Porphyry and Hydrothermal Cu-Au Deposits: A Global Perspective

The Skouries Porphyry Cu-Au deposit is part of the Kassandra Mining District in the province of Chalkidiki, northern Greece. This world class district is comprised of several large polymetallic replacement deposits and somewhat younger porphyry deposits as well as numerous prospects.
The Skouries deposit is centred on and around a series of small plugs and dykes of highly oxidized syenitic composition intruded during the early Miocene into a series of fine grained schists. The Skouries porphyry syenite system is represented at the surface by a small (180 x 250 metre) elliptical, composite intrusive pipe, and by several EW to NE trending dikes of the same composition, in a zone extending to the south and southwest. The overall alteration mineralization patterns and types are consistent with those known in other deep seated porphyry systems, but in detail the patterns become complicated due to the small size of intrusions. In general, hydrothermal alteration at Skouries occurs as a central silico-potassic zone (usually with very high magnetite content) and a propylitic zone which envelops and partially covers the previous zone. The overall mineralization pattern is also simple with central bornite-chalcopyrite followed outward by chalcopyrite and pyritic zones. The total content of pyrite is quite low at the surface and no leached cap or enriched zone was developed. In soil geochemistry the >550 ppm copper contour conforms closely to the >0.25% Cu at depth and the >150 ppm contour conforms closely to >0.1% Cu. Gold geochemical values are coincident but generally low with >0.1 ppm in rock represented by >20 ppb in soil samples. The magnetic survey data show a very good correlation with copper grade (>0.25% Cu = 1500 gammas over regional background). Skouries contains more than 500 Mt @ 0.47 g/t Au, 0.37% Cu, encompassing 150 to 200 Mt of sharply accentuated copper and gold grades. Since this last geological resource calculation in July, 1998, drilling continued in the southwest porphyry sector with the addition of approximately 40 Mt @ 0.5% Cu, 0.5 g/t Au and 200 ppm Mo.

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