Local Rocks Research Articles

The Afontova Gora IV (Ovrazhnaya) Site: An Analysis of a Complex with “Ocher” in the Structure of the Paleolithic Layer

We analyze a part of the Paleolithic layer of Afontova Gora IV (Ovrazhnaya) in Krasnoyarsk, evidencing intentional exploitation of outcrops of red sandstone and other local rocks. We describe archaeological finds and faunal remains, identify species important for subsistence. Based on the results of the intrasite spatial analysis, we separate an area of domestic activities centered on an open hearth. Scar-patterns and raw material links were analyzed. The preservation of the cultural context was demonstrated. The area likely functioned within a single activity episode. Types of activity are reconstructed. Primary reduction techniques applied to oval-flat pebbles to get first or second order blades were the same as those used to obtain ready wedge-shaped microcores transported to the site. To test the idea that red rocks were used as sources for mineral pigment, rock samples and archaeological artifacts were examined. In samples from Afontova Gora IV, no minerals that could be used to obtain the red pigment of the “ocher” type were found. Pieces of red rock brought to the site must have been used differently. The 14C-date of the complex with cultural remains is ca 18 ka cal BP.

Rocks and Their Sources in the Upper Paleolithic of the Altai: Relevance to Bifacial Technologies

On the basis of the analysis of thin leaf-shaped bifacial points, which are very elaborate and sensitive to the quality of rocks, we reconstruct the adaptive strategies of humans at the early stages of the Upper Paleolithic. Mineral raw materials and their exploitation relating to different resource bases of the central (the Ursul River basin) and northwestern (the Anuy River basin) parts of the Altai region are analyzed. To attribute the rock sources for bifaces, we have compiled a comparative database of petrographic and petrochemical characteristics of artifacts and pebbles from nearby rivers. Chemical criteria were proposed for differentiating rocks, including those that are hard to distinguish, and non-destructive techniques were applied to assess the chemical composition of rocks using a portable XRF spectrometer. Findings suggest that rocks available in the Anuy and Ursul basins met the conditions for biface manufacture. Bifaces from the Ursul valley were made of local fine-grained rocks—felsic volcanic tuff and ignimbrite; those from the Anuy valley were also of local rocks, but of lower quality—hornfels transformed (meta-sedimentary) siltstone and finegrained sandstone or felsic volcanic rocks. In the Anuy valley, scarcity of quality raw material was compensated for by imported high silica jasper-like rocks. Results suggest that the Early Upper Paleolithic inhabitants of the region, when implementing technical skills, showed stable behavioral and technological stereotypes despite habitat change and deterioration of the resource base.

О влиянии пространственной изменчивости прочности пород на удароопасность породных массивов

The The reliability of existing criteria and methods for predicting the hazard of rock burst occurrence is currently assessed as insufficient. Not all of the deep and large-scale deposits that are characterized as rock burst prone and hazardous by the current regulatory guidelines are experiencing rock bursts. This paper focuses on critical examination of the rock burst hazard in the rock masses, rather than solely relying on individual rock samples. The article proposes a hypothesis concerning how the homogeneity of a rock mass influences its brittleness and the rock bursts, referencing foundational research that supports this concept. A thought experiment is presented to clarify how the homogeneity of a rock mass can directly influence its brittleness and the rock burst hazard. In order to systematically assess the homogeneity of a rock mass, the proposed methodology involves quantifying the coefficient of variation of strengths in a localized rock mass zone under uniaxial compression and tension. A comprehensive evaluation was conducted to explore the correlation between the rock burst hazard of a rock mass and the coefficient of variation for compressive and tensile strengths, drawing upon empirical data collected from 44 rock varieties across 18 distinct mining locations. The study is concluded by revealing a correlation between the rock burst of rock masses and the coefficient of variation. Suggested threshold values for the coefficient of variation are provided, indicating the rock burst hazard of rock mass in situ. Furthermore, the influences of various factors on the coefficient of variation and of rock burst hazard are examined.

No One Home? New Evidence for MIS 3 Occupations in the Western Cape (South Africa) from Mertenhof Rock Shelter

Southern Africa features an intensively studied Stone Age sequence, though one with geographical and temporal gaps. The archaeology of Marine Isotope Stage (MIS) 3 remains understudied, particularly between ~ 50 and 25 ka. This period encompasses important ecological, demographic and cultural changes, most notably the transition from Middle Stone Age (MSA) to Later Stone Age (LSA) technologies. In western South Africa, previous research postulated a demographic hiatus during the second half of MIS 3, potentially due to hyperarid climatic conditions. Here, we provide evidence of occupation during this period at Mertenhof Rock Shelter (MRS) in the form of new chronometric and technological data. OSL estimates suggest two pulses of low-intensity occupations at ~ 50 ka and 41–37 ka, allowing for a diachronic assessment of technological changes. These sporadic MSA occupations complement the more widespread occurrence of open-air settlements along the Doring River during ~ 50–35 ka. At MRS, knappers procured local rock types and produced small flakes and some laminar elements via platform, bipolar and Levallois reduction. The retouched elements feature splintered pieces and denticulates but mostly lack points. Differences to contemporaneous sites in eastern southern Africa underscore ongoing technological regionalisation and demographic partitioning during MIS 3. The temporal changes in the sequence show some antecedents of Early LSA technological systems, which appear in the region around 25 ka, but not in a unidirectional manner. Lithic and chronometric evidence from MRS supports scenarios of a long MSA persistence within MIS 3 in southern Africa and a late emergence of the LSA sometime after 35 ka.

Sorting and Weathering Trends of Soil at Gale Crater, Mars: Implications for Regional Pedological Processes

AbstractDetailed soil characterization at Gale crater based on in situ observations has revealed compositional trends within soils, while the physical and chemical processes underlying the compositional trends remain to be evaluated. Here we use the grain‐morphometrical and geochemical trends across the Wentworth‐classes of 48 in situ soil targets at Gale crater to evaluate underlying pedological processes and potential chemical weathering signatures. The concentration of olivine minerals within the ∼250 to ∼500 μm size range indicates the prevalence of heavy mineral sorting in a granulometric sense in Gale soils that surpasses the possible effect of the cratering‐induced mixing processes. The extent of olivine sorting in soils varies spatially and is influenced by the targets' aeolian setting. The finest portion of Gale soils (<125 μm) is likely a mixture of allochthonous sediment, globally sourced from atmospheric suspension, and autochthonous counterparts from the weathering of local rocks, while the coarser soils (>125 μm) are mostly sourced from local rocks, with possible inputs from both the unaltered parent rock of the Stimson formation and the bedrocks that have undergone diagenetic alteration. If applicable globally, this would reinforce prior inferences that even dust‐mantled regions are geochemically heterogeneous owing to a substantial fraction of soils derived from underlying lithology. The low chemical weathering intensity and coupling of mobile elements in soils suggest localized, low pH and low water‐to‐rock ratio aqueous weathering conditions under predominantly cold and arid climates, which may occur either during post‐pedogenetic alteration in soils or during the acidic alteration of source rocks.

Origin, Migration, and Accumulation of Crude Oils in the Chaoyang Step-Fault Zone, Fushan Depression, Beibuwan Basin: Insight from Geochemical Evidence and Basin Modeling

The Fushan Depression is a hydrocarbon-rich depression in the Beibuwan Basin, South China Sea. In this study, 14 source rocks and 19 crude oils from the Chaoyang Step-Fault Zone and Southern Slope Zone were geochemically analyzed to determine their origins. The hydrocarbon generation, migration, and accumulation processes were also determined using two-dimensional basin modeling. Crude oils from the low-step area show a close relationship with the source rocks of the first and second members of the Eocene Liushagang Formation (Els1 and Els2). The oils from the middle-step area and the Southern Slope Zone are derived from the local source rocks in those areas, in the third member of the Eocene Liushagang Formation (Els3). Hydrocarbons generated from the Els3 source rocks of the Southern Slope Zone migrated along sand bodies to the Els3 reservoir. The fault system of the Chaoyang Step-Fault Zone controls hydrocarbon migration and accumulation in the low-step and middle-step areas. The resource potential of the middle-step area is limited by its shallow burial depth. The low-step area is a more favorable exploration area due to its proximity to the source kitchen.

Using UAVs to collect filtered water samples for mineral exploration: Will it take off?

The advent of unmanned aerial vehicle (UAV) assisted surface water sampling and ongoing technological advances in sampling and data acquisition, offers many opportunities to conduct high-quality hydrogeochemical surveys with low cost, high efficiency, and reduced human interactions. Hydrogeochemical mineral exploration is one area that could greatly benefit from a UAV sampling revolution, with survey sites often located in highly remote areas with limited existing infrastructure. Currently, a lack of point source filtration and complicated physiochemical data acquisition hinder mainstream UAV deployment in the context of hydrogeochemical studies. The aim of this paper is to provide guidance on effective UAV sampling methods and physiochemical data collection for use in surface water hydrogeochemical mineral exploration. To date, case study surveys have utilized sampling systems where sampled waters are filtered after collection or analyzed for ‘total’ (unfiltered) concentrations. This paper details a methodology for point-source filtration of water samples using a UAV system to recover filter sample aliquots for the determination of ‘dissolved’ (<0.45 μm) trace element concentrations and compares UAV methods to conventional sampling strategies. This study systematically compares the quality of analytical data collected from lakes, ponds, and rivers in the Long Lake area of southern Ontario, using conventional manual sampling (from a boat or canoe) and a series of UAV-based sampling methodologies. The waters sampled within the study area are highly meteoric and show evidence of solute input from water-rock interaction with local country rocks. The results of this study show that in general, conventional sampling methodologies are statistically comparable to samples collected using UAVs. However, there is some evidence of element variation related to lake stratification, with dissolved Cu concentrations higher in samples collected at depth compared to those from the surface. Similarly, samples filtered after collection typically have lower concentrations of Fe and Mn, potentially resulting from precipitation before filtration. An enclosed sampling system offered from peristaltic pumping with in-line filtration removes the potential for contamination from the surrounding environment and from the UAV itself.

Estimation and Comparison of Deflouridation of Flouridated Ground Water Using Four Natural Adsorbents: Multani Mitti, Chalk Powder, Orange Peel Powder and Ragi Powder

This study highlights the global issue of fluoride contamination in drinking water, affecting approximately 260 million people in 30 countries, with India facing significant challenges as endemic fluorosis impacts around one million individuals across 17 states. The elevated fluoride levels are primarily attributed to fluoride-bearing minerals in local rocks and soils. The World Health Organization recommends maintaining fluoride concentrations near 1 mg/L to balance dental health benefits while preventing fluorosis. In response, various defluoridation methods—such as precipitation and adsorption—are implemented in India to adjust fluoride levels to optimal ranges. Given the essential role of water in physiological processes for humans, animals, and plants, understanding the variable quality of surface and groundwater is crucial. This variability is influenced by local geological factors and the presence of contaminants, necessitating effective management strategies for safe drinking water access.

Provenance of the Mesoproterozoic Shennongjia Group in the north Yangtze Block, South China, and implications for reconstructions of the Nuna and Rodinia supercontinents

Magmatic activity in the range ca. 1.6−1.5 Ga is spatially restricted globally, and its distribution has been an important tool for constraining the reconstruction of the Nuna supercontinent. Abundant ca. 1.6 Ga detrital zircons have recently been discovered in the Luanshigou and Taizi formations of the middle Mesoproterozoic Shennongjia Group in the north Yangtze Block, South China. Detrital zircon age spectra and multi-dimensional scaling results indicate the Shennongjia Group was derived from variable sources. The ca. 1.6 Ga detrital zircons in the middle Mesoproterozoic units were probably sourced from Laurentia and Australia-Mawson, whereas detrital zircons of other age groups were provided by the local rock units in the north Yangtze Block. Similarities in sedimentary sequences, detrital zircon age spectra, and corresponding Hf isotopic patterns of the Shennongjia Group with other Mesoproterozoic successions in Yangtze Block (e.g., Baoban-Shilu, Huili, and Kunyang groups) suggest that the block contained a number of micro-blocks during the Mesoproterozoic. Furthermore, the compiled new and published detrital zircon data from the north Yangtze Block along with those from other continents containing ca. 1.6 Ga zircons reveal that the Yangtze Block was most likely situated within a rift zone between southeast Australia-Mawson and southwest Laurentia. The ca. 1.6 Ga zircons in the Shennongjia Group were derived from these bounding source regions during the middle Mesoproterozoic. By the late Mesoproterozoic, based on a comprehensive provenance analyses and comparison of detrital zircon data, the Yangtze Block was probably located on the margins of the Rodinia supercontinent, close to north-central India, Australia, and East Antarctica.

Multi-scale model for evaluating stress fluctuation in shale gas reservoirs considering geomechanical heterogeneity

In this article, a numerical model considering multi-scale flow and heterogeneity of shale reservoirs is developed to analyze the spatiotemporal evolution of the stress field in shale gas production. After considering the geomechanical heterogeneity, the variation in the local rock mechanical parameters of the reservoir, and the increase in the effective stress of the reservoir will cause local stress fluctuations. In the hydraulic fracture control area, the average stress fluctuation coefficient is higher, indicating a stronger “stress heterogeneity.” When the homogeneity increases from 5 to 100, the fluctuation range of the minimum horizontal principal stress increases by 28.89 MPa, and the fluctuation range of the principal stress difference increases by 7.35 MPa. The presence of natural fractures can significantly impact the coupled hydraulic-mechanical processes of the reservoir, increasing the number of high-speed permeation channels penetrating the system. The greater the density and permeability, the smaller the minimum horizontal principal stress and the larger the principal stress difference. The angle of natural fractures directly influences the direction of stress drop, with an average minimum horizontal principal stress occurring when the angle of natural fractures is at 60°/120°.

Rocking in Kasba: “band” music, contemporary Bengali cinema, and Anjan Dutta’s lost Kolkatas

ABSTRACT With the gradual obsolescence of the lip-synched romantic duet, the sonic texture of Bengali popular cinema has transformed radically in the new millennium. One of the most remarkable components of the rise of the Original Soundtrack in Bengali film specifically has been the incorporation of local pop, folk, and rock bands, whose lyrics are written in Bengali but whose music retains a decidedly western flavour. This paper situates this relationship between cinema and what has traditionally been understood as ‘band’ music in Kolkata in a longer history of the city and its colonial and postcolonial musical cultures. With the incorporation of the pop/rock stars into the diegesis, the productive tensions between star and singer, visible and invisible bodies and voices have been overturned in recent years. Conversely, the music that is commissioned by these films now contribute to the bands’ larger discography and bring their music to a wider listening audience. In some of these films, musicians and bands appear as themselves, bringing together multi-modal sites of fandom and entertainment. Finally, this essay demonstrates that singer/songwriter/filmmaker/actor, Anjan Dutta’s oeuvre emerges as the canvas on which many of these developments come to be visible.

ADHESIVE ABILITY OF GYPSUM-CONTAINING PLASTER COMPOSITIONS

The traditional material for the construction of buildings in the Northern Black Sea region is a cheap local stone ‒ limestone-shell rock. Most of the buildings in the central part of the city of Odesa, which are of historical and architectural value, are constructed of this material. With proper care and maintenance, these structures can perform their functions for hundreds of years, but as a result of shell rock moisture due to negligent operation and a number of other reasons, the supporting structures are damaged, followed by the collapse of the building. In many cases, the direct cause of the destruction of load-bearing walls is the damage or absence of the outer plaster layer. Repairing walls with cement compounds exacerbates the problem. The article discusses some aspects of the possible use of gypsum-based composite materials for repairing damaged walls of limestone-shell rock buildings. The requirements for the repair composition are formulated. The expediency of using gypsum as a binder for the repair plaster mixture for exterior repairs is substantiated. An ash-gypsum-cement composition was used to increase the water resistance of the plaster. Sufficient water resistance and vapor permeability of the proposed composition were confirmed. This paper presents the results of studying the adhesive strength of the contact of the developed composition with the surface of various materials. Methods and measuring equipment developed at the ODABA were used. The adhesion strength of the proposed mixture with the surface of shell rock is close to the standard strength. The use of the adhesive additive Ceresit CC 81 increases the adhesive strength of the joint of the proposed composition with shell rock by 1.5 ‒ 2 times. The optimal amount of the adhesive additive to be introduced will be determined by the results of a multifactorial experiment to study the effect of a complex of chemical additives of different functional purposes on the properties of the proposed repair composition.

Adsorption Behavior and Mechanism of Brilliant Green Dye onto Acid-modified Mesoporous Volcanic Pumice

Water pollution is a major problem in the environment. The important one is the dying effluent from the textile industry. Dye effluent has affected human health and aquatic life. Recently, natural adsorbents have been most commonly used for dye treatment wastewater. This study explores the adsorption mechanism of brilliant green onto HCl-modified pumice. It involves a comparative analysis of the raw and HCl-modified pumice's characterization and adsorption properties. The adsorption experiments were carried out by considering several parameters, such as pH, contact time, initial dye concentrations, and temperatures. The research indicated that the raw and acid-treated pumice possess Si-OH and Si-O-Si groups. These pumice adsorbents are classified as mesoporous, exhibiting BJH pore diameters of 3.23 nm for the raw form and 3.69 nm for the acid-modified variant. The adsorption data revealed that the uptake of brilliant green dye was maximal at a pH of 8. The equilibrium results closely matched the Langmuir isotherm model. The maximum adsorption capacities were 37.13, 40.17, and 42.73 mg g-1 for the raw pumice, and 46.72, 51.81, and 56.17 mg g-1 for the modified pumice at 20, 30, and 40 °C, respectively. Furthermore, the removal efficiency of brilliant green dye with modified pumice was 91.93%, 95.29%, and 96.27% at 20°C, 30°C, and 40°C, respectively. The pseudo-second-order model was the most suitable for elucidating the kinetic adsorption data. The thermodynamic analysis revealed that the adsorption process was endothermic, spontaneous, and physical. Dipole-dipole H-bonding interaction, Yoshida H-bonding, electrostatic interaction, n-𝝅 interaction, cation exchange, and pore filling were all engaged in its process. Consequently, the local pumice volcanic rock became a great, cheap, abundant, and environmentally friendly adsorbent for removing dyes from effluents.

Observation of ferroelectric domains in BaTiO3 by synchrotron radiation X-ray diffraction topography

X-ray diffraction topography was used to observe two distinct ferroelectric domains in BaTiO3. The use of highly-parallel X-rays and a high-resolution detector with approximately 200 nm resolution enabled us to successfully characterize two distinct domains, each with sizes of the order of 10 μm. Along with the local rocking curve of the bulk crystal, we generated width maps corresponding to crystal properties including defects and, strain. This information is beneficial for understanding domain behavior, and the measurement system can be expected to become a powerful tool for in situ measurements of processes requiring domain control.

Assessment of the influence of natural thermal cycles on dolomitic limestone rock columns: A 10-year monitoring study

Rock instabilities hazards can lead to major risks. Even if different external factors such as precipitation, seismic activity or freezing, are known to trigger rockfalls, it is more and more assumed that thermal cycling has a role in rock mass deformation, displacement and, moreover cracking initiation or propagation. Here we present 10 years monitoring of a 50-meter-high dolomitic cliff, located above an important highway in the south of France to support this thinking. Local rock surface temperature and joint apertures were recorded on eleven sensors. Their evolution is studied separately and together to characterise the influence of temperature variation on joint apertures. During small time periods, a reversible and proportional behaviour is observed, that can be attributed to thermoelasticity, but over the whole period, a significant drift in displacements is measured, meaning that at least a viscoplastic or fatigue behaviour should be considered.

Comparing geophysical inversion and petrophysical measurements for northern Victoria Land, Antarctica

SUMMARYBedrock geology from Antarctica remains largely unknown since it is hidden beneath thick ice sheets. Geophysical methods such as gravity and magnetic inverse modelling provide a framework to infer crustal rock properties indirectly in Antarctica. However, due to limited availability of rock samples, validation against direct geological information is challenging. We present a new rock property catalogue containing density and susceptibility measurements on 320 rock samples from northern Victoria Land. This catalogue is used to assess the reliability of local and regional scale inverse results, including a new local high resolution magnetic inversion in the Mesa Range region and a previously published regional scale joint inversion of gravity and magnetic data in northern Victoria Land and the Wilkes Subglacial Basin. We compare our density and susceptibility measurements to global and local measurements from the literature to access the correlation to rock types and geological units. Furthermore, the measured values are compared against inverted values. The close correspondence between inverted and measured rock properties allows us to predict locations of rock types where currently such information is missing. The utility of measured susceptibility and density relationships for interpreting inversion output provides a strong incentive to incorporate local rock samples into geophysical studies of subglacial geology across Antarctica.

A novel tool for seismic response analysis of tunnel in multilayered media based on kinematic earthquake source

Earthquake damage of underground structure indicates that the seismic response of tunnels is affected by the earthquake source, propagation medium, and local tunnel-surrounding rock system. Current research on the seismic response of tunnels primarily focuses on local tunnel systems, posing a challenge in comprehensively assessing the impact of earthquakes on tunnel group. This study introduces a theoretical seismological approach for the seismic response analysis of tunnels and presents a novel methodology for assessing the response. The proposed approach uses a kinematic seismic source as the earthquake source, assuming the geological strata as a layered medium and a tunnel as a point within a semi-infinite space. The wavenumber-integral method was used to solve for the seismic wave field and strain. To reflect the followability of underground structure to the surrounding rock deformation, we improved it and derived an analytical formula for the strain. The 2022 Menyuan earthquake was considered as a case study; the seismic damage to tunnels along the Lan-Xin Railway was analyzed using the proposed approach. The results confirm that there is a strong correlation between tunnel damage and free-field strain induced by earthquakes. The theoretical influence range of earthquake on tunnel was investigated using the diameter deformation ratio of the tunnel as an indicator. For tunnels embedded in a grade III rock mass, the theoretical range was approximately 7.0 km on both sides of the fault. For tunnels embedded in a grade V rock mass, the theoretical range can reach up to 25.9 km. The results also revealed that tunnels on the hanging-wall side of the fault had a more significant impact than those on the foot-wall side, although their affected areas were smaller.

Comprehensive review of rock dust for soil remineralization in sustainable agriculture and preliminary assessment of nutrient values in micronized porous basalt rock from Nghe-An province, Vietnam

This review delves into the utilization of rock powder as a mineral-derived fertilizer to support soil remineralization in the context of sustainable agriculture. Soil remineralization has emerged as a key strategy for ensuring long-term soil fertility and reducing the dependency on synthetic fertilizers. This review critically assesses the methodological approaches applied in various studies, taking into account factors such as local rock mineralogy, soil conditions, crop types, and nutrient uptake by plants. The review covers a range of methods, including nutrient value analysis, assessment of nutrient release rates, crop cultivation experiments in both laboratory and field settings, and the resulting implications for soil remineralization. Additionally, we present findings from a preliminary study focusing on the nutrient content of basalt rock from Nghe-An Province, Vietnam. This experimental investigation is centered on the assessment of nutrient values in a specific porous basalt material, which has been processed into micro-nanometer particles using a high-energy ball mill, thereby enhancing nutrient release efficiency. The study employs a range of analytical techniques, including XRD, XRF, SEM/EDS, and ICP-MS, to quantify macro- and micro-nutrient compositions. While the basalt rock samples may exhibit limitations in providing macronutrients (such as K) compared to commercial azomite rock, they offer distinct advantages in furnishing secondary macronutrients (like Ca). This comprehensive analysis provides insights into the potential use of micronized basalt rock for soil remineralization.

Earliest evidence of human occupations and technological complexity above the 45th North parallel in Western Europe. The site of Lunery-Rosieres la-Terre-des-Sablons (France, 1.1 Ma)

The site of LuneryRosieres la-Terre-des-Sablons (Lunery, Cher, France) comprises early evidence of human occupation in mid-latitudes in Western Europe. It demonstrates hominin presence in the Loire River Basin during the Early Pleistocene at the transition between an interglacial stage and the beginning of the following glacial stage. Three archaeological levels sandwiched and associated with two diamicton levels deposited on the downcutting river floor indicate repeated temporary occupations. Lithic material yields evidence of simple and more complex core technologies on local Jurassic siliceous rocks and Oligocene millstone. Hominins availed of natural stone morphologies to produce flakes with limited preparation. Some cores show centripetal management and a partially prepared striking platform. The mean ESR age of 1175 ka ± 98 ka obtained on fluvial sediments overlying the archaeological levels could correspond to the transition between marine isotopic stages (MIS) 37 and 36, during the normal Cobb Mountain subchron, and in particular at the beginning of MIS 36. The Lunery site shows that hominins were capable of adapting to early glacial environmental conditions and adopting appropriate strategies for settling in mid-latitude zones. These areas cannot be considered as inhospitable at that time as Lunery lies at some distance from the forming ice cap.

Stable isotopes (O, H) and quartz geochemistry provide insight to melt source and subsolidus fluid:rock interaction in the Cretaceous Little Nahanni LCT Pegmatites (NWT, Canada)

Previous studies of the mid-Cretaceous (ca. 85 Ma) LCT-type Little Nahanni Pegmatite Group (LNPG; Northwest Territories, Canada) document disequilibrium textures and pervasive metasomatism associated with rare-metal (e.g., Ta, Nb, Sn) mineralization. As in other pegmatite settings, the source of the melts and the nature and origin of pervasive metasomatism remain enigmatic. To resolve these latter issues, an integrated study of bulk O and H isotope analysis of mineral separates (quartz, K-feldspar, albite, muscovite, garnet), in situ Secondary Ion Mass Spectrometry (SIMS) isotopic (O) analysis of quartz and albite, and in situ Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) trace element analysis of quartz was done in concert with cathodoluminescence (CL) imaging and petrographic observations. Quartz with elevated δ18O values (δ18Oquartz = 10 to 16.3‰) also have high Ti-in-quartz temperatures (551 ± 17 °C to 603 ± 16 °C). These data along with their pristine nature from CL imaging suggest some localized melt-wall rock (WR) exchange occurred at the time of pegmatite melt emplacement. Furthermore, the elevated δ18O values indicate a crustal source (i.e., S-type granite) for the LNPG parental melt, which also overlaps with δ18Oquartz data for granitoids of the mid- to Late-Cretaceous Selwyn Plutonic Suite of this area. In contrast, the large range for δ18O values for metasomatic minerals, such as albite (−3.0 to +18.3‰) indicate a complex evolution involving multiple oxygen isotopic reservoirs, in particular incursion of meteoric water previously equilibrated with metasedimentary wall rocks. Finally, the large range for mineral pairs (e.g., Δquartz-albite = −5.1 to +14.3‰) and abundance of dissolution features in late-stage assemblages unequivocally indicates that sub-solidus fluid:rock interaction was responsible for such large spreads in δ18O and values δD values, although other processes (e.g., disequilibrium crystallization, thermal gradients, rapid cooling) might have also contributed, but to lesser extents.