Heavy Metals in Sediments of the Upper Hawkesbury‐Nepean River

There is little published information on heavy metals in surficial sediments of the upper Hawkesbury‐Nepean River in central New South Wales, Australia. In the current investigation, the fine fraction (<62.5 µm) of 90 sediment samples taken from this section of the river was analysed by flame‐Atomic Absorption Spectroscopy for nine heavy metals (Ag, Cd, Pb, Zn, Cu Co, Fe, Ni and Mn) to determine background and enrichment. Sediment in the upper Hawkesbury‐Nepean River is not heavily polluted by heavy metals. Maximum enrichment over background for Ni and Ag, Cd, Pb, Zn, Cu and Mn is 3x, 5.7x, 6x, 6.7x, 12x and 13.6x, respectively. Mean heavy metal concentrations for this, the upper section of the river, are about half the mean values for the Hawkesbury River between Windsor and Broken Bay in the lower, estuarine section of the river. The highest Cu, Pb and Zn concentrations (214, 108 and 334 mg kg^?1, respectively) occur in surficial sediments in Peachtree Creek at Penrith and the Nepean River near Jacksons Lane, Castlereagh. These metal concentrations are possibly associated with industrial activity at Penrith. Two of the six sewage treatment plants on the upper Hawkesbury‐Nepean River are associated with high metal concentrations (Cu, Zn, Fe and Mn) in sediments, that is, the West Camden and Penrith sewage treatment plants. Other possible sources of heavy metals are coal mining and washing which occurs at several places in the upper catchment. The highest Cd, Co and Fe concentrations (1.7, 27.6 mg kg^?1 and 4.81%, respectively) were found in sediments 400 m downstream of the Nepean Dam and the highest concentrations of Ni and Mn (54 and 790 mg kg^?1, respectively) were located in sediment from the Nepean River at Moresby Hill Road Bridge, near Robertson and at the Avon Dam Road Bridge. The source of these metals is unknown.     

The Environmental Status of Hawkesbury River Sediments

The Hawkesbury River of New South Wales, Australia is under increasing environmental stress. Pre-anthropogenic and current levels of heavy metal concentrations have been established for bed sediments between Windsor and Broken Bay. Sediment heavy metal concentrations in the main channel of the Hawkesbury River are close to background, but are substantially elevated in the headwaters of Berowra Creek, Cowan Creek and in southeast Pittwater. The Berowra Waters area and the upper catchment contribute both heavy metals and organochlorines/pesticides to the Berowra estuary. High contaminant levels above and below the Hornsby sewage treatment plant, and above and below the Calna Creek sewage treatment plant, make an assessment of the contribution by these plants difficult. Analyses of oyster tissue from the middle and lower reaches of the estuary indicate that heavy metal contaminants are entering the food chain.     

Five thousand years of atmospheric Ni,Zn, As,and Cd deposition recorded in bogs from NW Iberia: prehistoric and historic anthropogenic contributions

The analysis of environmental archives from across the world has demonstrated that human perturbation of the geochemical cycles of trace metals and the resultant atmospheric metal contamination date back, at least, several millennia. However, an understanding of the local processes and timing of changes in trace metal deposition is also essential for a proper global interpretation. The Iberian Peninsula was a major mining area since prehistoric times and the analysis of environmental archives provides a good opportunity to improve our understanding of the history of mining and metallurgy in Europe. We present the results from three ¹⁴C dated peat cores from the Xistral Mountains (NW Iberia). These records are used to reconstruct past atmospheric deposition of Ni, Zn, As, and Cd. The chronology of the changes in concentrations and metal accumulation rates was found to be concordant in the three bogs, and showed great similarity to total Pb, Hg, and Pb isotope ratios as determined in previous investigations. They present a consistent view of changes in atmospheric pollution and the importance of metals in the development of human societies, especially: i) the first evidence of atmospheric metal pollution 3400 years ago, which is simultaneous with the expansion of the Atlantic Bronze Koine; ii) a pollution event between 2350 and 2150 years ago, associated to the development of so-called Celtic culture (local Late Iron Age); iii) a dramatic increase of metal fluxes in Roman times; iv) a severe and rapid increase in the last 250 years corresponding to the beginning of the industrial revolution in Europe, reflecting the emergence of the new dominant sources of pollution, and v) the increase of long range atmospheric transport of pollutants. Our data suggest that all detected ancient (until ca. 1450 cal BP) periods of enhanced Ni, Zn, As, and Cd accumulation may have had an anthropogenic origin, related to the onset and development of mining and metallurgy.     

A Palaeoenvironmental Investigation of Sediments from the Prehistoric Mine of Copa Hill,Cwmystwyth, mid-Wales

This paper investigates the use of mine sediments to reconstruct the vegetational changes and atmospheric pollution history associated with prehistoric and Mediaeval metal mining in the Ystwyth valley, Dyfed, mid-Wales. Pollen, charcoal, plant macrofossils, fossil insects and chemical analyses are presented from radiocarbon-dated sediments contained within a prehistoric mine situated on the upper slope of Copa Hill, close to the village of Cwmystwyth. The results provide additional support to the hypothesis that prehistoric mining had a negligible impact on woodland and that deforestation took place after Bronze Age mining ceased. Although high concentrations of Cu, Pb and Zn were determined from sediments of prehistoric and Roman Age, the patterns bear little resemblance to off site atmospheric pollution records and to the archaeological evidence for metal mining. Interpreting geochemical data from mine contexts is problematic as numerous factors influence the distribution and concentration of metals. However, an on-site and off-site approach to investigate human-environment interactions caused by metal mining is advocated.     

Pyrite–sulfosalt reactions and semimetal fractionation in the Chinkuashih,Taiwan, copper–gold deposit: a 1 Ma paleo‐fumarole

The mineralized fracture system that underlay paleo‐fumarole field at Chinkuashih, Taiwan has been exposed by copper–gold mining to depths of about 550 m below the paleo‐surface. Its mineralogy and systematic variations in metal and semimetal (Fe, Cu, As, Sb, Bi, Hg, Cd, Sn, Zn, Pb, Se, Te, Au, Ag) concentrations provide insights into the chemical responses of a magmatic‐vapor phase as it expands through fracture arrays to the surface and discharges as fumaroles associated with more extensive solfatara. At Chinkuashih, following initial sealing of the fractures by silica‐alunite alteration, brittle failure reestablished discharge from an underlying reservoir of magmatic vapor. Crystalline pyrite was deposited first in the fractures and was succeeded and replaced by ‘enargite’ (Cu₃(As,Sb)S₄) as sulfosalt encrustations (‘sublimate’) on fracture surfaces and in extensional cracks. Subsequent recrystallization resulted in complex exsolution intergrowths with antimony fractionation to the evolving crystal–vapor interface. Heavy metal fractionation between sulfosalt and vapor enriched the vapor phase in heavy metals that subsequently precipitated as complex Bi–Hg–Sn sulfosalts in discrete areas (paleo‐fumaroles) close to the paleo‐surface in a manner analogous to modern‐day fumaroles on active volcanoes such as Vulcano, Italy. As in similar paleo‐fumaroles (e.g., El Indio, Chile and Lepanto, Philippines), the most characteristic reaction sequence is the partial replacement of the early pyrite by enargite and Fe‐tennantite. It is proposed that this reaction tracks the decrease in the pressure of the underlying magmatic‐vapor reservoir because of the sustained discharge of vapor to the surface.     

Invasive cordgrass (Spartina spp.) in south‐eastern Australia induces island formation,salt marsh development,and carbon storage

Invasive vegetation species can lead to major changes in the geomorphology of coastal systems. Within temperate estuaries in the southern hemisphere, especially Australia and New Zealand, the cordgrass Spartina spp. has become established. These species are highly invasive, and their prolific growth leads to the development of supratidal environments in formerly intertidal and subtidal environments. Here, we quantified the impact of Spartina invasion on the geomorphology and sequestration capacity of carbon in the sediments of Anderson Inlet, Victoria, Australia. Spartina was first introduced to the area in the 1930s to aid in land reclamation and control coastal erosion associated with coastal development. We found that Spartina now dominates the intertidal areas of the Inlet and promotes accretion (18 mm/year) causing the formation of over 108 ha of supratidal islands over the past 100 years. These newly formed islands are calculated to potentially contain over 5.5 million tonnes of CO₂ equivalent carbon. Future management of the inlet and other Spartina‐dominated environments within Australian presents a dilemma for resource managers; on the one hand, Spartina is highly invasive and can outcompete native tidal marshes, thereby warranting its eradication, but on the other hand it is likely more resilient to rising sea levels and has the potential for carbon sequestration. Whether or not the potential advantages outweigh the significant habitat change that is anticipated, any management strategies will likely require additional research into costs and benefits of all ecosystem services provided by Spartina including in relation to nutrient cycling, shoreline stabilisation, and biodiversity as well as in response to the longevity of carbon found within the sediments.     

Hydrothermal fluid flow models of stratiform ore genesis in the McArthur Basin, Northern Territory, Australia

This paper explores the role of basin‐scale fluid migration in stratiform Pb–Zn ore formation in the southern McArthur Basin, Australia. Mathematical models are presented for coupled brine migration and heat transport in the basin. The models account for: (i) topographically driven flow (forced convection) during periods when parts of the McArthur Basin were subaerial and elevated above the central Batten Fault Zone; (ii) density‐driven flow (free convection) during periods when the basin was mostly submarine; and (iii) transient flows associated with fault rupture during periods of transpression. These hydrologic models help to compare and contrast a variety of hypotheses concerning deep fluid migration and the origin of base metal ores in the McArthur Basin. The numerical results exhibit a strong structural control on fluid flow caused by the north‐trending fault systems that characterize the Batten Fault Zone. As a result, fluids descend to depths of a few kilometers along the western side, migrate laterally to the east through the clastic and volcanic aquifers of the upper Tawallah and lowest McArthur Groups, and then ascend along the eastern side of the fault zone. This recharge–discharge pattern dominates all of the hydrogeologic models. The basin‐wide flow pattern suggests that Na–Ca–Cl brines acquired base metals in the deepest levels of the basin stratigraphy as the fluids migrated eastwards through the aquifer system. Upward flow was relatively rapid along the Emu Fault Zone, so much so that fluid temperatures likely approached 130°C in the muddy sediments near the sea floor due to upward flow and venting at the HYC (‘Here’s Your Chance'). Transient pulses of flow characterized periods of transpressional stress and subsequent faulting may have punctuated the basin history. Large‐scale free convection, however, characterized notably long periods of diagenesis and ore mineralization during the Proterozoic in the McArthur Basin.     

Oscillatory zoning and trace element incorporation in hydrothermal minerals: insights from calcite growth experiments

Oscillatory zoning and fine‐scale variations in trace element chemistry are commonly observed in hydrothermal minerals. It has been suggested that fine‐scale chemical variations are caused by extrinsic changes in the parent hydrothermal system, such as varying fluid composition, pressure or temperature, as well as changes in mineral growth rate. In this study, LA–ICP–MS (laser ablation, inductively coupled plasma mass spectrometer) analyses were carried out on calcite crystals grown in Ca–NH₃–Cl solutions doped with rare earth elements (REE). The variety of crystal morphologies observed (euhedral to acicular), likely relate to variations in trace element abundance and calcite supersaturation state. Crystals display oscillatory and sector zoning, with significant variations in REE concentrations among zones. Cyclic variations in REE concentrations (exceeding 10‐fold) occur over distances of <1 mm along the growth direction of acicular calcite crystals. In general, trace element concentrations decrease during progressive crystal growth, implying that the concentration of trace and REEs within crystals reflects the overall composition of the growth solution. However, bulk changes in crystal composition are modulated by fine‐scale (<1 mm) variations, which are inferred to be caused by growth‐rate‐controlled incorporation of trace elements. These results have important implications for using hydrothermal minerals to infer fluctuations in fluid compositions in ancient, exhumed hydrothermal systems.     

The Impact of Urbanisation on the Bed Sediments of South Creek,New South Wales

The textural and geochemical characteristics of the bed sediments in South Creek are examined. The bed substratum in the urbanised reaches differs from that of the rural reaches, in terms of the volume and size of the fine matrix sediment and the concentration of heavy metals. The impact of urbanisation on the river-bed sediment is variable, with less matrix than ‘expected’ within the substratum of the urban reach and more than ‘expected’ in the below urban reach. The urban matrix sediment is also significantly finer in comparison to the rural reach matrix sediment. Heavy metal concentrations within the urbanised matrix sediment are up to 800 times greater than background levels and are considered to be indicative of extreme contamination despite only SO years of urbanisation.     

On the Possible Origins of an Unusual (Mid to Late Holocene) Coastal Deposit,Old Punt Bay,South‐East Australia

An unusual coarse, shelly sedimentary unit is found elevated above present mean sea level in a sheltered pocket embayment at Old Punt Bay in south‐eastern Australia. The coarse sediments, diverse microfauna, and large shelly macrofauna of mixed affinity suggest that the deposit is the result of high‐energy deposition. The deposit was previously thought to have been deposited 1000–1300 cal bp based on one shell dated using ¹⁴C and amino acid racemisation. However, additional ¹⁴C dating indicates a likely age of ～2500 cal bp . Regardless of age constraints, the presence of rock‐encrusting oyster shells and large articulated bivalves, suggests that the depositional event must have been capable of removing and transporting coarse sediments (rock clasts), bivalves, and oysters shells from a variety of seaward environments and depositing them with little abrasion, something storm waves are unlikely to do. The deposit may be tsunamigenic. If a tsunami origin is accepted, the new dating results indicate that it is possibly coeval with a tsunami event previously reported to have affected several other sites along the coast of New South Wales at c. 2900 cal bp . Consequently, this deposit provides evidence for the event at a new site and importantly, a tighter constraint on the likely date of the events occurrence. It further adds weight to the developing catalogue of palaeotsunamis that may have affected the south‐eastern coast of Australia. Regardless of the deposit's origins, if viewed from a coastal planning perspective, this deposit indicates that this part of the coast has experienced large‐scale overwash events in the past that if repeated, would be catastrophic. There are serious implications for risk management.     

Fences, Boats and Teas: Engendering Patient Lives at Peel Island Lazaret

Within institutions, a separate social world comes into existence. Gender is a crucial shaper of relations in this new world, defining status, relationships to others and personal identity. Understanding the gendered conditions of, and responses to, institutional care is an important social contribution of historical archaeology to contemporary society. Research on the Peel Island Lazaret in Moreton Bay, Queensland, uses a model for engendering archaeology, with modifications pertinent to historical archaeology. Analysis builds on the work of others who have investigated the ways in which men and women of the confined and confining classes experienced institutions and interacted with each other. This study also extends beyond these approaches in exploring the areas of “interpersonal agency” and relationship building, and the ways in which disadvantage minimization was mediated by the structuring principle of gender.     

The Library is on Fire,Now What? Assessing the Damage and How to Approach It: A Case Study from the Chesapeake Bay

ABSTRACT

The Longwood Institute of Archaeology conducted the Vulnerability, Potential and Condition (VPC) assessment of shoreline archaeological sites along 1990 km (1237 miles) of the Chesapeake Bay in Virginia. VPC assessment involves a three-pronged approach that includes (1) the assessment of site vulnerability due to changing shorelines using an analytical package called Analysing Moving Boundaries Using R – AMBUR, (2) the assessment of potential shoreline site locations through predictive modelling using Weights of Evidence – WofE – analysis, and (3) the assessment of current conditions of known sites through direct observation. Vulnerability assessment results indicated that 49% of site shorelines in the project area are moving landward. Potential assessment located high-probability site locations with an 83% efficiency. Condition assessment, conducted using standard field protocols, provided feedback of the sites’ current conditions. The intended outcome of this method is to provide resource managers with information needed to make informed, data-driven management decisions.     

Archaeological investigations in Bergen 1980–1986: Some new aspects on the development of the town

The last six years' emergency excavations in Bergen, by pure chance covering the major part of the medieval town, have provided new information on several issues concerning the town's earliest development and structure, enabling us to sketch a development of the two somewhat different from previous suggestions. The original shoreline appears to have left rather less building land than expected, and the evidence for originally two separate centres is strong. A particularly rapid growth in the south suggests this as the major harbour in the town's earliest phase. The settlement expansion in the twelfth century resulted in the gradual merging of the two centres into one town, completed with the rebuilding after the 1248 fire providing an apparently continuous waterfront along the eastern shore of Vågen.     

LA–ICP–MS,SEM–EDS AND EPMA ANALYSIS OF EASTERN NORTH AMERICAN COPPER‐BASED ARTEFACTS: IMPACT OF CORROSION AND HETEROGENEITY ON THE RELIABILITY OF THE LA–ICP–MS COMPOSITIONAL RESULTS*

This study discusses the relevance of compositions obtained using laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) for the purpose of identifying the provenance of copper‐based artefacts found in Virginia at Native American sites dated from the 16th to the 18th centuries. Ten artefacts were investigated by scanning electron microscopy – energy dispersive spectrometry (SEM–EDS) to visualize the corrosion and characterize the heterogeneities in the metal and electron probe micro‐analysis (EPMA) to determine separately the compositions of the intact metal and of the corrosion product. It is shown that the corroded surfaces are highly depleted in zinc but that representative concentrations can be determined by sampling the deeper, uncorroded metal. In contrast, lead values are highly variable because of the heterogeneous distribution of this metal within the bulk copper. Despite these problems, brass is easily identifiable and American native copper and European smelted copper can be unambiguously distinguished with LA–ICP–MS on unprepared artefacts using As, Ag, Ni and Sb trace elements.     

An experimental and modeling study of Na-rich hydrothermal alteration

Sodic alteration assemblages including clinoptilolite, mordenite, analcime and Na‐montmorillonite were locally observed in sediments in the eastern part of the Hachimantai geothermal region, northeast Japan. This study investigated the mechanisms of sodic enrichment in the sediments during alteration. Kinetic results for water/rock interaction experiments are reported here. Batch‐type experiments were conducted at 150–250°C under saturated vapor pressure. Pyroclastic rocks dissolved incongruently in these experiments, and the solubility and dissolution rates among elements varied as follows: the apparent steady‐state concentrations of major elements are Si > Na ? K > Ca > Al and the order of the dissolution rates is Si > Al > Na ? K > Ca. Na had the highest steady‐state concentration and fastest dissolution rate of the alkali and alkali earth metal ions. Based on surface analysis of plagioclase, dissolution was effected via a reaction layer of Na‐montmorillonite on the mineral surface. Additionally, a reaction model constructed based on the experimentally observed reaction mechanism quantitatively explains the dissolution behavior. These results show that Na‐montmorillonite can be precipitated by pyroclastic rock/meteoric water interactions without seawater involvement: the Na is derived from the host rocks.     

Modeling CO2 generation,migration, and titration in sedimentary basins

High mole fraction CO₂ gases pose a significant risk to hydrocarbon exploration in some areas. The generation and movement of CO₂ are also of scientific interest, particularly because CO₂ is an important greenhouse gas. We have developed a model of CO₂ generation, migration, and titration in basins in which a high mole fraction CO₂ gas is generated by the breakdown of siderite (FeCO₃) and magnesite (MgCO₃) where parts of the basin are being heated above approximately 330°C. The CO₂ reacts with Fe‐, Mg‐, and Ca‐silicates as it migrates upward and away from the generation zone (CO₂‐kitchen). Near the kitchen, where the Fe‐, Mg‐, and Ca‐silicates have been titrated and destroyed by previous packets of migrating CO₂, gas moves upward without lowering its CO₂ mole fraction. Further on, where Fe‐ and Mg‐silicates are still present but Ca‐silicates are absent in the sediments, the partial pressure of CO₂ is constrained to 0.1–30 bars and reservoirs contain a few mole percent CO₂ as described by Smith & Ehrenberg (1989) . Still further from the source, where Ca‐silicates have not been titrated, partial pressure of CO₂ in migrating methane gas are orders of magnitude lower. A 2D numerical model of CO₂ generation, migration, and titration quantifies these buffer relations and makes predictions of CO₂ risk in the South China Sea that are compatible with exploration experience. Reactive CO₂ transport models of the kind described could prove useful in determining how gases migrate in faulted sedimentary basins.     

Source and character of syntaxial hydrothermal calcite veins in Paleoproterozoic crystalline rocks revealed by fine‐scale investigations

Calcite veins in Paleoproterozoic granitoids on the Baltic Shield are the focus of this study. These veins are distinguished by their monomineralic character, unusual thickness and closeness to Neoproterozoic dolerite dykes and therefore have drawn attention. The aim of this study was to define the source of these veins and to unravel their isotopic and chemical nature by carrying out fine‐scale studies. Seven calcite veins covering a depth interval of 50–420 m below the ground surface and composed of breccias or crack‐sealed fillings typically expressing syntaxial growth were sampled and analysed for a variety of physicochemical variables: homogenization temperature (T_h) and salinity of fluid inclusions, and stable isotopes (⁸⁷Sr/⁸⁶Sr, ¹³C/¹²C, ¹⁸O/¹⁶O), trace‐element concentrations (Fe, Mn, Mg, Sr, rare earth elements) and cathodoluminescence (CL) of the solid phase. The fluid‐inclusion data show that the calcites were precipitated mainly from relatively low‐temperature (T_h = 73–106°C) brines (13.4–24.5 wt.% CaCl₂), and the ⁸⁷Sr/⁸⁶Sr is more radiogenic than expected for Rb‐poor minerals precipitated from Neoproterozoic fluids. These features, together with the distribution of δ¹³C and δ¹⁸O values, provide evidence that the calcite veins are not genetic with the nearby Neoproterozoic dolerite dykes, but are of Paleozoic age and were precipitated from warm brines expressing a rather large variability in salinity. Whereas the isotopic and chemical variables express rather constant average values among the individual veins, they vary considerably on fine‐scale across individual veins. This has implications for understanding processes causing calcite‐rich veins to form and capture trace metals in crystalline bedrock settings.     

Dry CO2–CO fluid as an important potential deep Earth solvent

Transport properties of reduced carbonic fluid have been studied experimentally at P = 2 kbar and T = 700–1000°C in internally heated pressure vessel (IHPV). Synthetic FeCO₃ and natural siderite were used to generate fluid during experiments using a platinum double‐capsule technique. A natural CaTiSiO₅ aggregate was placed into the inner capsule as an additional source of trace elements. The outer capsule was loaded with albite glass. No water was introduced to the system and oxygen fugacity was established near to graphite–oxygen (CCO) buffer due to transformation of FeCO₃ into a magnetite aggregate during decarbonation to yield CO and CO₂. The carbonates decomposed during initial heating of the experiments, causing their some constituent components to be dissolved in and transferred by the fluid to the pore space of the albite glass matrix. After temperature reached 1000°C glass, the shards annealed and then melted, as evidenced by a vesiculated glass in the quench products. Micro‐Raman investigation of the fluid in bubbles in the albite glass in experiments with decomposition of natural siderite yielded CO–CO₂ mixture where CO mole fraction was 0.15–0.16. We observe significant concentrations of Pt, Mn, P, and REE in the albite glass; in contrast, no Fe or Mg transfer was detected. LA‐ICP‐MS analysis of the albite glass product yielded the average Pt content of 2 ppm. Such high Pt signal came from Pt particles (100–500 nm in size), which were observed on the walls of the bubbles embedded in the glass. Olivines and aluminous spinel were observed in the Fe‐oxide aggregate, demonstrating transfer of SiO₂ and Al₂O₃ from the albite melt by the reduced carbonic fluid from the albite glass (large capsule). Our results demonstrate that dry CO–CO2 fluid can be important agents of dissolution and transport, especially for Pt and other metals. The data imply that metals are chiefly dissolved as carbonyl complexes.     

MINERALOGICAL AND PETROLOGICAL INVESTIGATIONS OF EARLY BRONZE AGE COPPER‐SMELTING REMAINS FROM THE KIECHLBERG (TYROL,AUSTRIA)

The prehistoric settlement on the Kiechlberg hilltop is located a few kilometres to the north‐east of Innsbruck, in the Tyrolean Inn Valley. Despite its rather isolated location, a multiphase settlement between the fifth and the second millennium bc was confirmed by archaeological investigations in 2007 and 2008. Metallurgical artefacts, such as copper ore fragments, copper slag and raw copper, as well as finished copper and bronze artefacts, are concentrated mainly in Late Copper Age to Middle Bronze Age layers. The chemical compositions of the slag and raw metals confirm Fe—Zn tetrahedrite–tennantite (fahlore) smelting. The ore was most probably imported from the 30–50 km distant copper ore deposits (mainly fahlore) of Schwaz–Brixlegg, in the Lower Inn Valley. The small amount of slag and the presence of slagged and thermally altered ceramic fragments suggest copper production in small‐scale workshops. Most probably, sulphide‐rich ores were smelted in crucibles in a hearth fire. The process was relatively reducing below the 2Sb + 1.5O₂ → Sb₂O₃ reaction (?8.5 log fO₂ at 1100°C), producing Sb‐rich (>10 wt% Sb in metal) raw copper. Inhomogeneous slag remains containing high amounts of sulphide and metal inclusions suggest a poor separation of the metal, matte (copper sulphide) and silicate/oxide melt during the smelting process.     

The Chronology of Settlements with Pre‐Inca and Inca Occupations Superimposed: the Case of Pucará de Tilcara (Humahuaca Gorge,Argentina)

The region of the Central and South Andes was, in about the ninth and 15th centuries ad , the stage for the development of political systems tending towards demographic centralization in villages with defensive structures, known as Pucará. The chronological accuracy for these phenomena still remains uncertain, mainly because it involves intervals of long and superimposed occupations, masked by the Inca domination. Thus, this paper analyses the history of the occupation at Pucará de Tilcara, one of the biggest populated centres of the Humahuaca Gorge (Quebrada de Humahuaca, Argentina). Twenty‐five radiocarbon dates are critically evaluated to judge its reliability. The Bayesian statistics show that all the dated spaces were used on a long‐term basis. The most ancient signs are in the middens and relate at least to the 10th century ad , and the occupation of the housing areas could be calculated to the 13th and 16th centuries. A phase of higher intensity of occupation is observed during the Inca period. This redefinition of this site occupation shows the need to statistically analyse the dates in order to differentiate the phases of occupation.