Geochemical exploration

NORMAT is a new technique for quantifying hydrothermal alteration in greenschist facies rocks using normative mineral ratios without precursor or mineralogical determination. Using five petrologic rules, the NORMAT calculations first compute normative alteration (paragonite, sericite, chlorite, pyrophyllite) and precursor minerals (albite, orthoclase, anorthite), as well as normative loss on ignition (LOI) and CO 2 contents. The results are then computed as alteration indices that quantify the overall alkali element depletion in terms of the paragonitization, sericitization, chloritization and pyrophillitization components. Equations for the alteration indices are ratios between the normative alteration and precursor minerals, thus providing a relative numerical measure of alteration intensity that is independent of protolith. Alteration by carbonatization is quantified by the IPAF index, which represents the position of the sample's analytical LOI value within a range bounded by CO 2-free normative LOI and maximum possible normative LOI-CO 2 content. This procedure also allows the CO 2 content to be estimated from LOI, which can then be used to calculate normative carbonate minerals. Alteration index (AI) values and normative minerals for 28 selected samples from the Val d'Or Formation illustrate the main properties of normative mineral ratio alteration indices.

Mineral exploration in areas of little bedrock exposure must increasingly rely on the predictive quality of geological, geochemical and geophysical data. In this contribution analysis of fluid inclusions is used to characterize fluid systems associated with alteration and mineralization in two locations in South Australia. In the Curnamona Province, fluids related to albitization and calc-silicate alteration with associated brecciation evolve from a saline sodic composition to a metalliferous, saline fluid also found associated with sulphide mineralization. The microthermometric distinction of inclusion types is evidence for pressure fluctuation as a cause for breccia formation. In the Central Gawler Craton gold province fluid inclusion studies have characterized the compositional and constrained the physical conditions of mineralizing fluids. Regionally identified low salinity CO 2 -bearing fluids at temperatures b 350°C and pressures b 1.5kbar indicate a shallow-level orogenic [Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic gold Deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews, 13, 7-27.] or intrusion-related [Lang, J.R., Baker, T., 2001. Intrusion related gold systems: the present level of understanding. Mineralium Deposita, 36, 477-489.] setting for the mineralization.

Hydrochemical data for meteoric waters of the uplifted carbonate platform of northern Guam show that, contrary to recent models of lowstand diagenesis, phreatic dissolution is active beneath a 60-180m thick vadose zone. Overland flow during high intensity rainfall events is focussed into surface detention ponds, which drain very rapidly via the epikarst and vertical fissures to the freshwater lens. We estimate that these waters contribute 13% of dissolved calcium in samples from pumping wells but may also deliver aggressive and/or organic-rich waters to the lens. Fast-flow vadose waters mix with lens-top waters to form fresher cap that discharges rapidly coastwards via cavernous porosity. Slower vadose percolation, sampled as cave drips, equilibrates with bedrock within the upper 30 m of the vadose zone, accounting for some 46% of dissolved calcium in the lens waters. The remaining 41% calcium is generated by net dissolution within the lens.

The quantitative relation between point source soil geochemical anomalies and their response in stream sediments is linked through the concept of productivity (area ð concentration). The equation proposed by Hawkes in 1976 is shown to be a subset of a wider range of equations proposed by Russian workers. These workers introduced two coefficients to account for the contrasting behaviour of different elements and the position of the soil anomaly within the drainage catchment. The calculation of these coefficients requires a series of samples downstream from the ending of anomalous soil input. The concept of productivity has particular application where multiple samples and anomalies are present in catchments. Plotting of productivity allows the discrimination of anomalous areas not detectable from raw element concentrations. The usefulness of these techniques is demonstrated from a small detailed stream sediment survey in NW Scotland. Dispersion from a gossan shows deviation from the Hawkes equation with the result that detailed sampling is required to detect soil anomalies. Plotting productivity allows the detection at the base of major slopes of anomalies that are diluted by upslope sediment.

Increasing land transformation in the Amazon basin, from forest to post-forest usage such as pastureland, agriculture and agroforestry, triggers significant changes in hydrology, soil fertility and regional climatology. However, relatively little is known about Amazon basin soil chemistry in general and about its possible alteration with recent land-use change. We present robust pedogeochemical data for 65 elements and oxides, and evidence for modification due to recent deforestation and post-forest land use on upland soils in Amazonas state, Brazil. Differences emerge in median element concentrations between these two land-cover types, and between central and southern parts of the basin. These new data, a product of the bi-national EcoRespira-Amazon (ERA) project, are based on triplicate sampling under different seasonal conditions at 29 sites, representing ca. 740,000 km2 and average annual meteorological conditions. Mineral soil samples (TOP: 0–20 cm; BOT: 30–50 cm) characterize ...

The sources and the potential availability of chromium were investigated in ultramafic soils from Niquelândia (Goïas State, Brazil), with chemical extractions associated to mineralogical studies, in order to evaluate its bioavailability and its potential impact on the soil biodiversity. Cr contents are particularly high in the studied soils and its partitioning among the solid phase varies with the position in the landscape and depth. Most of the Cr is associated to Fe-oxides but the amount of exchangeable Cr(VI) is high, particularly in one soil profile. Cr availability is higher than expected, and Cr-tolerant vegetation is probably growing on these soils. D

We conducted a study of the biogeochemical cycle of silicon in a rice field in Camargue (France) in order to evaluate the role of biogenic silicon particles (BSi) in the cycle. Opal-A biogenic particles (phytoliths, diatoms. . .), which dissolve more rapidly than other forms of silicate usually present in soils, are postulated to represent the easiest bioavailable Si for rice. We found 0.03-0.06 wt.% of BSi in soils (mainly phytoliths). This value is lower than other values from the literature. Each year, the exportation of BSi from rice cultivation is 270 F 80 kg Si ha À 1 . We show that BSi input by irrigation is mostly composed of diatoms and we estimate it at 100 kg Si ha À 1 year À 1 . This value is more than a third of the annual Si need for rice. The budget of the dissolved silicon (DSi) fluxes gives the following results: the atmospheric and irrigation inputs represents 1% and roughly 10%, respectively, of the annual need for rice; the drainage and infiltration outputs represent 17 F 14 and 12 F 9 kg Si ha À 1 year À 1 , respectively; the balance of our budget shows that at least 170 kg Si ha À 1 year À 1 are exported from the soil. If we consider the soil BSi as the only source of dissolved silicon, this stock could be exhausted in 5 years. D

Very limited research has been conducted on selenium (Se) in Lebanese soils and forage crops but no work has been done on Se in water and locally produced vegetables and grains. This research was conducted in order to quantify Se levels and its availability in agricultural soils, vegetables and grains in Lebanon. Sixty-six (66) soil samples were collected from 33 selected sites in Lebanon: the Bekaa Valley, coastal and mountainous regions. Thirteen (13) different plant types (86 samples) were sampled from the same locations. Also, 13 spring water and 10 bottled water samples were collected. Soil samples were analyzed for their physical and chemical properties. Selenium was extracted from soils with: deionized-distilled water (Soluble-Se), KH 2 PO 4-0.1 M (MKP-Se) and concentrated (HNO 3 + HCl) mixture (acid-Se). Plant Se was extracted by acid digestion on a hotplate. Selenium concentrations were measured by the inductively coupled plasma-mass spectrophotometer (ICP-MS). The values of Soluble-Se, MKP-Se and acid-Se ranged between 47 and 142, 147 and 400, and 1749 and 4713 μg/kg, respectively, with average values of 95, 306, and 3118 μg/kg and at a ratio of 1:3:30. Thus, Se extracted with deionized-distilled water is a good indicator for Se availability in the studied soils. The average Se concentration in plants was in the following order: radish N lettuceN cucumberN cabbage N parsley N alfalfa N onion (leaves)N broccoliN tomato N mintN chickpeas N wheatN onion (bulbs). The Se levels in water samples were in the safe range (less than 50 μg/L) and ranged between 2.14 and 17.6 μg/L. The levels of Se in the three soil extractants were positively correlated with each other and with organic matter content, salinity and phosphorus (P). Selenium levels in plant samples were positively correlated at a 0.01 significance level with clay and P content.

Bitumens of the Alberta tar sands share a similar primary source rock, but exhibit varying levels of degradation. In the Peace River tar sands area, the wide range of API gravity and sulphur content in Lower Cretaceous reservoirs is investigated in terms of biodegradation processes, using detailed geochemical analyses, burial history modelling and charge/degrade modelling. Decreasing tar sand degradation to the west can be attributed to increasing reservoir temperatures which retard biodegradation. Gething oils west of the Peace River tar sands are derived from the same source, but are minimally degraded due to reservoir pasteurization at 80°C shortly after charging. Long charge times, reservoir filling and possibly compositional or very low temperature degradation retardation have limited biodegradation of the Alberta tar sands despite long oil residence times and low reservoir temperatures.

During the regional and petrologic study of the Cameros Basin, vein deposits containing native sulphur, gypsum, quartz and rare sphalerite were found enclosed in lacustrine evaporites. The fluid inclusion study of the coeval quartz crystals revealed that the aqueous fluids were extremely scarce during vein formation. Surprisingly, the textural study, microthermometry and qualitative Raman analyses of these inclusions proved that the main fluid-trapped during vein formation was a mixture of molten sulphur and volatiles (N 2 , CO 2 and H 2 S). As far as we know, this is the first time that an almost pure sulphur-bearing fluid is described to occur in sulphur deposits. ᭧

Large-scale shallow-water deltas in lacustrine basins have recently been identified as important reservoir plays worldwide. The Poyang Lake, the largest fresh water lake in China, develops a series of modern shallow-water deltas, hence provides an excellent modern analogue for understanding various key depositional processes that control deltaic development and evolution. This paper uses SEDSIM, a three-dimensional stratigraphic forward modelling programme, to simulate the development and evolution of the shallow-water deltas in the Poyang Lake by considering a number of key processes and parameters affecting the deltaic deposition over 1200 years. The simulations show that the shallow water deltas have some unique characteristics. The delta plain is dominated by distributary channel sandbodies and thins towards the lake centre, whereas the delta front thickens lakecentre-wards. The major delta has very gentle delta slope less than 0.06°. The frequency of lake level oscillations appears to be a significant controlling factor in determining the deltaic architecture within the deltaic systems. The simulation indicates that the "Gilbert-type" deltas would not commonly develop in shallow-water basins even if the basin margin may be steeply sloped. The study has demonstrated that the process-based modelling approach can be effectively used to simulate complex geological processes and environments and quantify key controlling factors that otherwise cannot be easily acquired due to physical constraints.

Selenium is an essential trace element required in low amounts by humans and animals, but it can be toxic when ingested at high concentrations. Information regarding Se background levels in soils is important to prevent Se deficiency, to optimize human nutrition, and to prevent toxicological effects. Background Se levels in Brazilian soils were evaluated and correlated with other soil characteristics. Se concentrations were quantified in samples from the superficial layer (0-0.2 m) and from the subsurface layer (the highest portion of the B horizon) for 58 soils. Soils were selected across a wide range of soil types and parent materials. Se concentrations ranged from b0.08 to 1.61 mg kg −1 , with a mean of 0.19 mg kg −1 . Concentrations of Se in the samples collected in the superficial layer were positively correlated with cation exchange capacity, as well as with clay, organic matter, and oxide contents of the soils. In the subsurface samples, only pH and aluminum oxide content were correlated with Se concentrations.

Dissolution and leaching of silica in concrete aggregate leads to structural deterioration by the hygroscopic and swelling properties of the resulting gel, causing cracking of the concrete. The process is referred to as ASR: alkali-silica reaction. In Ž . Dutch concrete with relatively alkali-rich ordinary Portland cement OPC , chert pebbles are regarded susceptible to ASR owing to their fine-grained microstructural features and poor crystallinity. The damage in the three concrete structures presented in this study, however, is caused by reaction of fine-grained sandstone containing muscovite and interstitial clays. Despite the coarser microstructure and higher crystallinity, sandstone reacts more violently than chert in the same samples. Petrographical observations on reactive sandstone coincide with recent descriptions of catalyzed silica dissolution in diagenetically altered sandstones. Low Na O-equivalents decrease even further with increasing degree of cracking. The 2 combination of low bulk alkali content, microscopical characteristics of the reactive sandstone, and its resemblance to catalyzed quartz dissolution in diagenetic sandstones strongly suggests that a similar mechanism of catalyzed dissolution could play a significant role in ASR-induced aggregate deterioration in concrete. q 1998 Elsevier Science B.V. All rights reserved.

This paper describes the case history of a successful exploration programme for gold in Indonesia, initiated by CSR Minerals in 1984 and continued by Billiton Companies in Indonesia since 1988. Gold mineralization on Wetar island, Maluku, was first detected in 1986 as a stream sediment bulk leach extractable gold response of l0 ppb. Stream float mapping and sampling with systematic soil and rockchip sampling gave up to 13 g/t Au, with associated high Ag, Pb, As and Ba values at surface from W5 (Lerokis), one of seven promising initial anomalies. Detailed mapping and rockchip sampling, followed by scout diamond drilling, showed that most significant Au values were associated with barite-rich rocks in basinal structures. Systematic follow-up of the more promising anomalies began in 1987. The best results were obtained from W5 where a number of zones up to 200 × 500 m in size were outlined, with soil and rock values of 1 to 13 ppm Au. Ground geophysical surveys including electromagnetics (EM), induced polarization (IP) and resistivity gave several broad anomalies indicative of shallow conductors. Between 1987 and 1988, aerial reconnaissance was undertaken to locate other areas of visible alteration. This was integrated with Landsat thematic mapper data and defined seven red-stained anomalies in addition to W5, occurring within 5 km of the coast. Ground checks showed that only one of these anomalies, KK3 (Kali Kuning), contained significant surficial Au values. From 1989 to 1992, almost 20,000 m of diamond and reverse circulation (RC) drilling defined geological resources of 2.9 Mt at 3.5 g/t Au, 114 g/t Ag and 40% barite at Lerokis and 2.2 Mt at 5.5 g/t Au, 146 g/t Ag and 60% barite at Kali Kuning. Most other anomalies were then mapped and/or systematically sampled to delineate prospects outlined previously. Regional work is ongoing to define additional resources, using airphoto-based mapping and stream sediment sampling as the principal tools. Integrated exploration has discovered over 20 tonnes of near-surface Au on Wetar at a low cost. Mining operations began late in 1990 at Lerokis, and will begin in 1994 at Kali Kuning. This has formed the basis of an enterprise capable of giving direct employment to over 250 people for more than seven years and providing a return on exploration expenditure.

A comprehensive investigation of correlations for estimating convective heat-transfer coefficients (CHTC) of non-Newtonian drilling fluids used in the geothermal well completion was carried out. Five well-known empirical correlations were used to calculate CHTC at fully developed laminar and turbulent flow conditions. Transport properties of Newtonian and non-Newtonian drilling fluids (measured at the rheology laboratory) were compared and later used for computing CHTC in a useful temperature interval for geothermal drilling purposes (50 -180 jC). Viscosity was identified as one of the main properties that strongly affect the CHTC estimation. Newtonian and non-Newtonian fluid viscosities as a function of temperature showed significant differences, up to 98%. The use of Newtonian fluid viscosities generally produced an overestimation of the mud CHTC. This problem enables us to explain why the temperature profiles usually computed by some wellbore thermal simulators predict a fast cooling process in the well surrounding formation in comparison with CHTC estimated from actual non-Newtonian drilling fluid viscosities. D

A multidisciplinary geochemical study of the distribution, dispersion, and glacial dispersal, of the PGE and associated elements has been undertaken within soil, till, humus, vegetation and water at Ferguson Lake, Northwest Territories, Rottenstone Lake, Saskatchewan and Sudbury, Ontario.

Stratiform sediment hosted Zn-Pb-Ag deposits, often referred to as SEDEX deposits, represent an economically important class of ore, that have received relatively little attention in terms of defining lithochemical halos and geochemical vectors useful to exploration. This study concentrates on the Lady Loretta deposit which is a typical example of the class of Proterozoic SEDEX deposits in northern Australia. We examined the major and trace element chemistry of carbonate-bearing sediments surrounding the deposit and defined a series of halos which extend for several hundred metres across strike and up to 1.5 km along strike. The stratiform ore lens is surrounded by an inner sideritic halo . Primary geochemical and mineralogical dispersion in the vicinity of the Lady Loretta Zn-Pb-Ag deposit, North Queensland. J. Geochem. Expl. 22, 217-238], followed by an outer ankerite=ferroan dolomite halo which merges with low iron dolomitic sediments representative of the regional background compositions. Carbonate within the inner siderite halo varies in composition from siderite to pistomesite (Fe 0.6 Mg 0.4 CO 3 ), whereas carbonate in the outer ankerite halo varies from ferroan dolomite to ankerite (Ca 0.5 Mg 0.3 Fe 0.2 CO 3 ). Element dispersion around the stratiform ore lens is variable with Pb, Cu, Ba and Sr showing very little dispersion (<50 m across strike), Zn and Fe showing moderate dispersion (<100 m) and Mn and Tl showing broad dispersion (<200 m). Within the siderite halo Cu, Mg and Na show marked depletion compared to the surrounding sediments. The magnitude of element dispersion and change in carbonate chemistry around the Lady Loretta orebody has enabled the development of three geochemical vectors applicable to exploration. Whole rock analyses are used to calculate the three vector quantities as follows: (1) SEDEX metal index D Zn C 100Pb C 100Tl; (2) SEDEX alteration index D (FeO C 10MnO)100=(FeO C 10MnO C MgO); (3) manganese content of dolomite: MnO d D (MnO ð 30.41)=CaO. All three vectors increase to ore both across strike and along strike. The manganese content of dolomite (MnO d ) exhibits the most systematic pattern increasing from background values of about 0.2 wt% to a maximum of around 0.6 wt% at the boundary between the ankerite and siderite halos. Siderite within the inner halo contains considerably more Mn with MnO values of 0.4 to 4.0 wt%. It is suggested here that the basket of indices defined at Lady Loretta (Zn, Tl, metal index, alteration index, MnO d and MnO s ) is applicable in the exploration for stratiform Zn-Pb-Ag deposits in dolomite-rich sedimentary basins generally. The indices defined can firstly assist in the identification of sedimentary units favourable for SEDEX mineralisation, and secondly provide vectors along these units to ore. The alteration index and Ł MnO d , however, should only be used for exploration dolomitic sequences; they are not recommended for exploration in clastic sequences devoid of carbonates.

Geochemical anomaly separation using the concentration-area (C-A) method at Kahang (Gor Gor) porphyry system in Central Iran is studied in this work. Lithogeochemical data sets were used in this geochemical survey which was conducted for the exploration for Cu mineralization in dioritic and andesitic units at Kahang Cu-Mo porphyry system. Similar surveys were also carried out for Mo and Au exploration in these rock units. The obtained results have been interpreted using rather extensive set of information available for each mineralized area, consists of detailed geological mapping, structural interpretation and alteration data. Anomalous threshold values for the mineralized zone were computed and compared with the statistical methods based on the data obtained from chemical analysis of samples for the lithological units. Several anomalies at a local scale were identified for Cu (224 ppm), Mo (63 ppm), and Au (31 ppb), and the obtained results suggests existence of local Cu anomalies whose magnitude generally is above 1000 ppm. The correlation between these threshold values and ore grades is clearly interpreted in this investigation. Also, the log-log plots show existence of three stages of Cu enrichment, and two enrichment stages for Mo and Au. The third and most important mineralization event is responsible for the presence of Cu at grades above 1995 ppm. The identified anomalies in Kahang porphyry system, and distribution of the rock types, are mainly monzodiorite and andesitic units, do have special correlation with Cu and monzonitic and dioritic rocks, especially monzodioritic type, which is of considerable emphasis. The threshold values obtained for each element are always lower than their mean content in the rocks. The study shows threshold values for Cu is clearly above the mean rock content, being a consequence of the occurrence of anomalous accumulations of phyllic, argillic and propyllitic alterations within the monzonitic and dioritic rocks especially in monzodioritic type. The obtained results were compared with fault distribution patterns which reveal a positive direct correlation between mineralization in anomalous areas and the faults present in the mineralized system.

Total arsenic, dissolved organic carbon (DOC), iron, major cations and anions were measured in tube-well waters used for drinking by people to investigate the geochemical condition of subsurface aquifer, source of arsenic and mechanism of arsenic release to groundwater of Bangladesh. Solid phases of total arsenic, iron, manganese and aluminum oxide and organic carbon (TOC) content in sediments were determined to find out their interrelationships. Arsenic concentrations in groundwaters vary from 0.03 to 0.75 mg/l with the mean value of 0.41 mg/l that exceed the maximum permissible limit of WHO (0.01 mg/l) and Bangladesh (0.05 mg/l) for drinking water. Arsenic concentrations demonstrate negative covariation with the concentrations of sulfate and nitrate but correlate weakly with iron concentrations and positively with those of ammonium ions. Dissolved iron exhibits a negative covariance with the concentrations of sulfate. Very low concentrations of nitrate and sulfate and high concent...

Almost all Red Sea deeps contain metal-rich sediments covered by brine pools. It is generally agreed that these metal-rich deposits precipitated from overlying metal-rich brines that originated from migrating hydrothermal fluids. No brine pool has ever been reported in Thetis Deep, inciting us to evaluate if such a brine layer ever occurred in the deep during the past. In order to address that questioning, a study combining mineralogical, geochemical (major-, minor-, rare-earth elements) and isotopic (Sr, Nd, Pb) approaches was completed on cored sediments and extracted interstitial waters from inside and outside the deep. The sediments have an overall hydrothermal origin, as shown by the REE concentrations and patterns, metal contents, and Pb-Nd isotopic data, all pointing to a mantle signature. The intensity of the hydrothermal activity varied with time in the deep; the most intense episode resulting in an almost pure Fe-oxi-hydroxide layer. Varied chemical arguments, especially the Zr and REE data of the sediments, favor the fact that the whole sedimentation in Thetis Deep occurred in the absence of a stable, salt-rich and mineralized brine pool, and that no brine layer ever existed. This conclusion is supported by the constant Sr isotope composition of the sediment and its interstitial waters that are almost identical to that of the Red Sea seawater. The study also suggests that hydrothermal activity monitored fluid supplies that interacted differently with seawater in the different Red Sea deeps, resulting in an overall formation of metal-rich sediments, but along varied local conditions. j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j g e o ex p warmer, saltier and denser than seawater and fill most bathymetric depressions, allowing formation of brine pools separated from overlying deep seawater by temperature and salinity gradients (Shanks and

Acid mine waters have the potential to seriously impair the environmental quality of aquatic systems long after mining activities have ceased. This detailed study of dissolved and particulate metal fluxes from adits, drains and streams in the River Tamar catchment, southwest England, showed that seven specific sources, of the 25 adits and streams surveyed, accounted for more than 75% each of the 13 t a − 1 Fe, 4.3 t a − 1 Mn, 4.2 t a − 1 Cu, 3.6 t a − 1 Zn and 1.4 t a − 1 As that we estimated to be discharged annually from the abandoned metalliferous mining area centred around Calstock and Gunnislake. Upstream of this study area, widespread multi-metallic mineralisation contributed to the flux of Fe, Mn, As, Co, Cu and Zn within the River Tamar. Simple mass balance calculations indicated that a large proportion (≥ 50% for most dissolved and particulate metals) of the metal flux in the River Tamar was unaccounted for by our survey, and therefore is likely to have an important diffuse component, which is subject to ongoing investigations. Potential impacts of mine contamination on the estuarine environment are discussed. The study provided information necessary to prioritise monitoring and remediation efforts in the context of sustainable catchment management.

Resumo O grupo de geoquímica de Carajás (VALE-DIPM) desenvolveu um mapa de regolitos e regimes geomorfológicos regional de Carajás, abrangendo o Cinturão Cinzento e parte do entorno do depósito do Igarapé Bahia. Este mapa é fruto de um somatório de conhecimentos adquiridos a partir de estudos e pesquisas teóricas e de campo, desenvolvidas pela equipe de exploração da VALE em Carajás. O mapa de regolitos e regimes geomorfológicos regional de Carajás é composto por uma série de atributos permitindo, inclusive, a geração de subprodutos específicos. Posteriormente foi confeccionado um mapa simplificado ressaltando a natureza do material aflorante. As duas versões dos mapas objetivam dar uma primeira visão das unidades regolíticas para os trabalhos prospectivos geoquímicos de um alvo. Abstract The geochemistry group (VALE-DIPM) of Carajás has developed regional regoliths and geomorphological regimens map of Carajás, covering the Cinzento Belt and the surrounding portion of the Igarapé Bahia deposit. This map is the result of a sum of knowledge acquired with studies and field and theoretical research, developed by the VALE´s exploration team in Carajás. The regolith and geomorphological regimens regional map of Carajás comprises a series of attributes permiting the generation of specific subproducts. Afterwards was accomplished a simplified map highlighting the nature of the outcropping material. Both maps versions aim to give a first view of the regolithic units to the prospective geochemical works at a target.

The non-stoichiometric compounds of iron sulphide named pyrrhotite (Fe 1 À x S) are often associated with pyrite (FeS 2 ) in sulphidic ores and their waste products. The factors affecting pyrite and pyrrhotite oxidation are similar but the latter has received much less attention. As it is the case for pyrite, an increase in temperature has an increasing effect on the oxidation of pyrrhotite and the process follows the Arrhenius behaviour. Both ferric iron and bacteria act as catalysts in the oxidation reactions and play a significant role in the oxidation kinetics. Several spectroscopic techniques are used to study the oxidation mechanisms and products of pyrrhotite oxidation. This paper presents and discusses the main factors controlling pyrrhotite oxidation and the proposed mechanisms of oxidation under normal conditions of temperature and pressure. D Abbreviations: AES, Auger electron spectroscopy; AMD, acid mine drainage; EPR, electron paramagnetic resonance; FTIR, Fourier transform infrared; NL, non-equilibrium layer; SEM, secondary electron microscopy; SLS, sequential layer sputtering; ToF SIMS, time of flight-secondary electron mass spectrometry; XES, X-ray electron spectrometry; XRD, X-ray diffraction; XPS, X-ray photoelectron spectrometry.

We present the results of an experimental study into the replacement of magnetite by pyrite under hydrothermal conditions (85 to 210°C, vapor saturated pressure), a geologically important process in formation of a number of gold deposits. The formation of pyrite was studied as a function of time, temperature, pH, ƒ s and surface area. BSE imaging revealed a visible gap (on the μm scale) at the reaction front between the parent magnetite and the secondary pyrite, which is in contrast with other tightly coupled replacement reactions such as pentlandite to violarite where the reaction is coupled at nm scale. Depending on pH of the solutions either or both pyrite and marcasite can form. Marcasite was found only at pH 25°C b 4 and became the dominant iron disulfide at pH 25°C 1.10, while pyrite was the predominant sulfide at pH 25°C N 2 and can be formed even under basic conditions (up to pH 25°C 12~13). Pyrrhotite was also detected by X-ray diffraction co-existing with pyrite in some experiments with finegrained magnetite (i.e., large surface area). Direct heterogeneous nucleation of pyrite from solutions and pyrite formation via replacement of pyrrhotite (formed by replacing magnetite), are both proposed as reaction mechanisms based on textural and phase assemblage data. The formation of pyrite by replacement of pyrrhotite was demonstrated to proceed by the 'H 2 S pathway' under slightly acidic conditions (NpH 25°C 3.93) or by 'polysulfide pathway' in slightly alkaline solutions (b~pH 25°C 10). At pH 25°C ≤ 3.08, based of previous studies FeS (aq) plays a central role in the pyrite formation in solutions undersaturated in sulfide ions with respect to mackinawite. The overall transformation has a complex dependence on temperature: the overall reaction rate first increased from 85 to 125°C (following Arrhenius Law) and then decreased from 125 to 210°C (non-Arrhenian behavior) for experiments at pH 25°C N 2. In contrast, at pH 25°C 1.10, where marcasite is the dominant product, the kinetics are Arrhenian over the temperature interval of 125-210°C.

The probability of the occurrence of porphyry copper ore associated with subduction zone of the Neo-Tethys ocean and volcanic arc of Iran (Urumieh-Dokhtar) justifies the necessity of exploration and prospection of this type of ore in Iran. Zafarghand index and Kahang deposit of porphyry copper-molybdenum located in Isfahan province, center of Iran using Satellite data interpretations were discovered in the years of 2010 and 2003, respectively. Geological studies have indicated the presence of argillic and propylitic alteration halos associated with porphyry copper systems. The 250 rock samples were systematically collected at a sampling distance of 100 m and in the center of the porphyry system by a distance o f 50 m in Zafarghand. Also, 377 samples of lithogeochemicals (185 rock samples and 192 soil samples) were extracted systematically from Kahang deposit. The study of geochemical data of rock and soil samples showed similarity of these two types of mineralization with other mineralization of porphyry copper-molybdenum elsewhere in the world. Finally, the comparison of geochemical anomalies copper with rock units and alteration zones showed that atmospheric waters had washed out the copper in some of these zones and probably the supergene zone was formed in depth as porphyry copper-molybdenum deposit.

Elements of demonstrated immobility in hydrothermal alteration and metamorphism provide useful lithogeochemical parameters for mineral exploration in greenstone terranes. They yield precise identifications of precursor volcanic rock type and magmatic affinity, and quantitative estimates of mass, volume and mineralogical changes. Immobile incompatible elements (Zr, Y, Nb, REE) establish affinities, and monitor fractionation of compatible elements in tholeiitic and transitional volcanic suites. Mass changes in mobile components can be determined for a homogeneous rock unit or a continuous volcanic series. Mass change results also bear directly on the interpretation of REE profiles in altered rocks. Normative calculations allow chemical analyses to be portrayed as alteration minerals, which are also useful in interpreting oxygen isotope data. Immobile element techniques produce a large number of parameters that can be illustrated on maps and diagrams, and otherwise used in exploration. Usage of these techniques brings deeper insight to the evolution of volcanic stratigraphy and the hydrothermal processes that formed the alteration zones and ore deposits.

Geochemical exploration based on the analysis of indicator minerals (IMs) is becoming increasingly used as an effective method for mineral exploration for many types of mineral deposits. The types of IMs used or recommended for exploration for different types of deposits, their properties suitable for concentrating them, as well as those of other common minerals from which they must be separated are listed. There is a variety of methods for the concentration and recovery of IMs from samples, but all have limitations as to the particle size range that can be treated with optimum results. The different processing methods available; the types of devices marketed; and their operational parameters are described. It is shown that due consideration to the limitations in particle size range that may be processed by these devices is required so as to avoid poor IMs recovery, possible unnecessary analytical costs, and obtaining chaotic or misleading results.

This paper reviews the use of Greek industrial minerals into developing low-cost, high-tech solutions to remediate parts of the chemical pollution environmental problem. The remediation strategy, based on the application and implementation of the Greek industrial minerals potential, became a major line of investigation in projects to develop new environmental technologies. Although past and current experiments have been successful on a lab scale in a number of applications, the results have not always been implemented on industrial scales. Greek olivine has been successfully tested as neutralizing agent for acid wastes, co-producing exploitable amounts of silica gel, magnesium sulphate and magnetite. Vermiculite is currently tested as an environmental 'cleanser' in a variety of applications, i.e. metalliferous mine seepage and processing waters, organically contaminated waste water from the textilerdye industry and absorption material for oil spills. Wollastonite will be applied as long-term fertiliser and dolomite, as a substitute of asbestos in brake linings, as pollution controller of heavy metal concentrations in waste waters and as a binder to stabilize waste solids. Magnesite has been Ž successfully applied for neutralization of acid mine wastes produced from active sulphide deposits. Zeolites fly ash and . perlite converted to zeolites were also considered is an objective for several environmental applications, i.e. as floating absorbent for waste water ponds, as drinking water purificator or as smell abatement. q 1998 Elsevier Science B.V. All rights reserved.

Bottled drinking water constitutes a significant part of total water consumption in developed countries and national and EU legislation regulates their market production. In the framework of an international project carried out by the EuroGeoSurveys Geochemistry Expert Group 36 bottled waters were obtained from public markets in Hungary in order to determine their hydrogeochemical composition. The objective of this study is to investigate the possible relationship between groundwater aquifer lithology and the processed and marketed bottled waters, and to develop a classification of bottled waters, based on their dissolved mineral content. Analytical results of this study are compared with the composition shown on bottle labels, and with archive hydrochemical data from the producing wells. Results show that, while processing of original groundwater, such as oxygen addition, iron or hydrogen-sulphide removal can significantly alter water composition, bottled water composition can be used for selection of sites for detailed hydrogeochemical and hydrogeological characterization. A simple and useful classification of bottled water quality is also presented that is based on natural groups of sampled waters derived by means of statistical data analysis methods.

Geochemical analyses of intertidal sediments from the northern part of the Fowey Estuary, Cornwall, UK, reveal a clear pulse in Sn concentration in sediments which predate 1880. Sn concentrations at the base of the cores increase rapidly to peak values of 1200 ppm and then decrease to values of 200 ppm at the present-day sediment surface. The mineralogy of the

Kimberlites occur on every continent and the total number of known primary host rock occurrences is generally accepted as 5000, of which 500 are diamondiferous, 50 have been or are being mined and 15 are large active mines. Clifford' s Rule is shown to be valid in that economic kimberlites occur only on Archons, i.e. cratonic regions underlain by Archaean basement, whereas economic lamproites occur on some Protons, i.e. Proterozoic mobile belts adjacent to Archons. These Archons are distributed world wide in twelve potentially diamond producing regions which occur on seven continents. Three of these twelve regions, i.e. North America, Europe and Antarctica do not have any diamond mines, although significant primary diamond deposits have been found on the first two which will probably be mined in the next decade. The South American continent contains several cratons including the Guyana, Guapor6 and S~o Francisco Cratons which each enclose Archons. These are predominantly located in remote, tropical, heavily forested areas which have not yet been fully explored. Most kimberlites discovered so far in South America lie in Protons, i.e. Proterozoic mobile belts encircling the Archons and are not economic. Therefore almost all production from South America is from alluvial deposits. There is no commercial diamond production from the North American continent, although there are many occurrences of diamonds, kimberlites and lamproites. A great staking rush has taken place in Canada in the Northwest Territories, Alberta, Saskatchewan, Ontario and Qurbec and is still continuing. Two, and possibly five, diamond mines may be developed in the next decade. Diamond prospecting is proceeding at a fast pace in Canada and in a more limited way in the United States. The African continent contains three large cratons, the South African, Central African and West African cratons. The South African Craton includes the large Kalahari Archon on which the majority of the world's active major kimberlite diamond mines are located in South Africa, Botswana, Zimbabwe and Swaziland. They comprise 11 kimberlite pipe mines and 3 kimberlite dyke mines. Large alluvial, beach and offshore deposits also produce a large proportion of the world's total. The Central African Craton includes the Lunda-Kasai and the Tanzanian Archons which each contain one active kimberlite pipe mine in Zaire and in Tanzania. Several large kimberlite pipes in Angola may become mines in the next decade. The craton also contains several large alluvial mining areas in Angola (Lunda and Cuango), Zaire (Eastern and Western Kasai) and in the Central African Republic. The West African Craton includes the Man Archon and the Eburuean Proton. Diamondiferous kimberlite pipes and dykes are located on the Man Archon in Sierra Leone, Guinea, Liberia and Mali. Alluvial deposits immediately downstream from kimberlites are mined in Sierra Leone, Guinea and Liberia and occurrences of pipes and alluvials are being evaluated in Mali. Lamproite dykes located on the Eburnean Proton in Ivory Coast were mined in the past and large alluvial deposits, which cannot be traced to their primary host rock, are mined in Ghana and Ivory Coast. The basement of most of Europe is not conducive to the intrusion of diamondiferous kimberlites or lamproites, although there are many vague reports and rumours about diamond finds in several countries. The East European Craton covers most of western Russia and its neighbouring states and extends into Finland and northern Scandinavia. Several diamondiferous kimberlites and lamproites have apparently been found in the Ukraine, Belorus, Russia (Karelia and the Arkhangelsk district) and probably

The Hishikari gold deposit: high-grade epithermal veins in Quaternary volcanics of southern Kyushu, Japan EIJI IZAWA 1, YUKITOSHI URASHIMA 2, KENZO IBARAKI 3, RYOICHI SUZUKI 3, TAKE0 YOKOYAMA 3, KIYOSHI KAWASAKI 3, AKITO KOGA 4 and SACHIHIR0 TAGUCHI 5

Since the freeing of the market price of gold in 1971, exploration for epithermal gold deposits in the southwest Pacific region has been intense, and has been encouraged by some major successes. Sufficient discoveries have been made to summarise what has been found to date, and to assess what implications may be drawn for future exploration. Data are tabulated for 137 epithermal precious metal deposits and prospects in Australia (30), Fiji (2), Indonesia (43), New Zealand (22)) Palau and Yap (2), Papua New Guinea ( 18), the Philippines ( 19), and Solomon Islands ( 1).