Summary:
The mineral deposit type at Ilovica is “Alkaline Copper-Gold Porphyry”. The deposit has characteristics which are typical for this deposit type. The mineralisation is spatially, temporally and genetically associated with hydrothermal alteration of the intrusive bodies and host rocks.
As is typical of this deposit type, stockworks, veinlets and disseminations of pyrite, chalcopyrite, bornite and magnetite occur in large zones of mineralisation in and adjoining porphyritic intrusions of diorite composition.
Subsequent supergene leaching/enrichment and advanced argillic alteration have overprinted the typical hydrothermal alteration and mineralisation pattern in the upper portion of the deposit.
Ilovica is a porphyry copper-gold deposit, located in a northwest-southeast striking Cenozoic magmatic arc, that covers large areas of Central Romania, Serbia, Macedonia, Southern Bulgaria, Northern Greece and Eastern Turkey.
The Ilovica porphyry system is approximately 1.5 km in diameter and is associated with a poorly exposed dacite-granodiorite plug, emplaced along the north-eastern border of the northwest-southeast elongate Strumica graben. The exact location of the deposit is controlled by major north-south cross cutting faults and minor northwest-southeast faulting, parallel to the faulted border of the graben.
The Strumica graben is a typical post-collision extension structure, approximately 30 km by 10 km in size, and up to more than 1 km in depth. The graben has been filled with terrigenous clastic sediments and felsic volcanic rocks over the last 40 million years.
At surface, the Ilovica intrusive complex consists of a central dacitic breccia diatreme, approximately 1.3 km in diameter. The diatreme is intruded by at least one dacite and two granodiorite porphyry stocks that have generated several hydrothermal pulses, resulting in widespread, multi-phase veining within a mineralised stockwork.
The main sulphide mineral at Ilovica is chalcopyrite, followed by pyrite and secondary copper sulphides such as chalcocite, covellite and bornite. Molybdenite, galena and sphalerite are present in minor amounts, and occasional traces of sulphosalt minerals such as tetrahedrite-tennantite and tellurides of gold and silver are observed.
High temperature oxide mineralisation such as magnetite, dominates at depth, associated with pyrrhotite and chalcopyrrhotite in what is interpreted as the core of the system.
A variety of iron hydroxide group minerals are largely developed within the oxidation and cementation zones. Very occasionally gold nuggets are observed at the base of the oxidation zone.
Ilovica was known historically for minor lead-zinc (and minor copper) and gold occurrences (Cifliganec, 1993), confined to distal and peripheral silica-iron oxide and silica-alunite bodies outside of the pervasively-altered intrusive complex. Deep oxidation and leaching (up to 150 m) of the topographicallyelevated intrusive complex obscured its sulphide content.
The only visible evidence of copper mineralisation at surface includes: Traces of enargite found in one ledge; very rare green copper oxides, and thin chalcocite coatings on sparse un-oxidised pyrite deposits exposed in a creek below the leached cap to the west of the porphyry. Since the start of detailed exploration on the Property, copper mineralisation has become more obvious on surface, on newly bulldozed drill-roads.
Subsurface porphyry copper-gold mineralisation is expressed at surface by a limonitic, leached stockwork zone approximately 900 m by 600 m in size, containing 0.08 to 0.70 ppm Au, 50 to 450 ppm Cu and 10 to 128 ppm Mo.
At the highest elevations, central portions of this leached cap contain up to 50 to 100 quartz and limonitequartz veins per metre, comprising up to 25% of the rock volume, within a sericitised and intensely (supergene) clay-altered matrix.
Quartz-dominant veinlets are largely devoid of sulphide cavities and have the texture of both discontinuous veins as well as linear, centre-line veins.
Small exposures at lower elevations (circa 550 m) on the western side of the stockwork zone contain 3 to 7% veinlets and disseminated magnetite, approximately 1% goethitic limonite, and lesser quartzmagnetite veinlets, within a silicified, chloritised matrix, likely representing intermediate argillic overprint of former K-silicate alteration.
Ground magnetic surveys clearly define the subsurface magnetite alteration as a roughly north-northeast elongated, 80 to 1600 nT magnetic high, roughly 800 m long and up to 300 m wide, which appears to plunge to the east and south. Peripheral portions of the overall stockwork zone are characterised by sparse, hairline pyrite fractures with quartz-sericite halos, corresponding to D-type veins.
Surface rock chip sampling, limited drilling, and to a lesser extent soil sampling define a large body containing 0.1 to 1 ppm Au coinciding with the zone of stockwork veining.
Hypogene copper grades greater than 0.15% are largely due to disseminated chalcopyrite, which appears largely confined to the western two-thirds of the stockwork zone. The hypogene copper mineralisation is characterised by the presence of magnetite (+martite), chlorite and a relict biotite -K feldspar groundmass. The pyrite and chalcopyrite are usually present in equal proportions. There is an increase in the proportion of pyrite in the eastern zone of the porphyry at higher elevations, along with more intense phyllic/ argillic alteration, and an absence of magnetite.
A supergene-enriched zone ranging from 9 to 70 m in thickness and containing 0.25 to 0.69% Cu as chalcocite and covellite represents enrichment of about 1.5 to 3 times the hypogene grades.
The leached cap generally contains approximately 150 ppm Cu. Molybdenum averages 20 to 80 ppm throughout the copper/ gold mineralised zone and is present largely as molybdenite in quartz veinlets that lack regular distribution.