ARCHAEOMAGNETIC DATING OF COPPER SMELTING SITE F2 IN THE TIMNA VALLEY (ISRAEL) AND ITS IMPLICATIONS FOR THE MODELLING OF ANCIENT TECHNOLOGICAL DEVELOPMENTS

Site F2 in the Timna Valley, Israel, is a small copper smelting site of ‘primitive’ technology, dated by its excavator to the Pottery Neolithic (sixth to fifth millennium bce ). This early date challenges the common view of the beginning of smelting technology in the Levant and has been contested by various scholars since its publication. In this study, we present results of archaeointensity experiments conducted on slag fragments from the site. The slag yielded an excellent ancient geomagnetic value (64.1 ± 1.1 μT) that, when compared to the Levantine master curve, suggests an age not older than the second millennium and most probably between the 13th and 11th centuries bce . In addition to demonstrating the applicability of geomagnetic archaeointensity experiments to independent dating of slag, we discuss the implications of the current results for the socio‐historical picture of the Timna Valley, and in particular for the way in which technological developments were previously modelled in the archaeometallurgical research on the region.     

An Archaeomagnetic Study of a Roman Bath in Southern France

Absolute Thellier–Thellier archaeointensity determinations were conducted on 137 tiles and sedimentary blocks from five different structures from the ‘Site de la Molère’, southern France, to constrain the archaeological interpretation of a relative age difference between structures and add new data to the French secular variation database. We present 89 new archaeointensity and 20 new directional results, with averages of 57 (±8) μT in the second century ad and 68 (±7) μT in the third century ad . The overall data trend is consistent with the limited available data, indicating rapidly increasing field intensity from the second to the third century ad .     

ESTIMATION OF THE AGE OF A PRE‐INDUSTRIAL IRON SITE IN KOREA*

A pre‐industrial iron‐smelting site in Korea, whose period of active use is placed on typological grounds between the eighth and 18th centuries ad , has been dated using accelerator mass spectrometry and thermoluminescence. The ages of two charcoal samples were 77 ± 25 and 81 ± 25 years bp , with the calibrated date for both ranging from ad 1700 to ad 1955, while a clay fragment dated to ad 1650 ± 50. The results from typology and radiocarbon seem insignificant due to the considerable uncertainties involved, but in combination with the thermoluminescence result they place the most probable date of the site at around ad 1700.     

ARCHAEOMAGNETIC FIELD INTENSITY DURING THE ROMAN PERIOD AT SIWA AND BAHRYN OASIS,EGYPT: IMPLICATIONS FOR THE FIDELITY OF EGYPTIAN ARCHAEOMAGNETIC DATA

A preliminary survey was conducted in Siwa and Bahryn Oasis to test the possible influence of various rock magnetic and experimental constraints on the fidelity of the Egyptian archaeomagnetic field record. Five potsherds from the Roman era, which lasted from 1981 bp to 1555 bp , have been investigated. Archaeologists dated the localities to ～1620 bp . Ten ceramic specimens, two of each potsherd, were subjected to archaeointensity determination, including tests for domain state effects, magnetic anisotropy and magnetic cooling rate dependency. Six successful archaeointensity determinations are obtained from three individual cooling units, revealing an average field value of 37.7 μT for the late Roman period in Siwa and Bahryn oasis, which is comparable to the present‐day field strength. The error propagation of the individual uncertainties related to all applied experimental techniques results in a maximum uncertainty estimate of 4.4 μT. The obtained field value is significantly smaller than early results and slightly smaller than some more recent determinations of the field intensity in Egypt. The difference is attributed to a combined effect of alteration, magnetic anisotropy and magnetic cooling rate dependencies. Along with other high‐quality data from the south‐east Mediterranean, our data suggest a field intensity minimum during the Egyptian Roman era.     

RESEARCH REPORT: MAGNETIC INVESTIGATIONS AND THE AGE OF A MEDIEVAL KILN AT KUNGAHÄLLA (SOUTH‐WEST SWEDEN)*

The results from a magnetic survey and archaeomagnetic investigation of a medieval brick kiln at Kungahälla in Bohuslän (south‐west Sweden) are reported. Detailed magnetic total field and magnetic gradient measurements over known traces of the kiln showed marked local magnetic anomalies of up to 200 nT, revealing the rectangular shape of the kiln remains. Palaeomagnetic investigations of the remanent magnetization of 12 bricks from the kiln floor gave precise definitions of both the direction of the archaeomagnetic field [(D_m, I_m) = (66.7°, 8.8°), k = 655, α₉₅= 1.7°] and the palaeointensity [B_m= 69.0 ± 3.6 µT]. An archaeomagnetic date is obtained by comparing the direction of the archaeomagnetic field found in the kiln with a geocentral dipole‐transformation of the British master‐curve for secular variation. Of two possible archaeomagnetic dates (ad 1280 ± 50 or ad 1480 ± 50), the ad 1280 ± 50 age is in good accordance with the C‐14 ages and archaeological dates as well as with direct historical evidence, whereas a c. 100 years younger TL date appears to be too young.     

New results on the dip equator and the equatorial electrojet in India

The geophysical implications are examined of the continuing southward migration of the magnetic dip equator in India since 1965, its precise ground location in 1971, and thereafter its drift at 1–6 km/yr accelerating to 7 km/yr in the mid-1980s near its mean central position in the 80-yr secular oscillation, estimated to be about 10 km south of Trivandrum. Simultaneously its drift northwards near the antipodal point at Huancayo Observatory, in Peru (South America), is also observed.The ground projection of the mean axis of the equatorial electrojet for 1980 is clearly delineated about 55 km to the north of the dip equator in India, with positive Sq(Z) values of 25 nT recorded right on the dip equator, based on the ground geomagnetic survey 1971 and the magnetometer array experiment of 1980. The half-width and midday peak total current intensity of the Indian electrojet are determined from the H data recorded at Trivandrum, Annamalainagar and Hyderabad for the solar minimum year 1976 (146 ± 46 km, 137 ± 25 Amp/km) and the maximum year 1980 (169 ± 39 km, 203 ±49 Amp/km), assuming a uniform west-east current band model at a height of 107 km centred on its newly discovered axis. These new results are quite different from those of earlier determinations. Severe induction anomalies observed in the region due to subsurface geological bodies are also appropriately incorporated.     

A new approach for geomagnetic archaeointensity research: insights on ancient metallurgy in the Southern Levant

We present results from an archaeointensity investigation based on a relatively unexploited recording medium, copper slag deposits. Together with a recently improved experimental design for the archaeointensity experiment, we demonstrate the applicability of this medium, as well as other archaeometallurgical artifacts, for the study of the ancient geomagnetic field intensity. In addition to archaeointensity data from well-dated archaeological contexts, we obtained reliable archaeointensity results from poorly dated or contentious archaeometallurgical sites in the Southern Levant. These results shed new light on the dating of these sites, among them the copper smelting installation of Timna 39b – a site that has important implications for the beginning of metallurgy during the fifth millennium BCE. The paper also aims to introduce archaeointensity research to the archaeologist scholar, and to encourage further collaboration between the disciplines in future research.     

Full‐Vector Archaeomagnetic Dating of a Medieval Limekiln at Pinilla Del Valle Site (Madrid,Spain)

Archaeomagnetic dating based on the full geomagnetic field vector was carried out on a limekiln excavated at Pinilla del Valle archaeological site (Madrid, Spain). The limekiln tradition in this area is largely documented by historical sources for recent centuries but the date of the studied kiln's last use was unknown. The combination of mean archaeomagnetic directional and absolute archaeointensity results shows that the kiln was last used between ad 1296 and 1413, in good agreement with two independent radiocarbon dates. This study provides the first archaeomagnetic evidence that the local limekiln tradition dates back to at least late medieval times. Furthermore, the inclusion of these data in the Iberian secular variation curve and geomagnetic field models will help to improve the archaeomagnetic dating technique.     

Combined archaeomagnetic and thermoluminescence study of a brick kiln excavated at Fontanetto Po (Vercelli,Northern Italy)

A combined archaeomagnetic and thermoluminescence study was carried out as part of a rescue archaeological excavation on a kiln discovered during the installation of methane gas pipelines beneath a rice field, along the southern border of Fontanetto Po village (Vercelli province, Italy). A total of 23 independent brick samples have been collected, oriented in situ with an inclinometer; the use of magnetic and sun compass was not possible due to the existence of metallic tubes beneath the kiln and a plastic cover above it. Standard archaeomagnetic procedures have been used for the determination of the archaeomagnetic inclination and absolute geomagnetic intensity. Stepwise thermal demagnetization shows a very stable characteristic remanent magnetization and the calculated mean inclination of the 23 samples is I = 65.3° with α₉₅ = 2.4° and k = 156. Archaeointensity experiments have been performed using the classical Thellier method as modified by Coe, with regular partial thermoremanent magnetization (pTRM) checks. The cooling rate and remanence anisotropy effects upon thermoremanent magnetization (TRM) have been investigated in all the specimens. A total of 19 archaeointensity determinations (at specimen level) that correspond to linear NRM–TRM plots were used for the calculation of the site mean archaeointensity that is 46.4 ± 2.9 μT. Archaeomagnetic dating results show two possible dating intervals for the last 1000 years, calculated at 95% confidence interval: a first one from 1511 to 1614 AD, and a second one from 1768 to 1872 AD. Thermoluminescence (TL) study has been also performed on two brick samples from the kiln's internal wall, using conventional laboratory procedures. According to the thermoluminescence results the kiln's last usage lies between 1796 and 1914 AD. This age is in good agreement with the second dating interval obtained by the archaeomagnetic analysis. The combined archaeomagnetic and thermoluminescence results suggest that the last firing of the kiln could have occurred between the end of the 18th century and the beginning of 20th century.     

METHODOLOGICAL DEVELOPMENTS IN THE LUMINESCENCE DATING OF BRICK FROM ENGLISH LATE‐MEDIEVAL AND POST‐MEDIEVAL BUILDINGS*

Fired clay brick samples, obtained from a group of seven high‐status late‐medieval and post‐medieval buildings in England ranging in age from c. ad 1390 to 1740, were dated by the luminescence method using an optically stimulated luminescence (OSL) technique. The results obtained indicate that, when applied to quartz extracted from brick, the technique is capable of producing dates that are in consistently good agreement with independent dating evidence for the buildings. For six samples taken from a group of four dating ‘control’ buildings the mean difference between the central values of luminescence and assigned ages was 5 ± 10 years (SD, n = 6). The methodology used is appropriate for application to other standing buildings in other temporal and geographic regions, and may be used with confidence where conventional dating methods are less certain. The study also examines the luminescence characteristics of quartz and the characteristics of the lithogenic radionuclides in brick samples and identifies various aspects related to the assessment of experimental uncertainty in testing the reliability of the method.     

Satellite image analysis of changes in glacier cover in Canada's northern Mackenzie Mountain Range (1987–2017)

The state of a group of glaciers in the northern Mackenzie Mountains across the Yukon‐Northwest Territories border was investigated over a period of three decades, using Landsat TM and OLI imagery from 1987, 1994, 1999, 2004, 2013, and 2017 to examine changes in glacier extents. A thresholded red/shortwave infrared band ratio image was used to delineate glacier boundaries. The total area of 74 glaciers in the study area decreased from 52.78 ± 1.32 km² in 1987 to 24.89 ± 0.62 km² in 2017, a loss of 27.89 ± 1.39 km² or 52.8 ± 2.6%, with a mean rate of reduction of 1.8% · a^?1. Smaller glaciers experienced larger relative changes in area. In this study, the rates of reduction are high compared to decreases reported for other glaciers in the region in the late 20^th century. Based on linear extrapolation of the trend in values of total glacier area, it is predicted—subject to uncertainties in how glaciers diminish in size and eventually disappear—that the study area could be free of visible glacier cover within three decades.     

THE APPLICATION OF A PORTABLE X‐RAY FLUORESCENCE SPECTROMETER TO THE ON‐SITE ANALYSIS OF GLASS VESSEL FRAGMENTS FROM SOUTHERN THAILAND*

Ancient glass vessel fragments belonging to the seventh to ninth centuries ad , from the Ko Kho Khao, Laem Pho and Khuan Lukpad sites in southern Thailand, were studied. The glass vessel fragment samples are a collection belonging to the Department of Archaeology, the 15th Regional Office of Fine Arts of Thailand. The chemical compositions of the glasses were analysed using a modified portable energy‐dispersive X‐ray fluorescence spectrometer (OURSTEX 100FA‐II) by the introduction of a MOXTEK^® AP3.3 polymer window (5 mm²?) to the KETEK silicon drift detector for the measurement of light elements. The non‐destructive analysis was performed at the National Museum, Phuket, in Thailand. It is shown that the glass chemical compositions belong to mineral and plant‐ash based soda–lime–silicate glass. The origins of the glass artefacts are discussed in terms of raw materials and glass decoration, and compared with previously reported similar typological glasses from sites in the port city of Rāya and the Monastery of Wadi al‐Tur in Egypt.     

Hydrothermal palaeofluid circulation in the fracture network of the Baksa Gneiss Complex of SW Pannonian Basin,Hungary

A well‐developed fracture‐filling network is filled by dominantly Ca‐Al‐silicate minerals that can be found in the polymetamorphic rock body of the Baksa Gneiss Complex (SW Hungary). Detailed investigation of this vein network revealed a characteristic diopside→epidote→sphalerite→albite ± kfeldspar→chlorite1 ± prehnite ± adularia→chlorite2→chlorite3→pyrite→calcite1→calcite2→calcite3 fracture‐filling mineral succession. Thermobarometric calculations (two feldspar: 230–336°C; chlorites: approximately 130–300°C) indicate low‐temperature vein formation conditions. The relative succession of chlorites in the mineral sequence combined with the calculated formation temperatures reveals a cooling trend during precipitation of the different chlorite phases (T_chlorite1: 260 ± 32°C →T_chlorite2: 222 ± 20°C →T_chlorite3: 154 ± 13°C). This cooling trend can be supported by the microthermometry data of primary fluid inclusions in diopside (T_h: 276–362°C) and epidote (T_h: 181–359°C) phases. The identical chemical character (0.2–1.5 eq. wt% NaCl) of these inclusions mean that vein mineralization occurred in a same fluid environment. The high trace element content (e.g. As, Cu, Zn, Mn) and Co/Ni ratio approximately 1–5 of pyrite grains support the postmagmatic hydrothermal origin of the veins. The vein microstructure and identical fluid composition indicate that vein mineralization occurred in an interconnected fracture system where crystals grew in fluid filled cracks. Vein system formed at approximately <200 MPa pressure conditions during cooling from approximately 480°C to around 150°C. The rather different fluid characteristics (T_h: 75–124°C; 17.5–22.6 eq. wt% CaCl₂) of primary inclusions of calcite1 combining with the special δ¹⁸O signature of fluid from which this mineral phase precipitated refer to hydrological connection between the crystalline basement and the sedimentary cover.     

Syntectonic infiltration by meteoric waters along the Sevier thrust front,southwest Montana

Structural, petrographic, and isotopic data for calcite veins and carbonate host‐rocks from the Sevier thrust front of SW Montana record syntectonic infiltration by H₂O‐rich fluids with meteoric oxygen isotope compositions. Multiple generations of calcite veins record protracted fluid flow associated with regional Cretaceous contraction and subsequent Eocene extension. Vein mineralization occurred during single and multiple mineralization events, at times under elevated fluid pressures. Low salinity (T_m = ?0.6°C to +3.6°C, as NaCl equivalent salinities) and low temperature (estimated 50–80°C for Cretaceous veins, 60–80°C for Eocene veins) fluids interacted with wall‐rock carbonates at shallow depths (3–4 km in the Cretaceous, 2–3 km in the Eocene) during deformation. Shear and extensional veins of all ages show significant intra‐ and inter‐vein variation in δ¹⁸O and δ¹³C. Carbonate host‐rocks have a mean δ¹⁸O_V‐SMOW value of +22.2 ± 3‰ (1σ), and both the Cretaceous veins and Eocene veins have δ¹⁸O ranging from values similar to those of the host‐rocks to as low as +5 to +6‰. The variation in vein δ¹³C_V‐PDB of ?1 to approximately +6‰ is attributed to original stratigraphic variation and C isotope exchange with hydrocarbons. Using the estimated temperature ranges for vein formation, fluid (as H₂O) δ¹⁸O calculated from Cretaceous vein compositions for the Tendoy and Four Eyes Canyon thrust sheets are ?18.5 to ?12.5‰. For the Eocene veins within the Four Eyes Canyon thrust sheet, calculated H₂O δ¹⁸O values are ?16.3 to ?13.5‰. Fluid–rock exchange was localized along fractures and was likely coincident with hydrocarbon migration. Paleotemperature determinations and stable isotope data for veins are consistent with the infiltration of the foreland thrust sheets by meteoric waters, throughout both Sevier orogenesis and subsequent orogenic collapse. The cessation of the Sevier orogeny was coincident with an evolving paleogeographic landscape associated with the retreat of the Western Interior Seaway and the emergence of the thrust front and foreland basin. Meteoric waters penetrated the foreland carbonate thrust sheets of the Sevier orogeny utilizing an evolving mesoscopic fracture network, which was kinematically related to regional thrust structures. The uncertainty in the temperature estimates for the Cretaceous and Eocene vein formation prevents a more detailed assessment of the temporal evolution in meteoric water δ¹⁸O related to changing paleogeography. Meteoric water‐influenced δ¹⁸O values calculated here for Cretaceous to Eocene vein‐forming fluids are similar to those previously proposed for surface waters in the Eocene, and those observed for modern‐day precipitation, in this part of the Idaho‐Montana thrust belt.     

Investigating Dietary Patterns with Stable Isotope Ratios of Collagen and Starch Grain Analysis of Dental Calculus at the Iron Age Cemetery Site of Heigouliang,Xinjiang, China

Here, we present δ¹³C and δ¹⁵N results for the dietary reconstruction of nomadic pastoralists from the Iron Age (ca. 1000 bc –8 ad ) site of Heigouliang. The human (n = 27) δ¹³C values range from −19.6‰ to −17.0‰ with a mean value of −18.5 ± 0.5‰, and the δ¹⁵N results range from 11.5‰ to 13.8‰ with a mean value of 12.4 ± 0.6‰. The results indicated that animals, like sheep, were part of the predominately C₃ terrestrial diet, but two individuals have values greater than −18‰ that is indicative of some input of C₄ foods in their diets. Because of a lack of faunal samples and to supply complementary information concerning plant consumption, teeth from four individuals were analysed for dental calculus microfossils. Starch grains were found to correspond to Triticeae and Poaceae, possibly including wheat (Triticum aestivum), barley (Hordeum vulgare), highland barley (H. vulgare L var. nudum), foxtail millet (Setaria italica) and/or common millet (Panicum miliaceum). At the population level, no dietary differences were detected between burial owners and sacrificial victims, but variations were found when specific tombs were analysed. In particular, individuals with bone trauma associated with armed conflict also had distinct isotopic signatures possibly suggesting that some of the sacrificial victims could have been captured warriors that were sacrificed for the burial owners. While limited, the results are some of the first from an Iron Age population from Xinjiang and contribute to our understanding of the dietary patterns of this region. Copyright © 2015 John Wiley & Sons, Ltd.     

A STUDY ON LATE MEDIEVAL TRANSPARENT‐GLAZED POTTERY AND ARCHAIC MAJOLICA FROM ORVIETO (CENTRAL ITALY)*

Nineteen samples of medieval transparent‐glazed pottery and archaic majolica from Orvieto (central Italy) were studied. They were classified by archaeological criterion as follows: five transparent‐glazed fragments with green and brown decorations (first half of the 13th century), eight green transparent‐glazed fragments (13th century) and six tin‐glazed fragments with green and brown decorations (second half of the 13th century). SEM–EDX, XRD (the Rietveld method) and XRF were used to characterize the chemical and mineralogical compositions both of the bodies and the coatings. In all of the samples, the paste is Ca‐rich with CaO contents as high as 13–20 wt%. The mineralogical composition is compatible with a firing temperature of about 950°C, which is the typical temperature reached in a wood kiln. No difference was observed between the bodies of transparent‐ and tin‐glazed pottery. In the case of transparent glazes, the burial conditions lead to heavy weathering of the samples. However, on the basis of the analyses carried out in non‐weathered areas, the typical composition is PbO 55–65 wt%, SiO₂31–35 wt%. In tin glazes, the tin is scattered on the mass of the glaze as SnO₂crystals with a concentration of 7–14 wt%. Concerning the decorations, it is established that the green colour is due to the presence of copper, while manganese is responsible for the brown colour. These pigments, which represent the typical colours of ‘archaic majolica’, are spread through the glaze homogeneously, apart from one case in which there is clear evidence of manganese oxide crystals.     

COAL AND CREMATION AT THE TSCHUDI BURN,CHAN CHAN,NORTHERN PERU*

Analyses of a 20–30 cm thick, completely combusted ash at the 25 × 70 m Tschudi burn at Chan Chan, northern Perú, contain 52–55 wt% SiO₂, 180–210 ppm zirconium and are consistent with coal ash. Soil geochemistry across the burn showed elevated calcium and phosphorus content, possible evidence for reported human cremation. A calcined, 5 g, 4.5 cm skull fragment recovered from the burn was confirmed as human by protein radioimmunoassay (pRIA). X‐ray diffraction showed that the bone had been heated to 520°C. The burn took place c. ad 1312–1438 based on interpretation of a ¹⁴C date on carbonized plant tinder.     

ARCHAEOMAGNETISM IN ARCHAEOMETRY— A SEMI‐CENTENNIAL REVIEW*

The journal Archaeometry and its first co‐editor Martin Aitken played key roles in the development of archaeomagnetism. This paper briefly reviews all papers published in Archaeometry, and a few others, dealing with archaeomagnetic secular variation, archaeomagnetic dating, archaeointensity studies and related applications of magnetic studies to archaeology, to indicate some of the major developments over the past 50 years.     

Isotopic Evidence for Diet Among Historic Bedouin of Khirbat al‐Mudayna,Jordan

Interpreting the behaviours of nomadic groups from the archaeological record is particularly challenging owing to the ephemeral remains produced by their lifestyle. As such, human burials – even from isolated contexts – provide a wealth of information about these transient groups. Stable carbon and nitrogen isotope analysis of a series of human skeletal remains (n = 22) from isolated burials were utilized to reconstruct the diet of historic (ca. 13^th–19^th century CE) Bedouin from the Khirbat al‐Mudayna vicinity in modern‐day Jordan. Carbon isotope values ranging from −17.7 to −12.5‰ point to variable dietary contributions from both C₃‐ and C₄‐based foods, while corresponding faunal δ¹³C ratios ( = −19.0 ± 1.7‰, 1σ) exhibit depletion in ¹³C characteristic of a predominantly C₃ diet. While mean human δ¹⁵N values ( = 12.7 ± 1.9‰, 1σ) may suggest that the majority of protein consumed by these nomads came from animal and not plant sources, elevated δ¹⁵N ratios in some fauna may be indicative of ¹⁵N‐enriched soils as reported in some arid desert environments. Considerable variability in both δ¹³C and δ¹⁵N values also points to differences in individual life histories and subsistence economies over time. Despite a lack of temporal cohesion, these data illustrate the information that can be gleaned from the isolated interments of nomadic or semi‐nomadic individuals. Copyright © 2015 John Wiley & Sons, Ltd.     

Br/Cl signature of hydrothermal fluids: liquid–vapour fractionation of bromine revisited

Br/Cl ratios of hydrothermal fluids are widely used as geochemical tracers in marine hydrothermal systems to prove fluid phase separation processes. However, previous results of the liquid–vapour fractionation of bromine are ambiguous. Here we report new experimental results of the liquid–vapour fractionation of bromine in the system H₂O–NaCl–NaBr at 380–450°C and 22.9–41.7 MPa. Our data indicate that bromine is generally more enriched than chlorine in the liquid phase. Calculated exchange coefficients K_D(Br‐Cl)^{liquid‐vapour} for the reaction Br^vapour + Cl^liquid = Br^liquid + Cl^vapour are between 0.94 ± 0.08 and 1.66 ± 0.14 within the investigated P–T range. They correlate positively with D_Cl^{liquid‐vapour} and suggest increasing bromine–chlorine fractionation with increasing opening of the liquid–vapour solvus, i.e. increasing distance to the critical curve in the H₂O–NaCl system. An empirical fit of the form K_D(Br‐Cl)^{liquid‐vapour} = a*ln[b*(D_Cl^{liquid‐vapour}?1) + e^1/a] yields a = 0.349 and b = 1.697. Based on this empirical fit and the well‐constrained phase relations in the H₂O–NaCl system we calculated the effect of fluid phase separation on the Br/Cl signature of a hydrothermal fluid with initial seawater composition for closed and open adiabatic ascents along the 4.5 and 4.8 J g^?1 K^?1 isentropes. The calculations indicate that fluid phase separation can significantly alter the Br/Cl ratio in hydrothermal fluids. The predicted Br/Cl evolutions are in accord with the Br/Cl signatures in low‐salinity vent fluids from the 9 to 10°N East Pacific Rise.