Secondary Ore Research Articles

Hydro Geochemistry and Balance between Minerals and Solutions in the Mercurial Zone of Azzaba, Northeast of Algeria

The mercury ore deposit of Azzaba is located on the northern flank of the Limestone Chain, south of Azzaba town, North East Algeria. Mercury among other metals is regarded as an environmental problem of this area, following its potential impact on the environment and also on the health of the people. The area of Azzaba is geologically characterized by the various mineral-bearing indices which level and which are classified in poly metal (Pb, Zn, Cu) and mercuro polymetallic (Hg, Pb, Zn, Cu). 15 groundwater samples were analyzed to understand the chemical composition by selected traces elements. The results showed that Hg, Pb and As was identified like contaminants in almost all the groundwater samples. The bicarbonated calcic facies is explained by the presence of cavernous limestone and the calcareous sandstone of the Paleocene Eocene. The chlorided sodic and sulphated calcic facies are found in sandy and clayey reservoirs of Oligocene. The mercury and lead norms are largely exceeded in groundwater the standards tolerated by WHO. Geochemical modeling carried out to study the possibility of metal precipitation and the formation of the secondary ores, shows a super saturation with regard to calcite, dolomite and aragonite and under saturation with respect to halite, the gypsum and anhydrite. The minerals of Hg, As, Pb are under saturated in groundwater of the region of study.

AUTOMATED SCANNING ELECTRON MICROSCOPY (QEMSCAN(R))-BASED MINERAL IDENTIFICATION AND QUANTIFICATION OF THE JABALI Zn-Pb-Ag NONSULFIDE DEPOSIT (YEMEN)

Supergene nonsulfide Zn-Pb deposits consist mainly of Zn-Pb carbonates, Zn silicates, Fe hydroxides, and minor Zn-Pb phosphates, commonly associated with remnants of primary sulfides (sphalerite and galena). The relative abundances of these mineral phases are strongly dependent on the type of host rock. Their variable mineralogy is complex to characterize, and can lead to problems during the processing and recovery of the minerals from the ores. In this case study, mineralogical characterization and quantitative evaluation of the Jabali (Yemen) nonsulfide Zn-Pb deposit was carried out using automated scanning electron microscopy (QEMSCAN®). Both primary and secondary ores at Jabali are hosted in Jurassic dolostones. Smithsonite is the most abundant economic ore mineral in the supergene deposit, and it is locally intergrown with Fe hydroxides and remnants of primary sulfides (sphalerite and galena). The host dolomite is locally replaced by broad bands of Zn-rich dolomite, where Zn has substituted for Mg. The ZnO content in this dolomite can reach 22 wt %. Other Zn minerals such as hemimorphite and hydrozincite occur in limited amounts, as well as cerussite and anglesite. Small particles of Ag sulfide are associated with the secondary minerals. Gypsum, Fe (hydr)oxides (goethite > hematite), Zn-Mn (hydr)oxides, and Pb-Mn (hydr)oxides have been detected locally. The QEMSCAN technique, combined with data previously obtained from other analytical techniques (X-ray diffraction [XRD]), scanning electron microscope-energy dispersive spectrometry [SEM-EDS], optical petrography), has provided detailed mineralogical and textural information on the Jabali mineralization. A key outcome from this QEMSCAN study is the textural data and quantification of the Zn dolomite, which is fairly abundant in this deposit. The combination of techniques used to examine the Jabali supergene ore provides high-quality information that not only characterizes the deposit in detail, but also offers a better understanding for the design of ore processing options and a more realistic predicted recovery of economic minerals.

Occurrence of Manganese Ore Deposits and Their Mineralogy in Vizianagaram-Visakhapatnam Manganese Ores Belt (Andhra Pradesh) India

The Manganese deposits of Andhra Pradesh are associated with a thick sequence of Precambrian rocks, belonging to Khondalite and Charnockite groups of Dharwar Supergroup that forms part of 2500 to 3000 m.y. old Eastern Ghat complex of India. The study area is the Manganese deposits of Vizianagram-Visakhapatnam Manganese Belt of Andhra Pradesh. The study area lies about 150 km NE of Visakhapatnam between 18°12′N - 18°30′N and 83°20′E - 83°45′E. The mineralization of Manganese ores is confined to different rock types, belonging to both Khondalite and Charnockite groups, where they are dispersed throughout the country rocks as small lenses, pockets, veins and irregular bodies of varying dimensions. Quartz, garnet, clay, limonite and apatite are the common gangue minerals in the Manganese ores. The presence of quartz, garnet and apatite brings down the grade of the ore. Ferruginous laterite and ochre generally work as capping of the Manganese deposits. The various Manganese ore minerals present in these deposits are indentified as 1) Primary minerals-braunite, bixbyite, vredenburgite, jacobsite and hausmannite, 2) secondary minerals-psilomelane, cryptomelane, hollandite, pyrolusite and wad. The primary ore minerals are considered to be syngenetic and regionally metamorphosed while, the associated secondary ore minerals are formed due to alteration of the primary ores.

Acidophiles and its Use in Mineral Biomining with Emphasis on China

Acidophiles have been widely used in heap and dump bioleaching of secondary copper sulfide ores and biooxidation of refractory gold ores. 22 genera of acidophiles have been found in biomining environments. This paper gives a preliminary introduction to the application of mineral biomining in China. Challenges and technical trends for heap bioleaching of primary copper sulfide ores, purification of bioleaching solution of polymetallic sulfide ores and biooxidation of carbonaceous refractory gold ores are also recommended.

The Jabali nonsulfide Zn–Pb–Ag deposit, western Yemen

The Jabali Zn–Pb–Ag deposit is located about 110km east of Sana'a, the capital of Yemen, along the western border of the Marib-Al-Jawf/Sab'atayn basin. The economic mineralization at Jabali is a nonsulfide deposit, consisting of 8.7milliontons at an average grade of 9.2% zinc, derived from the oxidation of primary sulfides. The rock hosting both primary and secondary ores is a strongly dolomitized carbonate platform limestone of the Jurassic Shuqra Formation (Amran Group). The primary sulfides consist of sphalerite, galena and pyrite/marcasite. Smithsonite is the most abundant economic mineral in the secondary deposit, and is associated with minor hydrozincite, hemimorphite, acanthite and greenockite. Smithsonite occurs as two main generations: smithsonite 1, which replaces both host dolomite and sphalerite, and smithsonite 2, occurring as concretions and vein fillings in the host rock. At the boundary between smithsonite 1 and host dolomite, the latter is widely replaced by broad, irregular bands of Zn-bearing dolomite, where Zn has substituted for Mg. The secondary mineralization evolved through different stages: 1) alteration of original sulfides (sphalerite, pyrite and galena), and release of metals in acid solutions; 2) alteration of dolomite host rock and formation of Zn-bearing dolomite; 3) partial dissolution of dolomite by metal-carrying acid fluids and replacement of dolomite and Zn-bearing dolomite by a first smithsonite phase (smithsonite 1). To this stage also belong the direct replacement of sphalerite and galena by secondary minerals (smithsonite and cerussite); 4) precipitation of a later smithsonite phase (smithsonite 2) in veins and cavities, together with Ag- and Cd-sulfides.The δ18O composition of Jabali smithsonite is generally lower than in other known supergene smithsonites, whereas the carbon isotope composition is in the same range of the negative δ13C values recorded in most supergene nonsulfide ores. Considering that the groundwaters and paleo-groundwaters in this area of Yemen have negative δ18O values, it can be assumed that the Jabali smithsonite precipitated in different stages from a combination of fluids, possibly consisting of local groundwaters variably mixed with low-temperature hydrothermal waters. The carbon isotope composition is interpreted as a result of mixing between carbon from host rock carbonates and soil/atmospheric CO2.The most favorable setting for the development of the Jabali secondary deposit could be placed in the early Miocene (~17Ma), when supergene weathering was favored by major uplift and exhumation resulting from the main phase of Red Sea extension. Low-temperature hydrothermal fluids may have also circulated at the same time, through the magmatically-induced geothermal activity in the area.

Review on Cyanogenic Bacteria for Gold Recovery from E-Waste

Electronic waste (E-waste) is recognized as a new emerging and fast-growing waste stream, and may be considered as a secondary ore for the recovery of some precious metals (such as gold). A number of control technologies have been conducted for gold recovery, and in which, cyanidation is widely used. In recent years, an alternate approach to the gold cyanidation process is being considered, in which the aim is to replace with the microorganism, specifically cyanogenic bacteria such asChromobacterium violaceum,Pseudomonas fluorescens,Pseudomonas aeruginosaandEscherichia coli.All these species can produce cyanide ions and dissolve gold in their metabolic processes. The mechanism is a combination of chemical knowledge (interaction of metals and cyanide) with microbiological principles (biological cyanide formation) regarding metal solubilization from waste printed circuit boards and the formation of water-soluble cyanide complexes. And the activity of cyanogenic bacteria is affected by many factors, such as pH, dissolved oxygen pulp density and nutriment, especially several metal ions, which can serve as the catalyst in the metabolism. Now researchers are devoting themselves to looking for the proper conditions, not only from the bacteria themselves, but also the combination of many methods, which can reinforce the cyanide generation and improve gold leaching efficiency. At present the reported leaching efficiency of gold with cyanogenic is approximately 70%. As the continuous optimization of conditions, the industrial application can be expected soon.

Prehistoric Copper Extraction in Britain: Ecton Hill, Staffordshire

Major investigations were undertaken of the Ecton Copper Mines, Staffordshire, following the discovery of hammerstones and a red deer antler tool dating to the Early Bronze Age during surface and underground exploration in the 1990s. Ecton Hill was surveyed, the distribution of hammerstone tools examined, and two identified sites of potential prehistoric mining close to the summit of the hill excavated in 2008 & 2009. Excavations at Stone Quarry Mine revealed noin situprehistoric mining activity, but hammerstones and Early Bronze Age bone mining tools from upcast suggest that an historic mine shaft had intersected Bronze Age workings at around 10–25 m depth. On The Lumb one trench revealed evidence for medieval lead mining, while another examined the lowest of four primitive mines associated with cave-like mine entrances along the base of a small cliff. Evidence for prehistoric mining was recorded within a shallow opencut formed by during extraction of malachite from a layer of mineralised dolomite. Traces of the imprint of at least 18 bone and stone tools could be seen and seven different types of working were identified. Most prehistoric mining debris appears to have been cleared out during the course of later, medieval–post-medieval prospection; some bone and stone tools were recovered from this spoil. The tip of a worn and worked (cut) antler tine point was the only such mining tool foundin situat this site but nine tools were radiocarbon dated toc.1880–1640 calbc. Bayesian modelling of the dates from both sites probably indicates mining over a much briefer period (perhaps 20–50 years) at 1800–1700 calbc, with mining at Stone Quarry possibly beginning earlier and lasting longer than on The Lumb. A single date from The Lumb suggests possible renewed mining activity (or prospection?) during the Middle Bronze Age. The dating of this mining activity is consistent with the idea that mining and prospection moved eastwards from Ireland to Wales, then to central England, at the beginning of the 2nd millenniumbc. At Ecton the extraction of secondary ores may have produced only a very small tonnage of copper metal. The mine workers may have been Early Bronze Age farmers who occupied this part of the Peak District seasonally in a transhumant or sustained way

Biologically Assisted Copper Secondary Sulfide Ore Leaching in the Presence of Chloride

Mining operations today face a difficult challenge in terms of water availability, with most of these deposits located in arid areas where fresh water is scarce. This is especially relevant for bio-mining operations where not only the source but the water quality can be a decisive factor for its successful utilization. This research evaluates the metallurgical and microbiological performance of an adapted chloride and copper-resistant mixed culture during the leaching (laboratory scale columns) of a secondary copper sulfide at different chloride concentrations. Up to 6 g/l chloride all columns established Eh potentials over 750 mV with complete oxidation of ferrous iron in the PLS showing well established microbial activity. Copper recovery in solution, along with a high redox potential, was established faster in the mesophilic column but leveled off quickly over time. Copper extraction showed that the 6 g/l chloride column has the highest metallurgical performance (83% CuT) with 4 extra points of copper recovery over the 1.5 g/L and 3 g/l Cl- columns. These results are a good indication that comparable copper recovery rates –to the ones achieved using fresh water- can be reached in the presence of important chloride concentrations by way of using the use of a suitable and well adapted microbial population. The related process and chloride-resistant culture have been patented under the following ID N°: EP2313534/US0201095.

Biological, Chemical and Transport Phenomena which Control the Rate of Copper Leaching in Heap and Dump Operations

Bioleaching of secondary and low grade copper ores in heaps and/or dumps is to day a well established technology. However, there is still a strong need to improve the copper leaching rates and recoveries currently reached at plant level in order to increase the economic outcome and range of application of this technology. This work presents a conceptual model which helps to elucidate when a bioleaching process is controlled either by biological, chemical or transport phenomena. This model, mathematically simplified but scientifically well grounded, it is expected will facilitate discussions among biologists, metallurgists and process engineers to develop collaborative approaches to improve this technology integrating different expertise.

Depósito de Cu-Zn Pojuca Corpo Quatro: IOCG ou VMS?

Este trabalho trata do depósito de Cu-Zn designado como Pojuca Corpo Quatro, localizado na Província Mineral de Carajás, e procura estabelecer parâmetros para definir seu modelo metalogenético. O Depósito Pojuca Corpo Quatro está hospedado em rochas metavulcanossedimentares do Grupo Igarapé Pojuca, correlacionáveis às rochas do Grupo Grão Pará, de idade arqueana. A história metalogenética do depósito é complexa. Duas formas diferentes de ocorrência caracterizam os minerais de minério do depósito: uma mineralização stratabound, coerente com o bandamento das rochas hospedeiras e considerada primária, e um minério em brechas, vênulas e disseminado, aqui descrito como minério remobilizado ou secundário. As características das diferentes tipologias de minério sugerem duas fases de mineralização: mineralização primária, stratabound, cuja paragênese é constituída de calcopirita, pirrotita e esfalerita, considerada neste trabalho como sendo do tipo VMS, e a mineralização secundária ou remobilizada, de paragênese formada por pirrotita, calcopirita e molibdenita, descrita como sendo produto de eventos hidrotermais posteriores do tipo IOCG.

Letlhakane project: case study in complex uranium mineralogy and its geometallurgical implications

Uranium mineralisation within the Letlhakane tenement, Botswana, is complex and characterised by three different ores (primary, oxidised and secondary). From a geometallurgical viewpoint, most uranium occurs in coarse grained, and/or highly soluble minerals; favourable characteristics for conventional extractive metallurgical methods. However, there are several factors presenting challenging metallurgical issues including: the presence of refractory ore (<30% of the uranium); the frequent encapsulation of uranium minerals within the first two ore types; minor gypsum and major carbonate present within the secondary ore type; and high clay content throughout, potentially necessitating agglomeration of the ore. An optimised processing flowsheet has been developed involving two distinct flow paths. First, extraction of the secondary uranium ore through agglomeration and an acid heap leach. Second, a beneficiation stage involving fine grinding and radiometric sorting forming a preconcentrate; followed by a strong, two-stage acid agitation leach to extract the uranium from the refractory uranium bearing minerals.

Red Mud Characterization Using Atomic and Nuclear Analytical Techniques

Red mud is a toxic waste left as a byproduct in aluminum production Bayer process. Since it contains significant concentrations of other chemical elements interesting for industry, including Rare Earths Elements (REEs), it is also potential secondary ore source. Recent events in some countries have shown that red mud presents a serious environmental hazard if not properly stored. The subject of our study is evaluation of the red mud elemental composition, especially yttrium, scandium, gallium and REEs, from an ex-aluminum plant in Obrovac, Croatia, left from the processing of bauxite mined during late 70's and early 80's at the eastern Adriatic coast and stored in open concrete basins for more than 30 years since then.

Research on Jinchuan Mineral Processing Plant by Flotation Column

In this paper processing mineralogy analysis was carried on the secondary crude ore of which the characteristic of the separating was analyzed. Tests were carried on the crude ore, which is of the secondary grinding of the rich ore manufacture system of Jinchuan mineral processing plant, by using Cyclonic-static Micro-bubble Column Flotation. The result of the tests had proved that Cyclonic-Static Micro-bubble Columns Flotation is expert at recoverying the fine ores, and middling-regrinding is a feasible kind of method to improving the recovery.

Sphalerite Associated with Pyrrhotite-Chalcopyrite Ore Occurring in the Kotana Fe-Skarn Deposit (Giresun, NE Turkey): Exsolution or Replacement

The Kotana prospect is located about 30 km south of Giresun (NE Turkey). The ore mineralization is a Fe-skarn occurring within the low-grade pre-Lower Jurassic Pınarlar metamorphics, consisting of marble-phyllite intruded by the Upper Cretaceous-Eocene Aksu biotite monzogranite. The principal primary ore minerals include pyrrhotite and magnetite along with minor pyrite (I) and chalcopyrite, accompanied by trace sphalerite. Sphalerite is closely associated with chalcopyrite and to a lesser extent with hexagonal pyrrhotite. Secondary ore minerals include pyrite (II), marcasite, martite, hematite, goethite, lepidocrocite, and intermediate Fe-oxides-hydroxides. Gangue minerals are mainly calcite and quartz. Oxidation of the primary sulphides resulted in formation of diverse secondary ore textures containing bird's eye, martitic, spheroidal, colloform, rim, and veinlets. Distinct crystal shapes of sphalerite are of particular interest to this investigation due mainly to their proposed formation mechanisms. Three alternative mechanisms for their formation were considered: (i) quasi-exsolved bodies developed by hexagonal pyrrhotite replacement of chalcopyrite, (ii) interstitial formation between coalescing pyrrhotite crystals during crystal growth, and (iii) as genuinely exsolved bodies, and as such conflict with previous experimental results. Although the general absence of solute mineral outside the solvent mineral suggests solid solution at high temperatures (favouring the third mechanism), textures, modal, microprobe and sulfur-isotope data suggest that these are more likely to be pseudoexsolved bodies formed as a result of replacement of chalcopyrite by hexagonal pyrrhotite. The \delta^3^4S values of pyrrhotite and chalcopyrite are between 5.23 and 6.73 per mil (n= 12) and 2.29 and 3.26 per mil (n= 8), respectively, indicating continuous enrichment in heavy sulphur isotopes from prograde stage to retrograde stage within the typical range for skarn-type mineralization. Fluid inclusion analyses of calcite and quartz gangues indicate that the minimum homogenization temperature (Th) averaged 400±20 ºC with salinities < 15 wt% NaCl equivalent.

The manganese and polimetalic sulphures exploration impact in the Gândacu - Suh rzelul Mare mining zone (north-west of Suceava District, north of Eastern Carpathians) on the environment

The mining activity in Iacobeni – Cârlibaba area dates back as far as the XIII-th century, the first documentary certification being before 1241. After 1775 (when Bucovina was annexed like province to the Austrian Empire) Iacobeni –Cârlibaba area was scientifically examined by Austrian geologists. Geologically and structurally, the Gândacu – Suh rzelul Mare mining area belongs to the Crystalline Mesozoic Zone of the Eastern Carpathians. The Crystalline Mesozoic Zone is made up of a system of Alpine Nappes, called the Eastern Central Carpathian Nappes (S ndulescu, 1984). The exploration and geological surveying work was done in the metamorphic basement of the Sub-Bucovinian Nappe. In the Iacobeni – Cârlibaba mining area, the manganese ore deposits are located in the epimetamorphic Tulghe 2 level (Tg2) of Tulghe lithogroup and the polimetalic sulphures ore deposits in the Tulghe 3 level (Tg3). Geographically, the area Gândacu – Suh rzelul Mare is situated in the Suhard Mountains, on the right slope of the Golden Bistri a river, from an administrative point of view belonging to Cârlibaba, Cioc ne ti and partially to Iacobeni. The prospection works outlined three research perimeters: Puiu - Suh rzel, Humoru and Diaca – Gândacu. The geological study in the area Puiu – Suh rzel showed the presence of polimetalic sulphures ore in acid riolitic metavulcanites, sericite or sericite-chloritic schists. In the same perimeter, in the superior drainage basin of the Recele brook, its discovered a manganous level in black quartzite with intercalations of sericite-graphitic schists. The manganese ore is predominantly siliceous, made up of lens and nests in parallel disposition. On the left slope of the Suh rzelul Mare brook it uncovered polychrome limestone ores. In the Humoru and Diaca – Gândacu perimeters the prospection works highlighted a primary ore of manganese consisting of rhodonite, rhodochrosite, manganese silicates, quarts, calcite, pyrite, etc. The secondary ore of manganese, resulted from the alteration of the primary ore, appears sporadically and it is made up of manganese and iron oxides and hydroxides. The prospection and research works in the three perimetres ended in the interval 1991-1996.

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments

Oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600°C and 2 kbars. The replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation. Reaction rims of albite, up to 50 μm thick, can be readily achieved within 14 days. Re-equilibration of plagioclase in an 18O-enriched sodium- and silica-bearing solution results in oxygen isotope redistribution within the feldspar framework structure. The observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface-coupled dissolution–reprecipitation mechanism. Chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major, minor and trace elements also including elements such as Al and Ti which are commonly regarded as immobile during hydrothermal alteration. The results contribute to developing our understanding of the close association between large-scale albitisation and secondary ore mineralisation which is common in nature.

Specific features and composition of the Akkermanov manganese deposit

New data on the Akkermanov deposit characterized by specific structure and composition of primary (carbonate) and secondary (manganese oxide) ores are presented. Distribution of mineralization in host rocks and weathering crusts is considered. It is shown that manganiferous carbonate rocks, which host orebodies, formed in a marine basin with well-aerated bottom waters. Oxide ores are mainly composed of crystalline pyrolusite produced by multiple processes of the oxidation of manganese compounds. In this respect, the Akkermanov deposit differs drastically from all manganese deposits developed in Russia and Ukraine.

A Simulation Study on Model Predictive Control and Extremum Seeking Control for Heap Bioleaching Processes

Heap bioleaching processes are of increasing interest in the mining industry to recover metals from secondary ores. Recently, it has been proposed to use feedback control to improve the rate of mineral extraction. In this paper we compare two feedback approaches, namely Model Predictive Control (MPC) and Extremum Seeking Control (ESC), to improve copper extraction in a heap bioleaching process. Simplified linear models obtained in previous work are used to design an MPC strategy incorporating input constraints. ESC is tuned to maximise copper extraction rate using aeration rate. Simulation results run on a high complexity model of the process show that similar copper extraction rates can be obtained using either strategy. While better control efforts are obtained with MPC, ESC achieves similar results and shows potential for this intrinsically complex process, requiring little knowledge about the plant.

Distribution and mineralogy of platinum-group elements in altered chromitites of the Campo Formoso layered intrusion (Bahia State, Brazil): control by magmatic and hydrothermal processes

Polyphase, penetrative hydrothermal metasomatism in chromitites of the Campo Formoso layered intrusion produced spectacular chromite – ferrian chromite zoning and transformed the primary intercumulus silicates into a chlorite – serpentine – carbonate – talc assemblage. Alteration did not substantially modify the composition of chromite cores and the distribution of platinum-group elements (PGE) through the sequence of chromitite layers, which still are consistent with magmatic fractionation processes. Texture and composition of laurite and Os–Ir–Ru alloys included in chromite cores indicate that these PGM were not altered, and are probably magmaticin origin. In contrast, the PGM located in the intergranular chlorite matrix (laurite, Ir–Ru–Rh sulfarsenides and Pt–Pd compounds with Sb, Bi and Te) display evidence of hydrothermal reworking. These PGM are intimately intergrown with low-temperature Ni-sulfides. The paragenesis suggests that the Ni-sulfides-PGM assemblage formed at the expenses of unknown PGM precursors, which must have been originally present in the intercumulus silicate matrix. Mechanism of formation involves a sequence of dissolution-precipitation events controlled by variation of redox conditions during chromite alteration. The presence of a secondary ore mineral assemblage consisting of galena, bismuthinite, native antimony, and various Pb–Sb compounds suggests a possible contribution of fluids derived from the adjacent granite.

Estudio preliminar de las mineralizaciones de la mina de oro romana de Llamas de Cabrera (Leon, NO de España)

RESUMEN La mina de Llamas de Cabrera (Leon, Espana) es un yacimiento de oro explotado en epoca romana, en el que coexisten mineralizaciones de oro primario y de oro secundario. Las mineralizaciones de oro primario arman sobre todo en los tramos superiores de la Cuarcita Armoricana. Se trata de mineralizaciones filonianas, siendo muy abundantes las que encajan en fracturas tensionales de direccion N180°E/70-85°E y ocasionales las asociadas a fracturas de direcciones N70°E y N125°E. Estan formadas por cuarzo y arsenopirita muy dominante sobre pirita, galena, oro, calcopirita, bismutina, tetraedrita y covellina. Las alteraciones hidrotermales acompanantes son silicificaciones, sericitizaciones y cloritizaciones. Los minerales supergenicos determinados son escorodita, goethita y anglesita. El oro explotado es oro libre dispuesto generalmente en microfisuras en arsenopirita o cuarzo. Su contenido en plata varia desde 1,99 a 7,62%, mientras que el contenido en cobre es muy bajo, permaneciendo por debajo del limite de deteccion instrumental. El estudio realizado pone de manifiesto la existencia de dos fases de mineralizacion, producidas durante dos eventos hidrotermales de edad hercinica, ademas de la fase supergenica. Las mineralizaciones de oro secundario, explotadas en sedimentos aluviales y coluviales, se produjeron por la actuacion del ciclo exogeno sobre los yacimientos de oro primario. Se estima que el volumen total de material movido en epoca romana ascendio a 2 Mm 3 . Palabras clave: Mineralizaciones filonianas, arsenopirita, arrugia, sinclinal de Truchas, Espana.