ЭВОЛЮЦИЯ ГИДРОСЕТИ КАК ФАКТОР ФОРМИРОВАНИЯ РОССЫПЕЙ ЗОЛОТА В ПРЕДЕЛАХ ВИШЕРСКО-ВИСИМСКОЙ ДЕПРЕССИИ НА ЗАПАДНОМ УРАЛЕ

Placer gold along the upper portions of Gold Creek, near Deer Lodge, Montana, occurs in Pliocene(?) fossil alluvial placers, Pleistocene till, and alluvium. The upper Gold Creek placers yielded an estimated 175 to 200 kg gold during 1890 to 1990. The gold probably originated in veins, skarn, or replacement deposits in Paleozoic and Mesozoic sedimentary units near the contact with Late Cretaceous granodiorite of the Royal stock. Gold was initially concentrated in alluvial placers along the ancestral Gold Creek valley during late Tertiary (Pliocene) time. Pleistocene glaciers scoured the Pliocene placers from most parts of the valley, although the fossil placers were locally buried beneath till and gold was also incorporated into till that was deposited farther down valley. Gold from Pliocene and Pleistocene placers has locally been reconcentrated into alluvium as a result of postglacial stream incision.The placer gold occurs as coarse-sized, oval to elongate grains characterized by rounded protuberances and inclusions of quartz and sulfide minerals. In polished section the grains have alternating convex and concave borders interrupted by pits and embayments. Grain borders and interiors of embayments display supergene gold rims averaging 98.8 percent Au. Microprobe analysis of cores indicate average compositions of 83.6 percent Au and 16.5 percent Ag and spectrographic data indicate a trace element signature enriched in Cu, Pb, and Sb, which is compatible with derivation from mesothermal plutonic lode deposits associated with the Royal stock.

Analysis of the formation conditions of Quaternary gold placers in the mountain area of the Southern Urals on the example of the Suleymenskaya multilayer placer shows that the most productive are the Eopleistocene and Middle Neopleistocene placer cycles associated with the final phase of the continuously intermittent neoorogenic rise of the territory. At the same time, the productivity of placers increases with the increase in the scale of fluvial processing of sediments of the Eopleistocene paleo-cleft and the transition of placers to the Middle Neopleistocene. The source of gold of the Suleymenskaya placer is the zone of gold ore mineralization in the northern part of the Tungatarovskiy fault. Prospects for expanding the raw material base of the territory are associated with the productive sediments of buried Eopleistocene paleo-cleft, coinciding with the zones of goldsulfide mineralization.

Unravelling the formation histories of placer gold and platinum-group mineral particles from Corrego Bom Successo, Brazil: A window into noble metal cycling

Sources of gold in placers from one region in the USSR

A wide mineral scattering halo of fine and thin high-standard gold with still unidentified commercial
\nplacers and primary sources is typical for the East Siberian platform, particularly the
\ncentral part of the Viluy syneclise. It is related to the fact that the studied area overlaps with
\na thick layer of the Mesozoic-Cenozoic deposits, where traditional methods of prospecting for
\ngold deposits do not yield positive results. It is well known that placer gold can retain “genetic
\nmemory” of its primary endogenetic gold sources. In this connection, detailed mineralogical
\nstudies of placer gold were performed with the aim to identify mineral types of gold mineralization
\nand to forecast and assess primary gold content. Mineralogical-geochemical features
\nof gold and mechanisms of its distribution from channel fill and the Quaternary deposits of
\nnumerous water courses of the Lena-Viluy interfluve. Over 300 samples were analysed, and
\nthe analysis takes morphologic features of gold, granulometric composition, fineness, composition
\nof trace elements, inner structure and presence of micromineral inclusions into account.
\nPermanent admixtures of Pt (6–96 g/t), Pd (5–570 g/t) and Ni (5–100 g/t), as well as micro-inclusions
\nof the exotic mineral phase of platinum group are identified in placer gold of the Suntar
\narch in right-bank tributaries of the Viluy river (Kempenday, Chybyda, Tonguo, Kundayi
\nrivers etc.). Apart from that, micro-inclusions of hematite, ilmenite, rutile, sulfides (pyrite,
\nchalcopyrite, galena) and Fe—Mg-aluminisilicates, which correspond to ore mineralization
\nand are typical for magmatism of the basic composition, are found in gold. The combination
\nof identified mineralogical-geochemical features of gold indicates that the Precambrian hightemperature,
\ndeep depth mineralization processes were primary sources of gold. This allowed
\nto forecast the presence of primary sources of gold-platinoid mineralization, probably related
\nto basites of the Early Proterozoic and later age, within the Suntar arch for the first time.

Tertiary shorelines, Texas coastal plain

Identification of indicators on placer gold allowed predicting formation types of primary sources of gold and their location in the East Siberian platform, overlapped by thick cover of Meso-Cenozoic deposits, where traditional methods of prospecting of gold deposits are ineffective. Each gold-ore formation is known to have the corresponding geological-structural control. Based on study of mineralogical-geochemical features of placer gold and regularity of its distribution, it has been determined that primary sources of low-sulfide gold-quartz, gold-copper-porphyritic, gold-ferruginous-quartzite, gold—rare-metal and gold-platinoid formations are confined to basement outcrops and their framings; gold-sulfide-quartz formation — to metasomatites, developed within the zones of deep faults, tracing the terrigenous-carbonate series; and manifestations of gold-silver formation are localized in the zones of intracontinental paleorifts. In general, identification of geological-structural location of specific types of gold sources favors more correct selection of prospecting methods for gold deposits in areas with thick sedimentary cover, and evaluating their potential.

The Dambuki ore cluster of the Upper Amur region is characterized by numerous and high-grade gold placers. A few small primary deposits and occurrences of gold-quartz type were formerly considered to be the main source of placers. However, the study of widespread Early Cretaceous Cu- and Ni-bearing ultramafic intrusions has shown that gold occurring in primary Cu-Ni ores and products of their weathering practically does not differ from placer gold in morphology, fineness, or geochemical features. In both cases, elements typical of Cu-Ni ore (Cu, Fe, Pd, Ni, etc.) are detected as impurities of gold particles. These data indicate that the Au-and Pt-bearing Cu-Ni ore mineralization may be the main source of placer gold. This ore mineralization is genetically related to small pyroxenite-cortlandite sills and dikes, abundant in the Dambuki ore cluster. The primary gold-quartz deposits and occurrences also contributed to the placers, but their part was rather small.

The article presents the results of applying geophysical methods in the study of placers of various genetic types in the Khabarovsk Territory. The main research methods are vertical electrical and remote induction sounding. Geophysical studies of alluvial placers were carried out along river valleys, at the watersheds and small streams of the Turchikansky lode-and-placer gold cluster. The main tasks to be solved are the search for potential structural traps of gold (paleoriverbeds, ravines), determination of the nature of the bedrock surface and the thickness of the overlying loose deposits. The work performed allows us to identify a prospecting indicator for placer gold in a given territory, that is, lower electrical resistivity values in the presence of a local positive magnetic anomaly. The study on the coastal marine placer on the coast of the Gulf of Nicholas (Sea of Okhotsk) focused on the lithological breakdown of the geologic section by physical properties. The results of the work showed strong differences in the electrical conductivity of the bedrock at the base of the section, marine sediments, and continental deposits. The application of electrometry methods is supported by the fact that rocks differ very distinctly by electrical properties. This is confirmed by placer mining activities at the technogenic deposits of the Verkhnyaya Uda and the Sofia mine. Mining and geological factors complicating dredging operations, such as permafrost and bouldery debris, were studied at technogenic placers by induction methods. Research results revealed that the presence of boulders or frozen rocks is manifested in the same way in electrical readings, that is, in a sharp increase of electrical resistivity. Thus, areas of abnormally high resistivity are hazardous areas for the passage of the dredger. These findings indicate the high efficiency of the application of electrical exploration technologies in the study of different types of placer gold deposits.

The paper presents the results of the study of typomorphic characteristics of placer gold of the tributaries of the Kengeveem River, Magadan region. Placer gold was studied by optical and scanning electron microscopy at the Institute of Volcanology and Seismology of the Far East Branch of the Russian Academy of Sciences. As a result, the first information on the morphology, internal structure and chemical composition of placer gold from the southeastern part of the Taigonos Peninsula was obtained. Three types of the gold were determined. The first type is dominant. The grains are chacterized by sub-ore morphology, with weak and medium degrees of roundness. Only Au-Ag is present in the composition of native gold, other macrocomponents were not found. The gold grade is 750–950 ‰. Some gold grains bear signs of hypergene transformation, expressed in the development of high-grade gold rims and intergrain veins. The second type of gold is represented by well-rounded lamellar extractions with a grade of 980–990 ‰. The third type is loose aggregates of secondary high-grade mustard gold. The obtained data allowed us to determine the different drift distances of native gold and to consider the low-sulfide epithermal Au-Ag mineralization and presumably far-distant gabbroids as the primary sources of gold.

An analysis of the geological and geomorphological features of the formation and preservation of gold placers in the Pribelsky placer zone located in the central part of the Belsky intermountain depression in the Southern Urals revealed the following. Valley of River Belay within Belsky depression, inheriting a zone of the Zyuratkulsky deep break, has complex two-level structure. The upper tier is represented by a wide (up to 5 km) trough-like paleovalley with complexes of polygenic and polychronic Miocene-Pliocene formations, both preserved in deep (up to 20–37 m) erosion-karst depressions and in some places coming to the surface. In Beloretsky and Burzyansky prospective sites of these complexes gold-bearing was revealed. As a result of the Eopleistocene – Early Neopleistocene phase of the neo-tectonic uplift of the mountainous part of the Bashkir Urals and subsequent river incision into the bottom of the paleo-valley to a depth of 30 to 130 m, a complex of sediments of the lower tier of the modern Belay river valley was formed. Due to the incision and reworking of goldbearing formations of the upper tier, the weight contents of gold are also established in the braid deposits of the river Belay. It has been shown that the areas of paleo-valley river Belay with karst troughs-traps of placer gold associated with zones of increased fracturing and permeability at the junctions of the submeridional and secant transverse faults. Attention is also drawn to the sites of the inheritance of the paleo-valley by a modern network with a predicted greater concentration of metal in them, even if weakly gold-bearing loose formations.

One of the most serious obstacles of a natural character for the development of recreation and tourism are natural hazards and processes. The high-mountainous part of the republic is especially subject to such processes, where most of the recreational objects are concentrated. Of the entire spectrum of hazardous natural processes, mudflows, avalanches, landslides, karst, subsidence, slides, debris, flood and flooding are the most widespread in the republic. In the mountainous part because of strongly dissected relief with steep slopes and considerable depth of incision of narrow river valleys, avalanches, mudflows, landslides and debris, slides, glacial activities are most active. The flat part and the foothills have their own set of natural hazards, among which floods, flooding, subsidence, soil erosion, and droughts prevail. These areas are often exposed to hailstorms. The entire territory of the Kabardino-Balkar Republic is an area of seismic activity. Spontaneous natural processes and phenomena have the most significant impact on the live of the population of the republic and the functioning of recreational facilities located in the zone of their occurrence. Each demonstration of risks in recreational areas leads to undesirable consequences, from dissatisfaction with rest to death of people and wealth.

Today, the most problematic issues of age and genesis of the Ukrainian Carpathian relief are as follows: 1) alignment surfaces and relief stratification; 2) mountain and cover glaciation; 3) formation and restructuring of river valleys; 4) age of volcanic relief. Investigations of alignment surfaces and relief stratification by various researchers during the 20th and 21st centuries have been analysed. The formation of denudation and denudation-accumulative surfaces, as well as relief stratification, is connected with the theory of equilibrium of relief-forming forces. Attention has been drawn to the interesting theory of the development of slopes and river valleys, where the stages of destruction, accumulation and equilibrium alternate in the process of development, as well as to the possible equilibrium between endogenous and exogenous processes: exogenous processes are constantly late in relation to endogenous ones. An interesting concept of the formation of relief stratification for mountainous countries and uplands, which is connected with the erosion and denudation development of relief based on the formation of the decline surfaces on the watersheds, has been highlighted. The data on the role of denudation speed during relief formation in landscape zones for rocks of different lithological and petrographic composition have been proided. A detailed analysis of the ancient glacial relief forms, performed by many researchers, indicates the Mindelian age of glaciation in the Ukrainian Carpathians. A significant contribution to the study of cover and mountain glaciation by the first Ukrainian geomorphologist S. Rudnitsky has been demonstrated. Some issues of the formation and restructuring of the river network have been reconsidered. First of all, it was noted that on all stages of the development of the Ukrainian Carpathian relief, transverse rivers dominated. S. Rudnitsky’s explanation of the volcanic activity in the Pleistocene (the presence of tuffs on the Pleistocene terrace in the valley of the Uzh river) was confirmed. Key words: Ukrainian Carpathians, relief age, denudation, denudation and denudationaccumulative surfaces, cover and mountain glaciation, river valleys, volcanic relief.

Laboratory investigation of hydraulic fracture networks in formations with continuous orthogonal fractures

Unconventional gold placers of the China tectonic depression (Vitim Plateau, East Siberia)