Hydrothermal Rocks Research Articles

Применение пространственного геологического моделирования для оценки минеральных ресурсов медного месторождения Удоканское Читинской области

Introduction. The main goal of this study is to integrate geostatistical interpolation methods with a variety of geological and geophysical information to determine 3D-spatial and temporal relationships and cause - and - effect processes between ore bodies, altered rocks, metallogenic layers, and intrusive rocks. Materials and methods. The article present geostatistical methods used to create spatial models of porphyry copper deposits. These models include a variety of geological information about mineralization in the study region, such as geological, geophysical, geochemical, well and section data. Using this data, three - dimensional metallogenic geological objects were constructed that describe the distribution of mineralization in the rock mass. Results. The modelling results showed that the digital deposit model allows for accurate determination of copper grades for multiple ore bodies and the identification of continuous variations in copper grade within a single ore body. Discussion. It is known that many authors show great interest in the extraction and processing of spatiotemporal data. This also applies to geological and structural modeling of mineral deposits. However, these works do not cover, or do not cover in sufficient detail, the features of modeling complex geological systems at a high level of abstraction, without taking into account small details. In this article, the authors developed a methodology that is designed to study data on a mineral deposit, analyze anomalies and optimally display interpolation surfaces, as well as the uncertainties associated with them. In addition, this methodology allows for a more in - depth and detailed analysis of quantitative and qualitative characteristics based on a digital model of the deposit. The methodology for creating digital models of deposits based on geostatistical analysis methods can find wide application in forecasting the development of the deposit as a whole. Conclusions. Based on the study, a spatial relational database was obtained containing geological information about mineralization in the study area of the Udokanskoye deposit. 3D-models of metallogenic geological objects were built, including mineralization sequence, granodiorite, hydrothermal rocks and magnetic anomaly, which can be used to predict and identify potential mineralization targets. Resume. The modelling results showed that the digital deposit model allows for accurate determination of copper grades for multiple ore bodies and the identification of continuous variations in copper grade within a single ore body. Suggestions for practical applications and directions for future research. Further development of this method is possible due to the analysis of the work of a group of deposits, i.e. the assessment of indicators will be carried out for a separate deposit with subsequent aggregation of the studied processes using Markov chains and multi - channel mass service systems with failures. In the future, this will make it possible to use systemically significant assessments in making global decisions at all stages of the work of a mineral deposit.

Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central High Atlas were investigated through gemological and chemical studies, including infrared spectrum, Raman spectrum, SEM-EDS, and LA-ICP-MS. Two titanite samples are yellow, transparent–translucent with a greasy luster, 3.5 and 2.5 mm long. MA-1 and MA-2 have similar gemological properties, the refractive index (RI) is beyond the range of the refractometer (>1.78), the specific gravity (SG) values fall in the range of 3.52~3.54 and both are inert to short-wave and long-wave UV radiation. The spectral characteristics have high consistency with the RRUFF database. The major elements’ composition shows a negative correlation between Al, Fe, V, and Ti, suggesting the titanites underwent substitutions such as (Al, Fe3+) + (F, OH) ↔ Ti + O. The titanite samples, characterized by a low abundance of REE (802~4088 ppm) and enriched in LREE, exhibit positive Eu (δEu: 1.53~7.79) and Ce (δCe: 1.08~1.33) anomalies, indicating their formation in a hydrothermal environment with low oxygen fugacity. The 238U/206Pb and 207Pb/206Pb ratios of the titanites yield lower intercept ages of 152.6 ± 2.2 and 151.4 ± 5.3 Ma (1s), consistent with their weighted average 206Pb/238U ages of 152.3 ± 2.0 and 150.7 ± 3.2 Ma (1s) respectively. The results of U-Pb dating are matched with the second main magmatic activities in the High Atlas intracontinental belt of Morocco during the Mesozoic to Cenozoic period. Moreover, the two titanite samples have almost no radiational damage. All the results show that the titanite from High Atlas, Morocco, has the potential to be a reference material for LA-ICP-MS U–Pb dating, but further experiments are needed to be sure.

Atomic-scale environment of niobium in ore minerals as revealed by XANES and EXAFS at the Nb K-edge

Abstract. The mineralogy of niobium (Nb) is characterized by multicomponent oxides such as AB2O6, A2B2O7, ABO4, and ABO3 in which Nb is incorporated in the B site. Such complex crystal-chemistry prevents their unambiguous identification in ore deposits such as hydrothermal rocks and laterites which exhibit complex and fine-grained textures. The understanding of the processes controlling Nb ore deposit formation in various geological settings is therefore limited, although Nb is a critical element. In this study, we use X-ray absorption spectroscopy (XAS) at the Nb K-edge to investigate the local atomic-scale structure around Nb in a large set of natural and synthetic minerals of geological and technological importance. Our X-ray absorption near-edge structure (XANES) data at the Nb K-edge show three major features of variable position and intensity and then can be related to the local distortion and coordination number of the Nb site. Shell-by-shell fits of the extended X-ray absorption fine structure (EXAFS) data reveal that the NbO6 octahedra are distorted in a variety of pyrochlore species. At least two distinct first shells of O atoms are present while reported crystallographic data yield regular octahedra in the same minerals. Next-nearest Nb–Nb distances in pyrochlore and Nb-bearing perovskite mirror a corner-sharing NbO6 network, whereas the two Nb–Nb distances in columbite are typical of edge- and corner-sharing NbO6 octahedra. Such a resolution on the Nb site geometry and the intersite relationships between the next-nearest NbO6 octahedra is made possible by collecting EXAFS data under optimal conditions at 20 K and up to 16 Å−1. The local structure around substituted Nb5+ in Fe3+, Ti4+, and Ce4+ oxides suffers major changes relative to the unsubstituted structures. The substitution of Nb5+ for Ti4+ in anatase leads to the increase in the interatomic distances between Nb and its first and second Ti4+ neighbors. The substitution of Nb5+ for Ce4+ in cerianite reduces the coordination number of the cation from eight to four, and the Nb–O bonds are shortened compared to Ce–O ones. In hematite, Nb5+ occupies a regular site, whereas the Fe3+ site is strongly distorted suggesting major site relaxation due to charge mismatch. The sensitivity of XANES and EXAFS spectroscopies at the Nb K-edge to the local site geometry and next-nearest neighbors demonstrated in this study would help decipher Nb speciation and investigate mineralogical reactions of Nb minerals in deposit-related contexts such as hydrothermal and lateritic deposits.

Major and trace element emission rates in hydrothermal plumes in a tropical environment. The case of La Soufrière de Guadeloupe volcano

Hydrothermal or low-temperature volcanic emissions, most commonly occurring in fumarolic environments, dominate the global volcanic landscape. This work presents physicochemical characterization of the aerosols contained in steam- and H2S-rich plumes discharged from La Soufrière volcano, in conjunction with the first report on their heavy metal degassing emission rates. Our results indicate that the plume is enriched in certain lithophile (K, Ti, Si, Al, Mn, and Mg) and siderophile (Fe) elements, related to hydrothermal rock leaching, and chalcophile (Sb, As, Zn, Pb, and Tl) elements, which are usually degassed from the magma source. Heavy metal emission rates were found to be below 15 g/d, which are modest compared to available worldwide data. Nevertheless, Cr and Sb emission rates were very similar to those of Lascar volcano (Chile), which instead has produced magmatic eruptions in recent times. We propose that the depth of the magma chamber and the input of meteoric waters play an important role in scavenging heavy metals in the hydrothermal system of magmatic-hydrothermal volcanoes. Notwithstanding low heavy metal emission rates, La Soufrière can be regarded as an important pollution source in the Lesser Antilles volcanic arc.

Hydrothermal alteration of surficial rocks at Los Humeros geothermal field, Mexico: a magnetic susceptibility approach

Utility of the geothermal surface manifestations (GSMs; thermal springs, geysers, fumaroles, and zones of hydrothermal alteration) in the studies related to the geothermal exploration is widely recognized. The identification of hydrothermally altered rocks and zones of alteration is very important because their presence indicates the type and size of the geothermal reservoir and existing thermal conditions. The use of traditional methods (i.e., geochemistry, mineralogy, and petrography) requires expensive equipment, time-consuming, and laborious sample preparation methods. Some of the rock magnetic parameters, like magnetic susceptibility (χlf) and percentage of frequency-dependent magnetic susceptibility (χfd%), are potential to become effective additional tools in identification of the hydrothermal rocks during the initial stages of geothermal exploration. Three chemical methods, Chemical Index of Alteration (CIA), loss-on-ignition (LOI), and the binary plot (CaO + Na2O + K2O) vs. (Fe2O3 + MnO + MgO), along with two rock magnetic methods, χlf and the binary plot (χlf vs. χfd%), are applied to nine intensively altered andesite reference rocks. All the five methods have correctly identified that 99 out of the total 350 studied rocks are altered. More altered rocks are distributed surrounding the several faults in the study area. Various faults (e.g., Los Humeros fault and the Loma Blanca fault) favor fluid flow and present strong hydrothermal alteration at the surface. However, there are no altered rocks on the surface region between the E-W trending Las Papas and Las Viboras faults. The presence of only the deeper fluid pathway toward the east in the surroundings of these two faults result into the almost absence of hydrothermal alteration along their strike at the surface. Consequently, there are not many altered rocks observed surroundings these two faults at the surface. These features suggest that the surface hydrothermal alteration at Los Humeros Geothermal Field (LHGF) is controlled by faults. χlf and χfd% are reliable, simple to measure, fast, cost-effective, and have the potential to become reliable additional tools for future exploration studies.

Geophysical characterization of a low sulfidation epithermal gold and silver deposit, Mendoza, Argentina

The combined analysis of aeromagnetic and gamma-ray spectrometry data, allowed us to determine and differentiate the responses of hydrothermal rocks units and low sulfidation epithermal gold systems, in the south area of the San Rafael Block, in the Mendoza province. The data processing approach was focused on mapping geological limits and structures, and their response over the gold mineralization area, linked to hydrothermal zones. To do this, filtering algorithms, such as vertical derivative, tilt derivative, logistic function, and analytic signal were applied to the aeromagnetic data. For the analysis of gamma-ray spectrometry data, images of K, eU, and eTh concentrations, K/eTh ratios, and an F-parameter were used. The analytic signal filtering of the data reveals relatively low magnetic intensity zones associated with hydrothermally altered rock areas. The radiometric data delineate local anomalies that reflect enrichment with high potassium values in the deteriorated zones. A broad K/eTh anomaly correlates with the extension of the magnetic low intensity zones, indicating a generalized potassium enrichment in the Don Sixto area. These results indicate that the main structural directions are arranged in NW-SE strikes and the secondary ones in N–S strikes. These lineaments are spatially correlated with the most significant structures in the study area, evidencing that the mineral deposits located in the study area respond to the main lineaments. In addition, the main geophysical characteristics allowed us to identify the zone of hydrothermal alteration related to the low sulfidation epithermal gold and silver deposit Don Sixto, which would be related to high levels of K/eTh ratios and low intensity magnetic zones.

Rock alteration mapping in and around fossil shallow intrusions at Mt. Ruapehu New Zealand with laboratory and aerial hyperspectral imaging

Diagnostic absorption features in hyperspectral data can be used to identify a specific mineral or mineral associations. However, it is unknown how accurate hyperspectral mapping can be for identifying alteration mineral compositions at the resolution required to describe structures such as fossil intrusions, or whether it can accurately quantify the alteration present. This study compared petrographic observation with visible, near-infrared (VNIR), and shortwave infrared (SWIR) hyperspectral remote sensing at laboratory- (centimetre-scale) and aerial- (metre-scale) scales to characterise the abundance of surface hydrothermal rock alteration in and around a shallow fossil intrusion on Pinnacle Ridge, Mt. Ruapehu, New Zealand. We classified a high-resolution aerial hyperspectral image to develop a new surface alteration map using Spectral Angle Mapper (SAM) algorithm. The petrographic thin-section and the laboratory and aerial hyperspectral imaging revealed a spectrum of hydrous alteration phases as indicated by the presence of an absorption feature at 2207 nm. Moderate correlation exists between the depth of the absorption feature at 2207 nm and the point counting-derived alteration percent values, indicating reliability of laboratory-based hyperspectral analytical methods. In contrast, aerial hyperspectral data failed to provide any clear correlations to field-mapped alteration using a band-depth approach, and we interpret this due to ‘oversampling’ of surface (supergene) alteration, spectral mixing, and sensor limitations (e.g., bandwidth, signal-to-noise ratio). The hyperspectral image-derived alteration map, created using supervised image classification, can loosely be translated to a geotechnical map where porosity and permeability play a major role in localizing hydrothermal fluid flow and the formation of alteration mineral associations. • Laboratory SWIR hyperspectral scanning accurately quantified hydrothermal alteration. • Airborne hyperspectral imaging can detect presence of hydrothermal alteration minerals. • Intrusion related hydrothermal alteration was mapped using Spectral Angle Mapper.

Characterization of hydrothermal fluids that alter the upper oceanic crust to spilite and epidosite: Fluid inclusion evidence from the Semail (Oman) and Troodos (Cyprus) ophiolites

Pervasive alteration of basaltic oceanic crust by heated seawater at greenschist facies conditions produces two contrasting hydrothermal rocks. “Spilites”, consisting of chlorite + albite + quartz ± actinolite ± epidote, occur typically with regional extents. Locally spilites are metasomatically transformed to “epidosites” consisting of epidote + quartz + titanite + hematite or magnetite. Both alteration types have been proposed as markers of deep hydrothermal upflow in sub-seafloor convection cells, and as sources of the ore metals in basalt-hosted seafloor massive sulfide deposits. Little direct evidence is available for the chemical compositions of these fluids in their states deep in the upflow zones prior to their discharge at the seafloor. To better characterize them we have conducted a field, petrographic and fluid inclusion study of the lavas, sheeted dikes and plagiogranites in the Semail ophiolite, with supporting samples from the Troodos ophiolite. Our results show that both the spilite- and epidosite-forming fluids were single-phase aqueous liquids during the hydrothermal alteration. At some sites their salinity is 3.1–3.2 wt.% NaCleq, which we take to represent the chlorinity of Cenomanian seawater in the Semail realm. At other sites salinities are as low as 2.4 wt.% NaCleq or as high as 5.7 wt.% NaCleq, attributable to liquid–vapor separation and partial remixing deep in the crust along the dew curve of seawater, prior to ascent of the fluids to the sites of fluid inclusion trapping. Hypersaline brines, often accompanied by vapor, are restricted to plagiogranites in both the Semail and Troodos ophiolites and they represent magmatic–hydrothermal fluids that pre-date and are genetically unrelated to the spilite and epidosite alteration. The volcanostratigraphic locations of the samples constrain their maximum depths to 1470–3600 m below seafloor during alteration. The range of possible fluid trapping pressures for all samples is 31–68 MPa. Trapping temperatures vary between sites from 145 to 440 °C for spilite fluids and 255 to 435 °C for epidosite fluids. Quantitative analyses of 12 elements in individual fluid inclusions by LA-ICP-MS define the chemical characters of the two alteration fluids. The Br/Cl ratio in the spilite fluid is the same as in modern seawater and the other elements fit expectations from seawater–basalt experiments at elevated temperature. Accordingly, concentrations of Li, B, Na, Cl, K, Br and Sr in the spilite fluid match those in modern black-smoker vent fluids in basaltic crust. Exceptions are Ca and Fe, which are enriched in the spilite fluid. As these elements may precipitate below or at the seafloor prior to vent sampling, we conclude that the spilite fluids are plausible feeders of basalt-hosted black-smoker vents. The epidosite fluid has broadly similar elemental concentrations to the spilite fluid, but vastly lower Fe, reflecting the highly oxidized state of epidosites. This suggests that epidosite fluids are incapabable of forming basalt-hosted seafloor massive sulfide deposits.

Structural and lithological interpretation of aero-geophysical data in parts of the Lower Benue Trough and Obudu Plateau, southeast Nigeria

High resolution airborne magnetic and radiometric data were used to map probable sites for polymetallic-magmatic hydrothermal deposits in the study area. The first and second vertical derivatives, horizontal gradient, analytic signal and tilt angle derivative were used to enhance magnetic data in order to determine the location of short wavelength anomalies, magnetic sources and geologic boundaries. Also, to understand and detect radiometric anomalies controlling mineralization in host rocks, enhancement operations involving potassium (K), equivalent thorium (Th), equivalent uranium (U) concentrations and ternary imageries were carried out. All these operations enabled the delineation of responses associated with mineralization, lithology and geologic structures. Generally, lineaments trend in the NE-SW, NNE-SSW, NW-SE and E-W directions, and serve as potential pathway for hydrothermal fluid migration and mineralization. Radiometric anomalies from spectrometric imageries are caused by felsic minerals, hydrothermal rock alterations, widespread shales, residual clay, oxides and accessory minerals that constitute regolith of the area. The coincident high magnetic and potassium intensities sites in Anambra Bain (AB), Abakaliki Anticlinorium (AA), Ikom-Mamfe Rift (IMR) and Obudu Plateau (OP) are probable sites for polymetallic-magmatic hydrothermal deposits. Generally, the joint magnetic and radiometric results were able to establish link between lithology, geologic structures and hydrothermal alteration patterns.

Defects in olivine

Abstract. Olivine, a ferromagnesian orthosilicate, is the most abundant mineral in Earth's upper mantle and is stable down to the olivine–wadsleyite phase transition, which defines the 410 km depth mantle transition zone. Olivine also occurs in crustal environments in metamorphic and hydrothermal rocks and is expected to be the major mineral constituent of the Martian and Venusian mantles. The olivine atomic structure is also used in materials science to manufacture lithium batteries. Like any other crystalline solid, including minerals, olivine never occurs with a perfect crystalline structure: defects in various dimensions are ubiquitous, from point, line, and planar defects to three-dimensional (3-D) inclusions. In this contribution, I review the current state of the art of defects in olivine and several implications for key processes occurring in Earth's mantle. Intrinsic and extrinsic point defects are detailed, exemplifying the astonishing diversity of atomic impurities in mantle-derived olivine. Linear defects, one of the key defect types responsible for ductile deformation in crystalline solids, are examined in light of recent progress in 3-D transmission electron microscopy, which has revealed an important diversity of dislocation slip systems. I summarize the principal characteristics of interface defects in olivine: the free surface, grain and interface boundaries, and internal planar defects. As the least-studied defects to date, interface defects represent an important challenge for future studies and are the main application of numerical simulation methods in materials science. I provide an overview of melt, fluid, and mineral inclusions, which are widely studied in volcanology and igneous petrology. Special attention is given to new crystalline defects that act as deformation agents: disclinations (rotational defects) and the potential occurrence of disconnections in olivine, both of which are expected to occur along or near grain boundaries. Finally, I detail outstanding questions and research directions that will further our understanding of the crystalline specificities and paradoxes of olivine and olivine-rich rocks and ultimately their implications for the dynamics of Earth's upper mantle.

In situ S isotope analysis and source tracing of pyrite from lacustrine hydrothermal sedimentary rocks: the Chang 7-3 sub-member, Triassic Yanchang Formation, Ordos Basin

The Ordos Basin developed a large depression-type lake basin in the Late Triassic. Here, we report on pyrites from lacustrine hydrothermal sedimentary rocks that were found at the bottom of a black shale layer from the Chang 7-3 sub-member of the Triassic Yanchang Formation in Tongchuan and Yaoqu and Well Z9 sections, on the southern margin of the Ordos Basin. Observations of field outcrops and underground cores were used to identify vein and brecciated pyrites that are distributed within water-explosive dolomite breccias or sandwiched in a textured layer of hydrothermal sedimentary rock. Based on previous work, scanning electron microscopy observations, electronic probe microanalysis, nano-SIMS trace-element mapping and in situ sulfur isotope analyses were completed. The crystal form of pyrites is mainly cubic with surfaces mostly smooth and clean. Pyrites contain trace elements, such as As, Au, Co, Cu, Cr and Zn. The pyrite sulfur isotope values are enriched in 34S (δ34SV-CDT = 7.31–10.05‰; average 8.49‰) and show that the pyrite is related to hydrothermal deposition. Late Triassic hydrothermal activity at the bottom of the lake provided sulfate for pyrite formation, and hydrothermal sulfide may have also been an important sulfur source. KEY POINTS Pyrites from lacustrine hydrothermal sediments were formed at the bottom of a black shale layer from the Chang 7-3 sub-member of the Triassic Yanchang Formation on the southern margin of the Ordos Basin. The pyrite contains trace elements such as As, Au, Co and Ni. In situ pyrite sulfur isotope values are enriched in 34S and show that the pyrite is related to hydrothermal deposition with sulfur derived from sulfate and hydrothermal sulfide

The Peltetec ophiolitic belt (Ecuador): a window to the tectonic evolution of the Triassic margin of western Gondwana

ABSTRACT New field and petrographic observations, whole-rock major- and trace-element geochemical data, Nd and Sr isotope systematics and U-Pb SHRIMP zircon ages of the Peltetec metaophiolite and related rocks (Ecuador) allow the characterization of the igneous and sedimentary protoliths and the evaluation of the geodynamic evolution of the active western margin of Gondwana during the Mesozoic. The Peltetec ophiolitic belt, exposed along the western margin of the Cordillera Real (Ecuador) and previously considered of Cretaceous age, comprises slices of metamorphosed (greenschist facies) and variably deformed peridotites, gabbros (locally cumulate), basaltic lavas and dykes, hydrothermal breccias and sedimentary rocks. The geochemical characteristics of the tholeiitic basaltic rocks indicate a Sr-Nd isotope depleted mantle source with variable imprint of subduction zone-derived or continental crust-assimilated components, as indicated by enrichment in Th, negative anomaly of Nb and relative depletion in high field strength elements (HFSE). Geochemical diversity allows defining different groups of noncumulate igneous rocks with oceanic island arc and NMORB-like back-arc affinities. U-Pb zircon ages from a metabasite yielded 228.1 ± 1.7 Ma, interpreted as the crystallization age of the magma. These data allow proposing the generation of the Peltetec ophiolite in a back-arc setting as a consequence of late Triassic extension of the western continental margin of Gondwana. Granites located at the western margin of the Peltetec Unit with S-type affinity and equal Triassic age (U-Pb age of 228.2 ± 0.8 Ma) document coeval anatexis of the continental crust as a consequence of heating associated with the same extensional event that originated the ophiolite. Geologic correlation allows enlarging such tectonic scenario to include ophiolitic units of similar age in Colombia.

The molybdenite Re-Os isotope chronology, in situ scheelite and wolframite trace elements and Sr isotope characteristics of the Chuankou tungsten ore field, South China

(a), The sequence of wolframite and scheelite in the evolution of ore-formation fluid; (b), The four processes ore- formation fluid. Stage 1, The crystallization and destructure of wolframite; Stage 2, The occurrence of metasomatism between Sch-1 and wolframite; Stage 3, The fluid mixing (wall rocks and magmatic hydrothermal) and crystallization; Stage 4, The filling of later magmatic hydrothermal and Cementation for wolframite breccia . • The Chuankou tungsten ore is formed at 229 to 230 Ma. • Four major fluid processes can be identified effectively for Chuankou ore field. • Chuankou ore field might be formed at a relatively “free” space of regional extension. The Chuankou tungsten ore field, situated in the central area of the Qing-Hang ancient suture zone in South China, is characterized by predominantly quartz vein-type tungsten mineralization that formed near the contact between the Chuankou granite and slightly metamorphosed silt-bearing sericite slate. Based on field work, cathodoluminescence, molybdenite Re-Os dating and in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, the Chuankou tungsten ore was formed at 230.6 ± 2.9 Ma to 229.4 ± 2.6 Ma in a typical Indosinian metallogenic event. In addition, three distinct generations of scheelite and two types of wolframite can be clearly distinguished. Type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element (HREE) content and an obvious negative Eu anomaly. Type 2 wolframite grains are strongly altered as residual-pseudomorphic structures by ore-forming fluids and have relatively low REE contents. Sch-1 scheelite is present in the interior of the type 2 wolframite grains. The Sch-1 scheelite grains have an elevated REE content and low 87 Sr/ 86 Sr ratios with a strongly negative Eu anomaly, which suggests an inheritance signal of the host rocks. Comparatively, Sch-2 and the altered Sch-1 scheelite have characteristic extremely low REE contents and remarkably strong positive Eu anomalies. These scheelites also have increased 87 Sr/ 86 Sr ratios and low 88 Sr signals. Sch-3 is idiomorphic with perfect oscillating zoning. The REE content of Sch-3, which typically has the lowest 87 Sr/ 86 Sr ratios, is higher than those in Sch-1 and Sch-2, and the extremely high 88 Sr signals indicate a distinct thermal fluid event that was directly derived from the host rock. The correlations between the REE and Nb of scheelite imply a type B-substitution of Sch-1 and Sch-2 but a type C-substitution for Sch-3. The correlation of Eu N and Eu N * shows an Eu 3+ substitution process for stages Sch-1 and Sch-2 and an Eu 2+ substitution process for stage Sch-3. Thus, we confirm that ore-bearing hydrothermal rocks must undergo early-stage metasomatism and filling, middle-stage fluid mixing between wall rocks and magmatic hydrothermal activity, and refilling of late-stage magmatic hydrothermal activity during the metallogenic process. During the Indosinian period, the mineralization stages of polymetallic deposits in the Indosinian were composed of Stage 1 (240 to 220 Ma) and Stage 2 (220 to 200 Ma). The Chuankou tungsten ore field can be considered as the typical representation of the Stage 1 metallogenic event in South China. This ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the South China Block.

Calcium isotopes in high-temperature terrestrial processes

This chapter explores the growing body of stable and radiogenic Ca isotope measurements in high temperature terrestrial materials and covers the emerging applications for Ca isotope variability in igneous and metamorphic rocks and minerals. Calcium isotope fractionation at high temperature has been found to lead to larger effects than initially theorized, sometimes even exceeding those found in low temperature near-surface environments, yet many of the underlying fractionation mechanisms still remain poorly understood. Igneous whole-rocks span a δ 44 Ca range of ~2‰ (−0.9 to +0.9‰, relative to bulk-silicate Earth) and their constituent minerals have a range of ~2.5‰ (−1.2 to +1.3‰). Metamorphic whole rocks span a larger δ 44 Ca range of ~6‰ (−2.5 to +3.3‰), while metamorphic mineral separates span ~8‰ (−2.2 to +5.8‰). Observed Ca isotope variations can stem from a variety of sources including: (i) isolation of isotopically-distinct mineral components, such as during melting or crystallization, (ii) mixing of isotopically-distinct reservoirs into magmatic sources, such as during mantle metasomatism or assimilation of distinct crustal components, and (iii) isotopic rate differences (kinetic effects) during melting, crystallization, transport, and metamorphism, which are often governed by Ca diffusion. The emerging picture is that Ca isotopes are sensitive to a large number of high-temperature processes and can be used to understand the evolution of crust and mantle reservoirs, along with mechanisms leading to the formation of igneous, metamorphic, and hydrothermal rocks and minerals, through geologic time.

Formation of micro-spherulitic barite in association with organic matter within sulfidized stromatolites of the 3.48 billion-year-old Dresser Formation, Pilbara Craton.

The shallow marine and subaerial sedimentary and hydrothermal rocks of the ~3.48 billion-year-old Dresser Formation are host to some of Earth's oldest stromatolites and microbial remains. This study reports on texturally distinctive, spherulitic barite micro-mineralization that occur in association with primary, autochthonous organic matter within exceptionally preserved, strongly sulfidized stromatolite samples obtained from drill cores. Spherulitic barite micro-mineralization within the sulfidized stromatolites generally forms submicron-scale aggregates that show gradations from hollow to densely crystallized, irregular to partially radiating crystalline interiors. Several barite micro-spherulites show thin outer shells. Within stromatolites, barite micro-spherulites are intimately associated with petrographically earliest dolomite and nano-porous pyrite enriched in organic matter, the latter of which is a possible biosignature assemblage that hosts microbial remains. Barite spherulites are also observed within layered barite in proximity to stromatolite layers, where they are overgrown by compositionally distinct (Sr-rich), coarsely crystalline barite that may have been sourced from hydrothermal veins at depth. Micro-spherulitic barite, such as reported here, is not known from hydrothermal systems that exceed the upper temperature limit for life. Rather, barite with near-identical morphology and micro-texture is known from zones of high bio-productivity under low-temperature conditions in the modern oceans, where microbial activity and/or organic matter of degrading biomass controls the formation of spherulitic aggregates. Hence, the presence of micro-spherulitic barite in the organic matter-bearing Dresser Formation sulfidized stromatolites lend further support for a biogenic origin of these unusual, exceptionally well-preserved, and very ancient microbialites.

Geochemistry and isotopic geology of the Lagoa Seca gold deposit in the Andorinhas greenstone-belt, Carajás Province, Brazil

Abstract The Lagoa Seca is a gold deposit located in the Mesoarchean Andorinhas greenstone belt in the eastern portion of the Amazonian Craton, northern Brazil. It consists of clastic metasedimentary (metagreywacke and metasiltstone) and metavolcanic (metadacite and metaultramafic) rocks. It was operated by Troy Resources Ltd. as an open pit mine from 2008 to 2014, and it produced approximately 150 koz of gold. The hydrothermal alteration halo is directly associated with the internal zonation of the Lagoa Seca shear zone, and it includes i) a distal zone composed of chlorite-epidote-carbonate, ii) an intermediate zone with minerals from the distal alteration plus moderate silicification, iii) a proximal zone composed of biotite-magnetite (carbonate-amphibole-sulfide-gold), and iv) a gold-rich ore zone that has been affected by sulfidation and potassification. Whole-rock geochemistry and mineral chemistry studies on the hydrothermally altered host rocks show that Al2O5 and Na2O increase with silica content, while Fe2O3, MnO, MgO, CaO and the LOI decrease. The minor and trace elements are characterized by very good correlations among Zr, Nb, Ti and LREEs. The REE patterns of hydrothermal rocks show high to moderate fractionation with the La/Lu(cn) of the LREEs and HREEs towards the center of the hydrothermal conduit and are accompanied by a weak negative europium anomaly. The trace-element geochemistry is consistent with that of the subduction related calc-alkaline magmas in continental arcs. In addition, the tectonic discriminant diagrams show a calc-alkaline affinity and classify the host rocks as being derived from subduction processes. The hydrothermal chlorites are classified as brungsvite; mica is phlogopite and amphiboles range from actinolite, tremolite to Mg-hornblende. The main sulfide is pyrite, which is accompanied by minor amounts of chalcopyrite, galena, pyrrhotite and traces of millerite. The EPMA analysis of the pyrite shows that As, Co and Cu increase towards the center of the hydrothermal zone, as well as Zn, Ni and Au decrease in the opposite direction. Gold is present predominantly as inclusions in pyrite/chalcopyrite, with a high Au content. A chlorite geothermometer indicates that the temperatures ranged from 275 °C to 351 °C in the hydrothermal zones. The oxygen and carbon stable isotope data from the calcite of the ore zone return values of 8.12‰ SMOW and −6.36‰ PDB, respectively, which are compatible with a metamorphic fluid source. However, sulfur stable isotope displays 1.92‰ V-CDT, which may suggest a magmatic sulfur source. The composition of the fine-grained pyrite indicates that the hydrothermal fluid presents a deep crustal source of metamorphic origin, and it is accompanied by a mixed magmatic contribution, which was probably generated during the dominant TTG evolution of the area. The whole-rock Sm-Nd isotopic analyses produced a TDM of 2.92–3.04 Ga and an eNd (2.9) of +0.39 to +1.67 for metaultramafic rocks, a TDM of 2.78–2.92 Ga and an eNd of (2.9) +1.61 to +2.92 for metasedimentary rocks, and a TDM of 2.79–2.83 Ga and an ƐNd of (2.9) +2.83 to +3.02 for metadacite rocks. An Sm–Nd isochron age of 2867 ± 40 Ma indicates a Mesoarchean age for the host rocks.

Relationship of F-Be mineralization to granites and syenites at the Ermakovka deposit (Western Transbaikalia)

The paper presents the mineralogical and geochemical characteristics of two groups of hydrothermal rocks and their relation with subalkaline granites of the Ermakovskoe deposit. The first group includes fluorite-phenakite-bertrandite ore bodies, occurring outside the granite massif. The second group is presented by silicification bodies with sulfates, phosphates, kaolinite, muscovite and hematite. It bears REE (rare earth elements) mineralization (monazite, florencite, xenotime) and occurs within the massif. Our research included isotopic analyses of Sr, Nd and O, studies of trace, including rare-earth element compositions and age determination (U-Pb) of apatite from F-Be ores. Geochemical and isotopic studies are not according with relation between F-Be ores and granites. This is proven by the absence of Be-mineralization in granites and schlieren pegmatites, and a sharp difference in composition of their fluid phases. A reductive fluid specification forming F-Be ores (containing CH4, H2, N2, CO2 and H2S), contrasts sharply with fluid specification of granites. The granites are characterized by high oxygen fugacity, due to ferrous iron, sulfates and phosphates. Besides isotopic composition of oxygen in quartz (7.4 and 5.1‰ δ18О V-SMOW respectively), initial Sr ratios (0.7056-0.7065 and 0.707-0.709 respectively) and REE compositions are different.

Hydrothermal alteration mapping and structural features in the Guelma basin (Northeastern Algeria): contribution of Landsat-8 data

In this work, we use remote sensing tools to recognize and map outcrops of altered hydrothermal rock zones in the Guelma basin (Northeastern Algeria). This basin is characterized by many thermal springs which could be the origin of the hydrothermal alterations and the source of polymetallic mineralization of Zn, Sb, Pb, and As. Structural lineaments representing faults or faulted zones were successfully extracted using remote sensing processing. The superimposition of the known mineralization site map with the evidenced lineaments and hydrothermal alteration zones evidences that the zones of high fractures density and of great structural complexity are in agreement with the detected hydrothermal alterations zones.

Toy trains, loaded dice and the origin of life: dimerization on mineral surfaces under periodic drive with Gaussian inputs.

In a major extension of previous work, we model the putative hydrothermal rock pore setting for the origin of life on Earth as a series of coupled continuous flow units (the toy train). Perfusing through this train are reactants that set up thermochemical and pH oscillations, and an activated nucleotide that produces monomer and dimer monophosphates. The dynamical equations that model this system are thermally self-consistent. In an innovative step that breaks some new ground, we build stochasticity of the inputs into the model. The computational results infer various constraints and conditions on, and insights into, chemical evolution and the origin of life and its physical setting: long, interconnected porous structures with longitudinal non-uniformity would have been favourable, and the ubiquitous pH dependences of biology may have been established in the prebiotic era. We demonstrate the important role of Gaussian fluctuations of the inputs in driving polymerization, evolution and diversification. In particular, we find that the probability distribution of the resulting output fluctuations is left-skewed and right-weighted (the loaded dice), which could favour chemical evolution towards a living RNA world. We tentatively name this distribution ‘Goldilocks’. These results also vindicate the general approach of constructing and running a simple model to learn important new information about a complex system.

Dzierżanowskite, CaCu2S2 – a new natural thiocuprate from Jabel Harmun, Judean Desert, Palestine Autonomy, Israel

AbstractDzierżanowskite, , a thiocuprate, was found in larnite pseudoconglomerate rocks of the Hatrurim Complex at Jabel Harmun, Palestinian Autonomy, Israel. Dzierżanowskite occurs in larnite pebbles, which are embedded in a low-temperature mineral matrix. Associated minerals are larnite, brownmillerite, fluorellestadite, ye'elimite, gehlenite, periclase, ternesite, nabimusaite, vorlanite, vapnikite, fluormayenite, fluorkyuygenite, oldhamite, jasmundite, covellite, chalcocite and pyrrhotite. Electron microprobe analyses yield an average composition of Cu 55.25, Fe 0.13, S 27.46 and Ca 16.99, total 99.83 wt.%. The empirical formula of dzierżanowskite, based on 5 atoms, is Ca0.98Cu2.02Fe0.01S1.99. Dzierżanowskite forms grains up to 15 μm in size or rims on oldhamite and laminar intergrowths with chalcocite and covellite. Dzierżanowskite is dark orange, has a cream streak and a submetallic lustre. In reflected light it is grey, with a cream tint and characteristic yellow-orange internal reflections. The calculated density of dzierżanowskite is 4.391 g cm -3. Three bands at 300, 103 and 86 cm -1 are observed in the Raman spectrum. The strongest lines of the calculated powder diffraction pattern are [d, Å (I) hkl]: 2.358(100) 102, 1.970(93)110, 3.023(78) 011, 6.523(36) 001, 3.412 (28) 100, 1.834(28) 103. Dzierżanowskite was also found in unusual jasmundite rocks, forming small ‘paleofumaroles’ within areas of low-temperature hydrothermal rocks bearing larnite pseudoconglomerates at Jabel Harmun. Dzierżanowskite is a superimposed phase of the high-temperature alteration of pyrometamorphic rocks subjected to by-products (melts/fluids and gases) of pyrometamorphism originating in the deeper levels of combustion.