DEFINITION OF STRUCTURAL CONTROLS ON FORMATION OF LODE DEPOSITS OF ASSOCIATED TO MAYOR OTU SHEAR ZONE FAULT SYSTEM AT EL LIMON AU VEIN, ZARAGOZA - ANTIOQUIA, COLOMBIA

The region of interest is characterized by the occurrence of a sequence of metamorphosed Paleozoic rocks of the Cajamarca complex, which were intruded by Jurassic quartz-diorites and granodiorites associated to the Segovia batholith. All these units are covered by latest Tertiary and Quaternary alluvial deposits. In this geological context emplace a series of Au – Ag veins composed of pyrite, Pb-sulfides (galena) and sphalerite with quartz. These Veins mainly define NS trends and dip with varying inclinations to W.

To El Limon deposit has been predicted by Lopez (2004) and Monterroza (2005), stressing a direct relationship with the dynamics of the OTU fault and its associated secondary structures. This approach has been corroborated by detailed survey geological mapping during field work, showing that the structures in which the veins are located with variated width and mineralization (N05-10W/15-20W and N05-15W/30-45SW) but very well defined trends (fluid flow in cracks system associated with shear Zone - Riedel?) correspond to two overprinted Riedel shear systems and apparent shear zones with two temporal occurrences consistent with a very expressed change in the system of regional stress. That can be very important to wing cracks and development of schelones as veins, and veinlets as fractures. On the planes of the El Limon vein and other secondary veins, as well as faults that cut the vein, could be found gouge development, which has abundant sulfides and calcite.

To the East of the area can be found phyllonites and mylonites marking the trace of the OTU fault, with an obvious shear zone trend N10-30W and about 50m wide. There can be observed kinematic indicators showing a dextral movement, in the top of this shear zone may be found a folded and faulted alluvial terrace (not known the age of these deposits, thus to be able to know the age of the last movement) with about 60m of difference with the current Juan Vara creek level, gauge development on the veins and local faults, shows a clear recent tectonic activity in the area, the structures show that this last movement of the its fault was a OTU fault reversed displacement. All the collected evidence of structural, lithological and mineralogical nature associated with El Limon Deposit gives insights that this corresponds to a Shear Zone Hosted Orogenic Gold Deposit.