Ahmet Gökce

Fluid-Inclusion and Stable-Isotope Characteristics of the Inler Yaylasi Lead-Zinc Deposits, Northern Turkey

The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko-type) and vein-type Cu-Pb-Zn deposits. The Inler Yaylasi lead-zinc deposits are typical examples of the vein type and have been economically mined for 15 years. Three ore veins were identified along E-W-trending fault zones, hosted by extensively altered, Upper Cretaceous volcano-sedimentary rocks. A Tertiary granitoid intrusion occurs near the area of mineralization. The ore veins contain sphalerite, galena, and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite, and covellite as ore minerals, with quartz and calcite as gangue minerals. Fluid-inclusion studies show that the salt composition, salinity, and temperature of the hydrothermal fluids changed during various mineralization episodes. The temperature and salinity of the fluid were high (average temperature of 312.9°C and average salinity of 7.0% NaCl equiv.), and the fluid contained CaCl2, MgCl2, and NaCl during an early episode of mineralization characterized by quartz crystallization. During the sulfide crystallization, temperature and salinity were lower (average temperature of 272.0°C and average salinity of 4.0% NaCl equiv.), and the salts were mainly MgCl2, NaCl, and FeCl2. During subsequent mineralization episodes, temperature and salinity were still lower (average temperature 138.5 °C and average salinity 2.6% NaCl equiv.), and the salt content was dominated by NaCl, Na2CO3, NaHCO3, Na2SO4, and KCl. Oxygen- and hydrogen-isotope results (δ18O; +4.2 to +6.7 ‰ VSMOW and δ D; -83.0 to -59.0 ‰ VSMOW) suggest that magmatic water dominated the ore fluid. It is possible, however, that small amounts of meteoric water and/or formation water of meteoric origin were also involved. This isotopic composition may also be the result of interaction of meteoric water with magmatic rocks, as has been suggested for other deposits in the eastern Black Sea region. The decrease in temperature and salinity of the fluid and the increase in σ18O values of the water from 1725 to 1803 m levels also supports the hypothesis that these deposits formed where upwelling hot fluids met cold surfical fluids.

Fluid-Related Characteristics of the Çakmakkaya and Damarköy Copper Deposits, Northeast Turkey

The Çakmakkaya and Damarköy copper deposits in the Murgul (Artvin) area are typical examples of Kuroko-type volcanogenic sulfide deposits that occur widely in the Eastern Pontide region of Turkey. These deposits are hosted by volcanic rocks in a sequence that consists upward of andesitic lavas, brecciated dacite tuff, covering tuff, and dacite porphyry. Mineralizations occur mainly in the form of stockwork ores that are hosted by brecciated dacite tuff. A thin stratiform ore zone and a gypsum lens occur above the stockwork in the Çakmakkaya deposit. The stockwork sulfide veinlets contain mainly pyrite and chalcopyrite, with minor sphalerite, galena, tetrahedtrite, and marcasite. Quartz is the only gangue mineral. The deposition of sulfides was largely controlled by microfracturing of the dacitic tuffs, with high concentrations especially at the intersections of fractures. The stratiform ore zone within the Çakmakkaya deposit contains ore clasts that indicate fragmentation and resedimentation of sulfides during or after discharge of the hydrothermal fluids onto the sea floor. The ore clasts contain the same minerals as the stockwork ores. Fluid-inclusion studies indicate that the ore-forming fluids contain NaCl, CaCl2, and MgCl2. Salinities and temperatures were high during the initial deposition of the ore minerals, and decreased during later episodes of mineralization from a maximum of ~18% (NaCl equiv) and 254°C to 1% (NaCl equiv) and 110°C during mineralization. The σ18O values of aqueous fluid inclusions were calculated from the measured σ18O values of the host quartz and the temperatures derived by microthermometry. The calculated σ18O(H2O) values vary in a narrow range from -2.2 to +0.2‰ (SMOW). The σD values of the inclusion waters were measured by direct isotope determination of the water hydrogen extracted from the fluid inclusions. The σD values range from -61.6 to -35.5‰ (SMOW) and cluster around -60‰ (SMOW). These stable-isotope results of the Murgul deposits indicate that the hydrothermal solutions have a major meteoric component; however, there seems to be a small amount of sea water mixing. This study concludes that meteoric water, circulating through the continental crust underlying the volcano-sedimentary rocks, acted as mineralizing fluid, leached metals (Cu, Pb, Zn, Au and Ag) and sulfur from the surrounding volcanic rocks, and precipitated sulfides and sulfates along fractures within the brecciated dacitic host rocks and at the surface of the sea floor.

Sulfur-Isotope Characteristics of the Volcanogenic Cu-Zn-Pb Deposits of the Eastern Pontide Region, Northeastern Turkey

In the Eastern Pontide Region of northeastern Turkey, volcanogenic Cu-Zn-Pb deposits of the Kuroko type are widespread within the dacitic series of the Liassic-Eocene volcano-sedimentary succession. Sulfide mineralization within the studied deposits shows four different depositional styles: disseminated ore; polymetallic stockwork ores; polymetallic massive ores; and disseminated pyrite in the hanging-wall tuff units. Only the stockwork and massive ores are economically important, and usually one or the other dominates in each ore body. The δ34S of sulfide minerals belonging to the various styles of mineralization are in the range from −2.6 to +5.2% (VCDT): pyrite has the highest values and the galena lowest values in agreement with the usual isotopic-fractionation trends. Massive ores have heavier sulfur-isotope composition among the mineralization styles and the heaviest values are recorded in barite- and gypsum-rich deposits. The close similarity of the δ34S among the various mineralization episodes in some deposits indicates a single sulfur source having a stable and homogenous composition. The δ34S of sulfates fall into three groups: barites and primary gypsum (15.4 to 20.4%), close to coeval seawater sulfate; one value of barite (25.4%) heavier than coeval sea water; and values of secondary gypsum (2.2 to 8.0%) either very light compared to coeval seawater sulfate, or within the range recorded from sulfide minerals. The δ34S values of pyrite disseminated in the brecciated dacite tuff units are very close to zero and similar to the ones reported for magmatic rocks, suggesting a magmatic source for the sulfur of the earliest sulfide mineralization episode. These δ34S data are not sufficient to calculate the fraction of the reduced sulfur derived from seawater sulfate, as the associated fractionation factor cannot be constrained.

Fluid Inclusion and Stable Isotope Characteristics of the Arapuçandere Pb-Zn-Cu Deposits, Northwest Turkey

The Arapuçandere Pb-Zn-Cu ores are typical examples of vein-type lead-zinc deposits in the Biga Peninsula. Permian—Triassic metamorphic, Triassic metaclastic and metabasic rocks, Oligocene—Miocene granitoids, Miocene volcanic rocks, and Quaternary terrestrial sediments crop out in the study area. The veins occupy fault zones in Triassic metasandstone (meta-arkose and subarkose) and metadiabase, and contain galena, sphalerite, chalcopyrite, pyrite, marcasite, covellite and specular hematite as ore minerals, with quartz, calcite, and barite as gangue minerals. Based on macro- and micro-petrographic investigations, sulfide minerals formed in the earliest stage of mineralization, and were followed by quartz and calcite crystallization. Fluid inclusion studies showed that salinity (avg. 18.3%) was low, but that temperature was relatively high (avg. 301.4°C) during stages of sulfide precipitation. In contrast, the salinity (avg. 27.1% NaCl equiv.) increased and the temperature (avg. 240.2°C) decreased during crystallization of the quartz. Finally, the salinity and temperature of the fluid gradually declined through the later episode of mineralization when the primary and secondary inclusions in calcite formed. Isotopic compositions of the aqueous fluid (δ18O = -7.5 to -1.7%, and δD = -90 to -55%) indicate the presence of meteoric water modified slightly by fluid-rock interaction. A geologic and genetic relation between ore veins and Oligo-Miocene granitoids and Miocene volcanic rocks appears to be lacking. The ore and host-rock relations suggest only a post-Triassic age for the mineralization. Pb-isotope model ages suggest a pre-Eocene age for the mineralization, which predated Oligo-Miocene granitoid emplacement and Miocene volcanic activity. We conclude that the Pb-Zn-Cu veins in the study area formed by deeply circulating meteoric water. The metals and sulfur were leached from the surrounding pre-Eocene units and deposited along fault zones.

Microthermometric and stable isotopic (O and H) characteristics of fluid inclusions in the porphyry related Çöpler (İliç - Erzincan) gold deposit, central eastern Turkey

The Çöpler gold deposit occurs within the stockwork of quartz hosted by the Çöpler granitoid (Eosen) and by surrounding metasediments of Keban metamorphic (Late Paleozoic - Early Mesozoic) and the Munzur limestones (Late Carboniferous - Early Cretaceous).Native gold accompanied by small amounts of chalcopyrite, pyrite, magnetite, maghemite, hematite, fahlerz, marcasite, bornite, galena, sphalerite, specular hematite, goethite, lepidochrosite and bravoitic pyrite within the stockwork ore veinlets. In addition, epidote (pistazite - zoisite), garnet, scapolite, chlorite, tremolite/actinolite, muscovite and opaque minerals were determined within the veinlets occurred in skarn zones.The study of fluid inclusions in quartz veinlets showed that the hydrothermal fluids contain CaCl2, MgCl2 and NaCl and the salinities of the two phases (L+V) inclusions range from 1.7 to 20.6% NaCl equivalent. Salinity values up to 44% were determined within the halite bearing three phases inclusions. Their homogenization temperature values have a wide range from 145.0 to 380.0°C, indicative of catathermal/hypothermal to epithermal conditions. The δ18O and δD values of the fluid inclusion waters from the Çöpler granitoid correspond to those assigned to Primary Magmatic Water, those from the metasediments of Keban metamorphics fall outside of the Primary Magmatic and are within the Metamorphic Water field. A sample from a quartz vein within the skarn zone hosted by the Munzur limestones has a particularly low δD value.The results suggest that fluids derived from the granitoids were mixed with those derived from the metasediments of Keban metamorphics and the the Munzur limestones and resulting in quartz veinlets in these lithologies and the formation of stockwork ores. In view of the occurrence, the features described and processes envisaged for this study area may be applicable in similar settings.

Microthermometric and O- and H-isotope characteristics of the mineralizing fluid in the Akguney copper-lead-zinc deposit, NE Turkey

The Akgüney copper–lead–zinc deposit (Ordu Province) is actively mined in the eastern Black Sea Region of Turkey. This deposit consists of ore‐bearing veins emplaced along fault zones and hosted by slightly altered Upper Cretaceous andesites. Seven ore veins, D‐1 to D‐7, have been identified. These veins strike N 70–80°W with a dip of 50–60°NE, except for D7 which strikes E–W with a dip of 25°S. The ore‐bearing quartz vein outcrops are slightly limonitized and hematitized. Two different ore associations are distinguished within the D‐1 and D‐2 veins. The first contains only pyrite, whereas the second consists of coarse‐grained sulphides such as chalcopyrite, galena, sphalerite, tetrahedrite, and secondary limonite veinlets in addition to pyrite. Quartz and calcite are the gangue minerals. The mineral paragenesis has been identified as: pyrite→galena→chalcopyrite (I)→sphalerite→chalcopyrite (II)→(tetrahedrite ?)→quartz→calcite. Fluid inclusion data indicate that the ore‐forming fluids contained significant concentrations of divalent cations in addition to NaCl. The salinity of the fluids lies in the range 14–24% (ave. = 19.0) NaCl equivalent; liquid homogenization temperatures range from 276 to 349°C (ave. = 307°C) and decrease to 211°C through the later stages of mineralization. Oxygen and hydrogen isotope data are consistent with the mineralizing fluid being of meteoric origin, with modification of the oxygen isotope composition by exchange with the volcanic host rocks. However, low δD values suggest a magmatic water component in some samples. The combination of fluid inclusion and stable isotope data suggest that the Akgüney Cu–Pb–Zn vein‐type deposits were formed by the leaching of metals and sulphur from the surrounding volcano‐sedimentary rocks by deep‐circulating meteoric water.

Detecting Clay Minerals in Hydrothermal Alteration Areas with Integration of ASTER Image and Spectral Data in Kösedag-Zara (Sivas), Turkey

Remote sensing technology and its terrestrial components are more useful than classical geological investigation in mineral exploration and mapping the hydrothermal alteration areas and help to investigate larger areas in short time. Intrusive and volcanic rocks, namely Kösedag syenite and Karatas volcanics in Kösedag (Zara) area shows argillic alteration zones. Two different test area were chosen and sampled for mineralogical studies. XRD-CF investigations showed that kaolinite and illite are the dominant clay minerals in test areas of A and B respectively. The spectroradiometer measurements were carried out 5 times on different surfaces of clayey samples with self-illuminated contact-probe lens within the wavelength range of 350-2500 nm. The spectroradiometer measurements used as endmember were resampled to ASTER short wave infrared (SWIR) bandwidths. Band ratio, principal component and decorrelation stretching analysis were performed to visualize the distribution of clay minerals. In spectral classification method, matched filtering (MF) was used for integrating the satellite image and spectroradiometer measurement data. It was concluded that co-interpretations of the band ratio, principal component, decorrelation stretching analysis, MF results and geological map are very useful in determining, classifying and mapping of the argillic alteration zones related to hydrothermal processes on ASTER image and they seem to be very useful to identify the target areas for mineral exploration.