Ore-related Elements Research Articles

Widespread nearly or nanoscale natural amorphous particles in critical zones from ore deposits

The advancement of nanotechnology has drawn more attention on synthetic nanoscale particles, while naturally nanoscale particles are often overlooked, especially nearly or nanoscale natural amorphous particles (nearly or NNAPs). Here, we report nearly or NNAPs obtained from multiple media. The sample media, including groundwater, ascending gas, soil and plant tissue, were obtained from eight concealed deposits with different types of minerals and three blank control group areas in the critical zones in China. The morphology, elemental combination and structure of nearly or NNAPs in these samples were characterized via transmission electron microscopy (TEM). The results show that the nearly or NNAPs are widespread compounds. This study established the elemental combination relationship of nearly or NNAPs and defined the particles as a native metal, S–O-, P–O-, and Cl–(O)-bearing as well as oxide nearly or NNAPs. Nearly or NNAPs could carry high proportion of ore-related elements, such as W, Pb, and Co in oxide nearly or NNAPs; Cu in S–O-bearing nearly or NNAPs; and Zn in P–O-bearing nearly or NNAPs. Nearly or NNAPs that carry ore-related elements were obtained from the surface area of the concealed deposits but not in the blank control group areas. With strong geochemical features, nearly or NNAPs can carry ore-related elements from the concealed ore bodies to the surface. These phenomena indicate nearly or NNAPs can be prospecting concealed ore bodies while possessing the environmental risks with high proportion of metal elements.

In-situ monazite Nd and pyrite S isotopes as fingerprints for the source of ore-forming fluids in the Jiaodong gold province

The giant Jiaodong gold province has attracted a large amount of research on its geological features, ore-forming processes and genesis. Uncertainties as to the primary sources of ore-forming fluids, and whether host rocks contribute materials to gold mineralization, are still subject to intense debate. Here, we present comprehensive in-situ sulfur isotopic studies of pyrite from the Qujia and Xincheng gold deposits, and neodymium isotopic studies of monazite from the Xiadian, Zhuangzi, Hushan, Daliuhang, and Muping gold deposits, whose timing of gold mineralization has been constrained to ca. 120 ± 5 Ma using in-situ monazite U-Pb dating. The δ34S values among Py1 (+9.0 to +9.9‰), Py2 (+8.4 to +10.7‰) and Py3 (+6.9 to +12.3‰) are similar, showing consistence with that of other deposits in the Jiaodong gold province. It indicates that these gold deposits share the same dominant sources of sulfur and/or ore-forming fluids, potentially being exsolved from the contemporaneous magmas. Slightly wide range of δ34S for Py3 is likely due to the partially closed deposition spaces and intensive fluid-rock interaction. Hydrothermal monazite is intergrown with pyrite in the orebodies, suggesting that they were precipitated simultaneously from the same fluids. Our newly published Sm-Nd isotopic studies on monazite yielded inconsistent values of εNd (t = 120 Ma) among the Zhuangzi (−25.5 to –22.6), Xiadian (–23.3 to −20.2), Hushan (−20.6 to −18.4), Muping (−20.5 to −17.3) and Daliuhang (−13.7 to −11.6) gold deposits. These in-situ monazite Nd isotopes overlap with whole-rock Nd isotopes of their corresponding host rocks, indicating the material contribution of host rocks to the gold mineralization. This study provides robust evidences showing that the ore-forming fluids of the Jiaodong gold deposits share the same primary origin, but incorporate nonnegligible abundance of materials (REE, and potentially ore-related elements, such as Au, As, Fe) from the host rocks upon ascending, due to intensive fluid-rock interaction.

Efficiency of singularity and PCA mapping of mineralization-related geochemical anomalies: a comparative study using BLEG and <180μm stream sediment geochemical data

In gold (Au) exploration, the analysis of both bulk leach extractable gold (BLEG) and acid-extractable Au in the <180μm stream sediment fraction are the two most common approaches. The Eskişehir- Sivrihisar region in Western Türkiye hosts several orogenic type mineral deposits. The purpose of this study is to delineate geochemical anomalies of ore-related elements and track their dispersion, which may lead to discovery of unknown ore deposits. This research also compares the capability of conventional statistical and principal component analysis (PCA), with concentration area (CA) and number-size/concentration (N-S/C) fractal methods as well as singularity index method to differentiate anomalous and background Au distributions. Known Au mineralization in the region of interest is strongly reflected in stream sediment BLEG Au patterns, which have robust singularity indices with C-A and N-S multifractal modeling and PCA. A hundred % of the Au deposits were detected using either BLEG Au and Ag singularity index mapping with C-A fractal analysis whereas the factor analysis of which revealed 85% efficiency. Several strong Au-Ag anomalies defined by the singularity index and factor analysis in this study requires further follow up for the discovery of new deposits.

Quality and quantity assessment using multivariate compositional and univariate analysis in the Glojeh polymetallic vein mineralization

Background separation from anomalous concentration is a fundamental process in exploration geochemistry for polymetallic ore deposits. Therefore, fractal modeling and multivariate analysis have been applied to vein identification in the Glojeh polymetallic deposit, Tarom zone, northwestern Iran. The C-N fractal modeling demonstrated that the threshold value is equal to 103.34 ≈ 2000 ppb, and the total number of 100.89 ≈ 8 samples are anomalous for Au. Anomalous and background populations may do not represent major differences using the frequency distribution, but they possibly could be different in spatial patterns. Therefore, the application of single element fractal modeling would not be able to determine polymetallic veins and veinlet samples. Accordingly, a better anomaly identification may be approached using the multivariate analysis and compositional isometric log-ratio (Ilr) transformed data. It revealed that sample ID’s of 33, 29, 30, 28, 32, 35, 47, 81, 80, 31, 34 and 36 are concentrated from (Ag, Pb, As, Au) > (Te, Mo) > (Zn, S) > (W, Cu) > (Be and Cd). The factor analysis based on Ilr-transformed data indicated Au, As, Mo, W, Ag, Pb, Te, Be, and Zn are enriched and can be considered as pathfinder elements for tracing a polymetallic mineralization, while Al, K, Ba, Ce, La, Na, Zr, Rb, Y and Th have been depleted. These findings will complement and improve the results of fractal modeling to the determination of several ore-related elements, and they were quantitatively and qualitatively assessed. Finally, the mineralization type could be classified in a high sulfidation epithermal deposit.

Nanoparticles in groundwater of the Qujia deposit, eastern China: Prospecting significance for deep-seated ore resources

The characterization of nanoparticles in groundwater is recognized as an important tool that can be applied to mineral exploration. In this paper, we investigate the concealed orebodies of the Qujia gold deposit in the Jiaojia orefield of eastern China by analyzing ore-related nanoparticles in groundwater using transmission electron microscopy. The nanoparticles contain variable amounts of ore-related elements (e.g., Ag, Cu, Zn, La, Ce, Pb, Pt, and S). Some of these elements are rarely found in natural settings unrelated to orebodies or mineral extraction, but are strongly linked to concealed orebodies in the study area. These nanoparticles, which are diverse in their shapes, aggregated features, and degrees of crystallinity, can be grouped in terms of composition as: (i) native metal nanoparticles, (ii) metal-based nanoparticles, and (iii) carrier nanoparticles associated with trace elements. We propose that these three main types of nanoparticles enable the efficient transport of ore-forming elements in groundwater. The results of this study provide insights into the migratory behaviour of ore-related nanoparticles in groundwater, and our methods could be applied for detecting deep-seated mineral deposits.

A scale-integrated exploration model for orogenic gold deposits based on a mineral system approach

Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model. Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model. Plausible models involve metamorphic fluids, but the fluid source has been equivocal. Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits, and numerous Chinese provinces, including Jiaodong, where the only feasible fluid source is sub-crustal. If all orogenic gold deposits define a coherent mineral system, there are only two realistic sources of fluid and gold, based on their syn-mineralization geodynamic settings. These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or release from mantle lithosphere that was metasomatized and fertilized during a subduction event, particularly adjacent to craton margins. In this model, CO2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ​°C. This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales. Within these settings, it is then possible to define the critical gold mineralization processes in the system: fertility, architecture, and preservation. The geological parameters that define these processes, and the geological, geophysical and geochemical proxies and responses for these critical parameters can then be identified. At the geodynamic to province scales, critical processes include a tectonic thermal engine and deep, effective, fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin. At the district to deposit scale, the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems, with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps. Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.

A holistic model for the origin of orogenic gold deposits and its implications for exploration

The term orogenic gold deposits has been widely accepted, but there has been continuing debate on their genesis. Early syn-sedimentary or syn-volcanic models and hydrothermal meteoric-fluid models are now invalid. Magmatic-hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships. The most plausible models involve metamorphic fluids, but the source of these fluids is equivocal. Intra-basin sources within deeper segments of the hosting supracrustal successions, the underlying continental crust, subducted oceanic lithosphere with its overlying sediment wedge, and metasomatized lithosphere are all potential sources. Several features of Precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic-fluid source. These include the presence of hypozonal deposits in amphibolite-facies domains, their anomalous multiple sulfur isotopic compositions, and problems of derivation of gold-related elements from devolatilization of dominant basalts in the sequences. The Phanerozoic deposits are largely described as hosted in greenschist-facies domains, consistent with supracrustal devolatilization models. A notable exception is the Jiaodong gold deposits of China, where ca. 120-Ma gold deposits are hosted in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization. Other deposits in China are comparable to those in the Massif Central and elsewhere in France, in that they are hosted in amphibolite-facies domains or clearly post-date regional metamorphic events imposed on hosting supracrustal sequences. If all orogenic gold deposits have a common genesis, the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or the associated metasomatized mantle wedge, with CO2 released during decarbonation and S- and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 °C. Although this model satisfies all geological, geochronological, isotopic, and geochemical constraints, and is consistent with limited computer-based modeling of fluid release from subduction zones, the precise mechanisms of fluid flux are model-driven and remain uncertain. From an exploration viewpoint, the model re-emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction-related orogenic belts and importance of continental-scale lithosphere-tapping fault and shear zones to focus large volumes of auriferous fluid. It confirms the importance of the consistent spacing between world-class deposits, broadly equivalent to the depth of the Moho, as derived from empirical observations.

Biogeochemical mapping of metal contamination from mine tailings using field-portable XRF

Trace and major element composition of selected plant species and parts may be used to map geochemical dispersion from mineral deposits and contaminated areas. This study examines the application of field-portable X-ray fluorescence spectrometry (fpXRF) in obtaining real-time biogeochemical data. In situ analysis of parts of black and silver wattle (Acacia mearnsii De Wild. and Acacia dealbata Link) was conducted to map the extent of contamination surrounding the former Woodlawn base metal mine. High levels of ore-related elements were detected in the bark of these species in a zone extending up to 1 km down-drainage from the tailing ponds. Major elements are more elevated in bark on the side of the trees facing the tailings ponds and correlations between trace and major elements indicate dust contamination. The penetration distance for X-rays is dependent on the energy of the secondary X-rays measured, with the maximum depth of penetration in bark and leaf material <30 mm. There was a close correlation for most elements between the fpXRF and laboratory-based XRF analysis but with element-dependent attenuation by the organic matrix. Providing there is consistency in sampling and analytical methodology, in situ fpXRF analysis of vegetation is an effective method in both contamination surveys and biogeochemical mineral exploration for a range of trace and major elements.

Expanding the size of multi-parameter metasomatic footprints in gold exploration: utilization of mafic dykes in the Canadian Malartic district, Québec, Canada

Ore-forming hydrothermal fluids react differently with different country rocks, but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration. To develop this concept, 122 metamorphosed mafic dykes from the world-class Canadian Malartic gold district (18.6 Moz Au) were sampled and analyzed for mineralogy, physical properties, and lithogeochemistry (partial and total digestion). The mafic dykes intrude mainly metasedimentary rocks, post-date D1 deformation, and cross-cut early-D2 quartz monzodiorite intrusions, but they were deformed and altered during D2 deformation, mineralization, and metamorphism. They can be subdivided into three groups: Group 1 dykes are least-altered, characterized by amphibole-rich regional metamorphic assemblages and distributed throughout the Pontiac Subprovince. Group 2 and 3 dykes underwent ore-related hydrothermal biotite–calcite–pyrite alteration and are associated with density- and volume-adjusted concentration gains of over 100% in Au–W–Te–C–S–Ag–Cs–Mo–Cu–K–Rb–Se–U–Pb–Ba–F–Bi–Sn. They define a metasomatic footprint up to 6 km away from the deposit toward the SE and up to 2 km away from the deposit toward the SW. Fifty-eight variables that define halos around the Canadian Malartic deposit have been identified and integrated using principal component analysis. PC1 explains 30% of the variance, separates least-mobile elements from ore-related elements, and is interpreted to reflect the ore-forming alteration process. PC2 and PC3 represent igneous processes. PC4 highlights the calcite–pyrite and biotite alteration. Spatial variations of the modal abundances of amphibole, biotite, calcite, and pyrite are the simplest expression of the metasomatic footprint, and they can easily be documented during exploration at the camp scale.

Identification of geochemical signatures associated with seafloor massive sulfide mineralization at the Iheya North Knoll, middle Okinawa Trough

The geochemical signatures associated with seafloor massive sulfide mineralization recorded in pumiceous sediments in the Iheya North Knoll, middle Okinawa Trough, are examined. The key purpose of this research is to establish a method for the geochemical exploration of massive sub-seafloor volcanogenic sulfide deposits. Presently, the discovery of sub-seafloor mineralized zones is strongly method-oriented, including direct sampling and observation of ores. The utilizing of conventional method is even more complicated in the case of buried ore bodies. The well-characterized sub-seafloor hydrothermal systems of the Iheya North Knoll, containing delineated recharge-discharge zones, provide an opportunity to both verify and develop geochemical exploration methods. In this study, whole-rock geochemical data are obtained from samples taken from recharge and discharge zones, and from migration zones between these two regions. The resulting geochemical signatures are difficult to interpret due to variations in mineralization as well as magmatic effects. Normalization of the compositions of samples obtained from the discharge and migration zones relative to the composition of the recharge zone reveals the relationship between the average normalized values of rare-earth and ore-related elements. This method successfully distinguishes enrichment due to magmatic differentiation and mineralization. The approach described herein also allows the location of the discharge zone to be inferred, even in the case of a thin covering of sediment above the seafloor. This technique could allow surveying via systematic or grid sampling using dredging and/or piston-coring methods, both of which are simpler and less expensive than conventional methods.

The Proterozoic Vazante Hypogene Zinc Silicate District, Minas Gerais, Brazil: A Review of the Ore System Applied to Mineral Exploration

The Proterozoic Vazante zinc silicate district in Minas Gerais, Brazil, hosts world-class hypogene willemite deposits in dolomitic rocks interbedded with siliciclastic rocks deposited in subtidal to supratidal environments. Willemite ore bodies are structurally controlled along regional NE-trending structures which are interpreted as being active during the Neoproterozoic Brasiliano orogeny. The hydrothermal alteration is characterized by an early stage of Fe-dolomite, which replaced the host dolomitic rocks, followed by precipitation of minor sphalerite and then hematite and willemite. Elements commonly enriched in the zinc ore include As, Ba, Be, Bi, Cd, Co, Fe, Ge, In, Mo, Ni, Sb, Se, U, V and W. Mineralogical, fluid inclusion and isotopic data indicates that mixing of S-poor metalliferous saline fluids with meteoric water favored the formation of willemite ore. Carbonaceous phyllites from the underlying thick siliciclastic sequence show evidence of early enrichment in zinc (and ore-related metals) and remobilization, respectively, prior to and during the Brasiliano orogenic event. This unit is interpreted as a possible source of ore-related elements. It is proposed that during the Brasiliano orogeny, hot (T &gt; 170 °C) saline fluids (&gt;15 wt % eq. NaCl) leached metals from siliciclastic source rocks and precipitated willemite ore in the overlying dolomitic sequence along structures that favored mixing with oxidizing meteoric water.

Fluid evolution in the southern part of the Proterozoic Vazante Group, Brazil: Implications for exploration of sedimentary-hosted base metal deposits

The Proterozoic Vazante Group carbonate rocks were submitted to multiple stages of fluid circulation from diagenesis to orogenesis as documented by detailed mineralogical, fluid inclusion and isotopic studies of the Upper Morro do Pinheiro and Lower Pamplona members from the Serra do Poço Verde Formation in the southern part of the paleo-basin. These units are the main hosts for the hypogene, structurally-controlled zinc silicate deposits in the Vazante Zinc District, including the Vazante mine, which is considered to be the largest willemitic (Zn2SiO4) deposit in the world, with estimated total resources of 40–60Mt at 20% Zn. Five hydrothermal alteration types were identified in the Southern Extension of the Vazante Group. (I) Early stage alteration comprises dolomite substitution bands and nodules, associated with moderate salinity H2O-NaCl-CaCl2 fluids, with temperatures around 90°C, interpreted as late-diagenetic. The calculated C and O isotopic compositions of the fluids suggest meteoric and/or connate origin and interaction with organic carbon. (II) Pre-ore stage alteration is evidenced by dog-tooth dolomite and quartz with minor Fe-oxi/hydroxides which fills dissolution voids formed by H2O-NaCl-CaCl2±MgCl2 fluids at temperatures around 100° to 150°C. The C isotopic data also indicate interaction with organic carbon. The two first stages are poor in ore-related elements. (III) Ore stage encompasses four phases of mineral precipitation. The first is distal and characterized by red stained dolostones due to disseminated hematite and red dolomite. The second is the main phase of the ore stage, composed of massive red dolomite, massive hematite and willemite with enrichment mainly in Fe2O3, SiO2, Ag, As, Cd, Cu, Ni, Pb, Se and Zn. The third phase comprises white dolomite, hematite and traces of willemite with enrichment in MnO, Cd, Ni and Pb. The calculated C and O isotopic compositions of the fluids (at 180°C) associated with pervasive alteration yielded values heavier than the diagenetic stage and lower than the host rock. The fourth phase corresponds to Zn-chlorite and quartz which are associated with H2O-NaCl fluids of variable salinities and distinct temperatures (90–140°C and 170–190°C). (IV) Pyrite-bearing vein characterized by pyrite, sphalerite, white dolomite, fine hematite and late quartz, with C and O isotopic and fluid inclusion compositions that are similar to the three phases of dolomite of the ore stage. These data suggest a co-genetic relationship of these two alteration styles. (V) The late sulfide stage characterized by rare galena-bearing stringers with sphalerite, chalcocite, greenockite, covellite and white dolomite that cross-cut the main ore stage phases. The ore-related fluid compositions associated with the silicate zinc mineralization in the southern part of the Vazante Group are also similar to the fluids reported in previous work for the sulfide zinc-lead deposits in the northern part, indicating favorable conditions for metal transport during the Brasiliano Orogeny. Sulfide ore would have precipitated in zones where sulfur was available and silicate zinc in structures where mineralizing fluids interacted with evolved meteoric water. This finding implies that carbonate sequences in other districts with sulfide lead-zinc deposits may also host hypogene silicate zinc deposits.

Use of surficial geochemical methods to locate areas of buried uranium mineralization in the Jacque’s Lake area of the Central Mineral Belt, Labrador, Canada

Surficial geochemical methods were applied to delineate zones of anomalous uranium and related element concentrations in areas overlain by an extensive blanket of glacial sediments and dense vegetation cover in the Jacque’s Lake area of the Central Mineral Belt, Labrador, Canada. The study involved sampling and analyses of vegetation including black spruce twigs and bark, Labrador tea shoots, and humus. Ash derived from the vegetation samples was analyzed using inductively coupled plasma – mass spectrometry (ICP–MS) following ignition at 450 °C, and humus was analyzed with delayed neutron counting (DNC) for a suite of 35 elements. B-horizon soil was analyzed using aqua regia digestion to investigate potential chemical signatures of bedrock mineralization at the surface. Uranium concentration in humus varied from 0.05 to 885 ppm. Zones exhibiting anomalous U responses were associated with areas proximal to anoxic peat and sphagnum bogs where mobile U species were sequestered. Uranium and pathfinder element (e.g., Pb, V, Sr, and Mo) concentrations were low in the &lt;250 μm fraction of B-horizon soils. The soil geochemistry delineated bedrock U mineralization in areas with &lt;15 cm of overburden and U concentration varied from 50 to 405 ppm. Biogeochemical signatures of the bedrock mineralization in black spruce twigs produced greater anomaly to background contrasts for U and pathfinder elements (e.g., Be, Ag, Pb, Ca, and Sb) and correlated more precisely with the detected radiometric U/Th anomaly than did those of soil and humus. Principal component analysis of spruce twig data discriminated three major components, including plant nutrients, ore-related elements, and a mobile species. Uranium concentration varied from below detection limit to 23 ppm U in black spruce bark and from below detection limit in ∼40% of samples to 18 ppm in Labrador tea stem.

A comparison of fractal methods and probability plots in identifying and mapping soil metal contamination near an active mining area, Iran

Mining activities may contribute significant amounts of metals to surrounding soils. Assessing the potential effects and extent of metal contamination requires the differentiation between geogenic and additional anthropogenic sources. This study compares the use of conventional probability plots with two forms of fractal analysis (number–size and concentration–area) to separate geochemical populations of ore-related elements in agricultural area soils adjacent to Pb–Zn mining operations in the Irankuh Mountains, central Iran. The two general approaches deliver similar spatial groupings of univariate geochemical populations, but the fractal methods provide more distinct separation between populations and require less data manipulation and modeling than the probability plots. The concentration–area fractal approach was more effective than the number–size fractal and probability plotting methods at separating sub-populations within the samples affected by contamination from the mining operations. There is a general lack of association between major elements and ore-related metals in the soils. The background populations display higher relative variation in the major elements than the ore-related metals whereas near the mining operations there is far greater relative variation in the ore-related metals. The extent of the transport of contaminants away from the mine site is partly a function of the greater dispersion of Zn compared with Pb and As, however, the patterns indicate dispersion of contaminants from the mine site is via dust and not surface/groundwater. A combination of geochemical and graphical assessment, with different methods of threshold determination, is shown to be effective in separating geogenic and anthropogenic geochemical patterns.

Geology, mineralogy, and geochemistry of the Vazante Northern Extension zinc silicate deposit, Minas Gerais, Brazil

The Vazante Northern Extension orebodies (850kt at 16% Zn) are the continuation of the structurally controlled, hypogene, non-sulfide zinc orebodies of the Vazante deposit (18Mt at 19% Zn), Minas Gerais, Brazil. The Vazante orebodies are hosted in the dolomitized carbonate rocks of the Serra do Poço Verde Formation that were deposited in an intertidal to supratidal environment. The Serra do Poço Verde Formation is part of the Neoproterozoic Vazante Group, which is located in the Brasília Fold Belt along the western margin of the São Francisco Craton. The Northern Extension orebodies occur within major tectonic-hydrothermal breccias controlled by a NE-trending fault zone. The faults and the breccias are interpreted to be formed during the so-called D2 deformation event, which is related to the Late Proterozoic Brasiliano Orogeny. The faults were reactivated during their evolution and are cut by later transcurrent faulting.Four types of tectonic-hydrothermal breccia occur in the North Extension zone. Type 1 breccia is distal from the willemite ore and is comprised of weakly brecciated dolostone with Fe-carbonate alteration, whereas type 2 breccia exhibits strong Fe-bearing carbonate alteration (dolomite with 1.5 to 3.3wt.% FeO and 0.3 to 1.25wt.% ZnO) of the clasts, Fe-carbonate veinlets, a more intense brecciation of the clasts, and has overprinted the type 1 breccia. Type 3 breccia is composed mainly of hematite that replaced previously altered dolomite clasts and filled the breccia matrix. Type 4 breccia, which is typically proximal to type 3 breccia, is the willemite ore breccia which contains three generations of hypogene willemite as well as hematite, franklinite and minor amounts of quartz and ferroan (~1.99wt.% FeO) and zincian (~2.65wt.% ZnO) dolomite. Type 4 breccia commonly occurs in lenses surrounded by the type 3 hematite breccia, and willemite partially replaces hematite and altered carbonate clasts and fills breccia matrix and veinlets. In the southern part of the deposit, late sulfide-rich veinlets with galena, sphalerite, native silver, covellite, and stromeyerite cut the hypogene zinc silicate mineralization.Lithogeochemical analysis and mass-balance of the hydrothermal breccia were used to evaluate metals added during the hydrothermal period. The data show that the ore-related elements have been added to the system since the formation of the earliest breccia (Type 1 breccia). However, the type 3 breccia contains the highest average concentrations for As, Ba, Be, Bi, Fe, Ge, In, Mo, Ni, Sb, U, V, and W. Type 4 breccia is also enriched in the same elements and contains the highest average concentrations of Ag, Cu, Hg, Pb, S, Se, SiO2, and Zn. The evidence that the ore-related elements were added to the system during the formation of types 1 and 2 breccias, suggests that the metalliferous fluids were interacting with the host rocks, but were not able to effectively precipitate the ore-related elements. Important changes in the hydrothermal system would have increased its fugacity and pH allowing for formation, respectively, of type 3 hematite-rich breccia and type 4 willemite ore breccia, which are enriched in the other ore-related elements (e.g. As, Ba, Be, Bi, Cu, Fe, Ge, Hg, In, Mo, Ni, Pb, Sb, U, V, and W). These observations are consistent with a formation model proposed for the Vazante orebodies involving early interaction of metalliferous brines with the host rocks, followed by mixing of the metalliferous fluids with more oxidizing fluids, most likely meteoric water, leading to the precipitation of abundant hematite and willemite. Late, more reduced fluids formed the Pb, Cu and Ag-rich sulfide veinlets that cut the willemite mineralization.

The role of mineralogy and geochemistry in forming anomalies on interfaces and in areas of deep basin cover: implications for exploration

This paper examines how geochemical dispersion may be used in areas of deep transported cover to locate buried mineralization. Two regions with contrasting weathering history and transported cover were investigated. These are the Mt Isa region of northern Queensland and the Yilgarn Craton of Western Australia. At both locations, transported cover is from 20–70 m thick. A range of techniques and instruments, including bulk geochemistry, SEM, electron microprobe and selective extraction analyses were used to understand the vertical distribution and nature of ore-related elements. At the Eloise Cu-Au Deposit in the Mt Isa region, Mesozoic cover lies over prospective Proterozoic basement which is largely unweathered. At Eloise, the degree of weathering, below the unconformity and transported cover, is minimal so weathering-related dispersion in basement and cover is also minimal. There is no dispersion of indicator elements into the upper parts of the unweathered Mesozoic sediments. Mechanical dispersion dominates as is indicated by the SEM and petrographic study and is restricted to basal sediments (last few metres). Unweathered sulphides occur in the basement and in the fragments of clastic basement material and fossil organic matter in the silty matrix of the Mesozoic sediments. The palaeotopography governs the direction of dispersion and needs to be thoroughly understood before meaningful interpretation. The Lancefield South Au Deposit has a cover of highly weathered Permian to Quaternary sediments on Archaean basement of the Yilgarn Craton. Stacked weathering profiles in each sedimentary unit allowed transfer of Au, As, Cu and Zn across the weathering profiles (paleosols) by hydrogeochemical and vegetation interactions as they evolved. High paleo-watertables within the Permian sediments have allowed upward migration of metals reaching close to the surface of the Permian sediments. Bioturbation and transpiration pumped the anomalous metals into the overlying Tertiary and Quaternary sediments from the Permian. Although regolith anomalies are weakened, especially in the Tertiary and Quaternary cover by post-depositional weathering processes over a long time, they still clearly remain. Thus, a highly weathered sedimentary cover is likely to trap indicator elements more effectively than an unweathered sedimentary cover, such as at Eloise. In addition to basal sediments or interfaces, ferruginous horizons in weathered sediments high in the sequence can also be anomalous in ore-related metals.

Distribution of Heavy Metals around the Dashkasan Au Mine

The aim of the study is to determine the major source and extent of metal pollution in the vicinity of Dashkasan gold mine. Dashkasan mine has resulted in extensive contamination of soils by Arsenic (As) and potentially toxic ore-related elements including Mercury (Hg), Antimony (Sb) and Cadmium (Cd). Soils samples were collected and analyzed for As, Cd, Hg, Pb and Sb. The concentration of each heavy metal is controlled by different parameters (soil pH, iron and aluminum oxide content, clay content, organic matter and cation exchange capacity). The maximum content in the soils were 485, 3.2, 100, 2710 and 640 mg/kg for As, Cd, Hg, Pb and Sb, respectively. In particular, the extracted concentration of As, Cd, Hg and Sb are in excess of the tolerable levels. Positive correlation with organic matter and clay content but not with pH has been observed for most of elements analyzed in this study. Enrichment factor (EF) analysis and cluster analysis (CA) highlighted the lithogenic origin of heavy metals. It also revealed the need for detailed geochemical surveys in the future in order to decrease the uncertainty of discrimination between lithogenic and anthropogenic origin of metals of interest.

Mineral Paragenesis, Alteration, and Geochemistry of the Two Types of Gold Ore and the Host Rocks from the Carlin-Type Deposits in the Southern Part of the Goldstrike Property, Northern Nevada: Implications for Sources of Ore-Forming Elements, Ore Genesis, and Mineral Exploration

This study was undertaken to characterize the mineral paragenesis and metal zoning at the property scale, evaluate the potential sources of ore-related metals, quantify the relationship between intensity of alteration and gold grade, and propose a comprehensive genetic model for the Carlin-type Au deposits at the southern part of the Goldstrike property, Nevada. Mineralogy, textural relationships, whole-rock composition, and spatial distribution of the studied samples revealed two types of gold ore: Ore I and II. The former, which is hosted by the Roberts Mountains and Rodeo Creek Formations, and the Wispy, Planar, and Upper Mud units of the Popovich Formation, is the most abundant and widespread in the property. Ore I is characterized by intense hydrothermal alteration (e.g., carbonate dissolution, silicification, and precipitation of pyrite) and high amounts of trace elements (e.g., Ag, As, Au, Ba, Cd, Cu, Hg, Mo, Ni, S, Sb, Se, Te, Tl, and Zn). On the other hand, Ore II, which is hosted in the Wispy, Planar, and Soft Sediment Deformation units of the Popovich Formation, is mainly confined to the central-north-northwest portion of the Screamer deposit and is weakly altered with low concentration of trace elements. Both Ores I and II contain similar average concentrations of Au in whole rock (14 and 19 g/t Au, respectively) and in pyrite (290 and 540 ppm, respectively); however, auriferous pyrite from Ore I has higher trace element (As, Ag, Cu, Hg, Ni, Sb, Se, and Tl)/Au ratios than Ore II. The sedimentary units are interpreted to be the major local source of Cd, Mo, Ni, U, V, and Zn and minor As, Cu, Hg, and Se as denoted by the composition of least altered samples and diagenetic pyrite and sphalerite. this study reveals that Al2O3 and TiO2 are the most immobile compounds, and their distribution indicates a homogeneous source for the detrital components in the sedimentary rocks. Among the ore-related trace elements, Tl best correlates with Au grade ( R 2 = 0.69) and shows some relationship with the calculated amount of pyrite ( R 2 = 0.49), indicating that Tl would be the best element to vector toward zones of high-grade Carlin-type Au mineralization. Gold grades do not correlate with the amount of pyrite, degree of alteration, or organic C. Our results integrated with available thermodynamic data for AU, ore-related elements, and SiO2 lead us to suggest that the formation of Ore I occurred more proximal to the major mineralizing conduits as the hot, more acid, SiO2- and trace element-rich auriferous fluids interacted with Fe-bearing impure carbonate host rocks, intensely dissolving the carbonate rocks and precipitating quartz and auriferous pyrite in the Betze-Post and Rodeo deposits. As the fluids moved laterally throughout the favorable host rocks, the pH increased, leading to a decreasing in the rate of carbonate dissolution and in the solubility of silica, favoring the formation of more distal Ore II in the central-northern part of the Screamer deposit. Significantly, the gold concentrations in whole rock and in pyrite are, in some way, very similar in both ore types, being slightly higher in Ore II, suggesting that less acidic conditions were still favorable for the incorporation of gold in the structure of pyrite, even at lower concentrations of other trace elements.

Regolith evolution and geochemical dispersion in transported and residual regolith – Bronzewing gold deposit

Geochemical dispersion in the regolith was investigated at the Bronzewing gold deposit in a variety of geomorphological environments. A series of economic gold deposits are concealed by 5–35 m of sediments, and a thick residual profile about 100 m thick. Prior to mining, samples of regolith materials were collected from surface and drill cuttings, along several lines over the north–south trending, elongate zone of mineralization. These samples were examined in detail to determine element distributions, their relationship to regolith evolution and their significance to exploration. The residual materials (lateritic residuum and ferruginous saprolite) have Au, W and Cu anomalies in the vicinity of the deposit. Elements associated with the Au mineralization in the lateritic residuum of the Laterite Pit are Ag, Ba, Ce, W, Mo, As, Sb and Cu. Gold anomalies in lateritic residuum are less consistent in the Discovery Pit and, at both the Central and Discovery Pits, are enriched in Cu and W only close to the weathered primary mineralization. Three-dimensional modelling indicates that Au in saprolite is localized and largely residual. Geochemical dispersion from primary mineralization into the sediments is only minor, except immediately overlying the lateritic residuum or saprolite. This dispersion is, however, almost entirely mechanical and there appears to have been little, if any, post-depositional chemical dispersion. Ferruginous mottles developed in palaeochannel sediments have very low Au contents (&lt;5 ppb) but are slightly enriched in Cu. There is a significant concentration of Au (up to 300 ppb) in authigenic smectites formed at the residual-transported interface. The deposits are blind to soil sampling (10–30 cm depth) using total and several partial extraction techniques. The results demonstrate that dispersion of ore-related elements at Bronzewing is mostly confined to the lateritic residuum and ferruginous saprolite and that sampling of these materials, even if buried beneath transported overburden, will readily locate deposits of this type. However, it is important to distinguish between residual and transported regolith, especially nodules and pisoliths. In the absence of residual materials, sampling of the lowermost sedimentary units (gravelly sediments), possibly including the unconformity, is recommended because it may show the geochemical dispersion that is wider than the primary anomaly in saprolite or bedrock. The results also provide strong support for the use of multi-element geochemistry, with elements such as Cu and W being enriched close to primary mineralization.

Fluvial Contamination Associated with Artisanal Gold Mining in the Ponce Enríquez, Portovelo-Zaruma and Nambija Areas, Ecuador

Artisanal gold mining in the Ponce Enriquez, Portovelo-Zaruma and Nambija areas of Ecuador has resulted in extensive contamination of the fluvial environment by mercury (Hg) andpotentially toxic ore-related elements including arsenic (As),cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). Thisoccurs principally through the fluvial dispersion ofcontaminated mineral processing wastes and recycling of Hgsublimated during the burning of amalgam. Mercuryconcentrations in filtered ( 1000. The results highlight the need toensure that contaminated sediment and water do not entercommercial banana plantations and shrimp ponds downstream ofthe Ponce Enriquez mining district.