Immobilization of toxic elements in mine residues derived from mining activities in the Iberian Pyrite Belt (SW Spain): Laboratory experiments

In the mining environments of the Iberian Pyrite Belt (IPB), the oxidation of sulphide wastes generates acid drainage with high concentrations of SO₄, metals and metalloids (Acid Mine Drainage, AMD). These acid and extremely contaminated discharges are drained by the fluvial courses of the Huelva province (SW Spain) which deliver high concentrations of potentially toxic elements into the Gulf of Cádiz. In this work, the oxidation process of mine tailings in the IPB, the generation of AMD and the potential use of coal combustion fly ash as a possible alkaline treatment for neutralization of and metal removal from AMD, was studied in non-saturated column experiments. The laboratory column tests were conducted on a mine residue (71.6 wt% pyrite) with artificial rainfall or irrigation. A non-saturated column filled solely with the pyrite residue leached solutions with an acid pH (approx. 2) and high concentrations of SO₄ and metals. These leachates have the same composition as typical AMD, and the oxidation process can be compared with the natural oxidation of mine tailings in the IPB. However, the application of fly ash to the same amount of mine residue in another two non-saturated columns significantly increased the pH and decreased the SO₄ and metal concentrations in the leaching solutions. The improvement in the quality of leachates by fly ash addition in the laboratory was so effective that the leachate reached the pre-potability requirements of water for human consumption under EU regulations. The extrapolation of these experiments to the field is a promising solution for the decontamination of the fluvial courses of the IPB, and therefore, the decrease of pollutant loads discharging to the Gulf of Cádiz.     

Mapping Fe-bearing hydrated sulphate minerals with short wave infrared (SWIR) spectral analysis at San Miguel mine environment,Iberian Pyrite Belt (SW Spain)

Short-wave infrared reflectance (SWIR) spectra obtained from a Portable Infrared Mineral Analyser (PIMA) were applied to map acidic mine soils at San Miguel massive sulphide deposit, Iberian Pyrite Belt, Spain. Field spectral measurements and laboratory analysis were performed on samples from 58 stations from two very polluted grounds. These analyses identified secondary and tertiary Fe-rich sulphate–hydrate minerals associated with the alteration of sulphide-bearing mine wastes and other associated infrared active minerals. The spectral absorption features for the pure salt types found in these areas allowed the preparation of a specific reference library for automatic mineral identification.Using this approach three separate zones around the sources of contamination have been discriminated: a “proximal” zone dominated by rozenite + hexahydrite, a “transitional” zone dominated by copiapite + coquimbite and a “distal” zone of hydronium–jarosite. An additional zone of “gypsum” was also recognized locally at the areas, where, last decade the neutralization of the acid soils with limestones was attempted.In addition to discriminating distinct mineralogical zones quantitative spectral data allowed contoured mineral maps to be produced that are comparable with the estimated mineralogical data obtained from conventional methods, such as XRD and field observations. These maps demonstrate that sulphate minerals were firstly formed by oxidation of the pyrite-rich ores followed by dissolution and precipitation involving a combination of oxidation, dehydration, and neutralization reactions.The study shows the potential of SWIR spectral analysis to identify and understand the distribution of efflorescent salts and other products of pyrite decomposition and provides a methodology to assist the research and monitoring of sources of environmental contamination.     

Iron isotopes in acid mine waters and iron-rich solids from the Tinto–Odiel Basin (Iberian Pyrite Belt, Southwest Spain)

The isotopic composition of Fe was determined in water, Fe-oxides and sulfides from the Tinto and Odiel Basins (South West Spain). As a consequence of sulfide oxidation in mine tailings both rivers are acidic (1.45 < pH < 3.85) and display high concentrations of dissolved Fe (up to 420 mmol l^− 1) and sulphates (up to 1190 mmol l^− 1).The δ⁵⁶Fe of pyrite-rich samples from the Rio Tinto and from the Tharsis mine ranged from − 0.56 ± 0.08‰ to + 0.25 ± 0.1‰. δ⁵⁶Fe values for Fe-oxides precipitates that currently form in the riverbed varied from − 1.98 ± 0.10‰ to 1.57 ± 0.08‰. Comparatively narrower ranges of values (− 0.18 ± 0.08‰ and + 0.21 ± 0.14‰) were observed in their fossil analogues from the Pliocene–Pleistocene and in samples from the Gossan (the oxidized layer that formed through exposure to oxygen of the massive sulfide deposits) (− 0.36 ± 0.12‰ to 0.82 ± 0.07‰). In water, δ⁵⁶Fe values ranged from − 1.76 ± 0.10‰ to + 0.43 ± 0.05‰.At the source of the Tinto River, fractionation between aqueous Fe(III) and pyrite from the tailings was less than would be expected from a simple pyrite oxidation process. Similarly, the isotopic composition of Gossan oxides and that of pyrite was different from what would be expected from pyrite oxidation. In rivers, the precipitation of Fe-oxides (mainly jarosite and schwertmannite and lesser amounts of goethite) from water containing mainly (more than 99%) Fe(III) with concentrations up to 372 mmol l^− 1 causes variable fractionation between the solid and the aqueous phase (− 0.98‰ < Δ⁵⁶Fe_{solid–water} < 2.25‰). The significant magnitude of the positive fractionation factor observed in several Fe(III) dominated water may be related to the precipitation of Fe(III) sulphates containing phases.     

Mineralogy and environmental relevance of AMD-precipitates from the Tharsis mines,Iberian Pyrite Belt (SW,Spain)

This paper documents the solid phases associated to acid mine drainage (AMD) at the Tharsis mines (SW Spain). It provides an inventory of the AMD-precipitates, describing their main modes of occurrence and mineral assemblages. Results indicate that iron, aluminum and magnesium sulfates predominate in the assemblages. They occur as efflorescences composed of complex mixtures of metallic salts, and as ochres (jarosite combined with goethite). Also, their distributions illustrate two hydrochemical environments: the open pits, which reflect a proximal secondary paragenesis; and the downstream river banks (Meca River), which represent a more evolved paragenesis, resulting from the evolution of AMD produced throughout the system. These environments can be differentiated by composition and variety of minerals, which is considerably lower along the Meca River.The newly-formed minerals have monitoring significance and proved capable of participating in cycles of retention–liberation of hydrogen ions, sulfate, and metals. In a semi-arid climate, the importance of the AMD-precipitates as environmental indicators is stressed. They may help to understand the response of the system to the episodic rainfall events that occur after prolonged dry periods.     

Trace elements contamination of agricultural soils affected by sulphide exploitation (Iberian Pyrite Belt,Sw Spain)

Agricultural soils of the Riotinto mining area (Iberian Pyrite Belt) have been studied to assess the degree of pollution by trace elements as a consequence of the extraction and treatment of sulphides. Fifteen soil samples were collected and analysed by ICP-OES and INAA for 51 elements. Chemical analyses showed an As–Cu–Pb–Zn association related with the mineralisation of the Iberian Pyrite Belt. Concentrations were 19–994 mg kg⁻¹ for As, 41–4,890 mg kg⁻¹ for Pb, 95–897 mg kg⁻¹ for Zn and of 27–1,160 mg kg⁻¹ for Cu. Most of the samples displayed concentrations of these elements higher than the 90th percentile of the corresponding geological dominium, which suggests an anthropogenic input besides the bedrock influence. Samples collected from sediments were more contaminated than leptosols because they were polluted by leachates or by mining spills coming from the waste rock piles. The weathering of the bedrock is responsible for high concentrations in Co, Cr and Ni, but an anthropogenic input, such as wind-blown dust, seems to be indicative of the high content of As, Cu, Pb and Zn in leptosols. The metal partitioning patterns show that most trace elements are associated with Fe amorphous oxy-hydroxides, or take part of the residual fraction. According to the results obtained, the following mobility sequence is proposed for major and minor elements: Mn, Pb, Cd, > Zn, Cu > Ni > As > Fe > Cr. The high mobility of Pb, Cu and Zn involve an environmental risk in this area, even in soils where the concentrations are not so high.     

Resee矿山遥感监测系统变化向导模块在矿山变化信息提取中的应用

依靠自主研发的Resee矿山遥感自动监测系统中的变化向导模块可对矿区进行方法评价及变化图斑提取,辅助相关部门监视工作区存在的部分违规采矿行为,很好地实现对矿区采矿行为及影像的动态监测,对矿山环境的变化进行有效的监督管理,大大提高了矿山监测的效率和准确性.     

新疆矿山环境遥感监测成果综述

为进一步发挥遥感技术在矿山环境监测中的优势,采用多类型、多时相遥感数据,在充分分析监测区矿产开发状况、矿山地质环境和矿产资源规划执行情况等相关资料的基础上,从矿山辅助设施、道路、矿堆、矸石及地裂缝、采空塌陷等的宏观和微观形态特征出发,运用计算机自动分类和人机交互解译相结合的方法,首次对新疆矿山地质环境问题进行了全面的遥感调查与监测,获取了全区矿山开发中土地占用与损毁、矿山地质灾害、矿山环境污染以及恢复治理状况等方面丰富翔实的基础数据,分析了矿山地质环境与不同矿种、不同开发方式之间的关系。为新疆矿山环境的保护与治理提供了重要的基础数据和技术支撑,再次显示了遥感技术为矿山管理“一张图”工程做贡献的巨大潜力。     

遥感技术在辽宁省矿山环境监测中的应用

辽宁省矿产资源丰富,开发程度较高,但部分矿区开发秩序混乱,矿山生态环境破坏严重。通过2011—2014年4 a 的矿产资源开发环境遥感监测,基本查明了全省矿产资源开发状况,矿山开发占地、矿区地质灾害、矿山环境污染和矿山环境恢复治理等矿山地质环境问题,以及全省矿产资源开发规划执行情况;总结分析了辽宁省矿山开发易出现违法开采的区域、矿种和开采方式;开展了矿山地质环境评价,圈定出矿山开采对矿山地质环境影响严重区、较严重区、一般区和无影响区。监测工作为辽宁省矿产资源有序、高效开发和环境保护提供了基础资料和科学依据,并指出了目前存在的问题和努力的方向,为辽宁省矿山环境遥感监测的下一步工作提出了建议。     

Interaction of acid mine drainage with waters and sediments at the Corona stream, Lousal mine (Iberian Pyrite Belt, Southern Portugal)

This study investigates the geochemical characteristics of the acid mine drainage discharged from the abandoned mine adits and tailing piles in the vicinity of the Lousal mine and evaluates the extent of pollution on water and on the stream sediments of the Corona stream. Atmospheric precipitation interacting with sulphide minerals in exposed tailings produces runoff water with pH values as low as 1.9–2.9 and high concentrations of (9,249–20,700 mg l⁻¹), Fe (959–4,830 mg l⁻¹) and Al (136–624 mg l⁻¹). The acidic effluents and mixed stream water carry elevated Cu, Pb, Zn, Cd and As concentrations that exceed the water quality standards. However, the severity of contamination generally decreases 4 km downstream of the source due to mixing with fresh waters, which causes the dilution of dissolved toxic metals and neutralization of acidity. Some natural attenuation of the contaminants also occurs due to the general reduced solubility of most trace metals, which may be removed from solution, by either co-precipitation or adsorption to the iron and aluminium precipitates.     

基于GeoEye-1的矿山开发遥感调查与监测应用研究

以马鞍山矿区为研究区域,采用高分辨率Geoeye-1卫星遥感数据,通过影像的几何纠正、正射校正、融合等预处理,以Mapgis为数据平台,利用采矿权与遥感影像进行叠加,对开采面、矿山占地、尾矿库、矿山建筑、废弃采坑、矿山道路等信息进行解译,结合实地调查,实现矿产资源开发利用状况、矿山环境调查与监测工作。结果表明,Geoeye-1数据能够满足1：1万矿山开发遥感调查与监测,能够准确、客观、实时的监测矿山的越界开采、无证开采、擅自改变开采方式等多种违规类型及矿山开发引发的环境问题,为政府整顿矿山开发秩序、矿山地质环境恢复治理提供重要的技术支撑和决策依据。     

The natural attenuation of two acidic effluents in Tharsis and La Zarza-Perrunal mines (Iberian Pyrite Belt, Huelva, Spain)

The geochemical evolution of two acid mine effluents in Tharsis and La Zarza-Perrunal mines (Iberian Pyrite Belt, Huelva, Spain) has been investigated. In origin, these waters present a low pH (2.2 and 3.1) and high concentrations of dissolved sulphate and metals (Fe, Al, Mn, Cu, Zn, As, Cd, Co, Cr, Ni). However, the natural evolution of these acidic waters (which includes the bacterial oxidation of Fe(II) and the subsequent precipitation of Fe(III) minerals) represents an efficient mechanism of attenuation. This self-mitigating process is evidenced by the formation of schwertmannite, which retains most of the iron load and, by sorption, toxic trace elements like As. The later mixing with pristine waters rises the pH and favours the total precipitation of Fe(III) at pH 3.5 and, subsequently, Al compounds at pH 4.5, along with the sorption of trace metals (Mn, Zn, Cu, Cd, Co, Ni) until chemical equilibrium at circumneutral conditions is achieved.     

Solar influence and hydrological variability during the Holocene from a speleothem annual record (Molinos Cave,NE Spain)

We present a multi‐proxy approach to reconstructing Holocene climate conditions in northeastern Spain based on an excellent correlation among the lamina thickness, colour parameters and isotope (δ¹⁸O and δ¹³C) variations recorded in a speleothem. An age model constructed from five U/Th dates and annual lamina counting suggests that the uppermost 14.7 cm of the MO‐7 stalagmite grew between 7.2 and 2.5 ka before present but experienced a growth hiatus from 4.9 to 4.3 ka. Three spectral analysis methods were applied to 11 time series. The results reveal common solar periodicities on decennial (Gleissberg cycle) and centennial (De Vries‐Suess cycle) scales. The onset of Holocene carbonate precipitation in the MO‐7 stalagmite appears to be associated with a cold, wet period, whereas the hiatus and the end of growth are related to warm, dry periods. This environmental trend fits well within the regional Holocene climate.     

Evaluation of heavy metal bio-availability from Almagrera pyrite-rich tailings dam (Iberian Pyrite Belt,SW Spain) based on a sequential extraction procedure

The beginning of polymetallic sulphide ore exploitation at Almagrera, Iberian Pyrite Belt, SW Spain, has been dated back to pre-Roman times; mining activity lasted until 2001 when it was definitely halted. The Almagrera sulphide tailings dam was built at the Sotiel–Coronada mine, where Cu, Zn and Pb concentrates were obtained by flotation processes, and sulphide (mainly pyrite) wastes formed. The dam was built as a water-reservoir, on a tectonic fault; its hazard is currently documented by the released wastes after a strong storm in the region, then, its stability is not monitored by the owner.     

Closure of a seaway: stratigraphic record and facies (Guadix basin, Southern Spain)

During the late Tortonian (upper Miocene), the Guadix Basin in S Spain formed one of the Betic corridors that connected the Mediterranean Sea with the Atlantic Ocean. The closure of this connection occurred in a series of steps, documented by three sedimentary units. A lower unit, consisting of basinal marls, shallow-water calcarenites and sands records the formation of a wide seaway. During deposition of the following unit this narrowed to a strait no more than 2 km in wide, triggering an intensification of currents that caused migration of submarine dunes preserved as giant cross-beds in bioclastic sands and conglomerates. Current flowed from the Mediterranean to the Atlantic. The third unit constitutes the youngest marine episode of the filling of the Guadix Basin. At this stage, the connection between the Mediterranean Sea and the Atlantic Ocean was broken, and a system of coastal coral reefs was established in the northern part of the Basin.     

Geology and genesis of the Aznalcóllar massive sulphide deposits, Iberian Pyrite Belt, Spain

The Aznalcóllar mining district is located on the eastern edge of the Iberian Pyrite Belt (IPB) containing complex geologic features that may help to understand the geology and metallogeny of the whole IPB. The district includes several ore deposits with total reserves of up to 130 Mt of massive sulphides. Average grades are approximately 3.6% Zn, 2% Pb, 0.4% Cu and 65?ppm Ag. Mined Cu-rich stockwork mineralizations consist of 30?Mt with an average grade of 0.6% Cu. Outcropping lithologies in the Aznalcóllar district include detrital and volcanic rocks of the three main stratigraphic units identified in the IPB: Phyllite-Quartzite Group (PQ), Volcano-Sedimentary Complex (VSC) and Culm Group. Two sequences can be distinguished within the VSC. The Southern sequence (SS) is mainly detritic and includes unusual features, such as basaltic pillow-lavas and shallow-water limestone levels, the latter located in its uppermost part. In contrast, the Aznalcóllar-Los Frailes sequence (AFS) contains abundant volcanics, related to the two main felsic volcanic episodies in the IPB. These distinct stratigraphic features each show a different palaegeographic evolution during Upper Devonian and Lower Carboniferous. Massive sulphides occur in association with black shales overlying the first felsic volcanic package (V_A1) Palynomorph data obtained from this black shale horizon indicate a Strunian age for massive sulphides, and consequently an Upper Devonian age for the V_A1 cycle. Field and textural relationships of volcanics suggest an evolution from a subaerial pyroclastic environment (V_A1) to hydroclastic subvolcanic conditions for the V_A2. This evolution can be related to compartmentalizing and increasing depth of the sedimentary basin, which may also be inferred from changes in the associated sediments, including black shales and massive sulphides. Despite changes in the character of volcanism, the same dacitic to rhyolitic composition is found in both pyroclastic and subvolcanic igneous series. The main igneous process controlling chemical variation of volcanics is fractional crystallization of plagioclase (+accessories). This process took place in shallow, sub-surface reservoirs giving rise to a compositional range of rocks that covers the total variation range of felsic rocks in the IPB. The Hercynian orogeny produced a complex structural evolution with a major, ductile deformation phase (F₁), and development of folds that evolved to thrusts by short flank lamination. These thrusts caused tectonic repetition of massive and stockwork orebodies. In Aznalcóllar, some of the stockwork mineralization overthrusts massive sulphides. These structures are cut by large brittle overthrusts and by late wrench faults. The original geometric features of massive sulphide deposits correspond to large blankets with very variable thicknesses (10 to 100?m), systematically associated with stockworks. Footwall rock alteration exhibits a zonation, with an inner chloritic zone and a peripheral sericitic zone. Silicification, sulphidization and carbonatization processes also occur. Hydrothermal alteration is considered a multi-stage process, geochemically characterized by Fe, Mg and Co enrichment and intense leaching of alkalies and Ca. REE, Zr, Y and Hf are also mobilized in the inner chloritic zones. Three ore types occur, both in stockworks and massive sulphides, named pyritic, polymetallic and Cu-pyritic. Of these, Cu-pyritic is more common in stockworks, whereas polymetallic is prevalent in massive sulphides. Zoning of sulphide masses roughly sketches a typical VHMS pattern, but many alternating polymetallic and barren pyritic zones are probably related to tectonics. Although the paragenesis is complex, several successive mineral associations can be distinguished, namely: framboidal pyritic, high-temperature pyritic (300?°C), colloform pyritic, polymetallic and a late, Cu-rich high-temperature association (350?°C). Fluid inclusion data suggest that hydrothermal fluids changed continuously in temperature and salinity, both in time and space. Highest Th and salinities correspond to inner stockworks zones and later fluids. Statistic population analysis of fluid inclusion data points to three stages of hydrothermal activity, at low (<200?°C), intermediate (200–300?°C) and high temperatures (300–400?°C). ³⁴S values in massive sulphides are lower than in stockwork mineralization suggesting a moderate bacterial activity, favoured by the euxinoid environment prevailing during black shale deposition. The intimate relation between massive sulphides and black shales points to an origin of massive sulphides by precipitation and replacement within black shale sediments. These would have acted both as physical and chemical barriers during sulphide deposition. Hydrothermal activity started during black shale deposition, triggered by a rise in thermal gradient due to the ascent of basic magmas. We suggest a three-stage genetic model: (1) low temperature, diffuse fluid flow, producing pyrite-bearing lenses and disseminations interbedded with black shales; locally, channelized high-T fluid flow occurs; (2) hydrothermal cyclic activity at a low to intermediate temperature, producing most of the pyritic and polymetallic ores, and (3) a late high-temperature phase, yielding Cu-rich and Bi-bearing mineralization, mainly in the stockwork zone.     

Estimation of potential pollution of waste mining dumps at Peña del Hierro (Pyrite Belt,SW Spain) as a base for future mitigation actions

Peña del Hierro is an abandoned mine site located in the catchment area of the Tinto river (Pyrite Belt, SW Spain). As leaching from the spoils affect the quality of the stream water, the waste dumps have been characterized for mineralogy, geochemistry and granulometry to obtain an estimate of the potential pollution. Waste rock dumps in Peña del Hierro are very heterogeneous and are mainly composed of acid volcanic tuffs > gossan > shales > roasted pyrite ashes > floated pyrite. The volcanic tuffs, the gossan and the shales coexist in the same piles. The roasted pyrite ashes and the floated pyrite form more homogeneous dumps. The dissolution of pyrite concentrated in pyrite ashes and floated pyrite units can generate acid mine drainage. Nevertheless, acid volcanic tuffs, which are rich in pyrite and have no neutralizing minerals, are the main source of these acidic effluents. Only muscovite might partially neutralize the acidity, but the dissolution of this mineral is too slow to compensate for acidity. The occurrence of jarosite in the <2 mm fraction indicates that extreme acid mine drainage occurs. The gossan and roasted pyrite ashes have high contents of trace elements. According to their concentration, As (46–1710 ppm), Pb (113–3455 ppm) and Hg (0–53) are some of the most important toxic trace elements in these wastes. In dumps mainly composed of volcanic tuffs most of the trace elements derive from the gossan mixed in the piles. Gossan is stable in an oxidizing environment, but acidic effluents (pH < 2) can dissolve Fe oxyhydroxides from them and release high amounts of trace elements to the stream water. This research contributes to estimating the production of acid mine drainage and the actual contamination risk of potentially toxic elements in soils and waters of this area, and could be the base for possible future mitigation actions in other areas affected by mining wastes.     

Geochemistry and mineralogy of surface pyritic tailings impoundments at two mining sites of the Iberian Pyrite Belt (SW Spain)

Two pyritic tailings impoundments located in two mining areas of the Iberian Pyrite Belt (Cueva de la Mora and Minas de Ríotinto-Zarandas) were selected to asses their potential environmental impact. Mineralogical (XRD diffraction study), physico-chemical characterization (colour, particle size, pH, acid–base account, total Fe, As, Cu, Pb and Zn) as well as a speciation study (by means of a seven-step sequential extraction procedure) were performed in superficial (0–20 cm) tailings samples. Arsenic and metal contents in soils around the tailings impoundments were also studied. Zarandas dam, a reclaimed impoundment, which has been limed, partially topsoiled and planted, has supported and allowed the growth of pine trees and other plants for many years. The surface of this impoundment can be considered very acid but nonacid forming. Although total As and metal concentrations were relatively high, it is not possible to conclude that the Zarandas tailings have polluted the surrounding soils. Tailings in Cueva de la Mora showed high total and easily mobilizable concentration of toxic elements. The net neutralization potential was strongly negative as a consequence of the acid generation caused by the sulphide oxidation, the presence of secondary acid-generating minerals and the absence of neutralizing materials. Coquimbite and rhomboclase efflorescences formed during the Mediterranean dry summers on the surface of this impoundment contained very high levels of soluble As, Cu and Zn that were easily dissolved and released to the running water in the first rains of autumn.     

Hydrothermal alteration of felsic volcanic rocks associated with massive sulphide deposition in the northern Iberian Pyrite Belt (SW Spain)

Massive sulphide deposits of the northern Iberian Pyrite Belt (IPB) are mainly hosted by felsic volcanic rocks of rhyolitic to dacitic composition. Beneath most of the massive ores of this area (e.g., Concepción, San Miguel, Aguas Teñidas Este or San Telmo deposits) there is usually a wide hydrothermal alteration halo associated with stockwork-type mineralization. Within these alteration envelopes there are two principal rock types: (1) chlorite-rich rocks, linked to the inner and more intensely altered zones and dominantly comprising chlorite+pyrite+quartz+sericite (+carbonate+rutile+zircon+chalcopyrite), and (2) sericite-rich rocks, more common in the peripheral zones and showing a dominant paragenesis of sericite+quartz+pyrite+chlorite (+carbonate+rutile+zircon+sphalerite). Mass-balance calculations comparing altered and least-altered felsic volcanic rocks suggest that sericitization was accompanied by moderate enrichment in Mg, Fe and H₂O, with depletion in Si, Na and K, and a slight net mass loss of about 3%. Chloritization shows an overall pattern which is similar to that of the sericitic alteration, but with large gains in Fe, Mg and H₂O (and minor enrichment in Si, S and Mn), and a significant loss of Na and K and a minor loss of Ca and Rb. However, chloritization has involved a much larger net mass change (mass gain of about 28%). Only a few elements such as Nb, Y, Zr, Ti, P and LREE appear to have remained inert during hydrothermal alteration, whilst Ti and Al have undergone very minor mobilization. The results point to the severity of the physico-chemical conditions that prevailed during the waxing stage of the ore-forming hydrothermal systems. Further, mineralogical and geochemical studies of the altered footwall rocks in the studied deposits indicate that hydrothermal ore-bearing fluids reacted with host rocks in a multi-stage process which produced a succession of mineralogical and chemical changes as the temperature increased.