Page 60 - Handbook of Gold Exploration and Evaluation

Nature and history of gold 41

1.14 Roman mining works in the NW of the Duero Basin and Bierzo Basin
(modified from Perez-Garcia and Sanchez-Palencia, 2000).

Following the Cantabrian War in Spain (19 BC) and during the 1st and 2nd
centuries AD, more than 500 goldmines were operated by the Romans in the
north-west portion of the Iberian Peninsular (Fig. 1.14). An estimate of the total
volume of hard rock and alluvial gold material moved by mining operations in
the NW of Spain during Roman times is given in Table 1.11. This estimate of a
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total of 600,000 m is divided equally between quartz-vein and placer gold
deposits.
The alluvial deposits occurred in Miocene sediments (mainly alluvial fans)
derived from the Cantabrian Mountain and Leon Mountain uplifts, and
Quaternary deposits (principally regolith, fluvial terraces, moraine and fluvio-
glacial. The proximal facies targeted by the Romans is believed to have
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averaged only 100±150 mg Au/m . However, the gold was predominantly fine-
grained); recoveries must have been very low (probably less than 40% overall)
due to the primitive nature of the methods used.