A method of distinguishing nickel gossans from other ironstones of the Yilgarn Shield, Western Australia

A study of the trace-element content of ironstones of the Yilgarn Shield of Western Australia has shown that statistical groupings of Cu, Ni, Zn, Pb, Mn and Cr may be used to distinguish between nickel sulphide gossans from other ironstones. These groupings are supported by petrological and geological observations as well as drilling information. The paper also explains the use of Cu, Ni, Zn, Pb, Mn and Cr in establishing geochemical signatures for various lithologic types.     

Hydrothermal Alteration Mapping in Northern Khur, Iran, Using ASTER Image Processing: a New Insight to the Type of Copper Mineralization

Eastern Iran has great potential for the discovery of different types of mineralization. The study area encompasses Tertiary magmatism in the northern Lut block located in northern Khur, South Khorasan, eastern Iran and is mostly covered by volcanic rocks, which are intruded by porphyritic subvolcanic intrusions in some places. Application of the spectral angle mapper (SAM) technique to Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images detected sericitic, argillic, and propylitic alterations, silicification, and secondary iron oxides. The alteration is linear and associated within vein-type mineralization. Twelve prospective areas are selected for detailed exploration and based on our processing results, in addition to NW-SE faults, which are associated with Cu mineralization indications, NE-SW faults are also shown to be important. Based on the presence of subvolcanic rocks and numerous Cu ± Pb-Zn vein-type mineralizations, extensive alteration, high anomaly of Cu and Zn (up to 100 ppm), the age (43.6 to 31.4 Ma) and the initial 87Sr/86Sr ratio (0.7047 to 0.7065) of the igneous rocks, and the metallogenic epoch of the Lut block (middle Eocene-lower Oligocene) for the formation of porphyry Cu and epithermal deposits, the studied area shows great potential for porphyry copper deposits.     

Platinum-group element distribution in the oxidized Main Sulfide Zone, Great Dyke, Zimbabwe

In the Great Dyke mafic/ultramafic layered intrusion of Zimbabwe, economic concentrations of platinum-group elements (PGE) are restricted to sulfide disseminations in pyroxenites of the Main Sulfide Zone (MSZ). Oxidized ores near the surface constitute a resource of ca. 400 Mt. Mining of this ore type has so far been hampered due to insufficient recovery rates. During the oxidation/weathering of the pristine ores, most notably, S and Pd are depleted, whereas Cu and Au are enriched. The concentrations of most other elements (including the other PGE) remain quite constant. In the oxidized MSZ, PGE occur in different modes: (1) as relict primary PGM (mainly sperrylite, cooperite, and braggite), (2) in solid solution in relict sulfides (dominantly Pd in pentlandite, up to 6,500 ppm Pd and 450 ppm Pt), (3) as secondary PGM neoformations (i.e., Pt–Fe alloy and zvyagintsevite), (4) as PGE oxides/hydroxides that replace primary PGM as the result of oxidation, (5) hosted in weathering products, i.e., iron oxides/hydroxides (up to 3,600 ppm Pt and 3,100 ppm Pd), manganese oxides/hydroxides (up to 1.6 wt.% Pt and 1,150 ppm Pd), and in secondary phyllosilicates (up to a few hundred ppm Pt and Pd). In the oxidized MSZ, most of the Pt and Pd are hosted by relict primary and secondary PGM; subordinate amounts are found in iron and manganese oxides/hydroxides. The amount of PGE hosted in solid solution in sulfides is negligible. Considerable local variations in the distribution of PGE in the oxidized ores complicate a mineralogical balance. Experiments to evaluate the PGE recovery from oxidized MSZ ore show that using physical concentration techniques (i.e., electric pulse disaggregation, hydroseparation, and magnetic separation), the PGE are preferentially concentrated into smaller grain size fractions by a factor of 2. Highest PGE concentrations occur in the volumetrically insignificant magnetic fraction. This indicates that a physical preconcentration of PGE is not feasible and that chemical, bulk-leaching methods need to be developed in order to successfully recover PGE from oxidized MSZ ore.     

中国多金属结核开辟区沉积物中微量元素地球化学特征

分析了中国多金属结核开辟区沉积物中Ba、Ce、Co、Cr、Cu、Mo、Ni、Sr、V、Y和Zn等11个微量元素的含量。研究表明，开辟区沉积物中微量元素在不同沉积单元中的分布特征存在明显差异，反映了地质历史上沉积环境的不同。沉积物中的Zn、Ni和Mn具有共同来源，反映铁锰氧化物、氢氧化物对这些元素的吸附控制作用；Sr、Ba以及Ce和Y等元素在东区主要与岩源碎屑有关，而西区则主要来自生物碎屑；Cu具有多种来源，东区主要与生物组分和岩源碎屑有关，西区则主要与自生铁锰氧化物的吸附有关。而通常认为与有机物有关的Cr、V等元素在研究区内则主要来自岩源碎屑。     

Copper and zinc uptake by rice and accumulation in soil amended with municipal solid waste compost

Effect of addition of municipal solid waste compost (MSWC) on two metals viz. copper (Cu) and zinc (Zn) contents of submerged rice paddies were studied. Experiments were conducted during the three consecutive wet seasons from 1997 to 1999 on rice grown under submergence, at the Experimental Farm of Calcutta University, India. A sequential extraction method was used to determine the metal (Cu and Zn) fractions in MSWC and cow dung manure (CDM). Both metals were significantly bound to the organic matter and Fe and Mn oxides in MSWC and CDM. Metal content in rice straw was higher than in rice grain. Metal bound with Fe and Mn oxides in MSWC and CDM best correlated with straw and grain metal followed by exchangeable and water soluble fractions. Carbonate, organic matter bound and residual fractions in MSWC and CDM did not significantly correlate with rice straw and grain metal. The MSWC would be a valuable resource for agriculture if it can be used safely, but long-term field experiments with MSWC are needed to assess by regular monitoring of the metal loads and accumulation in soil and plants.     

重庆东北城口地区黑色岩系地球化学异常模式

重庆东北城口地区黑色岩系广泛发育,主要岩性有上震旦统到下武寒统的黑色碳质粉砂岩、含碳粉砂质板岩、含碳硅质岩等,在区内进行水系沉积物测量工作取得了良好的找矿效果.以区内的黑色岩系为重点研究对象,通过对样品分析数据的综合研究,指出了区内的主要成矿元素有Mn、V、Ag、Ba等,其中Mn主要富集在灯影组和陡山沱组中,V、Ag主要富集在鲁家坪组中,Ba则富集在巴山组中,初步确定了黑色岩系的地球化学异常模式,指明了区内黑色岩系的找矿方向.     

Geochemistry,mineralogy and tectonic setting of deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea

The geochemistry of two deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea suggests that they were deposited as metalliferous cherts enriched in manganese and iron by hydrothermal exhalative activity in an ocean ridge system. Subsequent blueschist facies metamorphism resulted in the formation of the assemblage deerite‐quartz‐albite‐iron oxides‐alkali amphiboles‐spessar‐tine‐stilpnomelane‐apatite, with calcium‐manganese carbonates in one specimen. Assemblages in associated metabasites suggest P‐T conditions of 7 kb at 320°C, which overlap with the P‐T field defined by one of the meta‐ironstones. Oxygen fugacity was probably an important control in determining variations in mineralogy and mineral chemistry. Preliminary data on the trace element geochemistry of associated metabasites are consistent with an ocean ridge environment for the formation of the meta‐ironstones.     

Gold exploration using lead isotopes at Tennant Creek,Australia

Lead isotope analyses have been undertaken as part of a program to evaluate the potential of geochemical methods for use in exploration in the Tennant Creek goldfield. Earlier exploration in this area was based on magnetic geophysical methods. Economic Au, Cu and Bi mineralization usually occurs in magnetic magnetite-chlorite lenses or pods (“ironstones”) which may be only 30 m across. Several hundred ironstones are found in the Tennant Creek field, of which only nine have been significant producers. Despite complications arising from the low Pb and relatively elevated U contents of the ore, determination of Pb isotope ratios in drill core material allows discrimination between economic magnetic ironstones and “barren” ironstones of similar mineralogy. A target signature for the Th-derived Pb isotope ratio, ²⁰⁸Pb/²⁰⁴Pb, is specific for lode mineralization, although it does not discriminate between Au-rich and Cu-rich lodes. The target signature is commonly found not only in the central Au-rich magnetite-chlorite zone, but also in the outer “barren” talc-magnetite and carbonate zones, offering up to a two-fold increase in the size of the target. The Pb isotope signature is retained in hematite-rich surface ironstones (termed “gossans” here) and it appears possible, at this stage of the project, to discriminate between gossans derived from mineralized magnetite lodes and “barren” magnetite lodes. A discrimination between weakly-mineralized (either Cu or Au) and economic deposits is equivocal at this stage. The difference between target and sample ²⁰⁸Pb/²⁰⁴Pb ratios (Δ208/204) ranges from −3 to +2% for the economic lodes, through weakly mineralized and “barren” magnetic ironstones (commonly in the range −20 to −40%) to the country rock magnetite shales (about −40 to −70%). These data are consistent with a significant Pb component in the “barren” ironstones being derived locally from the magnetite shales. Hematite shales commonly associated with economic lodes may have acted as limited channelways for the ore fluids as the target signature is discernible for up to 50 m along the hematite shale bands from the outer chlorite zones of the economic lodes. Further trace element and isotopic work is necessary to elucidate the genesis of the mineralization.     

Geochemical Characteristics and Genetic Significance of Datangpo‐Type Manganese Ore Deposits during the Cryogenian Period

The Datangpo‐type manganese ore deposits, which formed during the Nanhuan (Cryogenian) period and are located in northeastern Guizhou and adjacent areas, are one of the most important manganese resources in China, showing good prospecting potential. Many middle‐to‐large deposits, and even super‐large mineral deposits, have been discovered. However, the genesis of manganese ore deposits is still controversial and remains a long‐standing source of debate; there are several viewpoints including biogenesis, hydrothermal sedimentation, gravity flows, cold‐spring carbonates, etc. Geochemical data from several manganese ore deposits show that there are positive correlations between Al₂O₃ and TiO₂, SiO₂, K₂O, and Na₂O, and strong negative correlations between Al₂O₃ and CaO, MgO, and MnO in black shales and manganese ores. U, Mo, and V show distinct enrichment in black shales and inconspicuous enrichment in Mn ores. Ba and Rb show strong positive correlations with K₂O in manganese ores. Cu, Ni, and Zn show clear correlations with total iron in both manganese ores and black shales. ∑REE of manganese ores has a large range with evident positive Ce anomalies and positive Eu anomalies. The Post Archean Australian Shale (PAAS) normalized rare earth element (REE) distribution patterns of manganese ores present pronounced middle rare earth element (MREE) enrichment, producing “hat‐shaped” REE plots. ∑REE of black shales is more variable compared with PAAS, and the PAAS‐normalized REE distribution patterns appear as “flat‐shaped” REE plots, lacking evident anomaly characteristics. δ¹³C values of carbonate in both manganese ores and the black shales show observable negative excursions. The comprehensive analysis suggests that the black shales formed in a reducing and quiet water column, while the manganese ores formed in oxic muddy seawater, which resulted from periodic transgressions. There was an oxidation–reduction cycle of manganese between the top water body and the bottom water body caused by the transgressions during the early Datangpo, which resulted in the dissolution of manganese. Through the exchange of the euphotic zone water and the bottom water, and episodic inflow of oxygenated water, the manganese in the bottom water was oxidized to Mn‐oxyhydroxides and rapidly buried along with algae. In the early diagenetic stage, Mn‐oxyhydroxides were reduced and dissolved in the anoxic pore water and then transformed into Mn‐carbonates by reacting with HCO₃^? from the degradation of organic matter or from seawater. In the intervals between transgressions, continuous supplies of terrigenous clastics and the high productive rates of organic matter in the euphotic zone resulted in the deposition of the black shales enriched in organic matter.     

Distribution and enrichment of heavy metals in a sediment core from the Pearl River Estuary

A sediment core collected from coastal zone near the Qiao Island in the Pearl River Estuary was analyzed for total metal concentrations, chemical partitioning, and physico-chemical properties. Three vertical distribution patterns of the heavy metals in the sediment core were identified, respectively. The dominant binding phases for Cu, Pb, Cr, and Zn were the residual and Fe/Mn oxides fractions. Cd in all sediments was mainly associated with exchangeable fraction. Influences of total organic carbon content and cation exchange capacity on the total concentrations and fractions of almost all the metals were not evident, whereas sand content might play an important role in the distributions of residual phases of Cr, Cu, Pb, and Zn. In addition, sediment pH had also an important influence on the Fe/Mn oxides, organic/sulfide and residual fractions of Cr, Cu, and Zn. Contamination assessment on the heavy metals in the sediment core adopting Index of Geoaccumulation showed that Cr, V, Be, Se, Sn, and Tl were unpolluted, while Cu, Ni, Pb, Zn, Cd, and Co were polluted in different degrees throughout the core. It was remarkable that the various pollution levels of the metals from moderate (for Cu, Pb, and Zn) to strong (for Cd) were observed in the top 45 cm of the profiles. The relative decrease of the residual fraction in the upper 45 cm of the core is striking, especially for Zn and Cu, and, also for Pb, and Cr. The change in fraction distribution in the upper 45 cm, which is very much contrasting to the one at larger depths, confirms that the residual fraction is related to the natural origin of these metals, whereas in the upper part, the non-residual fractions (mainly the Fe/Mn oxides fraction) are increased due to pollution in the last decade. The possible sources for Cu, Pb, Zn, and Cd contaminations were attributed to the increasing municipal and industrial wastewater discharges, agricultural runoff, atmospheric inputs, and runoff from upstream mining or smelting activities, which may be associated with an accelerating growth of economy in the Pearl River Delta region in the past decade.     

Anomaly threshold estimation and data normalization using EDA statistics: application to lithogeochemical exploration in Lower Cretaceous Zn–Pb carbonate-hosted deposits,Northern Spain

A lithogeochemical survey of Lower Cretaceous sediments (1293 samples) in the Basque–Cantabrian basin (northern Spain) was carried out in order to estimate the mean contents of major oxides and Ba, Co, Cu, Ni, Pb, Rb, S, Sr, V, Zn and Zr in different lithological subsets and to identify anomalies related with Zn–Pb carbonate-hosted mineralization.After a detailed evaluation of different anomaly recognition methods, using both real and synthetic data, the cut-off values used in the Exploratory Data Analysis (EDA) were selected as thresholds. A prior classification of the rocks (based on chemical, mineralogical and petrographical data) guarantees appropriate homogeneous (with respect to major oxides) rock-groups during the evaluation of the data. A data standardization method was developed and applied to the samples collected from the Carranza sector (n=330). Zinc and Pb values for each sample were normalized to the particular threshold and interquartile range of their corresponding rock-type. These normalized values were plotted in geochemical maps.The results reveal the presence of Zn (up to 0.6%) and Pb (max. 1380 ppm) anomalies concentrated in carbonate facies, mainly in limestones, dolostones and dolomitic limestones. Magnesium-rich carbonates host the most significant anomalies. In the Carranza area, the great majority of outliers occur around known Zn–Pb mineral occurrences and are concentrated at the edge of the carbonate platform. In some cases fault control of the anomalies is indicated.     

Chemical fractionation of transition elements in Pacific pelagic sediments

Partitioning of transition elements in Pacific pelagic sediments (35 samples) was performed by sequential chemical leaching with barium chloride/triethanolamine (easily extractable fraction), acidic cation exchange resin (carbonate phases), and hydroxylamine hydrochloride and dilute hydrochloric acid solutions (hydrous oxides). Residual metal percentages are highest in red-brown clays and siliceous ooze, intermediate in calcareous materials and low in micronodules (2 samples, > 125 μm): residual metal contents seem to be controlled predominantly by the rate of admixture of volcanoclastic materials. At higher bulk metal concentrations, the non-residual fractions of Mn, Cu, Ni and Zn generally increase both in red-brown pelagic clays and in siliceous ooze. Mn, Ni, and Co concentrations are mainly associated with the easily reducible fraction (0.1 M NH₂OH·HCl), whereas Fe, Cu, and Zn exhibit higher percentages in the hydrochloric acid soluble fractions (0.3 M HCl); Zn and Cu are associated to some extent with the carbonate phase, copper with the easily extractable fraction.     

Geochemistry and genetic model of the ore-bearing sediments of the Parnok ferromanganese deposit, Polar Urals

The Parnok ferromanganese deposit is confined to the black shales of the western slope of the Polar Urals. The deposit area is made up of weakly metamorphosed terrigenous-carbonate rocks formed in a marine basin at a passive continental margin. Ore-bearing sequence is composed of coaliferous clayey-siliceous-calcareous shales comprising beds and lenses of pelitomorphic limestones, and iron and manganese ores. The iron ores practically completely consist of micrograined massive magnetite. The manganese ores are represented by lenticular-bedded rocks consisting of hausmannite, rhodochrosite, and diverse manganese silicates. With respect to relations between indicator elements (Fe, Mn, Al, Ti), the shales are ascribed to pelagic sediments with normal concentrations of Fe and Mn, the limestones correspond to metalliferous sediments, ferruginous sediments are ore-bearing sediments, while manganese rocks occupy an intermediate position. It was found that the concentrations of trace elements typical of submarine hydrothermal solutions (As, Ge, Ni, Pb, Sb, Zn, etc.) in both the ore types are in excess of those in lithogenic component. At the same time, the indicator elements of terrigenous material (Al, Ti, Hf, Nb, Th, Zr, and others) in the ores are several times lower than those in the host shales (background sediments). REE distribution patterns in iron ores show the positive Eu anomaly, while those in manganese ores, the positive Ce anomaly. In general, the chemical composition of the ores indicates their formation in the hydrothermal discharge zone. The peculiar feature of the studied object is the manifestation of hydrothermal vents in sedimentary basin without evident signs of volcanic activity. Hydrothermal solutions were formed in terrigenous-carbonate sequence mainly at the expense of buried sedimentation waters. The hydrothermal system was likely activated by rejuvenation of tectonic and magmatic processes at the basement of sedimentary sequences. Solutions leached iron, manganese, and other elements from sedimentary rocks and transported them to the seafloor. Their discharge occurred in relatively closed marine basin under intermittent anaerobic conditions. Eh-pH variations led to the differentiation of Fe and Mn and accumulation of chemically contrasting ore-bearing sediments.     

The Trace Element Distribution Patterns of Ediacaran-Early Cambrian Black Shales and the Origin of Selenium in the Guangning Area, Western Guangdong Province, South China

The Ediacaran and early Cambrian black shales are widespread across the South China Craton (Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirty-four black shale samples in the Lechangxia Group (Ediacaran) and thirteen black shale samples in the lower Bacun Group (early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values (EF) higher than 10, significantly enriched Bi and Rb (10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th (5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li (2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation (P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.     

新疆博格达东段多金属矿带化探原生晕与激电测量相结合的找矿效果

新疆博格达东段地表岩石风化剥蚀严重,直接找矿标志不明显,以大功率激电中梯测量为辅助功能的大比例尺岩石地球化学测量方法对发现和圈定隐伏矿体起到了重要作用。研究区原生晕微量元素定量分析结果表明,Cu、Zn、Mo、As等4种元素在勘查区为强富集元素,Pb、Sn、Co、Ba为富集元素,单元素具有水平分带性。根据化探原生晕元素组合特点及空间分布特征,以单元素异常下限值和陆壳克拉克值为划分标准,圈定了4个Ⅲ级化探异常带,异常评价初步认为Cu-Pb-Zn-Mo-As-Sn-Co-Ba-Fe-Ni-Hg多元素叠加异常区为找矿有利区。选择元素共生组合特点较明显的三个异常带开展大功率激电工作并进行化探异常的验证,最后在推断出的成矿有利部位布设钻孔并见矿。初步认为预测区成矿地质条件有利于形成黄铁矿型铜矿床。     

A mercury vapor survey in an area of thick transported overburden near Shanghai, China

Experimental surveys of Hg vapor in alluvium cover (up to 180 m thick) over a skarn copper deposit in the vicinity of Shanghai have shown encouraging results. Abundance and zoning of Cu, Pb, Zn, Ag, Mo, Mn, Sn, W, Ba, Bi, Co and Cl in soils and drill cores were studied for comparison.A distinct soil-gas Hg anomaly was discovered over the deposit. Repeated surveys carried out in different seasons during 1978 and 1979 show little variation in shape, dimension and intensity of the Hg anomalies.High soil-gas Hg values appear to be closely related to contacts, faults and fracture zones.Element zoning is well defined by the dispersion of Hg, Cu, Ag, etc. The zoning index of Hg and other elements shows that Hg is a typical front element.Thermo-release curves of Hg obtained by heating rock, ore and alluvium samples indicate that Hg has three forms of occurrence: easily volatilized Hg, chloride Hg, and sulphide Hg. Mercury chloride and volatile Hg represent the predominant phase in alluvium samples.     

宁沪高速公路句容段两侧土壤磁化率异常与重金属元素的关系研究

高速公路两侧土壤的磁化率从路中央向两侧具有逐渐降低的特征,相对应的样品中的重金属Cu、Pb、Zn、N i、Cr、Fe等元素的含量也具有从路中心向两侧逐渐降低的现象。相关分析表明,土壤磁化率与土壤中的Cu、Pb、Zn、N i、Cr、Fe的相关性显著,因而可以利用磁化率异常来指示高速公路两侧土壤的重金属污染状况。元素的赋存形态分析表明铁锰氧化物态与残渣态是Cu、Pb、Zn、N i、Cr、Fe的主要赋存形式;各元素的形态分析结果与土壤磁化率的相关统计分析表明,高速公路两侧土壤的磁化率与可交换态中的Cu、Pb、Zn、铁锰氧化物态中的Fe、Pb、Zn、有机还原态中的Cu、Cr、Fe、Zn和残渣态中的Cu、Pb、Zn、Cr、Co、N i具有明显的相关性。     

Cobalt as an exploration tool in the Outokumpu zone, Finland

The Outokumpu region in eastern Finland is an integral part of the Precambrian formations of the Karelidic orogeny. The copper-cobalt ore deposits discovered in the region are associated with a lithologic complex that consists of serpentinites, skarns, carbonate rocks and quartzites. The outer zone of this rock association adjacent to the surrounding mica schists is commonly occupied by black schists. The association constitutes the coherent stratigraphic sequence known as the Outokumpu zone, which is the environment in which the ore deposits of the Outokumpu type occur. The total length of the ribbon-like zone is about 240 km. Three Cu---Co ore deposits: Outokumpu, Vuonos and Luikonlahti are currently being exploited and four sub-economic ore showings have been found in the zone. All the deposits and ore showings are of the polymetallic sulphide type with copper, zinc, cobalt and nickel. There are also small amounts of silver, gold, tin and selenium in the orebodies. These stratabound ore deposits are submarine volcanic exhalative in origin. The immediate host rock of the ore is commonly quartzite, interpreted as a chemical silica precipitate.The Outokumpu copper-cobalt ore deposit was discovered in 1910. Owing to its economic potential, the Outokumpu zone is one of the most thoroughly studied parts of the Finnish Precambrian. More than 1000 holes have been drilled from the surface into the zone and provide a large source of material for lithogeochemical studies.The association does not lend itself easily to geophysical investigations because of its complex geology, characterized by black schists and other rocks giving a strong geophysical response. For this reason, and because of the extensive drilling, lithogeochemistry has become an important exploration tool in the region.The discovery of the blind Vuonos ore deposit in 1965 was the result of a comprehensive lithogeochemical study carried out in the early 1960's. Several old prospects were sampled in the Outokumpu zone and the sulphide phase was analyzed for Cu, Co, Ni and Zn.Clustering of the analytical data gives five groups of rock types: (1) quartzite-skarn-dolomite; (3) black schists; (4) mica schists; (5) copper-cobalt ore (Huhma and Huhma, 1970). The locations of these groups in Ni---Co and Cu---Co diagrams and in an Co---Cu---Ni triangular diagram are shown in Figs. 1, 2 and 3. The nickel content of serpentinites varies between 1500 and 2200 ppm and that of cobalt between 70 and 110 ppm. Thus the Ni/Co ratio averages 20:1. In the quartzite-skarn-dolomite-group the nickel content ranges from 900 to 3000 ppm and the cobalt content from 50 to 120 ppm. The Ni/Co 150 to 500 ppm and the cobalt content from 20 to 60 ppm. The Ni/Co ratio is about 10:1. Mica gneisses are poor in sulphides. Their nickel content averages from 40 to 90 ppm and the cobalt content from 15 to 30 ppm.The copper-cobalt ore occupies a discrete area in the Ni---Co diagram. Its nickel content varies between 1000 and 2000 ppm and the cobalt content between 1000 and 3000 ppm. The copper-cobalt diagram shows that the cobalt content of the serpentinites and the quartzite-skarn-dolomite group is fairly constant varying between 60 and 140 ppm. The copper content ranges from zero to 100 ppm in the former and from 10 to 100 ppm in the latter. In black schists the copper content varies from 100 to 300 ppm, the cobalt content being some tens of ppm. The mica gneisses are somewhat poorer in their Cu and Co contents. In this case too, the copper-cobalt ore has a Cu---Co content distinctly apart from those of the other groups.In the Cu---Co---Ni triangular diagram the serpentinite and the quartzite groups plot near the Ni apex of the triangle, the relative Ni content being 94–96% and that of Cu less than 1%. The black schists and mica gneisses have their own area near the centre of the Cu---Ni join with the Co content not exceeding 10%. There are several exceptions where points in the diagrams described above plot outside the normal field. Most of these anomalous points are located between the normal area of the rock type and that of the Cu---Co ore. The Ni---Co diagram in particular demonstrates that the deviations are due to the increase in the Co content.In summary, the anomalies of the Outokumpu type have: (1) a Ni/Co ratio lower than 15:1; and (2) a Cu percentage of the sum Cu+Co+Ni = 100 higher than 5. These anomaly units are applied to rank the analytical data of the Outokumpu zone. It is evident from the diagrams that the increase in cobalt content outside its normal field is the prime indication of the proximity of the ore. Being rather constant, the nickel content is used as a reference. Thus a decrease in the Ni/Co ratio indicates the presence of the ore. In some cases the decrease in the Ni/Co ratio may be due to a local decrease in the Ni content. The anomaly can be checked by the Cu/Cu+Ni+Co ratio. Except when testing the anomalies with Co, Cu and Ni as described above, the Co content alone can be used as an indicator of the proximity of a Cu---Co orebody. This was tested in one section of the Vuonos orebody (Fig. 4). The pyrite phase of the quartzites was selectively leached and its Co content analyzed. It was noted that the Co content of pyrite increased somewhat when the orebody was approached along strike.Before this method can be used more widely, the stratigraphic position and the structure of the potential ore horizon must be known fairly accurately. The proximity of an orebody can also be evaluated by means of the Co content of the black schists. As shown above, the Co content of the black schists is usually considerably under 100 ppm; it is usually over 100 ppm only adjacent to an orebody. Consequently, the extensive data on black schists in the Outokumpu zone can be sorted into potential and less potential ones.     

Iron mobility during synmetamorphic alteration in the Selwyn Range area,NW Queensland: implications for the origin of ironstone-hosted Au-Cu deposits

The Proterozoic metamorphic rocks of the Selwyn Range area in western Queensland contain a variety of styles of Au + Cu deposit including some (e.g. Selwyn mine and Osborne prospect) that are spatially associated with magnetite-rich ironstones. The area is characterized by extensive alkali-(chloride) metasomatism that occurred during the later stages of regional metamorphism. Existing experimental data indicate that hot saline fluids will dissolve and transport iron as they move through temperature/pressure gradients in the vicinity of the amphibolite-greenschist facies transition and predict that circulation cells will move iron and concentrate it in relatively cool, dilute and/or oxidized parts of such systems. New geological mapping coupled with geochemical data from the amphibolite facies zone of the Selwyn Range area suggest such processes occurred on a large scale and that large masses of Fe were mobilized, particularly in association with Na-metasomatism of biotite-bearing metasediments and high Fe-tholeiitic dolerites. Field and textural features of ironstones and other Fe-rich lithologies demonstrate that some of them at least formed by replacement of other rocks during metamorphism and deformation. Mineralization localized within such iron stones must itself be epigenetic.     

Composition of manganese nodules and manganese carbonates from Loch Fyne,Scotland

Manganese nodules and manganese carbonate concretions occur in the upper 10–15 cm of the Recent sediments of Loch Fyne, Argyllshire in water depths of 180–200 m. The nodules are spherical, a few mm to 3 cm in diameter, and consist of a black, Mn-rich core and a thin, red, Fe-rich rim. The carbonate occurs as irregular concretions, 0.5–8 cm in size, and as a cement in irregular nodule and shell fragment aggregates. It partially replaces some nodule material and clastic silicate inclusions, but does not affect aragonitic and calcitic shell fragments.The nodules are approximately 75% pure oxides and contain 30% Mn and 4% Fe. In the cores, the principal mineral phase is todorokite, with a Mn/Fe ratio of 17. The rim consists of X-ray amorphous Fe and Mn oxides with a Mn/Fe ratio of 0.66. The cores are enriched, relative to Al, in K, Ba, Co, Mo, Ni and Sr while the rims contain more P, Ti, As, Pb, Y and Zn.The manganese carbonate has the composition (Mn_47.7 Ca_45.1 Mg_7.2) CO₃. Apart from Cu, all minor elements are excluded from significant substitution in the carbonate lattice.Manganese nodules and carbonates form diagenetically within the Recent sediments of Loch Fyne. This accounts for the high Mn/Fe ratios in the oxide phases and the abundance of manganese carbonate concretions. Mn concentrations in the interstitial waters of sediment cores are high (ca. 10 ppm) as also, by inference, are the dissolved carbonate concentrations.