The geology of the northern part of the apliki Cyprus-type ore deposit

Abstract

The Apliki copper deposit, in the Troodos ophiolite complex of Cyprus, is part of the Skouriotissa mining district. Mining activity at Apliki has resulted in the production of 1,650,000 tons of copper ore. The mineralization is hosted within the sequence of Lower Pillow Lavas of the Troodos ophiolite complex in the western part of the Solea graben. Plagioclase, pyroxenes (augite), magnetite and ilmenite, and rarely olivine are the main magmatic mineral components. The prevailing secondary minerals are celadonite, calcite, analcime and quartz which occur within amygdules or are dispersed within the rock matrix. The mineralized zone is bounded by two N–S striking sub–parallel faults and is, therefore, controlled by local structures which allowed access to the hydrothermal fluids. The basaltic Pillow Lavas at Apliki possess the same low-temperature regional scale alteration as the sequence of Lower Pillow Lavas of the Troodos ophiolite. In the mineralized zone the following facies have been identified: (a) A stockwork zone (b) Veins of amorphous silica (c) Veins of gypsum (d) Oxidized vein of massive mineralization (“red zone”) (e) Oxidation zone The Apliki deposit is associated with cupriferous massive sulphide which has been mined out. The Apliki mineralization, presently exposed in the examined area, is a typical example of stockwork type sulphide mineralization, with more intense presence in the lower levels of the northern wall, where the semi–massive and massive ore are preserved. The stockwork ore is hosted within brecciated chloritized lavas. Weak silicification is observed in the upper parts of the brecciated lavas. Red jasper is spatially associated with the mineralized lavas and occurs as veins or open– space fillings within the mineralized zone. Pyrite, marcasite and chalcopyrite are the predominant ore minerals, whereas bornite, sphalerite, galena, and barite are accessories with quartz as the main gangue. Goethite, hematite, chalcocite, covellite, and Fe–, Cu–, Pb–, Al–, and Ca–sulphates were formed in the supergene environment. The sampling on the northern and southern wall, of the existing opencut, took place along a series of traverses based on a combined trench and rock-chip sampling method so to achieve the best representation of the samples taken. The spatial distribution of the major elements of the ore (Ag, As, Au, Cd, Co, Cu, Fe, Ni, Pb, S, Se, Sb and Zn) in the northern part of the opencut demonstrates an enrichment next to the western fault and at areas where the semi–massive ore is present. Similar work was carried out on the southern part with much lower concentrations, a fact that reflects the limited occurrence of disseminated ore in that region. The spatial distribution of the major elements throughout the Apliki deposit has demonstrated that the western fault may be the one which is the controlling structure, while the eastern one is the boundary for a gradational passage into the Lower Pillow Lavas. Gold grade does not exceed 0.1 g/t, while copper grades ranges between 0.01 to 3.5 wt. % and sulfur between 0.1 to 16 wt. %. Veins of gypsum, with a direction almost parallel to the western fault, and vein–like amorphous silica bodies both occur close to the western border within the mineralized zone. The “red zone”, with an N–S orientation, constitutes probably an oxidized vein of pyrite–chalcopyrite. The mineralogical assemblage of Apliki oxidation zone (iron oxides and hydroxides, cuprite) reflects almost neutral pH conditions, a fact which is the result of insufficient amount of pyrite which produces low pH supergene solutions. The spatial distribution of copper and its content, which is almost the same with the respective one of primary sulphide mineralization, demonstrate the limited mobility of copper that instead of leaching and moving downwards is concentrated to the oxidation zone.