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The Brass Nails of the Akko Tower Wreck (Israel): Archaeometallurgical Analyses
Abstract
The shipwreck designated as the Akko Tower Wreck was discovered inside Akko harbor, Israel, in 1966. It was surveyed in 1975 and 1981, and excavated in 2012-2013. Hull planks were connected to the frames by brass nails, some of which were in situ, emerging vertically from the planking, where frames had disappeared, and others were detached. The 105 nails that were retrieved were tentatively divided into two groups (A and B) according to their general shape and size. Nails sampled from each group were characterized by non-destructive and destructive metallurgical methods, including XRF, light microscopy, SEM-EDS, microindentation hardness measurements, and lead isotope analysis, in order to reveal their composition and microstructure, as well as to determine their manufacturing process and date the origin of the raw material. All nails were manufactured by casting and made of binary copper-zinc alloy: Type A with 35-36 wt% zinc, and Type B with 33-34 wt% zinc (XRF results). These compositions confirmed the preliminary typing of the nails. Their microstructure indicates that they were manufactured differently: Type A nails have Widmanstätten thin lamellae plates, and Type B nails have α-brass grains containing a dendritic microstructure. Based on their zinc and lead concentrations it is suggested that the nails were manufactured in the first half of the nineteenth century. The lead isotope analyses of the nails suggest that the raw material most probably originated in Great Britain. Hence, it is suggested that the Akko Tower Wreck is the remains of a European merchantman which sank in Akko harbor about the middle of the nineteenth century.
... In the course of the nineteenth century, brass was used for many marine applications, including nails [30], cases [32], hook-and-eye closures [33], flintlock musket fittings [34], oil lamp wick housings [35] and rolled sheets [36]. More than a hundred brass nails retrieved from the Akko Tower shipwreck, which was a 25-m-long European merchantman sunk about the middle of the nineteenth century in Akko harbour, were of two types: A (long nails) and B (short nails), distinguished by their general shape and size. ...
... All nails were post-cementation products, created by casting. Type A nails contained 35-36 wt% Zn and had a Widmanstätten lamella microstructure, and Type B nails contained 33-34 wt% zinc and had α-brass grains containing a dendritic microstructure, indicating that they were manufactured differently [30]. Analysis of anisotropy of magnetic susceptibility (AMS) revealed that Type A nails were of better quality than Type B [37]. ...
... Analysis of anisotropy of magnetic susceptibility (AMS) revealed that Type A nails were of better quality than Type B [37]. The lead isotope analysis of the nails suggested that their raw material probably originated in Great Britain [30]. ...
The 4.4-m-long vessel designated as Molyneux’s boat was built in England in 1836. During its conservation in 2008, metal fastenings were retrieved, and 12 of them were examined by XRF, metallographic and multifocal light microscopy, microindentation hardness measurement, and SEM-EDS analysis. The results show the use of manufacturing techniques developed at different times: the copper fastenings were made by traditional methods – intensive hammering to their final shape followed by annealing; the screws and nuts were made of brass containing ~36 wt% Zn, and were probably a post-1848 product; and the bolt was made of low carbon steel (produced by the Bessemer process) and shaped by plastic deformation, perhaps through a thread-rolling process. The bolt was galvanized, thus most probably manufactured after 1856. It appears that the boat was originally built using copper fastenings, and some of which were replaced by galvanized bolts and brass screws during minor refitting.
... Metallurgical analyses of the ship's brass fasteners, sheathing, and rigging elements indicated manufacturing dates during the first half of the 19th century (Cohen et al., 2015Cvikel et al., 2017). The glazed floor tiles found in the shipwreck were dated typologically from the late 18th through late 19th centuries, although the decorated tiles suggested a date towards the last quarter of the 19th century Cvikel, 2016). ...
... Previous analyses of the ship's metal elements placed the ship's construction during the first half of the 19th century Cohen et al., 2015Cohen et al., , 2017Cvikel, 2016;Cvikel et al., 2017). This is a slightly earlier date than our construction estimate, but these findings are not necessarily incongruous. ...
... Meanwhile, the Akko Tower Ship's rigging, fasteners, and sheathing were manufactured using British Imperial standards from ore likely originating in Great Britain (Cohen et al., 2015Cvikel et al., 2017). Direct British influence on Ottoman shipbuilding also began under Sultan Selim III, who placed part of the Ottoman Arsenal under British control in 1799 during Napoleon Bonaparte's siege of Egypt and the Levant. ...
The 19th century was an era of increasing mechanization and globalization, which transformed maritime networks and shipbuilding in and beyond the Mediterranean. Shipwrecks offer valuable physical evidence of such maritime connectivity and evolving shipbuilding techniques but must be dated within a high-resolution timeframe to be synchronized with, and thereby enhance, historical records. We focus here on high-resolution dating of the Akko Tower Shipwreck, the remains of an Ottoman merchant brig found inside the harbor of Akko, Israel. We use dendrochronology, ¹⁴C wiggle-matching, and Bayesian chronological modeling to determine that the ship was likely constructed in the mid-1850s, and therefore called at Akko’s harbor after the town’s 1840 bombardment, a period of decline traditionally under-studied in Ottoman historical narratives. Using dendroprovenancing methods, we find that the ship’s hull used timbers from the Anatolian Black Sea region, although it was built in the French construction tradition, and used British metal rigging and fasteners, which reflect shifting Anglo-French influence and socioeconomic interconnections with the Ottoman Empire during the 19th century.
The Akko Tower Shipwreck is the first shipwreck from Israel to be dendrochronologically dated and provenanced. Our results show how dendrochronology and Bayesian chronological modeling can be used successfully not only for high-precision dating, but also for untangling the shipbuilding processes and the socioeconomic networks that made ship construction possible. We also re-evaluate East Mediterranean oak sapwood datasets and develop an approximate new sapwood model that provides more robust estimates of felling dates for tree-ring analysis of this region’s oak wooden cultural heritage.
... More than one hundred brass nails were retrieved from the nineteenth century Akko Tower Wreck and were tentatively divided into two groups according to their overall shape and size (Cohen et al. 2015;Cvikel 2016). The nails were characterized by various methods, including VT, XRF, metallography, LM, multi-focal LM, SEM-EDS, microhardness measurements, lead isotope analysis, and anisotropy of magnetic susceptibility (AMS) examination (Cohen et al. 2015;Ashkenazi et al. 2019). ...
... More than one hundred brass nails were retrieved from the nineteenth century Akko Tower Wreck and were tentatively divided into two groups according to their overall shape and size (Cohen et al. 2015;Cvikel 2016). The nails were characterized by various methods, including VT, XRF, metallography, LM, multi-focal LM, SEM-EDS, microhardness measurements, lead isotope analysis, and anisotropy of magnetic susceptibility (AMS) examination (Cohen et al. 2015;Ashkenazi et al. 2019). Some of the nails (mostly of type B) were found broken and their tips were missing; therefore, it was assumed that they were used. ...
... Some of the nails (mostly of type B) were found broken and their tips were missing; therefore, it was assumed that they were used. The metallographic observation of the nails revealed a Widmanstätten microstructure in nail type A, and α-brass grains with a dendritic morphology in nail type B (Cohen et al. 2015). Based on the lead isotope analysis, it was suggested that the raw material of the nails originated in Great Britain (Cohen et al. 2015;Ashkenazi et al. 2019). ...
Metals and their alloys were used by ancient civilizations based on their appearance and properties. During antiquity, the production process of metal artifacts frequently caused strain hardening, cracking, and loss of strength. In addition, devastating failure has often occurred after long burial periods, resulting from residual stresses and continuous corrosion attack. Therefore, the present study aims to examine how a fracture mechanics approach, integrated with failure analysis tools, may assist archeologists in gaining additional information concerning ancient metal objects. For this purpose, a literature survey of post-mortem studies of the RMS Titanic ship’s failure is presented, followed by a review of various archeological and historical studies of metal objects and structures made of silver, lead, copper, iron, and their alloys. Lastly, based on the current literature review, a methodology is proposed for analyzing ancient metal artifacts. This approach may assist archeologists in gaining a better understanding of the manufacturing techniques of ancient metal objects, their original shape and dimensions, the cause of failure, and state of preservation and conservation. Moreover, the use of such an approach may be valuable for future conservation and restoration of such archeological metal artifacts.
... For the current study, five different types of artefacts were chosen: a copper nail from the fifth century BC Ma'agan Mikhael shipwreck (Cvikel et al., 2017a;Kahanov et al., 1999;Kahanov and Pomey, 2004); dozens of copper alloy coins from the Ma'agan Mikhael B shipwreck, dated to the seventh-eighth centuries AD (Cohen and Cvikel, 2019;Cohen et al., 2018;Inberg et al., 2018); and three artefacts from the nineteenth century AD Akko Tower shipwreckceramic floor tiles, brass nails and a fragment of a brass sheet (Ashkenazi et al., 2017Cohen et al., 2015;Cvikel, 2016;Cvikel et al., 2017b). ...
... Based on the multi-focal LM examination, the colour differences on the surface of the sheet are probably the result of its composition: green may be related to atacamite and/or brochantite; turquoise may be due to the presence of namuwite [(Zn,Cu) Cohen et al., 2015;Inberg et al., 2018, p. 401;Mathiazhan et al., 2010;Santos et al., 2006). The XRD results of the sheet's surface revealed the presence of metallic brass, as well as different oxides, including cuprite, namuwite, connellite and hydrated zinc chlorosulphate. ...
... The applied testing methods and their main advantages and disadvantages (Ashkenazi et al., 2017Bello and Galway-Witham, 2019;Cohen et al., 2015Cohen et al., , 2018Courtenay et al., 2019;Cvikel et al., 2017aCvikel et al., , 2017bInberg et al., 2018;Mat e-Gonz alez et al., 2017;M elard et al., 2016). ...
The multifocal 3D digital light microscope (LM) is an advanced tool which allows the high resolution tracking of surface topographies, morphologies and colours, and offers real-time measurements of parameters such as length and roughness, as well as in-situ field microscopic scale documentation. The use of a multifocal digital LM, equipped with powerful software, is examined in the present work as a justified tool for the study of ancient objects retrieved from shipwrecks. For that purpose, various archaeological objects were studied with an advanced multifocal LM system, which included an improved light sensitivity sensor. The results were compared to other methods, such as XRF, SEM-EDS, Raman spectroscopy and XRD. The use of a multifocal digital LM offers a unique opportunity to relate between the macroscopic and microscopic levels of the surface with colours as they appear in daylight, and correspondingly, in many cases, to expose the manufacturing process of the object.
... In the literature, brass-based metallic nails were studied in relationship with corrosion issues (mainly in shipwreck findings [29]). The history of brass refers to the deliberate addition of zinc to copper since the first millennium BC. ...
... There was also 30% of zinc added in Roman times (1st and 2nd centuries AD), then lowered in the following century [30]. Therefore, we cannot derive a strict chronological criterion to date the nail, though the low content presence of iron (up to 0.5%) and lead (less than 2%) suggests that nail 1 could have been produced in the 18th century [29]. Additionally, this nail, having a Cu/Zn ratio of 70/30, should have been produced before the use of the Muntz patent (concerning a brass metal having a Cu/Zn ratio equal to 60/40, patented in 1832 [29]). ...
... Therefore, we cannot derive a strict chronological criterion to date the nail, though the low content presence of iron (up to 0.5%) and lead (less than 2%) suggests that nail 1 could have been produced in the 18th century [29]. Additionally, this nail, having a Cu/Zn ratio of 70/30, should have been produced before the use of the Muntz patent (concerning a brass metal having a Cu/Zn ratio equal to 60/40, patented in 1832 [29]). ...
The production and manufacturing techniques of metals involve expertise, and the study of ancient artifacts relies on interdisciplinary skills. Metalworking processes used in the production of jewelry masterpieces can, for example, give indications on the provenance of an ancient object of an unknown origin and the techniques used. In this regard, metallic samples from the Chiaravalle Cross (a beautiful processional cross with a complex structure, dating to the 13th century) have been studied, combining bulk and point measurements. Neutron-based experiments (like Prompt Gamma Activation Analysis and neutron diffraction) provide the bulk of the elemental and mineralogical composition, while particle induced X-ray emission analyses evidenced important details on its manufacturing techniques.
... In a previous study [2], it was found that all nails had a protective oxide layer with some local corrosion on their external surface, but their bulk metal was well preserved. The nails were divided into two groups: Type A, with 35e36 wt% zinc, has Wid-manst€ atten thin lamellae plates microstructure; while Type B, with 33e34 wt% zinc, has a-brass grains containing a dendritic microstructure. ...
... Prior to the early 19th century, a-brass with up to 28 wt% Zn was produced in Europe by the cementation process [14e16]. In this process, copper was mixed with zinc ore and charcoal, and the ore was reduced at a temperature around 1000 C to pure zinc vapour, which diffused into the solid copper [2,17]. Each time that a brass alloy was recycled, it lost approximately 10 wt% of its zinc concentration, resulting in a serious reduction of the zinc content in the alloy after several recycles [9,17,18]. ...
... (Table 2), along with three other nails: nos. 135 (Type A), 139 (Type B), and 159 (Type B), which were previously studied [2]. All these nails were studied using non-destructive and destructive metallurgical testing: ...
The Akko Tower Wreck is the remains of a 25-m-long merchant brig dated to the first half of the 19th century. During the underwater excavations, 105 brass nails were retrieved from the shipwreck. The nails were divided into two groups based on their microstructure: Type A nails were characterized by Widmanstätten plates, while Type B nails by a dendritic microstructure. In each group there were miscellaneous nails, distinguished by their different shapes. Ten miscellaneous nails were characterized by XRF, light microscopy, SEM-EDS analysis, microhardness measurements, anisotropy of magnetic susceptibility examination, and lead isotope analysis. The brass nails were post-cementation products manufactured by casting. The microstructure combined with the AMS analysis, indicated that Type A nails were of better quality than Type B ones. The lead isotope analysis of the nails suggested that their raw material most likely originated in Great Britain.
... Approximately 400 English ships had been sheathed with this alloy by 1844 ( [55], p. 224). This study of a fragment of brass sheet is part of an ongoing series on the Akko Tower Wreck and its finds (e.g., [13,56]). Establishing and comparing the chemical composition, microstructure and properties of this piece provides information on its manufacturing process and date, in addition to the possible origin of the raw material, and its use in the ship. ...
... Lead isotope signatures of the sheet and nails nos. 135 and 139 ( [56], pp. 202-203) are almost identical, and despite the compositional differences, indicate that there was a common metal source for the materials (Fig. 12). ...
... The XRF results of the nails (after grinding) indicated a composition of 61.3-65.6 wt% Cu, 32.9-36.2 wt% Zn, 0.8-1.1 wt% Pb, 0.6-0.7 wt% Sn, and up to 1.1 wt% Si ([56], p. 193). ...
The Akko Tower Wreck is the remains of a 25-m-long merchant brig, dated to the first half of the 19th century. A well preserved piece of brass sheathing was found in the shipwreck, retrieved and examined by non-destructive and destructive metallurgical methods, including visual testing, XRF, OES, light microscopy, SEM-EDS examination, microindentation hardness measurements and lead isotope analysis. The results demonstrate that the sheet is made of α-brass, containing about 34 wt% Zn. Its thickness (average 0.85 mm) and microstructure indicate that it was produced as rolled sheet, annealed during its manufacturing process. Its composition and manufacturing process indicate that it was produced during the first half of the 19th century, thus supporting the dating of the ship. The lead isotope analysis suggests that the raw material most probably originated in Great Britain, similarly to brass nails retrieved from the ship. This is an example of the exploitation of the corrosion resistance of α-brass sheet for use as sheathing to protect a ship against Teredo navalis and to improve its sailing qualities by its anti-fouling properties.
... The decorated floor tiles are the subject of the present research, as part of an ongoing series of studies of the shipwreck and its artifacts [1][2][3][4][5][6][7][8]. Two types of tiles were found. ...
Fragments of decorated floor tiles were retrieved from the Akko Tower shipwreck, Israel. Most tiles were made of bright brown fired clay with a white glaze decorated with colored stenciled motifs (Type A); and others consisted of a red-brown fired clay body, coated with a brown pigment covered with transparent brown glaze (Type B). This study aimed to characterize the two tile types; to reveal information concerning the manufacturing process; and to determine the origin of their raw material. A multidisciplinary approach was used, including light microscopy, SEM-EDS, electron probe microanalysis with wavelength-dispersive X-ray spectroscopy (EPMA-WDS), XRD, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses. The characterization of both tile types demonstrated the use of different raw materials. The Type A tiles were covered with tin-opacified majolica glaze and colored with various mixtures of pigments. The blue color was due to pigment rich in cobalt; the yellow color was due to Naples yellow and lead-tin yellow I minerals; and the green, orange, and brown colors were all prepared by mixing the Naples yellow pigment with different minerals. These majolica glaze tiles were probably manufactured in Sicily. The brown coating of the Type B tiles was due to pigment rich in lead and iron minerals. These tiles were produced with different manufacturing processes, and apparently made in France.
This paper sets out new recommendations for recording structural iron nails. Despite their ubiquity, iron nails have received limited analytical and interpretative attention and recording practices are highly variable. Too often current recording is time‐consuming and costly without providing meaningful information. This paper proposes a new recording methodology, developed through analysis of the Roman structural nail assemblage from the MHI A14 Cambridge‐Huntingdon excavations alongside experiments in nail shaping, with wider context provided by medieval and post‐medieval assemblages from the City of London. This approach includes a new nail typology, recommendations for bulk recording of basic details for whole assemblages (using counts and typologies), alongside detailed recording (shank morphology and further metric data) for certain nail groups. Shank morphology is a particularly important aspect proposed here, being indicative of how nails were used in antiquity.
For European naval powers, whose economic and political well-being depended on the success of naval enterprises, warships played a fundamental role. Based on a multi-scalar and comparative approach, evidence from post-medieval (or historical) shipwrecks, can contribute to a better understanding of modern technology and society. This article deals with the innovations of British, French, and Spanish warships that sailed from about 1750 to 1815. An archaeological, archaeometric, and documentary study of wreck sites, with emphasis on ships’ structure, equipment, and ordnance, provided novel data to address the development of naval technology of the period. Based on this comprehensive approach, the information obtained allowed for a discussion of the impacts of industrialisation, warfare, and science on the innovation dynamic developed within the aforementioned states.
Lead isotope analysis (LIA) is a valuable means for assessing provenance of raw material used in artefacts from Antiquity. Available data on isotopic composition of Roman-period artefacts (e.g. lead ingots from shipwrecks) and samples from lead sources constitute an outstanding frame of reference to develop these studies. In this work, analysis was performed on five Roman period lead anchor stocks from Catalonia, Spain. Isotope data were obtained using two high resolution multi-collector thermal ionization mass spectrometers (TIMS). The lead isotope signature of samples, in conjunction with historical considerations, suggests that the mineral used for these objects came from Cartagena-Mazarron deposits.
Shipbuilding of naval and merchant ships of different types and sizes has required a profound knowledge of every constitutive element. Bolts and nails, in particular, played a significant role as they maintain joined and secured the main structural components of wooden hulls. This article aims to contribute to assess the technical issues of the elements used within the Spanish shipbuilding during the 17th and 18th centuries. Based on contemporary naval treatises, basic notions on morphology and size of metal bolts and nails will be described. Furthermore, manufacturing methods and materials used will be developed. This analysis is focused on ships from the Spanish Navy. The data obtained will contribute to discussing the standardization degree of the structural fastenings used for ships construction of the period, which are of special value for the analysis and interpretation of evidence from shipwrecks.
The Akko Tower Wreck is the remains of a 25-m-long merchant brig, dated to the first half of the 19th century, found in the ancient port of Akko in Israel. The ship's remains were covered with a significant amount of dark grey marlstones to argillaceous limestones with white calcite veins, apparently used as ballast. Petrographic studies of ballast stone samples including optical microscopy, X-ray diffraction, and scanning electron microscopy showed the presence of calcite, quartz and clay minerals (illite and chlorite) in all samples, and small amounts of dolomite in about half of them. Biostratigraphic analyses show that the stones are of Late Cretaceous age (Santonian-Campanian). The results confirm the homogeneous composition of the rock, which is not of local, eastern Mediterranean origin. The specific combination of lithology and depositional age enables comparison with likely provenance areas, while many of which can be ruled out on this basis. It is therefore possible that the sailing route of the ship extended to the western Mediterranean, the Adriatic, or theoretically even as far north as Normandy or eastern England. The estimated total weight of the stones was about 30 tons, which would have been an adequate ballast weight for a brig of these dimensions.
Archaeometric research carried out on materials recovered from historical shipwrecks has contributed to the knowledge of Modern technology and society, frequently on aspects beyond the mere naval scope. During the last decades, works on the characterization of metal components from the hull structure and nautical equipment of diverse wooden ships stand out. As this objects had to withstand the strains of sailing, they are of interest to analyze the knowledge once available on material behaviour and manufacturing means. For European maritime powers, whose economic and political well-being strongly depended on the success of certain naval enterprises, warships played a fundamental role. Their remnants, analyzed from a comparative perspective, account for the multiplicity of aspects that defined them through time. In this presentation we will refer to the archaeological study of diverse shipwrecks to explore the factors that interacted and originated changes during the beginning of the industrialization process in Western Europe.
The Akko 1 shipwreck is the remains of a 26-metre-long Egyptian armed vessel or auxiliary naval brig built at the beginning of the 19th century. Remains of six flintlock muskets were retrieved from the shipwreck, and characterised by various metallurgical methods. The research aimed to study the composition and microstructure of the musket fittings and their manufacturing processes, and if possible, to determine the date and origin of the raw materials. The lead isotope analysis of the fittings suggests that their raw material originated in Great Britain. Based on their typology and composition, the fittings were made in Great Britain of brass alloy and manufactured by casting, probably at the same workshop; and the staple was manufactured by casting and drawing. Considering the zinc content, combined with the manufacturing techniques, the fittings were manufactured between the latter part of the 18th and the early 19th centuries, which might indicate that they were purchased in the course of 19th century weapons trade to be used on board the Egyptian ship.
The shipwreck designated as the Akko Tower Wreck lies at the entrance of Akko harbour, Israel, 35 m north of the Tower of Flies, in 4.4 m of water. Following two seasons (2012 and 2013) of underwater excavation, it is suggested that it is the remains of a merchant brig of 200 tons, dated to the first half of the 19th century, and built under the influence of the French shipbuilding tradition in an established shipyard. The full story of the ship and its place in the maritime history of Akko, however, remains an enigma.
The Akko Tower Wreck was found inside Akko harbour, Israel, in 1966, next to the Tower of Flies, after which it was named. The shipwreck was excavated in 2012 and 2013. During the underwater excavations, two metal concretions were retrieved, X-rayed, and on opening were found to contain three almost identical iron-bound deadeyes. An iron bolt was also retrieved, covered with concretion. Metallurgical characterization was used to elucidate the manufacturing technology and to date the items. The artefacts were found to be made of annealed wrought iron. The use of wrought iron, forge-welding, and the presence of 0.1–0.2 wt.% Mn may indicate manufacturing in the mid-nineteenth century. Combined with the transition from hemp to chain cable for rigging in 1808, and by the 1840s to wire rope, all the indications are that the deadeyes were made in the second quarter of the nineteenth century. The size of the deadeyes, and the dimensions of their chain links, may indicate their use at the topmast of a brig of about 160 T. This agrees with other evidence in suggesting that the Akko Tower Wreck is the remains of a European vessel which sank in Akko harbour about the second quarter of the nineteenth century.
Without effective and durable hull fastenings, boats and ships-from the earliest days of seafaring through the twentieth century-could not have plied the seas. In Ships' Fastenings, this central element of boat construction receives its first detailed study. Author Michael McCarthy offers a fascinating, thorough description of a range from sewn-plank boats of the ancient world and Micronesia to Viking ships, Mediterranean caravels, nineteenth-century ocean clippers, and even steamships. Along with the comprehensive account of ship fastenings, McCarthy provides a history of many of the discoveries and innovations that accompanied changes in the kinds of fastenings used and the ways they were secured. He discusses copper sheathing, metallurgy, the advent of Muntz metal, rivets of all types, welding in the ancient and modern sense, and the types of non-magnetic fastenings needed on World War II minesweepers. He even takes a glance at the development of underwriting and insurance, because the registries kept by Lloyd's and others were not only guides to the suitability or a particular ship but also dictated the form and method of fastening. Ships' Fastenings will prove of value to shipbuilders, historians, and archaeologists. It is also written for the enthusiast and amateur boat builder.
The paper presents lead and copper isotope analyses of 51 copper ore samples from the Sierra Morena, South of Spain. They are from ancient mines of the Iberian Peninsula collected by Claude Domergue during various field campaigns in the central Sierra Morena from 1965 to 1975. Most samples consist of copper oxide minerals such as malachite, azurite and chrysocolla and stem from the surficial sections of the ore deposits. The aim of the study was to supplement the existing reference data bank on lead isotopic compositions of ancient copper mines from the Iberian Peninsula. This is particularly important for the Sierra Morena for which data exist mostly for lead-zinc but not for copper ores. The lead isotope ratios range from 18.165 to 19.712 (206Pb/204Pb), 0.797 to 0.859 (207Pb/206Pb) and 1.955 to 2.108 (208Pb/206Pb). Two separate fields can be distinguished with a major field intermediate between the ore deposits from SW and SE Spain and a second at higher 208Pb/206Pb values. Copper isotopes were analysed additionally to provide further constraints for provenance studies. The copper isotope ratios δ65Cu of the copper oxide samples are mostly positive and higher on average than those of sulphide minerals. They are a potential tool to distinguish between either sulphide ore or oxide ore deposit derived artefacts.
Forty-two lead objects (mainly sling bullets) from archaeological sites in Spain and Italy, dating into the late Roman Republican period, two ore samples from Portman (Cartagena region) and one further ore sample from a deposit on Ibiza were analysed for their lead isotope ratios by multicollector inductively coupled plasma mass spectrometry (MC ICP-MS). The objective of the present study was to answer questions, which cannot be solved by conventional archaeological methods alone but require further information on the materials composition. For this, MC ICP-MS as a modern and fast analytical method to obtain both chemical and isotopic information paired with very low material consumption is a helpful analytical tool to answer archaeological and technological considerations and questions like (a) on the origin of the raw metals used for the objects, (b) if individual production sites used more than one metal source and (c) if certain metal mining areas were preferred during particular periods in time. The results of this study, which were obtained by combining lead isotope analysis with common archaeological methods, clearly demonstrate that Late Republican sling bullets and some other lead objects of other usage from Menorca originate from ore minerals that were predominantly mined on the Iberian mainland. Mixing relationships also show that a number of them were manufactured from reprocessed material. This is also true for single Italian lead sling bullets. Additionally, some of the objects have lead isotope signatures interpreted as mixing relationships, which point towards a manufacturing from reprocessed material.
The pipe organ is the king of musical instruments. No other instrument can compare with the pipe organ in power, timbre, dynamic range, tonal complexity, and sheer majesty of sound. The art of organ building reached its peak in the Baroque Age (∼1600–1750); with the industrial revolution in the 19th century, organ building shifted from a traditional artisans' work to factory production, changing the aesthetic concept and design of the organ so that the profound knowledge of the organ masters passed down over generations was lost.
This knowledge is being recreated via close collaborations between research scientists, musicians, and organ builders throughout Europe. Dozens of metallic samples taken from 17th- to 19th-century organ pipes have been investigated to determine their composition, microstructure, properties, and manufacturing processes using sophisticated methods of materials science. Based upon these data, technologies for casting, forming, hammering, rolling, filing, and annealing selected leadtin pipe alloys and brass components for reed pipes have been reinvented and customized to reproduce those from characteristic time periods and specific European regions. The new materials recreated in this way are currently being processed and used by organ builders for the restoration of period organs and the manufacture of new organs with true Baroque sound.
Flow behavior of pure copper was studied as a function of friction, aspect ratio and specimen geometry. Ring compression tests were conducted to determine friction factor (m) during upsetting process. Specimens were deformed in compression between two flat platens to predict the metal flow at room temperature. Machine vision system was used to analyze the deformation of 4×4mm square grid marked at mid plane of the specimen. The finite element analysis results were compared with the analytical results of various stresses from the experimental measurements of axial, circumferential strains and found to be in good agreement.
Complementary surface and near-surface analytical techniques have been used to explore a brass (Cu-20Zn) surface before, during, and after exposure in air at 90% relative humidity. Volta potential variations along the unexposed surface are attributed to variations in surface composition and resulted in an accelerated localized growth of ZnO and a retarded more uniform growth of an amorphous Cu2O-like oxide. After 3 days the duplex oxide has a total mass of 1.3 μg/cm2, with improved corrosion protective properties compared to the oxides grown on pure Cu or Zn. A schematic model for the duplex oxide growth on brass is presented.
The evolution of texture and microstructure during recrystallization is studied for two-phase copper alloy (Cu–40Zn) with a variation of the initial texture and microstructure (hot rolled and solution treated) as well as the mode of rolling (deformation path: uni-directional rolling and cross rolling). The results of bulk texture have been supported by micro-texture and microstructure studies carried out using electron back scatter diffraction (EBSD). The initial microstructural condition as well as the mode of rolling has been found to alter the recrystallization texture and microstructure. The uni-directionally rolled samples showed a strong Goss and BR {236}385 component while a weaker texture similar to that of rolling evolved for the cross-rolled samples in the α phase on recrystallization. The recrystallization texture of the β phase was similar to that of the rolling texture with discontinuous 101 α and {111} γ fiber with high intensity at {111}101. For a given microstructure, the cross-rolled samples showed a higher fraction of coincident site lattice Σ3 twin boundaries in the α phase. The higher fraction of Σ3 boundaries is explained on the basis of the higher propensity of growth accidents during annealing of the cross-rolled samples. The present investigation demonstrates that change in strain path, as introduced during cross-rolling, could be a viable tool for grain boundary engineering of low SFE fcc materials.
One hundred and twenty-five new lead isotopic analyses on galena, mainly from the Los Pedroches – Alcudia Valley area of southern Iberia, are presented. These data allow us to define four compositional groups in the 207Pb/206Pb versus 208Pb/206Pb and 207Pb/206Pb versus 206Pb/204Pb diagrams. Group I compositions are intermediate between those previously reported for southeastern and southwestern Iberian ore mineral locations. The compositions of Group II, the largest group, overlap with ore data from southwestern Spain. Groups III and IV have compositions that have never before been identified in this region and are comparable to those from the Sardinian Cu ores, which might explain the previously assumed exotic origin for local Bronze Age artefacts.
The age of a shipwreck at Suffolk Park, northern New South Wales is reassessed. Using evidence from elemental analysis of metal artefacts, the construction style of the rudder, the age of an Aboriginal story possibly associated with the wreck, and local reports from the early 20th century, it is detemined that the vessel probably dates from the mid to late 19th century. This conclusion is in contrast with previous estimates of the vessel's antiquity, which suggested a much older age. The new evidence, however, is more secure, and supports earlier reservations about the presumed old age of the vessel.
This monograph presents an account of the archaeological and historical investigation of the seabed remains of the Flower of Ugie, a wooden sailing vessel built in Sunderland in 1838 and wrecked in the Eastern Solent, England in 1852. The vessel was discovered in 2003 when a fisherman snagged his nets on the wreck, following initial investigation by the Hampshire and Wight Trust for Maritime Archaeology (HWTMA), on-going survey was conducted on the site between 2004 and 2008. The shipwreck lies within an area that is licensed for aggregate extraction, placing the remains under potential threat from such activity. Liaison with the dredging company led to the establishment of a voluntary dredging exclusion zone around the site. The shipwreck lies in three main parts comprising two large sections of hull remains, with a dispersed area of broken, mainly concreted iron elements in between. The vessel is primarily constructed from oak, ebony and elm. At the time of sinking, the exterior of the hull was sheathed in yellowmetal. It was not possible to date the vessel through dendrochronology, but comparative analysis of the metal fastenings allowed a provisional date of c. 1820-1850 to be assigned. The vessel is representative of English wooden shipbuilding from the mid-19th century and of the contemporary global maritime world.
Age determinations on polymetallic, stratiform to stratabound lead sulphide deposits occurring in the Palaeozoic metasedimentary to metavolcanic host sequences in the Eastern Alpine nappe units are described. The study shows that the source of lead in these deposits should be sought in the crust. At one stage of their evolution these rocks were upper crustal, with high U/Pb and Th/Pb ratios. In a later stage, prior to extraction of Pb, the U/Pb ratio was lowered, probably due to loss of uranium during high-grade metamorphism or during weathering and sedimentation of source material. Through comparison with feldspar-lead isotope data presently available only for part of the area, it is tentatively concluded that the most likely source rocks could be represented by pre-Ordovician metasediments.-W.S.
Professor R. Pleiner of the Institute of Archaeology, Prague, who has provided this review of Dr Tylecote’s book, is one of theforemost authorities on the origins of ironmaking. He is Secretary of the Comite pour la Siderurgie Ancienne de I’Union Internationale des Sciences Prehistoriques et Protohistoriques, whose offices are also in Prague. Professor Pleiner has made a special study of replica-smelting of early furnaces and some of his recent publications include ‘Metallographic report on early iron artefacts’ (Stockholm, 1975), ‘Origins of the shaft furnace in European ironmaking’ (Prague, 1975),!‘Ironmaking in pre-medieval Central Europe’ (Miinster, 1975), ‘The problem of the beginningof the iron age in India’ (Berlin, 1972), ‘Forging and blacksmiths’ art in Moravia’ (Krakow, i971), ‘Experimental smelting of steel in early medievalfurnaces’ (Prague, 1969), ‘The beginnings of the iron age in ancient Persia’ (Prague, 1967), and ‘The work of the early European smith’ (Prague, 1962).
The Royal Navy's use of copper and other sheathing on ships as a protection against ‘worm’ is presented against a general background of the subject. Manufacturers', Admiralty and other marks found on metal sheathing are illustrated and identified as an aid to nautical archaeologists.
A phase field model accounting for inhomogeneous and anisotropic elasticity has been developed to study the growth of acicular precipitates. The diffusion-controlled growth of an isolated precipitate is investigated in the presence of elastic stresses generated by anisotropic transformation eigenstrains in isothermal conditions. It is shown that elastic anisotropy qualitatively changes the growth mechanisms and that a stationary regime may be reached. In light of these conclusions, the elastic anisotropies of several metallic alloys featuring Widmanstätten structures are analyzed. The growth regimes predicted by our analysis are consistent with experimental observations; this strongly suggests the primary importance of elastic anisotropy in the formation of these microstructures.
The Akko 1 shipwreck was a small Egyptian armed vessel or auxiliary naval brig built in the eastern Mediterranean at the beginning of the 19th century. During the underwater excavations, about 230 brass hook-and-eye closures were found, mainly in the bow area. In addition, 158 brass cases were found, mainly between midships and the aft extremity of the shipwreck. Metallurgical non-destructive and destructive characterization of selected items was performed, including radiographic testing, XRF, lead isotope analysis, optical microscopy, SEM-EDS and microhardness tests. The hook-and-eye closures and the cases were both found to be made of binary copper-zinc alloy (about 30 wt% zinc). While the brass cases were made from rolled sheets, hand-made using simple tools, and joined by tin-lead soldering material, the brass hook-and-eye closures were hand-made from drawn brass wire, and manufactured from commercial drawn brass bars by a cold-working process. The lead isotope analyses suggest different provenances of the raw materials used for making the brass objects, thus the different origins of the ores may hint that the brass wire and sheet were imported to the workshops in which the objects were manufactured.
In this work, alpha (α) brass was poured in green sand mould and metallic chill mould at about 1050 • C. Sand casting method and metallic chill casting method are representing the slow and fast cooling rates of the castings, respectively. The slow cooling rate in the sand mould produces larger grains, while the metallic chill mould produces smaller grains in the castings. As the grain size decreases, the strength of the cast brass increases; micro-porosity in the casting decreases and the tendency for the casting to fracture during solidification decreases. Thus, the faster cooling rate casting offers higher strength, density and hardness compared to the slow cooling rate casting.
The effect of titanium addition on the microstructure and mechanical properties of brass Cu40Zn has been studied via the powder metallurgy (P/M) route. The water-atomized Cu40Zn–1.0 wt% Ti alloy powder was consolidated at different temperatures in the range of 400–600 °C using spark plasma sintering (SPS) and hot extrusion subsequently. Results show that the super-saturated solid solution titanium element in rapidly cooled brass Cu40Zn powder created high chemical potential for a precipitate reaction, showing significant grain refinement effects on the consolidated Cu40Zn matrix. Consequently, excellent mechanical properties were obtained by precipitation hardening and work hardening after sintering and extrusion, with yield strength of 390 MPa, ultimate tensile strength of 617 MPa, and Vickers micro-hardness of 192 HV, which are 28.7%, 23.4%, and 23.9% higher values than those of extruded Cu40Zn brass, respectively.
The transformation texture of {alpha}/{beta} brass with a diffusional Widmanstaetten {alpha} growth morphology has been investigated. Electron micrographs and electron backscattered diffraction was used to determine that the orientation relationship between the {beta} phase and the {alpha} associated with nucleation at {beta} grain boundaries was 44.3 deg <1 1 6>. Crystallographic variant selection was observed across those prior {beta}/{beta} grain boundaries, but this has little effect on the transformation texture due to the crystal symmetry. The effect of the crystallographic variant selection on texture is further weakened by nucleation of diffusional transformed {alpha} in the grain interior.
Haydn Jones's Accounting, Costing and Cost Estimation (1985) uses the surviving records of numerous Welsh companies, engaged principally in metal manufacture between 1700 and 1830, to demonstrate the use made by managers of accounting data, as the basis for planning, decision making and control. This article relates the results of Jones's research to existing views regarding the development of industrial cost accounting, particularly because his findings call into question ‘single variable’ explanations for the development of management accounting, such as the level of industrialisation, the relative impact of fixed and variable costs, and the organisational structure of business activity. Jones's findings also require a reappraisal of established ideas concerning the relative sophistication of financial and management accounting procedures in use in earlier times, and our perception of the contributions of accountants and their techniques to business developments.
This article demonstrates how the fields of science and conservation have collaborated at the National Gallery of Art. Although
seemingly unlikely bedfellows, the two disciplines are, in fact, complementary and caution against underestimating the importance
of arguably incongruous combinations.
Nineteenth‐century Palestine mapping projects based on systematic land surveying reached a peak with the Ordnance Survey of Western Palestine between 1871 and 1877, conducted on behalf of the Palestine Exploration Fund by officers of the British Royal Engineering Corps. Various other nineteenth‐century proposals for an organized survey of the country—some of which bore partial results while others were never implemented—are also presented. The surveying of one region, Mesopotamia, during the 1830s and 1840s, forms the basis for the discussion of the reasons for the relative lateness of the topographical survey. The sacredness of the region seems not to have been a sufficiently convincing motive for entrepreneurs to organize and finance such a survey. The main reason for the delay in mapping the country as a whole was that it was not especially important, either strategically or geo‐politically, for the European nations engaged in the international struggles in the Middle East until the last quarter of the nineteenth century.
A microstructural examination has been conducted on nails removed from wreckage of an unknown wooden sailing ship found on Onslow Beach, North Carolina. Large nails (about 12cm long) were used to connect the planks to the timbers, and these were of cast brass of about 34% Zn. Some Pb and Sn were also present. Casting was probably done using a banded Fe mold. Small (about 1cm long) pure Zn nails were removed from the planks, and were probably used to attach Zn sheets. From information in the literature about the use of brass nails and Zn sheathing, and of wooden ship construction, it is estimated that the ship was constructed around 1820 if made in the United States and around 1850 if made in Britain.
Widmanstätten microstructures in Cu-Zn beta brass alloys have been studied via transmission electron microscopy. Morphological and substructural details are revealed at very early stages in the precipitation reaction. The Widmanstätten alpha particles are observed to attain a regular and faceted shape at a very early stage of growth. Grain boundary-nucleated particles are seen to immediately produce sympathetic grain boundary rotation as a result of crystallographic demands.
The two main problems of ore genesis are the origin of metals and the process(es) of emplacement. Lead isotopes have proven
to be a powerful tool for studying these questions. We have studied Pb-Zn mineralizations from Montagne Noire and Cevennes
(southern Massif Central, France) by means of lead isotopes. This study shows the existence of two populations of ore deposits
defined by 17.76 < 206 Pb/ 204 Pb < 17.94 and 18.25 < 206 Pb/ 204 Pb < 18.63. A general model of lead evolution in these deposits is proposed. After evolving in the earth's mantle until approximately
3 b.y. ago, the lead became incorporated into a segment of continental crust. Then, the less radiogenic population of ore
deposits was emplaced contemporaneously with the formation of Cambrian carbonate host rocks. The second population is related
to the emplacement of Hercynian granitoids or, in more general terms, to fluid circulations associated with the Hercynian
orogeny. It can also be shown that some of the deposits are remobilized from preexisting ore deposits.
The problem of the initiation and growth of shear bands in 12 different materials, namely, OFHC copper, Cartridge brass, Nickel 200, Armco IF (interstitial free) iron, Carpen- ter electric iron, 1006 steel, 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, Tungsten alloy, and Depleted Uranium (DU -0.75 Ti) is studied with the objectives of find- ing out when a shear band initiates, and upon what parameters does the band width depend. The nonlinear coupled partial differential equations governing the overall simple shearing de- formations of a thermally softening viscoplastic block are analyzed. It is assumed that the ther- momechanical response of these materials can be adequately represented by the Johnson-Cook law, and the only inhomogeneity present in the block is the variation in its thickness. The ef- fect of the defect size on the initiation and subsequent growth of the band is also studied. It is found that, for each one of these 12 materials, the deformation has become nonhomogeneous by the time the maximum shear stress occurs. Also the band width, computed when the shear stress has dropped to 85% of its peak value, does not correlate well with the thermal conduc- tivity of the material. The band begins to grow rapidly when the shear stress has dropped to 90°/0 of its maximum value.
The Ossa Morena zone in the Variscan belt of the Iberian Peninsula is characterized by a complex geotectonic evolution. It hosts a Neoproterozoic-Paleozoic sequence that records the existence of two orogenic events (Cadomian and Variscan) separated by rift and stable platform stages (Middle Cambrian to Late Devonian). Volcanogenic and sediment-hosted massive sulfides, skarns, magmatic Ni-(Cu) deposits, synmetamorphic and intragranitic and perigranitic veins, and replacement bodies are related to different magmatic-hydrothermal systems ranging in age from 650 Ma to about 250 Ma. The lead isotope signatures from 26 different mineral deposits show variable ratios of 206Pb/204Pb (17.49-18.44), 207Pb/204Pb (15.47-15.67) and 208Pb/204Pb (37.37-38.78) that have low average μ values (9.7) but high ω values (38.3). As a whole, the lead isotope data define an irregular cluster that plots around the Stacey and Kramers (1975) growth curve but clearly marks the existence of two main ore-forming events during Cadomian and Variscan times. The most radiogenic samples are from some minor Zn-Pb stratiform (sedimentary exhalative) mineralization. They are interpreted as having a dominantly crustal derivation (μ >10.1) in which most of the lead was leached from a pre-Cadomian continental basement with a long crustal history. This basement has strong geochemical affinities with the oldest rocks of the Iberian terrane. However, most of the ore samples investigated plot below the Stacey and Kramers (1975) reference curve, indicating polyphase but variable mixing of lead from upper crustal and mantle lead reservoirs at the terrane scale. Clear mixing lines between the two end-member reservoirs are evident only in the oldest volcanic rock- and sedimentary rock-hosted massive sulfide deposits related to the Cadomian (late Neoproterozoic-Early Cambrian) magmatic arc; in the other deposit types lead isotopes have more restricted values. The crustal lead is interpreted as having been derived from ancient crust (2.1-2.5 Ga) and the derived shales (Montemolín Formation) that predated the Cadomian orogeny. The mantle-derived lead may have been derived from three different sources: Neoproterozoic tholeiitic orthoamphibolite, syn-Cadomian calc-alkaline andesite, or calc-alkaline metaluminous plutonic rocks intruded during the Variscan orogeny. The first two sources probably controlled the lead isotope signatures of the Cadomian massive sulfide deposits and the Variscan synmetamorphic veins. The input of primitive lead is especially significant during Variscan times (350-300 Ma) and is interpreted as having been related to the existence of a large primitive reservoir that controlled the Variscan magmatic, metallogenic, and hydrothermal evolution of the Ossa Morena zone. This primitive lead is recognized in most of the magmatic-hydrothermal deposits, including the typically crust-derived W- and Pb-bearing perigranitic hydrothermal systems. Likewise, associated plutonic rocks have more primitive lead isotope signatures than their counterparts in other Iberian terranes. The lead isotope evolution of the region is consistent with recent geophysical data that suggest that a deep, large mafic sill was intruded below the Ossa Morena zone during Variscan times. This sill was a likely key factor in the different Pb isotope evolution of the Ossa Morena zone compared with the nearby Iberian terranes and the entire Western Mediterranean province, which are characterized by lengthy crustal histories with very little input of primitive lead. The extensive mantle-crust interaction probably explains the wide variety and the unusual metallogenic features of the Ossa Morena zone.
New effects are reported in the microstructures of dezincified free-machining brasses and interpreted as variations in porosity within the attacked material. Kinetic studies show that a parabolic-type rate law is followed. Evidence is produced to support the mechanism of the dissolution of both copper and zinc followed by the redeposition of copper.
An archaeometallurgical analysis is presented of 14 bronze artifacts retrieved from an Early Hellenistic-period farmstead in controlled archaeological excavations at Rishon Le-Zion, Israel, and dated to the first quarter of the third century BCE according to coins and pottery vessels. The bronze assemblage includes a needle, pins, spatulas and fibulas. The aims of the research are to determine the composition, microstructure and manufacturing process of these artifacts and to discover their place of production. This will provide a better understanding of Hellenistic technological abilities and material culture. The examination included optical microscopy, microhardness, SEM including EDS, and XRD. The results show that the collection consists of Cu-Sn binary alloys, with evidence for a controlled alloying process and the absence of recycling. Furthermore, the microstructure of the objects indicates that all artifacts were produced by a cold-working process. Moreover, the manufacturing process of the rectangular cross-section fibulas included sophisticated joining techniques of copper and iron.
The uses made of analyses of copper alloys from West Africa are critically discussed in relation to the techniques by which metal was produced in contemporary Europe and Islamic lands. The conclusions of this study are that it is likely to be very difficult to provenance the metal source, or date the artifact by composition except in the rare case of high zinc brasses. Some analyses of European copper alloys, manillas and further samples from Igbu-Ukwu are given.
The Royal Navy's use of copper and other sheathing on ships as a protection against‘worm’is presented against a general background of the subject. Manufacturers', Admiralty and other marks found on metal sheathing are illustrated and identified as an aid to nautical archaeologists. © 2000 The Nautical Archaeology Society
This paper reviews the research into the methodology of lead isotope provenance studies carried out at the University of Oxford the foundations of the lead isotope provenance methodology and resulted in a large database of analytical isotope and elemental results. In spite of the efforts of the authors, this database is still not comprehensively published or easily accessible in a digital format by all researchers interested in using this method for their projects. The possibilities of advancing this situation are discussed. The authors discuss in detail the basic restrictions and advantages of using the lead isotope compositions of ores in mineral deposits for finding the origin of the raw materials used for making ancient artefacts. Methods for the scientific interpretation of the data are discussed, including attempts to use statistical methods. The methodology of creating the Oxford lead isotope database (OXALID) is outlined and a summary is given of the lead isotope resource provided by OXALID.
Lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the Iberian Pyrite Belt, as well as
on overlying gossans and associated volcanic rocks. All the massive sulphide deposits (except for Neves-Corvo), and nearly
all the volcanic rocks show very similar isotopic compositions grouped around 18.183 (206Pb/204Pb), 15.622 (207Pb/204Pb) and 38.191 (208Pb/204Pb), indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated
volcanic rocks. The isotopic compositions are representative of the average south Iberian crust during the Devonian to Early
Carboniferous (Dinantian), and their constancy implies a homogenization of the mineralizing fluids before the deposition of
the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems. This isotopic
constancy is incompatible with multiple, small, independent hydrothermal cells of the East Pacific Rise type, and fits much
better with a model of hydrothermal convections driven by “magmatic floor heating”. Neves-Corvo is the only south Iberian
massive sulphide deposit to have a heterogeneous isotopic composition with, in particular, a highly radiogenic stanniferous
ore (206Pb/204Pb of the cassiterite is >18.40). A model of lead mixing with three components is proposed to explain these variations: (1)
one derived from the Devonian to Early Carboniferous (Dinantian) continental crust that generated all the other massive ores;
(2) an Eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides, but independent
of them; and (3) a Precambrian continental crust component. The juxtaposition of three different sources places Neves-Corvo
in a specific paleogeographic situation that could also explain its mineralogical specificity. The geodynamic context that
best explains all the obtained isotopic results is one of an accretionary prism. The fact that lead isotope signatures of
the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful
exploration tool for the Iberian Pyrite Belt.
(translated by E. Pascual) Se han realizado análisis de isótopos de plomo en 26 sulfuros polimetálicos masivos de la Faja
Pirítica Ibérica, así como en los gossans que los cubren y en las rocas volcánicas asociadas. Todos los depósitos de sulfuros
masivos (excepto el de Neves Corvo), y casi todas las rocas volcánicas muestran composiciones isotópicas muy similares, que
se agrupan en torno a 18,183 para 206Pb/204Pb, 15,622 para 207Pb/204Pb y 38,191 para 208Pb/204Pb, lo que indica que la mayor parte del plomo de los yacimientos derivó del mismo entorno cortical que las rocas volcánicas
asociadas. Las composiciones isotópicas son representativas de la corteza sudibérica media durante el Devónico y el inicio
del Carbonífero (Dinantiense), y su uniformidad implica una homogeneización de los fluidos mineralizantes anterior al depósito
de los sulfuros masivos a partir de los fluidos hidrotermales que circulaban por sistemas de fracturas regionales interconectados.
La uniformidad isotópica es incompatible con un sistema de pequeñas células hidrotermales independientes del tipo de las de
la dorsal del Pacífico oriental, y concuerda mucho mejor con un modelo de convección hidrotermal controlada por “magmatic
floor heating”. Neves Corvo es el único depósito de sulfuros masivos sudibérico que tiene una composición isotópica heterogénea,
en la que es de resaltar el carácter altamente radiogénico del mineral estannífero (206Pb/204Pb > 18,40 para la casiterita). Para explicar estas variaciones, se propone un modelo de mezcla de plomo con tres componentes:
uno, derivado de la corteza continental de edad devónica a dinantiense; otro, a partir de una mineralización estannífera eohercínica,
parcialmente removilizada durante el depósito de los sulfuros masivos pero independiente de ellos, y un tercero a partir de
un componente cortical continental precámbrico. La yuxtaposición de tres fuentes distintas coloca a Neves Corvo en una situación
paleogeográfica específica que explicaría también su mineralogía peculiar. El contexto geodinámico que mejor explica los resultados
isotópicos obtenidos es el de un prisma de acreción. El hecho de que la signatura isotópica de los gossans sea casi idéntica
a la de los depósitos de sulfuros infrayacentes implica que esta técnica puede ser una herramienta de exploración útil en
la Faja Pirítica Ibérica.
Stratiform deposits found in mesozoic sedimentary layers, in Marocco and in France, have been analysed to determine lead and sulphur isotopic compositions.
For the sulphur, the results indicate a low temperature formation, and are in good agreement with synsedimentary theories. The lead isotopic compositions are anomalous: J type for french galenas, B type for these of Marocco. The authors propose that the lead of these galenas have had a continental origin; the two different histories of the continental areas explain the galena anomalous compositions; two factors are particulary important: the age of the crust formation, and after that, the time of separation of lead from uranium and thorium in the continental crust.
Les Malines Mine (Cvennes, France) provides an example of Pb-Zn ore bodies that underwent a polyphased evolution. On the Pb-Pb diagram, experimental points of the Les Malines ore types always plot in the central part of the field defined for the Cvennes metallogenic province. This homogeneity, the similarities with the Pb isotopic compositions of the surrounding rocks and the comparison with Pb isotopes evolution of whole rocks and minerals of the neighbouring continental lands, which emerged during Triassic and Liassic times, rule out the participation of extraneous Pb during the successive concentration stages and agree with an initial metal stock transformed and mobilized in a Pb closed system. Hercynian K-feldspars are the main source of the Pb preconcentrated during Triassic times. Most of the Cvennes Pb-Zn ore bodies could derive from this Triassic metal stock; nevertheless, local Pb isotopic anomalies suggest hydrothermal sources for some Pb-Zn ore bodies located along the Cvennes fault.