Sierra Alta

Property and Location

The “Sierra Alta Property” is located in the Municipalities of Allande and Tineo, in the western part of Asturias region, NW Spain. The property is located approximately 65 km west of Oviedo, the Asturias Regional capital, and covers 90 claims totaling 2,500 ha.


Sierra Alta location map

Exploration History

Different companies along time have performed exploration works in the area. The most important contribution was carried out during 1990’s by RíoNarcea Gold Mines. Part of this exploration works include:- geological maps at regional scale (1:10,000) and detailed scale (1:1,000) of the most interesting zones; – geochemical soil survey (identification of 3 km long and 300 m wide anomaly with a peak concentration of 1.2 parts per million of gold); -litho-geochemistry survey of mineralized-altered rocks (up to 338 grams per ton gold).

Antiguos trabajos 1

Roman workings in La Freita

Antiguos trabajos 2

Detail of Roman workings in La Freita

Geology and Mineralization

Gold in Asturias is hosted in 3 belts (Oscos, Navelgas and Rio Narcea) that together form the Hercynian age Cantabrian Zone of the Iberian Massif and occurs in high grade epithermal veins, skarns and as intrusive related gold deposits (IRGD). The Sierra Alta project is located in one of these gold belts, the Navelgas Gold Belt (90 x 20 km).The Navelgas Gold Beltis comprising by Palaeozoic clastic sediments and carbonates units intruded by acid stocks.

Geological mapping during initial programs identified a large number of ancient Roman workings that align for over 10km strike length along a NNE SSW striking structure(La Freita-Carcabón de Orúa fault). These old workings goes from small trenches to large pits, being the largest the “La Freita” pit from where about 29 million tons of material have been mined outby roman ancient methods (i.e. Ruinamontium; Figure 3). Emerita geologists have also identified widespread ferruginous breccias, jasperiod alteration and silicification.

Modelo Mineral

Cross Section and Mineralization Model. Sierra Alta property

Deposit type

The Sierra Alta project is characterized by a sedimentary sequence of Hercinian age which includes also limestone units. The sequence is intruded by acidic stocks in an area along the “La Freita-Carcabón de Orúa” fault. This environment is favorable for Skarn, Hydrothermal and Carling-type deposits. The skarn deposits are form in the contact between the carbonate rocks and the acid stocks. The hydrothermal veins and breccias are found at the upper part of the system. The El Valle-Boinás Carlés deposit, currently in production, constitutes a valid exploration model for Sierra Alta project.


Gold panning in Sierra Alta property area

Panoramica desde abajo

Bottom view of La Freita

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