PRELIMANARY PETROGRAPHIC AND MICROTHERMOMETRIC STUDIES OF THE DOLOMITES AND SPHALERITE MINERALIZATION OF EL ABED ZN – PB DEPOSIT – TLEMCEN – NORTH WESTERN ALGERIA

El Abed is the eastern part of a broad “Touissit - Boubaker - El Abed: where the two first are in the Morocco territory” district that cover more than 30 kilometers from East to West. This deposit can be attached to large deposits so called “Mississippi Valley Type” or MVT. The deposit is located on the North Western part of Algeria at 70 km southwest of Tlemcen. The mineralization includes "stratabound" and fills of karstic internal sediment. It occurs in Aaleno-Bajocian dolomites. The paragenesis is simple with galena, sphalerite, marcasite, pyrite and chalcopyrite. Gangue minerals are dolomites of different generations, quartz, kaolinite and organic matter. Epigenetic sulphide mineralization occurs as open-space cavity fills and local replacement of internal sediments in carbonate strata. We are particularly interested to study the dolomitization which is exclusively associated to mineralization in "stratabound". Diagenetic dolomites consist to replecment of old calcarenites (allochemes ghost). Greyish dolomite is early, because it is represented by the DI dolomicrite and the DII or zebra dolomite, DIII or dolosparite is replaced by the DIV (dissolution re precipitation phase). Epigenetic Dolomites are represented by the white dolomite which has precipitated in fractures or in vugs DV / DVI. The mineralization is dominant sphalérite with incidentally of the Galena. The preliminary study of primary fluid inclusions of DV and DIV dolomites as well as the sphalerites suggested that the ore fluids that are hot brines (100 to 160°C).

The migration of brines from sedimentary basin transporting metals leached from basement rocks which encountered are trapped in Aaleno-Bajocian dolomites at Oligo-Miocene compression. The structural control and widespread dissolution suggest that the brines were acid and that they were transported into the basin along fractures without much interaction with the carbonate host rock.