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With the rising demand for mineral resources and the gradual depletion of shallow mineral resources in China, it has become an inevitable trend to mining new mineral resources by expanding to the depths. First, for the many challenges faced by the traditional rock drilling and blasting process in deep mining, the non-explosive continuous mining technology and equipment for hard rock deposits are introduced. Then, taking a deep hard rock mine as example, the application practice of non-explosive continuous mining technology are introduced in detail with the positive results brought about, which provides a case study for the non-explosive continuous mining of deep hard rock deposits; Finally, based on the practical experience and combining with cutting-edge technologies such as artificial intelligence, the ore slurry-making hydraulic transportation technology is proposed, which is expected to provide a more efficient and environmentally friendly solution for lifting ores in deep mines, and to further optimize and enhance the mining efficiency and safety of deep mines. [ABSTRACT FROM AUTHOR]

The safe and secure supply of strategic mineral resources is an important strategic need of China, and the extraction of mineral resources from the deep earth is an irreplaceable strategy for a long time in the future. To ensure the demand for mineral resources, the safe and efficient mining of high-stress hard rock is a major problem that must be solved in deep mining. Firstly, the technical challenges of deep high-stress hard rock mining and the transformative mining philosophy of "turning harm into benefit" was delineated. And a key engineering countermeasure to weaken the high-stress hard rock before mechanical rock breaking to achieve commercial mining was proposed. Next, the mechanism, characteristics and development status of contact and non-contact rock weakening methods were summarized, and the potentiality of these two types of rock weakening methods in the field of assisting mechanical breaking of high-stress hard rock was compared and analyzed. Finally, the safe and efficient continuous mining technology represented by mechanical rock breaking with thermal exfoliation damage weakening of deep high-stress hard rock was prospected. It provides useful guidance for the safe and secure supply of deep strategic mineral resources and the development of deep earth engineering. [ABSTRACT FROM AUTHOR]

Fragmentation by blasting is a critical process in hard rock mining. The interaction between the rock mass and blast energy influences the outcomes, specifically on the rock mass response to higher stresses and loading rates, and the properties of structures. In this study, LS-DYNA is used to model the nonlinear dynamic fracturing of the rock to understand the effects of rock mass properties on the blast outcomes. The results are verified and compared with the case study, and they show that the formation of damage zones around the charge is highly influenced by rock mass strength and discontinuity properties. [ABSTRACT FROM AUTHOR]

Three hundred and twenty-four data points on the saturated hydraulic conductivity (k) of various hard rock mine tailings are collected from previous publications. The applicability of existing empirical equations for hard rock mine tailings is assessed based on this database collected. Results show that with a greater exponent of d10, the correlation between the measured and predicted k is greatly improved. An empirically modified version of the Kozeny–Carman equation is then proposed for predicting the saturated k of tailings and compared with the database. The proposed equation gives the best fit with a varying exponent greater than 2 for d10. Finally, the impact of particle shape on k is discussed. [ABSTRACT FROM AUTHOR]

Rock fragment movement during blasting operations is a major cause of ore and profit losses in hard rock open-pit mines having a complex-orebody. To address this issue, a novel multilayer dig-limit approach, which well considers blast movement in dig-limit optimization, was proposed in this study by combining machine learning techniques and practical heuristic algorithms. First, horizontal and vertical blast-induced rock movement distances were predicted using a supervised learning model. Then, the movement direction of rock fragments was computed based on the initiation sequence. After meshing the blast block into rock units, the blasted muckpile and post-blast ore boundary were determined, providing a good basis for dig-limit determination. Finally, the optimized dig-limit with maximum profit can be calculated using a practical heuristic algorithm. By applying this method in a case study, the ore recovery and economic profit were improved, compared with manually drawn dig-limit method. Additionally, the impact of equipment size, number of layers and powder factor on the application of this method was discussed. The obtained results indicated that ore and profit losses can be reduced with a decreased equipment size, increased number of layers and decreased powder factor. Highlights: A multilayer dig-limit approach considering blast-induced rock movement and dig-limit optimization was proposed. The multilayer dig-limit approach yields higher ore recovery and economic profit compared to manually drawn dig-limit. Ore losses can be reduced by decreasing the equipment size, increasing the number of layers and decreasing the powder factor. [ABSTRACT FROM AUTHOR]

Burden is one of the most important parameter which plays an immense role in rock breakage using explosive energy. It is very difficult to select the optimum burden under different geotechnical and geomining condition. The selection becomes more critical when the excavation method is underground as very few researches or studies have been carried out in such cases. Therefore, in this paper, numerical simulation-based approach has been employed to estimate the optimum burden for ring blasting. The numerical models were created under different scenario including blasthole diameter and strength of the rock. The RHT concrete constitutive model has been used in this paper to study the damage contour under different circumstances. The model output has been used to calculate the volume of rock damage along the free face. This damage volume is further correlated with various parameters. This correlation shows that the damage volume along the free face initially rises with the increase in burden and then starts decreasing after a certain value. The burden value which recorded the maximum volume of rock excavated along the free face has been considered as the optimum burden in this paper. The trial blast has been also carried out at the experimental site for twenty-four rings. The optimum burden achieved from the experimental trial for 102 mm blasthole diameter and rock having uniaxial compressive strength as 92 MPa lies between 2.4 and 2.65 m. However, the optimum burden predicted through developed empirical equation from the numerical model is 2.6 m. The study shows that the simulation-based prediction exhibits a minor deviation within 15% with the experimental result. Hence, to assess the optimum burden under various geotechnical and geomining circumstances, numerical simulation-based approach may be carried out using the proposed methodology. Highlights: Burden for ring blasting is optimised using different numerical simulation models. Volume of rock excavated along free face (EV) has been calculated in each case. The optimum burden from experimental trial and empirical data is 2.4–2.65 m. The optimum burden predicted from developed model is 2.6 m. [ABSTRACT FROM AUTHOR]

Mass spectrometry is a widely used tool for analysis of uranium isotopic composition. For solution based inductively coupled plasma mass spectrometry, uranium isotopes are typically analyzed after purification from complex matrices. In this work, we tested the ability of three mass spectrometers (ThermoScientific iCAP TQ, ThermoScientific Neoma, and Agilent 8900) to analyze uranium isotopes in an unpurified NIST reference material (SRM2780a, Hard Rock Mine Waste) digest solution. Results indicate that 235U/238U can be analyzed within 1% of the true value. 234U/238U is a more challenging analysis due to low count rates and potential isobar interferences, but strategies to mitigate these effects, such as the use of reaction gases in a collision cell and desolvating nebulizer introduction system, are effective for the triple quadrupole instruments. However, the use of the Neoma MS/MS in reaction mode using O2 gas was problematic. Nevertheless, analysis of unpurified solutions for quick assessment of uranium isotope compositions is practical, especially when high precision is not required. [ABSTRACT FROM AUTHOR]

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This article delves into the debates, both in print and digital media, surrounding copper mining and its associated concerns, particularly those related to hardrock mining. Guided by agenda-building, pragma-dialectics, and stakeholder theories, this research employs topic modeling to scrutinize the media strategies and arguments employed by key stakeholders involved in an environmental movement. The aim is to unveil implicit communication activities that contribute to the emergence of public debates, shedding light on the nuanced dynamics within stakeholder discourses. The analysis shows that by referring to authoritative arguments, the local press distributes the places of power while representing conflicting standpoints and arguments. With digital media, the opponents build a pro-environmentalist network to publicize the issues relative to the mining project and the importance of defending southwestern habitats and landscape. Mining proponents similarly rely on business communities to underscore the importance of hardrock mining for things like decarbonized energy and modern living. Across groups, stakeholder communication situates differing conceptions of the relationship between humans and their natural environment. Our findings reveal that, consistently across various groups, the discourse maintains a degree of stability as topics and arguments persist over time. On one side, discussions highlight the destructive impacts of mining, while the opposing perspective underscores the significance of sustainable and resilient mining practices. This analysis of stakeholder discourses in the media helps uncover the various ways primary actors maintain their positionality and power in this particular case. [ABSTRACT FROM AUTHOR]

The article discusses the potential for decarbonization in the global steel industry through the use of green steel technologies. It highlights the energy-intensive steps involved in steel production and the various technologies, such as blast furnaces and electric smelting furnaces, that can help reduce carbon emissions. The text emphasizes the importance of integrating decarbonization efforts from mining to steel production and explores innovative technologies like carbon capture and storage, hydrogen injection, and the use of low-carbon energy sources. Additionally, it addresses the need for increased energy efficiency, waste reduction, and technological innovation in the steel industry to achieve low-carbon steel production. [Extracted from the article]

Introduction: The research concerns how making cut cavities improves drilling and blasting operations as well as the optimum parameters to arrange both snubber and auxiliary blastholes. Methods: The research methods include experimental and industrial activities to identify the optimum depth of the first-section snubber blastholes relative to the second-section blastholes. It also identifies optimum parameters of the snubber blastholes while driving mine workings and ore breaking in stopes with different mine working sections and different rock mass strengths broken using the technique of cut-cavity formation. Results and Discussion: Experimental explosions executed in a production environment have proved the efficiency of the proposed technique of sectional formation of a cut cavity, which helped increase the blasthole use coefficient (BUC) from 0.88 to 0.97. The depth of the first-section boreholes should be determined relative to the length of the second-section boreholes and the broken rock mass strength. The higher the strength of the broken formation, the larger the ratio between the first and the second-section blasthole lengths should be. The results of the experimental explosions indicate that the depth of first-section snubber blastholes varies from 0.5 and more of the second-section boreholes, depending upon the depth of the latter and the broken rock mass strength. If the strength of the broken rock mass is 12 on the Protodyakonov scale, and the second-section blasthole depth increases from 1.6 m to 2.6 m, then the depth of the second-section boreholes should be increased from 0.9 m to 1.54 m so as to be 0.55-0.56 of the second section blasthole length. If the strength of the broken rock mass is 18, and the length of the second section increases from 1.8 m to 2.82 m, then the first-section length varies from 0.9 m to 1.75 m, being 0.5-0.62 of the second section blasthole length. Applying the novel proposed procedure for a cut-cavity formation will increase the blasthole use coefficient and reduce the cost of drilling and blasting operations. Moreover, the procedure may also be practical for driving underground mine workings and for ore breaking within stopes. [ABSTRACT FROM AUTHOR]

To reveal the characteristics of overlying rock movement in hard and thick volcanic rock mining areas, a typical volcanic rock occurrence was used as a model. Similar simulation experiments were conducted, combined with on-site monitoring data, to systematically analyze the variations of surface and overlying rock deformation and damage with different mining steps, and compared with the model without hard and thick volcanic rocks. The results showed that compared to the model without hard and thick volcanic rocks, the presence of hard and thick volcanic rocks in the overlying strata led to an increased range of subsidence basin and a decrease in maximum subsidence value. The hard and thick volcanic rocks easily formed larger fractured spaces, which served as the main locations for the accumulation of gas and water in fractures. The "O"-shaped fractured circle formed after the rupture of the hard and thick volcanic rocks provided a favorable pathway for gas outbursts and water surges in the fractures. The rupture of hard and thick volcanic rocks easily triggered intense overlying rock movement and surface subsidence, leading to occurrences of underground and surface disasters such as dynamic ground pressure, outbursts of gas and water in fractures, and damage to surface structures and ecological environments. [ABSTRACT FROM AUTHOR]

Background and aims: Re-vegetation of mining-impacted landscapes reduces transport of toxic elements while improving soil fertility. This study evaluated whether the planting of a native perennial grass with a consortium of diazotrophic microbial endophytes and municipal waste compost—alone and in combination—enhanced plant growth while stabilizing metal(loids) in dolomite-amended tailings from a historically mined polymetallic mineral deposit. Methods: We grew Bouteloua curtipendula seedlings in tailings with hazardous concentrations of As, Cd, Pb, Mn, and Zn. We evaluated how plant growth, organic matter accumulation, and major, minor, and trace element mobilization and phytostabilization responded to microbial endophyte and/or compost amendments after the 45-day growth experiment. Results: Although most of the added endophytes were not uniquely identified, the best plant growth and fertility outcomes were achieved with a combination of amendments: dolomite to reduce acidity, compost to increase nitrogen, and a mixed consortium endophyte seed coating to synergistically increase organic carbon and grass biomass yields. Compost reduced shoot and root concentrations—but not yields—of contaminant metals. Endophytes increased foliar Cd, Co, Mn, and Pb yields but mobilized Pb and Zn from the tailings. Root stabilization of Cd, Co, Mn did not require amendments. Conclusion: The most effective means of revegetating these acidic, polymetallic tailings with the native B. curtipendula is with a simultaneous dolomite, compost, and endophyte seed treatment. Due to potential phosphate solubilization and siderophore production by this consortium of endophytes, strategies to capture solubilized metal(loids) may be needed for sulfidic tailings with metal(loids) associated with mobile mineral phases. [ABSTRACT FROM AUTHOR]

Real-time microseismic observations are extensively used in underground hard rock mines. However, microseismic monitoring in coal mines is not common. In this study, the features of microseismic (MS) event waveforms were discussed under conditions of thin-layered sedimentary media. The possibility of source mechanism evaluation was considered for the MS event recorded in coal mine. Moment tensor (MT) inversion of the waveforms can be challenging due to influence of thin-layered medium structure. Splitting of shear SH- and SV-waves is one of the characteristic features that affect MS records in coal mines. The effect of splitting was demonstrated using real microseismic data collected by an underground seismic array installed in the Polosukhinskaya coal mine, Russia. Velocities of shear SH- and SV-waves were estimated from travel times. The results reveal significant variations in shear wave velocities composed of a radial anisotropy of 75%, thus confirming the importance of a thin-layered model for moment tensor inversion. The thin-layered model was built for geological conditions at the Polosukhinskaya coal mine and synthetic seismograms were generated using QSEIS (Pyrocko OS). A full moment tensor of a single typical event was found employing the layered 1D velocity model. [ABSTRACT FROM AUTHOR]

Pillar stability is of paramount importance in ensuring the safety of underground rock engineering structures. The stability of pillars directly influences the structural integrity of the mine and mitigates the risk of collapses or accidents. Therefore, assessing pillar stability is crucial for safe, productive, reliable, and profitable underground mining engineering processes. This study developed the application of decision intelligence-based predictive modelling of hard rock pillar stability in underground engineering structures using K-Nearest Neighbour coupled with the grey wolf optimization algorithm (KNN-GWO). Initially, a substantial dataset consisting of 236 different pillar cases was collected from seven underground hard rock mining engineering projects. This dataset was gathered by considering five significant input variables, namely pillar width, pillar height, pillar width/height ratio, uniaxial compressive strength, and average pillar stress. Secondly, the original hard rock pillar stability level has been classified into three types: failed, unstable, and stable, based on the pillar's instability mechanism and failure process. Thirdly, several visual relationships were established in order to ascertain the correlation between input variables and the corresponding pillar stability level. Fourthly, the entire pillar database was randomly divided into a training dataset and testing dataset with a 70:30 sampling method. Moreover, the (KNN-GWO) model was developed to predict the stability of pillars in hard rock mining. Lastly, the performance of the suggested predictive model was evaluated using accuracy, precision, recall, F1-score, and a confusion matrix. The findings of the proposed model offer a superior benchmark for accurately predicting the stability of hard rock pillars. Therefore, it is recommended to employ decision intelligence models in mining engineering in order to effectively prioritise safety measures and improve the efficiency of operational processes, risk management, and decision-making related to underground engineering structures. [ABSTRACT FROM AUTHOR]

To investigate the influence of non-singular terms (T stress) in the stress field on the composite fractures of hard rock Type I–II, such as rock splitting failure and hydraulic fracture propagation, this study focused on hard rocks in metallic mines. Through splitting tests and hydraulic fracturing experiments, the impact of T stress on the characteristics of Type I–II composite fractures in hard rocks was analyzed. Utilizing the generalized maximum tangential (GMTS) stress criterion considering T stress, the stress intensity factors of hard rock Type I–II composite fractures with different pre-existing crack angles were predicted. The critical fracture pressure expression for hard rocks was derived based on the maximum tangential stress (MTS) criterion. The results indicate that the GMTS criterion, considering T stress, is more suitable for describing the characteristics of Type I–II composite fractures under rock-splitting loads. However, under hydraulic fracturing, T stress has a minor influence on the fracture characteristics of hard rock hydraulic fractures. Therefore, when predicting the critical fracture pressure of hydraulic fractures, T stress can be disregarded. This study provides a scientific basis and guidance for hard rock hydraulic fracturing engineering. [ABSTRACT FROM AUTHOR]

The article explores the history of the disposal of mine waste and tailings in British Columbia during the period of 1892 to 1982. It argues that historical debates in the province over mine waste management were rooted in a settler colonial conception of land and water as resources for metaphorical and literal accumulation that influenced approaches to tailings management. It discusses the impact of the mine waste management regime on the appropriation of Indigenous lands and waters.

Introduction: Cavability issues often arise in hard rock mines employing the block caving mining method. Hydraulic fracturing stands out as a promising preconditioning technology for hard rock masses, with its pre-conditioning effects dependent on variable parameters. Methods: The impact of cluster number, injection rate, and liquid volume on fracture propagation was investigated through on-site hydraulic fracturing practices. Fracturability was initially verified via true triaxial fracturing tests, and preconditioning parameters were subsequently optimized using numerical simulations. The optimized on-site construction was monitored using electromagnetic methods. Results: The study revealed a negative correlation between fracture radius and the number of clusters, gradually decreasing with an increase in cluster number. However, the fracture weakening area increased with the rise in the number of clusters. The fracture weakening area also increased with the injection rate. Additionally, the fracture radius initially increased and then decreased. Both fracture weakening area and radius increased with an increase in liquid volume. The optimized parameters were identified as four clusters, an injection rate of 4 m3/min, and a liquid volume of 500 m3. Discussion: Building upon these findings, on-site experiments were conducted and monitored using electromagnetic methods. The monitored results demonstrated that the optimized parameters effectively achieved hydraulic fracturing expansion, accomplishing the goal of weakening hard rock. [ABSTRACT FROM AUTHOR]

In recent years, with the gradual depletion of shallow mineral resources, the exploitation of deep mineral resources has become an inevitable trend. Microseismic monitoring is one of the main methods to solve high stress concentration problems such as rockbursts, roof caving and water inrush in deep mine. An accurate and fast microseismic location method is the basis of microseismic monitoring. At present, machine learning (ML) has become an important auxiliary method in the field of microseismic monitoring due to its powerful feature expression ability. Compared with other microseismic positioning methods, ML can construct a more objective positioning model. This paper uses three ML models including deep neural network (DNN), random forest (RF),and support vector regression (SVR) to construct a microseismic position method to search for the microseismic source. The travel time difference between stations is used as the input of the ML model. Since the number of field data sets is not enough to complete the training of the model, this paper uses a synthetic data set with a specific speed model as the training set and uses the field data set for testing. In order to analyze the location accuracy, we compare them with three traditional microseismic location methods. To improve the positioning performance of ML models, this paper uses a Bayesian optimizer (BO) to adjust their hyperparameters. The experimental results show that the performance of the ML model adjusted by the BO has been significantly improved. The positioning accuracy order of the three ML models is DNN > RF > SVR > traditional location method. The average positioning accuracies of the DNN inside and outside the sensors array are 27.81 m and 145.96 m, respectively. For the model proposed in this paper, the positioning accuracy inside the sensors array is significantly higher than that outside the array, which is similar to the traditional positioning method. In addition, the model has a certain tolerance to the error of the speed model. Highlights: Utilization of machine learning (ML) for accurate and objective microseismic source location. Comparative analysis of three ML models (DNN, RF, SVR) and traditional methods. Enhancement of ML model performance using Bayesian optimizer for hyperparameter tuning. Significant improvement in positioning accuracy with DNN model inside and outside the sensor array. Tolerance to speed model errors in the proposed ML-based microseismic positioning method. [ABSTRACT FROM AUTHOR]

To investigate the leaching rules and mechanism of a hard rock uranium ore, this paper conducted conventional leaching experiments based on the chemical composition and mineral occurrence status of the ore. Various factors affecting leaching were explored, and experimental data were fitted using the shrinking-core model. The results showed that uranium in the ore mainly existed in the form of pitchblende and coffinite, and the uranium grade of the sample was 0.15%. Under the leaching conditions of a temperature of 50 °C, a particle size of − 100 mesh, an acid dosage of 32 kg t−1, a pyrolusite dosage of 10 kg t−1, a liquid–solid ratio of 1:1, and an 8 h duration, the leaching rate of the uranium ore reached 99.12%. The leaching process was controlled by solid film diffusion, and the apparent activation energy was 11.6 kJ mol−1. Insoluble substances were present on the surface of the slag, and the solid film product was the main reason hindering leaching. [ABSTRACT FROM AUTHOR]

An experimental method is proposed to assess blasting requirements based on in-situ cratering behavior. The method relies on single hole blast (SHB) tests to derive burden-dependent relationships. A non-linear crater model of the form Y = C b s is calibrated from SHB test results to describe the cratering behavior. Parameters C and s represent characteristic blastability index parameters that depend on geomechanical and operational conditions. A series of experimental SHB tests were conducted at three hard rock mines. The craters were mapped to capture the breakout profile and calibrate the model. Results showed that coefficient C presents an inverse linear correlation with burden B , while exponent s is approximately constant for a considerable range of burden values. Experimental results are used to define burden dependent relationship for bench blast designs and blasthole placement in underground development rounds. A complementary analysis addresses the prevalence of multiple cratering mechanisms according to geology and burden dimension. [ABSTRACT FROM AUTHOR]

Numerical modelling is an important instrument for rock engineering; it can assist in the design and prediction of failure in rock masses. Dependable results can be obtained from the models if, and only if, the underlying assumptions, strengths, and weaknesses of the model are known. A set of guidelines to implement a numerical modelling program can also be used to obtain high-quality and reliable results. The importance of a well-structured numerical modelling program to attain practically reasonable results cannot be overstated. This paper presents an analysis of the results of modelling a rock engineering problem involving deep mining excavations prone to high-stress challenges. The study used Lamodel and Examine 2D. The results obtained show that the two software programs can be used together to complement each other in attaining a deeper understanding of the influence of high stresses on mining excavations at depth. Lamodel and Examine 2D are both boundary element code-based software and are quick and easy to use. More advanced numerical modelling tools could be used, but these two were found to be suitable for the problem at hand. Many diagrams and results can be obtained from the numerical modelling of any rock engineering challenge; in this paper, only those diagrams and results deemed to be most relevant and appropriate to demonstrate the capabilities, limitations, and validity of the numerical modelling of the problem have been presented. [ABSTRACT FROM AUTHOR]

Declines and extirpations of American pika (Ochotona princeps) populations at historically occupied sites started being documented in the literature during the early 2000s. Commensurate with global climate change, many of these losses at peripheral and lower elevation sites have been associated with changes in ambient air temperature and precipitation regimes. Here, we report on a decline in available genetic resources for an iconic American pika metapopulation, located at the southwestern edge of the species distribution in the Bodie Hills of eastern California, USA. Composed of highly fragmented habitat created by hard rock mining, the ore dumps at this site were likely colonized by pikas around the end of the 19th century from nearby natural talus outcrops. Genetic data extracted from both contemporary samples and archived natural history collections allowed us to track population and patch-level genetic diversity for Bodie pikas across three distinct sampling points during the last half-century (1948-1949, 1988-1991, 2013-2015). Reductions in within-population allelic diversity and expected heterozygosity were observed across the full time period. More extensive sampling of extant patches during the 1988-1991 and 2013-2015 periods revealed an increase in population structure and a reduction in effective population size. Furthermore, census records from the last 51 years as well as archived museum samples collected in 1947 from a nearby pika population in the Wassuk range (Nevada, USA) provide further support of the increasing isolation and genetic coalescence occurring in this region. This study highlights the importance of museum samples and long-term monitoring in contextualizing our understanding of population viability. [ABSTRACT FROM AUTHOR]

The dominant technology in hard rock mining is drilling and blasting; therefore, the importance of fragment size estimation is an essential problem in the mining industry. By using a theoretical foundation that explains rock-fracturing mechanisms by blasting, a 3D fragmentation model with general applicability was developed. The main capabilities of the model are the ability to consider different and complex blasting patterns, both with parallel and non-parallel boreholes, and different explosive and rock properties. The geological input of the model is defined by generating the primary blocks within rock mass using discrete fracture networks. The model handles different, complex geological setups and blasting scenarios that include bench, ring, and tunneling blasting. Also, it considers borehole deviation, misfires, and the influence of previous blasts. Full-scale ring blasts were carried out to validate the model against real-world data, and the results showed a high level of agreement between model predictions and in situ data. In situ data were collected using image processing methodology and WipFrag v4 software. X50 and X80 size values showed a maximum error in prediction of around 15%, while R2 values between fragmentation curves were approximately 90% without a detailed model calibration to the obtained data. [ABSTRACT FROM AUTHOR]

Rock blasting with explosives is the first stage of rock fragmentation and plays a key role in the results of the mining chain. Fragmentation optimization is achieved by considering the energy efficiency of the explosive, the optimal distribution of explosive energy in the rocky mass, and the programmed and controlled release of explosive energy during blasting. The quality of fragmentation is usually performed using tools that estimate the sizes of fragments via the analysis of two- or three-dimensional images. This article presents a study of the rock fragmentation optimization of very compact itabirites, based on four blasting tests, performed in a different way from the conventional blasting design. The fragmentation analysis was performed using the P o r t a M e t r i c s T M tool, and compared with the Kuznetsov and Rosin–Rammler particle size distribution model, to compare the reliability of this tool. Finally, the mine productivity after blasting was estimated from the particle size distribution obtained in the tests. The model presented idealistic results considering the technical parameters used in the equations. However, the P o r t a M e t r i c s T M tool suggests good performance for the preliminary evaluation of blast design. [ABSTRACT FROM AUTHOR]

This study investigated the use of a limit equilibrium model to simulate the time-dependent scaling of hard rock pillars. In the manganese bord and pillar mines in South Africa, extensive scaling is observed for pillars characterised by a high joint density. It appears that the scaling occurs in a time-dependent fashion. Evidence for this is the ongoing deterioration of pillars in old areas, even after the pillars are reinforced with thin spray-on liners. Monitoring of selected pillars were conducted in an attempt to quantify the rate of time-dependent scaling. Contrary to expectations, almost no additional scaling was recorded for the pillars during a 3-month monitoring period. The scaling distance for pillars of different ages could be measured and it seems as if most of the scaling occurred soon after the pillars are formed. Only a limited amount of additional time-dependent scaling seems to occur after this. Numerical simulations of the time-dependent scaling were conducted using a displacement discontinuity code and a limit equilibrium constitutive model. The postulated exponential decay of the failed rock mass strength at the edges of the pillars resulted in simulated behaviour that is qualitatively similar to the underground observations. The results from this study are encouraging and the method can be used to investigate the long-term stability of bord and pillar excavations. Further work is required to improve on the calibration of the model and to better quantify the rate of scaling of the underground pillars. Highlights: Time-dependent scaling gradually reduces the strength of pillars. This paper presents a study of this behaviour in a hard rock bord and pillar mine. A numerical modelling approach to simulate time-dependent pillar failure, on a mine-wide scale, is described in the paper. It consists of a displacement discontinuity boundary element method with a time-dependent limit equilibrium model. The behaviour of the hard rock pillars in the manganese mines in South Africa is used to test the proposed model. It provides valuable data for researchers interested in case studies of time-dependent pillar strength. The proposed modelling methodology seems valuable to design layouts where long-term stability is a requirement. Although the focus in this paper is on hard rock mines, it can also be used for coal pillars. [ABSTRACT FROM AUTHOR]

The re-vegetation of mining wastes with native plants is a comparatively low-cost solution for mine reclamation. However, re-vegetation fails when extreme pH values, low organic matter, or high concentrations of phytotoxic elements inhibit plant establishment and growth. Our aim was to determine whether the combined addition of municipal waste compost and diazotrophic endophytes (i.e., microorganisms that fix atmospheric N2 and live within plants) could improve plant growth, organic matter accumulation, and phytostabilization of trace element contaminants in two types of hard rock mine waste. We grew a widespread native perennial grass, Bouteloua curtipendula, for one month in alkaline waste rock (porphyry copper mine) and tailings (Ag-Pb-Au mine, amended with dolomite) sourced from southeastern Arizona, United States. B. curtipendula tolerated elevated concentrations of multiple phytotoxic trace elements in the tailings (Mn, Pb, Zn), stabilizing them in roots without foliar translocation. Adding compost and endophyte seed coats improved plant growth, microbial biomass, and organic matter accumulation despite stark differences in the geochemical and physical characteristics of the mining wastes. The widespread grass B. curtipendula is a potential candidate for re-vegetating mine wastes when seeded with soil additives to increase pH and with microbial and organic amendments to increase plant growth. This study quantifies improvements to plant growth, soil fertility, and trace element stabilization with a municipal waste compost topdressing and diazotrophic endophyte seed coating in two common hard rock mining wastes of the western United States. It establishes that a widespread perennial grass, Bouteloua curtipendula, can grow despite high concentrations of phytotoxic trace elements and minimal soil nutrients, and stabilizes trace elements on or in its roots, making it a suitable option for re-vegetation or phytostabilization of hard rock mining wastes. [ABSTRACT FROM AUTHOR]

North Dakota lignite has the potential to be a new source of mineral commodities that are vital to the economic and national security of the United States. There is little to no current domestic production for many of the raw mineral materials needed to manufacture many components in energy and defense applications, in addition to a wide array of modern electronic consumer goods. The U.S. currently relies on imports of many of these commodities, termed critical minerals, including the sixteen rare earth elements (REE). Some of the REEs (e.g., lanthanum and cerium) are relatively abundant and overproduced by traditional hard rock mines, but other, less abundant REEs (e.g., dysprosium, terbium, scandium) are highly valuable and thus may be economic at relatively low concentrations if cost-effective extraction methods can be developed. Broadly speaking, techniques which need to break down REE-bearing primary minerals to extract the elements are costly, but in coal, especially low ranks like lignite, an appreciable percentage of the REE content may be weakly bound into organic complexes and easily extracted. REE concentrations in U.S. coal are generally around three times lower than the average concentrations in rocks and sediment near the Earth's surface but occasionally can be found enriched or significantly enriched 5 to 10 times higher than average upper continental crust. Other high-value critical elements (e.g., gallium and germanium) may also occur in economic concentrations in lignite and could be co-produced with the REEs. With higher relative proportions of the more valuable REEs and other critical elements, easy extraction, and lower amounts of radioactive contaminants like thorium, lignite may be an economical source of REEs at far lower concentrations than traditional ores. The U.S. Department of Energy has proposed coal containing 300 ppm REE could be a potentially promising feedstock. The North Dakota Geological Survey (NDGS) has collected 324 samples of lignite and carbonaceous mudstone that exceed 300 ppm REE, from 1,706 samples collected from outcrops across western North Dakota. REEs are known to be mobilized by acidic waters during the weathering of clastic sediments. North Dakota lignites are found to be slightly enriched (364 to 910 ppm REE) where they occur below uplands that have experienced long-term, low-intensity modern weathering, and can be enriched (910 to 1,820 ppm REE) or even significantly enriched (over 1,820 ppm REE) where they occur below intervals of intense Paleocene weathering. The first REE-enriched lignite identified by the NDGS was from the Logging Camp Ranch area in Slope County, where several samples from the Harmon, Hanson, and H lignite interval showed elevated REE concentrations. The 768 sample analyses from 165 measured geologic sections in this report detail that initial elevated REE concentrations from the top of the Harmon lignite are very localized, likely the result of upland weathering as the slight REE enrichment is confined to a small terrace. The H lignite bed has been miscorrelated by previous authors, causing the name to previously be assigned to an REE-enriched coal in the Logging Camp Ranch area, but the detailed correlation in this report suggests an overlying, non-enriched lignite is the H bed, and the thinner REE-enriched lignite(s) below are unnamed coals within a zone of weathered strata known as the Rhame bed. The Rhame bed is a 10- to 30-foot (3 to 9 m) thick sequence of kaolinized sediment that was apparently weathered during an extended period of little to no deposition when the climate was much warmer than today, roughly 61 million years ago. Lignites below this thick bed of kaolinite can be significantly enriched in antimony, arsenic, barium, beryllium, germanium, lithium, molybdenum, uranium, and total REE, including the highest dry coal basis concentration (2,792 ppm REE) and dry ash basis concentration (5,642 ppm REE) from this project to date. [ABSTRACT FROM AUTHOR]

10.3390/en14165005 23 Wu J., Fu Q., Zhang J., Sun B. A Fast Calculation Method for Improving the Steering Arm of Mining Trucks with Macpherson Suspension. The study area is made up of thick quaternary alluvium deposited on top of older basement rock, and previous studies, including drilling and geo-electrical resistivity surveys, have been conducted in the area, but none of them managed to conclusively precisely determine the basement rock type and depth. Pilecka et al. [[4]] investigated the impact of high energy mining-induced tremors on building damage in the Upper Silesian Coal Basin (USCB), Poland, by analyzing one of the highest energy tremors (E = 4.0 × 10 SP 8 sp J). Mining is an essential sector for economic development, as it provides valuable resources that are crucial for modern living. [Extracted from the article]

Rock-burst is one of the most serious risks associated with hard rock tunnelling and mining at high depths. Monitoring of acoustic emissions emitted by the rock-mass during excavation and their interpretation now permits the early assessment of failure events and makes the safe management of the construction works possible. A reliable set-up of the alarm threshold is thus fundamental for the correct implementation of the procedures planned to minimise rock-burst related risk. This paper focuses on a novel in situ test specifically developed to provide an experimental basis for a more accurate assessment of the alarm threshold during tunnelling, representative of the local geomechanical conditions. The test, thanks to the compression induced by two flat jacks at the tunnel side wall, produces an artificial failure process during which acoustic emissions are measured and correlated to the mechanical response of the rock-mass, without the typical limitations of scale that characterised the laboratory experiments. The new methodology, named the Mules method, was successfully tested during the excavation of some stretches of the Brenner Base Tunnel in the Brixner granite, affected by mild spalling episodes. The case-history is fully described in the paper to illustrate the practical application of the proposed approach. Highlights: A new in situ test is proposed for the assessment of the rock-burst alarm threshold. The rock-mass is brought to failure at the tunnel side wall by two flat jacks and acoustic emissions are monitored. Two tests were carried out during the construction of the Brenner Base tunnel in a granite formation under high cover affected by mild spalling phenomena. The power spectrum density of the signals recorded during the tests displayed its maximum values before the rock-mass failure. Test results interpreted in terms of power spectrum density summation were adopted to set up the rock-burst alarm threshold during tunnel excavation. [ABSTRACT FROM AUTHOR]

Rockbursts occur as a direct consequence of underground mining or civil excavation. The general scale of their seismic disturbance and consequences depend upon known factors. However, uncertainty remains as to exactly when and where rockbursts will occur, as well as the effectiveness of ground support measures to fully mitigate their consequences. While the uncertainty in when and where is a dilemma shared with earthquake prediction, that associated with ground support capability is both a design and a management concern. Following a brief review of the known mechanisms that produce rockbursts, the paper explores the sources and scales of energy demands that characterize the risk of their damaging consequences upon underground excavations. We note that some of this risk continues to be associated with uncertainty with respect to rockmass properties and in situ stress, particularly in the context of deep mining. A review is presented of all available yielding ground support systems and their necessary design requirements, identifying practical weaknesses and limitations where these are known. The paper concludes with some suggested areas where further study and development could provide the ways and means to reduce the design uncertainty in managing rockbursts. [ABSTRACT FROM AUTHOR]

In mining industries, the prime concern is to overcome the challenges of using conical cutting bits for excavating hard and abrasive rocks. In this research, a speculative investigation was performed to measure the efficiency of rock cutting and identify the wear behavior of aluminum titanium nitride-coated conical cutting bits. A newly designed and customized shaping machine is used with a triaxial force dynamometer to cut the rock samples linearly and to calculate their associated powers. Coated conical bits have a maximum hardness range of 2,291 to 2,459 HV, and uncoated conical bits possess minimum hardness range of 1,945 to 1,948 HV. Two rock samples of fine-grained sandstone with UCS of 83.77 and 97.00 MPa are used in this study. Various cutting ranges were investigated and the best range of cutting parameters are identified between the variables, such as cutting forces and extracted volume of rock, cutting effectiveness, specific energy produced while cutting, and bit wear. The percentage decrease in wear rate of a coated conical bit compared with an uncoated conical bit is 40.36%, 52.28%, and 53.30% for Rock 1 and 42.67%, 54.76%, and 60.90% for Rock 2 under varying depths of cut. The worn surface has been significantly investigated through scanning electron microscopy and energy dispersive X-ray analysis. The output of this study helps in extending the application of a surface miner for excavating harder rocks in mines. [ABSTRACT FROM AUTHOR]

Flame jet-assisted mechanical rock breaking technology is an important method to achieve efficient NECMM (non-explosive continuous mechanized mining) in hard rock mines. Therefore, it is very important to understand the physical and mechanical properties of the spalling pit surrounding rock after flame jet. In this paper, thermal spalling tests were first performed on granite blocks using a flame with a power of 13.6 kW. Then, the mechanical behaviors of the specimens at different distances from the flame jet path were measured. The result showed that the Vp (P-wave velocity), BTS (Brazilian tensile strength), UCS (uniaxial compression strength), and E (Young’s modulus) of granite increased with increasing distance. Meanwhile, the mechanical properties of the specimen at 70 mm were slightly lower than that of the untreated specimen. Therefore, it can be assumed that the damage radius of granite after the flame jet was about 70 mm. In Brazilian test, according to the strain cloud diagram of DIC (digital image correlation) system, the high strain zone expanded from the center to both ends of the specimen, and the strain value gradually increased, eventually forming a through-wall crack along the loading direction. In the uniaxial compression test, AE (acoustic emission) counts within the compacted stage increased obviously as the distance from the specimen to the flame jet path decreased. This phenomenon indicated that the thermal damage of specimens near the center of the spalling pit was more severe, and more microcracks inside the specimens were compacted. The thermal spalling and thermal damage model of the rock under the flame jet was established, which can well explain the changes in mechanical properties of rocks. The fact that thermal damage area of the rock after the flame jet is much larger than thermal spalling area is responsible for the feasibility of flame-assisted mechanical rock breaking. Damage factors based on Vp and E can well describe the weakening of the mechanical properties of granite. The results are important for guiding flame jet-assisted mechanical rock breaking in hard rock mines. [ABSTRACT FROM AUTHOR]