西藏班公湖-怒江成矿带中段砂金成色特征

该区砂金成色具有明显的不均一性，继承性和后期改造性。成色变化范围大（531．48－1000），具有粒度越大成色越高的趋势，区同西部砂金矿床的溶蚀系数小于1．03，为近原生源砂金，东部的1．03－1．10，为中近原生源砂金，崩纳藏分布于1．10，为远原生源砂金。自然金化学成分研究表明其原生金矿为中低温热型金矿床，那朗沟一带的燕山晚期花岗岩体内部有找到原生金矿床的可能。     

River drainage reorientation during placer gold accumulation, southern New Zealand

Many alluvial placer deposits around the world occur in river systems that have been affected by tectonic events, causing drainage reorientation and severance of links between placers and their sources. This study documents tectonic rejuvenation of topography in the Otago giant placer goldfield, New Zealand, which has resulted in numerous river capture and drainage reorientation events. These events have induced changes to gold transport directions and numerous stages of separation of detrital gold from primary sources. Goldfield-wide reconstructions of drainage patterns through time are as yet only possible for Miocene–Recent, and numerous earlier drainage changes back to Cretaceous primary orogenic mineralisation are probable. Variations in basement lithologies permit auriferous gravel provenance determinations, facilitating paleodrainage pattern reconstruction and documentation of river capture events. River capture events and timing of these events for gold-bearing paleodrainages have also been documented using genetic divergences of populations of freshwater galaxiid fish that were isolated by drainage reorientation. Gold-bearing quartz pebble conglomerates had a southeastward drainage in the Miocene. This was disrupted in the Pliocene by mountain range uplift and gold placer recycling, with deposition of lithic conglomerates containing only minor gold placers. The most dramatic changes in gold transport directions occurred through the Quaternary, as antiformal ranges grew across the pre-existing drainages. Miocene and Pliocene placers were recycled with numerous local (1–10 km scale) changes in river directions and numerous capture events. Large axial rivers were segmented into a more complex drainage pattern, and on-going river capture resulted in growth of the main Clutha River catchment at the expense of neighbouring catchments. The most productive placers developed in the Clutha River in late Quaternary when increased discharge from captured mountain catchments enhanced gold transport and concentration. Similar river drainage reorientation has occurred in other placer fields around the world, but the lack of preserved evidence inhibits documentation of most such changes.     

Lanostanes in Cambrian organic matter (Southeastern part of the Siberian platform)

Sterane hydrocarbons (HCs) of bitumoids of organic matter (OM) from the Lower Cambrian Sinyaya formation of the northern slope of the Aldan anteclise were studied using the chromatography-mass spectrometry technique. Norlanostanes C29 and lanostanes C30 were first discovered in fossilized OM from Cambrian sedimentary basins. This report considers the features of sedimentation, diagenesis, and maturity of lanosteroid-containing organic matter. Lanostane HCs are recommended for usage as biomarkers of oilproducing rocks of the Sinyaya formation to determine the source of naphthides in the eastern part of the Siberian platform.     

Indicative features of placer gold for the prediction of the formation types of gold deposits (east of the Siberian Platform)

Prediction and search for gold deposits in the east of the Siberian Platform are problematic because the study area is overlain by a thick cover of MZ-KZ deposits. Search for gold deposits by the largest geological institutions using conventional methods have not yielded positive results, because the main attention was focused on the discovery of ancient gold-bearing conglomerates of the Witwatersrand type and on the evaluation of the gold ore potential of basic magmatism. Typomorphism of placer gold bears huge information about the genesis of native gold, both its primary endogenous origin and its exogenous transformation, which makes it possible to identify the formation type of mineralization, increases the reliability of the prediction of gold deposits, and ensures their purposeful search in the platform areas. The revealed indicative features of placer gold made it possible to substantiate the formation of the gold ore sources of Precambrian low-sulfide gold-quartz, gold-iron-quartzite, porphyry gold-copper, and gold-PGE mineralization and Mesozoic gold-silver, gold-rare-metal, and gold-sulfide-quartz mineralization in the east of the Siberian Platform. We have established that high-fineness placer gold with microinclusions of pyrite, arsenopyrite, quartz, and carbonates with recrystallized structures and lines of plastic deformation is specific to the ore sources of low-sulfide gold-quartz mineralization. A high content of Cu (up to 4%) in flaky high-fineness gold is one of indicators of porphyry gold-copper mineralization. The angular shape of gold grains, the fine fraction and high fineness of gold, its completely recrystallized and regrown internal structure, and the permanent presence of Fe, Bi, and Cu microimpurities and hematite, ilmenite, and corundum microinclusions are typical of gold-iron-quartzite mineralization. Flaky and laminated high-fineness gold particles with steady Pt, Pd, and Ni impurities and Pt-mineral phases and Au-Pt intergrowths in them testify to the ore sources of gold-PGE mineralization. Laminated and cloddy gold fractions of > 0.25-2.0 mm, the medium and low fineness of gold, its single-crystal or, sometimes, porous internal structure, the wide range of microimpurities (Pb, Zn, As, Sb, Cu, Te, etc.), and microinclusions of native Ag, adularia, Sr-barite, and calcite are indicators of gold-silver mineralization. Laminated, dendritic, and cloddy-angular gold grains, wide variation in gold fineness (307-950‰), and the presence of microinclusions of native bismuth, maldonite, arsenopyrite, and silver tellurides are indicative of gold-rare-metal mineralization. Laminated and cloddy gold grains, their size varying from dust to > 0.25 mm, their mono- and coarse-grained internal structure, wide variation in gold fineness (600-900‰), and the presence of Hg microimpurities (up to 6% and more) and microinclusions of quartz, calcite, pyrite, arsenopyrite, tellurides, selenides, and REE phosphates point to gold-sulfide-quartz mineralization. The established placer gold indicators of the particular formation types of ore sources in the east of the Siberian Platform made it possible to predict Precambrian gold deposits with low-sulfide-gold-quartz mineralization similar to the Kirkland Lake and Porcupine mines and gold deposits with Mesozoic gold-silver mineralization similar to the Cripple Creek mine. The developed criteria for determining the types of mineralization by indicative features of placer gold give an insight into the ore genesis and can be successfully applied to prediction and search for gold deposits and to evaluation of their gold resources.     

New Riphean microbiotas of the Billyakh Group,the north Anabar region (Fomich River basin): To Riphean biostratigraphy of the Siberian platform

Excellently preserved organic-walled and silicified microfossils are first found in the Lower Riphean Ust-Il’ya and Kotuikan formations of the Billyakh Group in the northern slope of the Anabar Uplift (the Fomich River basin). Similar assemblages were previously known only from sections located southward in the Kotuikan River basin, and taxonomic composition of organic-walled microbiotas from the Ust-Il’ya and Kotuikan formations became a corner stone in competitive microphytological models that are based on different approaches. In their composition and general appearance, microbiotas from the Kotuikan and Ust-Il’ya formations in the Fomich River basin are similar to microbiotas reported from the Kotuikan River basin, although northern sections of the above formations characterize deeper sedimentation settings than in localities known before. The Ust-Il’ya and Kotuikan assemblages of organic-walled microfossils include sphaeromorphic Chuaria circularis and Leiosphaeridia, two-layer vesicles the genus Simia, filamentous Plicatidium and Taenitrichoides, and some others. The silicified microbiota from the lower Kotuikan Subformation is largely composed of akinetes of Anabaena-like cyanobacteria Archaeoellipsoides, spherical Myxococcoides grandis, and short trichomes Filiconstrictosus and Orculiphycus representing initial germination stages of Anabaena-like cyanobacterial spores. Acanthomorphic acritarchs known from lithology-similar Lower and Middle Riphean (Mesoproterozoic) formations of Australia and China have not been observed in the Ust-Il’ya and Kotuikan microbiotas, which are probably of older age. The found microbiotas outline substantially wider distribution area of organic-walled and silicified microfossils, supplement microphytological characteristics of Riphean sediments in the Anabar Uplift, provide information on taxonomic composition of microbiotas from a wider spectrum of facies, and specify relationships between Early and Middle Riphean assemblages of microorganisms from different continents.     

西藏尼玛砂金矿中金和银的提纯与精炼

为提纯与精炼西藏尼玛砂金矿中的金和银，在王水介质中制作供还原的Au液，选择草酸作为还原剂很容易将Au还原，而且不与其他金属离子反应。砂金的提纯与精炼要经还原Au液、排除HNO3和砂金的2次溶解及Au的还原。尾渣以NaCO3、硼砂、KNO3为配料在焦炭炉中进行熔炼和泼珠，进而分离出金、银。在提取银的操作中，采用饱和NaCl水溶液。制定的金、银王水法提纯与精炼流程所产出金锭的成色大于等于99．99％，银锭成色大于等于99．90％。     

Holocene palaeoflood events recorded by slackwater deposits along the middle Beiluohe River valley,middle Yellow River basin,China

Palaeohydrological investigations were carried out in the middle Beiluohe River valley in the middle Yellow River basin. Palaeoflood slackwater deposits (SWDs) are natural records of overbank flooding and are often identified in the Holocene aeolian loess–soil profiles along the river valley. Three bedsets of palaeoflood SWDs were found within the mid‐Holocene Climatic Optimum palaeosol (S₀) on the right riverbank. Both the sedimentary and the analytical results, including magnetic susceptibility, grain‐size distribution and concentrations of chemical elements, indicate that these palaeoflood SWDs were deposited from the suspended sediment load of overbank flooding. We identified three episodes of extraordinary overbank flooding events. These hydro‐climatic events were dated to 7600–7400, 5800–5000 and 4200–4000 a BP, from optically stimulated luminescence (OSL) dating and pedostratigraphical correlation. The minimum flood peak discharges were estimated to have been between 12 600 and 14 100 m³ s^?1 using the slope–area method. These hydro‐climatic events are considered to be a regional expression of known climatic events and demonstrate that the mid‐Holocene climate was far from stable. These results show that the magnitudes of floods are highly sensitive to climate change in semi‐arid and sub‐humid regions with a monsoonal climate.     

藏北羌塘小盆湖-拉雄错砂金矿带地质特征

以小盆湖砂金矿床为典型的一系列砂金矿床、矿点在藏北羌塘中部构成一个呈东西向的砂金矿带,笔者1999年首次将其命名为"藏北羌塘小盆湖-拉雄错砂金矿带"。通过对小盆湖砂金矿床基岩地质、地貌、第四纪地质、矿床类型、成因类型、矿体特征、砂金特征的全面介绍及与该带其它砂金矿床、矿点的对比,结合区域地质背景,认为前泥盆系阿木岗群和石炭系中的火山岩层位是主要矿源层。此后若干不同时期的沉积不整合界面,都表征着其下古风化壳、其上底部碎屑岩的含金物聚源区可以直接或经改造就近形成金矿矿床。羌塘中央隆起带及其两侧和东西方向石炭系分布区具有广阔的金矿找矿前景。     

Isoferroplatinum mineral assemblage in the northwestern Salair gold placer

Isoferroplatinum mineral assemblage has been first discovered in the Simonovsky Brook gold placer localized in the Egor'evskoe gold-bearing district (Salair Range). It includes isoferroplatinum (Pt₃Fe) grains with inclusions of cuprorhodsite CuRh₂S₄, braggite (Pt,Pd)S, vysotskite PdS, high-Pt rhodarsenide (Rh,Pd,Pt)₂As, keithconnite Pd₃Te, hollingworthite RhAsS, Cu and Fe sulfides, basic plagioclase, magnetite, epidote, quartz, kaolinite, and leucoxene. The assemblage might have been produced from small gabbroid bodies widespread in the northwestern Salair region, including those of the Uralian platinum-bearing type, or from gabbroids of other complexes.     

Groundwater resources of the middle and upper Odra River basin, southwestern Poland

 The total amount of groundwater resources in the middle and upper Odra River basin is 5200×10³ m³/d, or about 7.7% of the disposable groundwater resources of Poland. The average modulus of groundwater resources is about 1.4 L/s/km². Of the 180 'Major Groundwater Basins' (MGWB) in Poland, 43 are partly or totally located within the study area. The MGWB in southwestern Poland have an average modulus of groundwater resources about 2.28 L/s/km² and thus have abundant water resources in comparison to MGWB from other parts of the country. Several types of mineral waters occur in the middle and upper Odra River basin. These waters are concentrated especially in the Sudety Mountains. Carbon-dioxide waters, with yields of 414 m³/h, are the most widespread of Sudetic mineral waters. The fresh waters of the crystalline basement have a low mineralization, commonly less than 100 mg/L; they are a HCO₃–Ca–Mg or SO₄–Ca–Mg type of water. Various hydrochemical compositions characterize the groundwater in sedimentary rocks. The shallow aquifers are under risk of atmospheric pollution and anthropogenic effects. To prevent the degradation of groundwater resources in the middle and upper Odra River basin, Critical Protection Areas have been designated within the MGWB. Received, January 1995 Revised, May 1996, August 1997 Accepted, August 1997     

The tectonic structure of the northern part of the West Siberian oil-and-gas basin

A structural-tectonic zonation of the northern part of the West Siberian oil-and-gas basin, for the purpose of distinguishing the main types of positive structures promising for hydrocarbons, is made. The first revealed type is related to the zones of ultradeep depressions and represented by large inversion swells. The second one is represented by highs located in the side parts of ultradeep depressions, in the zones of tectonic steps and monoclines.     

河南省砂金矿床地质特征

河南省砂金矿床广泛分布于黄河、长江两大水系的支流中,具代表性的有淅川寺湾及嵩县高都川两矿床,其成因类型分属于河床-河漫滩型与阶地型两大类。矿体展布形态与全新统地层分布状态一致,为近水平沿现代河流边部赋存的长条带状。在地质找矿方面,在两大水系交汇处、河流地形的缓坡以及河流的内湾一侧均为寻找砂金矿床的有利区段。     

Geochronology of the southern Siberian platform

Seventy-two determinations of the absolute age of minerals from ancient structures of the Siberian platform, including intrusives, in the 2600 to 600 million range, shed some light upon the highly involved geological history of the platform's South, far more difficult to untangle than the history of its analogues, the Ukrainian and the Baltic Shields, except for the Early Precambrian, when "the fortunes" of both the Siberian and the Russian platform were apparently the same.- -V. P. Sokoloff.     

Cavity structure in oil-saturated Bazhenov and Abalak shale rock in the Western Siberian basin

The cavity structure in oil-saturated Bazhenov and Abalak shale rock is analyzed. The Bazhenov reservoirs are of pore and pore–microcavern type. Their cavity structure is formed as a result of the transformation of the mineral component (biogenic silica) and organic component (kerogen) in the rock. The ratio of pore types depends on the mineral composition of the reservoir rock and its degree of catagenesis. Pyrite is the main mineral filling the pore volume and impairing the filtrational properties. The reservoirs of the lower Bazhenov formation are confined to the Correlation Layer and are of fracture-cavern type.     

Wall-rock metasomatism of carbonaceous terrigenous rocks in the Lena gold district

The Lena gold district is situated in the fold-and-shear belt of the southern framework of the Siberian Platform. The gold deposits are hosted in the Riphean-Vendian Khomolkho and Aunakit formations, revealing the strict control of ore mineralization by folding and shearing. The microstructure of metasomatically altered ore-bearing carbonaceous sedimentary rocks at the Sukhoi Log, Golets Vysochaishy, and Verninsky deposits (the latter includes the Pervenets vein zone) testifies to parallelism in the development of shearing, foliation, and ore-forming metasomatism. The local pressure gradients are marked by removal of silica from pressured zones into opened cleavage fractures and pockets. Two metasomatic stages are recognized: (1) early sodic metasomatism, which is characterized by the assemblage of magnesian siderite and paragonite, and (2) late potassic metasomatism, with formation of muscovite in association with sideroplesite and ankerite. The rocks altered at the early stage are distinguished by elevated Ni, Cr, and probably PGE contents. The second stage, close in age to the emplacement of Hercynian granitic plutons, was accompanied by the gain of chalcophile metals and deposition of the bulk of gold. In mineral composition, the metasomatic rocks are close to beresites, but the alteration differed in somewhat elevated alkalinity, so that microveinlets of albite and potassium feldspar occur in the ore zone together with muscovite. The ratio of modal muscovite to paragonite contents in orebodies is substantially higher than in the surrounding metasomatized rocks. This ratio directly depends on the degree of rock permeability and the intensity of the flow of ore-forming solutions. Carbonaceous matter (CM) in the ore zone underwent reworking and redeposition. CM is graphitized to a lesser extent than in the rocks affected by regional metamorphism. The spatial distribution of CM containing nitro and amino groups indicates more oxidizing conditions in the zone of ore deposition than at a distance from this zone. The temperature of metasomatic processes estimated from the muscovite, muscovite-paragonite, and chlorite mineral thermometers and fluid inclusions in quartz was 300–350°C at a pressure of about 1 kbar. The S, O, and C isotopic compositions of ore-forming fluids that pertain to the second stage of metasomatism (δ³⁴S= +8.5‰, δ¹⁸O = +10‰, and δ¹³C= ?11 to ?18‰) indicate their crustal origin. The generally similar conditions and products of the ore-forming metasomatic process at the giant Sukhoi Log deposit and at the small Golets Vysochaishy deposit are combined with some differences. The formation of the described deposits was related to the deep convection of fluids along shear zones followed by more local flows of postmagmatic solutions derived from the emplaced granitic magma.     

Isotopic-geochemical features of rocks of the Middle-Upper Cambrian Verkhnyaya Lena formation in the Siberian Craton

Isotopic compositions of carbon and oxygen in carbonates and sulfur in sulfates of the Verkhnyaya Lena Formation (ε₂–ε₃), which terminates the Cambrian section of the Irkutsk Amphitheater of the Siberian Craton, are studied. Sulfates of the Verkhnyaya Lena Formation are marked by unusually low δ³⁴S values (4.6–12.0‰) relative to sulfates of the underlying Angara Formation. This is likely caused by variations in the facies-paleogeographic sedimentation at the transition of the Angara and Verkhnyaya Lena formations, as well as associated variations in the water and salt alimentation budget in sedimentation basins, due to their isolation from open sea and intensification of the continental and underground discharge. The δ¹⁸O(PDB) value in carbonates decreases from ?4.4‰ at bottom to ?10.4‰ at top, reflecting variation in postsedimentary transformations and probable continuous freshening of sedimentation basin. Isotopic composition of carbon in most samples shows normal marine δ¹³C values (0 ± 1‰). Only in some samples, does the δ¹³C value increase up to ?3.8 and 2.2‰ due to specific features of postsedimentary processes. The Rb-Sr systems of the clayey component of marls from the 500-m-thick section of the Angara Formation and bottom of the Verkhnyaya Lena Formation record an age of 512 ± 10 Ma, which is close to the assumed stratigraphic age of the Verkhnyaya Lena Formation. The ⁸⁷Sr/⁸⁶Sr initial ratio is 0.7082 ± 0.0004.     

西藏崩纳藏布砂金矿地质特征及找矿方向

通过对区域地质背景、第四纪典型地貌及矿床地质特征等的研究，发现崩纳藏布砂金矿具有成矿时代新、成矿期短、物质来源多样性等特点。成矿过程明显具有2个阶段：早期可能与斑岩型铜－金－多金属矿床有关，含Au配合物近距离活化、迁移，在适宜的地方堆积成矿；晚期在原地吸收侧向补给的第四系含Au沉积物，次生富集成为富矿。     

Serpentinites as a possible source of the Adola placer gold,Sidamo, Ethiopia

It is proposed that the Adola placer gold was derived, ultimately, from the ultrabasic rocks which are now represented by serpentinites and talc-schists. During the process of serpentinisation the ultrabasic rocks expelled abundant silica and available gold, which were deposited as gold-quartz veins in the overlying brittle basalts. Erosion of these basalts, now amphibolites has resulted in concentration of the gold as placers in the overlying conglomerates and soils.     

藏北地区砂金矿特征及找矿方向初探

藏北地区砂金矿矿质来源于中酸性岩浆岩接触带，沉积地层不整合接触带及硅化岩带，具物源近，成矿时代新的特点。班公湖－怒江地缝合线及其两侧的羌塘隆起带和冈底期－念青唐古拉陆块，是区内最有利的砂金成矿区。