The initial exploration of the Osogovo area was undertaken during the years of the First World War by German geologists. During the period between the two world wars, further exploration was carried out, while in 1954-57 the igneous rocks and many of the mineral occurrences in the area were first described and detailed exploration was undertaken by Geoloski Zavod-Skopje, Geoloski Zavod-Belgrade and Mine Geological Services. This work concentrated almost exclusively on the polymetallic mineralisation at Sasa. Mining for lead, zinc and silver commenced at Sasa in 1966 and subsequently at Toranitza in 1988."

A ground magnetic survey was carried out over the Sasa-Osogovo-Toranitza area in 1971-72 by the Belgrade Geological Survey, which appears to show a weak magnetic low over the main intrusion, perhaps related to fracturing and brecciation within the intrusive.

Phelps Dodge carried out a programme of geological mapping and prospecting over the Osogovo permit area in 2001-02, focussing on the red Ridge intrusive and breccias and on Mechkin Kamen mountain. Stockwork densities were recorded in order to help delimit the stockwork zone and identify the core of the zone. Samples were collected for rock geochemical analysis and for microscopic study. Based on this work, the extent and intensity of the Osogovo intrusive breccia and stockwork zones were established, as outlined in Section 8.1.2 of this report above.

Phelps Dodge then investigated the porphyry copper target at Osogovo by completing four diamond drill holes in 2002. The first hole, PDOC-1, was collared within the quartz-latite to quartz-monzonite intrusive breccia at Red Ridge and drilled at 80_ to the west.  The hole was weakly mineralised to the final depth of 220.1m, with traces of chalcocite, covellite and chalcopyrite logged. It is interpreted that the hole did not penetrate deep enough to intersect the primary mineralised zone, if present. Hole PDOC-3 drilled the same intrusive breccia about 350m to the south-southeast of PDOC-1. This vertical hole also intersected weakly mineralised stockwork-type mineralisation before being stopped at 220.5m depth.

 

PDOC-2 was sited just over 100m southwest of DH-7 (referred to above) , angled at 80° to the southwest. A shallow supergene zone of weak chalcocite-covellite copper sulphides was noted, followed by a moderate to strongly developed quartz-sulphide stockwork within the metamorphosed country rocks, containing 1-3% pyrite, as well as minor copper and molybdenum mineralisation. Further down the hole, from 323.0 to 360.0m, a 37m zone of weakly stockworked country rock assayed 0.16% Cu. The hole finished at 582.0m. An east-west fault is interpreted between this hole and DH-7, which may explain the differences noted between the two holes in tenor and grade of mineralisation.

 

The final hole, PDOC-4, was located near the peak of Mechkin Kamen mountain. It was drilled vertically to a final depth of 668.0m. The hole passed through an extensive zone of generally moderately altered and stockworked country rock, mainly gneisses, to 533m depth. A thin leached cap at the top of the hole was followed by a weak supergene enrichment zone with chalcocite and covellite mineralisation to approximately 100m depth. From 280m depth, the stockwork becomes more pronounced and from there to the bottom of the hole low order pyrite, chalcopyrite and molybdenite mineralisation is seen, assaying generally ~0.1% Cu, ~0.05% Mo, but with a number of substantial intervals of higher grades – see Table 2 below.