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District-scale geology and controls on mineralization, Pataz gold field

Pataz gold field, Pataz

This 12 month post-doctoral research programme was funded by Poderosa to map the geology (at 1:25 000) of the Pataz district, where the company operates several undergorund gold deposits (<4 Mill oz Au) hosted by the Pataz batholith in the underexplored Eastern Andean Cordillera of Peru.  The goal of this applied research was to determine the controls on mineralisation and propose exploration targets based on the results of this investigation. 

The CET produced the first detailed map of the Pataz district, recognising in the process previously unrecorded stratigraphic units and geological relationships  Three new SHRIMP U-Pb in zircon ages of  intrusions in the Pataz district were obtained to constrain the magmatic history of the district.  The new geological map was used as the basis to determine the distribution of far field stress axis during the Carboniferous mineralisation event. This "stress-mapping" was conducted in collaboration with Dr. Juhani Ojala.  Whole-rock geochemical samples were obtained to determine the origin and metallogenic affinities of the Pataz batholith.  ASD analyses of diamond core samples were carried out to document in detail the hydrothermal alteration mineralogy and zones associated with batholith-hosted gold mineralisation.  Results of the mapping showed that the main gold-producing veins are concentrated around dilational jogs and step-overs on the fault-bound western margin of the Pataz batholith.  The batholith-bounding faults dip steep and were poorly oriented for reactivation during the Carboniferous shortening event, leading to fracture and vertical exension in the adjacent, competent batholith intrusions.  Stress modeling identifed several relatively unexplored areas, where Carboniferous gold mineralisation could be predicted.  The ASD analyes showed that proximal alteration around mineralised veins are phengitic, in contrast to distal muscovite and illite.  It was concluded that the Pataz batholith was an unlikely source for the ore fluid because the NE-dipping contacts were deformned by ductile deformaton at relatively high temperatures prior to uplift and formation of the auriferous veins.