Differentiation of Heavy Minerals in the Alongshore Debris Flow and Modeling of Processes of Coastal-Marine Placer Formation

The mode of material transportation and differentiation in the coastal zone of shelf is analyzed with the Val'kumei coastal-marine tin placer (Chaun Gulf, East Siberian Sea) as example. The placer incorporates two zones of cassiterite concentration. The first zone with coarse-grained cassiterite is located within the beach and adjacent coastal water area. The second zone with relatively fine-grained cassiterite is located on the submarine coastal slope in the distal area. This type of placer structure reflects the polymodal grain-size distribution of cassiterite in the bedrock source and peculiarities of material distribution in the alongshore debris flow. The proposed mathematical diffusive–convective model of coastal-marine placer formation adequately reflects the real placer structure and makes it possible to predict placer parameters in unilateral (alongshore) debris flow areas based on the composition of placer-forming source and lithodynamic parameters of the coastal water area.     

中国砂金矿成矿特征及找矿方向

我国砂金点多面广,很多江河水系都有砂金.为实现黄金生产发展的规划目标,当前加强砂金地质工作,对我国发展黄金生产建设具有重要现实意义.     

中国东北寒区的风化壳与砂金矿床

大、小兴安岭北部寒区发育有3个砂金富集区.大量的找矿实践表明, 区内砂金矿床与内生成矿作用没有必然的联系, 砂金矿床与区域发育的风化壳有着密切的空间关系, 风化壳中的低温地球化学作用对区域砂金矿床的形成具有一定的控制作用.在砂金的形成过程中寒冻气候条件至关重要, 寒冷的气候条件有利于风化壳的保存, 同时, 冰冻条件下的水文地质条件及电化学作用也有利于金在其中的活化、迁移、富集和生长.     

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.     

吉林省汪清县金仓砂金矿地质特征及来源探讨

金仓砂金矿是吉林省延边地区著名的第四纪砂金矿床。其砂金含矿层中砾岩多呈棱角状,砂金粒度及形态沿河流流向分异现象不明显,砂金的连生矿物、伴生重砂矿物、成色、微量元素、稀土元素、铅及硫同位素、气液包裹体成分特征均可和矿区内原生金矿化对比。据此,初步从为金仓河砂金主要来源于金仓河谷中、上游底部基岩含金蚀变破碎带中的原生金。     

190Pt–4He Age of Native Platinum Minerals of the Baimka Gold Placer Cluster,Western Chukotka

Doklady Earth Sciences - The results of 190Pt–4He dating of placer-forming minerals of platinum (PMP) from the Baimka gold placer cluster (Western Chukotka, Russia) are reported. PMPs are...     

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。     

Lithofacies zoning and titanium-zirconium potential of the Mansi and North Sos’va areas,Transural placer region

The lithofacies and morphostructural analyses of the Mansi and North Sos’va areas of the Transural placer region allowed us to establish factors of the spatial and lithostratigraphic control of titanium-zirconium placer potential. It was established that the placers are localized in sediments of the upper stage of the Oligocene-Miocene complex and rocks of Oligocene basin shows facies zoning. The most promising are the paleolittoral and shoal facies formed under moderate hydrodynamic activity. In tectonic aspect, the position of promising areas and their lithofacies composition are controlled by flank zones of local domes that experienced epeirogenic movements. Regressive regime in the Oligocene basin suggests the highest probability for the discovery of titanium-zirconium placers of the littoral type in inner zones of neotectonic domes.     

东海外陆架晚更新世沉积物中的有用重矿物及其资源潜力

对东海外陆架中部表层沉积物34个样品,南部两个岩心75个样品的沉积物特征和重矿物特征进行了分析,计算了其中有用重矿物砂的品位。东海外陆架晚更新世残留沉积中有用的重矿物砂来源于中国大陆,其含量与细砂含量、重矿物总量、沉积物的粒度和分选性呈正相关关系。重矿物砂赋存在海退层位中,形成于滨岸带,并经过后期海侵过程的改造和进一步富集,主要分布在水深100～200 m范围内。外陆架中部有用重矿物砂高品位异常区面积达1.2×10.4 km锆石和石榴石品位达到Ⅰ级异常。南部岩心中异常品位的有用重矿物砂的厚度1.5～2 m,锆石品位达到工业边界品位,研究区钛铁矿普遍出现Ⅱ级和Ⅱ级以上的异常品位。东海外陆架区浅海砂矿成矿条件较好,具有较大的资源潜力,值得进一步调查研究。     

新疆锡矿化类型及成矿规律研究

通过对新疆锡矿的研究，划分出8个锡矿成矿带，即诺尔特、阿勒泰、克拉麦里、克拉玛依北、阿拉套、哈尔克─库米什、南天山、星星峡。归纳出新疆锡矿矿化类型有3类：热液型、矽卡岩型和砂矿型，分析了每种类型的分布和产出特征，总结了新疆锡矿的成矿规律。     

Structural position of large gold ore districts in the Central Aldan (Yakutia) and Argun (Transbaikalia) superterranes

Gold ore districts in the Siberian (North Asian) craton and bordering terranes have been studied. Studies showed the long duration of gold concentration processes (Early Cambrian to Late Mesozoic and Cenozoic) and the influence of structural geological, magmatic, and metallogenic factors on the formation of ore districts. The largest Late Mesozoic (J–K) accumulations of gold deposits in southeastern Russia were discovered in the Aldan–Stanovoi Shield and at the northern margin of the Argun superterrane in the Aldan (Yakutia), Balei (Transbaikalia), and Gonzha (Upper Amur area) ore–placer districts.The geological and geophysical positions of these three districts have been compared. All of them are situated in zones of influence of variously trending long-lived deep faults, bordered by large Precambrian uplifts, and spatially (paragenetically) related to local magma chamber domes of Late Mesozoic (J–K) intrusive, subvolcanic, and extrusive–effusive bodies, dikes, and terrigenous pyroclastic blankets. The areas of Jurassic–Cretaceous volcanoplutonic rocks are related to the influence of the East Asian sublithospheric “superplume.”All this confirms the important ore-controlling role of large long-lived deep faults (in the form of global and regional gravity gradient zones) in the distribution of highly productive precious-metal ore–magmatic systems. This suggests that the junctions between gravity gradient zones of different trends and ranks are important to the identification of gold prospects in metallogenic prediction studies and small-scale prospecting. The Archean–Proterozoic age and the great occurrence depth of the tectonic zones suggest that extensive long-lived mobile zones (before the post-Cambrian breakup of the Siberian craton) significantly affected further evolution of the orogenic belts bordering the craton and their metallogeny, including the distribution of precious- metal deposits.     

内蒙古狼山—渣尔泰山地区与黑色岩系有关的铂族元素矿床找矿前景

铂族元素(PGE)为中国急缺的矿产资源。近年来,国外(如俄罗斯)在黑色岩系内发现了非传统类型的PGE矿床,中国南方也发现了与黑色岩系有关的PGE矿化。黑色岩系将成为PGE和稀有金属的一种新来源。内蒙古中西部狼山—渣尔泰山地区属中元古代裂谷系,具有类似的区域成矿构造背景,黑色岩系极为发育,并在黑色岩系分布区发现有砂铂矿床、PGE重砂异常及一系列与黑色岩系有关的金铜多金属矿床等良好的找矿线索,具有寻找与黑色岩系有关的PGE矿床的找矿前景。     

Forecasting of technogenic placer dynamics in the shore zone of the sea on the basis of numerical modeling: The case of the Val’kumei deposit

As natural placer and primary ore deposits are exhausted, the role of technogenic deposits is increasingly growing. In some cases, technogenic components accumulate in the shore zone of the shelf. The proposed numerical dynamic model is based on data concerning the technogenic tin deposit formed as a product of 50 years of operations at the Val’kumei Mining and Concentrating Combine, which disposed of tin ore flotation tailings in the coastal zone of the Chaun Gulf of the East Siberian Sea. The developed model describes adequately the current placer dynamics and forecasts a change in the morphology and geochemical parameters of a technogenic fan, opening the way to modeling behavior of natural geochemical anomalies in the coastal zone under conditions of active lithodynamics.     

Delayed accumulation of placers during exhumation of orogenic gold in southern New Zealand

The giant gold placer system on the Otago Schist of southern New Zealand was derived from Mesozoic orogenic gold deposits in the underlying schist basement. The core of the schist basement was exhumed in the middle Cretaceous, coeval with the accumulation of the oldest preserved nonmarine sedimentary rocks in the area (ca 112 Ma). Those sedimentary rocks contain quartz clasts, with distinctive ductile deformation textures, that were derived from structural zones in, or adjacent to, major orogenic gold deposits. Quartz textures in these structural zones are readily distinguishable from the rest of the schist belt, and hence provide a fingerprint for erosion of gold. The earliest sedimentary rocks on the margins of the gold-bearing schist belt are immature, and were derived from unoxidised outcrops in areas of high relief. Gold was not liberated from unoxidised basement rocks during erosion, and was removed from the system without placer concentration. Placer concentration did not begin until about 20 million years later, when oxidative alteration of gold deposits had facilitated gold grain size enhancement from micron scale (primary) to millimetre scale (secondary). Subsequent erosion and recycling of gold in the early Cenozoic, and again in the late Cenozoic, caused additional concentration of gold in progressively younger deposits. The Klondike giant placer goldfield of Canada had a similar geological history to the Otago placer field, and Klondike placer accumulation occurred in the late Cenozoic, at least 70 million years after Mesozoic exhumation of orogenic gold. The giant placer deposit on the western slopes of the Sierra Nevada in California occurs in Eocene and younger sedimentary rocks, at least 40 million years younger than the timing of major exhumation of the source rocks. Circum-Pacific giant gold placers formed under entirely different tectonic regimes from the emplacement of their source orogenic deposits, and these giant placer deposits do not form in foreland basins associated with convergent orogens. Formation of giant placers requires less active erosion and more subdued topography than the collisional orogenic activity that accompanied emplacement of source gold deposits in basement rocks, as well as oxidative alteration of the primary deposits to liberate gold from sulfide minerals and enhance secondary gold grain size.     

Locations of nonstructural hydrocarbon traps on the shelf of the northern Barents Sea

This paper considers the results of summarized integrated geophysical investigations that were carried out from 2006 to 2012. The investigations included common depth point (CDP) seismic reflection survey, over water gravity survey, and differential hydromagnetic exploration with a total work scope of 30 000 linear kilometers. The deep structural tectonic plan, the structural and lithofacies features of the sedimentary cover section on the basic reflecting boundaries, and the features of the seismogeological complexes and seismic sections on a depth scale have been studied, and geological oil-and-gas zoning of the Northern Barents shelf has been made. Seventy-nine local anticlinal highs have been revealed, and the zones with potential nonstructural hydrocarbon traps have been determined. Due to the lack of huge anticlinal highs in the northern Barents Sea region, nonstructural traps are of interest in studying and replacing the mineral raw material base of Russia, as well as for arranging marine exploration.     

俄罗斯东部地区油气资源远景分析

俄罗斯东部地区油气资源十分丰富,而且远景储量巨大。其石油储量远景区主要圈定在东西伯利亚地区晚元古代-早古生代陆源碎屑岩-碳酸盐岩含油气盆地,远东地区中-新生代大陆架硅质岩含油气盆地和远东滨海坳陷中古新世-始新世杂砂岩含油气建造等。而且,远东地区含油气盆地的形成时代自西向东逐渐变年轻,具体由侏罗纪、白垩纪过渡为新生代。俄罗斯东部地区中-新生代煤层气盆地广布,其中最主要的煤层气盆地为勒拿河流域盆地和南雅库特盆地。煤层气的成因及分布特征主要受控于盆地的基本地质特征,即上覆、下伏地层层系和褶皱断裂构造、变质作用等。俄罗斯远东地区萨哈林大陆架、鄂霍茨克海以及白令海阿列乌特深水海盆中蕴藏大量的天然气水合物资源。天然气水合物中的甲烷一般被认为来自深部油气层,但也有专家认为它可能来自大陆架以外的深海海域。     

Reconnaissance geochemical survey in the Marahiq area,Wadi Allaqi region,south Egypt: a preliminary assessment of stream sediments for gold placer and environmental hazard

The Marahiq area represents a portion of the Pan-African belt from the Neoproterozoic age in south Egypt and includes metamorphosed ultramafic rocks, metavolcanic rocks, and granodiorite pluton. The area is characterized by the ancient abandoned Au mine and the recent active talc mines. The present paper provides a preliminary assessment of stream sediments for gold (Au) placer and environmental hazard. Steam sediments from 36 stations were analyzed using ICP-MS for determining the concentration of 53 elements. Various statistical techniques, graphical representations, a set of complementary sediment quality assessment methods, and different mapping methods have been applied. The results showed that Au and the investigated elements were influenced by long history of the ancient mining activities and weathering processes, leading to elevate Au and some heavy metal(loid)s concentrations and exhibit enrichment ratios as follows: Te > As > Au > Cu > Cd > Co > Ni > V. Whereas Cd, Co, and V were attributed to geogenic origin, As, Au, Cu, Ni, and Te were derived from anthropogenic mining activities. It is found that the anomalies of Au and the element of interest are indicative of Au placer and point out a new perspective Au-sulfide mineralization hosted along the favorable tectonic zones that were the main source of Au placer. Both As and Te are good pathfinders to explore Au placer and related mineralization. Environmentally, the excess of As, Cu, Ni, and Te could generate moderate levels of contamination and low level of ecological risk in the sediments. Although As, Cu and Ni posed medium–low potentially adverse effects and low toxicity levels, they cannot cause harmful influences on biological life. Accordingly, streambed sediments are considered as safe and acceptable as inoffensive materials for environmental management. Overall, this study is as reference values for governmental organizations for appraising future environmental pollution in the area. Also, it is fruitful for Au placer and promising with success for Au exploration along the shear zones and strike-slip faults.     

Internal structure of placer gold in the middle Lena River basin,Southeastern Siberian platform

The internal structure of placer gold depends on its residence time under exogenetic conditions. Two types of placer gold are distinguished in the middle Lena River basin by typomorphic features. Gold of distal transfer (type I) is characterized by recrystallized structure, deformation lines, and thick high-fineness rims indicating long-term residence under exogenetic conditions; and multifold redeposition in transitional reservoir rocks. Gold of proximal transfer (type II) is characterized by a vague zonal structure, thin or discontinuous high-fineness rims, granulation, and disintegration structures indicating short-term residence time under the exogenetic conditions. Gold of proximal transfer is spatially confined to the zones of ancient long-living faults. Thus, it is possible to suggest that this type of gold might have derived from local Middle Paleozoic or Mesozoic gold sources.     

A new method for identification of protocatagenesis, mesocatagenesis, and apocatagenesis zones in a terrigenous sedimentary cover by applying layer seismic velocities

This method pertains to oil and gas geology and to geology of sedimentary basins prospective for oil and gas. It includes identifying catagenesis zones in drilled areas within the sedimentary cover of the basin based on assay results for drill cores and cuttings using the standard methods. Analysis is primarily made in order to determine rock catagenesis based on the optical characteristics of vitrinite. A correlation between catagenesis zones and layer seismic velocities obtained from regional and exploration seismic data is made for a drilled area. Both the layer seismic velocities and the degree of rock catagenesis increase with depth under the influence of increasing rock density. Correlations between layer velocities and the degree of rock catagenesis have been established. The following ratios have been determined for the Scotian shelf, Canada, and the Barents shelf, Russia: a protocatagenesis zone (the cap) corresponds to layer seismic velocities (V _lay) of 1.5–3.3 km/s, a mesocatagenesis zone (the principal hydrocarbon generation area) corresponds to V _lay of 3.3–5.0 km/s, and an apocatagenesis zone (an area with a very low hydrocarbon potential) corresponds to V _lay of over 5.0 km/s. An advantage of the new method of identification of catagenesis zones is that it can be used prior to drilling. Its conceptual originality and cost efficiency lie precisely in this.     

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers, NW Pakistan

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan. Two grids covering an area of 10x18 m2 and 8x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer. The anomalous zones obtained were plotted on contour maps, 2D and 3D magnetic intensity maps. Based on the magnetic anomalies, grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis. These zones contain gold concentrations, ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm. Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.