Arqueología en el valle del Duero. Del Paleolítico a la Edad Media. 6 ISBN: 978-84-947952-1-3, pp: 204-213 ARCHAEOMETALURGICAL ANALYSIS AND ARCHAEOLOGICAL CONTEXTUALIZATION OF A BRONZE SPEARHEAD FROM GRALHEIRA (MURO MOUNTAIN RANGE, , , NORTH )

Maria Antónia D. Silva1 Fernando Castro2 Ana M. S. Bettencourt3 António Manuel S. P. Silva4 Alexandre Manteiga Brea5

RESUMO Este trabalho visa dar a conhecer o contexto de achado e a composição química de uma ponta de lança de alvado curto e de folha ligeiramente losângica com nervura central, inserível no Bronze Final e inédita. Esta foi encontrada na serra do Muro, de Baltar, concelho de Paredes, distrito do . A serra do Muro corresponde a um monte com uma implan- tação orográ ca dominante na região sobre os vales dos rios Ferreira e Sousa, este a uente da margem norte da bacia do Douro, em área rica em recursos primários e secundários de estanho. No topo deste acidente geomorfológico foi edi cado um povoado proto-histórico que gura na literatura arqueológica especialmente pelo grande perímetro e espessura das suas muralhas pétreas. Apesar da proximi-

1 Gabinete de Arqueologia da Câmara Municipal de Paredes, Portugal ([email protected]). 2 Laboratório de Análises Químicas da TecMinho; Departamento de Engenharia Mecânica da Universidade do Minho, Guimarães, Portugal ([email protected]). 3 Laboratório de Paisagens, Património e Território - Lab2PT; Departamento de História da Universidade do Minho, Braga, Portugal ([email protected]). 4 Bolseiro de Doutoramento da FCT na Univ. de Santiago de Compostela. Centro de Investigação Transdisci- plinar Cultura, Espaço e Memória – CITCEM-Univ. Porto ([email protected]). 5 Laboratório de Paisagens, Património e Território - Lab2PT/Universidade do Minho, Portugal ([email protected]).

204 A                   G  dade destes dois contextos arqueológicos não há qualquer indicação precisa de que estejam vinculados, podendo esta peça constituir um depósito. Não sendo muito frequente o achado de pontas de lança no NO português, conhecem-se todavia alguns contextos, todos eles correspondentes a depósitos. É o caso da ponta de lança de Badim, de morfologia similar, que apareceu enterrada na base do monte cónico de Nossa Senhora da Graça, em Monção, e desvinculada do castro aí existente, localizado, aliás, em vertente oposta. Outros achados simi- lares associados a montes são os do Outeiro do Rego, em Lama Chã, Montalegre, e o da Quinta do Telhado, no Monte da Penha, em Guimarães, ambos associados a a oramentos. Apesar das diversas pontas de lança conhecidas no NW português, apenas as duas de Vale Travesso, em Montalegre, foram alvo de análise de composição química (BOTTAINI 2012: 49-52), pelo que os resultados das análises arqueo- metalúrgicas obtidas por espectrometria de  uorescência de raios X da ponta de lança do Muro, contribuirão, certamente, para o conhecimento da metalurgia do Bronze Final do NO.

Palavras-chave: NO. de Portugal; Bronze Final; Ponta de lança; Contexto; Com- posição química.

1. THE FIND AND ITS CONTEXT ponds to the “entrance” of the single natural passage between the valleys he artifact was found at the bo- of the rivers Sousa and Ferreira, both T ttom of the eastern slope of the located north and south of the Muro Muro mountain range, in a fallow eld mountain range, respectively (Figs. known as Loto or Veloto, in Gralhei- 1 and 2). According to the Geologi- ra, Baltar parish, Paredes municipality, cal Map of Portugal, scale 1:50.000, .  e approximate geogra- 9-D (Pena el), the area is dominated phical coordinates in degrees, minutes by porphyroid coarse-grained granites and seconds, in the WGS84 system with two-micas, but essentially bioti- are: 41° 11’59.65’’N; 8° 22’49.65’’O. tes, commonly found at the surface. WGS84, at an altitude of c. 350 m (see  ey occur in veins of aplite-pegma- Figs. 1 and 2). tites (MEDEIROS et al., 1980).  e  e location of the nd constitutes municipality of Paredes is rich in pri- an open platform, of easy access, over- mary and secondary mineral resources, looking the Baltar stream, which  ows including tin, gold and silver, although into the River Sousa, a tributary on the these are not known in the vicinity of right bank of the Douro. It also corres- the nd spot.  ese are found only at

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2 km northwest of the Muro mountain 2. DESCRIPTION OF THE OBJECT range, in the tin mines of , and at 5 km to the south, in the gold e artifact under study constitutes a and silver mines of “Covas de Castro- short socketed spearhead with a central mil” (DGE; COUTO 1993: g. 3). midrib, present on both sides. With ere is no evidence about other ar- an almost conical section, it is solid chaeological sites ascribed to the Bron- between 11.9 cm and 13.7 cm, from ze Age in the limit of this parish. e which seems to be again hollow. e only settlement that has been identi ed base has two circular holes, both sym- to date is the Muro de Vandoma hill- metrical and aligned with the edges, fort, at the top of the Muro mountain designed to secure the spearhead, and range, whose speci c occupations are the leaf is of slightly losangic shape. It poorly known (AZEVEDO 1898: 194, has been partially broken at the tip and SILVA 1986: 85, SILVA 2000: 100). It in the socket, therefore it’s not possible has been classi ed as a Monument of to know its exact length. It currently Public Interest6. e settlement was measures, 14.5 cm in height, 3.6 cm of acknowledged in the archaeological maximum width of the leaf and 2.5 cm literature due to the large perimeter of maximum width of the socket. e and thickness of its stone walls (SIL- maximum thickness in the socket is 0.3 VA 1963, 1966), together with some cm, and at the tip (broken) is 0.6 cm. other particular features. Despite the Weights 82.5687 gr (Figs. 3 and 4). proximity of the two archaeological It presents a greenish patina resul- contexts, the settlement and the nd ting of the actual state of corrosion, spot of the spearhead (which occurred however it has been recently under- at about 250 m to the east of the hill- going chemical stabilization, including fort walls), there is no clear indication a volumetric and chromatic reintegra- that both are connected, therefore, the tion process with a pigmented epoxy spearhead possibly constitutes a delibe- resin. It is curated by the family of the rate deposition. e artefact was found heirs of Mr. José Vicente da Silva7, in in a property owned by José Vicente da Gralheira, Baltar, Paredes. Silva, during the opening of an access road to his thickets, in the late 1950s, however the circumstances of discovery are unknown.

6 Dec. nº 45/93. Diário da República. I Série. 280 (30- 7 Presently it is in the possession of Mr. Engineer 11-1993): 6698-6701. Manuel Cunha.

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Fig. 1: Approximate location of the nd in the Military Map of Portugal, esc. 1:25.000, pgs. 111 and 123 (IGE-1998-99).

Fig. 2: Approximate area of the nd spot in an orthophotomap (ETRS89-EN-TM06. CM Paredes).

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Fig. 3: Gralheira spearhead. Front and side views (Photos by M. A. Silva).

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Fig. 4: Gralheira spearhead. (Drawing by Maria Antonia Silva).

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3. CHEMICAL COMPOSITION structure of the alloy through a scanning AND MICROSTRUCTURE electron microscope focused on the inner zone of the fragment, in order to avoid e determination of the chemical the surface corrosion layer, allowing for composition was made through quan- the identi cation of the following ele- titative archaeometalurgical analysis ments, as illustrated in Figures 5 and 6: obtained by X-ray uorescence spec- trometry, in the Chemical Analysis La- Z1 - Cu with 6.9% Sn; boratory of TecMinho (Department of Z2 - Cu2O; Mechanical Engineering, Minho Uni- Z3 - Cu “pure”; versity, Guimaraes) and through meta- Z4 - Cu with 30% Sn and llographic examination in a scanning Z5 - Cu2S electron microscope, in the CEMUP, Materials Center at Porto University. e results of this analysis allowed e sample, about 1x1 mm, was re- to consider that the spearhead corres- moved with a mechanical saw, at the ponds to a bronze of biphasic type (a distal end of the spear. e chemical + δ), with a predominance of α phase. analysis focused on the cutting surfa- Given the tin content at this stage, it ce, using a suitable analytical program seems to us that the cooling after soli- for copper alloys, and calibrated by a di cation was processed at high speed, set of certi ed reference materials. For derived, for example, of air cooling. the purpose of observation by scan- ere have been recognized the di- ning electron microscopy, the cutting vision in zones of the internal a pha- section was mounted in epoxy resin, se, which is normal in these materials followed by polishing of the silicon (SCOTT 1991). It is also evident the carbide with sandpaper, and nally in presence of internal oxidized zones, diamond suspension grain of 1 mm. and of a smaller amount of sulphides. As can be seen in Table 1, the results e presence of almost pure copper showed that the artefact was made in (Z3 zone), even if occurring in a rare a binary copper alloy with 88.71% co- form, it seems abnormal to us, althou- pper and 8.6% tin, being this a typical gh possibly motivated by an incomple- composition of the alloys used for the te dissolution between the two metals manufacture of metal objects (SCOTT Cu and Sn. 1991). e analysis of the metallographic

Table 1 - Composition of the alloy Sample N.º Cu Sn Pb Al Fe P S SI LAQ 88,7 8,6 - 1,31 0,13 0,10 0,35 0,80 2015/80 values in % weight

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Fig. 5: Examination in a scanning electron microscope. General appearance of the sample.

Fig. 6: Detail of the metallographic structure of the alloy.

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4. FINAL CONSIDERATIONS which are closer to the results obtained by the Muro’s artefact.  e spearheads attributed to the Later If we take into account the results of Bronze Age, similar to the one subject the archaeometalurgical analysis of the of study, are not very frequent in the spearhead of Gralheira, this once again Northwest of Portugal. However a few proves that the metallurgy of the Later contexts are known, corresponding to Bronze Age of the Northwest of Portu- hoards or isolated nds, interestingly, gal is essentially binary, and well made, all of them associated with mountains. which is in line with what is known In the rst case we have the spear- for the metallurgy of this period in the head of Badim, of similar morpho- North of the country (VILAÇA 1997; logy, which was buried at the base of BETTENCOURT 1998; BOTTAINI the conical hill of Nossa Senhora da 2012). Graça in Monção (MARQUES 1984) and disconnected with the proto-his- toric settlement existing there, located, ACKNOWLEDGEMENTS in fact, at the opposite side of the hill (Marques 1987). Similar nds associa-  e authors thank the Engineer Ma- ted with hills and mountains are Outei- nuel Cunha for ceding the object for ro do Rego, in Lama Chã, Montalegre8, study and for the information provided Quinta do Telhado, in Monte da Penha, with regards to the discovery circum- Guimarães (SAMPAIO 2014), both as- stances. To Vítor Hugo Torres, from sociated with rocky outcrops, and Chão the Museum D. Diogo de Sousa in de Meses, in Barcelos, on the northwest Braga, we thank the stabilization of the slope of the Arefe Mountain9. artefact. Even though we know several spear-  is work was carried out under the heads in the Portuguese NW, only the project: Natural spaces, architectures, two found at Vale Travesso, in Mon- rock art and depositions from the Late talegre, were the subject of analysis of Prehistory of the Western front of Cen- their chemical composition (BOTTAI- tral and Northern Portugal: from actions NI 2012: 49-52).  ese correspond to to meanings - ENARDAS (reference binary copper alloys, with Cu percen- PTDC/HIS-ARQ/112983/2009), su- tages between 84.2 ± 0.9 and 90 ± 1, pported by FCT, Compete and Feder and Bronze Age Hoards of the Western Atlantic facade of Iberia between the Vouga and Ulla Rivers: Contexts and In- 8 Information resulting from the eldwork carried out during ongoing doctoral research of one of us terpretations. (A.M.B.), entitled Bronze Age Hoards of the Western Atlantic facade of Iberia between the Vouga and Ulla Rivers: Contexts and Interpretations. 9 Idem.

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BIBLIOGRAPHY MEDEIROS, Artur Cândido de; Perei- ra, Eurico; Moreira, Armando 1980. AZEVEDO, Pedro A. 1898. “O território Carta geológica de Portugal na escala de «Anegia»”. O Archeólogo Português 1:50.000: notícia explicativa da fol- 4 (7-9): 193-221. ha9-D Pena el. Lisboa: Serviços Geo- BETTENCOURT, Ana M. S. 1998. “O lógicos de Portugal. conceito de Bronze Atlântico na Penín- SAMPAIO, Hugo A. 2014. A Idade do sula Ibérica”. In Susana O. Jorge (ed.), Bronze na Bacia do Ave (Noroeste Existe uma Idade do Bronze Atlântico?, de Portugal). Braga: Universidade do Trabalhos de Arqueologia – 10, Lisboa: Minho (Ph.D esis). Instituto Português de Arqueologia, SCOTT, David A. 1991. Metallography 18-39. and Microstructure of Ancient and BOTTAINI, Carlo M. 2012. Depósitos Historical Metals. Marina del Rey, CA: metálicos no Bronze Final (Sécs. XI- e Getty Conservation Institute in as- II-VII A.C.) do Centro e Norte de Por- sociation with Archetype Books. tugal. Aspectos Sociais e Arqueometa- SILVA, Armando C. F. 1986. A Cultu- lúrgicos. Coimbra: Faculdade de Letras ra Castreja no Noroeste de Portugal. da Universidade de Coimbra (Ph.D Paços de Ferreira: Câmara Municipal thesis). de Paços de Ferreira. COUTO, Maria Helena 1993. As Mine- SILVA, Armando C. F. 2000. “Proto-His- ralizações de Sb-Au da Região Duri- tória e Romanização do Porto”. Al-Ma- co-Beirã. Porto: Faculdade de Ciências dam 2nd s., 9: 94-103. da Universidade do Porto (PhD thesis). SILVA, José da 1963. “Os recintos forti - DGE - DIREÇÃO GERAL DE ECONO- cados de Baltar e do Montemuro”. Lv- MIA. Viso-Porto (Arquivos da Antiga cerna 3: 126-135. Circunscrição Mineira do Norte) – Mi- SILVA, José da 1966. Os recintos forti - nas de Estanho de Rebordosa (lugar de cados e a cultura castreja. Lvcerna 5: Aboim). Processo nº 2. 1839; Minas 519-525. das “Covas de Castromil”. Processo nº VILAÇA, Raquel 1997. “Metalurgia do 2091.1944. Bronze Final da Beira Interior: revisão MARQUES, José A. M. 1984. “Elementos dos dados à luz de novos resultados” para o estudo da Idade do Bronze no Estudos Pré-Históricos 5:123-154. Alto Minho (Ponta de Lança do Castro da Senhora da Graça – Monção)”. Hu- manidades Revista Crítica de Ciências Sociais e Humanas 4: 37-44. MARQUES, José A. M. 1987. “Sonda- gem Arqueológica no Castro da S.ª da Graça (Badim/Sá – Monção)”. Lvcer- na. 2nd s., 2: 41-65.

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