Ore Paragenesis Research Articles

Characteristics of the gold-bearing and barren quartz veins at the Zaylik-Sarilar epithermal deposit, Ahar-Arasbaran Zone, NW Iran: Evidence from mineralogy, alteration, texture and fluid inclusion

The Zaylik-Sarilar epithermal deposit is located 35 km southeast of Ahar in the Ahar-Arasbaran Zone in the Alborz-Azerbaijan Magmatic Belt, NW Iran. Exposed rocks in the Zaylik-Sarilar deposit are mainly composed of Eocene volcanic rocks and Miocene dacite-rhyodacite that are intruded by younger intrusions. The deposit occurs within a sequence of Eocene porphyritic andesite and andesitic lithic tuff. Mineralization occurs as open space filling, taking place as irregular veins, veinlets, and hydrothermal breccias. The mineralization zones can be categorized into two main groups according to sulfides and sulfosalts mineralogy, alteration assemblages, ore textures, and fluid inclusion data. The first group consists of gold-bearing quartz-sulfide ± breccia veins, silicified-phyllic ± argillic zones, and a few quartz-calcite veins. The second group is composed of barren milky (or white) quartz veins, silicified lithocaps, and argillic-kaolinite ± silicic zones. Pyrite, chalcopyrite, bornite, galena, sphalerite, and Au-Ag sulfosalts were identified in ore paragenesis of the gold-bearing veins. Pyrite is the main sulfide mineral in the barren quartz veins and silicified lithocaps. Gold and silver were enriched during oxidation and supergene alteration of the gold-bearing veins. Textural evidences from the gold-bearing veins, such as mosaic breccia monomicts, floating clast breccias, hydrothermal breccias, colloform-crustiform textures, ginguro bands, dendrite textures, and rarely lattice- and parallel-bladed calcite replacement textures, suggest that boiling occurred in the veins. Comb, cockade, reed molds, zonal, and feathery textures are common in the barren veins and silicified lithocaps. Fluid inclusion data show a decreasing trend in salinity and homogenization temperature (Th) from the gold-bearing quartz veins to the barren ones. The average salinity and homogenization temperature (Th) of fluid inclusions from the gold-bearing veins are 1.05 wt% NaCl equiv. and 297 °C, respectively; higher than the average salinity (0.68 wt% NaCl equiv.) and homogenization temperature (192 °C) of fluid inclusions from the barren quartz veins. Th versus salinity diagram suggests that boiling was the main mechanism of ore deposition in the gold-bearing quartz veins and silicified zones. These data propose that the barren quartz veins and silicified lithocaps were formed by cooling. A combination of the geologic, mineralogic, alteration, and fluid inclusion data from the Zaylik-Sarilar deposit represents an epithermal system of low-sulfidation type. Structurally, mineralization has been controlled through the NW-trending strike-slip principal displacement zone and it’s subsidiary Riedel fractures in response to a N-trending compression in the Arabia-Eurasia collision zone.

Geology, mineralogy, ore paragenesis, and molybdenite Re-Os geochronology of Sn-W (-Mo) mineralization in Padatgyaung and Dawei, Myanmar: Implications for timing of mineralization and tectonic setting

• Magmatic-hydrothermal activity occurred as several discrete events in the Western Granite Province of SE Asia. • The Sn-W (-Mo) mineralization constrained to Cretaceous to Paleocene age. • Extensive granite-associated Sn-W (-Mo) mineralization events in the Western Granite Province occurred during ca. 75 Ma and 60 Ma. The Sn-W (-Mo) deposits of Myanmar are mostly located in the Western Granite Province that is well known for its world-class Sn-W (-Mo) deposits. Previous studies have constrained the age of the granitic intrusions of the province and the timing of mineralization for a few deposits, but most of the mineralization ages are not well established. In this study, new molybdenite Re-Os dating of two Sn-W-(Mo) regions, Padatgyaung and Dawei, together with their geological setting and mineral paragenesis are carried out to constrain the timing of ore formation and geodynamic setting. In the Padatgyaung region, two weighted average Re-Os model ages of 64.23 ± 0.29 Ma (MSWD = 0.49, 2σ) and of 60.54 ± 0.45 Ma (MSWD = 1.3, 2σ) from vein molybdenites are considerably younger than molybdenite from tin mineralized greisen which has a weighted Re-Os model age of 68.5 ± 2.7 Ma (MSWD = 0.14, 2σ). This demonstrates that the vein-type W-Mo mineralization formed after tin mineralized greisenization. Combining our new age data with previous geochronological data, the Re-Os model age of 63.09 ± 0.17 Ma from the Wagone quartz vein suggests that the Sn-W(-Mo) mineralization in the Dawei region took place at around 70–60 Ma (Late Cretaceous to Paleocene). This study indicates the presence of a significant and discrete granite-related Sn-W(-Mo) mineralization with an age of 75–60 Ma in the Western Granite Province, although the overall age range of Sn-W mineralization in the belt spans from 120 to around 40 Ma emplaced during normal subduction and roll-back of the Neo-Tethyan oceanic crust.

Au-Pd in Bi-Se piriti in halkopiriti iz rudnika bakra, Bućim, Vzhodna Makedonija

In the Buchim porphyry copper deposit, we determined several representative rare mineral phases, comprising metals from the gold-palladium group as well as those from the bismuth-selenium (Cu-Bi-Se-Te-As) group. The bismuth-selenium rare mineral phases are represented by new rare mineral phases in the Buchim porphyry copper deposit, bismuthinite, galenobismutite, krupkaite, friedrichite, emplectite, laitakarite and native bismuth as well as mineral phases of gold-palladium, including gold and palladium with their elemental mixtures. It should be stressed that both types of rare mineral phases were determined in pyrite and chalcopyrite from major ore paragenesis in the Buchim deposit. The bismuth-selenium mineral phases were related to the major quartz-pyrite-chalcopyrite paragenesis, while the gold-palladium phases were related to a slightly higher temperature, oxido-sulphide parageneses such are magnetite-pyrite-chalcopyrite (Mt-Py-Cp) and pyrite-chalcopyrite (Py-Cp).

Occurrence and Distribution of Silver in the World-Class Río Blanco Porphyry Cu-Mo Deposit, Central Chile

Abstract Porphyry Cu-Mo deposits (PCDs) are the world’s major source of Cu, Mo, and Re and are also a significant source of Au and Ag. Here we focus on the world-class Río Blanco PCD in the Andes of central Chile, where Ag is a by-product of Cu mining. Statistical examination of an extensive multielemental inductively coupled plasma-mass spectrometry data set indicates compositional trends at the deposit scale, including Ag-Cu (r = 0.71) and Ag-In (r = 0.53) positive correlations, which relate to Cu-Fe sulfides and Cu sulfosalts in the deposit. Silver is primarily concentrated in Cu ores in the central core of the deposit, and significant variations in the Ag concentration are related to the different hydrothermal alteration types. The concentration of Ag is highest in the potassic core (avg 2.01 ppm) and decreases slightly in the gray-green sericite (phyllic) zone (avg 1.72 ppm); Ag is lowest in the outer propylitic alteration zone (avg 0.59 ppm). Drill core samples from major hydrothermal alteration zones were selected for in situ analysis of Ag and associated elements in sulfide and sulfosalt minerals. To ensure representativeness, sample selection considered the spatial distribution of the alteration types and ore paragenesis. Chalcopyrite is the most abundant Cu sulfide in Río Blanco, with Ag concentration that ranges from sub-parts per million levels to hundreds of parts per million. The highest concentration of Ag in chalcopyrite is associated with the high-temperature potassic alteration stage. Bornite is less abundant than chalcopyrite but has the highest Ag concentration of all studied sulfides, ranging from hundreds of parts per million up to ~1,000 ppm. The Ag concentration in bornite is higher in lower-temperature alteration assemblages (moderate gray-green sericite), opposite to the behavior of Ag in chalcopyrite. Pyrite has the lowest Ag content, although concentrations of other critical elements such as Co, Ni, and Au may be significant. The highest Ag concentrations, i.e., thousands of parts per million up to weight percent levels, were detected in late-stage Cu sulfosalts (enargite, tennantite, and tetrahedrite). The Ag content in these sulfosalts increases with increasing Sb concentrations, from the Sb-poor enargite to the Sb-rich tetrahedrite. The earliest Ag mineralization event is related to the potassic alteration stage represented by early biotite and transitional early biotite-type veinlets and where the predominant sulfides are chalcopyrite and bornite. Silver mineralization during this stage was predominantly controlled by crystallization of Cu-Fe sulfides. The second Ag mineralization event at Río Blanco is associated with the transitional Cu mineralization stage, which is represented by the gray-green sericite alteration (C-type veinlets). In this alteration type, Ag was partitioned preferentially into chalcopyrite, bornite, and to a lesser extent pyrite. The last Ag mineralization event is related to the late quartz-sericite alteration stage, characterized by D- and E-type veinlets with pyrite-chalcopyrite and enargite-tennantite-tetrahedrite. Our data indicate that Ag was associated with several Cu mineralization episodes at Río Blanco, with Ag concentration apparently controlled by cooling, changes in pH, fO2 and fS2 of the hydrothermal fluids, and the intensity of alteration. Overall, our results provide information on critical metal partitioning between sulfides, plus the distribution of critical element resources at the deposit scale. Knowledge of the mineralogical occurrence of critical metals in PCDs is necessary to better assess their resources and evaluate the potential for their recovery.

Gold-telluride-sulfide association in the Jinqu Au deposit, Xiaoqinling region, central China: Implications for ore-forming conditions and processes

The Jinqu Au deposit, located in central Xiaoqinling gold field along the North China Craton’s southern margin, has total reserve of 21 t of Au with 4.23 g/t Au on average. It consists cccmainly of ore-bearing auriferous quartz veins in amphibolite facies metamorphic rocks of the Archean Taihua Group. The deposit’s mineral paragenesis and ore-forming processes have never been studied. This paper reports its mineral paragenesis, which includes sulfides (pyrite, galena, chalcopyrite, pyrrhotite, sphalerite, molybdenite and bornite), oxides (rutile, scheelite, hematite, magnetite), tellurides (sylvanite [(Au, Ag)2Te4], hessite [Ag2Te], petzite [Ag3AuTe2], krennerite [Au3AgTe8], calaverite [AuTe2], stützite [Ag5−xTe3], empressite [AgTe], rucklidgeite [(Pb, Bi)3Te4], altaite [PbTe], volynskite [AgBiTe2], tetradymite [Bi2Te2S], lingbaoite (AgTe3) and melonite [NiTe2]) and native elements (tellurium and gold). Based on our data, the associated ore-forming processes can be deduced as: iron oxides → (CO2(g) and H2S(g) loss, ƒTe2/ƒS2 ratio increase) sulfides, Au-Ag-tellurides → (condensation of H2Te vapor) Pb-Bi-tellurides → (mixing with meteoric water) carbonate. It has been indicated by thermodynamic modelling that formation of Au-Ag-Te-bearing minerals occurred under physico-chemical conditions of logƒTe2 values from −7.28 to −3.21, logƒO2 values from −26.67 to −26.44, logƒH2S values from −1.34 to 0.34, logƒS2 values from −9.53 to −5.64, logαAu+(aq)/αAg+(aq) values from −4.72 to −4.55 and pH values from 3.33 to 4.20 at 365 ℃ and logƒTe2 values from −10.53 to −6.62, logƒO2 values from −31.99 to −30.98, logƒH2S values from −0.65 to −0.36, logƒS2 values from −13.62 to −7.20, logαAu+(aq)/αAg+(aq) values from −6.42 to −6.21 at 335 ℃. The changes in physico-chemical conditions and in precipitation of Au-Ag-Te-bearing minerals were due to boiling or to condensation of Te-rich magmatic gas into ore-forming fluids. These reflect evolution from an early oxidizing to a later relatively reducing mineralization environment. Therefore, compared with the Dahu Au-Mo deposit and with the Yangzhaiyu Au deposit, which exist in the southern and northern parts of the Xiaoqinling region, respectively, the ore paragenesis and ore-forming physico-chemical conditions of the Jinqu Au deposit were different such that its characteristics are similar to low-sulfidation Au deposits.

Geology and Geochemistry of Carbonate Hosted Pb-Zn Deposit on North-east Part of Kahramanmaraş (Helete) in Engizek Belt

The aim of this study is to reveal the geological and geochemical properties of Pb-Zn mineralizations associated with carbonate rocks along the Helete (Kahramanmaraş) district in Taurus Orogenic belt. The Paleozoic Malatya metamorphics and Eocene sedimentary rocks are present in the Helete region within the area defined as Engizek Belt (North of Kahramanmaraş) in the Eastern Taurus Orogenic belt. In the Gümüşbanı region, there are bariteed Pb-Zn mineralizations in the Paleozoic Malatya metamorphic rocks. Epigenetic mineralization observed in fractures and cracks is vein-type and disseminated. The thickness of the veins varies between 1 cm and 10 cm. The ore paragenesis contains barite, galena, sphalerite, chalcopyrite, fluorite and covellite. In geochemical analysis of samples taken from ore zone, Pb reaches maximum 50.21%, Zn maximum 51.99% and BaO 52.13%.  In geochemical analysis, the ore zone has a maximum of 50.21% Pb and Zn a maximum of 51.99%. In the isotope geochemistry study, the value of δ34S was determined between 10.92 and 11.24‰. As a result of the field and laboratory studies, it was determined that the mineralization was limited to the fractured lines and Paleozoic aged carbonate rocks, and S in the ore-forming solution pointed out to the continental origin. 

Contribution of fluorite mining waste to mercury contamination in coastal systems.

Samples from 13 beaches along the northern Spanish coast, a region with a history of heavy industries, were first screened to identify signs of pollution. High concentrations of Hg and Ba on Vega beach were found, both elements belong to the fluorite ore paragenesis, mined in the surroundings. Samples of beach and fluvial sediments, and nearby soils were collected in Vega beach area to address potential Hg pollution, fate and sources. Most samples showed a similar pollutants fingerprint to that of beach samples, especially those taken from white dunes, registering notable Hg concentrations. Hg was enriched in the finer fractions, and overall the main input was attributed to the mining waste discharged along the coast in the past. Although a specific risk assessment and study of the submerged sediments are advisable for this area, Hg bioavailability and methylation were low, thus indicating that this metal poses a reduced environmental risk.

A 2D and 3D nanostructural study of naturally deformed pyrite: assessing the links between trace element mobility and defect structures

The links between deformation-induced micro- and nanostructures and trace element mobility in sulphide minerals have recently become a popular subject of research in the Earth sciences due to its connections with metallic ore paragenesis. It has been shown that plastic deformation in pyrite creates diffusion pathways in the form of low-angle grain boundaries that act as traps for base- and precious-metals. However, the plastic behavior of pyrite and the physiochemical processes that concentrate these trace elements in deformation-induced micro- and nanostructures remain poorly understood. In this study, we develop strategies for 2D and 3D analysis of naturally deformed sulphides by combining electron backscatter diffraction, electron channeling contrast imaging and atom probe tomography on pyrite in an attempt to better understand the underlying diffusion processes that mobilize trace elements. The combined results reveal structures associated with crystal-plastic deformation in the form of dislocations, stacking faults, and low-angle grain boundaries that are decorated by As and Co. Although our data support a dislocation-impurity pair diffusion model, we have evidence that multiple diffusion mechanisms may have acted simultaneously. In this study, we applied new data processing techniques that allow for orientation measurement of nanostructural crystal defects from atom probe tomography data. Dislocations within our studied sample occur along the (110) planes suggesting glide on {110}.

Geology and He-Ar-S-Pb isotope constraints on the genesis of the Sidaogou gold deposit in Liaodong Peninsula, northeastern North China Craton

The large Sidaogou gold deposit in the Liaodong Peninsula is a typical alteration-type gold system, hosted in Paleoproterozoic metamorphic rocks of Gaixian Formation. Ore paragenesis indicates Sidaogou mineralization occurred in four stages: (1) early ore stage S1 (quartz + albite), (2) main ore stage S2 (quartz + sericite + pyrite + gold), (3) secondary ore stage S3 (quartz + polymetallic sulfide ± scheelite ± biotite ± gold), and (4) late ore stage S4 (calcite + ankerite ± quartz ± sulfide). Associated hydrothermal alterations in wall rocks are dominated by albitization (S1), silicification (S1 to S4), sericitization (S2), sulfidation (S2 to S3), and carbonatization (S4), with minor biotitization (S3) developed locally. Gold mineralization was primarily occurred in S2 stage with intensive silicification, sericitization, and sulfidation in metamorphic wall rocks, and occurred to a lesser extent in S3 stage with weak alteration possibly due to fairly weak activity and small fluxes of the ore fluids.At gold precipitation stages (S2 to S3), three generations of ore-related pyrite (Py1, Py2, and Py3) are identified. NanoSIMS in situ S isotope analyses show that both Py1 and Py2 from the S2 stage have relatively broad ranges of δ34S values with significant intra-grain variations (Py1 = 7.7–16.5‰; Py2 = 3.7–14.8‰), varying between those of wall rocks (11.6–20.3‰) and typical magmatic sources, as well as the regional contemporary magmatic-hydrothermal gold system (CMHGS). This can be interpreted by a mixed process formed by magmatic-hydrothermal fluids leaching different proportion of sulfur from wall rocks during extensive fluid-rock interaction. Py3 in the S3 stage has relatively narrow range of δ34S values (Py3 = 0.6–3.7‰) similar to those of adjacent CMHGS, indicating a magmatic origin without notable wall-rock contamination due to weak fluid-rock interaction. The S2 stage gold-bearing pyrite (Py1-dominated) shows 206Pb/204Pb ratios from 17.882 to 18.938, 207Pb/204Pb ratios from 15.592 to 15.825, and 208Pb/204Pb ratios from 37.811 to 39.003, which are between those of nearby Early Cretaceous Sanguliu granitic pluton and wall rocks ((206Pb/204Pb)i = 17.958–20.085, (207Pb/204Pb)i = 15.664–15.976, and (208Pb/204Pb)i = 37.474–40.021), implying that the lead was originated from mixture sources.Ore fluids from the S2 stage pyrite (Py1-dominated) have 3He/4He ratios range from 0.21 ± 0.01 to 0.57 ± 0.03 Ra (average 0.34 Ra), indicating a crustal source with minor mantle contributions. Moreover, the 3He/4He ratios are similar to those of the adjacent CMHGS, demonstrating a similar magmatic origin for the ore fluids. The 40Ar/36Ar ratios range from 547 to 11994, indicating that the ore fluids contained 48 to 98% crust-derived radiogenic 40Ar* which most likely inherited from wall rocks. Combining the geologic evidences and isotopic results, we propose that the Sidaogou deposit was formed by magmatic-hydrothermal fluids exsolved from Sanguliu pluton or its deep magma. During fluid-rock interaction, sulfur, lead, and 40Ar* were partly scavenged from the wall rocks and then sequestered by ore-related pyrite. Nevertheless, gold was mainly of magmatic origin. Our study reinforces the previous conclusion that S-Pb isotope compositions of ore-minerals could be strongly modified by wall rocks during fluid-rock interaction.

Mineral Paragenesis and Ore‐Forming Processes of the Dongping Gold Deposit, Hebei Province, China

AbstractThe Dongping gold deposit is located near the center of the northern margin of the North China Craton. It is hosted in the Shuiquangou syenite and characterized by large amounts of tellurides. Numerous studies have addressed this deposit; the mineral paragenesis and ore‐forming processes, however, are still poorly studied. In this contribution, a new mineral paragenesis has been evaluated to further understand ore formation, including sulfides (pyrite, chalcopyrite, galena, sphalerite, molybdenite, and bornite), tellurides (altaite, calaverite, hessite, muthmannite, petzite, rucklidgeite, sylvanite, tellurobismuthite, tetradymite, and volynskite), and native elements (tellurium and gold). Molybdenite, muthmannite, rucklidgeite, and volynskite are reported for the first time in this deposit. We consider the Dongping gold deposit mainly formed in the Devonian, and the ore‐forming processes and the physicochemical conditions for ore formation can be reconstructed based on our newly identified ore paragenesis, that is, iron oxides → (CO2 effervescence) → sulfides → (fTe2/fS2 ratio increase) → Pb‐Bi‐tellurides → (condensation of H2Te vapor) → Au‐Ag‐tellurides → (mixing with oxidizing water) → carbonate and microporous gold → secondary minerals → secondary minerals. The logfO2 values increase from the early to late stages, while the fH2S and logfS2 values increase initially and then decrease. CO2 effervescence is the main mechanism of sulfides precipitation; this sulfidation and condensation of H2Te vapor lead to deposition of tellurides. The development of microporous gold indicates that the deposit might experience overprint after mineralization. The Dongping gold deposit has a close genetic relationship with the Shuiquangou syenite, and tellurium likely originated from Shuiquangou alkaline magmatic degassing.

The Quebrada del Diablo Lower West Au deposit (Gualcamayo mining district, Argentina): A Carlin-type mineralization?

The Gualcamayo Mining District (GMD), located in the eastern margin of the Argentini an Precordillera includes three Au deposits: Amelia-Ines, Magdalena, Quebrada del Diablo Main, and QDD Lower West. The district has reserves of 491,000 oz. and resources of 2.3 million oz of Au.The metallogenetic analysis of these Au deposits based on previous work and new micro-geochemistry (LA- ICP- MS), isotopic (C-O-S-Pb) and fluid inclusions studies revealed that they are genetically linked and share many characteristics with Carlin-type deposits, including the lithology of host rocks, structural control, geochemical signatures, ore paragenesis, and dissolution and decarbonization processes. However, they also display some noticeable differences. The sulfur isotopic composition supports a genetic link between these gold deposits and the precursor magmatism of the porphyry-type mineralization of the area. Besides, the fluids responsible for the Au mineralization proved to be neutral to slightly alkaline and Au-saturated. The link with the magmatism along with the character of the mineralizing fluids and the presence of significant base metal sulfides allowed classifying the GMD deposits as “distal disseminated gold deposits” that occur on the distal edges of magmatic-hydrothermal systems.

Structural Controls of Ore Mineralization in a Polydeformed Basement: Field Examples from the Variscan Baccu Locci Shear Zone (SE Sardinia, Italy)

The Baccu Locci mine area is located in a sector of the Variscan Nappe zone of Sardinia (the Baccu Locci shear zone) that hosts several type of ore deposits mined until the first half of the last century. The orebodies consist of lenses of Zn–Cu sulphides, once interpreted as stratabound, and Qtz–As–Pb sulphide ± gold veins; the implication of structural controls in their origin were previously misinterpreted or not considered. Detailed field mapping, structural analyses, and ore mineralogy allowed for unraveling how different ore parageneses are superimposed each other and to recognize different relationships with the Variscan structures. The sulphide lenses are parallel to the mylonitic foliation, hosted in the hinges of minor order upright antiforms that acted as traps for hydrothermal fluids. The Qtz–As–Pb sulphide veins crosscut the sulphide lenses and are hosted in large dilatational jogs developed in the hanging wall of dextral-reverse faults, whose geometry is influenced by the attitude of reverse limbs of late Variscan folds. The ores in the Baccu Locci shear zone are best interpreted as Variscan orogenic gold-type; veins display mutual crosscutting relationships with mafic dikes dated in the same district at 302 ± 0.2 Ma, a reliable age for the mineralizing events in the area.

Estudo de inclusões fluidas em quartzo do garimpo do Papagaio, um sistema magmático-hidrotermal, Província Aurífera de Alta Floresta (MT), Cráton Amazônico

O garimpo aurífero do Papagaio, localizado em Paranaíta, Mato Grosso, insere-se no setor noroeste da Província Aurífera de Alta Floresta, sul do Cráton Amazônico. Está hospedado em dacito porfirítico inicialmente afetado por alteração potássica, sobreposta por forte alteração sericítica pervasiva e, por fim, por alteração propilítica. O minério é representado pela paragênese pirita + calcopirita + esfalerita ± galena ± calcocita ± covelita e ocorre associado a sistemas de veios de quartzo e stockworks que truncam os setores de alteração potássica e sericítica. Estudos de inclusões fluidas dos veios mineralizados e estéreis presentes no garimpo permitiram identificar três grupos de inclusões fluidas: tipo I) inclusões aquocarbônicas; tipo II) aquosas bifásicas; tipo III) aquosas tri a multifásicas. Nos veios mineralizados houve a crepitação das inclusões do Tipo I a 325ºC. Foram encontradas temperaturas de homogeneização de 115,1 a 216,2ºC e salinidades entre 0,5 a 24,0% para as inclusões do Tipo II. Nos veios estéreis, as inclusões do Tipo II resultaram em temperaturas de homogeneização total entre 135,9 e 190,3ºC e salinidades de 26,0 a 30,2%. No Tipo III a homogeneização total ocorreu entre 323,2 e 402,9ºC com salinidade superior a 40,0%. Portanto, fluidos de elevada temperatura e salinidade com características de origem magmática tiveram um papel essencial na formação das zonas mineralizadas do garimpo. Nesse contexto, a colocação de corpos subvulcânicos teria sido essencial na gênese da mineralização aurífera do Papagaio, pois teria servido como fonte de calor, fluido e metais para a instalação de um sistema magmático-hidrotermal profundo, relacionado ao ambiente dos depósitos do tipo pórfiro e intrusion-related gold systems (IRGS).

Pyrite-walled tube structures in a Mesoproterozoic sediment-hosted metal sulfide deposit

Unusual decimeter-scale structures occur in the sediment-hosted Black Butte Copper Mine Project deposit within lower Mesoproterozoic strata of the Belt Supergroup, Montana. These low domal and stratiform lenses are made up of millimeter-scale, hollow or mineral-filled tubes bounded by pyrite walls. X-ray micro−computed tomography (micro-CT) shows that the tube structures are similar to the porous fabric of modern diffuse hydrothermal vents, and they do not resemble textures associated with the mineralization of known microbial communities. We determined the sulfur isotopic composition of sulfide minerals with in situ secondary ion mass spectrometry (SIMS) and of texture-specific sulfate phases with multicollector−inductively coupled plasma−mass spectrometry (MC-ICP-MS). The sedimentological setting, ore paragenesis, sulfur isotope systematics, and porosity structure of these porous precipitates constrain the site of their formation to above the sediment-water interface where metalliferous hydrothermal fluids vented into the overlying water column. These data constrain the geochemistry of the Mesoproterozoic sediment-water interface and the site of deposition for copper-cobalt-silver mineralization. Metals in the hydrothermal fluids titrated sulfide in seawater to create tortuous fluid-flow conduits. Pyrite that precipitated at the vent sites exhibits large sulfur isotope fractionation (>50‰), which indicates a close association between the vents and sulfate-reducing microbiota. In the subsurface, base metal sulfides precipitated from sulfide formed during the reduction of early diagenetic barite, also ultimately derived from seawater. This model suggests dynamic bottom-water redox conditions at the vent site driven by the interplay between sulfate-reducing organisms and metalliferous fluid effluence.

A novel nuclear forensic tool involving deposit type normalized rare earth element signatures

AbstractIdentifying the provenance of uranium‐rich materials is a critical objective of nuclear forensic analysis. Rare earth element (REE) distributions within uranium ores are well‐established forensic indicators, but quantifying and correlating trace element signatures for U ores to known deposits has thus far involved intricate statistical analyses. This study reports average chondrite normalized (CN)‐REE signatures for important U deposit types worldwide, which are then employed to evaluate U ore paragenesis using a simple linear regression analysis. This technique provides a straightforward method that can aid in determining the deposit type of U ores based on their REE abundances, and combined with other forensic indicators (e.g. radiogenic isotope signatures) can provide essential provenance information for nuclear materials.

Geology, S–Pb isotopes, and 40Ar/39Ar geochronology of the Zhaxikang Sb–Pb–Zn–Ag deposit in Southern Tibet: implications for multiple mineralization events at Zhaxikang

Several Au, Sb, Sb–Au, Pb–Zn, and Sb–Pb–Zn–Ag deposits are present throughout the North Himalaya in southern Tibet, China. The largest Sb–Pb–Zn–Ag deposit is Zhaxikang (18 Mt at 0.6 wt% Sb, 2.0 wt% Pb, 3.5 wt% Zn, and 78 g/t Ag). Zhaxikang veins are hosted within N–S trending faults, which crosscut the Early–Middle Jurassic Ridang Formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin. Ore paragenesis indicates that Zhaxikang mineralization occurred in two main phases composed of six total stages. The initial phase was characterized by assemblages of fine-grained Mn–Fe carbonate + arsenopyrite + pyrite + sphalerite (stage 1), followed by relatively coarse-grained Mn–Fe carbonate + Fe-rich sphalerite + galena + pyrite (stage 2). The second phase was marked by assemblages of quartz + pyrite + Fe-poor sphalerite and Ag-rich galena + tetrahedrite + sericite (stage 3), quartz + Sb–Pb sulfosalt minerals mainly composed of boulangerite and jamesonite (stage 4), quartz + stibnite ± cinnabar (stage 5), and quartz ± calcite (stage 6). Sulfides of stage 2 have δ34SV–CDT of 8.4–12.0‰, 206Pb/204Pb ratios of 19.648 to 19.659, 207Pb/204Pb ratios of 15.788 to 15.812, and 208Pb/204Pb ratios of 40.035 to 40.153. Sulfides of stage 3 have similar δ34SV–CDT of 6.1–11.2‰ and relatively more radiogenic lead isotopes (206Pb/204Pb = 19.683–19.792). Stage 4 Sb–Pb sulfosalt minerals have δ34SV–CDT of 5.0–7.2‰ and even more radiogenic lead (206Pb/204Pb = 19.811–19.981). By contrast, stibnite of stage 5 has δ34SV–CDT of 4.5–7.8‰ and less radiogenic lead (206Pb/204Pb = 18.880–18.974). Taken together with the geological observations that the Pb–Zn-bearing Mn–Fe carbonate veins were crosscut by various types of quartz veins, sphalerite and galena of stage 2 underwent dissolution and remobilization, and that Sb–Pb(−Fe) sulfosalts formed at the expense of Pb from stage 2 galena and of Fe from stage 2 sphalerite, we argue that the early Pb–Zn veins were overprinted by later Sb-rich fluids. Stage 2 fluids were likely acidic and oxidized and leached lead from high-grade metamorphic rocks of the Greater Himalayan crystalline complex (GHC) and sulfur from reduced rocks, such as slate of the Ridang Formation, along N–S trending faults, leading to precipitation of Pb–Zn sulfides and Mn–Fe carbonate and formation of solution collapse breccias. Later Sb-rich fluids leached Pb from the GHC and the pre-existing sulfides and deposited Fe-poor sphalerite, Ag-rich galena, tetrahedrite, Sb–Pb sulfosalts, and stibnite in quartz veins that cut pre-existing Pb–Zn-bearing Mn–Fe carbonate veins. The Sb-rich fluids also likely leached Pb from Early Cretaceous gabbro and formed stibnite at shallow levels where early Pb-Zn-bearing Mn-Fe carbonate veins are absent. A sericite 40Ar–39Ar plateau age of 17.9 ± 0.5 Ma from stage 3 veins represents the timing of the onset of stage 3 mineralization.

Isotopic characteristics of the ermakovskoe fluorite–bertrandite–phenakite deposit (Western Transbaikalia)

Isotope-geochemical study of the Ermakovskoe fluorine–beryllium deposit was carried out to estimate the ore sources and role of host carbonate rocks in its formation. We analyzed oxygen and carbon isotope compositions in marbles, skarn carbonates, ore and post-ore parageneses; oxygen isotope compositions in oxides, silicates, apatite; and sulfur isotope composition in sulfides and sulfates. Sources of fluids participating in the rock and ore formation were determined using hydrogen and oxygen isotope compositions in hydroxyl-bearing minerals: phlogopite from marbles, vesuvian from skarns, eudidymite and bertrandite from ore parageneses, and bavenite of the post-ore stage. Isotopic studies suggest crustal source of sulfur, oxygen, and carbon dioxide, while oxygen and hydrogen isotope compositions in the hydroxyl-bearing minerals points to the contribution of meteoric waters in the formation of the fluorine-beryllium ores.

Carbonates and sources of fluids in ores and metasomatites of the Ermakovka fluorite-bertrandite-phenacite deposit (western Transbaikalia)

We present results of isotope-geochemical study of the Ermakovka F-Be deposit, including data on the oxygen and carbon isotope compositions in dolomite and calcite marbles and in carbonates accompanying skarns, of early and late stages of ore formation and of post-ore parageneses. To elucidate the sources of fluids participated in the ore formation, we calculated the oxygen isotope composition in water and the hydrogen isotope composition in hydroxyl-containing minerals. Phlogopite in marbleized dolomites, vesuvianite and amphibole in skarns, eudidimite and bertrandite in ore parageneses, and bavenite formed during post-ore processes are analyzed. Most of the ore-stage minerals are depleted in heavy oxygen. Their 518O values are lower than 5-6%c (SMOW). Oxygen in carbonate minerals of the initial stage (dolomite and bastnaesite) is heavier (1.3-4.9%c) than that in calcite (+2 to -3.7%c). The 518O values of water in equilibrium both with carbonate and with silicate minerals (-4 to -14%c) suggest the contribution of meteoric water to the mineral formation. A magmatic fluid (518O from +6 to +9%c) participated in the skarn formation at the initial stage, and a meteoric fluid, at the final stage (518O from -1 to -9%c). A meteoric source is confirmed by the depleted hydrogen isotope composition in minerals (5D from -119 to -192%c).

Composition and metal contents of ore-forming fluids of the Kalguty Mo–W(Be) deposit (Gorny Altai)

Based on results of study of fluid inclusions, we have established the specific fluid regime of formation of the Kalguty Mo–W(Be) deposit (Gorny Altai). Using classical thermobarogeochemistry (cryo- and thermometry) and modern microprobing methods (Raman spectroscopy and LA-ICP-MS), we studied fluid inclusions in quartz of quartz–wolframite veins (ore formation stage I), specific “quartz core” (quartz lens), and pyrite-chalcopyrite-molybdenite paragenesis (ore formation stage II). The results of study show that the quartz–wolframite veins of the Kalguty deposit formed with the participation of reduced W-Sb-bearing fluids with a salt content of up to 5.9 wt.%. Their gas phase consisted of CO2, N2, and CH4. Formation of pyrite-chalcopyrite-molybdenite mineralization involved oxidized hot (530–420 °C) fluids with the average salt content of 9.3 wt.%. Their gas phase was of high density (up to 0.55) and consisted of CO2, N2, and H2S. The pressure of the mineral-forming environment varied from 50 to 25 MPa. The fluids contained Cu, Mo, Bi, and S. The productive greisen-vein Mo–W(Be) mineralization of the Kalguty deposit resulted from the superposition of greisen molybdenite-chalcopyrite mineralization on parageneses of earlier formed quartz-wolframite veins. Oxidized metal-bearing fluids that formed the Mo mineralization of the Kalguty deposit have high contents of S and are geochemical analogs of magmatic metal-bearing ore-forming fluids of the Central Aldan porphyry Cu-Au-Mo deposits, which are genetically related to alkaline massifs. This suggests the significant influence of the mantle source on the formation of the Kalguty rare-metal ore-magmatic system. The same is evidenced from the sulfur isotope composition of chalcopyrite, molybdenite, and pyrite from ore parageneses, falling in the narrow range of δ34S‰ from −1.2 to +2.9 corresponding to the isotope composition of mantle sulfur.

Indium mineralisation in SW England: Host parageneses and mineralogical relations

The SW England ore region contains significant amounts of indium (In) in Early Permian granite-related skarn and lode parageneses and, to a lesser extent, Triassic epithermal “crosscourse” veins. Ore parageneses that predate granite emplacement (Devonian and Lower Carboniferous sedimentary exhalative and vein parageneses) are largely devoid of In. Cadmium (Cd) and gallium (Ga) occur widely in all sulphide-bearing parageneses across the region with sphalerite concentrations locally reaching 1.74wt% Cd and 1750ppmGa.Indium displays a strong affinity to sulphide-bearing magmatic-hydrothermal parageneses. It occurs in silicate-sulphide skarns, polymetallic sulphide lodes and sulphide-bearing portions of greisen-bordered sheeted vein systems and quartz-tourmaline lodes across the region. Magnetite-silicate skarns and quartz-tourmaline lodes that are devoid of sulphide, in contrast, were comparatively unfavourable for In precipitation. The highest In concentrations are found in mineral lodes associated with the Carnmenellis and St Agnes granites, which are the districts that had the highest historical production of Sn. Total In concentrations in these areas locally exceed 430ppm, while concentrations elsewhere are systematically below 200ppm.The principal In hosts are chalcopyrite, sphalerite and stannite group minerals with local concentrations within cassiterite and tennantite. Surprisingly, chalcopyrite accounts for the majority of the In budget throughout the region, although concentrations are highest in sphalerite and stannite group minerals. Sphalerite locally contains up to 1.42wt% In, chalcopyrite has up to 2200ppm and stannite group minerals up to 6800ppm. No In was detected in löllingite, arsenopyrite, rutile, haematite, magnetite, tourmaline, biotite, chlorite, galena, bornite, chalcocite or pyrrhotite. Scattered concentrations in pyrite relate to impurities rather than incorporation by solid solution. Roquesite and possibly dzhalindite or native In formed locally where In-bearing chalcopyrite or sphalerite has been replaced by bornite and quartz. The In partitioning between sphalerite and chalcopyrite varies broadly between 1:1 and 10:1.Sporadic In was included in Triassic crosscourse veins as a result of interactions between migrating CaCl2-rich basinal brines and earlier formed granite-related parageneses. The interactions involved at least two distinct components: 1) Incorporation of clasts of magmatic-hydrothermal veins in crosscourse veins during faulting, and 2) Dissolution and re-precipitation of magmatic-hydrothermal vein minerals in crosscourse fluids. Local concentrations reach 140ppm In.The magmatic-hydrothermal parageneses in SW England are comparable to the South China Tin Belt, Mount Pleasant, as well as Erzgebirge/Krušné Hory. Magmatic-hydrothermal fluids associated with peraluminous granites have developed a variety of skarn, greisen, lode and veins parageneses by interactions with their host rocks and contained fluids. Crosscourse epithermal mineralisation occurred as In was transported by CaCl2-rich basinal brines in a similar manner as In-bearing veins in the West Shropshire ore field.