Suhoyloge(суXOклог, also translated as "dry valley") deposit is a precious metal deposit occurring in black rock series, located in Irkutsk region of eastern Siberia, Russia. 196 1 year, and a large amount of precipitation occurred in 1970s. It has been proved that the deposit contains not only a large amount of gold, but also platinum, palladium and silver. At present, the technical and economic evaluation of the deposit before development is under way. As of June 2005, 65438+1 October1,the mineral deposits listed in the Russian national reserve balance table are 38 1.72× 1.04t, of which Au1.041.2t. 73g/t and Pt 0. In the recent technical and economic evaluation, it is also calculated that Ag is 154 1t, and the Ag content in the ore is about1~ 2g/t. ..
Sukhoiloge is the largest primary gold mine in Russia at present. In addition to Sukhoiloge deposit, some small gold deposits of the same type with small reserves have been discovered in this area.
Although Sukhoiloge deposit is a precious metal deposit in black rock series, it contains many precious metals due to its large scale. Therefore, after we explain the prospecting model of black rock series gold deposits, we will introduce the prospecting model of this mine again.
Second, the geological characteristics
1. Regional geological background
Sukhoiloge deposit is located in Bodebo syncline. As shown in figure 1, Bodebo syncline is composed of metamorphic sedimentary rocks of early, middle and late Li Fei era, and unconformity covers Archean-Proterozoic metamorphic rocks.
The strata in the early rift are subdivided into Pulboer Formation and Medewezevsk Formation. The former is composed of conglomerate, sandstone and shale in greenschist facies, while the latter is composed of volcano and volcanic-terrigenous rocks. Andesite, andesite-basalt and tuff interbedded with sandstone, conglomerate and iron quartzite.
The stratum in the middle of the rift valley starts from Balaganahe Group and is 2500m thick. It is mainly composed of terrigenous gravel-sand-silty sedimentary rocks, followed by calcareous sandstone and limestone. The sedimentary rocks of Rifidenigray Group in the middle and late stage are subdivided into Buzhuyita Formation, Ugohan Formation, Homohuo Formation and Yemniah Formation. Although the thickness usually decreases due to strong plastic deformation, their total thickness can still reach1500 m.
The rhythmic layered sandstone, shale, carbonaceous shale, limestone and sandstone of Wendeji Bodebo Group have a total thickness of 2,500m, and the Neoproterozoic strata have ended. The characteristic of this area is that terrigenous carbonaceous rocks are rich in organic matter. The deposition period of carbonaceous sediments in the middle and late Rifeida is the strongest. The content of organic matter gradually increases from carbonate rocks to sandstone until argillaceous rocks, followed by strata with normal sedimentary sequence.
Foreland basins related to the intracontinental rift system may have developed and formed in the middle and late rifts. Continental carbonaceous rocks were formed in continental margin basins. A small amount of early volcanic rocks interbedded with coarse clastic rocks and iron quartzite. At the same time, ophiolite assemblage including ultrabasic rocks and tholeiite was formed nearby, which further developed during the formation of early Paleozoic syncline. The complex structure of syncline is caused by the interaction of shallow folds and destructive low-angle fault zones.
The biotite subfacies metamorphic to greenschist facies in the central syncline. The surrounding rocks have undergone regional metamorphism of epidote-amphibole and amphibole facies, accompanied by the formation of granite gneiss dome and new granite plutonic rocks.
Magmatic rocks related to the Middle Paleozoic Kunkude-Mamakan complex occur near the Sukhoiloge deposit. Konstantinovsk rock mass is located about 6 kilometers southwest of the deposit. Large Paleozoic granite intrusions, such as Cegedakar pluton, are exposed around Bodebo syncline.
Map 1 Geological map of Sukhoiloge mining area in Russia (quoted from V. V. Distler et al., 2004)
2. Geological characteristics of the deposit
Sukhoiloge deposit is located in the axial part of the inverted anticline (Figure 2), and its bedding is inclined to the west with an inclination angle of 5 ~ 20. The axis of the anticline is gently inclined, and the strike changes from east-west to northwest with an inclination of 30 ~ 40. The normal wing inclination in the north is15 ~ 30, and the inverted wing inclination in the south is 30 ~ 50. There is a fault zone on the axis of the fold, where the thickness of the ore-hosting rock becomes smaller and deformed. There is an overthrust fault zone in the south wing of the ore field.
Fig. 2 stereoscopic map of geological structure and gold distribution of Sukhoiloge deposit in Russia (quoted from V. V. Distler et al., 2004).
Fig. 3 Location map of gold mineralization geological structure of Sukhoiloge deposit (Yinjiu11Al Kapnehko et al., 2008).
Gold mineralization is mainly distributed in Homor Huo Formation, which consists of thin black schist and siltstone, and there is also a small amount of low-grade gold mineralization in carbonate schist and siltstone at the bottom of Yemniah Formation (Figures 2 and 3). Ore-bearing surrounding rocks can be subdivided into three types: timely carbonate sericite schist, siderite schist and timely siltstone or shale schist. Due to regional metamorphism and metasomatic alteration, the shale area is transformed into greenschist facies, the carbonate terrigenous sediments rich in organic matter are transformed into syenite-sericite schist, and the carbonate substances are transformed into variegated disseminated bodies of iron-magnesium carbonate, usually containing carbonaceous inclusions.
The strongest mineralized zone of the deposit has no obvious geological boundary, but it can be delineated according to several standards, including the gold test of core samples taken at intervals of 1m (Figure 3). Embryonic ore has central symmetrical zoning in section. There are differences in the quantity, mineralization intensity and morphology of sulfide precipitation in each sub-zone. The outer sub-region shows the increase of disseminated fine-grained pyrite, large-grained metamorphic pyrite and Yanshi-pyrite aggregate. The central subzone contains a small amount of sulfide or timely sulfide veinlets. The central inner subregion appears in the axial part of the fold, and contains a large number of timely sulfide veinlets with complex shapes inherited from the folds and microfold of the parent rock (Figure 4).
Fig. 4 shows the main morphological types of chronological-sulfide mineralization and the distribution of Au, As and Co (quoted from V. V. Distler et al., 2004), and the cross section of the Sukhoiloge ore body made from the core of No.6 borehole.
There are several sulfide time-dependent veins with a thickness of 2m at the top of the ore belt, accompanied by veinlets and disseminated mineralization. In the deep part of the deposit (330 ~ 400 meters below the surface), a single gold-poor time pulse can be seen after mineralization.
The main gold reserves of the deposit are related to the mineralization of veinlet disseminated timely sulfide. They can be divided into three zones, namely, upper ore zone (upper outer sub-zone), embryonic ore zone (middle and middle sub-zone) and lower ore zone (bottom outer sub-zone).
There are six main types of gold mineralization in the deposit (Figure 4):
1) fine-grained and medium-grained pyrite interlayers and lenses.
2) Layered ovoid pyrite disseminated body.
3) flake and foliated fine-grained pyrite and pyrrhotite disseminated bodies.
4) Large banded pyrite phenocrysts with timely edges.
5) Granular metamorphic pyrite aggregate.
6)2 ~ 4 cm thick layered and staggered timely sulfide veinlets.
Among the above-mentioned mineralization morphological types, the first four are also produced outside the deposit, but usually there is no ore or only low-grade embryo ore.
Verb (abbreviation of verb) V. Distler et al. (2004) found that there are as many as 79 kinds of ore minerals in Sukhoiloge deposit, among which the natural metals are Au, Pt, Ag, Fe, Sn, Pb, Cu, Ti, W, Cr, In, * * *1; 14 solid melts of various metals and intermetallic compounds; 17 sulfides; Arsenide and arsenic sulfide11; Telluride and thiotelluride 8 kinds; 3 kinds of selenides; 5 kinds of antimonides; 7 kinds of oxides, phosphates and tungstates; 3 kinds of halides; There is also a certain amount of carbonaceous material. Pyrite is the main gold-bearing mineral. Thin-bedded and veinlet disseminated pyrite has the highest gold content, followed by fine disseminated pyrite, and porphyritic metamorphic pyrite has the lowest gold content. Besides pyrite, it is also the most common gold-bearing mineral. Unlike pyrite, the gold content is weak. The gold in the ore is natural gold, which exists in pyrite in the form of fine inclusions and is easy to recover. Platinum in ore exists in the form of natural metal particles. Ag exists in two ways, one is silver related to gold, and the other is silver in sulfide (chalcopyrite, galena, sphalerite) in isomorphic form.
The age of major events in Sukhoiloge deposit has been determined by isotopes. The terrigenous ore-bearing strata were formed in the early and middle period (about 800Ma) and the metamorphic time was (516 22) Ma. The rubidium-strontium method indicates that the mineralization age is (320 16) Ma. Similar age values (350 ~370Ma) have been obtained from isotopic dating of the Bodebo syncline granite, which is equivalent to the period of tectonic magma reactivation and granite formation. The lead model age of galena is (380 ~400) Ma. It can be seen that mineralization is much younger than sedimentation and regional metamorphism
Three. Genesis of ore deposits and prospecting criteria
1. Genesis of the deposit
The genesis of Sukhoiloge deposit is still controversial. Traditionally, endogenous fluid is the main factor for the formation of gold deposits after folding. At present, the metamorphism-hydrothermal model put forward by B.A. Briac, the discoverer of the deposit, is considered to be the most well-founded. According to this model, the mineralization of gold deposits was formed in three stages, namely, sedimentary-diagenetic stage, early metamorphic stage and metamorphic-hydrothermal stage. Ore-bearing fluids mainly come from high temperature metamorphism and granitization areas.
Verb (abbreviation of verb) V. Distler et al. (2004) constructed the genetic model of gold-platinum mineralization in Sukhoilogue according to isotopic age data and geophysical simulation results of deep structure of Sukhoilogue deposit (Figure 5). They believe that the main factors controlling mineralization are the tectonic environment reactivated in the early-middle Paleozoic and the accompanying endogenous fluid. In this environment, regenerated granite and activated ore components are formed. These ore-forming components come from a large number of early Precambrian basement and ancient ultrabasic rocks, as well as upper crust rocks including carbonaceous terrigenous rocks. The combination of regional events in the huge sedimentary basin superimposed on the basic-ultrabasic rock belt and the local intrusion of granite has created the unique composition and structure of Sukhoiloge deposit and a large number of precious metals enrichment in the deposit.
2. Prospecting signs
(1) regional geological prospecting indicators
1) deposit occurs in the terrigenous sedimentary strata of Rifeian (about 800Ma), which is mainly composed of conglomerate, sandstone, siltstone and shale, and there is a certain amount of volcanic rocks in the early strata of Rifeian.
2) The terrigenous sedimentary rocks are rich in carbon, and the deposition thickness of carbonaceous sediments reached the maximum in the middle and late Li Fei era, and the organic carbon content gradually increased from carbonate rocks to sandstone, siltstone and argillaceous rocks.
3) The continental carbonaceous rocks were formed in the continental margin basin, belonging to the foreland basin related to the rift system.
Fig. 5 Genetic model of gold-platinum mineralization in Sukhoi, Russia (quoted from V. V. Distler et al., 2004).
4) The terrigenous rocks suffered from regional metamorphism dominated by greenschist facies.
5) There are medieval magmatic rocks near the mining area, and there are large Paleozoic granitoids around the slope in the direction of Bodabofu where the deposit is located.
(2) Local geological prospecting indicators
Fig. 6 Mineral geochemical prospecting model of Sukhoiloge deposit (quoted from сгкряев, 20 10)
1) reverses the axis of the anticline, and the bending part, bending part, steep scour zone and low-angle cleavage zone of the axis are the most promising areas for mineralization.
2) The ore-bearing rocks are flysch-like complexes in the middle and late Li Fei era. Carbonaceous and calcareous siltstone, argillaceous rock, shale and sandstone appear alternately in the ore-bearing surrounding rocks, and carbon is the most abundant in the middle section.
3) On the mineralization profile, the embryonic ore has a central symmetrical zoning; Fine-grained pyrite, large-grained metamorphic pyrite and Yanshi-pyrite aggregates scattered in the outer sub-zone increased; The middle subzone contains a small amount of sulfide or timely sulfide veinlets; The central sub-zone contains a large number of timely sulfide veinlets with complex shapes.
4) There is a quartz vein with a thickness of 2m at the top of the ore belt. Although this barren quartz vein cannot form a separate gold deposit, it is a sign of deep gold sulfide mineralization.
5) paragonite and sericite occur in Sukhoiloge deposit, and the carbonate mineral is magnesite-ankerite, while the periphery of the deposit is polycrystalline muscovite and muscovite, and the carbonate mineral is mainly calcite.
(3) Geophysical exploration standards
The formation of mineralization is related to granite. If there is a negative gravity anomaly, it shows that granite may be buried at a depth of about 2 ~ 3 kilometers.
(4) Geochemical prospecting criteria
The ore-forming elements of 1) deposit can be divided into two geochemical assemblages, one is the Fe-Ni-Co-Cr-Ti-Pt-Pd assemblage of basic-ultrabasic rock type; The other is the combination of granite type zinc, copper, lead, tin, tungsten, rare earth and zirconium. The chemical anomalies formed by the latter base metal (Cu-Pb-Zn) provide more information than those formed by iron group elements (Ni-Co-Cr).
2) The occurrence of primary gold anomalies in the surrounding rocks of ore bodies is an extremely important prospecting indicator (Figure 6).
3) The δ34S of pyrite and δ 13C of ore-bearing bed in Sukhoiloge deposit increase rapidly organically (Figure 6), which is an important indicator for prospecting for mineralization.
According to (Jin Xiang)