Clay Alteration Research Articles

Origin of a multi-stage epithermal Ag-Zn-Pb-Sn deposit: the Miocene Cortaderas breccia body, Pirquitas mine, NW Argentina

The Miocene aged polymetallic (Ag-Zn-Sn-Pb) Pirquitas deposit of NW Argentina, hosted in an uplifted horst of Ordovician metaturbiditic rocks, defines the southern extent of the Andean Tin Belt. The nearby and recently discovered Cortaderas breccia-hosted Ag-Zn deposit contrasts markedly with the main Pirquitas deposit. To address these differences, a comprehensive geological, mineralogical, and geochemical study was undertaken and here reported. Ore formation commenced with brecciation and clay alteration of host rocks followed by six polymetallic ore stages and a waning stage. The complex mineralization (Ag, Sb, As, Sn, Fe, Zn, Cu, Pb, and Bi) consists of pyrite, marcasite, sphalerite, arsenopyrite, galena, cassiterite, quartz, dickite, siderite, hydrous phosphate minerals, and various sulfosalts and sulfides; metal assays indicate a telescoped system. Sphalerite-rich domains are characterized by massive, colloform, dendritic, and cockade textures. Silver and Sn principally occur in various sulfosalts (tetrahedrite, pyrargyrite, miargyrite, pirquitasite-hocartite, and canfieldite). Fluid inclusions reflect mixing of a ca. 5 wt% eq. NaCl fluid having a maximum Th value of 340 °C with heated meteoric water; in addition, fluid unmixing and flashing are documented to have accompanied ore formation. The δ34S values for pyrite and sphalerite constrain δ34SH2S to ≈ 5‰ which suggests a magmatic reservoir. Collectively the data support a model, whereby the Cortaderas breccia reflects focusing of magmatic-sourced mineralizing fluids along an episodically dilating fault zone. Fluids ascended and depressurized following brecciation of the host rocks which initiated fast and slow boiling. The latter processes accounts for the intimate association of colloform- and dendritic-textured sphalerite. Subsequent sealing of the system allowed temperature gradients to rise which resulted in telescoping of the system and generation of this polymetallic ore zone.

Structural controls and metallogenic model of polyphase uranium mineralization in the Kiggavik area (Nunavut, Canada)

The Kiggavik area is located on the eastern boundary of the Paleo- to Mesoproterozoic Thelon Basin (Nunavut, Canada) and hosts uranium mineralization in Archean basement rocks. The major fault/fracture network in the Kiggavik area is mainly oriented ENE-WSW and NE-SW, consisting of polyphased fault zones initiated during the Thelon and Trans-Hudsonian orogenies (ca. 1900–1800 Ma). These faults were subsequently mineralized in four stages referred to as U0, U1, U2, and U3. The first event U0 is inferred to be of magmatic origin and is related to microbrecciation and weak clay alteration under a WSW-ENE σ1. U0 is a ca. 1830 event which predates intense quartz brecciation (QB) and veining at ca. 1750 Ma. QB is associated with emplacement of the Kivalliq Igneous Suite and caused pervasive silicification of former fault zones, which in turn controlled subsequent fracture development and behaved as barriers for later U mineralizing fluids (U1 to U3). U1, U2, and U3 postdate deposition of the Thelon Basin. U1 and U2 occurred under a regional strike-slip stress regime, with the direction of σ1 evolving from WNW-ESE (U1) to NE-SW /ENE-WSW (U2); both formed at ~ 1500–1330 Ma and are related to circulation of Thelon-derived uranium-bearing basinal brines. A post U2, but pre-Mackenzie dykes (ca. 1270 Ma), extensional/transtensional stress regime with σ3 oriented NE-SW caused normal-dextral offset of the orebodies by reactivating NNW-SSE and E-W trending faults. This fracturing event triggered circulation of hot (~ 300 °C), probably acidic, fluids that dissolved quartz, and caused illitization and bleaching of the host rocks. Finally, U3 records remobilization of the previous mineralization along redox fronts through percolation of low-temperature meteoric fluids during two main tectonic events at ca. 550 and 350 Ma. This study provides evidences for the presence of a primary, pre-Thelon Basin uranium stock within the Kiggavik prospects, and a strong structural control on mineralization in the Kiggavik area. Our study also shows a nearly similar evolution of uranium mineralization in this area compared to the world-class uranium district of the Athabasca Basin (Saskatchewan, Canada).

Aspects of hydrothermal alteration assemblages around Bakwani-Bagwa, Northwestern Nigeria; Insights from multifractal analysis of measured thresholds for mineral exploration.

This study is aimed at identifying highly altered zones by applying concentration area (C-A) fractal model technique on Landsat ETM+ image of area around Bakwani-Bagwa, Northwestern Nigeria. Multifractal analysis was used to quantify degree of alteration on satellite images processed using crosta technique. A log–log plot was used to display the multifractal characteristics for clay and iron altered images and identify threshold values. Maximum and minimum threshold values obtained from fractal analysis are 1.74 and 4.01 for clay altered images and 0.607 and 3.04 for iron altered images. High clay and iron alteration zones accounts for 5.89% and 7.84%, covering an area of 22.28km2 and 29.65km2 respectively. Delineating highly altered zones from these images reveals higher alteration largely within silicified sheared rocks and areas around faults. The current study proved the multifractal processing techniques to be valuable mapping tools for geological reconnaissance which can be extended to a large area of the Nigerian basement and provide preliminary hydrothermal alteration maps that are accurate as well as cost and time effective.

Occurrence, composition, and origin of analcime in sedimentary rocks of non-marine petroliferous basins in China

Abstract Natural analcime, a highly brittle aluminosilicate mineral that dissolves easily during diagenesis, occurs in the sedimentary rocks of eight main non-marine petroliferous basins in China. This mineral has been well documented for the past 30 years and has proved to be significant for the formation of high-quality hydrocarbon reservoirs. The present study fully reviews analcime occurrences, chemical compositions, Si/Al ratios, origin and controlling factors, and influence on the hydrocarbon reservoir quality in Permian to Paleogene sedimentary rocks. Previous research has shown that analcime is commonly distributed within argillaceous laminae (l-type); occurs as intergranular cement (c-type), replacement (r-type), and crack filling (f-type) forms; or is closely intergrown with other authigenic/exhalative minerals (a-type). Analcime in lacustrine basins is slightly Al-rich and Na-poor, and its Si/Al ratios range from 1.95 to 2.80. The geochemical compositions of the analcime- and ankerite-bearing exhalites are characterised by enrichment in light rare earth elements and 13C and depletion in heavy rare earth elements and 18O, with negative Eu and positive Ce anomalies. Diagenetic analcime forms by the alteration of volcanic glass, clays, or zeolite precursors in saline-alkaline lakes or during buried diagenetic stages in sedimentary rocks. In addition, it coexists with other authigenic zeolite, carbonate, and clay minerals as well as albite. Hydrothermal analcime presumably precipitates from hydrothermal fluids and is not dependent on a local precursor mineral or volcanic glass; this type is commonly related to exhalative mineralisation of hydrothermal springs. The formation of natural analcime is controlled by various factors such as the composition of the parent material, temperature prevalent during crystallisation, chemistry of the fluid phase, and thermodynamic characteristics of the geological environment. As zeolites are formed in alkaline fluid phases, they become unstable in acidic pore water. Secondary pores created by analcime mineral dissolution, and intercrystalline micropores among analcime minerals, are highly significant in hydrocarbon reservoirs. Analcime-bearing mudstone, siltstone, dolostone, and exhalite are favourable lithofacies for unconventional hydrocarbon accumulation owing to its high brittleness and selective dissolution of analcime and other associated minerals.

Geochemical heterogeneity of sublacustrine hydrothermal vents in Yellowstone Lake, Wyoming

ROV-based submersible operations in Yellowstone Lake (Yellowstone National Park, Wyoming, USA) have identified two locations with chemically and mineralogically distinct sublacustrine hydrothermal fluids and deposits: The Deep Hole east of Stevenson Island (SI Deep Hole) and the SE West Thumb Deep Vent field (SE WT Field). The SI Deep Hole is the deepest part of Yellowstone Lake (120m), and hosts up to 174°C fluids heated by steam that condenses on contact with cold lake water. The resulting hot fluids exit through a clay alteration cap that largely consists of kaolinite. The SI Deep Hole hydrothermal vents are analogous to steam-heated hot springs elsewhere in Yellowstone National Park (YNP) (e.g. the Mud Volcano area), which are typified by fumaroles and acid-sulfate fluids. These deep sublacustrine vent fluids are more aptly termed “carbonic-acid-sulfide”, owing to a lack substantial sulfate from H2S oxidation and acidity attributed to dissolved CO2. At 53m depth, vent fluids at the SE WT Field achieve temperatures of up to 141°C. These neutral-chloride fluids are largely similar to those that produce siliceous deposits in many subaerial YNP geyser basins. Geothermometry calculations and binary mixing relationships indicate the SE WT Field fluids equilibrated at 207 to 224°C following mixing between oxygenated dilute cold groundwater and a fluid with T=345 to 364°C, Cl=400ppm, and δD=−149 ‰ (VSMOW); broadly similar to the putative deep parent fluid that supplies most geyser basins in YNP. The δD values of SE WT Field fluids cannot be derived from lake water, implying km-scale lateral hydrothermal fluid flow from outside the boundary of Yellowstone Lake. The fluid compositions and hydrothermal processes operating in the two sublacustrine vent systems are distinct but the overarching influence of magmatic heating, complex degassing, and alteration mineralization effects are broadly comparable to those that affect their subaerial counterparts. The high temperatures and hydrostatic pressures of the sublacustrine vents, however, provide a window into the evolution of fluid chemistry in more deeply seated and less accessible regions of the subsurface YNP and similar volcanically active hydrothermal systems elsewhere.

Surficial arsenic redistribution above gold-mineralised zones in East Otago, New Zealand

ABSTRACTGroundwater-driven clay alteration of gold-mineralised Otago Schist has caused leaching and redistribution of arsenic (As). At Macraes mine in East Otago, there is a zone of alteration up to 50 m thick beneath a Cretaceous-Cenozoic regional unconformity where hydrothermal As concentrations >1000 ppm have decreased to <150 ppm. Where periglacial aeolian silt (loess) overlies mineralised Otago Schist, As has migrated in near-surface groundwater to form geochemical enrichment anomalies in loess and colluvium, with As concentrations locally as high as 500 ppm. Most As in the clay-altered basement and Pleistocene cover is closely associated with iron oxyhydroxide (HFO) and occurs as adsorbed As(V) on the HFO or as ferric arsenate minerals. However, initial As mobility was most effective as more soluble As(III) during oxidative transition from original sulphides to arsenate. Upward As migration into Pleistocene debris on the metre scale can facilitate location of gold-mineralised rocks that have been obscured by the young cover.

The effect of active extensional tectonics on the structural controls and heat transport mechanism in the Menderes Massif geothermal province: Inferred from three-dimensional electrical resistivity structure of the Kurşunlu geothermal field (Gediz Graben, western Anatolia)

The current study in the Menderes Massif geothermal province aims to assert a crustal-scale geoelectrical evidence showing the role of extensional tectonics on the flow of geothermal fluids through both high-angle and low-angle normal (detachment) faults and on the heat transport mechanism in the convection dominated-amagmatic geothermal play systems, on the basis of three-dimensional electrical resistivity structure of the Kurşunlu geothermal field, Gediz Graben, western Anatolia. The electrical resistivity structure was derived from the three-dimensional inversion of the magnetotelluric data acquired from 74 sites in the period range from 0.001 s to 1000s. The resistivity model brings out two different types of reservoirs, namely (i) a shallow low resistivity reservoir (secondary reservoir) corresponding to the Kurşunlu hot spring in the sedimentary layer of the Gediz Graben and (ii) a deep more resistive reservoir (primary reservoir) beneath a prominent highly conductive (≤ 10 ohm-m) hydrothermal clay alteration zone. The circulation of geothermal fluids in reservoirs is dominantly controlled by high-angle normal faults including the main graben-bounding fault and low-angle Gediz detachment fault. The possible heat source for the geothermal system has been attributed to high heat arising from upwelling asthenosphere through the mantle window in the northward subducting and retreating African slab, which has been accompanied by crustal extension resulting in a thin crust and shallow mantle, and the deeply penetrating main graben-bounding fault acting as a conduit through which heat is transported from the deeper parts of the crust to near surface probably controls heat transport in the area.

Formation Damage Associated With Mineral Alteration and Formation of Swelling Clays Caused by Steam Injection in Sandpacks

Summary Thermal-recovery methods are commonly used for production of viscous crude oil. Injected hot fluids react with reservoir rock, and some of these reactions might result in a change to the reservoir mineralogy. Depending on the physicochemical conditions and initial mineralogy, some such alterations can lead to formation damage and flow-assurance issues. This paper investigates these mineral reactions, the conditions in which they occur, and the effects of these processes on porosity and permeability of sandstone rocks with various initial mineralogy. Quartz, calcite, dolomite, kaolinite, and montmorillonite were used for preparation of 12 rock samples of various mineralogical contents. These mixtures were packed and used for steam-injection experiments. Porosity and permeability of the initial and steamed sandpacks were determined using computed-tomography (CT) scans and coreflood experiments, respectively. Composition of the collected condensate samples was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Rock mixtures were aged in high-pressure/high-temperature (HP/HT) cells. Rock morphology and pore-space configuration were studied using scanning-electron-microscope energy dispersive X-ray spectroscopy (SEM-EDS). Mineralogy of the samples was analyzed using X-ray-diffraction (XRD) analysis. Mixtures of quartz with calcite were found to be the least prone to formation damage associated with steam injection. Silica dissolution/precipitation reaction resulted in 5% initial permeability reduction and 1 to 2% initial porosity reduction. Mixtures of quartz, kaolinite, and carbonate minerals (calcite or dolomite) after steam injection lost 11 to 22% of initial permeability and 2 to 7% of initial porosity. Kaolinite fines were shown to be mobilized during steam treatment. Aging of these rock mixtures for 10 days at 400°F and 1,000 psi led to formation of swelling smectite clay (Ca montmorillonite). Growth of montmorillonite was demonstrated to be possible only at low carbon dioxide (CO2) partial pressures. Mixtures with dolomite are shown to produce more montmorillonite than mixtures with calcite. Steam injection in montmorillonite-rich sandstone caused up to 84% loss in the initial permeability and up to 8% loss in initial porosity. The principal formation-damage mechanism proved to be clay swelling, which led to filling of pores with montmorillonite. The microporous network that filled the pores significantly restricted the flow. Aging of montmorillonite-rich mixtures did not reveal mineral alterations but did allow visualization of the morphological reorganization of montmorillonite and its pore-bridging effect. This paper describes interactions between superheated steam and rock samples. This study further characterizes formation-damage mechanisms caused by hydrothermal alterations and their effects on petrophysical properties of reservoir rocks. Data about conditions of mineral reactions can be used to shift the physicochemical or operational conditions to prevent growth of swelling clays such as montmorillonite.

Geothermal Exploration in Some Interest Geothermal Area in Republic of Yemen

The first geothermal area (Al Lisi–Isbil Geothermal field) is located about (100) km from Sana’a capital city of Republic of Yemen, and the second geothermal area (Alsyani – Algandeah Geothermal field) is located about (250) km from Sana’a capital city of Republic of Yemen. In addition, the third geothermal area (Red Sea geothermal area) is located about (290) km from Sana’a capital city of Republic of Yemen. The geothermal mapping was carried out in (Al Lisi and Isbil and Alsyani – Algandeah Geothermal field) in the western area of Yemen.The rocks type in Al Lisi–Isbil Geothermal area was classified To six group, trap series, the post trappic volcanic activity, Isbil volcanic complex, Al Lisi volcanic complex, Basaltic Fissure volcanism and recent and active sedimentary deposits, The main structural feature are trend (NNE-SSW), (NE-SW),The rocks type in the second geothermal area Alsyani – Algandeah Geothermal area was classified to (4) type of Rocks, Tertiary Volcanic (Basalt, Rhyolite, and Tertiary intrusive rocks), Tawilah Sandstone Group, Medj-Zir Sandstone and Quaternary Deposits. The main structural feature is trend (NE-SW). In Al Lisi and Isbil Geothermal area The Geothermal manifestations (steam, clay alteration and slight alteration)common in many deferent site in the Geothermal area, two types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, yellowish to white colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a whitish color due to the presence of opline silica, clay minerals and iron oxides. In addition, the Albit, Montomornillonite, Biotite, Kaolinite, Chlorite Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Al Lisi and Isbil Geothermal area. The temperatures of steam that exceed 92°C and They are 118 hot well in the area the temperature between (25°C) to (59°C).And the Geothermal manifestations(slight alteration)In Alsyani–Algandeah Geothermal area are common in many deferent site in the Geothermal field, one types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, to yellowish colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a Brownish, reddish and yellowish color due to the presence of opline silica, calcite veins, clay minerals and iron oxides. In addition, the limonite, Heulandite, Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Alsyani–Algandeah Geothermal area.They are (42) hot well in the area the temperature between (27°C) to (75°C), the thermal wells to 340 meters deep (75°C), are in the area.Also The Red Sea geothermal area is located in west area of western Yemen volcanic part, was covered by drilling is does not exceed 3000 km2,but data from several areas throughout the world, including neighboring countries such as Ethiopia yielded similar temperatures and geothermal gradients. In the Present, the temperature logs from the boreholes show temperatures of 190°C at 2458 m depth in the Red Sea geothermal area.

Engineered extremes: microbial interactions with steel and bentonite in a geological disposal facility

The conditions of the deep subsurface, combined by perturbations caused by geological disposal of radioactive waste create multiple extreme conditions (limited space availability, high pH, high temperature etc.) for microbial communities. Microbial activity has the potential to cause corrosion of steel and alteration of bentonite clays used in geological disposal facilities. To understand the limits on microbial growth, and the potential for microbial activity to affect the swelling behaviour of the bentonite and metal corrosion, a suite of laboratory experiments is being conducted. In situ repository conditions have been replicated in the MIND (Horizon2020) project. Preliminary results show evidence of corrosion in all experiments, an increase in the basal spacings of smectites in the zone immediately surrounding the steel and inoculated samples had evidence of calcite crystal formation, accompanied by differences in the iron phases. These experiments simulate the in situ conditions well, but the complex nature of this experimental design (high pressure and flow) reduces the practicality of varying the environmental conditions. To complement these investigations, a low-tech solution has been implemented with unpressurised, hydrated bentonite batch experiments. The simpler nature of this set-up allows for investigation of more parameters. Microcosms with artificial groundwater used in the MIND set-up are being compared to the MIND groundwater composition, modelled to represent permafrost conditions. The effect of incubation temperature is also being investigated. Combined, these experiments will help to understand the influence of microbes under the extremes of geological disposal facilities and how their behaviour may change by external parameters.

Detection of mineral alteration induced by hydrocarbon microseepages by using remotely sensed data in the Fateh Jang area of the Northern Potwar region of Pakistan

Mineral alteration can be induced by the hydrocarbon seepages at the earth surface that can be detected by the use of earth observation data. The long-term seepage of hydrocarbons in the subsurface can induce different types of chemical and mineralogical alterations in the rosk and soil. Mapping of these mineral alterion is important to explore hydrocarbon. In this study, satellite images were used to identify the surface mineral alterations due to hydrocarbon microseepages in the Fateh Jang area of the Northern Potwar region, Islamabad, Pakistan. Landsat TM band ratios of 7/5, 3/1, and 5/4 are used to detect ferric minerals, clay minerals, and ferrous iron minerals bearing sedimentary rocks, respectively, which are applied to distinguish the altered and unaltered rocks. Such rocks have specific spectral responses in various bands of the electromagnetic spectrum and thus give rise to a number of anomalies indicating the presence of hydrocarbons. This study uses enhancement techniques of principal component analysis (PCA), band ratio, false color composite (FCC), and thermal anomaly composition for surface expressions caused by microseeps. It is revealed that spectral reflectance signify that the ferrous iron and red bed bleaching have reflection band and absorption band in TM bands 1, 3, and 4, respectively. Clay minerals and kaolinite have enormous reflection in band 5 and absorption capacity in TM band 7. These results can be used as a model to identify the alteration induced by hydrocarbon seepages. The study area is categorized into northern, eastern, southern, and western zones on the basis mineral alteration. The northern zone is characterized by strong anomalies and is relatively rich in clay alteration and ferrous as compared to other zones. Two types of hydrocarbon microseepages were observed in the Fateh Jang area which includes active seepages (gas microseepages and oil seepage) and passive seepage (bleaching effects).

Elaboration De La Carte Géotechnique De La Ville De Lubumbashi Guide Technique De Sélection Des Sites D’implantation D’ouvrages Du Génie Civil

Geotechnical data processing that ignores the spatial aspect leads to loss of information, specification errors, non-convergent and ineffective estimation, and prediction errors. These data often present a spatial dependence (problem of spatial autocorrelation) and a heterogeneity in space (clustering problem) and sometimes temporal. The geotechnical mapping of Lubumbashi soils based on 1672 observations according to the AASHTO classification system (designation ASTM D-3282 M145), divided these soils into 11 subgroups: A-1-a (sandy gravels with clays), A-1-b (gravelly sands with clays), A-2-4 (gravelly sands with silts), A-2-5 (sandy gravels plastic silts), A-2-6 (gravelly sands with clays), A-2-7 (gravelly sands with active clays), A-4 (silts with sands), A-5 (plastic silts with sands), A-6 (clays with sand), A-7-5 (active clays), A-7-6 (active clays). Class A-3 has not been identified. Soils with an index 5 contain clays of the illite type whereas the others consist of kaolinites on plasticity Casagrande chart. Class A-1 and A-2 are good for foundation engeneering and form the potential aquifers of the city (groundwater, drainage zone, groundwater recharge zone). They also constitute favorable sites for the implantation of the cimeteries (aerated soils) because the time necessary for the destruction of bodies is brief. In this case the rotation of 5 years can be used without problem for a city with dense population like the city of Lubumbashi. Soils A-4 and A-5 are also good for subgrade-foundations, but are highly vulnerable to erosion and liquefaction. Soils A-6 and A-7 form impervious bedrock substrates. These sites can be used as the landfill site. They are also considered clay deposits in the manufacture of ceramics and refractory products. Taking into account the nature of the source rocks, the same lithology can give several types of soils depending on the parameters influencing weathering: climate (Lubumbashi's tropical climate), pH, Eh, topography, anthropization, etc. One type of soil may also come from several rock formations. The geotechnical map developed compared to the geological map of Lubumbashi, shows that soils A-1 and A2 come from conglomerates, sandstones and the lateritization process of rock formations very rich in iron such as dolomitic shale and shale. Soils A-4 and A-5 are often alteration products of silty shales and siltstones, while soils A-6 and A-7 are derived from the alteration of clay and dolomitic rocks: shales, dolomitic shales, silty shales, limestones and dolomites. The geological map is fondamental but not sufficient document for geotechnical studies. A detailed study of the soils and the state of weathering of the different parts of a rock mass is inevitable.

Alteration mineral mapping to identify primary tin potential using Landsat 8 images and geographic information system in Rimba Kulit Area, Southern of Bangka Island

Remote sensing data has been proven to provide geographic information such as geographic structures, land covers, lithologies and hydrothermal alteration minerals, as shown in previous researches. Nonetheless, in this research, Landsat 8 images as one of remote sensing images are utilized in hydrothermal alteration mineral mapping to identify primary tin which is located in Gadung village, Toboali sub-district, South Bangka District. This research is intended to identify the distribution of primary tin based on types and alteration mineralogy in the research area by using Landsat 8 images. Accordingly, the method employed in this research is defoliant method for each mineral: 4/3;2/1 band ratio for quartz identification, 4/3;6/5 band ratio for illite identification, 4/2;7/6 band ratio for chlorite identification, and 4/3;7/6 band ratio for iron oxide. Further, the observations of morphology, lithology and geological structures used 5/4;6/3;4/2 and 5/3;6/4;5/4 composite image combinations. Moreover, petrography, X-Ray Diffraction (XRD) and XRF analyses served as confirmation for the result of image interpretation. The composing lithology of the research area is generally composed of sandstone units, whereas alteration which develops is predominantly dominated by clay alteration (illite mineral) and sulphide dominance in hydrothermal solution. The primary tin mineralization developed in the research area is classified as oxide mineral characterized by the presence of wolframite, pyrite, arsenopyrite, and cassiterite, and deposited in big polymetallic veins, as well as allegedly influenced by NNW-SSE-trending main geological structure and associated to iron oxide mineral in form of goethite and hematite. Meanwhile, the type of tin mineralization developed in the research area in form of mineralization in ironstone or gossan units is the result of supergene process carried by cassiterite which associated with iron oxide minerals.

Regional scale demarcation of alteration zone using ASTER imageries in South Purulia Shear Zone, East India: Implication for mineral exploration in vegetated regions

Regional scale demarcation of alterations is an important preliminary step in mineral exploration. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imageries here have been used for alteration mapping and iron-rich (e.g., Gossans) area demarcation in a highly vegetated and relatively unexplored part of Eastern India, namely, South Purulia Shear Zone (SPSZ). The area is surrounded by mineral-rich Singhbhum Shear Zone (SSZ), but the mineral potentiality of SPSZ has not yet been proven. Alteration mineral assemblages are comprise of iron-rich alteration (gossan), clay alteration with varying amounts of iron content, sericitization, ferruginization and chloritization. In this paper, we discuss a few advantages and limitations of commonly used satellite image processing techniques for mineral mapping. We integrate the outputs of band ratio, Principal Component Analysis (PCA), PCA-loading, and thresholding; termed as Directed PCA (DPCA) for delineating mineral potential areas. Our approach mapped the alteration zones with overall 74% accuracy. Our study leads to demarcation of 28% alteration area within a 10 km wide and 60 km long stretch of SPSZ. Two areas, namely, Lawa (23° 1′ 39.31″ N, 86° 4′ 2.55″ E) and Sindurpur (23° 4′ 38.30″ N, 86° 5′ 3.99″ E) were identified as mineral potential zone. Samples from those areas were studied using XRF, microscope and SEM with the conclusive presence of mineralization. Lawa is potential for hydrothermal polymetallic sulfides along with gold mineralization. Sindurpur is potential for secondary iron and manganese mineralization. The study shows that DPCA is a useful tool for ASTER data processing for narrowing target area in preliminary stages of exploration in vegetated zones.

Fluid P-T-X characteristics and evidence for boiling in the formation of the Phoenix uranium deposit (Athabasca Basin, Canada): Implications for unconformity-related uranium mineralization mechanisms

The Phoenix uranium deposit in the southeastern Athabasca Basin (Canada) is a typical unconformity contact-hosted uranium deposit, characterized by an association with reactivated basement faults, graphite-rich rocks in the underlying basement, and a pervasive clay alteration halo surrounding the mineralized zones. Petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events. Uraninite and clay-size minerals (tourmaline, kaolinite, illite and minor chlorite) mainly precipitated in the desilicification periods whereas hydrothermal quartz (mainly drusy quartz) formed during the silicification periods. Primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore-forming fluids even though quartz did not co-precipitate with uraninite. The coexistence of multiple types of fluid inclusions (liquid-dominated biphase, vapor-dominated biphase, vapor-only and halite-bearing triphase) within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping. Bulk fluid inclusion volatile analysis by mass spectrometry indicates H2O as the dominant species, with less than 1 mol% non-aqueous volatiles that show a compositional trend typical of fluid boiling. Microthermometric and cryogenic Raman spectroscopic analyses indicate that the mineralizing fluids are of H2O-NaCl-CaCl2 ± MgCl2 composition, with salinities ranging mainly from 23.4 to 31.1 wt%. The liquid-dominated biphase inclusions (excluding those interpreted to have resulted from heterogeneous trapping) have homogenization temperatures from 90 to 157 °C. These data are generally consistent with the classical diagenetic-hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults, and precipitated uraninite near the unconformity through reaction with reducing agents. However, the relatively low fluid inclusion homogenization temperatures documented in this paper, together with fluid boiling inferred from fluid inclusion assemblages, suggest that the deposit may have formed in a shallower environment (∼2.5 km) than assumed in the conventional diagenetic-hydrothermal model (>5 km). Abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling (flash vaporization) changing the fluid pH and promoting uraninite precipitation, with the alternating liquid-vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively.

Clay minerals trap hydrogen in the Earth's crust: Evidence from the Cigar Lake uranium deposit, Athabasca

Hydrogen (H2)-rich fluids are observed in a wide variety of geologic settings including gas seeps in serpentinized ultramafic rocks, sub-seafloor hydrothermal vents, fracture networks in crystalline rocks from continental and oceanic crust, and volcanic gases. Natural hydrogen sources can sustain deep microbial ecosystems, induce abiotic hydrocarbons synthesis and trigger the formation of prebiotic organic compounds. However, due to its extreme mobility and small size, hydrogen is not easily trapped in the crust. If not rapidly consumed by redox reactions mediated by bacteria or suitable mineral catalysts it diffuses through the rocks and migrates toward the surface. Therefore, H2 is not supposed to accumulate in the crust. We challenge this view by demonstrating that significant amount of H2 may be adsorbed by clay minerals and remain trapped beneath the surface. Here, we report for the first time H2 content in clay-rich rocks, mainly composed of illite, chlorite, and kaolinite from the Cigar Lake uranium ore deposit (northern Saskatchewan, Canada). Thermal desorption measurements reveal that H2 is enriched up to 500 ppm (i.e. 0.25 mol kg−1 of rock) in these water-saturated rocks having a very low total organic content (<0.5 wt%). Such hydrogen uptake is comparable and even exceeds adsorbed methane capacities reported elsewhere for pure clay minerals or shales. Sudoite (Al–Mg di-trioctahedral chlorite) is probably the main mineral responsible for H2 adsorption in the present case. The presence of multiple binding sites in interlinked nanopores between crystal layers of illite-chlorite particles offers the ideal conditions for hydrogen sorption. We demonstrate that 4 to 17% of H2 produced by water radiolysis over the 1.4-Ga-lifetime of the Cigar Lake uranium ore deposit has been trapped in the surrounding clay alteration haloes. As a result, sorption processes on layered silicates must not be overlooked as they may exert an important control on the fate and mobility of H2 in the crust. Furthermore, the high capacity of clay minerals to sorb molecular hydrogen may also open up new opportunities for exploration of unexpected energy resources and for H2 storage based on geo-inspired materials.

Mineralogy and geochemistry of various colored boles from the Deccan volcanic province: Implications for paleoweathering and paleoenvironmental conditions

Boles are markers of hiatus in successive eruptions of the Deccan flood volcanism (DFV) emplaced at the Cretaceous-Paleogene boundary that are interpreted to retain paleoenvironmental information from their subaerial exposure. To evaluate paleoenvironment during these hiatuses, mineralogy and geochemistry of three different colors of boles, i.e., red (dark = 10R-3/6 and light = 10R-4/8), brown (5YR-4/4) and green (5G-6/2) were examined. The plagioclase index of alteration (PIA) (loss of Ca and Na relative to Al) was between 76 and 81 for all the boles, indicating moderate chemical weathering that is probably due to their short subaerial exposures. Mass balance calculations show significant enrichments of K, Si, Mg and Rb in green and brown boles suggesting an allochthonous input that is interpreted as volcanic ash fallout. Mineralogically, the red bole is dominated by montmorillonite and hematite, the brown bole of ferruginous smectite and montmorillonite, and the green bole of celadonite and nontronite.Montmorillonite and hematite genesis in red boles indicates leaching in an oxidative environment at near neutral pH (~5.5 to 8) conditions. Further, heating of the altered basalt from emplacement of upper lava flows under subaerial-dry conditions could have also promoted the formation of hematite in red boles. The hydrothermal alteration of K and Mg enriched volcanic ash admixed with the altered lower flow basalt under slightly reducing oxidation potential led to the genesis of nontronite and celadonite in the green bole. The aluminous Fe-smectite in brown bole occurred from hydrothermal alteration of aluminous clays (e.g., montmorillonite). The different colored boles, therefore, suggest a range of weathering processes including chemical leaching to hydrothermal alteration in oxidative to reducing environmental conditions throughout DFV emplacement that could reflect changing surficial conditions associated with volcanically forced changes to the environment.

Influence of leachate on the Oligocene-Miocene clays of the İstanbul area, Turkey

Oligo-Miocene clay outcrops on the European side (west and northwest part) of Istanbul were analysed. Formerly, a landfill and sanitary landfill were built on the clay. Mineral liners of the current and extending parts of the Istanbul landfill consist of these clays, since they include a considerable amount of smectite, illite, and kaolinite. With this feature, these clays are also an important candidate for the buffer material of repositories for nuclear wastes of newly planned nuclear power plants. In this context, one Miocene and two Oligocene clay samples were subjected to leachate under low stress using an odometer device during a period of 30 days, 180 days, and 360 days to understand the chemical and mineralogical transformations and subsequent changes in the clay structure. The results of this work and our ongoing other research revealed that Istanbul clays are mostly illite/smectite mixed-layer minerals. Illites considerably increased while the illite/smectite mixed-layer minerals decreased in the first 15-30 days. The kinetics of the three clays was studied to understand the reasons for the illite increase. Increase of the activation energy over time may be attributed to the successive intercalation of illite lattice layers as alteration of mixed-layer illite-smectite clays. Mineral dissolution, however, is still the primary mechanism for illitization when the low activation energy is considered. With these findings, the utilization of Istanbul clays is questionable for clay barriers of landfills or sealing material of hazardous wastes.

The Structure and Significance of Anhydrite-Bearing Vein Arrays, Lienetz Orebody, Lihir Gold Deposit, Papua New Guinea

The Lihir Au deposit (also known as Ladolam), Papua New Guinea, has a 56-Moz resource and is the world’s largest alkalic Au deposit in terms of contained Au. The Au deposit is in an amphitheater, inferred to be a remnant of the original ~1.1-km-high volcanic cone that underwent NE-directed sector collapse(s) and prolonged tropical weathering. The ore deposit is situated in the footwall of the sector collapse detachment surface and consists of several orebodies. Late-stage, Au-rich, alkalic low-sulfidation epithermal mineralization was superimposed upon early-stage, porphyry-style alteration. A threefold vertical alteration architecture at Lihir is interpreted to broadly represent this evolution. With increasing depth, the alteration zones consist of (1) a surficial, generally barren, steamheated clay alteration zone that is a product of modern high-temperature geothermal activity, (2) a high-grade (>3 g/t Au), refractory sulfide and adularia alteration zone that represents the ancient epithermal environment, and (3) a comparatively low-grade ( Early porphyry-style hydrothermal activity in the Lienetz orebody resulted in a magmatic-hydrothermal breccia complex and associated hydrothermal veins, most of which contain anhydrite. A spectacular anhydrite ± carbonate vein array is exposed in the deeper levels of the Lienetz open pit and reveals a dynamic structural evolution where veins were reactivated but with grossly similar geometries and kinematic histories. Early localized compression is evident from low-angle thrust faults and tensile vein arrays with both subvertical and subhorizontal dips. This occurred in the porphyry-style environment under low differential stress and an oscillating subhorizontal to subvertical σ1 and temporarily elevated fluid pressures that resulted from mineral sealing. The variable stress conditions and nucleation of vein arrays with low-angle dips are interpreted to relate principally to instabilities in the volcanic-magmatic environment, triggered in part by volume changes within the underlying magma chamber and exsolution of hydrothermal volatiles. Protracted or multistage NWdirected extension with a mostly subvertical σ1 predominated for the rest of the porphyry- to epithermal-stage evolution, possibly reflecting the greater control of far field tectonic stresses and instabilities in the shallow volcanic environment. This is best documented by the principal vein array at Lienetz, which consists of large hybrid to shear veins with low-angle dips (~30°) to the north. Linking these large, low-angle veins are sets of tensile to hybrid veins and breccia veins with high-angle dips (~65°) to the northwest. Kinematic indicators record dominantly extensional displacement, with N- to NW-directed, top-block down sense of shear. Significant modification of the early formed veins and breccias occurred during the transition from porphyrystyle to epithermal conditions, leading to recrystallization, dissolution seams, stylolites, volume loss, and solution collapse breccias. The modified veins localized some shear and may have had some control of lubrication for the sector collapse event(s); however, they are not kinematically linked. High-grade, epithermal-style, Au mineralization followed vein modification and sector collapse(s). Mineralization was partly facilitated by preconditioning provided by porphyry-stage events, as auriferous hydrothermal fluids flowed through cavities created by the dissolution of early formed anhydrite. Mineralization was also localized at depth by NE-striking faults. Continued extension with top-block down to the northwest preferentially reactivated the principal vein array with low-angle dips to the north. Porphyry-stage veins were modified during epithermal mineralization due to reactivation under extensional conditions. Reactivation produced NE-striking tensile to hybrid veins and breccia veins with high-angle dips and rhombic dilational jogs that localized high-grade Au. The NE- to ENE-striking structural grain, evident at both the island scale and the deposit scale, was inherited from the basement. These structures were weaknesses that were reactivated throughout the evolution of Lienetz. Similarly oriented deep-seated faults contributed to the northeast elongation of the volcanic amphitheater and were fundamental for the structural control of vein formation and Au localization. The unique characteristics of the Lihir Au deposit, in particular the preserved relationships of hybrid ore and volcanic architecture, provide insights into transitional processes between porphyry and epithermal end members. Reactivated structures and anhydrite dissolution were significant factors in Au mineralization in the Lienetz orebody. As such, they should be regarded in the exploration and understanding of other magmatichydrothermal ore deposits.

The Contact uranium prospect, Kiggavik project, Nunavut (Canada): Tectonic history, structural constraints and timing of mineralization

Uranium mineralization in the Kiggavik area, on the eastern border of the Thelon basin (Nunavut, Canada), hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity-related deposits’ structural controls and therefore exploration of these types of deposits in this prospective district. This article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered, basement-hosted prospect in the Kiggavik area, named Contact. The Contact prospect is located along the Andrew Lake Fault (ALF), a major NE-SW fault corridor in the area. This study combines field work, drillcore logging, sampling, and macro- to micro- petro-structural analyses. Key results from this study highlight that the NE-trending ALF, along with the ENE-trending Thelon (TF) and Judge Sissons (JSF) faults, formed early during intracratonic rifting and deposition of the Baker Lake and Wharton groups (ca. 1850–1750 Ma) in response to the Thelon and Trans-Hudsonian orogeny. The ALF was affected by a strong silicification-brecciation event that likely developed at ca. 1750 Ma, and partitioned later deformation and fluid circulation. In the Contact prospect, the ALF was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns, alteration, and mineralization types. Ten fracture stages have been identified at the Contact prospect, f1–f10. The first stage of mineralization, coeval with f5, is related to fluids of unconstrained origin that circulated through E-W faults in the area that locally re-activated quartz veins of the brecciation event at the intersection with the ALF. Mineralization at this stage is polymetallic and associated with weak clay alteration. The second stage of uranium mineralization occurred coeval with transtensional reactivation of the NE-SW trending ALF (f6c) and in relation to circulation of oxidizing basinal brines within the fault zone. Mineralization at this stage is monometallic and associated with illite and sudoite alteration. Later reactivation of the inherited fracture network (f8) led to strong illitization and bleaching of the host rock, with local reworking of the ore body. Finally, reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re-concentration along redox fronts, with strong illitization and bleaching of the host rock. Unlike the classic unconformity-related uranium deposits in the Athabasca Basin where clay alteration halos occur around the ore bodies related to mineralizing processes, in the Contact prospect the strongest clay alteration event (f8) postdates both main stages of mineralization. Along with uranium remobilization, the basement-hosted Contact prospect is likely a relict of what was once a larger deposit.