Castilla la Mancha, Spain

Main commodities: Hg
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The Almadén mercury mine is located in Castilla la Mancha province of Spain, some 120 km north of Cordoba.

Almaden is the largest known mercury source in the world.   A series of less significant mines are also known in the surrounding district.   Grades have ranged from 7.6% Hg in 1796, to 5.8% Hg in 1944 to 1.0% Hg in 1980.   The deposit has yielded 8 million flasks (1 flask = 34.473 kg, or 76 lb), or 275 000 tonnes of mercury, approximately one third of historical world production.   This has been extracted from approximately 13.5 million cubic metres of ore.   Mining has taken place in the district for over 2000 years.

The geology in the area comprises a 6000 to 7000 m thick Proterozoic basement comprising a lower monotonous greywacke slate sequence, unconformably overlain by a similar sequence which also includes conglomerates, grits and limestone intercalations.   These are in turn overlain above an angular unconformity by a 2700 to 3000 m thick Lower Palaeozoic (Silurian) package of quartzarenite, rhythmic sandstone-shale alternations and black shale with intercalations of minor limestone and dolomite, and thick, abundant mafic volcanics.

There are four conspicuous quartzite horizons, the third (from the base) of which, the 60 m thick Criadero Quartzite, is the host to all of the significant mercury ore occurrences.   The Criadero Quartzite is composed of two quartzite bands, an upper black and a lower white unit separated by a shale band.   In the mine area the footwall is composed of shales and the hangingwall is a sequence of alternating detrital sediments and spilitic volcanics.

The ore is stratabound and impregnates the vertical Criadero Quartzite following stratification at three positions, one at the top of the lower quartzite, the other two in the upper member. In the plane of the host on all three levels the orebody has an oval shaped with lateral extents of around 400 m and thicknesses of 3 to 8 m and a vertical dimension of around 600 m.   In longitudinal projection all three closely occupy the same lateral and vertical intervals.

Ore occurs as pyrite and cinnabar occurring as massive accumulations, stockwork veins, impregnations (between or within quartz grains), in healed fractures or within pyrite grains.   The mineralisation does not extend outside of the well defined orebodies, nor are there apparent roots.   In the upper levels of the mine the Criadero Quartzite is faulted against a 60 m thick, 300 m diameter pebble breccia body (possibly related to the hangingwall volcanic activity) known as the Frailesca, which has minor cinnibar and pyrite in quartz and dolomite veining, and adjacent to the Criadero Quartzite it is mineralised over very small volumes.

For detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1989.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Hernandez A, Jebrak M, Higueras P, Oyarzun R, Morata D, Munha J  1999 - The Almaden mercury mining district, Spain: in    Mineralium Deposita   v34 pp. 539 - 548
Higueras P , Munha J, Oyarzun R, Tassinari C C G and  Ruiz I R  2005 - First lead isotopic data for cinnabar in the Almaden district (Spain): implications for the genesis of the mercury deposits: in    Mineralium Deposita   v40 pp 115-122
Higueras P, Oyarzun R, Biester H, Lillo J, Lorenzo S  2003 - A first insight into mercury distribution and speciation in soils from the Almaden mining district, Spain: in    J. of Geochemical Exploration   v80 pp 95-104
Higueras P, Oyarzun R, Lunar R, Sierra J, Parras J  1999 - The Las Cuevas deposit, Almaden district (Spain): An unusual case of deep-seated advanced argillic alteration related to mercury mineralization : in    Mineralium Deposita   v34 pp 211-214
Jebrak M, Higueras P L, Marcoux E, Lorenzo S  2002 - Geology and geochemistry of high-grade, volcanic rock-hosted, mercury mineralisation in the Nuevo Entredicho deposit, Almaden district, Spain: in    Mineralium Deposita   v37 pp 421-432
Jebrak M, Huigueras P L, Marcoux E, Lorenzo S  2002 - Geology and geochemistry of high-grade, volcanic rock-hosted, Mercury mineralisation in the Nuevo Entredicho deposit, Almaden district, Spain: in    Mineralium Deposita   v37 pp 421-432
Saupe F  1990 - Geology of the Almaden Mercury deposit, province of Ciudad Real, Spain: in    Econ. Geol.   v85 pp 482-510

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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