Intermediate sulfidation epithermal gold-base metal deposits in Tertiary subaerial volcanic rocks, Sahinli/Tespih Dere (Lapseki/Western Turkey)

Abstract

Gold in the Sahinli and Tespih Dere intermediate sulfidation gold-base metal deposits in Western Turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures, including plumose quartz, vug infills, comb and cockade textures and matrix-supported milled breccias. The total sulfide content of the veins in the area is variable ranging from < 1% to 60% and is dominated by pyrite, galena, sphalerite and chalcopyrite. Sphalerite is Fe-poor (0.6 to 1.4 mol% FeS). Minor amounts of Ag-rich tetrahedrite are present. Primary hydrothermal alteration minerals include illite/muscovite, mixed-layer illite/smectite (11.6 Å) and clinochlore towards the east and, alunite, dickite/nacrite and pyrophyllite towards the west at Sahinli; major illite/muscovite and dickite occur at Tespih Dere and Sarioluk, respectively. Fluid inclusions in main-stage quartz at Sahinli are only liquid-rich, with homogenization temperatures ranging from 220 to 322 °C and the majority of T h values between 250 and 300 °C. Salinity ranges from 4.3 to 6.9 wt.% NaCl equiv. First ice-melting temperatures ( T mf) between −24.5 and −19.0 °C indicate that the fluids were dominated by NaCl – H 2O during mineralization. The relatively higher average T h at the Tespih Dere deposit (295 °C) is attributed to a relatively deeper level of exposure. Calculated δ 18O values indicate that ore-forming hydrothermal fluids in the study area had δ 18O H2O ranging from + 1.1 to + 9.7‰ (average = 3.8‰), strongly 18O-enriched compared with present-day hydrothermal meteoric water in the area ( δ 18O = −8.5‰). δD values of fluid inclusions in quartz range from −58 to −93‰ and δD values of clay minerals and alunite from −40 to −119‰. δD values from intermediate argillic alteration (average = −68‰) in the study area are very similar to δD values of the present-day local geothermal system (average δD = −54‰) whereas δD values from advanced-argillic alteration (average δD = −33‰) are very different from the present-day local geothermal system. The δ 34S values in samples from the Sahinli and Tespih Dere deposits average −2.9‰ for pyrite; −3.3‰ for chalcopyrite; −5.4‰ for sphalerite and −7.6‰ for galena. These data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock.