Estudio analítico de los materiales arqueometalúrgicos procedentes de Los Castillejos de Alcorrín (Manilva, Málaga). Yacimiento del Bronce Final/Inicio de la Edad del Hierro en el entorno del Estrecho de Gibraltar
https://doi.org/10.34780/3dun-x4wa
Abstract
Some iron slags were found in 2004 at Los Castillejos de Alcorrín, in the southern front
of its fortification (stratigraphic units 11, 12 and 13). This site dates back to the end of the
Bronze Age and is strongly linked to the Phoenician sphere of influence.
An in-depth analysis of the slags was carried out in 2011 as part of a German-Spanish
cooperation project run by the German Archaeological Institute of Madrid, in collaboration
with the Spanish National Research Council (CCHS-CSIC, Madrid) and the Deutsches
Bergbau-Museum of Bochum.
According to the results obtained, most of the slags can be interpreted as the subproduct
of iron production by smelting complex ores. Only two samples from UE 13 have been
interpreted as post-reduction slags. This finds are particularly noteworthy as they are among
the earliest evidence of ferrous metallurgy in Western Europe.
Both smelting slags from UE 11 and UE 12 and post-reduction slags from UE 13 belong
to the same chronological phase and have similar microstructural features.
All the samples analysed are fayalite-rich slags with low content of iron oxide, being the
only exception CALC-13 S1-1. The matrix of these specimens, with well-crystallised fayalite,
suggests that the slag melted enough to separate from the iron bloom. Their microstructure
is similar to the one of tap slags of later periods but their morphology is different as these
last usually have a surface with wrinkles and other typical indicators of flow. Tap slags are
common finds on the Iberian Peninsula only in Roman times; in fact, Alcorrín slags seem to
have solidified inside the fire structure and not have been tapped out. Therefore, considering
their early dating, the high quality of the slags is particularly noteworthy as the loss of iron
is quite low. This can be explained by the nature of the host rock of the ores processed at
the site that consisted mainly of quartz. The high SiO2 content provided by host rock was
sufficient to react with the iron oxide to form fayalite, working as fluxing agent to promote
the formation of a low melting point slag.
At present, for the 8th century BC there is no clear evidence that flux agents were intentionally
added to metallurgical processes. Contemporary slags usually have a higher loss of
metal, either in the form of iron oxide or metallic inclusions. Slags similar to those presented
here are known only during the Iberian period, that is from the 5th century BC.
In the case of the slags form Alcorrín, the temperatures in the furnace had to be well
controlled and the conditions were reducing enough to maintain the high arsenic contents
detected in the metallic phases of the slags, since arsenic easily oxidises and evaporates. Hence,
it has to be supposed that closed pyrometallurgical structures were used at site.
In 2011 the DAI department of Madrid initiated an interdisciplinary project to answer the
question whether at the time of Alcorrín’s occupation, that is between the end of the 9th and
the end of the 8th century BC, local mining resources were being used and what type of ores
were exploited. With this aim, prospecting surveys were carried out in an area of about 30
km around Los Castillejos de Alcorrín in order to trace evidence of ancient mining activities
in the region and to carry out a characterisation of local ore deposits. The collected samples
are currently being examined at the Laboratory of Materials Science of the German Mining
Museum in Bochum (Germany) by means of X-ray diffraction (XRD) and inductively coupled
plasma mass spectrometry (ICP-MS). Also, lead isotope composition (LIA) of the samples
is being measured at the Institute of Earth Sciences of the Goethe University in Frankfurt
am Main to perform a provenance study. The analytical results will fill a gap in the research
on this topic; in fact, the importance of the mining region situated at east of Gibraltar has
remained completely unnoticed, as all relevant studies on mineral exploitation for this period
focused on Huelva province and its ore-rich hinterland.
Both the mining district around Los Costillejos de Alcorrín and the other mountain
ranges of the region, which go from the Serrania de Ronda to the Montes de Malaga, are
characterised by a high complexity of its mineralisation with a noticeable polymetalism. Therefore,
the presence of elements in the analysed slags such as nickel, arsenic, chromium, etc.
is not surprising, suggesting that local resources could have been used in Alcorrín, possibly
coming from the nearby Sierra Crestellina, Sierra Utrera or Sierra Bermeja.
There is also clear evidence of metallurgical activities in other settlements of the region,
such as the slags and metallurgical vessels found at contemporary Acinipo and Ronda, situated
in the upper stream of the Guadiaro River, that support the possibility of an ancient
exploitation of ore deposits in the Serrania de Ronda.
The evidence of metallurgical activities, in particular of iron production, at Los Castillejos
de Alcorrín, Acinipo and Ronda, shows how quickly technological innovations coming from
the Near East could spread through the hinterland. This rapid technology transfer can only
be explained by close contact between local communities and Phoenicians. In the Iberian
Peninsula this interaction made it possible to effectively exploit local resources and to use
the ›imported‹ technology for a successful groundbreaking production that went beyond the
local context to be incorporated in the new trans-Mediterranean economic power unfolding
at the time. Autochthonous sites like the fortified settlement of Los Castillejos de Alcorrín
may have fulfilled a key function in these trade networks.
Keywords:
Los Castillejos de Alcorrín, Late Bronze Age, Early Iron Age, Phoenicians, colonisation, economy, trade networks, tecnology, slags, metallurgy, iron, bronze, SEM-EDX, XRD, ICP-SFMS