Deep Drilling Research Articles

Alteration mineralogy, characteristics and shortwave infrared spectroscopy of white mica in the Zijinshan ore field, Fujian Province: Implications for porphyry Cu prospecting

The Zijinshan ore field is situated in the southeastern part of China. in which contains the large Zijinshan high-sulfidation Cu-Au deposit, the Luoboling porphyry Cu-Mo deposit, the Yueyang low-sulfidation Au-Ag deposit, the Longjiangting and the Wuziqilong tansitional Cu deposit, and the Xi’nan porphyry Cu-Mo prospect. Debates on genetic relationship among these deposits, especially the relationship between the Zijinshan Cu-Au deposit and the adjacent Luoboling deposit is a question of importance for further exploration in this ore field. In this contribution, the alteration mineralogy, alteration texture, zonation and mineral chemistry, in combination with shortwave infrared spectroscopy (SWIR) analysis of white mica were used to help focus exploration and assessment of hydrothermal deposits in the Zijinshan ore field.In this study, diaspore-pyrophyllite alteration zone, chlorite-sericite alteration zone and propylitic alteration zone were first identified in the deep drill core of the Zijinshan Cu-Au deposit, which gives way upward to quartz-alunite-kaolinite zone, quartz-alunite zone and the silicic alteration zone. In the Xi’nan Cu-Mo prospect, diaspore-pyrophyllite alteration zone was first recognized in the shallow level with the chlorite-sericite alteration zone and propylitic alteration zone in the deeper level. Andalusite- sericite ± diaspore alteration zone was first recognized in the upper part of the Luoboling Cu-Mo deposit and the deeper part of the Wuziqilong Cu deposit. It indicates that a pervasive occurrence of diaspore -pyrophyllite ± andalusite alteration zones in the Zijinshan ore field, which may potentially represent a transitional environment between the top of porphyry alteration zones and the base of advanced argillic alteration zones. Minerals of the white mica group are extensively distributed in various alteration zones of the Zijinshan ore field. The SWIR analysis of white mica indicated that the wavelength position of the Al-OH (∼2,200 nm; wAlOH) absorption feature increases gradually from the shallow kaolinite-dickite alteration zone to the deep potassic alteration zone. In the advanced argillic alteration zones, the range of wAlOH values of white mica is less than 2205 nm. Conversely, in the porphyry alteration zones, it always exceeds 2205 nm. It is evident that the andalusite-sericite alteration zone with higher wAlOH values (average of 2203 nm) is always proximal to the porphyry mineralization, which may act as indicators for deep porphyry prospecting. The results of electron probe microanalysis (EPMA) reveal that the early enrichment of Mg and depletion of Fe in white mica can be attributed to the preferential incorporation of Fe into iron oxides and iron sulfides in the potassic and propylitic alteration zones. Overall, there is a negative correlation between wAlOH and Al, while wAlOH exhibits a positive correlation with the sum of Fe + Mg + Mn. The distribution characteristics of alteration zones and the variation patterns of the wAlOH of white mica indicate that there are probably several paleo-thermal centers in the deep parts of the Zijinshan ore field, located respectively in the deep parts of the Xi’nan Cu-Mo prospect and the deep part of the Zijinshan Cu-Au deposit and the deep parts of the Wuziqilong Cu deposit, and the latest seems to be more fertile and deserves further exploration.

Spatial and temporal stable water isotope data from the upper snowpack at the EastGRIP camp site, NE Greenland, sampled in summer 2018

Abstract. Stable water isotopes stored in snow, firn and ice are used to reconstruct climatic parameters. The imprint of these parameters at the snow surface and their preservation in the upper snowpack are determined by a number of processes influencing the recording of the environmental signal. Here, we present a dataset of approximately 3800 snow samples analysed for their stable water isotope composition, which were obtained during the summer season next to the deep drilling site of the East Greenland Ice Core Project in northeast Greenland (75.635411° N, 36.000250° W). Sampling was carried out every third day between 14 May and 3 August 2018 along a 39 m long transect. Three depth intervals in the top 10 cm were sampled at 30 positions with a higher resolution closer to the surface (0–1 and 1–4 cm depth vs. 4–10 cm). The sample analysis was carried out at two renowned stable water isotope laboratories that produced isotope data with the overall highest uncertainty of 0.09 ‰ for δ18O and 0.8 ‰ for δD. This unique dataset shows the strongest δ18O variability closest to the surface, damped and delayed variations in the lowest layer, and a trend towards increasing homogeneity towards the end of the season, especially in the deepest layer. Additional information on the snow height and its temporal changes suggests a non-uniform spatial imprint of the seasonal climatic information in this area, potentially following the stratigraphic noise of the surface. The data can be used to study the relation between snow height (changes) and the imprint and preservation of the isotopic composition at a site with 10–14 cm w.e. yr−1 accumulation. The high-temporal-resolution sampling allows additional analyses on (post-)depositional processes, such as vapour–snow exchange. The data can be accessed at https://doi.org/10.1594/PANGAEA.956626 (Zuhr et al., 2023a).

Tectonic Basis for Oil and Gas Potential in the North Kara Prospective Oil and Gas Region (Western Arctic, Russia)

—Russia’s Arctic shelf and, in particular, the Kara Sea shelf, is one of the unique regions in the world with enormous hydrocarbon potential; however, due to the harsh climate conditions, it has been studied unevenly. The lack of deep and parametric drilling data in the northern Kara Sea leads to numerous uncertainties in regional geological structure models and, as a consequence, in assessing the resource potential of this Arctic region. A vast number of 2D CDP seismic explorations were carried out in the northern Kara Sea. The results of these studies made it possible to refine the geological structure of the Kara Plate, substantiate the boundaries of the North Kara independent prospective oil and gas region and promising areas within it, and assess hydrocarbon resources.

Lithium systematics in the Krafla volcanic system: comparison between surface rhyolites and felsic cuttings from the Iceland deep drilling project -1 (IDDP-1)

The unexpected discovery of felsic magma by the Iceland Deep Drilling Project-1 (IDDP-1) in the Krafla volcanic system (KVS) presents a unique opportunity to investigate pre-eruptive lithium (Li) dynamics and establish a more direct connection between magma reservoirs and volcanic deposits. Our study provides new insights into Li abundances and isotope compositions in bulk-rock, minerals, and groundmass glass from rhyolitic lavas at KVS, encompassing various stages of groundmass crystallisation. Additionally, we examined felsic cuttings retrieved from the IDDP-1 well, comprising crystal-poor obsidian and crystal-bearing to -rich ‘felsite’ particles. Groundmass glasses from surface lavas show limited variability in K/Na, indicating limited secondary hydration of the glasses and that their Li contents seem to not be affected by this post-eruptive process. Lithium inventories in groundmass glasses and minerals within lavas exhibit variations consistent with the cooling history of the deposit, resembling patterns seen in Snake River Plain ignimbrites. Lithium contents of glassy rhyolitic lavas, whether bulk-rock (avg. 27.2 ± 3.1 μg/g) or groundmass glass (average 28.4 ± 4.7 μg/g), and their bulk isotopic compositions (avg. δ7Li =+ 4.4 ± 0.2‰) overlap with those observed in IDDP-1 obsidian cuts (avg. 24.9 μg/g Li in bulk, 28.6 ± 1.5 μg/g in groundmass glass, and δ7Li = 4.5 ± 0.2‰). Glassy lavas lacking spherulites may potentially preserve pristine magmatic Li element and isotope compositions, while areas with extensive groundmass crystallisation reveal Li enrichments in phenocrysts. Plagioclases in slowly cooled parts of the deposit record a two-fold increase in Li contents compared to plagioclase found in glassy counterparts, along with evidence of open-system degassing marked by heavier bulk Li isotope compositions and lower bulk Li contents of the crystallised lava portions (avg. δ7Li = +7.2 ± 0.1‰ and 7 ± 0.8 μg/g Li) relative to bulk glassy lithologies (avg. δ7Li = +4.1 ± 0.1‰ and 28 ± 2 μg/g Li). Partition coefficients derived from IDDP-1 cuts successfully predict Li inventories in vitrophyres of rhyolites on the surface of the KVS. Lithium isotope compositions of the crystal-rich IDDP-1 cuts are significantly heavier (avg. δ7Li = +7.2 ± 0.2‰) than lavas and IDDP-1 obsidian cuts, casting doubt on the notion that the IDDP-1 rhyolitic magma could result from the melting of felsite lenses in the KVS. Lithium contents in groundmass glasses within IDDP-1 crystal-rich cuts show higher Li contents (avg. 55.1–60.7 μg/g), correlating with the higher crystal content and an increase in other incompatible elements (avg. 250 μg/g Rb) relative to obsidian cuttings (avg. 75 μg/g Rb).

The Apollo 17 Regolith: Induced Thermoluminescence Evidence for Formation by a Single Event ∼100 Million Years Ago and Possibly the Presence of Tycho Material

AbstractWe explored the geological history of the Taurus‐Littrow Valley at the Apollo 17 landing site through the induced thermoluminescence (TL) properties of regolith samples collected from the foothills of the Northern and Southern Massifs, from near the landing site, and from the deep drill core taken in proximity to the landing site. The samples were recently made available by NASA through the Apollo Next Generation Sample Analysis program in anticipation of the forthcoming Artemis missions. We found that the two samples from the foothills of the massifs exhibit induced TL values approximately four times higher than those of the valley samples. This observation is consistent with their elevated plagioclase content, indicating their predominantly highland material composition. Conversely, the valley samples display induced TL values characteristic of lunar mare material. The samples from the deep drill core demonstrate uniformly induced TL properties, despite originating from depths of up to 3 m. Notably, one of the samples from the lower section of the deep drill core presents anomalous‐induced TL readings. This anomaly coincides with elevated levels of low‐potassium KREEP along with reduced quantities of anorthositic gabbro and orange glass, and could be due to the traces of phosphate minerals. Alternatively, this observation raises the possibility that this sample contains Tycho impact material. The induced TL data is consistent with the regolith, extending to a depth of at least 3 m, having been deposited by a singular event approximately 100 million years ago. This timing aligns with the hypothesized formation of the Tycho crater.

Hydrological constraints on the potential of enhanced geothermal systems in the ductile crust

Continental crust at temperatures > 400 °C and depths > 10–20 km normally deforms in a ductile manner, but can become brittle and permeable in response to changes in temperature or stress state induced by fluid injection. In this study, we quantify the theoretical power generation potential of an enhanced geothermal system (EGS) at 15–17 km depth using a numerical model considering the dynamic response of the rock to injection-induced pressurization and cooling. Our simulations suggest that an EGS circulating 80 kg s−1 of water through initially 425 ℃ hot rock can produce thermal energy at a rate of ~ 120 MWth (~ 20 MWe) for up to two decades. As the fluid temperature decreases (less than 400 ℃), the corresponding thermal energy output decreases to around 40 MWth after a century of fluid circulation. However, exploiting these resources requires that temporal embrittlement of nominally ductile rock achieves bulk permeability values of ~ 10–15–10–14 m2 in a volume of rock with dimensions ~ 0.1 km3, as lower permeabilities result in unreasonably high injection pressures and higher permeabilities accelerate thermal drawdown. After cooling of the reservoir, the model assumes that the rock behaves in a brittle manner, which may lead to decreased fluid pressures due to a lowering of thresholds for failure in a critically stressed crust. However, such an evolution may also increase the risk for short-circuiting of fluid pathways, as in regular EGS systems. Although our theoretical investigation sheds light on the roles of geologic and operational parameters, realizing the potential of the ductile crust as an energy source requires cost-effective deep drilling technology as well as further research describing rock behavior at elevated temperatures and pressures.

Timescales of mafic magmatic fractionation documented by paleosecular variation in basaltic drill core, Snake River Plain volcanic province, Idaho, USA

The timescales over which fractional crystallization and recharge work in mafic volcano-plutonic provinces is subject to great uncertainty. Currently modeled processes are subject to the scale of measurement: monogenetic basaltic fields accumulate over hundreds of thousands of years, consistent with U-Th-Ra isotopic variations that imply 50% crystallization of basic magmas on timescales of 100,000 years or more, whereas crystal diffusion modeling implies phenocryst residence times of ∼1−1000 years. Monogenetic basalts of the Snake River Plain in southern Idaho, USA, are up to 2 km thick and postdate passage over the Yellowstone−Snake River Plain hotspot. Detailed lithologic and geophysical logging of core from deep drill holes, along with chemical stratigraphy and high-resolution paleomagnetic inclination measurements, document individual eruptive units, compound lava flows, and basaltic flow groups that accumulated over 1−6 m.y. Hiatuses are commonly marked by loess or fluvial interbeds that vary from ∼0.1 m thick to 20 m thick. Radiometric (40Ar-39Ar, detrital zircon U-Pb) and paleomagnetic timescale ages show that the deepest hole (Kimama drill hole, 1912 m total depth) accumulated over ∼6 m.y. Cycles of fractional crystallization and recharge are recognized in the chemical stratigraphy as up-section shifts in major and trace elements; these fractionation cycles commonly represent 40%−50% fractionation. Individual fractionation cycles may comprise 20−40 eruptive units (8−17 lava flows) with little to no change in paleomagnetic inclination (0°−1°), whereas adjacent cycles may differ by several degrees from one another or reflect changes in polarity. Rates of paleosecular variation in Holocene lavas and sediments dated using 14C document significant shifts in magnetic inclination over short timescales, ranging from ∼0.05° to 2°/decade, with an average of ∼0.5°/decade and a minimum rate of 0.05°/decade. This implies that fractionation cycles with ≤1° variation in magnetic inclination formed on timescales of a few decades up to a few centuries (20−200 years). Thus, the lavas collectively represent only a few thousand years of eruptive activity, with major flow groups separated in time by tens to hundreds of thousands of years. We suggest that the rates defined by paleosecular variation capture the timescales of magmatic chamber evolution (fractionation/recharge) in the seismically imaged mid-crustal sill complex; in contrast, we suggest that crystal diffusion modeling captures the residence times in shallow subvolcanic magmatic chambers that underlie individual monogenetic volcanoes.

Numerical Simulation of Rock Breaking by Diamond Particles Under Ultra Deep Drilling Conditions

In the quest to access deeper fossil energy reserves, the past three decades have witnessed a concerted effort by scientists to develop and refine technologies capable of efficient drilling in environments characterized by high temperatures and pressures. Despite these advancements, our comprehension of the physical phenomena at play remains incomplete. A fundamental challenge pertains to the interaction between the rock and the drilling bit during drilling operations. This study delves into the influence of drilling bit pressure and rotation speed on the rock-breaking efficacy of impregnated diamonds under geostress conditions of 240 MPa and temperatures of 200℃.It juxtaposes these findings with those from rock-bit interaction experiments executed on a physical simulator, which was designed in accordance with similarity principles, in a controlled laboratory setting. Our findings indicate that for ultra-deep formations, a high Weight on Bit (WOB) coupled with a lower rotation speed results in enhanced rock cutting efficiency and a reduced rate of bit wear. Consequently, we recommend optimal drilling parameters of 8.0 to 8.5 kN for WOB and a rotational speed range of 180 to 240 rad/min. Furthermore, the study underscores the profound impact of horizontal differential stress on the rate of penetration (ROP). The insights gleaned from these tests are instrumental in refining the design of rock-breaking tools and optimizing drilling parameters, thereby augmenting the efficiency of rock breaking in challenging drilling environments.

Improving Drill-String Extended Reach Efficiency in High-Temperature and High-Pressure Conditions: An Experimental Investigation

Abstract Drill string buckling behavior is of interest to the oil and gas industries. Buckling severity increases as drilling continues and causes a lock-up condition beyond which drilling cannot commence. The friction force between the drill string and the wellbore is key in influencing drill string buckling initiation and progression. Herein, the effects of adding nano-sepiolite (NSP) as an additive to water-based drilling fluids on the friction between the drill string and wellbore wall were investigated. Various samples with different sizes and compositions of NSP were tested for their ability to reduce the coefficient of friction (COF) that delays the onset of buckling to facilitate deep drilling by providing improved lubrication characteristics. The drill string sinusoidal and helical buckling and lock-up condition and the axial force transfer (AFT) were experimentally investigated. The water-based drilling fluids’ lubricity, COF between the drill string and the wellbore wall, and the stability of the rheological properties of the NSP-modified water-based drilling fluids containing 1–6 wt% NSP were tested in a high-temperature and high-pressure (HTHP) environment utilizing an in-house experimental setup. Sepiolite in nano-form at 4 wt% and with a size distribution of 30–60 nm improved the stability of the water-based drilling fluids rheology, significantly decreased the COF of the water-based drilling fluids, and improved the drill string axial force transfer. NSP additives significantly improved the COF and the drill string AFT in the HTHP environment compared with that of other commercial drilling fluids.

ABOUT THE MAIN RESULTS OF DEEP DRILLING IN THE TERRITORY OF THE PREDVERKHOYANSKAYA OIL AND GAS AREA

This article presents the results of drilling wells in the Predverkhoyanskaya oil and gas area, where deep exploratory drilling for oil and gas was started in 1954 at the Kitchan, Sangar and Ust-Vilyu structures pre-pared by the seismic survey in combination with structural core drilling.According to the results of deep drilling in the Predverkhoyanskaya oil and gas area, the section of the sedimentary cover was studied, and ideas about the material composition of the foundation upper part were obtained. The pro-spects of oil and gas potential are evaluated: the reservoir properties are possessed by rocks of the subsalt Nizhnevendsky, Vendian-Lower Cambrian terrigenous and carbonate complex-es, which are associated with industrial oil and gas potential in nearby fields.The following fluid-bearing complexes are distinguished in the sedimentary section of the Preverkhoyanskiy trough: Permian (P), Lower Triassic (T1), Triassic-Lower Jurassic (T2–3–J1), Middle Upper Jurassic (J2-3), Lower Cretaceous (K1).Deposits of the Lower Triassic aquifer complex are deposited on Permian formations. The capacity of the complex is variable, due to the structural features of the Lower Triassicsediments, and it has not been established with-in the Predverkhoyanskiy trough. Thermobaric data were not obtained during the test. Reser-voir pressures are close to hydrostatic. Reser-voir temperatures, as in the Permian complex, increase from west to south-east to the Predverkhoyanskiy trough from 50 °C to 95 °C.The deposits of the Middle-Upper Triassic – Lower Jurassic aquifer complex are more widely developed. During the sampling and test-ing of oil and gas exploration wells, water and gas inflows were obtained from the deposits of the complex, including industrial ones on Ust-Vilyuiskaya, Sobo-Khainskaya Square. The flow rates of water inflows reached 300 m3/day (Sangarskaya 2), gas inflows up to 1800000 m3/day (Ust-Vilyuiskaya area). In the Sobo-Khainskaya 1 well, an industrial gas in-flow was obtained from the interval of 1328–1349 m.The prospects for oil and gas exploration at the Preverkhoyanskaya oil and gas area are associated with its northern part (Setas struc-ture), on which the Setas parametric well No. 1 with a design depth of 4000 m is being laid, and its southern part, where it is advisable to drill 2 parametric wells with a planned depth of 3000 m.

Damage evolution and destabilization precursors in granite under splitting load at different temperatures

Brazilian splitting acoustic emission (AE) tests were conducted on the granite specimens that were heated at the temperatures from 50 to 600 °C to investigate the mechanical and damage characteristics of granite under high temperatures and splitting load in deep drilling. The results indicate that temperature variations significantly alter the mechanical characteristics and AE properties of granite, thereby influencing the evolution of fractures. At the temperature above 500 °C, the tensile strength of granite decreases significantly and the proportion of shear-induced damage modes increases. Furthermore, the rate of fracturing also exhibits a noticeable increase. Damage parameter mutation points on the damage parameter evolution curves of hit counts and energy counts were defined to determine the rock damage precursor. Mutation points based on hit counts arrive earlier than rock instability signals. The greater the damage is, the earlier the mutation points arrive. This time difference can be used to identify rock destabilization signals.

In-process approach for editing the subsurface properties during single-lip deep hole drilling using a sensor-integrated tool

Single-lip deep-hole drilling (SLD) is characterized by high surface quality and compressive residual stress in the subsurface of the drill hole. These properties depend significantly on the thermomechanical conditions in the machining process. The desired subsurface properties can be adjusted in-process via process monitoring near the cutting zone with a sensor-integrated tool and closed loop control when the thermomechanical conditions are maintained in the optimum range. In this paper, a method is presented to control the thermomechanical conditions to adjust the properties in the subsurface. The process model integrated in the controller is implemented as a soft sensor and takes into account the residual stresses, the roughness, the hardness and the grain size in the surface as well as in the subsurface depending on the process control variables, such as the feed rate and cutting speed. The correlation between the process variables, the thermomechanical conditions of the cutting process and the subsurface properties are investigated both experimentally and by finite element (FE) simulations. Within a justified process parameter range, characteristic fields for the soft sensor were established for each property. In addition, the procedure of controller design and the employed hardware and interfaces are presented.

On new prospects for petroleum and gas capability of Paleozoic sediments of the Karpovski projection

The article presents the geological data of recent years – the results of seismic exploration and deep drilling, which allow us to make new constructions of the model of the structure of the Paleozoic sedimentary complex of the northern side zone of the Caspian basin. In the historical development of the Caspian sedimentary basin, multiple geotectonic collisions have been observed, leading to transgressions and regressions of the Paleocean, as well as erosion of accumulated sedimentary strata, as well as interruptions in sedimentation. In the northern side zone, the determining influence of the structural sedimentation factor affected the age-varying carbonate ledges of the Karachaganak carbonate platform of the Aksaiblock, the Teplov-Tokarev zone of the Karpovsky tectonic ledge. Most of the oil, oil and gascondensate and gas condensate fields identified in the subsalt complex of the north of the Caspian Basin are associated with these zones. A comparative comparison of the deposits of the instrument zones of the Caspian basin has shown a fundamental difference in the conditions of accumulation of productive horizons, which lies in the nature of the location and in the significant variability of the filtration and capacitance properties of formations in natural reservoirs. The presence of deep-submerged carbonate structures is predicted in the deep part of the depression, on the slopes of carbonate platforms. Prospects for the detection of organogenic structures in the inner part of the paleobasin are assumed on the eastern extension of the Karpovsky ledge of the foundation and inside the Pogodaevo-Ostafyevsky trough, where, according to the results of 2D and 3D seismic surveys, promising structures Cretaceous, Orlovskaya and a number of others have been identified.

Structure design on a new type of coupled impactor

Improving drilling efficiency and reducing drilling cost are new challenges for deep drilling. Based on this, a coupling impactor is designed by applying the principle of hydraulic pulse pressurization and axial impact. Based on the impactor compression structure and principle, the fluid flow equation of the drilling fluid flowing through the compression mechanism and the mechanical balance equation of the piston body are established in order to study the pressure pulsation characteristics of the coupled impactor fluid.

The primary geology of the Paleoproterozoic Mt Weld Carbonatite Complex, Western Australia

Abstract The paleoregolith overlying the c. 2.06 Ga Mt Weld carbonatite (eastern Yilgarn Craton, Western Australia) hosts one of the largest Rare Earth Element (REE) deposits globally. Historic exploration and research has focussed on this weathered material, with a lack of unweathered samples preventing a thorough investigation into the nature of the underlying carbonatite. Recent deep drilling has allowed this first in-depth study into the primary geology, mineralogy and geochemistry of the carbonatite complex. Mt Weld shares a similar lithological architecture to other global carbonatite complexes, such as Ngualla (Tanzania, Bonga (Angola), Chilwa Island (Malawi) and Mirima Hill (Malawi), displaying a central (~600 m diameter) unit of magnesio- to ferrocarbonatite is surrounded by a broad (~1.2 km) annulus of calciocarbonatite, itself surrounded by a fenitic halo. Primary REE mineralisation occurs within the central magnesio- to ferrocarbonatites (~2% Total Rare Earth Oxides in bulk rock) and is dominated by fine-grained monazite hosted within fractures and voids, as well as late magmatic synchysite/bastnäsite. Both high and low phosphourous ferrocarbonatites occur within this central magnesio- to ferrocarbonatite unit that display (respectively) monazite or synchysite/bastnäsite mineralisation with textural evidence for these REE-bearing carbonates occasionally forming as polycrystalline pseudomorphs of earlier burbankite group minerals. Magnesio- to ferrocarbonatite dykes with zhonghuacerite/olekminskite/ancylite assemblages occur throughout the otherwise REE-poor calciocarbonatites (~0.2% Total Rare Earth Oxides in bulk rock). Late hydrothermal events strongly influenced the modern-day mineral assemblages with much of the existing ore mineral textures interpreted as hydrothermal reworkings of pre-existing REE-bearing minerals. A comparison of the fresh carbonatite and the paleoregolith geochemistry suggests minimal horizontal migration of ore elements during paleoregolith formation, with the overlying paleoregolith material broadly reflecting the underlying carbonatite trace and minor element signatures. This allows the inference of an approximately 5× upgrade in REE (and Nb) concentrations from the primary carbonatite to the overlying paleoregolith. Mt Weld shows distinct geological, mineralogical and isotopic differences to other currently mined carbonatite-associated REE deposits, such as Bayan Obo (China), Mountain Pass (USA) and the Mianning-Dechang belt (China), which suggests that fundamentally different carbonatite mantle sources and evolutionary paths can form world-class REE ore bodies.

Subsurface conditioning in BTA deep hole drilling for improved component performance

When bores with high length-to-diameter ratios (l/D > 10) and large diameters (D > 40 mm) are required, usually, the Boring and Trepanning Association (BTA) deep hole drilling process is used. Common industrial applications of this process are aerospace engineering and petrol exploration, where drilled components range from landing gears and engine shafts to drill collars. Since such parts tend to be particularly costly and highly safety–critical, ensuring favorable surface integrity during drilling is crucial to guarantee their reliability and performance. This study aims to identify correlations between the BTA deep hole drilling process and the resulting surface integrity using experimental and simulative approaches. The impact of feed and cutting speed on the thermomechanical loads and the resulting surface integrity are analyzed, also taking into account the occurrence of dynamic process disturbances. Particularly, the formation of white etching layers (WEL) is investigated using well-established, conventional techniques such as optical microscopy and microhardness testing. Additionally, innovative micromagnetic methods are employed. Magnetic Barkhausen noise (MBN) analysis is qualified as a well-applicable approach for rapid, non-destructive detection of WEL. To enhance understanding of MBN analysis and increase its robustness, the underlying mechanisms, governing the magnetic behavior of the subsurface are elucidated in detail by X-ray diffraction (XRD), electron backscatter diffraction (EBSD), magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) microscopy. The methodology will serve as a basis for controlled subsurface conditioning in BTA deep hole drilling.

Iron isotope systematics of the Jiajika granite-pegmatite lithium deposit, Sichuan, China

The Jiajika deposit in western Sichuan is the largest pegmatite-type lithium deposit in China, but the mechanism of rare metal element enrichment in this giant deposit remains a topic of debate. This study presents a comprehensive Fe isotope study of granites, aplites, pegmatites, metamorphic rocks, and associated mineral separates from the 3211 m long deep Jiajika scientific drilling core (JSD-1) to constrain the magmatic-hydrothermal processes in the Jiajika deposit. Aplites and pegmatites have variable δ56Fe values that range from –0.12 ± 0.02 ‰ to 0.38 ± 0.02 ‰, by contrast, two-mica granite samples show limited variation in δ56Fe compositions (0.11 ± 0.04 ‰ to 0.21 ± 0.04 ‰). The Fe isotope data of the coexisting Fe-bearing minerals can impose critical constraints on crystal fractionation. Garnet shows the lightest δ56Fe compositions (–0.19 ± 0.06 ‰ to –0.06 ± 0.02 ‰) and tourmaline has the highest δ56Fe values (0.15 ± 0.01 ‰ to 0.22 ± 0.02 ‰) among all the investigated minerals, whereas the δ56Fe values of biotite range from 0.06 ± 0.02 ‰ to 0.18 ± 0.02 ‰. According to the compositional homogeneity of minerals and the relatively consistent offsets in δ56Fe between the three Fe-bearing mineral pairs, the co-existing Fe-bearing minerals in the Jiajika granitic pegmatites are interpreted to be in Fe isotope equilibrium. Additionally, based on the differences in mineral composition and geochemistry of bulk-rock samples at different observation depths, as well as the modeling results, the significant Fe isotope variation in Jiajika deposit reflect the combined results of biotite fractionation, hydrothermal alteration (tourmalinization), and garnet accumulation during multistage magmatic-hydrothermal processes. Spodumene-bearing pegmatites located in the upper portion of the drill core exhibit enrichment in heavy Fe isotopes (0.18 ± 0.04 ‰ and 0.30 ± 0.03 ‰) which can be attributed to their higher degree of magma evolution and the most abundant magmatic fluids related to enrichment and migration of rare metals. Furthermore, we conducted a comprehensive statistical analysis on the available Fe isotope data of granitic pegmatites, providing new insights into granite-pegmatite systems and related rare-metal mineralization processes from a Fe isotope perspective.

Archaeal lipid biomarkers in near-surface sediments at a giant colony of the bivalve Calyptogena: Molecular records of a massive methane release event associated with methane hydrate dissociation

To investigate the possibility that dissociation of subsurface methane hydrate (MH) in the eastern Nankai Trough, offshore of Japan, led to the formation of a giant colony of the bivalve Calyptogena (currently mostly dead), the carbon isotope ratios (δ13C) of archaeal lipids and methane were measured in near-surface core sediments at Daini-Tenryu Knoll. The irregular variation of porewater methane δ13C with depth (from −75 ‰ to −26 ‰) suggested that originally low δ13C microbial methane was degraded in different proportions by anaerobic methane oxidation. Consistent with this inference, biomarkers of anaerobic methanotrophic archaea (ANME), namely, crocetane (2,6,11,15-tetramethylhexadecane), PMI (2,6,10,15,19-pentamethylicosane), and diethers (archaeol and hydroxyarchaeols), were detected in lipid extracts. The low diether δ13C values (−121 ‰ to −104 ‰) were characteristic of ANME, but less variable than the methane δ13C values, and the relationships between diethers and methane δ13C values deviated from regression lines derived using worldwide data from modern methane seep sites. In contrast, δ13C values of the ANME source methane predicted from those regression lines and the diether δ13C values agreed well with methane δ13C values in MH samples obtained by nearby deep drilling. This result strongly suggests that most of the diethers were produced by ANME that proliferated during a past massive methane release event associated with MH dissociation. The crocetane δ13C value, measured in a mixture with phytane and estimated from the correlation of the δ13C of the mixture with the mole fraction of crocetane, was about −127 ‰. More than half of the PMI δ13C values were greater than −100 ‰, suggesting the background presence of fossil PMI from methanogens.

Petrogenesis and metallogenic potential of granodiorite porphyry in the Kalatag district, East Tianshan, NW China: Constraints from geochronology, mineral geochemistry, Sr–Nd–Hf–O–S isotopes and sulfide trace elements

The Hongshi epithermal Cu deposit is located in the northern margin of the Dananhu arc in the East Tianshan Orogenic Belt, NW China. The Hongshi deposit is hosted by andesite and is famous for its lode type sulfide ores. Recently, the deep drill hole exploration shows a porphyry Cu mineralization and is predominantly hosted in granodiorite porphyry in the Hongshi. As for porphyry mineralization, the metallic minerals mainly include chalcopyrite, magnetite, and pyrite, with minor amounts of molybdenite. Ore minerals occur as dense dissemination and veins. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating of zircons showed that the ore-bearing granodiorite porphyry was emplaced at ca. 434 Ma, recording the early subduction of the Paleo-Tianshan oceanic plate. Major element geochemical characteristics show that granodiorite porphyry samples have A/CNK values of 1.04–1.10 and moderate Mg# values of 45–49, indicating an I-type granitoid attribute. Trace element geochemical analysis indicates that ore-bearing granodiorite porphyry samples exhibit obvious large ion lithophile elements (LILEs) enrichment, high field strength elements (HFSEs) depletion, together with mantle-like bulk Sr–Nd ((87Sr/86Sr)i = 0.706417–0.708601; εNd(t) = 6.3–7.0) and zircon Hf–O isotope signatures (εHf(t) = 15.5–21.7, δ18O = 3.8 ‰–4.7 ‰), indicating that they were generated from partial melting of metasomatized mantle by the subducted slab fluids. In situ S isotope results of pyrite (1.46 ‰–2.07 ‰) and chalcopyrite (0.79 ‰–1.93 ‰) imply that granodiorite porphyry magmas and volcanic rocks provided ore-forming components (S and metals) for porphyry Cu mineralization in the deep drill hole ZK7501. The ore-bearing granodiorite porphyry samples have high logfO2 values ranging from − 12.4 to − 10.7, corresponding to ΔFMQ values of 0.6–5.2 (FMQ is the fayalite-magnetite-quartz buffer). Zircons from granodiorite porphyry have high Ce4+/Ce3+ ratios ranging from 74 to 187 and high Ti-in-zircon temperatures (764 to 869 °C). Electron microprobe analyses (EPMA) composition results of plagioclase, apatite and amphibole reveal that granodiorite porphyry magma had systematically high oxygen fugacity, high water contents (7.6–8.4 wt%), and low Cl contents (0.08–0.27 wt%), further demonstrating that granodiorite porphyry may be beneficial to the porphyry Cu mineralization in the deep drill hole ZK7501. Pyrite in the deep drill hole ZK7501 is enriched in Co, Ni, Ag, Cu, As, and Pb, but poor in Mn, Ga, Ge, Cd, In, Sn. Mn, As, Tl, Pb and Sb in pyrite substituted Fe2+ by coupled mechanisms, while Ag and Cu can enter the mineral lattice in the form of solid solution or micro-inclusions, which was also demonstrated by LA–ICP–MS mapping and textural studies. Pyrite shows variable Co/Ni ratios ranging from 10 and 455, indicating that ore-forming fluid originated from a magmatic source. The involvement of highly oxidized magmas is fundamental for the formation of porphyry Cu mineralization in an arc tectonic setting. Additionally, water concentrations also play an important factor that controlled metal fertility of the Early Paleozoic porphyry Cu mineralization in the Kalatag district.

Numerical modelling of the BTA deep hole drilling process

The BTA deep hole drilling process is applied in order to produce bores with a large length to diameter ration at comparably high diameters of the bores. During drilling, first, the bore is cut by the cutting edge and shortly after that, a guide pad slides over the newly produced bore wall, burnishing the surface. These two effects condition the bore wall and alter its surface integrity depending on the process parameters. In the past, extensive destructive and non-destructive tests were conducted to obtain information on the surface integrity of the machined parts. Furthermore, a large number of in- and off-process measurements were carried out in material and cost-intensive experiments to determine values such as residual stresses or white etching layers. The presented work shows different finite element models of the BTA deep hole drilling process using continuous remeshing and, in order to reduce the calculation times, the Coupled Eulerian-Lagrangian (CEL) method as well. The results simulated based on this models comprise temperatures, process forces and surface properties that are compared to measured values from pervious works for validation. The various approaches are evaluated to determine whether they predict the bore hole surface integrity and thus support future investigations.