NON-SULFIDE ZN MINERALIZATION IN EUROPE: A POSSIBLE RECORD OF POST-COLLISIONAL WEATHERING

European non-sulfide Zn ore deposits represented the historical basis for the zinc mining and smelting industry. Based on their geological characteristics, they have been assigned to the Calamine group, derived from the alteration of carbonate-hosted MVT and Sedex deposits.

The non-sulfide mineralization, consisting mostly of an association of smithsonite, hydrozincite and hemimorphite, is related to the oxidation of primary sulfides under a warm and humid climate, and to their preservation as replacement aggregates and karst-cavity infillings. Their genesis is related to tectonic uplift subsequent to primary mineralization, which promotes oxidation and the development of karst systems, as well as to brittle fracturing of the host rock, which favours the flux of oxidizing fluids and the mobilization to a favorable depository.

The principal exploited orebodies (at the moment of no economic significance) occur in Belgium, Poland, South West Sardinia and Spain. Minor occurrences have been recorded in the East Alpine district, in Greece and in the British Isles. The Belgian deposits, the Irish and the Sardinian non-sulfide ores, replace stratabound deposits hosted in Paleozoic carbonates. The Calamine ores from Poland, Northern Spain, Greece and Eastern Alps, are derived from the alteration of Mesozoic-hosted primary sulfide bodies. In most of these deposits, the depths of maximum oxidation, as well as the mineralogical zoning of the newly formed minerals, point to repeated weathering processes related to different geological periods.

It might be postulated that, for at least part of the Paleozoic-hosted primary sulfide deposits, the weathering process leading to the formation of non-sulfide mineralisation could have been initiated after the Variscan collision, followed by uplift and erosion. For the Mesozoic-hosted orebodies, however, the alteration leading to the formation of the Calamine ores, should be viewed in association with the late- to post-Alpine uplifts and denudation which took place from Eocene onwards.