The geochemistry of carbonate-hosted Pb-Zn-Ag mineralization in the Lavrion District, Attica, Greece: fluid inclusion, stable isotope, and rare earth element studies

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2008-01-01
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Bonsall, Todd
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Carbonate-replacement Pb-Zn-Ag deposits in the Lavrion district, Greece, are spatially related to a 7 to 10 Ma granodiorite intrusion and various sills and dikes of mafic to acid composition. The Plaka granodiorite contains porphyry molybdenite mineralization and is spatially associated with a Cu-Fe skarn. Carbonate-replacement deposits occur predominantly in marbles (Upper and Lower marble of the Basal Unit), Kaesariani schists, and along a major detachment fault. Orebodies are mainly manto-style, but mineralization also occurs in veins. The mineralogy of carbonate-replacement deposits is dominated by base metal sulfides and sulfosalts of Ag, Bi, Sn, Sb, As, and Pb, particularly at Plaka and Kamariza. Carbonates are intergrown with earlier sulfide and sulfosalt mineralization, but are more abundant late in the paragenetic sequence with fluorite and barite. Fluid inclusion studies of sphalerite, fluorite, calcite, and quartz in carbonate-replacement deposits suggest that they were deposited in thermal pulses (132°-365°C) from CO2-poor, low- to moderately-saline (1 to 20 wt% NaCl equiv) fluids.;Carbon and oxygen isotope compositions of calcite (delta13C = -15.6 to -1.5‰ and delta18O = -9.2 to 17.3‰) intergrown with sulfides reflect variable exchange of the ore-bearing fluid with the Upper and Lower marbles and proximity to the Plaka granodiorite. Post Archean Australian Shale (PAAS)-normalized rare earth and yttrium (REY) patterns of the Upper and Lower marbles, and calcite intergrown with sulfides show positive Eu and negative Ce anomalies as well as Y/Ho ratios between 40 and 80. Normalized REY patterns of fluorite also have positive Eu and negative Ce anomalies. Such anomalies for both the carbonates and fluorite reflect the high pH or low fO2 conditions of the late-stage hydrothermal fluids and the likely derivation of Ca for these minerals from marine carbonates (precursors of the Upper and Lower marbles).;The range of sulfur isotope compositions for sulfides (delta 34S = -4.9 to 5.3‰, with one outlier of 9.4‰) is due to a magmatic sulfur source and a possible contribution of reduced seawater sulfate). Assuming an average temperature of 250°C, as based on fluid studies, sulfides in carbonate replacement deposits were deposited at values of log fO2 = -41 to -36, and a pH = 5.8 to 9.1. Sulfur isotope compositions of barite (delta34S = 17.2 to 23.7‰) reflect a seawater source. The carbonate replacement deposits resemble manto-type sulfide deposits in Mexico, central Colorado, Nevada, and northern Greece.

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Geological and atmospheric sciences;Geology;
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