GEOLOGY OF THE ALMADEN MERCURY DEPOSIT, PROVINCE OF CIUDAD-REAL, SPAIN

Almaden is the largest known mercury deposit in the world. It is formed by three lenticular strata-bound cinnabar impregnations in the two quartzite members of the Criadero quartzite formation of Lower Silurian age. The most probable source of mercury is the Ordovician black shales rather than a positive mercury anomaly in the mantle. Data suggest that mercury may have been transported as a sulfide complex and/or as Hg 0 (aq). The deposit and its host rocks were folded vertically and faulted during the Hercynian orogenesis. The regional metamorphism is of very low grade (210°-270°C, 1 kbar). A sequence of events which best accounts for the various field and laboratory observations is presented. -from Author