with variable orientations. Veinlets of pyrite of this generation are associated with zones of high structural deformation and intensive beresitization. Other sulphides, if they occur, are also associated with this phase of pyrite.
Gold in primary ores is documented as generally being free-milling. A minor component of gold is associated with pyrite. Angular particles of gold are encountered in quartz as well as in very small fractures and voids in pyrite. The coarsest gold grains seem to be associated with the strongly berezitic altered ore.