Epithermal Gold Deposits Research Papers (original) (raw)

The Tethyan-Eurasian Metallogenic Belt, stretching nearly 10,000 km across southern Europe through Anatolia and beyond into Asia is host to a wide variety of mineral deposits, particularly porphyry and epithermal style mineralization. The Efemçukuru low sulfidation, vein-hosted, epithermal gold deposit located southwest of Izmir, western Turkey is one such deposit and contains a measured and indicated resource of 5.89 Mt grading at 8.71 g/t Au. The deposit comprises two separate mineralized quartz-rhodochrosite veins: Kestanebeleni and Kokarpınar which dip moderately E- to NE, respectively. The veins are hosted in an Upper Cretaceous ophiolitic mélange sequence (Bornova Flysch) which is metamorphosed to phyllite and schist on the deposit scale, and occur adjacent to fine-grained quartz phenocrystic rhyolite dikes that dip to the NE. An aureole of hornfelsed phyllite and schist occurs within a 250-500 m wide zone around to the veins and rhyolite dikes.
The vein mineralogy is variable but consists primarily of colloform-banded quartz, rhodonite (commonly replaced by rhodochrosite), adularia, and axinite with sulfide assemblages comprising pyrite, sphalerite, galena, chalcopyrite, and minor tetrahedrite. Alteration related to epithermal veins is variable depending on the host rock type, but is typically dominated by muscovite, chlorite, and halloysite in the schist and phyllite, actinolite and epidote within the hornfelsed rocks, and minor illite in the rhyolite dikes. Four main styles of Kestanebeleni veining are identified on the basis of mineralogy and texture, each with several subclasses and distinct paragenetic sequence. Gold is found in the later stages of rhodonite veins and as inclusions in disseminated pyrite and galena in late-staged sulfide and sulfide base metal veins. The southern part of the Kestanebeleni vein contains significantly more quartz and rhodonite with lesser, and narrower sulfide and base metal veinlets. The central and northern segments of Kestanebeleni typically have more rhodonite while sulfide veins are wider, coarser-grained, and more dominant at depth. Structural mapping of the area identified two main sets of normal faults: I) NE-dipping faults often with SW-dipping conjugate faults and II) cross-cutting NW-dipping faults associated with SE-dipping conjugate faults. Several distinct structural domains of foliation direction (S1) can be explained by local scale folding and syn- to post-mineralization faulting. The difference in strike direction between the two main mineralized veins can be explained by relay zones linking major faults during progressive regional extension. The structural geometry and mineralization style of the Efemçukuru system may be analogous to other potential epithermal systems within the regional extensional regime.

- by
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- Structural Geology, Economic Geology, Gold Mineralization, Epithermal Gold Deposits
- by Radolf Malau
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- Coal Mining, Coal Geology, Epithermal Gold Deposits, Porphyry Cu-Au

SEG Special Publication Number 22

The Late Paleozoic Kairagach epithermal gold deposit belongs to the high-sulfidation (acid–sulfate) type. It is located at the northern slope of the Kuramin Ridge in the central Tien Shan, 3.5 km northwest of the Kochbulak deposit, being confined to the volcanic andesite–dacite sequence (C2–3) composing the northeastern segment of the Karatash caldera. Volcanogenic sequences are intruded by subvolcanic dacite–porphyry and diorite–porphyry intrusions, as well as granodiorite–porphyry and porphyritic diabase dikes of the northeastern strike. The gold–sulfide–selenide–telluride mineralization of the Diabazovaya zone, which encloses the main gold resources, associates with these dikes. Unlike typical epithermal deposits of the high-sulfidation type with Au–Cu geochemical specialization of ores, the Kairagach deposit is characterized by distinct Au–Sn–Bi–Se–Te mineralization, which includes over 80 ore minerals, including new and rare ones. This paper discusses data on the geological structure of the deposit, ore geochemistry, variations in chemical composition, mode of occurrence and parageneses of native elements (Au, Ag, Te, Sn, Bi); sulfides of Fe, Cu, Pb, Zn, and Ag; fahlores of the tetrahedrite–tennantite–annivite–goldfieldite series; bismuthinite–aikinite, junoite, and pavonite sulfosalts; Cu and Fe sulfostannate; various Au, Ag, Pb, Fe, Hg, Bi, and Sb tellurides and Bi sulfoselenides; and Fe and Sn oxides. The chemical composition of ordinary, high-grade, and bonanza ores and the vertical and lateral (including hidden) mineralization zoning, as well as the succession of mineral parageneses, P–T parameters, composition of mineral-forming fluids, and main factors and mechanisms responsible for the formation of goldproductive mineral associations, are considered. The variations in the S, C, O, and H compositions of ore minerals are used to define probable sources of water and ore components in ore-forming fluids. The results of thermodynamic modeling of probable gold occurrence and transportation in the mineral-forming solution are also discussed.

The Western Tethyan Metallogenic Belt hosts a wide variety of mineral deposits, particularly those of porphyry and epithermal types. The Efemçukuru low-/intermediate- sulfidation, epithermal gold deposit, southwest of Izmir, Turkey is one of such deposits and contains a measured and indicated resource of 5.62 Mt at 8.47 g/t Au (1.53 Moz Au). The deposit, hosted in a variably metamorphosed Upper Cretaceous ophiolitic mélange sequence (Bornova Flysch), comprises two mineralized quartz-rhodochrosite veins: Kestanebeleni and Kokarpınar that coincide with moderately E- to NE-dipping structures and cut similarly dipping rhyolite dikes. Calc-silicate altered (hornfelsed) host rock commonly occurs within a 250-500 m wide zone around the veins and dikes. Vein mineralogy is variable but consists primarily of colloform-banded quartz, rhodonite, and rhodochrosite with minor adularia and axinite with sulfide assemblages of pyrite, sphalerite, galena, and chalcopyrite. A detailed analysis of Kestanebeleni identified five main stages of vein development based on crosscutting relationships. The earliest veins consist of quartz-epidote-actinolite-chlorite-pyrite (Stage I). These are cut by several stages (Stages II, III, IV) of quartz-rhodonite-rhodochrosite-pyrite veins and the vein textures suggest they formed due to boiling (colloform banding, bladed carbonate, cockade). Later (Stage V) veins are characterized by an increased abundance of base metal sulfides with quartz and rhodochrosite. Gold mineralization occurs as electrum and inclusions in pyrite in the later-forming quartz-rhodochrosite veins and base metal-sulfide veins (Stages III, IV, and V), commonly associated with cockade and crustiform textures. Spatially, rhodonite-rich veins of Stages II and II are more commonly observed in vein intercepts in the southern portions of Kestanebeleni. Base metal sulfide-rich veins are more abundant in the central and northern parts of the vein and are generally wider, coarser-grained, and dominant at depth.

- by Kaleb Boucher
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- Structural Geology, Economic Geology, Gold Mineralization, Epithermal Gold Deposits

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.

- by Ali Imer
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- Turkey, Anatolia, Maar-Diatreme Volcanism, Epithermal Gold Deposits

One third of the largest producing gold deposits in the world today are of the high sulphidation (HS) type. In terms of geologic target models utilized by most international gold exploration programs, the volcanic-hosted high sulphidation gold model is applied as frequently as greenstone belt targets, porphyry copper-gold systems and others. Considering that some high sulphidation gold deposits can occur in settings with only minor historic mining activity and with few or no associated placer gold occurrences, these high sulphidation gold systems may be easily overlooked. Discovery outcrops of the oxide portions of these deposits can be quite nondescript in their appearance. Pueblo Viejo is a classic example where sulphide mineralization was first mined 500 years ago, but the most profitable oxide portion of this gold deposit was not recognized until 1969. Even the largest gold company in the world had an outcropping high sulphidation gold deposit on one of its concessions for over a decade before it was sampled, targeted and drilled as a discovery in 2015 at Alturas in Chile. The following select discovery histories exemplify how many of these high sulphidation deposits were recognized as major gold mineralized systems. Photo: Extensive advanced argillic alteration in an arid setting; Pascua-Lama.

- by Michael Thomsen
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- Economic Geology, Gold Mineralization, Mineral exploration, Mineral Resources
- by Cathy Busby
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- Volcanology, Economic Geology, Volcanic Geology, Appalachian Geology
- by Ali Aluç
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- Turkey, Silver, Epithermal Gold Deposits, Balıkesir

Tourmalines from the Kalinovka porphyry copper deposit with epithermal bismuth-gold-basemetal mineralization and the Michurino gold-silver-base-metal prospect have been studied in the South Urals. Tourmaline from the Kalinovka deposit occurs as pockets and veinlets in quartz-sericite metasomatic rock and propylite. The early schorl-“oxy-schorl” [Fetot/(Fetot + Mg) = 0.66−0.81] enriched in Fe3+ is characterized by the homovalent isomorphic substitution of Fe3+ for Al typical of propylites at porphyry copper deposits. The overgrowing tourmalines of the second and third generations from propylite and quartz-sericite metasomatic rock are intermediate members of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.05−0.46] with homovalent substitution of Mg for Fe2+ and coupled substitution of X▭ + YAl for XNa + YMg. These substitutions differ from the coupled substitution of YAl + WO2− for YFe2+ + WOH− in tourmaline from quartz-sericite rocks at porphyry copper deposits. At the Michurino prospect, the tourmaline hosted in the chlorite-pyrite-quartz veins and veinlets with Ag-Au-Cu-Pb-Zn mineralization is an intermediate member of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.20−0.31] with homovalent substitution of Mg for Fe2+ and coupled substitutions of X▭ + YAl for XNa + YMg identical to that of late tourmaline at the Kalinovka deposit. Thus, tourmalines of the porphyry and epithermal stages are different in isomorphic substitutions, which allow us to consider tourmaline as an indicator of super- or juxtaposed mineralization.

- by Ivan Balsheev and +1
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- Mineralogy, Silicate mineralogy, Porphyry, Tourmaline

This study presents a detailed study of the dimensions, geometry, textures and breccias of a well-exposed epithermal vein system, the Kestanelik gold deposit in the Biga Peninsula, NW Turkey, and investigates the permeability enhancement mechanisms in epithermal gold deposits. Here mineralization is associated with quartz veins up to 13.6 m thick. Vein textures and breccia components indicate repeated sealing and subsequent brecciation of wall rock and pre-existing vein infill. Field and petrographic analyses characterize east-west-trending veins as left lateral faults, whereas NE-SW-trending veins are extensional (Mode I) fractures. Cataclasite and tectonic breccia of wall rocks and early quartz, hydrothermal crackle breccias, and matrix-supported chaotic breccias of pre-existing vein infill, all of which are cemented by late iron-oxide-bearing quartz, indicate that co-seismic rupturing and hydraulic fracturing are two major permeability enhancement mechanisms. In addition, transient variations in local stress direction, caused by syn-mineralization dyke intrusion, may have enhanced permeability on misoriented surfaces and at locations where the dip changes. This study emphasizes the importance of understanding structural geology and kinematics as controls on the location of boiling and mineralization mechanisms in epithermal gold deposits.

- by Nilay Gülyüz and +2
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- Hydrothermal systems, Permeability, Hydrothermal Ore Deposits, Epithermal Gold Deposits

The Triades-Galana Pb-Zn-Ag-Au mineralization is a shallow-submarine epithermal mineralization located along NE-trending faults, NW Milos Island, Greece. It is hosted in 2.5–1.4 Ma pyroclastic rocks and is genetically related to andesitic/dacitic lava domes. Mineralization occurs as breccias, quartz-barite-galena veins and stockworks within sericite-adularia or kaolinitic altered rocks. The mineralization is enriched in Mo, W and base-and precious metals (e.g. Pb, Zn, Ag) similarly to the neighbouring mineralization at Kondaros-Katsimouti and Vani, indicating common source of metals from a deep buried granitoid feeding western Milos with metals and volatiles. Paragenetic relations suggest early deposition of pyrite, followed by famatinite, polybasite and Ag-rich tetrahedrite, and then by enargite, suggesting fluctuating sulfidation states during ore formation. The evolution from Sb-towards As–rich enrichment indicate a renewed magmatic pulse (probably in the form of magmatic gases) in the hydrothermal system. Silver is present in the structure of sulfosalts (up to 66.2 wt.% in polybasite-pearceite, 15.1 wt.% in tetrahedrite and 60 wt. % in pyrargyrite). Boiling processes (as evidenced by the presence of adularia accompanying intermediate-sulfidation ore) and mixing with seawater (presence of hypogene lead chlorides) and contemporaneous uplift, contributed to ore formation.

- by Christos Kanellopoulos
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- Ore Geology, Silver, Epithermal Gold Deposits, Milos Island

The host rock of mineralization within the deposit is a part of Eocene, Oligo-miocene age. The composition of these rocks is mainly from moderate to basic volcanic units of porphyritic pyroxene andesite that approximately has covered most of the area. The geological sequence of the locality is cut by some stocks and diabasic dykes. Tree zones of alteration were detected from TM satellite images with W-E elongation in area including silisification, prophilitic, phyllic, Argillic, quartz-calsedonit-Alunite and advanced argillic alteration. The mineralization displays alteration pattern consisting of a core of residual (vuggy) silica, bordered outward by zones of quartz-kaolinite, alunite and montmorillonite. Some veins have occurred in alteration zones including gold-copper bearing veins in the west area and silver and base metals bearing veins in the middle area. Mineralization studies of alteration in the west area around silica veins by XRD indicated association of quartz, kaolonite, alunite, montmorillonite, jarosite, anatase. Mineralization studies on polished samples of silica veins by optical microscope and scanning electron microscope have showed anatase, tree generation of pyrite, enargite, tenantite, native gold, electrum with some barite and chromium minerals. The composition of veins varied in different veins. The veins are formed of vuggy silica which the vuggs (usually 5-20µm) hosted gold bearing third generation thin pyrite. Oxidation of the sulfides extricated gold in to secondary residual limonite. The type of mineralization, alteration, textures and situation of deposit forming in relation to intrusion bodies shows similarity to an epithermal high sulfidation deposit type with variation of mineralization in veins.

- by Ahmad Rabee and +1
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- Iranian Studies, Gold Mineralization, Epithermal Gold Deposits, Epithermal Veins
- by Ali Imer
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- Tectonics, Epithermal Au deposit, Geodynamics, Petrology and Geochemistry

The Çöpler Au deposit (measured and indicated resource of 122.8 million tonnes at 1.7 g/t Au, 4.8 g/t Ag, and 0.1 wt % Cu) is centered around shallow-level dioritic to granodioritic intrusive rocks of the middle Eocene Çöpler-Kabatas¸magmatic complex, which have been emplaced into a succession of regionally metamorphosed late Paleozoic-Mesozoic sedimentary and carbonate rocks. The deposit comprises a centrally located subeconomic porphyry Cu-Au system characterized by a potas-sically altered (biotite-K-feldspar-magnetite) core overprinted by a more extensive phyllic (quartz-sericite) alteration zone. The potassic alteration zone is associated with early M-type hairline magnetite and crosscutting B-type quartz ± magnetite ± sulde veinlets, whereas the enveloping phyllic-altered rocks contain abundant D-type quartz-pyrite and lesser polymetallic quartz-sulde veinlets. Intermediate-suldation epithermal Au mineralization that overprints the porphyry occurred in two stages. Main-stage epithermal mineralization is characterized by carbonate sulde veinlets consisting of manganocalcite, arsenical pyrite, arsenopyrite, marca-site, chalcopyrite, tennantite/tetrahedrite, galena, and sphalerite. Late-stage sooty pyrite veinlets contain some realgar and orpiment and are associated with zones of extensive carbonate alteration. In the carbonate sulde veinlets, invisible gold is primarily hosted within arsenical pyrite and, to a lesser extent, by arsenopyrite, tetra-hedrite, and tennantite. In sooty pyrite veinlets, invisible gold is associated with ne-grained arsenical pyrite. Manto-type carbonate-replacement zones occur in the distal portions of the porphyry system and constitute a signicant gold resource. These carbonate-replacement bodies display a mineral paragenesis similar to that of the epithermal carbonate sulde veinlets in that they contain abundant arsenical pyrite together with lesser chalcopyrite, arsenopyrite, and marcasite, and sparse sphalerite, galena, tennantite, and tetrahedrite. Invisible gold in these ores is contained mainly within pyrite and chalcopyrite and, to a lesser extent, in arsenopyrite, tetrahedrite, and tennantite. Polyphase brine inclusions (~47–62 wt % NaCl equiv) in early B-type quartz ± magnetite ± sulde vein-lets were trapped together with low-salinity (~3–5.5 wt % NaCl equiv), vapor-rich inclusions at temperatures ~390°C and at a depth of ~1.5 km under lithostatic conditions. Fluids associated with the overprinting phyllic alteration were slightly cooler (~370°C) and less saline (37–42 wt % NaCl equiv). Fluid inclusions in man-ganocalcite and sphalerite from epithermal carbonate sulde veinlets trapped moderate-salinity (4–15 wt % NaCl equiv) uids at ~290°C, whereas uid inclusions hosted in barite and realgar from sooty pyrite veinlets were formed from low-temperature (~100°C) and low-to moderate-salinity (1–14 wt % NaCl equiv) uids. These data indicate that the Au-mineralizing system at Çöpler progressed from a high-temperature porphyry system to a relatively low temperature, intermediate-suldation epithermal system. Deposition of gold in the early stages of epithermal mineralization resulted from cooling, suldation, and neutralization of predominantly magmatic sourced hydrothermal uids, whereas a meteoric water component is evident in the latest stage of mineralization. Deposit-scale geologic observations combined with uid inclusion and stable isotope evidence suggest that mineralization at Çöpler records activity of a relatively deep epithermal system and that its formation was structurally and lithologically controlled. Specically, the thick, premineralization carbonate sequence once overlying the deposit acted as a pressure seal and also as a neutralizing agent during the build up of the mag-matic-hydrothermal system. The weakening of this carbonate cover by igneous intrusion and subsequent hydro-thermal activity may have contributed to later selective erosion of the alteration zone, thereby telescoping the intermediate-suldation epithermal system onto the earlier porphyry system and creating the Çöpler window.

- by Ali Imer
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- Economic Geology, Epithermal Gold Deposits, Porphyry Cu-Au
- by Prabodh R Sahoo and +1
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- Ore Geology, Mineral exploration, Epithermal Gold Deposits, Mineral Deposits
- by Mohamed Abd El Monsef
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- Epithermal Gold Deposits, Gold Deposits
- by Ali Imer
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- Tectonics, Epithermal Au deposit, Geodynamics, Petrology and Geochemistry

-Utilization of geothermal potential of a smooth geothermal field for heating-cooling of buildings
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-Some historical data on epithermal gold
-Chemical Technology and Biotechnology
Chemical leaching of uranium ore and bacterial lixiviation of uranium ore

- by Dimitris Minatidis and +1
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- Biotechnology, Geothermal Energy, Chemical Technology, Epithermal Gold Deposits

The paper describes sphalerite composition (Fe, Mn, and Cd contents) from five epithermal base-metal deposits of the Baia Mare district: Nistru, Herja, Baia Sprie, Cavnic, and Cisma. Sphalerite is usually featured by X FeS decrease with... more

- by Olga Y Plotinskaya
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- Mineralogy, Epithermal Gold Deposits

- by Vsevolod Yu. Prokofiev and +1
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- Mineralogy, Thermodynamics, Ore deposits, fluid Inclusions

Tellurides are significant minerals in gold deposits both as gold carriers and as indicators of PTx-conditions. In the Inner Carpathians belt tellurides are abundant in most deposits of the golden Quadrilateral (Apuseni Mountains) and sporadic in the Banska Stiavnica zone and the Zlata Bania zone. In the presenr paper we describe for first time altaite and tetradymite occurences in the Baia Mare district proved by e-probe data. Altaite (PbTe) was found in the Cavnic deposit in assemblage with sphalerite, galena, and rhodonite. It’s chemical composition is close to stoichiometric: Te 37.61 wt. % and Pb 60.51 wt. %, total 98.12 wt. %. In the Cu-Bi assemblage of the Nistru deposit occurs tetradymite (Bi2Te2S) in intergrowth with chalcopyrite, gustavite, and native Au. Tetradymite appears as very small grains with the composition Te 36.99 wt.%, Bi 61.93 wt.% S 4.55 wt.% and calculated formula Bi2.03Te1.99S0.98. Paratellurite (TeO2), found in assemblage with native gold and gustavite, forms intergrowth with a 2-microns phase containing Au and Te. Thermodynamic constrains supported by fluid inclusions data indicate that altaite formation at Cavnic was likely to be a result of temperature decrease from 300 to 250-200oC and fS2 drop. At Nistru tetradymite formation does not require temperature decrease and might be a result of fS2 drop and/or fTe2 increase.

- by Vsevolod Yu. Prokofiev and +2
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- Mineralogy, Ore deposits, fluid Inclusions, Epithermal Gold Deposits

The Vani Ag prospect is a high-grade epithermal mineralization located along the NW-trending Kondaros-Katsimouti-Vani fault, NW Milos Island, Greece. The prospect is hosted in calc-alkaline dacite domes and volcaniclastic sandstones and represents the NW extension of the Pb-Zn-Ag-Mn Katsimoutis-Kondaros mineralization. It occurs proximal to the Vani exhalative manganese deposit. The Ag content of the prospect is derived from Ag-bearing phases (native silver, argentite/acanthite, silver halides and argentian covellite). Mineralogical evidence like the presence of skeletal habits of sulfides, presence of hydrothermal anglesite, covellite and silver halides that were formed after dissolution of the primary silver and lead-bearing minerals, verifies earlier work that mineralization along the Kondaros-Katsimoutis fault is the product of seawater oxidation and was formed in a submarine setting after reaction of hydrothermal fluids with seawater.

- by DIMITRIOS ALFIERIS
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- Ore Geology, Hydrothermal Ore Deposits, Epithermal Gold Deposits
- by Olga Plotinskaya
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- Geology, Mineralogy, Hydrothermal systems, Ore deposits

Mineral assemblages and formation conditions of precious metals (Au, Ag, PGE) in ores of the Mikheevskoe porphyry copper deposit (South Urals) are the subject of our study. Three mineralization types can be distinguished: (1) Gold-silver-telluride mineralization overlapping porphyry-style bornite-chalcopyrite ores includes native gold (fineness 863–873), electrum (fineness 593–672), galena, hessite, coloradoite, and, more rarely, petzite, stützite, Au-Ag ditellurides, native tellurium, tellurobismuthite, tetradymite–kawazulite, altaite, and extremely rare melonite NiTe2, merenskyite PdTe2, and sopcheite Ag4Pd3Te4; (2) Gold-arsenopyrite-basemetal mineralization within quartz-tetrahedrite-sphalerite veinlets cutting porphyry-style mineralization; (3) Gold-telluride mineralization with argillic alteration and mineralogically similar to that of type (1) but distinct because of the presence of Au-Ag, Ag, and Pb selenides. Textural relationships supported by fluid inclusions data and chlo...

- by Reimar Seltmann
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- Geology, Geochemistry, Epithermal Gold Deposits, Epithermal Veins

The paper reports Rb-Sr isotopic data obtained by the authors on ore-hosting rocks from the Kairagach epithermal Au-Ag deposit in the Kurama ore district in the Central Tien Shan, Uzbekistan. The influence of mineralizing hydrothermal solutions on the host volcanic rocks of andesite-dacite composition and the metasomatic alterations of these rocks are proved to have been resulted in with the homogenization of the Sr isotopic composition, i.e., its equalization between various modes of Sr occurrence. This offers additional possibilities of the application of the Rb-Sr isochron method in dating hydrothermal processes. The application of Rb-Sr isotopic methods in studying samples from the Kairagach deposit allowed the authors to obtain dates whose reliability corresponds to isochron one (291 ± 3 Ma) or is very close to it (290 ± 6 Ma). The data thus obtained provide good reasons to believe that the corresponding epithermal mineral deposits in the Kurama ore district (Kairagach, Kochbulak, and others) were genetically related to and simultaneous with the emplacement subvolcanic porphyry intrusions.

- by Olga Y Plotinskaya and +1
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- Geochronology & isotope Geology, Epithermal Gold Deposits
- by Reimar Seltmann
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- Geology, Geochemistry, Epithermal Gold Deposits, Epithermal Veins

The Triades-Galana Pb-Zn-Ag-Au mineralization is a shallow-submarine epithermal mineralization located along NE-trending faults, NW Milos Island, Greece. It is hosted in 2.5–1.4 Ma pyroclastic rocks and is genetically related to andesitic/dacitic lava domes. Mineralization occurs as breccias, quartz-barite galena veins and stockworks within sericite-adularia or kaolinitic altered rocks. The mineralization is enriched in Mo, W and base- and precious metals (e.g. Pb, Zn, Ag) similarly to the neighbouring mineralization at Kondaros-Katsimouti and Vani, indicating common source of metals from a deep buried granitoid feeding western Milos with metals and volatiles. Paragenetic relations suggest early deposition of pyrite, followed by famatinite, polybasite and Ag-rich tetrahedrite, and then by enargite, suggesting fluctuating sulfidation states during ore formation. The evolution from Sb- towards As-rich enrichment indicate a renewed magmatic pulse (probably in the form of magmatic gases...

- by Panagiotis Voudouris
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- Ore Geology, Silver, Epithermal Gold Deposits, Milos Island

The Late Paleozoic Kochbulak and Kairagach deposits are located on the northern slope of the Kurama Ridge, Middle Tien Shan, in the same volcanic structure and the same ore-forming system. Au–Ag–Cu–Bi–Te–Se mineralization is confined to veins and dissemination zones accompanied by quartz-sericite wall-rock alteration. The tellurides, calaverite, altaite, hessite, and tetradymite are widespread at both deposits; at Kairagach selenides and sulfoselenides of Bi and Pb are common, while at Kochbulak Bi and Pb telluroselenides and sulfotelluroselenides are typical. The paragenetic sequence of telluride assemblages are similar for both deposits and change from calaverite + altaite + native Au to sylvanite + Bi tellurides + native Te, Bi tellurides + native Au, and, finally, to Au + Ag tellurides with time. These mineralogical changes are accompanied by an increase in the Ag content of native gold that correlates with a decrease in temperature, fTe2 and fO2 and an increase in pH.

- by Reimar Seltmann
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- Geology, Mineralogy, Epithermal Gold Deposits, Mineralogy and Petrology

- by Olga Plotinskaya
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- Mineralogy, Thermodynamics, Ore deposits, fluid Inclusions

The western Tethyan Metallogenic Belt hosts a variety of mineral deposits, particularly those of porphyry and epithermal types (Ovacık, 0.63 Moz Au at 4.34 g/t and 0.40 Moz Ag at 2.79 g/t Ag; Kiṣladağ, 10.4 Moz Au at 0.62 g/t). The Efemçukuru epithermal gold deposit, southwest of Izmir, Turkey is one of such deposits and contains a resource of 1.69 Moz Au (8.39 g/t, average grade). Hosted in carbonaceous phyllites of an Upper Cretaceous ophiolitic mélange sequence (Bornova Flysch), Efemçukuru comprises two mineralized quartz-rhodochrosite veins: Kestanebeleni and Kokarpınar.
Vein mineralogy and textures have been subdivided into six main stages based on crosscutting relationships. Early veins of quartz, chlorite, and calc-silicates (Stage I) are cut by two stages of brecciating and banded veins of quartz, rhodochrosite, rhodonite, and pyrite (II, III). Later veins with disseminated (IV) and massive base-metal sulfides (V) cut previous phases, and subsequently by late quartz-carbonate veinlets (VI). Gold mineralization occurs as electrum and with pyrite and galena in Stages III, IV, and V.
Both veins are controlled by moderately to steeply dipping NW- to NNW-trending structures that cut similarly striking rhyolite dikes. A structural analysis of the main fault, vein and rhyolite trends combined with rock and soil geochemistry indicate that the highest and most prolific gold grades are associated with the most NNW-trending vein structures, indicative of a fault-relay geometry.
Carbon and oxygen isotope analysis of vein carbonates indicate a mixed meteoric and magmatic source of the Efemçukuru hydrothermal fluids. Variations in δ13C and δ18O values reveal two trends of vein carbonate deposition; one through mixing of meteoric fluids with host rocks, and the second by strong degassing and cooling (i.e. boiling) of meteoric and magmatic fluids. The fluid-rock mixing trend is common in both Kestanebeleni and Kokarpınar veins, while boiling is a dominant process in the Kestanebeleni vein. The combined structural setting and fluid evolution suggest Efemçukuru can be classified as a non-adularia type low- to intermediate-sulfidation epithermal system hosted in sedimentary basement rocks in an extensional setting, making it atypical when compared to the standard volcanic-hosted model proposed for epithermal deposits.

- by Vladimir Kovalenker and +2
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- Mineralogy, Epithermal Gold Deposits
- by Andy Yahya
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- Mineralogy, Ore Geology, Epithermal Gold Deposits

Tellurides are significant minerals in gold deposits both as gold carriers and as indicators of PTx-conditions. In the Inner Carpathians belt tellurides are abundant in most deposits of the golden Quadrilateral (Apuseni Mountains) and sporadic in the Banska Stiavnica zone and the Zlata Bania zone. In the presenr paper we describe for first time altaite and tetradymite occurences in the Baia Mare district proved by e-probe data. Altaite (PbTe) was found in the Cavnic deposit in assemblage with sphalerite, galena, and rhodonite. It's chemical composition is close to stoichiometric: Te 37.61 wt. % and Pb 60.51 wt. %, total 98.12 wt. %. In the Cu-Bi assemblage of the Nistru deposit occurs tetradymite (Bi2Te2S) in intergrowth with chalcopyrite, gustavite, and native Au. Tetradymite appears as very small grains with the composition Te 36.99 wt.%, Bi 61.93 wt.% S 4.55 wt.% and calculated formula Bi2.03Te1.99S0.98. Paratellurite (TeO2), found in assemblage with native gold and gustavite...

- by Olga Plotinskaya
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- Geology, Mineralogy, Thermodynamics, Ore deposits
- by Olga Plotinskaya and +1
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- Genetics, Geochemistry, Geochronology & isotope Geology, Case Study
- by Reimar Seltmann
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- Geology, Mineralogy, Hydrothermal systems, Ore deposits
- by Florencia Gargiulo and +1
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- Epithermal Gold Deposits, Hydrothermal Alteration
- by Panagiotis Voudouris
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- Epithermal Gold Deposits
- by Olga Y Plotinskaya and +1
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- Mineralogy, Ore deposits, Epithermal Gold Deposits
- by Florencia Gargiulo and +1
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- Epithermal Gold Deposits, Hydrothermal Alteration