V. G. Moiseenko

Analysis of the productivity of gold deposits of Amur province

By the amount of extracted placer and primary gold (~1300 t), Amur province is one of the major gold provinces of Russia. Its numerous placers yielded almost 1132 t Au in contrast to ~180 t from primary deposits. The central part of the province is most productive for placer and primary gold in comparison with the periphery. Native gold from placers has moderately high and high fineness, and its composition corresponds to that of gold from dominant gold–quartz and gold–quartz–sulfide deposits and occurrences. The preponderance of placer gold in gold production indicates significant prospects for discovery of new gold deposits.

Geochemical relationship between Au, U, and Th

562 Geochemical investigations were carried out mainly within the Mamyn Block of the Early Precam brian continental crust together with other blocks composing the basement of the post Paleozoic Amur Plate. The Mamyn Block occurs as an arch uplift bor dering the Mongol–Okhotsk orogenic belt from the north and is overlain by terrigenous deposits of the Mesozoic paleobasin from the west, south, and east. Precambrian crystalline formations with carbonate– terrigenous deposits are observe in the geological structure of the Mamyn Block.

Platinum potential of the Stanovaya metallogenic zone (Far East, Russia)

447 The Stanovaya metallogenic zone occurs along the southeastern margin of the Northern Asian Craton with a length of 1300 km and a width of ~250–300 km. The metallogenic zone is located in the eastern part of the Stanovoi megablock limited by the Stanovoi deep fault from the north and by the Mongol–Okhotsk deep fault from the south. A megablock surrounds the Aldan protomassif, represented by a folded–block or granite–greenstone area that underwent Mesozoic tectonomagmatic activization. The structure of the territory includes a number of blocks composed of Early Archean (Zverevsko–Chogarskii and Zeiskii Complexes) and Late Archean (Stanovoi and Gily uiskii Complexes) metamorphic rocks. Intercratonic troughs are filled by formations of the Early Protero zoic Dzheltulakskii Complex represented by phyllite like, biotite, and two mica schists, quartzites, meta conglomerates, and metaeffusive rocks [1].

Accumulation of gold nanominerals during the formation of ores of the Pokrovskoe deposit

591 The Pokrovskoe gold deposit is situated in the west ern part of the Umlekano–Ogodzhinskii volcanoplu tonic belt, localized in Cretaceous granitoids of the Sergeevskii massif and in younger volcanogenic for mations of the Ulunginskaya volcanotectonic struc ture [1]. Granitoids and volcanic rocks break Upper Jurassic terrigenous series enriched in interbeds of car bonaceous argillite. According to the level of gold ore in the structures of Mesozoic tectonomagmatic activ ization, the deposit corresponds to subvolcanic ones [2]. According to the peculiarities of the mineral com position, it is related to the gold–adular–quartz or poor sulfide formation [3]. The deposit is character ized by great abundance of faults and rocks, which underwent propylitization, argillization, sulfidization, and silicification. Ore zones are represented by the totality of steeply and gently pitching quartz and quartz–carbonate veins, veinlets, and breccias of quartz composition located in the zones of jointing and tectonic dislocations. Five stages of ore formation are distinguished on the deposit: (1) quartz–hema tite–pyrite; (2) productive gold–carbonate–quartz; (3) main productive gold–adular–quartz; (4) quartz– carbonate–sulfide; and (5) barren quartz–carbonate. Zones of vein–impregnation mineralization repre sented by a network of thin quartz veinlets with impregnation of pyrite, chlorite, and hematite were formed at the first stage. The second stage is character ized by thick veins of fine granular quartz with a small concentration of gold. The third stage is the most pro ductive and represented by two associations: gold– adular–quartz and gold–sulfide. Banded colloform textures of ores are typical of gold bearing quartz– adular formations. In addition to the prevailing pyrite, the gold–sulfide association contains small portions of galena, sphalerite, pyrargyrite, proustite, polybasite, and other rare ore minerals. Quartz–sulfide and quartz–carbonate–sulfide veinlets with pyrite, arse nopyrite, chalcopyrite, siderite, and apatite with rare elements were formed at the fourth stage. The post ore, carbonate stage is represented by veinlets and thin veins of quartz–dolomite and calcite compositions. Accounting for the difficulties in extraction of gold minerals as a whole and especially nanominerals and the fragility of sulfides, the methodology of sample preparation without grinding was originally worked out for study of gold nanoparticles in mineral aggre gates. For this purpose, a representative sample (50– 300 km) is passed in a sparing mode through a jaw crusher with successive change of the hole size to –1 mm at the exit. The +1 mm fraction is returned for further crushing, and usually 3–4 cycles are required for separation of the whole sample into two fractions: –1+0.08 and –0.08 mm. Using such method, we divide natural gold into two classes: visible and invisi ble to the naked eye (nanosized by 90%). Then we obtain two concentrates of heavy minerals with gold, which are studied on a scanning microscope and ana lyzed by different methods. The solution formed dur ing concentration of minerals together with suspended particles is successively passed through three filters: +10 μm, +3.5 μm, and ~1 μm. Later precipitates are analyzed on filters, and filtrates are subjected to sepa ration of nanosized particles. We worked out the method of measurement of size and concentration of nanogold in aqueous solutions using an apparatus of vacuum filtration PVF 47B with a set of Vladipor microfiltration membranes of the MFAS type (average pore sizes are 450, 200, 100, and 50 nm). Precipitates on filters and all solutions are analyzed on a Solar M6 spectrophotometer with a graphite atomizer on other instruments.

Nanoparticles of noble metals in peat of the Upper and Middle Amur Region

Swampy soils of the Upper and Middle Amur Region territory occupy an area of 5663.5 km 2 accounting for 13.6% of the whole territory of the Amur Region. Swampy soils are formed under sphagnum mosses and, partly, sedges. In the zone of deciduous forests, these soils are formed from different grasses. The upper peat-bearing horizon of soils consists of vegetation in the stage of semidecay. This horizon is underlain by a mineral glue layer consequently transforming into rock. About 600 deposits of peat with summary potential resources of 1.3 billion tons are located on the investigated territory [1]. The aim of this work was to study the concentration levels of the following noble metal elements (NMs) in peats of the Amur Region: Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au. Mass shares of NMs were detected in the laboratory of chemical analysis of the Institute of Geology and Nature Management, Far East Division, Russian Academy of Sciences, from 10 g samples after stepwise ashing at temperatures below 600 ° C with a heating speed of 100 ° C per hour. The mass shares of Au, Ag, Rh, Pd, and Pt have been detected by the atomic adsorption method [2, 3]. The kinetic method was used for detecting Os and Ir [4, 5], and the catalytimetric method for Ru detection [6] (the average values are shown in Table 1). Analysis was performed according to the III accuracy category with the maximal error of NM determination amounting to ± 30%. Oxidized forms of NMs are well dissolved in mineral acids that are not oxidants. In contrast, metal forms of NMs are practically insoluble in it. This feature was used for extracting the oxidized forms of NMs by an acid extract. Peat samples of 10 g in weight were processed by a definite amount of strong hydrochloric acid (with a density of 1.19 g/cm 3 ) during 1 hour of mixing. The concentration of the solution was further brought to 2‐3 M of HCl, and then it was heated under a cover up to boiling. The hot solution was passed through the double filter “blue band” with a pore diameter of 1‐2 µ m, and then it was twice washed by a hot solution of 3 M HCl. The acid extract consists of nanoparticles of NMs with dimensions less than 1 µ m and ions of oxidized forms of NMs. The filtrate was analyzed due to the methods of [2‐6]. The concentration of oxidized forms of NMs was determined from the acid extracts by their extraction of the following mixture: 0.025 M paraalkilaniline and 0.05 M diethylhexylditiophosphoric acid in toluene. The oxidized forms of Pt, Pd, Ir, and Os were additionally instrumentally determined with the help of the inversion voltamperometric analyzer TA-4. Thus, the proposed method allows separating ions of the oxidized forms of NMs and their nanoparticles from silicate and organic matrixes and performing their separate determination by instrumental and extracting methods of quantitative chemical analysis. Within the Amur Region, the investigated area con

New types of gold-platinum metal mineralization in the upper Amur region

Kyanite‐sillimanite metasomatites. The garnetbearing kyanite and kyanite‐sillimanite metasomatites (Talgin Formation) of the Dzhalta sector (Dzhalta‐ Ul’degit river basin) incorporate thick zones of silicification, sericitization, chloritization, and nest-stringer sulfidization (pyrrhotite, chalcopyrite, pyrite, and pentlandite). The ICP-AAA analysis of 30 lump and chip samples (IRGIREDMET Laboratory, Irkutsk) showed that the sulfidized kyanite‐sillimanite metasomatites contain Au (0.05‐1.5 g/t). Contents of noble metals in samples with quartz veins are as follows (g/t): Au up to 1‐3, Ag 0.07‐3.5, Pt 0.09‐0.79, and Pd 0.04‐0.14 [1]. Mineralogical analysis of pan samples of the chloritoid‐kyanite schists made it possible to divide the heavy fraction into the (1) magnetic, (2) electromagnetic, and (3) nonmagnetic fractions. The magnetic fraction includes iron globules (0.1‐1.0 mm in size) and magnetite. The electromagnetic fraction can be divided into three types. Type I is composed of ilmenite (up to 75%) and chloritoid. Type II is composed of chloritoid (up to 85%) and kyanite. Type III is composed of chloritoid and kyanite. The nonmagnetic fraction includes kyanite (up to 85%). The inversion voltamperometric analysis (analytical center of the ZolotoPlatina Territorial Production Association, Tomsk) made it possible to determine concentrations of noble metals in the samples (Table 1). Based on the ICP-AAA analysis, contents of noble metals in kyanite fractions (7 samples) are as follows (g/t): Pt 0.24‐1.45, Pd 0.04‐0.1, Au 0.22‐1.14, and Ag 0.3‐2.5. The microscopic examination by V.I. Gvozdev (Far East Geological Institute, Vladivostok) revealed that kyanite samples contain Au and Pt particles (0.04‐0.3 mm in size) and abundant microinclusions of monazite, zircon, magnetite, and sulfides (pyrite, pyrrhotite, and chalcopyrite). Thus, platinum mineralization discovered in metamorphosed rocks of the Talgin Formation indicates that “discordant” bodies of the upper Amur region are enriched in Pt. Ferruginous quartzites. In basins of the Goratsiev and Radostnyi creeks (Dzhalta River system), graphite, graphite‐biotite, and biotite gneisses of the Early Archean Kamrai Formation incorporate thick magnetite‐amphibole quartzite units (up to 30‐40 m) with rare sulfide dissemination (pyrrhotite, chalcopyrite, and pyrite). Based on magnetic and geological survey data,

Sulfur Isotopic Composition of Sulfides in Skarn and Vein Mineralization of the Dal’negorsk Ore Region (Primorye)

The S isotopic composition in the ore-forming minerals galena and sphalerite was studied in different Ag–Pb–Zn deposits of the region. It was pointed out that the δ34S modal values range from–1.2 to +6.7‰ in the minerals with a positive value for the skarn mineralization. In the flyschoid formation, the vein-type mineralization is characterized by negative and positive values. The narrow range of δ34S values indicates the marginal-continental type of the mineralization and the multiple origins of its sources.

Ranking the Productivity Potential of Ore-Placer Nodes of the Amur Gold-bearing Province

Ore-placer nodes with a high, moderate, and low productivity were distinguished according to the level of gold mining in the Amur Province. It has been shown that highly and moderately productive oreplacer nodes are naturally attributed to metallogenic zones of the central part of the province, and low productive nodes, to the peripheral parts. This is due to the presence of large ore-leading faults in the central part of the province. The areas with highly productive ore-placer nodes are the most promising to explore ore gold; the areas with moderately and low productive ore-placer nodes are less and much less promising, respectively.

Geochemical Peculiarities of Galena and Sphalerite from Polymetallic Deposits of the Dal’negorskii Ore Region (Primorsky Krai, Russia)

New data on the composition of the major minerals from the skarn and vein polymetallic deposits of the Dal’negorskii ore region are reported. Analysis of galena and sphalerite was carried out by the X-ray fluorescent energy-dispersive method of synchrotron radiation for the first time. It is shown that the minor elements in major minerals of different deposits are typomorphic. Among these elements are Fe, Cu, Ni, Cd, Ag, Sn, and Sb, as well as In in sphalerite and Te in galena. The high concentrations of Ag, Cu, Te, Cd, and In in the extracted minerals indicate the complex character of mineralization. The compositional patterns of ore minerals characterize the sequence of mineral formation from the skarn to vein ores, and the sequence of deposits from the mesothermal to epithermal conditions. This provides geochemical evidence for the stage model of the formation of mineralization in the Dal’negorskii ore region.

A unique ore-placer area of the Amur region with high-Hg gold

This work presents the geological structure and a description of the gold-ore occurrences and gold placers of the Un’ya-Bom ore-placer cluster of the Amur gold-bearing province. The host rocks are Late Paleozoic and Mesozoic black shales. Intrusive formations occur rarely. The sublatitudinal Un’ya Thrust is the principal ore-controlling structure. Paleozoic sandstones are thrust over Mesozoic flysch deposits along the Un’ya Thrust. The gold-ore occurrences are represented by quartz-vein zones. The ores are gold–quartz, low-sulfide. Ore minerals are arsenopyrite, scheelite, ferberite, galena, and native gold. High-Hg native gold was revealed in the ore occurrences and placers. The high Hg content in native gold is explained by the presence of the frontal part of the gold-bearing column located within the cluster; the rich placers were formed due to crushing of this column.