Ore Mineralogy of High Sulfidation Çorak-Taç Epimesothermal Gold Deposit (Yusufeli-Artvin-Turkey) (original) (raw)
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2010
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 b 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 2 O 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 18 O values indicate that ore-forming hydrothermal fluids in the study area had δ 18 O H2O ranging from +1.1 to +9.7‰ (average= 3.8‰), strongly 18 O-enriched compared with present-day hydrothermal meteoric water in the area (δ 18 O=−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 34 S 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.
The Murgul (Artvin, NE Turkey) massive sulfide deposit is hosted dominantly by Late Cretaceous calc-alkaline to transitional felsic volcanics. The footwall rocks are represented by dacitic flows and pyroclastics, whereas the hanging wall rocks consist of epiclastic rocks, chemical exhalative rocks, gypsum-bearing vitric tuff, purple vitric tuff and dacitic flows. Multi-element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in K, Rb and Ba and depletion in Nb, Sr, Ti and P. The chondritenormalized rare earth element (REEs) patterns of all the rocks are characterized by pronounced positive/negative Eu anomalies as a result of different degrees of hydrothermal alteration and the semi-protected effects of plagioclase fractionation. Mineralogical results suggest illite, illite/smectite + chlorite ± kaolinite and chlorite in the footwall rocks and illite ± smectite ± kaolinite and chlorite ± illite in the hanging wall rocks. Overall, the alteration pattern is represented by silica, sericite, chlorite and chlorite-carbonate-epidote-sericite and quartz/albite zones. Increments of Ishikawa alteration indexes, resulting from gains in K 2 O and losses in Na 2 O and the chlorite-carbonate-pyrite index towards to the center of the stringer zone, indicate the inner parts of the alteration zones. Calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks. Abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone. Relative K increments are linked to the sericitization of plagioclase and glass shards and the formation of illite/smectite in the sericite zone. In addition, Fe enrichment is always met by pyrite formation accompanied by quartz and chlorite. Illite is favored over chlorite, smectite and kaolinite in the central part of the ore body due to the increase in the (Al + K)/(Na + Ca) ratio. Although the REEs were enriched in the silicification zone, light REEs show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy REEs' behavior. Hydrothermal alteration within the hanging wall rocks, apart from the gypsum-bearing vitric tuffs, is primarily controlled by chloritization with proportional Fe and Mg enrichments and sericitization. The δ 18 O and δD values of clay minerals systematically change with increasing formation temperature from 6.6 to 8.7‰ and −42 to −50‰ for illites, and 8.6 and −52‰ for chlorite, respectively. The O-and H-stable isotopic data imply that hydrothermal-alteration processes occurred at 253-332°C for illites and 136°C for chlorite with a temperature decrease outward from the center of the deposit. The positive δ 34 S values (20.3 to 20.4‰) for gypsum suggest contributions from seawater sulfate reduced by Fe-oxide/-hydroxide phases within altered volcanic units. Thus, the hydrothermal alteration possibly formed via a dissolution-precipitation mechanism that operated under acidic conditions. The K-Ar dating (73-62 Ma) of the illites indicates an illitization process from the Maastrichtian to Early Danian period.
SEG Special Publications v. 24 - Tectonomagmatic Influences on Metallogeny and Hydrothermal Ore Deposits: A Tribute to Jeremy P. Richards, 2021
Öksüt is a breccia-hosted high-sulfidation epithermal gold-copper deposit, situated within the Develidag Volcanic Complex in south-central Anatolia. The volcanic complex, exposed on the northern edge of the Tauride range, is largely made up of late Miocene andesitic to dacitic porphyries, covered by a succession of Pliocene basalts and basaltic andesites. A series of N-S-to NNW-trending faults of the regional central Anatolian fault zone partly cut and border the volcanic complex to the east and west. Mineralization at Öksüt follows a predominant north-northwest trend that correlates well with the regional stress regime. The bulk of the mineralization occurs in two domains, the Keltepe and Güneytepe orebodies, where steeply dipping and pervasively supergene oxidized breccia zones exploited funnel-shaped diatreme conduits within pyroxene andesite porphyry. Emplacement of these phreatomagmatic breccias was largely controlled by vertical to subvertical faults with dominant normal-slip components. Mineralized breccias comprise a central zone of residual vuggy to massive silica alteration, laterally and vertically grading into zones of quartz-alunite and quartz-alunite-clay alteration. These silica-altered breccias contain relatively high gold grades, whereas significant mineralization was also encountered in quartz-alunite-clay alteration. In the oxide zone, gold occurs in native form, whereas in the hypogene zone it occurs both as native gold or within pyrite-enargite accompanied by marcasite, and rare chalcopyrite and tetrahedrite. To the west of Keltepe and in Güneytepe, at depth, the altered and mineralized breccias pass into barren zones of argillic and then into biotite-magnetite ± K-feldspar ± anhdyrite alteration, the latter typical of porphyry-type systems. Sporadic zones of calc-silicate alteration, represented by grossularite, diopside, and vesuvianite, are also present. Three 40 Ar/ 39 Ar ages obtained from alunite and illite range between 5.7 to 5.5 Ma and are concordant with previously reported U-Pb and 40 Ar/ 39 Ar ages (~6-5.5 Ma) from host pyroxene andesite porphyry. This suggests that high-sulfidation alteration and mineralization developed contemporaneously with postsubduction magmatism at the Develidag Volcanic Complex, in relationship to regional E-W-directed extension that commenced at ~6 Ma. Our new ages also confirm Öksüt as the youngest epithermal gold deposit discovered to date in Anatolia, and possibly in the entire Western Tethyan metallogenic belt. The topographic prominence of the volcanic edifice combined with high permeability of the breccias favored deep supergene sulfide oxidation, thereby rendering Öksüt economically viable. Gold encapsulated in hypogene sulfides was liberated during the oxidation, whereas the copper was leached to produce a discontinuous chalcocite-and covellite-dominated enrichment zone, up to 50 m thick, at the base of oxidation.
Early Tertiary epithermal gold mineralization, Bahcecik prospect, northeastern Turkey
Mineralium Deposita, 2000
The Bahcecik prospect is located in the eastern Pontide tectonic province of the eastern Black Sea region of Turkey. It is one of the ®rst low sul®dation epithermal systems to be described from this area of Turkey. Gold mineralization occurred within Late Cretaceous to early Tertiary volcanic rocks and is localized along east-trending normal faults and lithologic contacts. An early quartz±sericite alteration event was focused along the major fault in the area and resulted in precipitation of arsenian (?) pyrite with anomalous gold. A later, more spatially extensive, advanced argillic alteration event overprinted the quartz±sericite event. Native gold was precipitated during this event as disseminations and fracture ®llings in quartz. Gold mineralization is restricted to the hightemperature portion of the alteration zone characterized by quartz veins with diaspore±pyrophyllite selvages. The prospect area was subjected to Tertiary to Holocene supergene alteration.
Ore Geology Reviews, 2017
Upper Cretaceous volcano-sedimentary sequences of the Eastern Pontide orogenic belt, NE Turkey, are host to significant VMS mineralization, including near Tunca. The initial stages of felsic volcanism within the mineralized area are marked by the eruption of dacitic lavas and breccias of the Kızılkaya Formation. This was accompanied by the emplacement of domelike hematitic dacites. Autobrecciated and volcaniclastic rocks, both in situ and resedimented, were likely generated from extrusive portions of these dacite bodies. Basaltic volcanism is marked by the eruption of the lava flows and pillow lavas of the Çağlayan Formation. Hiatuses in basaltic activity are marked by thin horizons of volcaniclastics and mudstones. The uppermost felsic volcanic units were accompanied by resedimentation of autoclastic facies from previous volcanism and represent the latest phase of Upper Cretaceous volcanism in the area. The semimassive sulfide mineralization is associated with a late stage of the initial felsic volcanism. U-Pb LA-ICP-MS zircon dating of a dacitic tuff breccia yielded an age of 88.1 ± 1.2 Ma (Coniacian-Upper Cretaceous), which is interpreted to be the age of the sulfide occurrences. A concentric zoned alteration pattern is observed in the footwall rocks. The alteration pattern is considered to have formed by lateral migration of hydrothermal fluids which had ascended along the discharge conduit. Fluid inclusion data indicate precipitation or mobilization processes within a relatively narrow temperature range of 152° to 255°C (avg. 200°C). The low-salinity fluids in the fluid inclusions, less than 5.9 wt.% NaCl equivalent, are consistent with typical modified seawater-dominant hydrothermal vent fluids. Sulfur isotope analysis of the Tunca sulfides yields a narrow range of 1.5 to 4.1 per mil. These δ 34 S values are also typical of many VMS deposits. Most of the recorded δ 18 O values (+7.1 to +14.0 per mil) are greater than 9 per mil. The most intensely hydrothermally altered rocks tend to have lower δ 18 O values relative to the less altered rocks. Collectively, the geologic relationships, mineralization style, and the lack of seafloor ore facies suggest that mineralization is principally of sub-seafloor origin. The most geologically reasonable interpretation of the genesis of the Tunca mineralization is the continuous interaction between the host rocks and seawater-derived fluids, without significant involvement of a magmatic fluid.
Ore Geology Reviews, 2006
Deposits of stibnite and cinnabar show a strong spatial association with metamorphic rocks and occur mainly within orogenic belts. Our study addresses the Emirli stibnite and HalVkö y cinnabar deposits within the Menderes Massif in western Turkey. Stibnite mineralisation occurs as stratabound lenses in graphite-and mica-schist, and as structurally controlled veins. Both types have a common mineral paragenesis containing pyrite, arsenopyrite, stibnite, gold, base metal sulphides, marcasite, realgar, orpiment and cinnabar. Realgar, orpiment and cinnabar are not present in the stratabound lenses. Quartz is the principle gangue mineral in all the deposits. The initial fluids were dilute, carbonic and rather hot (with Th N 300 8C). Deposition of pyrite and arsenopyrite is probably due to cooling of the fluids and to sulphidation and/or decreasing fO 2 , caused by interaction with syn-sedimentary sulphides in the country rocks. Arsenopyrite geothermometry indicates an average depositional temperature of 330 8C in the initial quartz vein. Vein formation increased the fluid pressure and caused effervescence, which resulted in a sudden pressure drop from 1.4 kbar during the initial quartz formation to~440 bars, and stibnite precipitated at 232 to 307 8C. Boiling and concomitant sulphur loss during stibnite precipitation may have also initiated gold deposition. Further cooling below 190 8C under a pressure of V 600 bars caused cinnabar deposition, mainly in the HalVkö y deposit. Salinity of the fluids during stibnite and cinnabar precipitation is 0.8 to 7.1 wt.% NaCl eq. and suggests a meteoric fluid. The structural framework induced by the initiation of extensional tectonics served as conduits for the penetration of surficial fluids to the environs of a possible magmatic heat source evidenced by thermal waters in the region. Stibnite from the stratabound (graphite-schist hosted) lenses and the crosscutting veins in the Emirli deposit have sulphur isotope compositions in a range of À 5.8x to À8.9x. d 34 S values of pyrite from the graphite-schist zones and mica-schists are in the ranges of À8.9x to À 7.7x and À 10.2x to À 11.7x, respectively. It is therefore concluded that the sulphur in stibnite originated from sulphide minerals in the country rocks, which in turn may have a source related to bacterial reduction of sulphate within the pre-metamorphic sediments.
Bulletin Of The Mineral Research and Exploration, 2016
The Kocadal base and precious metal mineralizations are located in the southwest of Gümüşhane province of the eastern Pontide orogenic belt. In the vicinity of the Kocadal mineralization, Gümüşhane granite, lithologies of the Hamurkesen, Berdiga, and Mescitli formations, dacite porphyry and andesite porphyry are present with abundant alluvium. Based on geological, mineralogical, and geochemical features, three mineralization styles have been recognized at the Kocadal area: (i) Mineralizations around Batarya tepe include (ia) Zn mineralization within the conglomerates and sandstones of the Hamurkesen formation and (ib) Zn-Pb-Ag-(Au) mineralization associated with dacite prophyry, (ii) Au mineralization, which occurs to the southwestern of Batarya tepe, and (iii) Cu mineralizations related to quartz veins and veinlets at Gözelerin Dere. Mineralized gravels within the conglomerates contains mainly sphalerite and pyrite, whereas hydrothermal mineralizations associated with porphyritic dacite comprise pyrite and sphalerite, with minor galena, chalcopyrite, pyrrhotite, arsenopyrite, marcasite, fahlerz, pyrargyrite, and proustite. Alteration patterns of hydrothermal mineralization in the field, from older to younger, are classified as: (i) tremolite-actinolite±garnet, (ii) quartz-sericite-chlorite, and (iii) carbonatequartz. Mineralized gravels within the conglomerates contains mainly sphalerite and pyrite, whereas pyrite, chalcopyrite, and galena are common in quartz veins at Gözelerin Dere. Geostatistical studies based on the results of geochemical analysis of core samples reveal the presence of the distinct element associations for the different styles of mineralizations. Table 2-In whole of the drill core samples, elements showing meaningful correlations with each other. SouthWest of Batarya Hill (
Journal of Geochemical Exploration, 1977
Three related types of sulphide mineralization in the Eastern Black Sea volcanic province (Eastern Pontids) of Turkey were studied with a view towards developing geochemical techniques both for their detection and differentiation: (1) Zn-Cu-Pb massive sulphide deposits; (2) Cu-pyrite stockwork deposits; and (3) pyritic impregnation deposits. Bedrock surveys utilizing samples of the host dacites and overlying basic rocks were effective in outlining various types of primary haloes associated with the sulphide deposits. The most indicative elements are F, Pb, Zn, Cd, Cu, Ag, As and Ba; the dispersion of Hg is restricted, and the element is not a good indicator. Quantitative evaluation of the clay (kaolinite plus montmorillonite plus illite-sericite)/ feldspar ratio by X-ray methods is useful in detecting the presence and intensity of hydrothermal activity related to sulphide mineralization and also for estimating proximity to mineralization. On a regional basis, the mineral potential of exposed stockwork and impregnation zones can be assessed by their elemental content. Barren impregnation pyritic deposits generally report only anomalous Fe and Cu contents. Cu-pyrite stockworks with no associated massive sulphides are enriched in Fe, As and Cu, whereas those accompanying massive sulphides are marked by enrichments of some or all of Fe, As, F, Cu, Pb, Zn, Ag, Cd and Mo.
Geoscience Frontiers, 2013
The Arzular mineralization is one of the best examples of epithermal gold deposits in the eastern Pontides orogenic belt. The mineralization is hosted by the subduction-related basaltic andesites and is mainly controlled by EeW and NEeSW trending fracture zones. The main ore minerals are galena, sphalerite, pyrite, chalcopyrite, tetrahedrite and gold. Homogenization temperatures of fluid inclusions are between 130 and 295 C for quartz and between 90 and 133 C for sphalerite. Sulphur isotope values obtained from pyrite, galena and sphalerite vary between À1.2& and 3&, indicating that sulphur belongs to magmatic origin and was derived from the Lutetian non-adakitic granitic intrusions in the region. Oxygen isotope values are between 15.0& and 16.7&, and hydrogen isotope values are between À87& and À91&. The sulphur isotope thermometer yielded temperatures in the range of 244e291 C for the ore formation. Our results support the hypothesis that the Arzular mineralization is a low-sulfidation epithermal gold deposit associated with non-adakitic subductionrelated granitic magmas that were generated by slab window-related processes in a south-dipping subduction zone during the Lutetian.