Epithermal Gold Deposits Research Papers (original) (raw)

2025, Minerals

The Silvermines Pb-Zn-Ag-Ba orebodies comprise vein, replacement, cross-cutting and stratiform mineralization mostly hosted in Lower Carboniferous limestones in the vicinity of a major ENE and E-W trending normal fault array and represent a classic example of Irish-Type Zn-Pb mineralization. Historically the deposits have been exploited at various times, but the major limestone-hosted Zn-Pb-Ba mineralization was not discovered until the 1960s. Structurally controlled crosscutting vein and breccia mineralization represent pathways of hydrothermal fluids escaping from the Silvermines fault at depth that exhaled and replaced shallowly buried Waulsortian limestones creating the larger stratiform orebodies such as the Upper G and B-Zones. The B-Zone, comprising a pre-mining resource of 4.64 Mt of 4.53% Zn, 3.58% Pb, 30 g/t Ag has a locally highly variable host mineralogy dominated by pyrite, barite, siderite, within dolomitic and limestone breccias with local silica-haematite alteration. A small, highly unusual pod of very high-grade Ag-rich mineralization in the B-Zone, the 4611 Pod, discovered in 1978, has not been previously documented. Unpublished records, field notes, and mineralogical and chemical data from consultant reports have been assimilated to document this interesting and unusual occurrence. The pod, representing an irregular lens of mineralization ca 2 m thick and representing 500 t, occurs within the B-Zone orebody and comprises high grade Zn and Pb sulfides with significant patches of proustite-pyrargyrite (ruby silvers) and a host of associated Pb, Ag, Sb, As, Cu, Ge sulfide minerals, including significant argyrodite. Although evidence of any distinct feeder below the pod is lacking, the nature of the pod, its unusual mineralogy and its paragenesis suggests that it represents a small, possibly late source of exotic hydrothermal fluid where it entered the B-Zone stratiform mineralizing system.

2025, Professional Paper

Comparison of medians for 12 elements in analyses of samples of the Pumpernickel Formation from a sparsely mineralized area (group 1) and from around the skarn (group 2) ________________________________________________ _ Array of numbers ofpaired-element analyses and Spearman correlation coefficients calculated from analytical determinations on 185 samples of sparsely mineralized rock of the Pumpernickel Formation (group 1, see text) ________ _ Array of numbers of paired-element analyses and Spearman correlation coefficients calculated from analytical determinations on 211 rocks of the Pumpernickel Formation from around the west ore body (group 2, see text

2025, International Journal of Engineering

The Rumbia Mountains, which in this study named Rumbia Complex is an east-west oriented, composed by a high-pressure/low-temperature, and a medium-pressure/low-temperature metamorphic rocks. The complex is identified as mica schist, glauchopane schist, and green schist. Rumbia Complex known as the location of gold deposits prospects discovered by local communities since 2007. The results of research showed that the metamorphic rocks are as hosts. There are two period of gold mineralization that occurs in this area, namely: 1) Associated with tectonic deformation and metamorphic rocks exhumation as a first period, and 2) Gold deposits related to post-tectonic as a result of hydrothermal activity in the Rumbia Complex. Radiometric age dating used 40 Ar/ 39 Ar geochronology, indicate that the first period of gold mineralization in the Rumbia Complex occurred ≈23 million years ago (MA), and the second period were subsequently overprinting at ≈6.8 million years ago (MA).

2024, Canadian Mineralogist

The newly discovered Bellerophon-Nelson telluride-bearing gold deposit at the St. Ives camp, Western Australia, is hosted by meta-sedimentary rocks of the lower Black Flag Group and alkaline intrusions. Four stages of mineralization are recognized; from oldest to youngest these are: quartz-carbonate veins (Stage I), quartz-albite-carbonate-pyrite veins and sericitepyrite seams (Stage II), quartz-pyrite veins (Stage III), and carbonate ± chlorite veins (Stage IV). Stages II and III contain economic gold mineralization, and the gold grains are strongly associated with pyrite. Intense albite and hematite alteration surround the mineralized veins, and trace amounts of gold precipitated in these altered rocks. The albite and hematite alterations are synchronous and derived from the same oxidized fluid as the auriferous veins. The occurrence and absence of hematite within the alteration zone reflects variable amounts of magnetite in the precursor rocks. Thirteen species of telluride and sulfosalt minerals have been identified in Stages II and III. The most common telluride minerals include calaverite, petzite, tellurobismuthite, and altaite, and these minerals have similar occurrences to native gold. In addition to native gold, telluride and sulfosalt minerals are also major Au carriers and account for at least 15% of the gold in this deposit. The mineral associations of PbCl(OH)-Pb 2 Cl 3 (OH)-Te-TeO 2 and BiOCl-BiO(OH,Cl)-Te-TeO 2 were formed as replacement of earlier telluride minerals as the result of reactions with Cl-bearing fluids. The intergrowth between native gold and Cl-bearing minerals + native Te/Te-oxide indicates that Au in telluride minerals was remobilized and re-deposited. The phase diagram for the telluride and sulfosalt mineral association suggests that during Stage II logƒS 2 decreased from -8 to -11, and that logƒTe 2 increased from -8 to the level required for the formation of Te-oxide. The values of logƒTe 2 and logƒS 2 in the Stage III veins were -8 to -11 and -9 to -11.5, respectively. The highly oxidized, tellurium-enriched hydrothermal fluid, which formed the Bellerophon gold telluride deposit, is consistent with the involvement of magmatic fluid, and sulfidation is the likely cause of gold precipitation.

2024

Nova Scotia produces over $250 million worth of industrial minerals and structural materials annually. Because of the importance of non-metal mining as a foundation industry in Nova Scotia, the Nova Scotia Department of Natural Resources (NSDNR) continues to evaluate the province's mineral resources with the long term goal of maintaining and increasing mineral development and employment in Nova Scotia. As part of this effort, review of NSDNR Assessment Reports and publications identified deposits of the mineral pyrophyllite near Coxheath, Cape Breton County. The pyrophyllite occurrence has been known since the late 1800s, however it was only recognized as a 'fire clay'. Greig (1943) identified the 'fire clay' as actually being the mineral pyrophyllite. Since the early 1900s the occurrence and/or economic significance of pyrophyllite as an industrial commodity has been forgotten. Lynch and Ortega (1997) mention pyrophyllic alteration and mapped occurrences in the Coxheath Cu-Mo-Au deposit area. During the fall of 2002, NSDNR staff located one of the main pyrophyllite bodies, and conducted trenching, sampling and geochemical analysis. This report focuses on the location, extent and industrial mineral potential of the pyrophyllite deposit(s). The relationship between the occurrence of pyrophyllite and previously described Cu-Mo-Au mineralization at the Coxheath deposit DeWolfe, 2001) and a complete ore model describing the Coxheath plutonic-volcanic belt and associated porphyryepithermal mineralized system is described by .

2024

Kolarite PbTeCl2 and radhakrishnaite PbTe3(Cl,S)2 are new mineral species found in gold-quartz ores ofthe Kolar deposit (India) at a depth of 1500 m. The minerals occur mostly intergrown as 20-40 pm aggegates that replace altaite inclusions in galena. Under reflected light the kolarite is grey with no visible anisotropism; radhakrisnaite is rosebrown with distinct anisotropism, in grains of 0.5 to I pm under magnification. Reflectance in air at 580 nm: kolarite 29.2o/o , radhakrishnaite 32.4q0 . Kplarite is orthorhombic, a 5.93(5), b 3.25(5), c 3.!9(5) A. the strongest seven diffractionlines [d in A(l)(hk[)I are: 3.91(4X001), 3.27(l0Xl0l,0l0), 2.35(5x201), 2.00(4x300), 1.79(3x301), 1.50(3X021,400), 1.35(3)(410,221). The calculated density is 9.14 g,/cmr for the mean composition, witb Z= l. Radhakrishnaite is tetragonal, a 5.7 l(5), c 3.77 (5) A. The strongest seven diffraction-lines are: 3.78(6)(@l), 3. I 6(1 0X0 I l), 2.73(4)(rrr),2.29(4)(021),1.92(5X030),r.78(5)(012,22r), 1.59(4X2...

2024, Society of Economic Geologists

The geochemical footprint of the giant Fruta del Norte (FDN) epithermal gold-silver deposit, located in the sub-Andean zone of south-eastern Ecuador, is examined using insightful quantitative geochemical and spatial studies. We look at intuitive coding and thematic attributes in ME-ICP and XRF data at deposit and at district scales. These are explored in iterative steps for the purposes of geological modeling, in providing vectoring strategies to mineralization and in relating FDN in terms of its structural and geochemical context to the Cordillera del Cóndor metallogenic district. The methodology entailed defining the percentile associations of Au, Ag and Cu with traditional pathfinder and commodity elements as an empirical targeting rationale from stream sediment and rock sample data. In addition, the molar element ratios of these samples semi-quantitatively track the effects of K-metasomatism through variations in alteration indices (e.g. ISer, Ishikawa, CCPI) and weathering indices (A-CNK). Furthermore, major oxides as well as REE distributions and other trace elements reveal variations in primary arc magmatic compositions, useful in the evaluation of porphyry copper potential (e.g. Sr/Y vs SiO2). FDN is hosted in andesitic volcanic successions and dacitic diatreme breccias of the Jurassic calc-alkaline Piuntza volcanic unit of the Santiago Formation. The deposit is buried by up to 300 m of late-mineral basinal volcaniclastics, tuffs and lavas of the Chapiza and Misahuallí Formations and is further capped by post-mineral Early Cretaceous quartz sandstones of the Hollín Formation. With locally spectacular visible gold, bonanza grades of up to 2447 g/t Au, its exquisite preservation of crustiform, colloform and often brecciated epithermal textures, added to its extensional structural geological and regional tectonic settings, FDN is renowned as an exemplary green-field exploration success and a valuable example for economic geologists working in arc terrains with significant late or post-mineral cover. The study illustrates the composite fault architecture of the FDN ore-body from a dataset obtained between 2006 to 2008 by Aurelian Resources Inc. These are rendered in Leapfrog-Geo and illustrate the concentric Au grade increase towards the northern part of FDN. Dramatic displacement of this portion of high grade Au to the north may imply the preservation of a late-stage catastrophic faulting dynamic involved in the Au grade distributions. Our work further relates the geochemistry and structure of FDN to that of the Cordillera del Cóndor metallogenic district which is well endowed with other epithermal gold-silver as well porphyry copper, molybdenum, gold and skarn gold deposits.. In order to elucidate key elements of the Cordillera’s metallogeny, alteration and structure we examine the percentile overlaps of key pathfinder and commodity elements from a substantial inventory of ME-ICP rock, soil and stream sediment sample data. The critical element associations are reduced to a matrix of points and these are further networked by Voronoi polygons so as to illuminate the Au-Ag-Cu potential of the Cordillera. The study reveals how the 2006 discovery of this completely buried gold deposit relates to regional structural and lithological controls on hydrothermal alteration and the resulting geochemical and Au grade domains within FDN. It further demonstrates how the integration of multi-element geochemistry to 2D and 3D modeling can be strategized in all stages of mineral exploration, resource evaluation and thus in understanding and reducing the associated project risks.

2024, Acadia University Press

The Fruta del Norte gold-silver discovery in southeastern Ecuador displays key aspects of low-and intermediate-sulphidation style mineralization, including an overlying siliceous sinter horizon. Base metal-poor, quartzadularia-calcite veins are spatially related to a distinctive feldspar quartz porphyry whereas Mn carbonate-and base metal-rich quartz veins dominate the deposit in andesite to the south and at depth. Both vein styles are succeeded upwards by silicic ore consisting of disseminated marcasite in chalcedonic silicification, veins and breccia. The lowsulphidation veins in the north are partly hosted by the feldspar quartz porphyry (160 Ma) whereas intermediatesulphidation veins cut Middle Jurassic or older andesite (host to 169 Ma molybdenite). Both underlie the Suárez pull-apart basin, a Late Jurassic clastic-volcanic depocenter linked to the regional Las Peñas fault zone. The exceptional preservation of the epithermal deposit is due to deposition of conglomerate on top of the still-active epithermal paleosurface. Alteration (silicification ± marcasite without gold) continued after the initial burial by conglomerate but ceased before the eruption of Late Jurassic andesitic lava (ca. 157-154 Ma) at the top of the Suárez basin sequence.

2024, Japan Geoscience Union

The origin of the eruption types of Izu Oshima Volcano, Japan, was reexamined mainly by geological and historical data. We once revealed the detailed synand post-caldera eruptive history of Izu Oshima Volcano by tephra and loess stratigraphy (Koyama and Hayakawa, 1996, J.Geogr.). Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 explosive eruptions occurred for the past 1500 years. Reexamining the relationship between the level of magma head and the period of ash spouting in the final stage of each eruption, we reclassified all the eruptions including effusive/small ones of Izu Oshima Volcano into five types: 1) effusive eruption with small-middle discharge mass of magma, occurred repeatedly during 1876-1974: a period of high magma head 2) explosive eruption with middle discharge mass of magma, associated with deposition of ash falls outside the caldera but with no dike intrusion (5 eruptions) 3) explosive eruption with middle discharge mass of mag...

2024, Field Conference of Pennsylvania Geologists, 83rd Annual Field Conference, Spring Valley, PA, Poster Session.

A caldera collapse model explains the origin of the Late Proterozoic volcanic rocks in the South Mountain region of Pennsylvania. The caldera collapse model includes development of a ring fault system, explosive eruption to form pyroclastic ash-flow sheets, catastrophic collapse due to evacuation of the magma chamber, down-faulting to form a topographic depression and subsequent caldera infilling. DEVELOPMENT OF THE BIG HILL CALDERA The Late Proterozoic was a time of crustal thinning and extensional faulting in the South Mountain region of Pennsylvania. A ring-fault system developed with a diameter of at least 12 miles extending from the Carbaugh-Marsh Creek Fault at the southern edge to the Bermudian Creek Fault at the northern edge. A magma chamber composed of rhyolitic material rose as the crust thinned. The Snaggy Ridge Rhyolite, an obsidian flow, was extruded from the early ring fault system.

2024, Revista de la Asociacion Geologica Argentina

La zona de alteración Arroyo La Chilca-Zanjón del Buitre está ubicada en el bloque de San Rafael (35°24'8" S; 68°19'25,8" O), Mendoza. Estudios previos definieron preliminarmente que corresponde a un sistema de tipo pórfiro cuprífero vinculado genéticamente al magmatismo gondwánico. Esta área de alteración se desarrolla en una secuencia compuesta por brechas ignimbríticas e ignimbritas traquiandesíticas con intercalaciones de areniscas tobáceas y coladas andesíticas a las que intruyen cuerpos subvolcánicos andesíticos y traquiandesítico-dacíticos. La litología de la secuencia volcánica así como sus características geoquímicas confirman su correlación con la sección inferior del ciclo magmático Choiyoi (Pérmico inferior). El área de alteración presenta una zona potásica con una asociación compuesta por feldespato potásico-cuarzo-magnetita. A ésta se superpone alteración fílica con una asociación de cuarzo-muscovita-pirita-(rutilo) acompañada por venillas de cuarzo-pirita. Por último se reconoce una carbonatización tardía. En las proximidades de la zona de alteración afloran vetillas con mineralización de pirita-calcopirita-galena-esfalerita en ganga de cuarzo. La geoquímica de metales indica moderadas anomalías de Ag y Au y pequeñas anomalías de Cu, Mo, Pb y Zn. El análisis estadístico permite definir la existencia de un pulso mineralizante de Cu-Mo y un segundo pulso de Mo reconocido solamente en Zanjón del Buitre. Asimismo se definen dos pulsos de Zn, uno de los cuales estaría genéticamente vinculado al Cu.

2024

A rarely occurring complete tetrahedrite-tennantite solid solution has been reported from the Schendleck area (Lower Austria). The fahlores from this region (“Schendleck-type ” fahlore) represents an unique type, exhibiting a strong inhomogeneity and a wide range of the Sb/(Sb+As) ratio (from 5 to 95 % tetrahedrite-content). The presence of the Schendleck-type fahlore indicates that the complete fahlore solid solution between the nearly pure Sb-endmember and the nearly pure As-endmember exists in nature. Zusammenfassung Das seltene Vorkommen einer kompletten Fahlerz-Mischkristallreihe (Tetraedrit-Tennantit) wird aus dem Bereich Schendleck (Niederösterreich) dokumentiert. Die einzigartigen Fahlerze dieses Gebietes („Schendleck-Typ “ Fahlerze) zeigen starke Inhomogenitäten und einen weiten Bereich des Sb/(Sb+As) Verhältnisses (von 5 bis 95 % Tetraedrit-Gehalt). Das Auftreten dieses Schendleck-Typ Fahlerzes weist darauf hin, dass die komplette Fahlerz-Mischkristallreihe zwischen dem na...

2024, Journal of Geochemical Exploration

The Amensif Cu-Pb-Zn-Ag-(Au) deposit is located on the northern flank of the western High Atlas Mountains, Morocco. This carbonate-replacement deposit occurs predominantly in Lower Cambrian carbonates along a major detachment fault that separates the Basal unit from the Upper unit. Orebodies are mainly massive replacements of carbonate strata, although sulphides also occur in veins. Silicification, chloritization, local skarn formation and sulphidation are the most important hydrothermal alteration features observed. The mineralogy is dominated by base metal sulphides with subordinate sulphosalts of Ag, Bi, Sb, Pb, and Au. The ore consists of chalcopyrite, pyrite, galena, sphalerite, arsenopyrite, tetrahedrite, tennantite, and Bi-Ag-Sb-Cu-Pb-Te sulphosalts (matildite, schirmerite, native bismuth, bismuthinite, freibergite, hedleyite, and krupkaite), anglesite, covellite, malachite, and azurite. Silver commonly occurs as Ag-Bi-Sb-Pb sulphosalts intimately associated within galena. SEM analyses confirm the occurrence of invisible gold within sulphides. Although S E M analysis of auriferous sulphides indicates the presence of gold in sufficient quantities to explain the bulk gold concentrations; native gold has not been detected in our polished sections. Gangue minerals include predominantly chlorite, epidote, tremolite, calcite, Mn-dolomite, saddle dolomite, quartz, sericite, with minor andradite and vesuvianite. The presence of a bismuth association at the Amensif deposit is typical, and was effective in scavenging gold and silver. Lead isotope compositions of galena sampled from two

2024, Minerals

The Ruwai skarn deposit is located in the Schwaner Mountain complex within the central Borneo gold belt and is currently considered the largest Zn skarn deposit in Indonesia. The deposit has been known to host Zn-Pb-Ag mineralization in the form of massive sulfide ore bodies; however, the occurrence of Ag-bearing minerals has not been identified yet. This study documents the mineralogical characteristics of several Bi-Ag sulfosalts and sulfoarsenides, as well as their chemical compositions. Ten Bi-Ag sulfosalts were identified, including native bismuth, tetrahedrite, cossalite, tsumoite, bismuthinite, joseite-B, Bi6Te2S, Bi-Pb-Te-S, Bi-Ag-S, and Bi-Te-Ag. Three sulfoarsenides were identified, including arsenopyrite, glaucodot, and alloclasite. The occurrence of Bi-Ag sulfosalts is typically associated with massive sulfide mineralization, although tsumoite can also be found associated with massive magnetite. In terms of sulfoarsenides, both arsenopyrite and glaucodot are associated w...

2024, Minerals

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

2024

Within most porphyry copper systems disseminated mineralization occurs as stockworks and veins. Contrary to accepted thoughts on the homogeneity of porphyry copper deposits, the mineralized fractures and microfractures impart strong anisotropies of rock properties and ore grades, which record changing stress regimes during the hydrothermal systems evolution. The Domeyko Cordillera ofnorthern Chile hosts several gigantic porphyry copper deposits. These porphyries have developed within active regional brittle shear systems during the Tertiary. Detailed structural sampling of domains and subdomains within a major deposit, at scales from centimetres to tens of metres, identifies a relative timing sequence and consistency of orientation for independent vein sets. Vein sets comprising the stockwork are characterized by consistent textures and mineralogies. Comparison of data derived from mining scale mapping (1: 1000; 1:2000) with the detailed scales shows a correlation only if the relatively earliest formed veins are considered. Interpretation of vein set and fault orientations with respect to the master fault direction indicates an ore control by Riedel (synthetic and antithetic) fractures, at the various scales, formed by regional simple shear. 40 Ar/39 Ar geochronology of alteration minerals from the different alteration phases impose restrictions on the relative and absolute timing of deformation and mineralization events. This is a contribution to IGCP Project Number 342 "Age and Isotopes of South American Ores".

2024, BJSTR

Among geologists, there is no common view on the most fundamental issues of the geological structure, composition, genesis, age, formation affiliation, formation conditions, and the characteristics of the metallogenic specialization of the Malguzar dike belt of the Southern Tien Shan. Some researchers distinguish them as a gabbrodiorite-diabase formation, others as a picrite-gabbro-diabase, gabbro-diabase-rhyolite dike, gabbro-diabase, gabbro-dolerite complex, etc. In this regard, some provisions and views on the genesis cannot be unambiguous.

2024, Ore Geology Reviews

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 NiTe 2 , merenskyite PdTe 2 , and sopcheite Ag 4 Pd 3 Te 4 ; (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 chlorite geothermometry provide evidence that occurrence of precious metals minerals at the Mikheevskoe deposit is mostly linked to epithermal overprint of the porphyry mineralization and was deposited at ca. 300 to 200 o C from moderately saline fluids (ca. 5 to 10 wt.%-eq.NaCl). It is suggested that the observed variability in Au and Ag minerals results from small fluctuations of S 2 and/or Te 2 fugacity. 2 Geological background The Mikheevskoe deposit is located in the South Urals approximately 200 km south of Chelyabinsk city (Fig. 1, inset). The deposit is part of the Novonikolaevsk ore cluster, which is confined to a ca. 20 km wide north-trending volcanic terrane at the junction of the East-and Transuralian terranes (or megazones), both of which are considered most prospective for porphyry-style mineralization in the Urals (Plotinskaya et al., 2017; Hammarstrom et al., 2017). Volcanic sequences of the Transuralian, as well as dioritic porphyry intrusions and related porphyry copper and skarn mineralization, are linked to a subduction event which lasted from the Late Devonian to the Early Carboniferous (Samygin and Burtman, 2009; Puchkov, 2017 and references therein). The Mikheevskoe deposit is hosted by a Late Devonian to Early Carboniferous (Tournaisian) volcano-sedimentary sequence comprising two lithological units (Belgorodskii et al., 1991). The lower unit consists of interbedded sandstone, tuffaceous sandstone, basaltic andesite, and tuffaceous breccia with subordinate siltstone, carbonaceous−cherty rocks, and basalt. The upper unit comprises of aphyric basaltic lava and pyroclastics with intercalated sandstone, quartzite, and carbonaceous-cherty rocks with numerous serpentinite bodies (Fig. 1). The intrusive rocks belong to Late Devonian to Early Carboniferous Ulyanovsk and Mikheevsky calk-alkaline igneous complexes (Grabezhev and Belgorodskii, 1992; Grabezhev, 2014). Intrusions of the earlier Ulyanovsk Complex are stocks and dikes of porphyritic diorite and andesite, and less frequent dacite, rhyodacite, and dolerite of the low-K series. Intrusions of the later Mikheevsky Complex, which are supposed to be linked to porphyry Cu mineralization (Belgorodskii et al., 1991), belong to the moderate-K series. These comprise equigranular and porphyritic rocks forming porphyry stocks and dykes, among which diorite, diorite porphyry, and plagiogranodiorite porphyry are the most common (Figs. 1 and 2a) (Grabezhev and Belgorodskii, 1992; Grabezhev, 2014). Post-ore dykes of plagiogranodiorite porphyry are also ascribed to the Mikheevsky complex (Grabezhev, 2014). Diorite porphyry of the Mikheevsky Complex was dated as 356 ± 6 Ma (U-Pb SHRIMP zircon age; Grabezhev and Ronkin, 2011), which is in good agreement with the Re-Os age of molybdenite (357.8 ± 1.8 Ma and 356.1 ± 1.4 Ma) obtained by Tessalina and Plotinskaya (2017). Porphyry-style mineralization is confined to a swarm of dykes of diorite, plagiogranodiorite and their porphyry equivalents of the Mikheevsky complex, covering an area of ca. 0.5 × 3 km that trends approximately north-south in between two large diorite stocks (Figs. 1 and 2).

2024, Mineralogy and Petrology

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-BiTe -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 þ altaite þ native Au to sylvanite þ Bi tellurides þ native Te, Bi tellurides þ native Au, and, finally, to Au þ 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, f Te 2 and fO 2 and an increase in pH.

2024, Geology of Ore Deposits

The Bereznyakovskoe ore field is situated in the Birgil'da-Tomino ore district of the East Ural volcanic zone. The ore field comprises several centers of hydrothermal mineralization, including the Central Bereznyakovskoe and Southeastern Bereznyakovskoe deposits, which are characterized in this paper. The disseminated and stringer-disseminated orebodies at these deposits are hosted in Upper Devonian-Lower Carboniferous dacitic-andesitic tuff and are accompanied by quartz-sericite hydrothermal alteration. Three ore stages are recognized: early ore (pyrite); main ore (telluride-base-metal, with enargite, fahlore-telluride, and gold telluride substages); and late ore (galena-sphalerite). The early and the main ore stages covered temperature intervals of 320-380 to 180 ° C and 280-300 to 170 ° C, respectively; the ore precipitated from fluids with a predominance of NaCl. The mineral zoning of the ore field is expressed in the following change of prevalent mineral assemblages from the Central Bereznyakovskoe deposit toward the Southeastern Bereznyakovskoe deposit: enargite, tennantite, native tellurium, tellurides, and selenides → tennantite-tetrahedrite, tellurides, and sulfoselenides (galenoclausthalite) → tetrahedrite, tellurides, native gold, galena, and sphalerite. The established trend of mineral assemblages was controlled by a decrease in , and and an increase in pH of mineral-forming fluids from early to late assemblages and from the Central Bereznyakovskoe deposit toward the Southeastern Bereznyakovskoe deposit. Thus, the Central Bereznyakovskoe deposit was located in the center of an epithermal high-sulfidation ore-forming system. As follows from widespread enargite and digenite, a high Au/Ag ratio, and Au-Cu specialization of this deposit, it is rather deeply eroded. The ore mineralization at the Southeastern Bereznyakovskoe deposit fits the intermediate-or low-sulfidation type and is distinguished by development of tennantite, a low Au/Ag ratio, and enrichment in base metals against a lowered copper content. In general, the Bereznyakovskoe ore field is a hydrothermal system with a wide spectrum of epithermal mineralization styles.

2024, IJASS JOURNAL

The target of this research is the Meri Block in the Kotamobagu area, North Sulawesi. This study aims to determine the relationship of alteration and mineralization of the Meri Block to indications of South BolaangMongondow gold availability. The research was carried out by observing outcrops, taking samples, measuring geological structure data, and analyzing them. The analyzed were studio analysis, thin section, XRF, AAS, and XRD. The analysis results show that the Meri Block belongs to two original landform units: structural and denudational. The stratigraphy of the research location is composed of four units: andesite, travertinesilicified, sandstone, and diorite intrusive. The structure at this location is generally dominated by right-wing faults trending NNW-SSE and WNW-ESE. The Meri Block has a structure with a steep slope leading to the Northeast-Southwest and Northwest-Southeast. The Northwest-Southeast structural zone has quartz veins of Low Sulfidation Epithermal. The geological structure in the Meri Block is controlled by a right-hand fault with an NW-SE or N036E/52 direction. This fault is a boundary between the Andesite and Sandstone Unit and controls alteration traps. The deposit in this block is a Low Sulfidation Epithermal in the transition horizon from precious metal to base metal. The grade in the Meri Block is around 0.02-0.26 ppm, probably because the rock is still undergoing alteration outside the mineralized system, and no characteristic quartz veins have been found, even though the alteration has been intense. In the comparative chart analysis, the elements Au and Ag generally correlate positively, a characteristic of Low Sulfidation Epithermal. However, the elements Au and the base metals Pb, Zn, and Cu negatively correlate.

2024, Ore Geology Reviews

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Chlorite, white mica and clay minerals as proximity indicators to ore in the shallow porphyry environment of Quebrada de la Mina deposit, Argentina

2024, Geology of Ore Deposits

The distribution of Re in ores of the Mikheevskoe Mo-Cu deposit in the South Urals is studied. It is established that the grade of Re in the ores usually does not exceed 0.5 g/t. A positive correlation between concentrations of Re and Mo (correlation coefficient 0.94), and Re and Cu (correlation coefficient 0.52) is found. EMPA of individual flakes of molybdenite showed that a Re content higher than the detection limit has been measured in most flakes studied, as a rule as high as 0.4-0.5 wt %, but occasionally reaching 1.34 wt %. Re within flakes of molybdenite is irregularly distributed. Patchy, linear, and concentric zoned patterns of zones with elevated Re content (usually 0.5-1 wt % Re, sometimes higher) are found against the lower con tent (up to 0.2 wt % Re) that is regularly distributed within the flake. Later hydrothermal processes and mechanical deformation of flakes result in epigenetic Re redistribution in molybdenite that leads to homogenization of molyb denite composition and smoothing of primary pattern, or removal of Re from molybdenite.

2024, Mediterranean Geoscience Reviews

Dikkartın is a monogenetic lava dome emplaced on the southern flank of Erciyes stratovolcano (3917 m) in central Anatolia, Turkey. Stratigraphic, granulometric, morphometric and textural variations are presented to obtain quantitative physical volcanological insight and to interpret eruption and emplacement mechanisms in Dikkartın eruptive sequence. Contrasting fragmentation and transportation dynamics in the stratigraphic sequence of the Dikkartın eruption is related to the ratio of magma and external water during each phases of the activity. We suggest four eruptive phases. The eruption begins with a dry, purely magmatic Plinian eruption with a column height of 20 km. According to the isopleth and isopach maps, the plume stretched in a NNE-SSW direction. The amount of water interacting with magma modified the course of the Dikkartın eruption. During a phase dominated by phreatomagmatism, an explosion crater and a tuff ring were formed. Exhaustion of the water in the environment and depletion of initial magmatic volatiles in the course of time resulted in extrusion of a lava dome. Sequential Fragmentation/Transport (SFT) theory has been applied on tephra samples to comment on fragmentation and transportation dynamics using grain size data. The magmatic and phreatomagmatic characters contained in each explosion sequence were numerically demonstrated. The relationship between the porosity time and the magma-water interaction time was investigated by detailed SEM analysis and roughness values calculated on volcanic ash. Surface analysis on volcanic ash suggested that most of the phreatomagmatic eruptions producing the tuff ring were dry with superheated steam but little vapour condensation occurred allowing adhesion of fine material on surfaces. Considering the c. 20 km plume height calculated for the climactic eruption column (Phase 1), the prevailing winds directed the cloud to the south, but due to the decrease in the plume height (Phase 2), the cloud was later directed to the northeast. According to the direction of seasonal winds, it is suggested that Dikkartın erupted during winter.

2024, Ore Geology Reviews

The Patricia ore deposit represents an unusual example of economic Zn-Pb-Ag mineralization at the northernmost end of the Late Eocene-Oligocene metallogenic belt in Chile. It is hosted by volcanosedimentary units, which are typically tuffaceous and andesitic breccias. The ore body consists of a set of subvertical E-W vein systems developed under a sinistral strike-slip regime that included transtensive domains with generalized extensional structures where the ores were deposited. The deposit is divided into two blocks by a set of NNW-ESE-trending reverse faults, which uplifted the eastern block and exhumed thicker and deeper parts of the deposit. At least 200 m of volcano-sedimentary pile hosting the mineralization has been eroded in this block. By contrast, the western block exposes a shallower part of the system where cherts, amorphous silica and jasperoids occur. Three main stages of mineralization have been defined: (1) pre-ore stage is characterized by early quartz, pyrite and arsenopyrite, (2) base-metal and silver stage; characterized by sphalerite (6 to 15 mol.% FeS), galena, chalcopyrite, pyrrhotite and Agbearing minerals (freibergite, polybasite, stephanite, pyrargyrite, freieslebenite and acanthite) and (3) post-ore stage; characterized by late quartz, kutnohorite and minor sulfides (arsenopyrite, sphalerite,

2024, Earth-Science Reviews

The study discusses the presence, formation and destruction of graphitic material in fault rocks of exhumed fault zones. Because of the low strength, the presence of lubricating graphitic material along fault zones has important implications for understanding tectonic movements in various crustal levels. Fault zones are permeable for ascending and descending fluids and represent, therefore, effective pathways of fluids between deep lithospheric levels and Earth´s surface, and this plumbing system is part of the carbon exchange system of the global carbon cycle between deep lithosphere and atmosphere. Processes of formation, structure and microfabrics of the graphitic material and the implications for the global carbon cycle in natural fault zones are still poorly understood. This paper gives an overview on the range of the origin of graphitic material along fault zones (e.g. organic vs. carbonatic vs. fluid origin) and its physical formation and destruction mechanisms. The presence of graphitic carbon permits: (1) to recognize faults with graphitic lubricants during faulting and allow assess, therefore, crustal strength over various temporal and spatial scales, (2) how carbon-bearing material is moving through the fault zone hence recording the complex structural history, (3) how carbon represents a monitor of fluid transport through fault zones, and (4) how graphitic material allow to pinpoint peak temperature conditions of the faulting process. The data implies also carbon transfer between depth and surface, which contributes to the global carbon cycle, but to a hitherto unknown extent. The presence of graphitic carbon in fault rocks has also implications on fault mechanics, engineering geology, nuclear waste repositories and assessment of seismic hazard.

2024, Earth-Science Reviews

2024, Mining of Mineral Deposits, 2022, Vol 16, Issue 3, p86 ISSNMining of Mineral Deposits, 2022, Vol 16, Issue 3, p86 ISSN

This paper aims to understand the genesis and nature of the manganese ore deposits associated with the Ras Samra Member of the Um Bogma Formation in the southwest of Sinai. Methods. Mineralogical and geochemical studies of 50 selected samples of manganese ores and host shale have been conducted. These samples have been taken from different sites representing the Ras Samra Member. Findings. The dominant manganese minerals are pyrolusite and hausmannite. In most samples, helvite and hematite are noted in association with pyrolusite. In the investigated manganese ores, wide ranges of MnO (17.70-81.90 wt. %) and Fe2O3 (1.16-65.49 wt. %) concentrations are observed. Based on their Mn/Fe ratio, they can be classified into high-Mn ore content (76.94-6.46%), medium-Mn ore content (4.87-2.58%), and low-Mn ore content (1.51-0.30%). Originality. The compositions of major and trace elements in Ras Samra manganese ores, together with their textures and mineralogical compositions, suggest an epigenetic hydrothermal contribution for high-Mn ores, as well as syngenetic sedimentary precipitation for medium-Mn and low-Mn ores. The epigenetic nature of the high-Mn samples may be related to a younger phase of hydrothermal activity associated with Tertiary basalt flows. Ore-bearing hypogene solutions, which penetrate the bedding planes, have impregnated and cemented non-diagenetic terrigenous sandstones and shale. Practical implications. In contrast to low-Mn ores, high-Mn and medium-Mn ores of Um Bogma are preferable for obtaining a significant economic effect in the production of ferromanganese alloys. However, low-Mn ores need to be processed appropriately to achieve the desired quality in order to meet the present level of manganese demand in Egypt.

2024

2024, Geology of Ore Deposits

2024, Economic geology and the bulletin of the Society of Economic Geologists

The Çöpler Au deposit is centered around shallow-level dioritic to granodioritic intrusive rocks of the middle Eocene Çöpler-Kabataş 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 potassically altered core overprinted by a more extensive phyllic alteration zone. The potassic alteration zone is associated with early M-type hairline magnetite and crosscutting B-type quartz ± magnetite ± sulfide veinlets, whereas the enveloping phyllic-altered rocks contain abundant D-type quartz-pyrite and lesser polymetallic quartz-sulfide veinlets. Overprinting intermediate-sulfidation epithermal Au mineralization occurred in two stages. Main-stage epithermal mineralization is characterized by carbonate-sulfide veinlets consisting of manganocalcite, arsenical pyrite, arsenopyrite, marcasite, chalcopyrite, tennantite/tetrahedrite, galena, and sphalerite. Late-stage sooty pyrite veinlets contain realgar and orpiment and are associated with zones of carbonate alteration. In the carbonate-sulfide veinlets, invisible gold is primarily hosted within arsenical pyrite and, to a lesser extent, by arsenopyrite, tetrahedrite, and tennantite. In sooty pyrite veinlets, invisible gold is associated with fine-grained arsenical pyrite. Gold-bearing manto-type carbonate-replacement zones, occurring distally to the porphyry system, display a mineral paragenesis similar to the epithermal carbonate-sulfide 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 mainly contained within pyrite and chalcopyrite. Polyphase brine inclusions (~47-62 wt % NaCl equiv) in early B-type quartz ± magnetite ± sulfide veinlets 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 manganocalcite and sphalerite from epithermal carbonate-sulfide veinlets trapped moderate-salinity (4-15 wt % NaCl equiv) fluids at ~290°C, whereas fluid 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) fluids. These data indicate that the Au-mineralizing system at Çöpler progressed from a high-temperature porphyry system to a relatively low temperature, intermediate-sulfidation epithermal system. Deposition of gold in the early stages of epithermal mineralization resulted from cooling, sulfidation, and neutralization of predominantly magmatic sourced hydrothermal fluids, whereas a meteoric water component is evident in the latest stage of mineralization. Deposit-scale geological observations combined with fluid 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. Specifically, the thick

2024, Precambrian Research

The dispersed carbonaceous matter (kerogen), illite, and magnetic response of the Tindelpina Shale Member in the lower part of the thick, extensive Tapley Hill Formation provide three complementary methods for zoning the incipient metamorphic character of rocks comprising the late Precambrian Adelaide System where they crop out between Adelaide, Olary, and Marree in the Adelaide Geosyncline. The methods are based on the following parameters: kerogen structure (as determined by X-ray diffraction) and composition (percentage carbon, hydrogen to carbon atomic ratio, 5 ~3CpDB); illite crystallinity;

2024, Mineralogy and Petrology

Electrum, hessite, petzite and sylvanite have been recorded from veins at Tyndrum, Scotland. Electron probe micro-analyses have also revealed two un-named Ag-Te-S phases. Fluid inclusion studies suggest that the mineralising fluids responsible for the precious metal mineralization contained ~ 7.0 mol % CO2 and 7 wt % NaC1. TH (temperature of homogenisation) determinations were in the range 295 °C to 325 °C and a depth of vein formation ~ 4 km is indicated. Mineral precipitation was probably caused by cooling and adsorption of gold onto pyrite. ~348 values of + 1.8%0 for galena from the Au + Ag + Te veins suggest a different (possibly igneous) sulphur source to that producing the Pb + Zn vein mineralization in the Tyndrum area. Although an age of ~ 380 Ma was obtained using K-feldspar in the veins the data are not conclusive. It is argued that the Au + Ag mineralization at Tyndrum is due to hydrothermal activity related to Cu + Mo mineralization associated with the Late Caledonian granites.

2024, Goldschmidt2022 abstracts

2024, Geology of Ore Deposits

The first findings of Au and Ag tellurides (sylvanite and petzite) in sulfide-quartz ore of the Shi rokinsky ore and placer cluster located in the Sette Daban Horst Anticlinorium are described. These miner als were found for the first... more

2024, Geologica Carpathica

A well-preserved volcaniclastic sequence crops out in Pleistocene marine sediments along the Tyrrhenian coastline of the Calabrian-Peloritani arc (Sicily, Italy), testifying the occurrence of Lower-Middle Pleistocene volcanic activity in Southern Tyrrhenian Sea. The presence of dominant highly vesicular and minor blocky glassy particles indicates that the volcanic clasts were originated by explosive events related to the ascent and violent emission of volatile-rich magmas accompanied by and/or alternated with hydromagmatic fragmentation due to magma-sea water interaction. Field investigations and sedimentological features of the studied volcaniclastic units suggest a deposition from sediment-water density flows. The chemical classification of the pumice clasts indicates prevalent rhyolitic and dacitic compositions with calc-alkaline to high-K calc-alkaline affinity. The geochemical features of immobile trace elements together with the presence of orthopyroxene are indicative of a pr...

2024, Open-file report /

The Whitehorse caldera is a Miocene collapse structure located in southwest Oregon, about 15 km northwest of the McDermitt caldera complex. Eruption of the peralkaline rhyolite tuff of Whitehorse Creek at 15.0+.3 m.y. resulted in the formation of a circular caldera 15 km in diameter. Rhyolite domes and associated flows were emplaced around the margin of the caldera and the caldera was subsequently filled with tuffaceous sediments and pyroclastic deposits. Lithologic studies of a 135 m thickness of caldera-fill deposits encountered in a 226-m deep drill core document a quiet lacustrine sedimentation record repeatedly interrupted by rapid deposition of thick volcanic ash beds. The upper 37 m of the deposits consist primarily of diatomaceous earth with subordinate volcanic ash interbeds. A vertical zonation in alteration mineralogy occurs in the core with the upper 110 m being unaltered and the lower 35 m altered to zeolites and potassium feldspar. Phillipsite and erionite occur in the upper part of the alteration zone and with increasing depth clinoptilolite and potassium feldspar are present. Radipmetric logging of the drill hole for uranium and thorium showed no anomalous zones.

2024, Resource Geology

The Bulawan gold-silver telluride deposit in Negros Occidental, Philippines, has characteristics which are similar to other Te-rich Circum-Pacific gold deposits, such as its occurrence in volcanic rocks, occurrence with sericite alteration, and occurrence with hydrothermal breccias. Hydrothermal alteration in the Bulawan deposit is dominated by sericite and carbonate deposition, similar to Kelian (Van Leeuwen et al., 1990). The host rocks in Bulawan are dacitic breccia pipes which resemble diatremes in Montana Tunnel (Sillitoe et al., 1985). A few examples of other gold telluride deposits are Acupan

2023, Collected reprint series

Craters, calderas, and bedded hyaloclastites are commonly associated with seamounts. New Sea MARC 1 side-looking sonar data for the summit of MOK seamount located near the East Pacific Rise (EPR) at 10øN show that MOK has a large caldera consisting of three coalesced circular depressions. These data also reveal many features such as stepped crater walls, talus deposits, ring faults, intracaldera flows, small cones, lava tubes and channels,•and other features. Results of an ALVIN submersible dive in the crater of seamount "F" near the EPR at 21722'N, 108ø37'W revealed the presence of bedded hyaloclastite deposits; bedded hyaloclastites were also recovered by dredging of six other volcanoes all with summit craters. The bedded hyaloclastites are thin blankets of several types of basalt glass shards in a matrix of bottom sediment, clay, and ferromanganese minerals. The glass shards are chemically homogeneous and similar to midocean ridge basalts and transitional basalt lavas typical of young seamounts. Hyaloclastite deposits are crudely inverse graded with tabular, platy shards parallel to bedding. The characteristics of bedded hyaloclastites on seamount suggest an origin by rapid eruption rate, explosive mixing of magma and seawater, followed by rapid transport and deposition, such as may occur during submarine lava fountaining. MARC 1 side scan sonar data for the summit area of MOK seamount near the East Pacific Rise at 10øN detail the morphology of the walls and floor of a complex summit caldera. The caldera on MOK and the crater of F strongly resemble features on better studied subaerial basaltic shield volcanoes. For this reason we interpret their origin and evolution by processes known to occur on subaerial shield volcanoes of Hawaii and the Galapagos islands. The second purpose of this paper is to present field and laboratory data on the bedded hyaloclastite on seamount F and Other young seamounts near the East Pacific Rise. All the seamounts known to contain bedded hyaloclastites also have summit craters or calderas. Our data constrain the types of eruptions that produce bedded hyaloclastites on seamounts. Although similar bedded hyaloclastites are also found within normal ocean crust [Schmincke et al., 1978], we speculate that on seamounts the eruptive activity near summit craters can produce bedded hyaloclastites of the type we have observed. The question of genetic links between caldera collapse and the formation of bedded hyaloclastite on seamounts remains unanswered.

2023, Terra Nova

A mechanism is presented for the pulses of high fluid pressure (P F) necessary for fluid-assisted brecciation. Establishment of hydraulic-or pneumatic-connectivity between rock masses with different P F can cause overpressure in the higher rocks because the P F gradient is parallel to the hydrostatic gradient (the centroid effect). P F can become high enough to create a fracture network, Accepted Article This article is protected by copyright. All rights reserved. with an influx of fluids and mineralisation occurring as fluids migrate to areas of lower P F. Changes in P F caused by the centroid effect can cause other structures and seismicity.

2023, Arabian Journal of Geosciences

At the Echo Bay mine, vein type U-Ni-Ag-Cu deposits occur along NE-SW-trending fracture zones in ca. 1,800 m.y. old andesitic tuffs. The mineralization stages within veins of the Echo Bay mine are: 1. Quartz-hematite stage. 2. Pitchblende stage. 3. Co-Ni arsenides with native silver and bismuth stage. 4. Early acanthite stage. 5. Main sulfide and dolomite stage. (Within this stage, acanthite, chalcopyrite, bornite, sphalerite, and galena occur in up to three phases of mineralization.) 6. Late native silver stage. 7. Mckinstryite stage. Both primary and pseudo-secondary fluid inclusions, in the dolomite and quartz of the later stages, contain NaCI crystals. The heating experiments on these samples and the analyses on the extracted fluids indicate a salt concentration of about 30 weight percent and K/Na atomic ratios of H0.4 to H0.2. The temperatures of mineralization suggested by the occurrence of native bismuth and mckinstryite, the fluid inclusion filling temperatures, the sulfur isotopic compositions of coexisting sphalerite and galena, and the oxygen isotopic compositions of coexisting quartz and hematite were: around 120 ø C for the first four stages, about 200 ø C for stages 5 and 6, and below about 95 ø C for the last stage. The original depth of ore deposition suggested from the temperature and the stratigraphic data was between 2.5 and 4.5 km. The oxygen isotopic compositions of quartz, hematite, calcite, and dolomite samples, together with the temperature data, suggest that the oxygen isotopic composition of hydrothermal water was nearly constant throughout the entire depositional stages with /•O •8 values of q-l.0 =l= 2.5 • (SMOW). These/•O•8a2o values suggest very little, if any, contribution of magmatic water in the Echo Bay ore-forming fluids. The/•C •a values of dolomite and calcite of different stages are similar and within the range of-4 to-1.5• (PDB). However, the/•S s4 values of the vein sulfides show a very large spread of H50•, with a definite trend of increasing/•S a4 values toward later stage sulfides: from ca.-22• for the earliest sulfide (acanthite), H-4 to for stage 5 sulfides, to ca. q-27• for the last stage sulfide (mckinstryite). This wide range in the/•S a4 values of the hydrothermal minerals contrasts with the uniform/•S values (+2 to +5 ff•) of the pyrite in the host rock tuffs. The data on the mineralogy, temperature, and the sulfur and carbon isotopic compositions of the hydrothermal minerals were used to evaluate the chemistry of hydrothermal fluids. Both the mineralogical and the isotopic data appear to be best explained if: (1) the oxidation state of the fluids decreased continuously with time from that within the hematite stability field, through near the pyrite-hematite-magnetite triple point, to near the pyrite-pyrrhotite-magnetite triple point (also near the quartzmagnetite-fayalite boundary), (2) the pH remained relatively constant at around 4.0, (3) 2S content decreased from •-,10-2 to H10-4 t6ward the later stages, (4) 2C content decreased from H1 m to H10-2 toward the later stages, (5) 2Ag concentration in the fluids decreased from H1 ppm to H0.1 ppm toward the latter stages, and (6) the mean isotopic compositions of sulfur and carbon in the fluids remained constant at = q-25 =l= 3 and/•C•a•c =-5 =l= 2•. The/•OlSa2o and/•Sa4•s values and the initial high oxidation state of the hydrothermal fluids possibly reflect an origin as surface water. A model which involves the circulation and boiling of sea water caused by the intrusion of diabase at about 1,450 m.y. ago is presented to explain the concentration of salts, enrichment of O •s, reduction of oxidation state, decreasing of pH of the fluids, and leaching of heavy metals from volcanic rocks. 635 636 1•. W. ROBINSON AND H. OHMOTO Introduction THE Echo Bay mine, one of Canada's richest silver producers, is situated adjacent to the old Eldorado mine at Port Radium .on the east shore of Great Bear Lake, Northwest Territories (Figs. 1 and 2). It is about 50 km south of the Arctic Circle, or about 1,400 km north of Edmonton at longitude 118ø02'W and latitude 66ø05'N. The Eldorado mine produced silver and uranium concentrates during the period of 1934 to 1960, and Cominco operated the Echo Bay property from 1930 to 1941. The current mining operation at Echo Bay (Echo Bay Mines Ltd.) commenced in 1964 as an extension of Nos. 1 and 2 adits driven by Cominco in the 1930s. In 1967 a third adit was opened for high-grade silver and uranium ore recovery. The sinking of a three-compartment shaft was completed in 1968, and the shaft is now being extended to service eight levels. During 1971, the mine produced approximately 75 tons of silver and 300 tons of copper. The present study is one of several geochemical projects aimed at understanding the genesis of ore deposits in the Northwest Territories. In this paper, data on the mineralogy, paragenesis, fluid inclusions, and stable isotopes of oxygen, carbon, VICTORIA BEAR [AI• PORT / I SLAVE PROVINCE I ()2390 m.y.) I YELLOWKNIFE GREAT SLAVE LAKE-. ,•BOUNDARY OF •' ß CANADIAN SHIELD •. ___BOUNDARY OF ' BEAVERLODGE Fro. 1. Location map of the Echo Bay mine and the Bear Province, Northwest Territories, Canada. The ages of the basement rocks are from Wanless et al., 1968. and sulfur are presented. These data together with recently developed concepts on isotopic behavior in hydrothermal ore deposits (Ohmoto, 1972)are used to define the chemistry and the origin of ore-forming fluids. Geologic Setting The east shore of Great Bear Lake constitutes part of the Bear Province which contrasts in age (2,390-1,640 m.y.) with the adjoining Slave Province (>2,390 m.y.) (see Fig. 1). It is also a discrete metallogenic province characterized by NE-SWtrending faults and by vein type deposits of uranium, native silver and bismuth, cobalt-nickel arsenides, and copper sulfides. A detailed description of the geology and the results of geochronologic studies of the east (or McTavish) Arm of Great Bear Lake are presented in Robinson (1971) and Robinson and Morton (1972). They are also summarized in Table 1. Three sedimentary-volcanic stratigraphic groups, the Echo Bay (oldest), Cameron Bay, and Hornby Bay Groups, have been distinguished in the McTavish Arm. The former two groups crop out primarily in the eastern part, and the last in the northern part of the area. Intrusive rocks, which range in ages from •-1,800 to •-1,400 m.y. and in composition from feldspar porphyry, granodiorite, granite, to diabase, are also the predominant rock types of the area. The structure of the area is relatively simple. The sedimentary and volcanic rocks occur as northerly elongated roof pendants within the intrusive granitoids. Folding is not common. Three main fault and fracture systems are recognized: the E-W system, oldest and characterized by intrusions of diabase dikes; the NE-SW system, characterized by mineralized veins; and the N-S system, the youngest. 638 TABLE 1. B. W. ROBINSON AND H. OHMOTO Sttatigraphy and Geologic Events within the East Arm of Great Bear Lake Stratigraphic Column Geologic Events Age (m.y.) Paleozoics (?) < 600 Uplift/Erosion Intrusions of quartz-diabase sills & dikes/U-Ag mineralization/ Intrusions of giant quartz veins Faulting (NE trending) Intrusions of diabase dikes Faulting (E trending) Hornby Bay Group (300+ m) Subsidence > 1,500 Uplift/Erosion Regional metamorphism (?) •1,650 (?) Intrusion of granites & granodiorites •1,800 Intrusions of porphyries Cameron Bay Group (300+ m) Subsidence N1,800 ? Uplift/Erosion Upper Echo Bay SubGroup (1,500+ m) Volcanism •1,800 Lower Echo Bay SubGroup (1,200+ m) Cliff Series (300 m) Hornblende Porphyry Series (180 m) Tuff Series (390 m) Mine Series (350+ m

2023, Geological Society of America eBooks

2023

The Perama Hill deposit is a high-to intermediate-sulfidation Au-Ag-Te epithermal system hosted within silicic and argillic altered andesitic hyaloclastic rocks and overlying sandstones. New combined EPMA and fluid inclusion data from the deeper parts of the deposit suggest early deposition of native gold, Bichalcogenides (kawazulite/tetradymite solid solutions) and thiostannates (probably at 291-349°C), followed by precious metal tellurides and electrum between 193 and 269°C. There is a trend from high-to intermediate-sulfidation state fluid conditions with time. The coexistence of both liquid-and vapor-rich inclusions homogenizing within the same temperature range demonstrates that boiling occurred during formation of the ore minerals. The kawazulite/tetradymitess-gold association at Perama Hill suggests that it could have formed from a sulfide melt in the system Bi-Au-Se-Te system as gold was scavenged from the hydrothermal ore-forming fluid at elevated temperatures.

2023, IOP conference series

Kerinci area is a small part of the Barisan Range where the Magmatic Arc Zones and a valley extending from the northwest to the southeast flanked by hills with steep slopes on both of sides that flank it. Isolated hill which is on the Kerinci Lake is the main focus to be studied because its existence is located in the middle of a part of the depression Kerinci Lake. In additions, in the vacinity of the research site there has never been research conducted both of in general and specifically. The research was conducted by interpreting the geological controlled by mechanism on isolated hill morphology forming based on geomorphoogical approach and petrographic analysis. Kerinci Lake on the south side of the research site is indicated as volcano-tectonic lake. The isolated hill is thought to be related to the formation of Kerinci Lake. In saveral location along the path of the Sumatran fault saveral lakes were found which were controlled by this fault. Sumatran fault formation is influenced by strike slip, while the formation of the lake is influenced by extensional stress. Based on it is existence, understanding the location of the research could be done analyzedg of volcanism and structural geology.

2023, Minerals

A rare gold–telluride montbrayite from the large Svetlinsk gold–telluride deposit (South Urals, Russia) was comprehensively studied using optical microscopy, scanning electron microscopy, electron microprobe analysis, reflectance measurements, electron backscatter diffraction, and Raman spectroscopy. Significant variations in the composition of the mineral were revealed (in wt%): Au 36.98–48.66, Te 43.35–56.53, Sb 2.49–8.10, Ag up to 4.56, Pb up to 2.04, Bi up to 0.33, Cu up to 1.42. There are two distinct groups with much more-limited variation within the observed compositional interval (in wt%): (1) Au 36.98–41.22, Te 49.35–56.53, Sb 2.49–5.57; (2) Au 47.86–48.66, Te 43.35–44.92, Sb 7.15–8.10. The empirical formula calculated on the basis of 61 apfu is Au16.43–23.28Sb1.79–6.09Te32.01–38.89Ag0–3.69Bi0–0.14Pb0–0.90Cu0–1.96. Two substitution mechanisms for antimony are proposed in the studied montbrayite grains: Sb→Au (2.5–5.6 wt% Sb) and Sb→Te (7–8 wt% Sb). The dependence of the ref...

2023, Turkish Journal of Earth Sciences