Bronze Age Archaeometallurgy of the Mediterranean - ACS Publications

9 Bronze Age Archaeometallurgy Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: July 1, 1989 | doi: 10.1021/ba-1988-0220.ch009

of the Mediterranean: The Impact of Lead Isotope Studies Noël H . Gale and Zofia A. Stos-Gale Department of E a r t h Sciences, University of Oxford, 1 Parks Road, Oxford O X 1 3 P R , England

For more than 50 years, it has been a goal to use scientific methods to establish which ore deposits were the ultimate sources of the metals from which Bronze Age metal objects were made. Solution of this problem would allow ancient trade routes and cultural contacts to be established. Approaches based solely on trace element analyses have largely failed, and, in many cases, have resulted in archaeological confusion. Success necessitates an approach that takes into account metallurgy; ore deposit geology; and isotope geochemistry, especially lead isotope studies. The methodological background and the success that we have attained in solving this problem are discussed against the background of our archaeometallurgical investigations into the sources of silver, lead, and copper in the Bronze Age Mediterranean.

THE AEGEAN REGION,

the area o c c u p i e d b y m o d e r n G r e e c e , C r e t e , a n d w e s t e r n T u r k e y , saw a n u m b e r of r e m a r k a b l e a n d original changes i n the years r o u g h l y b e t w e e n 3500 a n d 1500 B . C . A t the b e g i n n i n g of this p e r i o d , life t h r o u g h o u t the A e g e a n m a y be d e s c r i b e d as " n e o l i t h i c . " L i f e was a m a t t e r of s i m p l e f a r m i n g a n d fishing, a n d the p o p u l a t i o n l i v e d i n s m a l l villages a n d was o c c u p i e d w i t h the crafts of pottery, w o o d w o r k , a n d perhaps w e a v i n g . Tools w e r e almost e x c l u s i v e l y of stone or b o n e . B y the e n d of the t h i r d m i l l e n n i u m , the first true c i v i l i z a t i o n of E u r o p e was b o r n i n C r e t e . T h e great M i n o a n palaces t h e r e , such as Knossos, P h a i s tos, a n d M a l l i a , f u n c t i o n e d as p r o d u c t i o n a n d d i s t r i b u t i o n centers w i t h a 0065-2393/89/0220-0159$11.00/0 © 1989 A m e r i c a n C h e m i c a l S o c i e t y

In Archaeological Chemistry IV; Allen, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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w r i t t e n script for r e c o r d k e e p i n g . A l o n g w i t h the r i c h site of A k r o t i r i o n T h e r a , the M i n o a n palaces w e r e centers of h i g h artistic achievement. T h r o u g h o u t the A e g e a n , there h a d d e v e l o p e d at different times, other s m a l l , p r o t o u r b a n , c o m m u n i t i e s , each acting as a center for its r e g i o n , a n d as a focus of p r o d u c t i o n a n d trade. M o r e o v e r , society h a d b e c o m e stratified, b o t h h i e r a r c h i c a l l y a n d functionally into a n u m b e r of craft specializations, a m o n g t h e m , the p r o d u c t i o n a n d w o r k i n g of metals. B y 1200 B . C . , the p r o c u r e m e n t of metals h a d b e c o m e a v e r y i m p o r t a n t matter for A e g e a n societies. T h i s situation is reflected i n the L a t e B r o n z e A g e c o p p e r o x h i d e * ingots that w e r e d i s t r i b u t e d throughout the M e d i t e r ranean from S a r d i n i a i n the W e s t , t h r o u g h G r e e c e , C r e t e , B u l g a r i a , a n d C y p r u s to S y r i a , A n a t o l i a a n d E g y p t i n the E a s t (1-3). I n the L a t e B r o n z e A g e , t i n b r o n z e b e c a m e the d o m i n a n t alloy i n use. T i n deposits do not occur i n the A e g e a n r e g i o n a n d , therefore, m u s t have b e e n a c q u i r e d s o m e w h e r e else. O u r thesis is that the adoption of the s m e l t i n g a n d w o r k i n g of metals was a decisive step, perhaps one of the m o r e i m p o r t a n t steps that l e d d i r e c t l y to the e m e r g e n c e of c i v i l i z a t i o n i n the A e g e a n . M e t a l l u r g y created a n e w k i n d of w e a l t h that l e d to increasing social stratification. T h e practice of m e t a l l u r g y created n e w classes of craftsmen a n d t h e i r products: tools, w h i c h transformed c a r p e n t r y a n d s h i p b u i l d i n g , a n d weapons, w h i c h r e v o l u t i o n i z e d war. T h e p r o c u r e m e n t of metals l e d to the early d e v e l o p m e n t of u n d e r g r o u n d m i n i n g a n d gradually l e d to the d e v e l o p m e n t of trade. T h e p r o d u c t i o n of metals from t h e i r ores, w h i c h i n v o l v e d the d e v e l o p m e n t of s m e l t i n g , furnaces, a n d e v e n t u a l l y a l l o y i n g technologies, was a c r u c i a l step i n the m e t a l l u r g i c a l r e v o l u t i o n , because o n l y w h e n these t e c h nologies h a d b e e n d e v e l o p e d c o u l d c o p p e r be p r o d u c e d o n a scale large e n o u g h to have a significant i m p a c t on society. T h e earliest c o p p e r objects w e r e p r o b a b l y fashioned f r o m native c o p p e r , w h i c h was e x t r e m e l y scarce e v e r y w h e r e i n the A e g e a n b u t c o m m o n i n parts of T u r k e y , or from c o p p e r p r o d u c e d b y small-scale c r u c i b l e s m e l t i n g of o x i d i z e d ores. T w o - t h o u s a n d years elapsed from the t i m e the first m e t a l objects w e r e made i n the A e g e a n to the s u p r e m e accomplishments of the Shaft G r a v e s i n M y c e n a e . M e t a l l u r g y was adopted slowly because of the t i m e r e q u i r e d to u n d e r s t a n d that metals c o u l d b e p r o d u c e d from ores, a n d t h e n the t i m e n e e d e d to master the slagging a n d furnace technology r e q u i r e d to p r o d u c e metals i n sufficient quantity. E v e n w i t h m o d e r n k n o w l e d g e of the physics a n d c h e m i s t r y of the processes i n v o l v e d , successful r e p l i c a t i o n of ancient methods of c o p p e r s m e l t i n g is a l o n g a n d tedious business, as the w o r k of Tylecote a n d others has s h o w n (4). * An oxhide ingot is a copper ingot that weighs approximately 30 kg. It has the approximate shape of the flayed skin of an ox. Oxhide ingots form an important and characteristic component of Late Bronze Age trade in copper in Cyprus, Greece, and Egypt.


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A p a r t from the M i n o a n s a n d , later, the M y c e n a e a n s , the E a r l y C y c l a d i c p e o p l e p l a y e d a n i m p o r t a n t part i n t h e d e v e l o p m e n t o f M e d i t e r r a n e a n m e tallurgy. I n fact, t h e C y e l a d i e islands o f t h e c e n t r a l A e g e a n came i n t o e x traordinary p r o m i n e n c e i n t h e t h i r d m i l l e n n i u m B . C . T h e islands w e r e t h e h o m e o f a flourishing c u l t u r e w i t h p r o m i n e n t settlements, a rather abundant p o p u l a t i o n , w e l l - d e v e l o p e d pottery, a n d s t r i k i n g achievements i n m a r b l e sculpture. P r o d u c t i o n o f silver, l e a d (5), a n d c o p p e r from t h e i r ores was d e v e l o p e d early, along w i t h a rather vigorous trade. A l t h o u g h t h e y d i d not d e v e l o p any indigenous use o f t i n b r o n z e (6), t h e C y c l a d i c peoples w e r e p r e e m i n e n t i n t h e i r use o f arsenical copper. T h e C y c l a d i c peoples w e r e t h e d o m i n a n t seafarers o f the early t h i r d m i l l e n n i u m A e g e a n . T h e i r cemeteries, as d e s c r i b e d b y R e n f r e w (7) a n d D o u m a s (8), give e v i d e n c e o f a gradually d e v e l o p i n g social stratification that was associated w i t h t h e i r d e v e l o p m e n t o f m e t a l l u r g y .

Trade in Metals Studies o f the d e v e l o p m e n t o f ancient m e t a l l u r g y a n d o f the trade i n metals that e v e n t u a l l y e n s u e d are c e n t r a l to L a t e C h a l c o l i t h i c a n d B r o n z e A g e archaeology. R e a l progress i n these studies c a n b e a c h i e v e d o n l y b y u s i n g an integrated approach that involves archaeology, m e t a l l u r g y , geology a n d ore m i n e r a l o g y , m i n i n g studies, t h e analyses o f stratified m e t a l objects, a n d the analysis a n d d a t i n g o f the remains o f ancient m i n i n g a n d m e t a l s m e l t i n g . A c e n t r a l p r o b l e m i n archaeometallurgical studies is t h e d e t e r m i n a t i o n of t h e provenance o f copper, l e a d , silver, t i n , etc. T h e d e v e l o p m e n t , i n recent years, o f the l e a d isotope t e c h n i q u e for analyses o f m e t a l artifacts (9, 10) has p r o v i d e d , for t h e first t i m e i n t h e history o f archaeometallurgy, a d i r e c t analytical m e t h o d for l i n k i n g m e t a l artifacts to o r e deposits. L e a d isotope analysis m u s t b e u s e d w i t h i n t e l l i g e n c e a n d caution against t h e backg r o u n d o f m e t a l l u r g y a n d geology. T h e study o f t h e m e t a l resources u s e d b y different cultures a n d o f m e t a l t r a d i n g networks is so i m p o r t a n t that t h e i m p a c t of the lead isotope m e t h o d for m e t a l p r o v e n a n c i n g has b e e n c o m p a r e d w i t h t h e d e v e l o p m e n t o f C - 1 4 dating. R e c e n t w o r k u s i n g this t e c h n i q u e has, radically changed t h e archaeological theories o f the past 40 years c o n c e r n i n g the sources o f c o p p e r , l e a d , a n d s i l v e r i n t h e B r o n z e A g e M e d i t e r r a n e a n .

Foundations and Development of Lead Isotope Archaeology R e c e n t reviews (11-12) m a k e i t unnecessary to d o m o r e than d r a w attention to some salient points o f lead isotope archaeology. F o r m a n y years, c o m parative l e a d isotope studies o f ancient metals a n d ores from t h e appropriate ore deposits have b e e n i n t h e forefront o f m e t a l provenance studies i n a r chaeology (13-15). T h e earliest l e a d isotope studies b y B r i l l (17-18) a n d


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Grôgler et al. (19) w e r e h a m p e r e d b y the l o w accuracy of isotope composition m e a s u r e m e n t that was t h e n attainable (the absolute 2 σ errors i n the isotope ratios w e r e about 1%), b y the lack of a sufficient data base for ore samples, a n d b y the lack of a c o h e r e n t archaeological strategy. N e v e r t h e l e s s , this early w o r k p r o v i d e d a base for the subject of l e a d isotope archaeology. I n contrast, c h e m i c a l analyses of m e t a l artifacts have not solved the p r o b l e m of d e t e r m i n i n g the sources of m e t a l (20-22). I n d e e d , a comparison of analyses of m i n o r elements of m e t a l artifacts a n d ore deposits may n e v e r p i n p o i n t the sources of ore used. N o t o n l y do the m i n o r elements usually v a r y w i d e l y i n content t h r o u g h a g i v e n ore b o d y , b u t i n the s m e l t i n g of an ore to y i e l d a m e t a l , differences b e t w e e n of the m i n o r elements i n the ore a n d the m e t a l c o m e from the a d d e d flux, the fuel, a n d from variable par t i t i o n i n g b e t w e e n m e t a l a n d slag (4). I n a d d i t i o n , some elements w i l l b e lost b y volatilization, d e p e n d i n g o n the o x i d i z i n g or r e d u c i n g e n v i r o n m e n t e n countered. L e a d isotope analysis presents an alternative to c h e m i c a l analysis i n the d e t e r m i n a t i o n of m e t a l sources. L e a d isotope analysis is a p h y s i c a l m e t h o d that d e p e n d s o n the v a r i a b i l i t y of the isotopic composition of l e a d (present e i t h e r as the c h i e f or as a subsidiary element) i n m e t a l ore sources a n d on comparative analyses of the l e a d isotope composition i n m e t a l artifacts a n d ore sources. L e a d isotope analysis is free from most of the limitations of c h e m i c a l analysis. T h e isotopic c o m p o s i t i o n of l e a d usually varies o n l y w i t h i n n a r r o w l i m i t s i n a g i v e n ore b o d y . T h e l e a d isotopic composition of the ore passes u n c h a n g e d t h r o u g h the s m e l t i n g , r e f i n i n g , w o r k i n g , casting, or c o r rosion processes into the m e t a l (23). T h o u g h corrosion does not alter l e a d isotope compositions b y fractionation (24), c o r r o d e d samples of c o p p e r ob jects of l o w l e a d content can be dangerous for l e a d isotope analysis. C o r r o s i o n may alter the t r u e l e a d isotope composition of an artifact b y exchanging its l e a d w i t h l e a d of different isotopic composition from other objects i n the b u r i a l e n v i r o n m e n t or from the soil itself (25). N a t u r a l l y o c c u r r i n g l e a d is m a d e u p of four isotopes i n v a r y i n g p r o p o r tions. A c c o r d i n g to t h e i r atomic mass, m e a s u r e d i n atomic mass u n i t s , they are designated P b , P b , P b , a n d P b . P b is nonradiogenic i n o r i g i n . T h e other t h r e e isotopes of l e a d d e r i v e , i n part, from the radioactive decay of u r a n i u m a n d t h o r i u m . F o r a p a r t i c u l a r ore b o d y , the present-day l e a d isotope ratio is d e t e r m i n e d b y the integrated effects of a l l associations w i t h u r a n i u m a n d t h o r i u m b e t w e e n some i n i t i a l t i m e a n d a later t i m e , w h e n the ore was f o r m e d . A f t e r the ore is f o r m e d , the lead is usually no longer associated w i t h u r a n i u m a n d t h o r i u m . 2 0 4

2 0 6

2 0 7

2 0 8

2 0 4

So far, the o n l y available t e c h n i q u e capable of sufficiently accurate m e a s u r e m e n t of l e a d isotope compositions, b o t h for isotope geochemistry a n d for archaeological applications, is t h e r m a l ionization mass spectrometry. A n y w e l l - e q u i p p e d laboratory can r o u t i n e l y measure l e a d isotope ratios w i t h


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absolute 2 σ errors of 0 . 1 % o n samples of 100 n g of l e a d . T h e accuracy o f d e t e r m i n a t i o n of the isotopic c o m p o s i t i o n of l e a d i n a particular laboratory can b e assessed b y m a k i n g replicate measurements of the l e a d isotopic c o m position o f standards i s s u e d b y the U n i t e d States N a t i o n a l B u r e a u o f S t a n dards ( N B S ) . F o r archaeological purposes, the usual w a y of p r e s e n t i n g the l e a d isotope measurements is to relate the atomic ratios of P b / P b and 206 04 207 206 s u r e m e n t s o f N B S standards 2 0 8


p b / 2

p b

t Q

t

h

e

r a t i Q

o

f

p b /

p b

0

u

r

2 0 6

m e a

demonstrate r e p r o d u c i b i l i t y of b e t t e r than one part p e r t h o u s a n d (1/1000) for each of these three ratios. A r c h a e o m e t r i s t s often ask w h e t h e r the isotopic c o m p o s i t i o n o f l e a d i n an ore deposit is u n i f o r m throughout. D o u b t has also b e e n expressed as to w h e t h e r the l e a d i n different m i n e r a l s from the same ore deposits, especially from the p r i m a r y sulfides (as o p p o s e d to o x i d i z e d minerals) w i l l have t h e same isotopic c o m p o s i t i o n . T o answer these doubts, a n u m b e r o f i n v e s t i gations have b e e n c a r r i e d out b y isotope geochemists. F o r two deposits i n A u s t r a l i a , G u l s o n (26) has s h o w n that the c o m p l e t e range of l e a d isotope compositions i n the p r i m a r y sulfide ores varies less than 0 . 3 % , a n d that the o x i d i z e d ores i n the o v e r l y i n g gossan have l e a d isotope compositions i n d i s tinguishable from the d e e p p r i m a r y sulfide ores. S i m i l a r results w e r e o b t a i n e d i n O x f o r d for a range of ores from C y p r u s a n d L a u r i o n (27). T h e q u e s t i o n o f l e a d isotope u n i f o r m i t y i n a n ore b o d y has also b e e n investigated i n several other laboratories. M a n y ore deposits, especially the so-called strata-bound or comformable ore deposits, have a l e a d isotope c o m p o s i t i o n that varies v e r y little t h r o u g h o u t the w h o l e deposit, often b y less than 0 . 3 % . S u c h ore deposits c o m m o n l y have l e a d isotope compositions that l i e close to a single-stage m o d e l e v o l u t i o n c u r v e (28). S u c h a s i m p l e m o d e l cannot describe the c o m p o s i t i o n i n any r e a l ore b o d y . S e v e r a l , m o r e realistic, models have r e c e n t l y b e e n c o n s t r u c t e d (29). T h e i m p o r t a n c e of these models is that they a l l o w calculations of the soc a l l e d " m o d e l ages" from the o b s e r v e d l e a d isotope c o m p o s i t i o n o f a p a r t i c ular ore b o d y . T h e s e calculations s h o u l d give the geological age of the t i m e of e m p l a c e m e n t of the ore body. T h e i m p o r t a n c e of this i n f o r m a t i o n for isotope archaeology is that, once the l e a d isotope c o m p o s i t i o n of a m e t a l artifact has b e e n m e a s u r e d , a m o d e l age can b e calculated that w i l l give a guide to the r o u g h geological age of the ore deposit that s u p p l i e d its m e t a l . T h i s calculation indicates w h i c h ore deposits s h o u l d be investigated i n f u r t h e r p r o v e n a n c e studies. I n contrast w i t h conformable ore deposits, some v e i n - t y p e ore deposits have variable l e a d isotope compositions that plot as l i n e a r arrays of data points i n one or b o t h l e a d isotope diagrams. S u c h anomalous, or multistage, ore deposits c a n sometimes cause difficulties for archaeological provenance studies (30-31). F o r t u n a t e l y , deposits of this type are not c o m m o n i n the r e g i o n o f the M e d i t e r r a n e a n ; i n d e e d , none have yet b e e n f o u n d . O n l y i n


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F e n a n , T i m n a , a n d c e n t r a l A n a t o l i a , have o r e sources b e e n f o u n d that r e t a i n sufficient u r a n i u m o r t h o r i u m to cause variable p r e s e n t - d a y l e a d isotope compositions i n a single ore deposit.


Methodology and Problems Encountered S e v e n years ago w e started t h e first systematic research p r o g r a m o n t h e application o f the l e a d isotope techniques to provenance studies i n archaeology. P a r t i c u l a r stress was p l a c e d o n t h e sources o f metals i n t h e M e d i t e r ranean B r o n z e A g e . F o r t h e first 2 years w e w o r k e d m o s t l y o n t h e sources of l e a d a n d s i l v e r i n B r o n z e A g e G r e e c e , C y p r u s , a n d E g y p t (32-36). I n 1982, w e p i o n e e r e d t h e a p p l i c a t i o n o f the l e a d isotope m e t h o d for p r o v e n a n c i n g copper-based artifacts (15, 37-38). C o n s i d e r i n g the q u a n t i t y o f m e t a l from B r o n z e A g e archaeological sites i n the M e d i t e r r a n e a n , a n d the q u i t e insufficient geological i n f o r m a t i o n about the o r e deposits i n this r e g i o n that m a y have s u p p l i e d t h e m e t a l , t h e w o r k was i m m e n s e . D u r i n g the past c e n t u r y , archaeological sites of a technological nature, such as s m e l t i n g sites, slag heaps, a n d ancient m i n i n g galleries, have b e e n largely i g n o r e d b y archaeologists. T h e r e is , therefore, a necessity for extensive field w o r k based o n geological a n d historical information i n p a r a l l e l w i t h laboratory studies. A p a r t f r o m d i r e c t studies o f ancient m i n i n g o r m e t a l l u r g i c a l r e m a i n s , extensive fieldwork is n e e d e d also to establish the lead isotope characteristics of c o p p e r a n d l e a d - s i l v e r deposits that c o u l d have, o r are k n o w n to have b e e n , w o r k e d i n t h e B r o n z e A g e . I n t h e past 8 years w e have e x p l o r e d o r e deposits i n G r e e c e , C y p r u s , Sardinia, a n d t h e Sinai. O u r fieldwork has t w o m a i n objectives: 1. to collect ores a n d slags for c h e m i c a l , m i n e r a l o g i c a l , a n d l e a d isotope analyses, a n d 2. to establish w h e t h e r any archaeological t e c h n i q u e (like C - 1 4 or t h e r m o l u m i n e s c e n c e dating) o r other e v i d e n c e (like p o t tery, tools, tool m a r k s , o r character o f mining) points to t h e B r o n z e A g e exploitation o f the deposit. L e a d isotope a n d c h e m i c a l analyses o f byproducts o f c o p p e r s m e l t i n g from archaeological sites are i m p o r t a n t for t h e i n t e r p r e t a t i o n o f the technology that m i g h t have i n f l u e n c e d the l e a d isotope ratios o f the m e t a l p r o d u c e d o n a g i v e n site. C o p p e r ores u s u a l l y contain u n w a n t e d gangue that has to b e separated from t h e m e t a l i n t h e s m e l t i n g process b y t h e a d d i t i o n o f a flux. I n p r i n c i p l e , lead o f an isotopic c o m p o s i t i o n different f r o m that i n t h e m e t a l ore m i g h t b e i n t r o d u c e d w i t h t h e flux o r t h e fuel ash. Siliceous fluxes g e n erally have a v e r y l o w l e a d content. F e r r u g i n e o u s fluxes have usually b e e n



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taken f r o m the nearest source, w h i c h w i l l usually b e the gossan of t h e ore source itself, a n d have t h e same l e a d isotope c o m p o s i t i o n as t h e ore source. F u e l , chiefly charcoal, usually has a l o w l e a d content a n d , i n m a n y cases, the trees from w h i c h i t came w e r e g r o w i n g near the ore deposit a n d t e n d to have i n c o r p o r a t e d l e a d o f t h e same isotopic c o m p o s i t i o n as t h e ore deposit. I n most cases, t h e isotope c o m p o s i t i o n of l e a d i n t h e s m e l t e d c o p p e r has n o t b e e n p e r t u r b e d away from that o f l e a d i n the c o p p e r ore. F u r t h e r isotopic comparisons of c o p p e r ores a n d associated B r o n z e A g e c o p p e r slags are n e e d e d to examine this question m o r e extensively. C o m p a r i s o n s that have already b e e n m a d e bear o u t t h e hypotheses j u s t advanced. T o establish t h e range o f l e a d isotope compositions, t h e l e a d isotope field characteristic for a g i v e n ore deposit, o f about 50 samples o f ores, o r ores a n d slags f r o m a g i v e n ore deposit s h o u l d b e analyzed. F i g u r e 1 d e m onstrates t h e construction of l e a d isotope fields characteristic o f three different c o p p e r deposits i n t h e E a s t e r n M e d i t e r r a n e a n . T h e final result o f the d e t e r m i n a t i o n o f t h e l e a d isotope composition characteristic of a g i v e n ore deposit consists o f a set o f three l e a d isotope ratios: **tbl**Pb Pb/ Pb, and P b / P b . T h e s e ratios f o r m a t h r e e - d i m e n s i o n a l , approximately e g g shaped, d i s t r i b u t i o n i n space. T w o - d i m e n s i o n a l representation of t h e l e a d isotope data requires t w o separate diagrams that present t h e ratios P b / P b versus P b / P b and 206p 204p 207p 206 g ^ l (206 /204p 2 0 7

9

2 0 6

2 0 6

2 0 4

2 0 8

b/

b

v

e

r

s

u

s

b/

pb

s h ( ) w s

2 0 6

2 0 7

a

t

e

r

n

a

t

i

v

2 0 6

e

pb

b

versus P b / P b ) diagram for the same c o p p e r deposits as i n F i g u r e 1. S o m e t i m e s , o n l y b y u s i n g a l l three m e a s u r e d l e a d isotope ratios is i t possible to d e c i d e i f particular characteristic fields overlap. F o r example, the C y p r i o t and K y t h n i a n fields overlap o n F i g u r e 1, b u t are well-separated o n F i g u r e 2. 2 0 7

2 0 6

A better representation of the t h r e e - d i m e n s i o n a l lead isotope fingerprint can b e made b y u s i n g a m u l t i v a r i a t e d i s c r i m i n a n t analysis. F i g u r e 3 shows the characteristic l e a d isotope composition o f the same three ore deposits that was p r e p a r e d b y u s i n g m u l t i v a r i a t e d i s c r i m i n a n t analysis ( P o l l a r d , M . , U n i v e r s i t y of Cardiff, personal c o m m u n i c a t i o n i n 1986). It shows clearly, as the t w o - d i m e n s i o n a l diagrams do not, that these fields m a y b e r e s o l v e d b y u s i n g a l l three isotopic ratios. C e r t a i n ore deposits m a y partially overlap i n t h e i r l e a d isotope c o m p o s i t i o n . I n such a case, i t m i g h t n o t b e possible to d e c i d e o n the basis o f the l e a d isotope data alone w h i c h o f the ore deposits i n question p r o v i d e d the ore for m e t a l artifacts that have l e a d isotope compositions that fall into the o v e r l a p p i n g space. S o m e t i m e s , o n e o f these ore deposits c a n b e r u l e d out b y u s i n g trace e l e m e n t data, p a r t i c u l a r l y f r o m gold a n d silver analyses (6). L e a d isotope analyses b y themselves c a n make a negative statement w i t h absolute certainty i n a w a y w h i c h c h e m i c a l analysis can n e v e r hope to do. If the l e a d isotope c o m p o s i t i o n o f an artifact falls w e l l outside t h e l e a d isotope field characteristic o f a particular ore deposit t h e n i t is certain that t h e m e t a l




166

Figure 1. Lead isotope compositions for ores and slags from Cyprus, Kythnos, and Laurion. The fields overlap in this two-dimensional diagram but can be separated by using all three available lead isotope ratios.


9.

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Bronze Age Archaeometallurgy

Γ


τ

167

18.3L

0.830

0.840 207p

b

/206

p

0.850

b

Figure 2. The alternative lead isotope diagram for Cyprus, Kythnos, and Laurion fields.



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CANONICAL VARIABLE

Figure 3. Stepwise discriminant analysis by M. Pollard of all three measured had isotope ratios for ore samples from Cyprus, Kythnos, and Laurion ore deposits.

for that artifact d i d not c o m e f r o m that ore source. T h i s statement requires r e v i s i o n o n l y i f there is e v i d e n c e of p e r t u r b a t i o n of the l e a d isotope c o m position of the m e t a l away f r o m the lead isotope composition of the m e t a l ore. T h i s p e r t u r b a t i o n c o u l d be caused b y l e a d from the f u e l a n d flux u s e d i n s m e l t i n g . I n the few cases e x a m i n e d so far b y workers i n M a i n z a n d i n O x f o r d , e v i d e n c e of such p e r t u r b a t i o n has not b e e n found. F o r each ore deposit u n d e r investigation, the ore for l e a d isotope a n a l yses was collected from various parts of the deposit to check the u n i f o r m i t y of the characteristic lead isotope composition w i t h i n the deposit. Various types of minerals w e r e analyzed. If available, stratified archaeological m a terial r e p r e s e n t i n g byproducts of ancient m e t a l p r o d u c t i o n from that ore deposit (e.g., slags a n d litharge) w e r e used for construction of a set of l e a d isotope ratios characterizing the ore source. T h e results of this approach for the C y p r i o t c o p p e r ores are s h o w n i n F i g u r e 4, i n w h i c h the lead isotope ratios for each of the i n d i v i d u a l C y p r i o t ore deposits clusters tightly together, i n d e p e n d e n t l y of the m i n e r a l o g i c a l type a n d spatial o r i g i n w i t h i n the deposit of the sample analyzed. I n a d d i t i o n to the l e a d isotope analyses, it is necessary to take into account isotope geochemistry, m e t a l l u r g y , a n d ore deposit geology. I n seek-



9.

h

GALE & STOS-GALE

2.06

A AG AL AM AP D Κ ΚΑ Kl L M Ρ ΡΕ S SH TR

Bronze Age

Archaeometallurgy

169

Alestos AGROKIPIA Almyras Ayia Marina Apliki

φ

Drapia Kinousa Kataliondas Kition Limni ΜΑΤΗΙΑΤΙ Peristerka Perevasa

Pyrite/chalcopyrite

•

Rich sulphidic Cu ores

•

O x i d i s e d Cu ores

Ο

Umbers

φ

Galena

X

Bronze Age slag

+

' C l a s s i c a l ' slag

SKOURIOTISSA SHA TROULLI 207 p 1

0.83

0.84 _L

b

/

2 0 6

p

b

^

J-

Figure 4. Lead isotope compositions for ores and copper slags from Cyprus. Copper ores, umbers, galena and copper slags have lead isotopic compositions falling into the same field. Error bars at the 9 5 % level for the lead isotope ratios are shown on this and subsequent figures. (Reproduced with permission from ref. 3. Copyright 1986 University of Birmingham.)


170



i n g the provenance of c o p p e r it is necessary to compare o n l y artifacts w i t h the lead isotope compositions of c o p p e r ore deposits. P e r n i c k a et a l . (42) c o m p a r e d c o p p e r artifacts w i t h p y r i t e - b l e n d e - g a l e n a ore deposits that c o n t a i n e d no c o p p e r . I n some cases, b o t h c o p p e r a n d l e a d ores occur i n the same ore deposit (e.g., F u n t a n a R a m i n o s a i n Sardinia). I n such cases, the l e a d isotope compositions of the c o p p e r ores w i l l usually (in base m e t a l ore deposits free of u r a n i u m a n d thorium) be the same as those of the lead ores. A k n o w l e d g e of the geology is i m p o r t a n t i n o r d e r to d e t e r m i n e the proportions of lead a n d c o p p e r a n d w h e t h e r the c o p p e r a n d lead ores may have b e e n so finely i n t e r g r o w n that it was impossible for B r o n z e A g e peoples to separate o r e v e n recognize t h e m . A g a i n , careful investigations of isotopic h o m o g e n e i t y are necessary i n the case of v e i n deposits of c o p p e r , i n w h i c h variable c o n t a m i n a t i o n b y c o u n t r y rocks may have o c c u r r e d . C a u t i o n is again i n d i c a t e d i f h i g h U / P b ratios i n a g i v e n c o p p e r deposit are suspected. It is v e r y h e l p f u l i f m i n i n g or m e t a l l u r g i c a l (slags) activities associated w i t h a g i v e n c o p p e r ore deposit can b e dated a n d i f it can be established that nearby archaeological sites have u s e d the ores at a k n o w n p e r i o d . T h e application of l e a d isotope analyses to p r o v e n a n c i n g almost p u r e c o p p e r artifacts seems r e l a t i v e l y straightforward i n most instances, b u t w h a t of arsenical c o p p e r a n d t i n b r o n z e alloys? I n p r i n c i p l e , the arsenic i n arsenical c o p p e r may have b e e n d e r i v e d from high-arsenic minerals (such as tennantite or basic c o p p e r arsenates) c o n t a i n i n g lead of a different isotopic c o m p o s i t i o n from that of the c o p p e r ore u s e d to p r o d u c e the copper. H o w e v e r , absolutely no archaeological o r other e v i d e n c e of proves that this was e v e r d o n e i n the B r o n z e A g e A e g e a n . O n the contrary, at K y t h n o s definite e v i d e n c e shows that arsenical c o p p e r was p r o d u c e d i n E B I I times from arsenical c o p p e r ores of variable (sometimes zero) arsenic content b u t of u n i f o r m lead isotope composition. T i n b r o n z e is another matter because, apart from rare c o p p e r ore d e posits also c o n t a i n i n g t i n (e.g., some of those i n C o r n w a l l ) , t i n from a q u i t e different source than the c o p p e r has almost always b e e n a d d e d to c o p p e r to p r o d u c e b r o n z e . T h e o n l y t i n m i n e r a l that is l i k e l y to contain lead is stannite, w h i c h is not c o m m o n except as a m i n e r a l o g i c a l curiosity. T i n has always b e e n o b t a i n e d i n v e r y large quantities from cassiterite, w h i c h almost n e v e r contains e v e n a trace of l e a d . T h e t i n ingots found u n d e r w a t e r off the coast of Israel contain no lead. O u r w o r k o n C y p r i o t L a t e B r o n z e A g e bronzes indicates no p e r t u r b a t i o n away from the characteristic C y p r i o t lead isotope c o m p o s i t i o n , e v e n for bronzes c o n t a i n i n g 1 8 % t i n . T h e most serious p o t e n t i a l p r o b l e m for the use of lead isotope analyses for p r o v e n a n c i n g c o p p e r i n copper-based alloys is the possible r e m e l t i n g together of m e t a l d e r i v e d from different ore sources. T h e effect of m e l t i n g together, i n various proportions, two c o p p e r artifacts of different l e a d isotope compositions is to generate a n u m b e r of objects h a v i n g isotopic compositions falling, i n the u s u a l lead isotope diagrams, o n a straight l i n e j o i n i n g the two


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e n d - m e m b e r compositions. M e l t i n g together i n r a n d o m ways a n u m b e r of objects, each o f w h i c h has a different l e a d isotope c o m p o s i t i o n , w o u l d g e n erate e v e n m o r e smeared-out isotope compositions. I f r e m e l t i n g together of scrap from d i v e r s e c o p p e r ore sources w e r e c o m m o n , t h e n one w o u l d c o m m o n l y observe " s m e a r e d - o u t " l e a d isotope patterns that c o v e r e d larger areas than are characteristic of ore deposits. So far, w e have not seen these l e a d isotope patterns i n o u r studies; this finding argues that r e m e l t i n g m a y not have b e e n a c o m m o n practice i n the A e g e a n B r o n z e A g e . S o m e archaeological e v i d e n c e that suggests that r e m e l t i n g m a y not have b e e n a v e r y c o m m o n practice at any t i m e i n the A e g e a n , w h e r e it was, at a l l times, c o m m o n to b u r y m e t a l objects w i t h the d e a d (7). F o r M i d d l e M i n o a n C r e t e , J e n n i f e r M o o d y (39) has s h o w n that m e t a l objects are p r e d o m i n a n t l y f o u n d not i n settlements or palaces, b u t i n graves w h e r e they w e r e largely safe f r o m reuse. F u r t h e r , B r a n i g a n (40) has s h o w n that the r e r i v e t i n g o f daggers was a c o m m o n practice i n E a r l y a n d M i d d l e M i n o a n C r e t e , a n d some 1 5 % of r e r i v e t e d daggers show clear e v i d e n c e o f h a v i n g b e e n r e r i v e t e d o n t w o o r m o r e separate occasions. B r a n i g a n (40, p. 46) c o m m e n t s that all the rerivetings are perhaps indicative of the trouble to which Minoans of the Early Bronze Age went in order to avoid scrapping their weapons, or even having them melted down and recast. I n fact, i t was always easier to r e p a i r r i v e t i n g or r e w o r k a d a m a g e d edge than to m e l t d o w n a n d recast a tool or a w e a p o n . E v e n i n the L a t e B r o n z e A g e , the A e g e a n was u n u s u a l i n comparison to other parts o f E u r o p e i n that the q u a n t i t y of h o a r d e d m e t a l was v e r y small i n absolute t e r m s a n d also i n c o m p a r i s o n to the a m o u n t of m e t a l deposited i n graves (22). T h e quantities of m e t a l d e p o s i t e d i n M y c e n e a n a n d M i n o a n graves w e r e m u c h greater than i n most of E u r o p e . I n m a n y cases, hoards of m e t a l i n the A e g e a n w e r e not m e t a l w o r k e r s ' hoards b u t clearly m e t a l possessions h i d d e n away i n t i m e of danger that the o w n e r h o p e d to recover i n h a p p i e r times. E v e n i f a l i m i t e d a m o u n t of m e l t i n g a n d m i x i n g of m e t a l from d i s c a r d e d objects d i d take place, i t m a y not have caused m u c h confusion i n the l e a d isotope p a t t e r n . I f the various d i s c a r d e d objects i n a founder's h o a r d w e r e a l l m a d e from c o p p e r that d e r i v e d from the same ore source, t h e n the m i x i n g together of t h e i r m e t a l to m a k e n e w objects w o u l d not alter the l e a d isotope c o m p o s i t i o n characteristic o f that ore source. S t r o n g e c o n o m i c a n d t e c h n i c a l arguments suggest that, at a g i v e n t i m e , a particular site or area w i l l t e n d to receive c o p p e r p r e d o m i n a n t l y from one, or perhaps t w o , ore sources. F o r the L a t e M i n o a n I I founder's h o a r d f o u n d i n the U n e x p l o r e d M a n s i o n i n C r e t e , this seems to b e the case. E i g h t y - f i v e p e r c e n t of the objects w e r e m a d e of c o p p e r from the L a u r i o n ore source, a n d 1 5 % f r o m other c o p p e r ore sources (41).



172


P e r n i c k a a n d his colleagues (42) have suggested a v e r y valuable m e t h o d to p r o v e w h e t h e r a g i v e n b o d y of data exhibits m i x i n g . T h e m e t h o d d e p e n d s o n h a v i n g b o t h l e a d isotope a n d trace e l e m e n t data for the m e t a l artifacts i n question. C o l l i n e a r i t y b e t w e e n three objects i n a particular l e a d isot o p e - t r a c e e l e m e n t d i a g r a m admits the p o s s i b i l i t y that the m i d d l e object may have b e e n made of m e t a l m i x e d f r o m the other two. T h i s hypothesis is negated if, i n another such d i a g r a m , for different trace elements, these three objects do not l i e i n a straight l i n e . T h e m e t h o d is laborious because all possible object combinations must be e x a m i n e d , b u t this c o u l d r e a d i l y done b y u s i n g a c o m p u t e r . W e have a p p l i e d this t e c h n i q u e to investigating w h e t h e r the a n a l y z e d objects f r o m T r o y a n d the " T r o a s " (6, 42) w e r e m a d e from mixtures of r e m e l t e d objects: they w e r e not. T h e question of the " r e m e l t effect" is still stressed b y archaeologists w h o have not p r e s e n t e d any p r o p e r l y discussed archaeological e v i d e n c e that it was a c o m m o n p h e n o m e n o n i n the E a s t M e d i t e r r a n e a n B r o n z e A g e .

Ore Sources for the Bronze Age

Mediterranean

T h e t h r e e c o p p e r ore deposits m e n t i o n e d ( K y t h n o s , L a u r i o n , a n d C y p r u s ) p l a y e d i m p o r t a n t roles as c o p p e r sources i n the E a s t e r n M e d i t e r r a n e a n at different stages of the B r o n z e A g e . A m o n g these deposits, o n l y C y p r u s h a d the r e p u t a t i o n as a c o p p e r source i n the archaeological literature at the outset of o u r research. T h e o r i e s about the m e t a l sources e x p l o i t e d i n B r o n z e A g e G r e e c e v a r i e d from the use of s m a l l sources local to any of the c u l t u r a l centers throughout G r e e c e , (see references 43 a n d 44), to the theory of c e n t r a l i z e d c o p p e r p r o d u c t i o n o n C y p r u s (1) and the s u d d e n i n t r o d u c t i o n of metals a n d m e t a l l u r g y into the A e g e a n f r o m the E a s t [the " m e t a l l s e h o c k " theory i n t r o d u c e d b y S c h a c h e r m e y r (45)] i n E a r l y B r o n z e A g e I I t i m e s . Early Bronze Age. O u r w o r k o n the E a r l y B r o n z e A g e m e t a l sources started as an investigation of the sources of lead a n d silver for the E a r l y C y c l a d i c p e o p l e (5). T h e result of this w o r k , as s h o w n i n F i g u r e 5, was p r o o f that the d o m i n a n t source of silver a n d l e a d for the E a r l y B r o n z e A g e C y c l a d e s was the C y c l a d i c i s l a n d of S i p h n o s , a n d that i n the later part of the E a r l y B r o n z e A g e the L a u r i o n l e a d - s i l v e r deposits also p r o v i d e d these metals (16). Since 1982, w e have extended o u r research to the possible sources of c o p p e r i n G r e e c e a n d have s u r v e y e d m a n y of the k n o w n c o p p e r deposits for any e v i d e n c e of B r o n z e A g e exploitation. I n this research, perhaps the most r e w a r d i n g site was d i s c o v e r e d o n K y t h n o s . K y t h n o s , a C y c l a d i c i s l a n d i n the n e i g h b o r h o o d of K e a a n d S e r i p h o s , came to o u r attention w h e n s u r v e y i n g the C y c l a d i c ore deposits. F i e d l e r , a G e r m a n emissary of K i n g O t t o of G r e e c e , m e n t i o n e d i n his report (46) a n ancient i r o n slag heap o n K y t h n o s (46). A f t e r o u r field w o r k o n K y t h n o s i n 1982, it b e c a m e clear that the slag heap near A y i o s Yoannis B a y c o n t a i n e d


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not i r o n b u t c o p p e r slag a n d that most p r o b a b l y i t was the residue of E a r l y B r o n z e A g e c o p p e r p r o d u c t i o n (47). O n t h e basis of the lead isotope analyses of the slags a n d ores f o u n d w i t h i n t h e slag, as w e l l as other ores nearby, w e have established t h e l e a d isotope field characteristic of the K y t h n o s c o p p e r ore deposit. D a t i n g t h e site was m a d e possible b y fragments of E a r l y C y c l a d i c II pottery f o u n d w i t h i n t h e slag heap. K y t h n o s i s , therefore, t h e earliest p r o v e n c o p p e r s m e l t i n g site k n o w n i n G r e e c e . T h i s archaeological e v i d e n c e was c o n f i r m e d b y t h e results of some lead isotope analyses of E a r l y C y c l a d i c c o p p e r artifacts. F i g u r e s 6 a n d 7 show t h e lead isotope data for t h e K y t h n o s H o a r d , a h o a r d o f E a r l y C y c l a d i c tools n o w h e l d i n t h e B r i t i s h M u s e u m (48), a n d E a r l y C y c l a d i c daggers f r o m t h e A s h m o l e u m M u s e u m collection. A l l tools from the K y t h n o s H o a r d a n d 12 out of 17 daggers from A m o r g o s w e r e consistent w i t h t h e l e a d isotope ratio characteristic for K y t h n i a n slag a n d ore, as seen b y c o m p a r i n g F i g u r e s 6 a n d 7. K y t h n i a n c o p p e r was d i s t r i b u t e d to other islands i n the A e g e a n . S e v e r a l E a r l y B r o n z e A g e c o p p e r objects o f K y t h n i a n o r i g i n w e r e f o u n d o n t h e i s l a n d of K e a ( F i g u r e 8), a n d p r e l i m i n a r y w o r k w i t h K . Davaras shows that the majority of m e t a l objects f r o m the E a r l y M i n o a n site of A y i a P h o t i a i n E a s t e r n C r e t e originate from K y t h n i a n copper. T h e latter is n o t too s u r p r i s i n g b e cause the general archaeological affinities of the A y i a P h o t i a c o p p e r , ceramic, a n d m a r b l e finds are C y c l a d i c . C h e m i c a l analyses o f slags a n d ores from t h e A y i o s Yoannis slag heap o n K y t h n o s y i e l d e d some i n t e r e s t i n g technological information. F r a g m e n t s of ore f o u n d a m o n g t h e discarded slag at this site p r o v e that t h e c h i e f c o p p e r ore s m e l t e d there was malachite plus azurite i n a ferruginous matrix. A n a l yses show that the ore sometimes contained a f e w p e r c e n t of arsenic. Analyses of c o p p e r p r i l l s contained w i t h i n different fragments of t h e s m e l t i n g slag show arsenic levels f r o m zero to 4 . 5 % . T h e arsenic levels p r o v e that i n t h e t h i r d m i l l e n n i u m B . C . arsenical c o p p e r was sometimes accidentally p r o d u c e d i n the s m e l t i n g of c o p p e r from its ores. M o s t l i k e l y , t h e superior properties o f some batches o f this accidentally p r o d u c e d arsenical c o p p e r w e r e r e c o g n i z e d , a n d these batches o f c o p p e r w e r e selected for m a k i n g weapons a n d tools. A c c i d e n t a l s m e l t i n g o f arsenical c o p p e r was l i k e l y w h e r e v e r c o p p e r was s m e l t e d a n d t h e ores used h a p p e n e d to contain some arsenic. T h e w i d e spread early use of arsenical c o p p e r c o u l d possibly be the result of accidental i n d e p e n d e n t " i n v e n t i o n " i n m a n y different c o p p e r - p r o d u c i n g centers. So far, there is no e v i d e n c e that c o p p e r was p r o d u c e d o n K y t h n o s before or after E a r l y C y c l a d i c I I times. T u r n i n g to another i m p o r t a n t C y c l a d i c site, t h e settlement of K a s t r i o n Syros, first excavated b y Tsountas (49) a n d systematically excavated later b y Bossert (50), occupies t h e u p p e r m o s t part of a b a r r e n tongue-shaped h i l l , s u r r o u n d e d b y d e e p ravines. Across a v e r y steep ravine from K a s t r i lies t h e




174


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4

A E 158 Amorgos, Kapros, Ag Bowl

•

AE 253 Amorgos, Ag Bracelet

•

A E 254 Amorgos, Ag Bracelet

175

Φ A E 255 Amorgos, Ag Bracelet •

A E 260 Amorgos, Ag Bracelet


Φ AE 243 Amorgos, Arkesine, Pb object A

1929.26 Naxos, Pb Boat Model

•

1938.725 Naxos, Pb Boat Model

•

1938.726 Naxos, Pb Boat Model 5 5 - 6 6 - 1 8 0 Naxos, Pb Boat Model NM 5234 Syros, Kastri, Ag Diadem NM 5144 S y r o s , Chalandriani, Ag Pin

A n

• • •

NM 5323 Syros, Kastri, Pb Weight NM 5240 Syros, Kastri, Pb Rivet

Δ CHE Cheiromylos, Pb fragment m

•

A Antiparos, Pb Figurine, BM 84, 12-13, 20 NM 11.310 Naxos, Pb Rivets

Figure 5—Continued large necropolis o f C h a l a n d r i a n i , also excavated b y Tsountas. M o d e r n a r chaeological studies show (51) that, whereas K a s t r i was o c c u p i e d o n l y for a short t i m e i n E C I I I A times, t h e c e m e t e r y at C h a l a n d r i a n i was i n u s e b o t h before a n d d u r i n g t h e occupation o f the settlement o f K a s t r i . M a n y authors have r e f e r r e d to t h e occurrence o f E a r l y C y c l a d i c t i n b r o n z e artifacts (e.g. 48, 52), b u t a closer examination shows that t h e o n l y t i n b r o n z e objects from p r o v e n E a r l y C y c l a d i c contexts are those from K a s t r i o n Syros (6, p p . 4 1 - 4 2 ) . T i n b r o n z e was not f o u n d at a l l i n o u r analyses o f 31 E a r l y C y c l a d i c objects from A m o r g o s , Paros, K y t h n o s , a n d C h a l a n d r i a n i o n Syros (53). I n other ways, t h e nature of the K a s t r i settlement is not p u r e l y C y c l a d i c . Bossert (50, p p . 7 0 - 7 5 ) r e m a r k e d that although i t was difficult to find parallels b e t w e e n t h e finds at K a s t r i a n d those i n t h e graves o f C h a l a n d r i a n i , t h e differences w e r e v e r y apparent. A l t h o u g h sauce boats f o u n d at C h a l a n d r i a n i p o i n t e d to connections w i t h t h e G r e e k m a i n l a n d , they w e r e c o m p l e t e l y absent at K a s t r i , w h e r e t h e d i s t i n c t i v e pottery forms have clear A n a t o l i a n comparisons at T r o y I I . N o t a b l e features o f the finds at K a s t r i are t h e m e t a l objects a n d t h e e v i d e n c e that m e t a l l u r g y was p r a c t i c e d t h e r e . Tsountas (49)




176

Figure 6. Lead isotope compositions for the Kythnos Hoard and Early Cycladic copper-based alloy artifacts from Amorgos.



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177

Archaeometallurgy

M8.4 •

K y t h n o s H o a r d , tools.

Δ

Amorgos, daggers.

W

M8.3 0.83

Ι

2 0 6

Pb

—

Ο.84

Figure 7. Alternative lead isotope diagram for the Kythnos Hoard and Early Cycladic copper alloy artifacts from Amorgos.



Figure 8. Lead isotope composition of the Early Bronze Age objects from Aghia Irini on Kea.


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a n d Bossert (50) f o u n d crucibles c o n t a i n i n g traces of b r o n z e a n d l e a d ; m o l d s for casting flat axes, arrowheads, swords, spearheads a n d chisels (54); SL silver d i a d e m a n d some l e a d objects (5); a few objects of arsenical c o p p e r ; a n d m a n y objects of t i n b r o n z e .


A l t h o u g h r i c h c o p p e r ores, p a r t i c u l a r l y azurite, malachite, or c u p r i t e , can be s m e l t e d i n c r u c i b l e s , the so-called " s l a g " from K a s t r i r e p o r t e d b y Tsountas (6, p p . 3 1 , 42) is, i n fact, a l u m p of arsenical c o p p e r m e t a l . W e c o n c l u d e d that there is no positive evidence of s m e l t i n g at K a s t r i . T h e archaeological e v i d e n c e is for m e l t i n g a n d casting metals only. H o w t h e n the m e t a l artifacts from T r o y I I compare w i t h those f r o m K a s t r i o n Syros? C h e m i c a l analyses of 19 objects from T r o y I I (see also reference 42) r e v e a l e d that 14 are h i g h t i n bronzes (6, p p . 3 9 - 4 0 ) . T i n b r o n z e was not c o m m o n at this t i m e i n A n a t o l i a , b u t i t seems to have b e e n q u i t e abundant i n T r o y a n d i n T h e r m i o n L e s b o s (43). T h e l e a d isotope analyses of copper-based objects from T r o y show that T r o y o b t a i n e d c o p p e r from a s u r p r i s i n g l y large n u m b e r of sources (see also reference 42). F i g u r e 9 shows the results of the l e a d isotope analyses of these objects c o m p a r e d w i t h the l e a d isotope c o m p o s i t i o n of the objects from K a s t r i o n Syros a n d C h a l a n d r i a n i . O n the basis of o u r measurements of the a m o u n t of variation i n l e a d isotopic c o m p o s i t i o n f o u n d for other c o p p e r ore deposits, w e have estimated approximate bounds for at least five different c o p p e r ore sources from w h i c h Trojan c o p p e r m u s t have b e e n d e r i v e d . A s yet, there is not e n o u g h lead isotope data o n the A n a t o l i a n c o p p e r ore deposits to b e able to d i r e c t l y l i n k the estimated lead isotope fields w i t h p a r t i c u l a r c o p p e r occurrences. H o w e v e r , because the l e a d isotope c o m p o s i t i o n is, to a first a p p r o x i m a t i o n , c o n t r o l l e d b y the geological age of the ore deposit, these five different ore sources, of w i d e l y different l e a d isotope compositions, m u s t have b e e n f o r m e d at q u i t e different times. T h e r o u g h geological age of ore formation c o r r e s p o n d i n g to l e a d isotopic compositions that fall into various parts of a d i a g r a m , such as F i g u r e 9, can b e calculated from models of the e v o l u t i o n w i t h t i m e of ore l e a d isotope compositions (55). O n this basis, one can d e d u c e the approximate geological m o d e l ages of the c o p p e r ore deposits associated w i t h the five groups of Trojan artifacts as follows: Group Group Group Group Group

A Β C D Ε

P l i o c e n e to Oligocène (2-34 m i l l i o n years ago) E o c e n e to Triassic ( 3 4 - 2 0 0 m i l l i o n years ago) Triassic to D e v o n i a n ( 2 0 0 - 3 6 0 m i l l i o n years ago) S i l u r i a n to P r e c a m b r i a n (400-700 m i l l i o n years ago) P r e c a m b r i a n (700-900 m i l l i o n years ago)

T h e T u r k i s h M i n e r a l R e s e a r c h a n d E x p l o r a t i o n Institute has classified T u r k i s h c o p p e r ores according to geological age. F i g u r e 10 shows eight different regions i n A n a t o l i a a n d one i n B u l g a r i a w h e r e c o p p e r deposits exist


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9.

Bronze Age Archaeometallurgy of the Mediterranean - ACS Publications

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