GEOCHEMICAL TRACERS IN COPPER DEPOSITS AND ANCIENT

Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2008-2009
GEOCHEMICAL TRACERS IN COPPER DEPOSITS AND ANCIENT ARTEFACTS: A
DATABASE FOR PROVENANCE
Ph.D. candidate: ILARIA GIUNTI, Tutor: Prof. GILBERTO ARTIOLI
Co-tutors: Prof. PAOLO NIMIS, Prof. PAOLO OMENETTO Cycle:XXIII
Abstract
A database of Alpine copper mineralisations is being developed as a reference frame for metal extraction and diffusion in the
past. This point is one of the most crucial that archaeologists wish to discover, mainly for a better understanding of the ancient
trade courses and technology knowledge of Prehistoric culture. Here database protocol changes and improvements are
presented, together with several statistical techniques used to inquire the database and discriminate the ore mineral
provenance. Geochemical and minerogenetic informations of copper deposits are also treated. Archaeometric applications
such as the Monte Cavanero (Chiusa di Pesio, CN) and Millan case are reported. Finally the Agordo case is described:
besides copper ores, recent copper fragments and slags, and also archaeological metal finds found in this area were
analyzed.
Introduction
The provenance of metal artifacts in the early history of metallurgy has been a major question in
archeology for many decades. Pb isotope ratios (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) are commonly used
for provenancing in archaeometry (Gale & Stos-Gale, 2000; Hauptman, 2007), but the interpretation is
hardly debated (see Pollard, 2009 and Gale, 2009) and it can sometimes be ambiguous because natural
ore deposits frequently have overlapping Pb isotopic compositions. So, besides lead isotopes, the database
is based on abundances of about 60 minor and trace elements, including most transition metals and
chalcophile elements, and the REE (Ixer, 1999; Pernicka, 1999). Moreover, the feasibility of the routine
reliable measurement of the 65Cu/63Cu isotope ratio (Ciceri et al., 2005) and its use as a possible ore tracer
is tested.
Several statistical methods are used for correlating these data; mainly the treatment of the
chemical/isotopic datasets of the mines was carried out with PCA (Principal Component Analysis) and
PLS-DA (Partial least Square-Discriminant Analysis) with the purpose of discriminating the ore minerals.
Sampling is much more considerable, since we have samples from about 40 mining areas, in all more than
300 samples, and almost 100 prehistoric artifacts included both metal objects and slags. Actually about
180 samples were analyzed.
Some of the most well known copper deposits in the Eastern Alps (Agordo area in Veneto, Valsugana,
Val dei Mocheni, Valle Aurina e Val Venosta in Trentino-Alto Adige) were selected and compared with
very different minerogenetic deposits from the French Queiras (Saint Veran), the Western Alps and the
Ligurian Apennines (Libiola, Monte Loreto). More than 40 archeological samples were also analyzed,
then compared to the copper based minerals, and projected into the statistical mine models.
Experimental methods
The samples were first characterized mineralogically and petrologically (XRD, RL-OM), and then they
were analysed by ICP-QMS (Inductively Coupled Plasma-Quadrupolar Mass Spectrometry), to
investigate trace elements and Rare Earth Elements.
Multicollector ICP mass spectrometry (MC-ICP-MS) was used to determine precise Pb isotopic ratios
(206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) and is being used for 65Cu/63Cu ratios as well; the instrument is at
the Institut für Geologie, in Bern where I spent a large extent of the year.
A very interesting part of my work in this year consisted in developing a new separation method that let
us to analyze copper isotopes by means of MC-ICP-MS and testing the feasibility of this measurement.
Several proofs were realized using different exchange ionic resins, different conditioning agents and
eluents to separate copper isotopes from their isobars and to avoid isotopic fractionation; we had only a
few good results but work is still in progress.
Advanced strategies based on multivariate analysis were then used to discriminate the ore mineral
provenance. Data were treated with the chemometric software “The Unscrambler Version 9.5” (CAMO
AS, Trondheim, Norway). Data pre-treatment, PCA (Wold et al., 1987) and PLS-DA (Geladi &
1
Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2008-2009
Kowalski, 1986) models were performed as implemented in the software. The availability of such
unprecedented and complete amount of data of Alpine copper deposits also yields information relevant
for the geochemical and minerogenetic intepretation of the deposits themselves.
Applications and results
Samplings, lead isotopes analyses and experimental tests on copper isotopes extraction were the main
activities for this second year.
Pb data are almost finished and gave very interesting results if we consider them geologically; instead if
we use lead isotopes only for estabilish the provenance of copper artifacts, they often seem to be very
ambiguous because natural ore deposits frequently have overlapping Pb isotopic compositions.
The discriminating power of the database was applied to the provenancing of copper metals and slags
from the Agordo area and the recently found prehistoric copper fragment and slags from Millan
(Bressanone, BZ). The same thing was made with the only Pb isotopes data about the Western Alps,
Ligurian Appennines and copper artefacts from Monte Cavanero (Chiusa di Pesio, CN).
Data of metal artifacts and slags, found in Agordo area, show that the discriminant model selected to
identify the Agordo ores, is perfectly applicable to the copper samples, clearly indicating that the metal
was extracted from the local ores.
For the Millan case, the discriminating model of the deposits that best describes the copper fragment is
the one that identify the Val Venosta area (Oris, Val Martello, Stelvio mines), located 80 km to the West
of the archaeometallurgical site of Millan. This result suggests that the copper sample is genetically
unrelated to the large amount of associated slags produced during the smelting of copper from a
sphalerite/galena-rich chalcopyrite ore, since Val Venosta ores have a rather different mineralogical
character. Lead isotopes data about the Western Alps, Ligurian Appennines and copper artefacts from
Monte Cavanero, show that minerals employed for copper smelting are primary sulfides (chalcopyrite,
bornite). Copper objects have a similar isotopic compositions of Western Alps ores, and so we can
exclude ophiolitic ores of the Appenninic area (Libiola mine). Probably the presence of Sn in artifacts
causes the 207Pb/204Pb enrichment. The availability of such unprecedented and complete amount of data of
Alpine copper deposits also yield interesting information concerning the geochemical and minerogenetic
intepretation of the deposits themselves.
Conclusions
Application of PCA to the geochemical and isotopic data proved to be a very powerful tool to
discriminate the ore source areas and geochemical character. The presented preliminary applications to
copper metal samples and slags seem to indicate that the analysis can be successfully performed on
archaeometallurgical specimens for provenancing and diffusion investigations. Future efforts are directed
towards (1) completion of the mine database with the inclusion of Pb data, (2) investigation of
archaeological copper slags, (3) interpretation of the geochemical tracers, and (4) their behaviour during
the copper smelting processes.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2008-2009
References
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determinazione del rapporto isotopico 63Cu/65Cu mediante ICP-QMS. In: Atti del XIX Congresso di Chimica Analitica, 11-15
settembre 2005. Università degli Studi di Cagliari.
GALE, N.H., 2009. A response to the paper of A.M. Pollard: what a long, strange trip it’s been: lead isotopes and archaeology.
In: From mine to microscope. Edited by A.J. Shortland, I.C. Freestone and T. Rehren. Short Run Press, Exeter, UK. 191-196
GALE, N.H. & STOS-GALE, Z. 2000. Lead isotope analyses applied to provenance studies. - In: Ciliberto, E. Spoto, G. (eds).
Modern analytical methods in art and archaeology. New York, 503-584.
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HAUPTMANN, A. 2007. The archaeometallurgy of Copper. Springer, Berlin.
IXER, R.A. 1999. The role of ore geology and ores in archaeological provenancing of metals. In: S.M.M. Young, A.M.
Pollard, P.Budd, R.A. Ixer, Metals in Antiquity. BAR International Series n. 792. Archaeopress, Oxford, UK, 43-52.
POLLARD A.M., 2009. What a long, strange trip it’s been: lead isotopes and archaeology. In: From mine to microscope.
Edited by A.J. Shortland, I.C. Freestone and T. Rehren. Short Run Press, Exeter, UK. 191
PERNICKA, E. 1999. Trace element fingerprinting of ancient copper: a guide to technology or provenance? In: S.M.M.
Young, A.M. Pollard, P.Budd, R.A. Ixer, Metals in Antiquity. BAR International Series n. 792. Archaeopress, Oxford, UK,
163-171.
RENFREW, C. & BAHN, P. 2000. Archaeology: Theories, methods and practice. Thames & Hudson, London.
WOLD, S., ESBENSEN, K., GELADI, P. 1987. Chemometrics Intell. Lab. Syst. 2, 37.
SUMMARY of LAST YEAR’S ACTIVITY
Courses:
BOESSO S.: Corso introduzione alla biblioteca, Dipartimento di Geoscienze, Università degli Studi di Padova
OMENETTO P.: “Mediterranean tectonics and metallogenesis”, Dipartimento di Geoscienze, Università degli Studi di Padova
SCOTT D.A.: Summer course on “Ancient and historic metals: technology, microstructure and corrosion”, 5-12 Luglio 2009,
UCLA-University College of Los Angeles, Los Angeles (CA)
Communications:
I. GIUNTI, G. ARTIOLI, B. GIUSSANI, M. MARELLI, S. RECCHIA, I. ANGELINI, B. BAUMGARTEN, P.
OMENETTO, I.M. VILLA. Chemical and isotopic provenance tracers in ancient copper and bronze artifacts: a geochemical
database of copper mines.
G. ARTIOLI, I. GIUNTI, I. ANGELINI, P. OMENETTO, I.M. VILLA AND M. VENTURINO GAMBARI. The Final
Bronze Age Hoard of Chiusa Pesio, Cuneo: Pb Isotopes Studies and copper Provenancing. Archaeometallurgy: Technological,
economic, and social perspectives in Late Prehistoric Europe Meeting in honour of Salvador Rovira, TESME, Madrid, 25-27
Novembre 2009
Publications:
G. ARTIOLI, I. ANGELINI, I. GIUNTI, P. OMENETTO, I. M. VILLA. 2009. La provenienza del metallo degli oggetti di
Monte Cavanero: considerazioni basate sugli isotopi del Pb e sulla geochimica delle mineralizzazioni cuprifere limitrofe. - In:
Il ripostiglio del Monte Cavanero di Chiusa Pesio, a cura di Marica Venturino Gambassi. LineLab Edizioni, Alessandria. 167178.
G. ARTIOLI, I. GIUNTI, I. ANGELINI, GRUPPO ARCA, B. GIUSSANI, M. MARELLI, S. RECCHIA, P. NIMIS, P.
OMENETTO, I. M. VILLA. 2009. Legami geochimici tra miniere scorie e metallo: verso un modello per determinare la
provenienza e la diffusione del rame preistorico. FRAMMENTI Conoscere e tutelare la natura Bellunese. Provincia di Belluno
Editore. Belluno. In press
Other:
SUMMER SCHOOL: “SILS: X school on synchrotron radiation: fundamentals, methods and applications”, 7-18 Settembre
2009, Duino, Trieste
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2008-2009
Experimental activities:
Mines sampling activity
ICP-Q-MS samples preparation and analysis of trace and REE elements, at Insubria University, Como
HR-ICP-MC-MS samples preparation and analysis of Lead and Copper Isotopes, at Institut fur Geologie in Bern University,
Bern (CH)
Experimental tests for Copper isotopes separation, with several ionic exchange resins and eluents at the Clean Lab of the
Institut fur Geologie in Bern University, Bern (CH)
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