Lateritic nickel deposits of Brazil

Many nickel deposits are known in Brazil, accounting for about 350 · 10⁶ tons of ore with an average of 1.5% Ni. All are of the lateritic type. These deposits are scattered throughout the country, being rarer in the Northeastern Region and in the South, below 25 °S latitude. They are mainly associated with mafic-ultramafic massifs of large dimensions and ultramafic alkaline complexes, and occur in climatic regions of contrasting seasons. The weathering profile developed over the fresh rock consists, from bottom to top, of the following horizons: altered rock, coarse saprolite, argillaceous saprolite, ferruginous saprolite and lateritic overburden. The thickness of each horizon varies from one deposit to another, the whole profile generally exceeding 20 m. The saprolitic horizons with inherited minerals (serpentine, chlorite) or neoformed minerals (smectites) constitute the silicated nickel ore and are thicker were climatic conditions are drier; the ferruginous upper horizons made up of iron oxide-hydroxides are more developed in more humid regions. In Brazil, the silicated ore generally prevails over the oxidized ore. The main Ni-bearing minerals are serpentine, smectite, garnierite and goethite. The lateritic nickel deposits of Brazil may be correlated with two erosion surfaces, corresponding to the Sul Americano (Lower Tertiary) and Velhas (Upper Tertiary) levelling cycles. The degree of dismantling of the higher and more ancient surface and the consequent development of the Velhas Surface control the position of the nickel accumulation in the landscape. Thus, the deposits may be found either in the lowlands or in the highlands, where they are always covered by a silcrete layer. The alteration profiles in the Brazilian lateritic nickel deposits are broadly similar to those described elsewhere in the world. However, they present two characteristic features: the silicated ore prevails over the oxidized ore, and a silicified layer covers the profies developed on the highlands.     

The gold content of volcanogenic massive sulfide deposits

Volcanogenic massive sulfide deposits contain variable amounts of gold, both in terms of average grade and total gold content, with some VMS deposits hosting world-class gold mines with more than 100?t Au. Previous studies have identified gold-rich VMS as having an average gold grade, expressed in g/t, exceeding the total abundance of base metals, expressed in wt.%. However, statistically meaningful criteria for the identification of truly anomalous deposits have not been established. This paper presents a more extensive analysis of gold grades and tonnages of 513 VMS deposits worldwide, revealing a number of important features in the distribution of the data. A large proportion of deposits are characterized by a relatively low gold grade (<2?g/t), with a gradual decrease in frequency towards maximum gold grades, defining a log-normal distribution. In the analysis presented in this paper, the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade, especially when comparing deposits within individual belts and districts. The geometric mean gold grade of 513 VMS deposits worldwide is 0.76?g/t; the geometric standard deviation is +2.70?g/t Au. In this analysis, deposits with more than 3.46?g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7?t Au, with a geometric standard deviation of +26.3?t Au. Deposits containing 31?t Au or more (geometric mean plus one geometric standard deviation) are also considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46?g/t Au and 31?t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in VMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g., early arc rifting or rifting front). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic, aluminous, strongly siliceous, or potassium feldspar alteration) and trace element signatures may be recognized (e.g., Au?CAg?CAs?CSb ± Bi?CHg?CTe), suggesting a direct magmatic input in some systems.     

Garnierite in nickel deposits of the Urals

Oxide-silicate ore deposits containing approximately 10% of Ni reserves of Russia are located in the Sverdlovsk, Chelyabinsk, and Orenburg districts of the Urals. Garnierite is among the most important industrial minerals of supergene nickel deposits. We studied this mineral in metasomatites and ores of the Cheremshan, Sinar, Elov, Sakhara, and Buruktal deposits based on the chemical, thermal, and X-ray phase analysis data. It is shown for the first time that garnierites of the Ural province are composed of both exogenous and hydrothermal mineral associations. The spatial distribution of minerals suggests that the hydrothermal association is a lateral and vertical (depth) continuation of mineralization in the Uralian supergene deposits. This conclusion widens significantly the scope of prospecting for new mineralized sectors in old deposits and the possibility of discovery of new deposits.     

Hydrothermal nickel deposits: Secular variation and diversity

Hydrothermal nickel systems are one of the most puzzling mineral systems that involve trace element mobility in the Earth’s crust. Nickel is an abundant element in the crust. However, the processes that are involved in its mobility and accumulation at ore scale are challenging. A new empirical-stochastic model is required to gain a deeper insight into these systems. This Special Issue presents several studies on hydrothermal nickel accumulations world wide aiming to stimulate the debate on this intriguing deposit type.     

Segregation roasting of nickel,copper and cobalt from deep-sea manganese nodules

The recovery of nickel, copper and cobalt from ocean manganese nodules by a segregation roasting technique was investigated under a wide range of conditions with several nodule samples all of which gave similar results. The best conditions for the segregation of the metals were achieved with CaCl₂ as the chloride source at a batch retention time of approximately two hours; the highest recoveries were obtained at approximately 850°C for copper and at 1,050°C for nickel and cobalt. At 850°C, copper recovery was 75%, but nickel and cobalt recoveries were only about 25%. At 1,050°C, the nickel and cobalt recoveries were increased to about 60%, but the copper recovery dropped to only 35%. Electron-probe microanalysis showed the segregated metal to be an alloy, indicating that gaseous reactions play an important role in the reduction of chlorides to metal during the process.     

Variability of the metal content of flood deposits

Fresh flood deposits were sampled in the flood-plains of two river systems, the River Meuse, with a catchment area of 33,000 km² and the River Geul, with a catchment area of 3,000 km². As a result of industrial and mining activities, both rivers have a history of severe metal pollution, especially with zinc, lead, and cadmium. The flood deposits of both rivers are heterogeneous mixtures of contaminated bottom sediments (with relatively long residence times in the river) and clean sediments derived from soil erosion on agricultural cropland (with very short residence times). An additional source of sediment is formed by erosion of older, locally highly contaminated streambank deposits. These older sediments are polluted as a result of solid waste disposal containing metalliferous ore and tailings in the sand fraction. This is especially the case in the River Geul, which drains an old zinc and lead mining area. The metal content of the Meuse sediments, however, originates largely from liquid industrial wastes and occurs mainly in the clay fraction. For this reason, the positive correlation between textural composition, organic matter content, and heavy metal concentration, which is often reported, was not observed, and normalization of the metal content was not possible. Nevertheless, a clear decrease of contamination was noticed along the River Geul; this trend was absent along the River Meuse. An attempt has been made to model the longitudinal decay pattern for each of the investigated havey metals.     

煎茶岭与金川超大型镍矿中的伴生金及其比较分析

在对比研究煎茶岭大型镍矿与金川超大型镍矿的矿床地质球化学特征基础上,对两个矿床中的伴生金与镍及超基性岩的成矿关系进行了分析比较,两区不同的构造环境控制了超基性岩的不同分布。两矿床中的Ｎｉ、Ａｕ均来自超基性岩,且Ｎｉ矿床中金均为伴生矿,金川伴生金的丰度与镍成正比,而煎茶岭Ｎｉ矿中僮生金的丰度与镍成反比,其原因可能与各自不同的成矿环境及岩浆活动有关,尽管两镍矿中金的成矿机理基本相似。     

Ship-borne geochemical investigations of deep-sea manganese-nodule deposits in the Pacific using a radioisotope energy-dispersive X-ray system

A radioisotope energy-dispersive X-ray (EDX) system has been used on board the German research vessel “Valdivia” during an exploration expedition in the northern equatorial Pacific in 1973. The instrumentation used consisted of an X-ray detection system incorporating a 30 mm² effective-area Si (Li) detector with a measured energy resolution of 195 eV for Mn Kα X-rays, standard nuclear electronics, a 1024-channel analyser and a data read-out unit. The X-ray spectra in the manganese-nodule samples were excited by a 30-mCi ²³⁸Pu source.The six elements Mn, Fe, Co, Ni, Cu and Zn were analysed on board. Precision values for the analyses were less than 3% for Mn, Fe, Ni, Cu and Zn and about 5% for Co. A total amount of 350 analyses was carried out during a one-month cruise.Average contents of 190 analysed whole manganese-nodule samples from all the sampling sites of the covered area were 23.3% Mn, 6.7% Fe, 0.23% Co, 1.16% Ni, 0.94% Cu and 0.10% Zn. The average content of the base metals expressed as the sum of the Co, Ni, Cu and Zn contents was 2.48%. A linear relationship between Mn and Ni in all analysed samples, including whole manganese-nodule samples, zones of manganese nodules and manganese crusts, was observed. The Mn/Ni ratio calculated by regression analysis was 23.0. Zonal variations of the chemical contents of the six elements in the manganese nodules were found. A size classification of the manganese nodules has been suggested. Geochemical correlations of Cu and Ni versus Mn/Fe in the investigated samples are given.     

印度尼西亚苏拉威西岛某红土型镍矿床地质特征及成因浅析

文章通过对印度尼西亚苏拉威西岛某红土型镍矿床的成矿地质条件、矿床地质特征、矿石类型变化规律及矿床成因的分析与研究,认为矿床是由超基性岩橄榄岩在热带及亚热带常年高温、雨旱交替且年降雨量较大的地区经风化、淋滤、沉积富集而成矿;与在中生代、新近纪、第四纪的热带、亚热带气候条件下形成的蛇纹岩风化壳有关.     

Kabanga magmatic nickel sulphide deposits,Tanzania: morphology and geochemistry of associated intrusions

Mafic magmatism is a widespread feature of the Kibaran Orogenic Belt of central Africa, some of which hosts important deposits of Ni and Co. This paper describes mafic intrusions associated with Ni sulphides in northwest Tanzania, and attempts to define the tectonic environment of their emplacement. The Kabanga Ni deposits occur in small, layered mafic-ultramafic intrusions, comprising olivine and orthopyroxene cumulates. These intrusions are spatially associated with widespread gabbro-noritic sills emplaced within the enclosing Meso-proterozoic intracratonic metasedimentary rocks prior to deformation. The marginal rocks of the sulphide-bearing intrusions comprise gabbro-norite and melanorite, similar in texture, lithology and trace element geochemistry to the mafic sills. Marginal rocks of the mineralised intrusions with textures indicative of rapid cooling of largely crystal-free magma (strongly acicular pyroxene and skeletal olivine) are siliceous high Mg basalts, with enriched LREE and negative Sr, P and Ti anomalies, suggesting a metasomatically-enriched mantle source region and/or a strong crustal component. The Kabanga sulphide-bearing intrusions are inferred to have been emplaced as small feeder conduits supplying magma to larger adjacent and overlying gabbro-noritic intrusions within a foreland basin, prior to or during inversion and folding. 2000 Elsevier Science Limited.     

The gold content of some Archaean rocks and their possible relationship to epigenetic gold-quartz vein deposits

Gold mineralization in Archaean granite-greenstone environments, especially gold-quartz veins, contributes considerably to the world's gold production. The formation of epigenetic gold mineralization in greenstone belts is generally explained by the metamorphic secretion theory. This theory is based on the assumption that the source of the gold may be komatiitic or tholeiitic lavas, pyritic chemical or clastic sediments and even granitic rocks from which, as a result of regional metamorphic overprinting, gold was extracted and concentrated in suitable structures.It has been shown that in proposed potential source rocks, gold is predominantly associated with sulfide minerals and thus relatively easily accessible to secretion and reconstitution processes.A large number of various rock types originating from granite-greenstone terranes of the Kaapvaal and the Rhodesian cratons were geochemically investigated, and the following ranges for gold determined:volcanic rocks (komatiitic and tholeiitic): 0.1–372 ppbgranitic rocks of the basement: 0.3–7.8 ppbiron-rich chemical sediments: 1.0–667 ppbStatistical treatment of the data reveals that volcanic rocks as well as iron-rich chemical sediments are favorable sources for epigenetic gold mineralization formed by metamorphic secretion, while the granitic rocks make less suitable primary gold sources. This finding explains the close spatial relationship which is common between gold-quartz veins and greenstone belts. The conspicuous abundance of epigenetic gold mineralization in the Archaean, however, is attributed to the unique geologic and metamorphic history of the granite-greenstone terranes.     

中国镍矿成矿规律的量化研究与找矿方向探讨

镍矿曾经是中国的传统优势矿产,但目前已大量进口,成为典型的关键矿产(critical minerals)。本文基于镍矿地质大数据,系统分析了世界及中国镍矿的资源概况,总结了中国镍矿的时空分布规律,采用量化方法研究了中国省、市、县级、Ⅲ级成矿区带及各成矿时代的镍矿成矿密度与成矿强度。研究表明,中国镍矿资源丰富,分布相对集中,具有较大的资源潜力和找矿前景。类型以岩浆型为主,主成矿期为晚古生代;将中国镍矿划分为30个成镍带并分为重要和一般成镍带两个等级,其中重要成镍带有12个;厘定18个镍矿成矿系列,23个亚系列;指出今后深部找矿、西部找矿、有找矿潜力的现有矿山及成矿强度较高矿山的深部、边部及外围是镍矿找矿的重点工作区域,并对未来镍资源调查和产业发展提出了建议。     

Supergene alteration of sulphides,II. A chemical study of the Kambalda nickel deposits

An electrochemical study of nickel sulphide ore from three Kambalda shoots shows that the various parameters measured correlate both with depth and the degree of alteration of the ore. Eh and pH, respectively, vary from about ?0.3 V (SHE) and 8–9 for the deeper primary ore to about +0.3 V (SHE) and 5–6 for the shallower weathered ore. Leaching and simulation experiments as well as resistivity measurements all give results that support the hypothesis that galvanic corrosion resulting from differential aeration is the major mechanism in weathering of the ore. The release of iron from the ore to solution, and its subsequent hydrolysis, could exert a major influence on the pH, as indicated by the reaction: Fe²⁺ + 3H₂O → Fe(OH)₃ + 3H⁺ + e^?. The redox potential of the original mineral assemblage also plays an important role in pH control. Exploration and metallurgical consequences are discussed.     

The paleomagnetic record from deep-sea sediment cores

The paleomagnetic record of deep-sea sediment cores is compared with that which would be expected from our knowledge of the Earth's magnetic field. It is found that some of the scatter in directions of magnetization obtained from deep-sea cores is removed in cores with very low sedimentation rate, the cause being that the secular variation of the Earth's magnetic field is more completely averaged out over the finite size of each sample, when these samples comprise a longer time span of sedimentation. Corrections have been applied to the results from a series of cores in order to obtain the inclination of the average direction of magnetization from the average inclination and the scatter of inclination. These corrected inclination values confirm the hypothesis that the average Earth's field over the past few million years has been similar to an axial dipole displaced towards the North Pole. The amount of displacement obtained was 168 km. The record of short-period polarity intervals within the Brunhes, the Matuyama and the Gauss epochs was studied. It was shown that these intervals are very scattered in position. It is thought that some hitherto undiscovered short-period polarity intervals may be responsible for part of the scatter, but it is also highly likely that many samples give spurious reversals (i.e., ones not caused by the Earth's magnetic field).The possible correlation between climatic changes and the Earth's magnetic field is examined. It is concluded that the cores which show correlations between direction and/or intensity of magnetization and climatic indicators, thus suggesting the possible correlation between climate and the Earth's magnetic field, are not accurately recording the relevant parameters of the Earth's magnetic field. The correlation must be caused by climatic effects which have a direct influence on the magnetization of the sediments.Very little is known about the mechanisms of magnetization in deep-sea sediment cores, and there are several unexplained phenomena, such as the fact that many cores have maximum susceptibilities which are vertical, and the fact that cores differ widely in their ability to record accurately the Earth's magnetic field.     

澳大利亚伊尔岗克拉通科马提岩型镍矿成矿作用及找矿方法

澳大利亚西部伊尔岗克拉通卡尔古利地体是世界上太古宙与科马提岩有关的硫化物镍矿床最为集中的地区。该区科马提岩型硫化镍矿床主要有两大类型：①由高品位的块状、海面陨铁状和网状矿石组成,赋存于科马提岩熔岩流（主要为火山橄榄岩）底部,以卡姆巴尔达矿床为代表;②以低品位的浸染状镍硫化物矿石为主,赋存于厚层纯橄榄岩的中部,以芒特基斯为代表。与镍成矿有关的科马提岩形成于晚太古代（2．70Ga）,具铝不亏损（Al2O3／TiO2=15～25）地球化学特征,一般形成于具含硫围岩的动态高岩浆流环境。伊尔岗克拉通科马提岩型镍硫化物矿床形成于经历岩浆作用（结晶、分异和浓集）和地壳硫混染作用的硫不饱和镁铁质-超镁铁质岩浆的熔岩通道或管道中。在矿床成因讨论的基础上,提出该类型矿床的找矿标志和勘查方法。     

澳大利亚伊尔岗克拉通科马提岩型镍矿成矿作用及找矿方法

澳大利亚西部伊尔岗克拉通卡尔古利地体是世界上太古宙与科马提岩有关的硫化物镍矿床最为集中的地区。该区科马提岩型硫化镍矿床主要有两大类型：①由高品位的块状、海面陨铁状和网状矿石组成,赋存于科马提岩熔岩流(主要为火山橄榄岩)底部,以卡姆巴尔达矿床为代表;②以低品位的浸染状镍硫化物矿石为主,赋存于厚层纯橄榄岩的中部,以芒特基斯为代表。与镍成矿有关的科马提岩形成于晚太古代(2.70Ga),具铝不亏损(Al2O3/TiO2=15~25)地球化学特征,一般形成于具含硫围岩的动态高岩浆流环境。伊尔岗克拉通科马提岩型镍硫化物矿床形成于经历岩浆作用（结晶、分异和浓集）和地壳硫混染作用的硫不饱和镁铁质—超镁铁质岩浆的熔岩通道或管道中。在矿床成因讨论的基础上,提出该类型矿床的找矿标志和勘查方法。     

氧化钕中杂质氧化镍含量的测定及测量结果的不确定度分析

采用电感耦合等离子体发射光谱法(ICP-OES)法测定氧化钕中杂质氧化镍的含量,得到氧化镍含量为0.002 7%,分析了检测过程中的各个影响因素,并对测量结果的可靠性以相对扩展不确定度表示(U_rel=12%,k=2)。相对不确定度分量计算结果表明,标准曲线拟合时引入的相对不确定度分量最大,u_rel(c₂)=5.639%,其次为标准溶液配制过程中引入的相对不确定度分量u_rel(c₁)=0.879%。本文可为相关检测人员的结果不确定度分析提供参考。