GEOLOGICAL CONTROLS ON THE COAL QUALITY OF THE MEQUINENZA SUBBITUMINOUS COAL DEPOSIT, NORTHEAST SPAIN

The results of geological, petrographical, geochemical and mineralogic al studies, performed to determine the coal-forming paleo-environmenta l conditions which gave rise to anomalous enrichments in organic sulph ur, molybdenum and uranium in the Oligocene Mequinenza subbituminous c oal deposit of northeastern Spain, are summarized. This paper demonstr ates the major influence exerted by the paleohydrology of the depositi onal framework on the early diagenetic evolution of the precursor peat deposits. The S, Mo and U enrichments, the preservation of aragonite and chlorophillinite, and the high degree of gelification of the Mequi nenza coal are a consequence of alkaline syngenetic conditions in the depositional environment. Similar conditions can be inferred for many Mesozoic and Tertiary coal deposits in the Mediterranean region (Mallo rca, Sardinia, Hungary, Bulgaria, Serbia, Greece and Turkey). However, the source of sulphur may have been different and have included Trias sic and Early Jurassic sulphate recycling scenarios or volcanic source s, Whatever the source, sulphur enrichment is always influenced by the alkaline depositional environments developed in basins generated duri ng the Alpine Cycle in circum-Mediterranean mobile belts.