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Despite Elevated Gold Grades at the Fakos Prospect (Limnos Island, Greece), Economic Development is Unlikely

Andrew P. Fornadel1, Panagiotis Voudouris2, Paul G. Spry1, and Vasilios Melfos3
1Iowa State University
2University of Athens
3Aristotle University of Thessaloniki

To assess the efficacy of mine development at the underexplored Fakos deposit, for which scant exploration reports show elevated levels of gold, we studied the geology and geochemistry, and evaluated the metallogenesis, of the prospect.

The deposit is hosted in a ~20 Ma quartz monzonite that intruded Paleogene sedimentary rocks, where metallic mineralization formed in three stages. Porphyry-style (Stage 1) metallic minerals consist of base metal sulfides and molybdenite. Stage 2 mineralization is composed of sulfide-poor quartz- tourmaline veins. Stage 3, epithermal-style mineralization, contains base metal sulfides, tellurides, gold, and electrum.

Five types of fluid inclusions exist in Stage 1 veins. Type I, liquid-vapor, homogenize at 190 to 403° C and have salinities of 15 to 20 wt. %. Type II, III, and IV are hypersaline and homogenize significantly higher temperatures than Type I inclusions, and Type V, vapor-rich inclusions. Stage 3 veins contain Type I, liquid-vapor inclusions homogenize at 192 to 310°C and salinities of 1 to 10 wt. %., and Type II, vapor-rich inclusions.

Sulfur isotopes of sulfides range from -6.8 to -0.8 ‰ and overlap for porphyry and epithermal sulfides, suggesting a common source for the two styles of mineralization, likely the Fakos quartz monzonite. Late-stage barite is inferred to have formed during mixing of seawater with magmatic ore fluids.

Fakos is a porphyry copper system transitional to an epithermal gold system that was emplaced along localized faults. However, despite elevated ore grades (≤ 13 g/t gold), the remote location of the deposit likely precludes mine development.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013