Les Ferreres mine, Rocabruna, Camprodon, Girona, Catalonia, Spaini

Regional Level Types
Les Ferreres mine	Mine (Abandoned)
Rocabruna	Village
Camprodon	- not defined -
Girona	Province
Catalonia	Autonomous Community
Spain	Group of Countries

Filling of karstic cavities in Cambrian-Ordovician dolomites with baryte, quartz and Cu-Pb-Zn-Ag sulfides.
The mineralization is located under an erosive surface covered by red beds of Garumnian facies (Late Cretaceous to Paleocene) that also contain baryte disseminations. It consists of metric-size lenticular lenses and irregular bodies within carbonates.
The deposit is cited in documents from 1225, but mining workings developed from the middle 18th century until the 1960s, when the mine was abandoned.

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GEOLOGY

The mineralization of the Ferreres mine is located in a geological region (mantle of Cadí) defined by:
1) Paleozoic series (Cambrian and Ordovician) which were deformed, with folds and thrusts for the Hercynian orogenesis.
2) Granitic intrusions from the late Paleozoic.
3) Mesocenozoic sedimentary materials (Cretaceous – Paleocene), a period in which the whole was affected by the Alpine orogenesis that built the present structure of strata, folds, faults, and thrusts.

The material where the mineralization occurs consists of Ordovician dolomite affected by the Hercynian orogenesis (Upper Paleozoic), in discordant contact with sedimentary Garumnian materials (Upper Cretaceous-Paleocene), which are located around and above the dolomite masses. According to some 1980s studies (Soler, 1983; Soler and Ayora, 1985), the accumulation of materials of the mineralization (essentially baryte and sulphides) was made by filling existing cavities, of karstic origin, inside the dolomite.

But according to subsequent studies (Corbella et al., 2007), the formation of cavities and its filling, takes place more or less at the same time (hydrothermal karst) by geochemical processes of dissolution and precipitation of sulphur-bearing acid-rich hydrous fluids, on the one hand, and in barium and metals (Cu, Zn, Sb,…) from Paleozoic materials from the other hand. These fluids, produced by a continuous process, cause the dissolution of the dolomite, with the formation of cavities and, at the same time or just immediately after, the precipitation of sulphides in the area of contact with the dolomite and the baryte filling of the whole cavity.

The dissolution of the dolomite expresses itself with the formation of cavities, but also with alteration phenomena in areas where there is contact with sulphides. At the bottom of the cavities there are some fragments of dolomite, sometimes surrounded by baryte, presenting different stratification directions and are partially coated and altered by sulphides. This proves that the dolomite was dissolving and collapsing at the same time that sulphides and baryte precipitated into the cavity (Corbella et al., 2007).


The result of all processes are isolated baryte fillings or, more commonly, joined among themselves by fissures, filled in the dolomite and generally developed following the stratification and the diaclasis. The size of these fillings is highly variable (between centimetre-sized to metre-sized) and are formed by the accumulation of spatic aggregates, often with large crystals grown radially from the base of the cavity. In the area of contact of barytes fillings and dolomite, we can find masses of sulphides, with thicknesses varying between millimetre to centimetre sized. These masses of sulphides appear to be more important in the lower parts of the cavities.

Therefore, what we can find on the walls of the galleries are not true baryte and sulphide veins, but the visible part of the baryte fillings, surrounded by the layer of sulphides (largely altered), and the whole fitting within the dolomites, usually very compact. Alteration of sulphides has resulted in the formation of many secondary minerals, which are the main object of the present study. These secondary minerals fill fissures and small geodes within the sulphide layer and on the edges of the contact of this layer with baryte or dolomite.

In addition, there are some sections of the lower levels where there is no dolomite outcrop, but masses of grey schists, which are altered and fragmented. These masses of schists typically appear below the layer of dolomite, which can be clearly seen in some galleries (schist on the walls and dolomite on the ceiling).

Other Regions, Features and Areas containing this locality

References