Degree Type

Thesis

Date of Award

2010

Degree Name

Master of Science

Department

Geological and Atmospheric Sciences

First Advisor

Paul G. Spry

Abstract

Reduced intrusion-related gold systems are generally characterized by a Au-Bi-Te-W metal assemblage genetically linked to the emplacement of granitoids. The Palea Kavala ore system, Greece, consists of ~150 minor Fe-Mn (PbyZnyAg), Fe-Mn-Au, Fe-As-Au, Fe-Cu-Au, and Bi-Te-Au ore occurrences that occur primarily in quartz-calcite-sulfide veins (hypogene mineralization), or as supergene bodies, in overlapping zones centered on the ~21-22 Ma granodioritic Kavala pluton, which intrudes metamorphic rocks of the Paleozoic Rhodope metamorphic core complex. The pluton consists mostly of granodiorite with lesser amounts of diorite, tonalite and monzodiorite, which was emplaced along the regional E-W trending Kavala-Komotini fault.

The recently discovered, ~4 km long, E-W trending so-called Kavala vein is a sheeted quartz vein system of Bi-Te-Pb-SbyAu mineralization that crosscuts the Kavala pluton and the schists and gneisses of the Rhodope Massif. The Kavala vein system is comprised of quartz with lesser amounts of K-feldspar, plagioclase, and muscovite. Quartz-sericite-pyrite alteration is pervasive but minor kaolinite is also present. Pyrite (~5% of vein volume) contains inclusions of tetradymite (some gold-bearing), bismuthinite, and cosalite. Sulfur isotope values (n = 27) of pyrite from the Kavala and Chalkero veins, as well as pyrite and galena from Garizo Hill Fe-Mn-Pb vein range from -1.9 to 1.0 per mil (with one outlier of -4.6 per mil) and suggest a magmatic sulfur source. Homogenization temperatures (Th) of type I (two-phase aqueous liquid-vapor) and type II (three-phase, H2O-CO2-rich) fluid inclusions that homogenize into the liquid phase in quartz from the Kavala and Chalkero veins range from 216.0y to 420.0yC (n = 216) and 255.7y to 414.0yC (n = 112), respectively. The Th of type III (two-phase aqueous liquid-vapor), which homogenize into the vapor phase, ranges from 210.4o to 323.4yC (n = 28). The salinities of type I and type II inclusions range from 15.9 to 22.6 wt. % NaCl equiv. and 5.5 to 11.2 wt. % NaCl equiv., respectively. Eutectic temperatures of -58.5o to -44.3yC for type I inclusions suggest the presence of appreciable CaCl2 in addition to NaCl. Clathrate melting temperatures for type II inclusions of ~-56.7yC indicate that CO2 is the major component of the gaseous phase. The presence of a zoned metallogenetic district centered on Bi-Te-Pb-SbyAu mineralization within the Kavala pluton and the two high-temperature, high-salinity, immiscible carbonic and aqueous fluids associated with the Kavala and Chalkero veins are consistent with them being part of a reduced intrusion-related gold system.

The Fakos porphyry Cu-(Mo) and epithermal-style Au-Te deposit, Limnos Island, Greece, is hosted in ~20 Ma quartz monzonite and shoshonitic subvolcanic rocks that intruded Paleogene sedimentary basement rocks. Metallic mineralization formed in three stages in quartz and quartz-calcite veins. Early porphyry-style (Stage 1) metallic minerals consist of pyrite, chalcopyrite, galena, bornite, sphalerite, molybdenite and iron oxides, which are surrounded by halos of potassic and propylitic alteration. Stage 2 mineralization is composed mostly of quartz-tourmaline veins associated with sericitic alteration, whereas stage 3, epithermal-style mineralization is characterized by polymetallic veins containing pyrite, chalcopyrite, sphalerite, galena, enargite, bournonite, tetrahedrite-tennantite, hessite, petzite, altaite, an unknown cervelleite-like Ag-telluride, Au-Ag alloy, and native Au. Stage 3 veins are spatially associated with argillic, silicic, and alunitic alteration.

Fluid inclusions in quartz from stage 1 (porphyry-style) mineralization contain five types of inclusions. Type I, liquid-vapor inclusions, which homogenize at temperatures ranging from 189.5 to 403.3yC have salinities of 14.8 to 19.9 wt. % NaCl equiv. Type II, liquid-vapor-NaCl, type III liquid-vapor-NaCl-CaCl2, and type IV, liquid-vapor-hematiteyNaCl homogenize to the liquid phase at temperatures of 209.3y to >410.0y C, 267.6y to >410.0y C, and 357.9y to >410.0y C, respectively. The porphyry-style inclusions are associated with type V, vapor-rich inclusions. Stage 3 quartz contains two types of fluid inclusions, type I, liquid-vapor inclusions that homogenize to the liquid phase (191.6y to 310.0y C) with salinities of 1.40 to 9.73 wt. % NaCl equiv., and type II, vapor-rich inclusions. Mixing of magmatic fluids with meteoric water in the epithermal environment is responsible for the dilution of the ore fluids in stage 3 veins. Eutectic melting temperatures of -35.4y to -24.3yC for type I inclusions in both porphyry and epithermal veins suggest the presence of CaCl2, MgCl2, and/or FeCl2 in the magmatic- hydrothermal fluids.

Sulfur isotope data from sulfides show a range in δ34S of -6.82 to -0.82 per mil and values overlap for porphyry and epithermal sulfides, which suggest a common sulfur source for the two styles of mineralization. The source of sulfur in the system was likely the Fakos quartz monzonite for which the isotopically light sulfur isotope values arose from changes in oxidation state during sulfide deposition (i.e. boiling) and/or from disproportionation of sulfur-rich magmatic volatiles upon cooling. It is less likely that sulfur was derived from the reduction of seawater sulfate or leaching of sulfides from sedimentary rocks given the absence of primary sulfides in sedimentary rocks in the vicinity of the deposit.

Petrological, mineralogical, fluid inclusion, and sulfur isotope data indicate that the mineralization at Fakos Peninsula represents an early porphyry system that is transitional to a later intermediate- to high-sulfidation epithermal gold system. This style of mineralization is similar to porphyry-epithermal mineralization found elsewhere in northeastern Greece (e.g. Pagoni Rachi, St. Demetrios, St. Barbara, Perama Hill, Mavrokoryfi, and Pefka).

Copyright Owner

Andrew Fornadel

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

181 pages

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