234 Economic Geology (Posters)

Wednesday, 31 October 2007
1:30 PM - 5:30 PM

GEOLOGY, MINERALOGY, AND GEOCHEMISTRY OF CARBONATE-HOSTED BEDDED REPLACEMENT LEAD-ZINC-SILVER DEPOSITS IN THE LAVRION DISTRICT, GREECE

Paper number: 234-1
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Carbonate replacement Pb-Zn-Ag deposits (CRDs) in the Lavrion district, Greece, are spatially related to an Upper Miocene granodiorite intrusion (7 to 10 Ma) and various sills and dikes of intermediate to acid composition. The Plaka granodiorite contains low-grade porphyry molybdenite mineralization and is spatially associated with a Cu-Fe skarn. CRDs 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 CRDs 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 suggest that CRDs were deposited in thermal pulses (132o-365oC) from CO2-poor, low- to moderately-saline (1 to 20 wt% NaCl equivalent) fluids.

Carbon and oxygen isotope compositions of calcite (δ13C = -15.6 to -1.5‰ and δ18O = -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. PAAS-normalized rare earth and yttrium (REY) patterns of the Upper and Lower marbles, and calcite intergrown with sulfides all 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 (δ34S = -4.90 to 9.38‰) is due to a mixed sulfur source (magmatic and reduced seawater sulfate) and to sulfide deposition over a relatively small range of fO2 conditions from neutral to moderately high pH hydrothermal fluids. Sulfur isotope compositions of barite (δ34S = 17.24 to 23.68‰) reflect a seawater source. The CRDs resemble carbonate-hosted sulfide deposits in Mexico, central Colorado, Nevada, and northern Greece.