Abstract

The Olympias, Madem Lakos, and Mavres Petres Pb-Zn(Au,Ag) sulfide ore deposits are developed in calcitic-rhodochrositic marbles of the Paleozoic or older Kerdilia Formation, eastern Chalkidiki Peninsula, Northern Greece. Regionally the ore distribution is structurally controlled.The geologic setting of the ores consists predominantly of marbles, biotite-hornblende gneisses, and amphibolites. These rocks have been regionally deformed and metamorphosed to amphibolite facies. This event in the Kerdilia Formation seems to have lasted until the early Tertiary and culminated in anatexis and calc-alkaline magmatism. These phenomena are represented by deformed and undeformed varieties of pegmatites-aplites, lamprophyre dikes, and the 30-Ma Stratoni granodiorite. This stage is also characterized by contact metamorphic phenomena and retrogression to the greenschist facies.Geochemical and mineralogical evidence indicates that the biotite gneisses are of either sedimentary or igneous origin; the amphibolites have been derived from basaltic to basaltic-andesite protoliths with midocean ridge basalt geochemical affinity; the pegmatites-aplites are of anatectic origin from a magma produced at deeper crustal levels; the lamprophyre dikes are considered to be mantle derivatives; and the Stratoni granodiorite has been formed from a magma of hybrid nature consisting of mantle- and crustlike components.The Olympias deposit is generally strata bound or fracture controlled and in places stratiform. It develops along the upper contact of the lower marble unit with the overlying biotite gneiss and within this marble; it strikes north-northeast for 1,500 m, dips 30 degrees to 35 degrees southeast to a depth of at least 300 m, and has an average thickness of 12 m. The contacts between the ore mineralization and the host marble are sharp, concordant or discordant to the foliation. However, in all cases a chemical reaction front in the marble is present.The Olympias deposit occurs in undeformed and deformed varieties. The former predominates and is present in several forms such as cavity- and fracture-filling, banded, or disseminated. The latter is of limited presence and occurs as banded or in veins exhibiting shear folding and brecciation. S-type deformation in skarns near the 30-Ma Stratoni granodiorite and regional deformation-metamorphism data may place the time of ore formation in the Tertiary period. The same type of deformation is also observed in skarn minerals closely associated with the ore at the Madem Lakos deposit.The main ore mineral paragenesis at Olympias regardless of deformation is pyrite, galena, sphalerite, and arsenopyrite with quartz, calcite, and rhodochrosite as gangue minerals.Lead isotope compositions of deformed or undeformed ore galenas indicate a crustal source and are homogeneous and identical with K feldspar leads from the Stratoni granodiorite and other Tertiary Greek orogenic granites. These data suggest that the source of the ore leads should be sought in the source of the magmas. Moreover, the crustal affinity and homogeneity of the studied lead isotopes are in agreement with the crustal component contributing to the Tertiary granite formation, even though leaching of lead from crustal rocks cannot be completely disregarded.The narrow range of sulfur isotope ratios in all the sulfides, and their proximity to 0 per mil, combined with the relatively limited occurrence of sulfates (e.g., gypsum) at Madem Lakos may suggest the combined effects of high reduced/oxidized sulfur species ratios, relatively high temperature, and small delta 34 S initial -delta 34 S (sub H 2 S) values, thus suggesting an igneous origin for the sulfur. Fluid inclusion studies in ore-related quartz from Olympias have shown that both deformed and undeformed ore varieties have formed by the same H 2 O-dominated CO 2 -bearing fluids of low to medium salinity, at temperatures of 300 degrees to 400 degrees C, and pressures of 300 to 800 bars. Preliminary fluid inclusion data from Madem Lakos show higher homogenization temperatures up to 480 degrees C and complex salt (NaCl-KCl-CaCl 2 ) contents.Oxygen isotope analyses of ore-related quartz and calcites combined with thermometric data from fluid inclusions and arsenopyrite composition suggest that the mineralizing fluids were of either magmatic or metamorphic derivation with late involvement of meteoric waters. Oxygen and carbon isotope analyses from upper marble-, host marble- to ore-related calcites show a depletion primarily of oxygen indicating an isotopic exchange with infiltrating H 2 O-dominated mineralizing fluids. This depletion is correlatable with the degree of hydrothermal alteration expressed by enrichment in the ore host marble compared with the upper marble horizon.Bulk ore compositions in terms of Cu-Pb-Zn, Cu-Pb+Zn-AgX10 3 ternary diagrams, and Pb-Ag relations show a similarity of the Olympias with the skarn replacement ore type, rather than with the sediment-hosted or the volcanogenic Pb-Zn types. These data, together with data from mineralogical and fluid inclusion studies, suggest that Olympias is predominantly a distal (replacement), whereas Madera Lakos is a proximal (skarn) phase of a skarn replacement ore system.Therefore, our preferred interpretation is that both deformed and undeformed ore varieties at the Olympias (also presumably at Madem Lakos) deposit formed during the same Tertiary skarn replacement metallogenetic event from fluids of primarily magmatic derivation through reaction with the host marbles at low pressures (300-800 bars) and relatively high temperatures (300 degrees -400 degrees C).

First Page Preview

First page PDF preview
You do not currently have access to this article.