共查询到20条相似文献，搜索用时 31 毫秒
1.
《Applied Geochemistry》2000,15(2):245-263
Since the 80's, studies have shown that Au is mobile in supergene lateritic surficial conditions. They are based either on petrological, thermodynamic studies, or experimental works. In contrast, few studies have been done on the mobility of the Pt group elements (PGE). Moreover, at the present time, no study has addressed the differential mobility of Au, Ag and Pd from natural alloys in the supergene environment. The aim of this study is to understand the supergene behavior, in lateritic conditions, of Au–Ag–Pd alloys of the Au ore locally called Jacutinga at the Maquiné Mine, Iron Quadrangle, Minas Gerais state, Brazil.The field work shows that the host rock is a “Lake Superior type” banded iron formation (BIF) and that the Au mineralization originates from sulfide-barren hydrothermal processes. Primary Ag–Pd-bearing Au has developed as xenomorphous particles between hematite and quartz grains. The petrological study indicates that the most weathered primary Au particles with rounded shapes and pitted surfaces were found, under the duricrust, within the upper friable saprolite. This layer, however is not the most weathered part of the lateritic mantle, but it is where the quartz dissolution resulting porosity is the most developed. The distribution of Au contents in the weathered rocks are controlled by the initial hydrothermal primary pattern. No physical dispersion has been found. Most of the particles are residual and very weakly weathered. This characterizes early stages of Au particle weathering in agreement with the relatively low weathering gradient of the host itabiritic formations that leads essentially to the development of isostructural saprolite lateritic mantle. Limited dissolution of primary Au particles issued from the friable saprolite induces Pd–Ag depleted rims compared to primary Au particle Pd–Ag contents.In addition, limited very short distance in situ dissolution/reprecipitation processes have been found at depth within the primary mineralization, as illustrated by tiny supergene, almost pure, Au particles. The supergene mobility order Pd>Ag>Au as reflecting early weathering stages of Au–Ag–Pd alloys under lateritic conditions is proposed. 相似文献
2.
Yu. A. Kalinin G. A. Palyanova N. S. Bortnikov E. A. Naumov K. R. Kovalev 《Doklady Earth Sciences》2018,482(1):1193-1198
The supergene Au in weathering crusts of both the Suzdal and Raygorodok deposits is characterized by enhanced fineness, grain size, crystallinity, and the appearance of botryoidal aggregates of crystals. In the weathering crust of the Suzdal deposit, the exogenous Au is associated primarily with scorodite and carbonates; for Raygorodok, with chalcocite, bornite, hydrocarbonates and Cu hydrosulfates. The difference in the mineral associations of supergene Au at the deposits is determined by the occurrence of various mineral concentrators of Au in the primary endogenous substrate: arsenopyrite and pyrite at the Suzdal deposit and chalcopyrite with pyrite at the Raygorodok deposit. Due to the much greater mobility of Ag in the supergene zone, the weathering crusts are likely to contain submicron microinclusions of Ag minerals beyond the zones of Au concentration. 相似文献
3.
《International Geology Review》2012,54(12):1149-1165
The Gay deposit, situated in the Orenburg region, is identified with one of Russia's principal occurrences of pyrite (pyrite deposits are an important source of Russia's gold). It belongs to the west subzone of the Magnitogorsk synclinorium and occurs in Devonian rhyolite-basaltic volcanic rocks. The deposit comprises five large pyrite-chalcopyrite, pyrite-chalcopyrite- sphalerite, and pyrite orebodies. The supergene zone extends to 120-240 m below surface and consists of the following three subhorizontal zones (from bottom to top): the secondary sulfide enrichment, the leaching, and the oxidation zone (where ores are enriched in gold). There are two levels of secondary gold enrichment in the weathering profile. The lower level, located in the leaching zone, corresponds with the level of water table fluctuations. The rich, flat-lying horizon (1.5-10.0 m) is composed of bedded, friable native sulfur-quartz ores; it contains 19.0-52.2 ppm Au and up to 389 ppm Ag. Native gold and silver halides (chlorargyrite, iodargyrite, and embolite) are the principal precious-metal minerals. Electrum, native silver, acanthite, and uytenbogaardtite constitute the minor ones. The upper level of the enrichment is located in the lower part of gossan. This bonanza is composed of hematite-quartz ochres. Gold concentration is 13.5 to 21.2 ppm. Native gold of high fineness and silver halides apparently are associated here with poorly crystallized iron oxides. The formation of supergene gold enrichments may result partly from residual concentration and partly from mobilization and reprecipitation of the precious metal. Rich horizons form by repeated gold redeposition in accordance with weathering and a gradual erosion surface lowering. The lower bonanza forms at first in the process of oxidation involving pyrite and native sulfur. Gold may be transported by complexes with metastable sulfur oxy-anions: sulfites, thiosulfates, or polythionates. The upper enriched horizon forms in the course of further evolution of the weathering profile in the stage of hematite recrystallizaiton and its transformation into goethite. 相似文献
4.
丘岭金矿床是西秦岭地区重要的卡林型金矿之一, 金矿化赋存于上泥盆统南阳山组和下石炭统袁家沟组地层中, 容矿岩石的岩性为钙质粉砂岩、粉砂质页岩和泥质灰岩.金矿石中主要金属矿物为黄铁矿和毒砂, 非金属矿物则以石英、方解石和绢云母为主.通过对矿石矿物黄铁矿和毒砂的扫描电镜-能谱分析、电子探针分析和激光剥蚀电感耦合等离子体质谱分析, 对丘岭金矿床金的赋存形式和富集机理进行了较为详细的研究.结果表明, 丘岭金矿床中金主要以次显微不可见金的形式存在, 其次为显微可见金.次显微金包括: (1)固溶体金(Au+), 主要存在于环带状细粒黄铁矿的含砷增生边区域和毒砂中, 少量存在于环带状黄铁矿的核部不含砷区域; (2)纳米级自然金颗粒(Au0), 存在于粗晶黄铁矿中.环带状细粒黄铁矿核部的次显微金可能主要以胶体吸附的形式存在, 暗示容矿岩石在沉积成岩过程中有金的初步富集, 而环带状黄铁矿幔部和毒砂中的Au则主要来源于成矿流体, 以S和As的络合物形式搬运.显微可见金主要分布在细粒黄铁矿的晶体边缘和热液蚀变绢云母、石英及方解石中, 粒径通常小于3~5 μm, 其形成可能与成矿流体中金的局部过饱和及成矿流体对细粒黄铁矿和毒砂中次显微金的活化和再次富集有关. 相似文献
5.
Hong Hanlie Wang Qinyan The Center for Material Research Testing Wuhan University of Technology Wuhan Bian Qiujuan Faculty of Earth Sciences China University of Geosciences Wuhan 《中国地质大学学报(英文版)》2001,12(1)
1The Shewushan gold dePOsit consists of a series of mineralized faults containing high gold grades (1. OX 10-6 to 19. 5 X10-s ) in a larger lower 'grade zone (0. 2 X 10-8 to 1. 0 X 10-6 )peripheral to these. The total reserve was approximately I X10,tons with an average grade around 2. 2 X 10-s. The discovery outcrop is of intense silicification and anomalous gold values(up tO 3. 4 X 10-e ). Hubei No. 4 Geological Party investigatedthe data from Hubei Regional Measuring Party and Hubei… 相似文献
6.
安徽铜陵狮子山矿田夕卡岩型金矿床的矿物组合、化学成分及成因意义 总被引：19，自引：1，他引：19
包村和朝山金矿床位于安徽铜陵狮子山矿田，属于夕卡型岩金矿床，侵入岩体分别为包村石英闪长岩体和白芒山辉石闪长岩体。通过矿相鉴定和电子探针分析，对矿床中的自然金进行了详细的观察和研究。结果表明，在两个矿床中，金矿物均以独立的自然金颗粒形式产出，且常具有“银边结构”，但在自然金的嵌布方式、载体矿物、形态、大小、金银含量变化和成色等方面表现出显著差别。根据自然金的不同特征，对金矿床的成因进行分类，包村金矿床属于Cu-Au共生，而朝山矿床为Cu-Pb-Zn-Au共生型金矿床。不同矿床不同的金产状主要是由于金的运移、络合物种类、温度、pH和金银络合物活度比值等因素赞成的。此外，包村矿床和朝山矿床在地表均遭受氧化作用形成表生矿床，其表生金成色均明显高于原生金，且成分均一。 相似文献
7.
红土型金矿床综述(英文) 总被引：1，自引：0，他引：1
近二十年来 ,热带地区普遍存在的红土型风化作用及其对矿床与矿化带的影响引起了普遍的关注。红土型风化壳的主要矿物成分是以铁铝的氧化物及氢氧化物和粘土矿物为主 ,如针铁矿、赤铁矿、铝土矿、高岭石及石英等 ,与其未风化的母岩相比 ,含有相当高的铁和铝。红土型风化过程中 ,易溶元素均不同程度地被淋滤 ,而难溶元素则相对富集。红土型金矿床就是在这样强烈的风化作用中由原生的金矿化带进一步富集而成 ,并可形成极富的矿体。金矿体常常赋存于风化壳的上部 ,易于露天开采。目前 ,在澳大利亚、巴西、巴布亚新几内亚、印度以及非洲的一些国家均发现了红土型金矿床。红土型风化剖面一般可分为 5个特征带 ,由上而下为 :表土带、铁质带、斑点带、浅色带、腐岩带 ,下面即为未风化的母岩 ,金矿体主要赋存于铁质带和斑点带中。红土型风化壳厚度变化很大 ,薄则几米 ,厚可达数百米。金在风化过程中往往向矿化带两侧运移 ,矿体常呈上宽下窄状。次生金常呈自形晶、树枝晶、浑圆状及不规则状产出 ,并常常与铁质结核共生。一般地说 ,次生金的成色很高 ,因为红土型风化作用常常是在氧化并且酸性的地球化学环境中进行 ,金和银主要以氯化物的形式运移 ,局部地球化学环境的变化可导致金的沉淀 ,而银的氯化物则较稳定 ,? 相似文献
8.
中国南方红土型金成矿系列研究综述 总被引：6，自引：0，他引：6
红土型金矿床是原生金矿化遭受红土化作用改造所形成的一种表生金矿床,包括"红色粘土型"和"铁帽型"金矿床.中国红土型金矿以风化再造型为主,受气候影响而主要分布在南方,并与岩金成矿系列分布基本一致.风化壳常量元素、稀土元素、粘土矿物系统研究表明,成矿作用环境时空变化整体受风化强度控制,其风化作用早期呈中碱性、晚期呈酸性,风化壳下部偏碱性、还原,项部偏酸性、氧化的特点.典型矿床因子分析揭示,红土型金成矿作用可分为氧化和水解两个阶段.氧化阶段风化较弱,基岩释放大量碱性离子,使成矿流体保持中性,金溶解并主要以Au(S2O3)23-形式迁移;水解阶段风化较强,硅酸盐矿物发生脱碱去硅作用,随着大气降水不断参与,成矿流体性质由中碱性缓慢过渡到中-酸性条件,金以胶体或氯化物络合物形式迁移.金一般在风化壳下部富集,表生矿物吸附、氧化还原界面处被Fe2 、Mn2 还原以及不同性质流体混合都能促使金的沉淀. 相似文献
9.
10.
Minerals of native elements (Pd, Pt, Au, Ag, and Au-Ag solid solutions) as well as Pb, Zn, Cu, Bi, Fe, Cr, Ni, W, Al, and
their intermetallides, and a number of other ore minerals were discovered in brown coals of the Erkovets field. The structural
reorganization of the noble metal grains and most of the other minerals found in the brown coals suggest their authigenic
paragenesis. The input of noble metals in brown coals is possible in an ionic mode from the surface and underground waters
as mineral particles transported by wind from goldfields. 相似文献
11.
微生物影响硅酸盐矿物风化作用的模拟试验 总被引：18，自引：1，他引：17
研究了硅酸盐细菌对矿物的风化作用。选用土壤中常见的钾长石、伊利石等矿物作为细菌风化作用的对象,通过在含有矿物颗粒的无氮培养基中培养硅酸盐细菌,使其在培养液中与矿物颗粒发生相互作用,再取样并处理后进行电镜观察和X-射线衍射分析。电镜观察结果表明细菌对矿物试样表面确实发生了溶蚀作用,被细菌作用后的矿粉,颗粒浑圆,边缘模糊不清,表面呈凹凸不平状,矿物颗粒被大量的菌体物质所覆盖。用X-射线衍射分析检测到细菌对具不同晶体结构矿物的“选择性”破坏作用,在有多种矿物同时存在的情况下,细菌对较易分解的矿物破坏作用速度较快。结合矿物学与微生物学相关知识,初步分析了细菌培养液中细菌与矿物界面之间的相互作用以及土壤生态系统中矿物的生物风化作用过程。 相似文献
12.
Yu.A. Kalinin K.R. Kovalev E.A. Naumov M.V. Kirillov 《Russian Geology and Geophysics》2009,50(3):174-187
A comparative analysis of morphology and geochemistry was made for gold from the primary ores and weathering crust of the Suzdal' gold deposit, Eastern Kazakhstan. The deposit is localized in Carboniferous carbonaceous-terrigenous strata and is of gold-sulfide type. Study of gold from primary ores showed that it occurs mainly in two species: free and so-called invisible. Free gold is crystallomorphic segregations and irregular-shaped grains up to tens of microns in size; it occurs in intergrowths with sulfides, quartz, carbonate, and mica-chlorite aggregate. Most of gold particles have a fineness of 930–980‰, with some grains showing wide variations in composition. Invisible gold (probably chemically combined) is present in fine-acicular arsenopyrite and, less frequently, pyrite.Being transported to the weathering crust, all this gold served as a source for “neogenic” gold of diverse morphologic forms. We recognized crystalline (isometric, prismatic, acicular, and tabular) particles and drusoid gold aggregates in the form of exotic intergrowths of crystallomorphic and sinter-shelly grains. The grains tend to coarsen from bottom to top of the weathering crust. Several generations of gold of different granulometric classes are observed. We have revealed seed and layer growth and dissolution structures in crystals of early generations overgrown with fine grains. All these gold varieties are associated with hypergene minerals. Most of this gold is of high fineness (on the average, 995‰). The hypergene gold particles are chemically homogeneous high-grade, without rims.The results of studies suggest that the high-grade hypergene gold formed in the weathering crust as a result of the dissolution of invisible gold of sulfides and its local redistribution and deposition in oxidizing media. This is also evidenced from the tendency of gold to coarsen from bottom to top of the weathering crust. A distinctive feature of secondary gold is well-expressed crystals and their great diversity. 相似文献
13.
At Dondo Mobi in the gold district of Eteke, south Gabon, gold mineralization was studied in a tropical forest setting. The mineralization occurs in quartz veins within amphibolites of an Archaean gneiss-amphibolite series. Gold distribution patterns were studied in the different horizons of the weathering profile and in the different grain-size fractions of the materials sampled from three pits sunk in the weathered zone: upslope (pit P1), directly overlying (pit P2) and downslope (pit P3) of the mineralization.The weathering profile consists of an upper, thick, loose sandy argillaceous horizon (H1), an irregular nodular horizon with laterite nodules or blocks (H2) and a saprolite layer (H3) up to 70 m thick. In each pit, the specific geochemical signature of the bedrock is recognized in the three horizons of the weathering profile. Some groups of elements, e.g., Cr-Ni or Ba-V-P2O3, characterize amphibolite or black shale, respectively. Signal attenuations in the upper horizon can be explained by a homogenization effect. That can be related to a mushroom supergene dispersion, simultaneously inducing vertical decrease and lateral enrichment in element contents. Gold also mushrooms extensively in the different horizons of the weathering profile. The dispersion pattern is somewhat anisotropic, a strong enlargement being observed in the upper (H1) and intermediate nodular (H2) horizons alike. However, the evolution of Au distribution is not the same for all grain-size fractions: (a) in the finest fraction, Au is regularly distributed in the weathering profile at the anomalous top and tends to preserve an equivalent level of concentration laterally; (b) in the coarsest fraction, the maximum Au content is found in the upper horizon just above the mineralized structure; it is rapidly decreases laterally, in the surface halo.The Au geochemical dispersion halo consists mainly of fine-grained gold developed from rather coarse-grained mineralization. Its characteristics suggest that Au dispersion was produced as a result of Au dissolution together with collapse of the weathering profile causing gold migration over short distances.The minimal volumetric reduction of saprolite in the upper horizon can be estimated to be in the range of 60%, on the basis of the content of the different grain-size fractions and the density variations in the various horizons.In exploration, geochemical techniques, even using wide sample spacing, are proving quite adequate to prospect for Au in tropical rainforest weathering environment. Indeed, significant, well-contrasted dispersion haloes facilitate detection of rather confined mineralization. 相似文献
14.
风化壳是不同地质历史时期风化作用的环境和物质记录,其组成、厚度、成熟度、保存程度等是古气候条件、区域构造活动性及地貌演化的直接反映。风化壳的形成年代是风化壳研究的关键内容,精确的风化壳年龄数据是查明一系列区域甚至全球事件的重要途径。风化壳中次生矿物（主要是钡硬锰矿族矿物和明矾石族矿物）的40Ar/39Ar年代学研究首次实现了对风化壳和风化作用的直接和精确定年,所获得的年龄数据为风化壳的形成演化、区域古气候古环境恢复、化学风化历史与矿床次生富集过程及新构造运动和山脉隆升历史等一系列重大地质问题的解决提供了重要途径。然而,风化壳中次生矿物定年存在的潜在问题及风化壳剖面取样的不完整性,有可能使风化壳的年龄分布变得相当复杂,导致对化学风化历史、风化壳形成过程和形成环境等的认识出现困难。为此,必须开展对风化壳的详细野外地质研究和精细取样,并综合采用多种先进测试手段,才能获得可靠的风化壳年龄数据。在对风化壳年龄数据进行解释时,还需要系统分析多种地质、环境资料（如古生物、盆地沉积物等）,才可能获得有意义的地貌、构造和古气候信息。我国华南地区广泛分布的红色风化壳中含有丰富的钡硬锰矿族矿物,是研究该区新生代以来化学风化、大规模次生富集成矿及古气候古环境演变的理想对象。 相似文献
15.
Deep weathering of basalt-hosted sulphidic gold mineralisation has resulted in remobilisation of the gold and the formation of a supergene deposit. The deposit occurs beneath an ephemeral lake system and is at least partially saturated by highly saline groundwater. A general downward movement of an iron redox front associated with the weathering has controlled the distribution of the gold and its morphology. It is unusual in that the high fineness gold crystals formed are coarse and well-preserved. Small octahedra, up to 50 μm, are the most abundant form of gold crystals but large, up to 3 mm, octahedral plates are common. Crystal morphology variations described here suggest that the gold is initially precipitated as euhedral octahedra and plates. Subsequent dissolution and recrystallisation associated with fluctuations in the chemical environment above the redox front has led to the development of the more common irregular dendritic or wire gold forms observed in other supergene deposits. 相似文献
16.
The mines in the Milluachaqui district, located near Salpo in the northern part of Peru, show a vertically zoned, epithermal silver-gold mineralization. Colonial production was obtained from oxidized, high-grade ores, consisting mostly of native silver and cerargyrite. More modern development exposed, from the top of ore shoots to their base, the "bonanza" ores (the pyrargyrite-polybasite-acanthite zone), silver-copper ores (the tetrahedrite zone), silver-lead ores (the galena-sphalerite zone), and the basal zone ores (the sphalerite zone). The ratio of gold to silver in the "bonanza" ores was about 1 to 100, by weight. Interpretation of mineralogical textures and the composition of minerals in the sulfide zone suggests that supergene movement and enrichment of silver at Milluachaqui was not a significant factor. Silver tended to be fixed in place during weathering as the chloride and native mineral. The "bonanza" ores are interpreted to be hypogene sulfide accumulations. These findings contrast to hypotheses proposed for some epithermal districts in the U.S. which assume supergene activity to have been significant in the accumulation of high grade, near-surface silver ores. 相似文献
17.
由于40Ar/39Ar定年方法在技术上极具复杂性,目前,国内在开展干旱区研究中很少使用风化矿物定年研究手段。重点介绍黄钾铁矾矿物40Ar/39Ar定年法的基本流程,并针对该方法的技术问题初步探讨了解决办法。研究表明,科学的野外采集样品、仔细的挑选矿物并综合采用多种测试手段（X衍射、扫描电镜、电子探针）进行监测可以获得纯净的风化矿物,并结合精细的40Ar/39Ar阶段加热技术,能够获得比较可靠的风化矿物40Ar/39Ar年龄。 相似文献
18.
《Journal of South American Earth Sciences》2000,13(3):217-224
At São Bartolomeu, central Brazil, chemical weathering of auriferous sulphide-rich quartz veins has produced a gold-bearing gossan. In the gossan, gold is present both as a residual primary mineral and as a neoformed secondary mineral. Primary gold particles contain varying amounts of silver. They are always more or less weathered, presenting rough surfaces pitted by numerous micrometric cavities. Other dissolution features identified in primary particles are indented shapes and jagged rims. Secondary gold occurs as aggregates of minute pseudohexagonal particles strongly depleted in silver. The presence of sulphur-containing complexes formed during the oxidation of the sulphides appears adequate to explain both the dissolution features on primary gold particles and the formation of pure supergene gold. 相似文献
19.
《Chemie der Erde / Geochemistry》2021,81(4):125770
The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg−1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg−1 while the rubble layer has a gold high of 6.1 mgkg−1. The individual soil horizons show no systematic gold trends and given the presence of gold in all layers, the patterns point towards supergene dissolution and redistribution of gold. Gold enrichment within the upper horizons in the weathering blanket is attributed to sequestration by Fe oxides of chemically remobilized gold. However, the high gold content within the sap rock and saprolite layers suggests that migration of gold in the particulate form supersedes chemical gold redistribution. Particulate gold obtained by panning samples from the pits varies in shape from euhedral, elongated to irregular. Electron microprobe analysis on the grains record high contents of gold in the rim zones (90.0 to 99.8 wt%). The cores are relatively rich in Ag (12.6 to 14.2 wt%) while the rims are poor in Ag. The low Ag content in the rims is attributed to the preferential leaching of Ag. The soil pH value in this area varies between 3.6 and 7.3. Under such acidic to near neutral conditions, bisulfide and thiosulfate ions can dissolve and transport Au and Ag to be precipitated under surficial conditions creating authigenic Au haloes especially in the saprolite and sap rock layers. Such pH values together with oxidizing Eh conditions explain the solubility of gold in the area. These results are important for geochemical exploration of gold in tropical terrains, and confirm previous studies. 相似文献
20.
Copper isotope fractionation in the Meiduk porphyry copper deposit,Northwest of Kerman Cenozoic magmatic arc,Iran 
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下载免费PDF全文 The Meiduk deposit possesses three different Cu reservoirs each with a unique Cu isotope signature. δ65Cu for the leached cap minerals ranges from ?2.5 to +0.49‰ to ?0.45 to +0.3‰ for hypogene minerals and from +1.3 to +4.4‰ for supergene enrichment minerals. Oxidation of hypogene sulphides and effective trapping of copper (from solutions derived from the leached cap) in the supergene enrichment zone caused this relationship. A systematic pattern of low Cu isotope values close to the surface and higher isotope values with depth reveals a palaeo‐fluid pathway in the northwest–southeast direction over the deposit. Thus, the copper isotope data from leached cap and enrichment minerals can be used to monitor copper migration during supergene weathering at the Meiduk deposit. 相似文献