Narrow Vein Mining Research Articles

Underground Rock Mass Behavior Prior to the Occurrence of Mining Induced Seismic Events

The variations of seismic velocity prior to the occurrence of major seismic events are an indicator of the rock mass performance subjected to mining-induced stress. There have been no prior field-scale studies to examine stress change within the rockmass volume immediately prior to potentially damaging mining-induced seismicity. Monitoring stress change is critical for mine stability and operation safety and eventually improves production by optimizing mine designs and mining practices. In this study, five major seismic events that occurred in a narrow-vein mine were used as case studies in order to investigate any significant changes in P-wave velocity distribution, on a daily basis, within a week of seismic events with Mw > 1; if observed, such changes could provide a warning to mine engineers and workers. It was observed there was no consistent significant velocity change of more than 1% within 200 m of the hypocenters within 6 days prior to the events. Additionally, the influence of blasting in the week of the occurrence of events was investigated however no recognizable trend was observed between blasting and changes in the seismic velocity distribution within the rock mass on the day of a blast or the following day.

Seismic imaging of a near-vertical vein using controlled-source seismic interferometry

New methodologies for narrow-vein mining are making thin, steeply dipping mineralized veins economically viable mining targets. Drilling is the normal method for delineation and resource evaluation prior to mining. However, for the evaluation of narrow veins, significant drilling of barren rock is required. Controlled-source seismic interferometry has the potential to significantly decrease the costs of target delineation by providing high-resolution seismic images of thin, steeply dipping mineralized veins. We present a case study that employs seismic interferometry in conjunction with a walkaway vertical seismic profiling survey to image a thin (0.5–4 m), steeply dipping barite vein. The footprint of the seismic data acquisition is relatively small and compatible with operations in areas with limited access (e.g., mining camps). The technique requires some care with experimental design and data processing, but it is clearly demonstrated to produce a high-resolution seismic image. Furthermore, we demonstrate that inversion of the depth-migrated image can be used to quantify vein thickness and provide direct information for resource evaluation and reserve estimation.

Time-Dependent Monitoring of Seismic Wave Velocity Variation Associated with Three Major Seismic Events at a Deep, Narrow-Vein Mine

One of the most difficult challenges in underground mining is to forecast significant seismic events prior to their occurrence in order to support the safety of miners and to minimize damage to the underground operation. Passive seismic tomography is a tool to image the seismic velocity changes in a rockmass, which can potentially reveal the rockmass behavior before and after a significant seismic event. In this paper, the changes in seismic velocity of the rockmass before and after three major seismic events are investigated to determine whether there are identifiable precursory velocity changes associated with the major seismic events. Conventional mechanics imply that the induced stress at the hypocenter would continue increasing until failure, in the form of an induced seismic event, occurs. With passive seismic tomography we can image changes to the seismic wave velocity distribution within a rockmass and hence infer the changes to the induced stress near the hypocenter. This paper evaluates the hypothesis that induced stress at the hypocenter (as inferred by the p-wave velocity) increases until the seismic event occurs. In addition to analyzing p-wave velocity changes near the hypocenter, changes to the p-wave velocity at “zone centers” were also analyzed. These “zone centers” are regions within the rockmass that consistently have a p-wave velocity that is much higher than the average p-wave velocity for the rockmass. It is found that the p-wave velocity did not increase at any of the three hypocenters prior to the seismic event occurring, however the p-wave velocity did increase in the closest “zone center” for two of the three events.

Empirical and Numerical Finite-Element-Based Model to Improve Narrow Vein Mine Design in Peruvian Mining

This paper proposes a numerical finite-element-based model aimed at optimizing narrow-vein stope stability. This model combines empirical and numerical methods to develop a sequence, which may determine an acceptable stope safety factor. A stope stability analysis was conducted through the Mathews stability graph method, which requires two factors: the hydraulic radius (HR) and stability number (N’). The Mathews stability graph method is used to assess the stability of an underground design. Variations in stope dimensions are estimated by changing the HR and Factor A within the N’, which is determined through numerical methods. The results of the numerical simulation indicate that the HR increases with an increase in stope dimensions, while Factor A maintains an inverse relationship with the maximum stress induced on the excavation walls. This document demonstrates the potential of combining empirical and numerical methods in stope design optimization, especially when developed in small narrow vein mines.

Опыт применения низкопрофильной роботизированной погрузо-доставочной машины XLPD при отработке маломощных пластообразных рудных тел Рудника № 8 ПАО «ППГХО» им. Е.П. Славского»

Опыт применения низкопрофильной роботизированной погрузо-доставочной машины XLPD при отработке маломощных пластообразных рудных тел Рудника № 8 ПАО «ППГХО» им. Е.П. Славского»

Thermal Fragmentation as a Possible, Viable, Alternative Mining Method in Narrow Vein Mining?

In currently used mining methods, blasting techniques often causes dilution of valuable ore and results in costly processing requirements. In the context of narrow vein mining of thin and highly concentrated orebodies there is a need of a mining method that can reduce dilution in order to remain economically viable. This research project explored the viability of a new mining technology, thermal fragmentation, in narrow vein mining. Thermal fragmentation technology uses a flame jet to produce extreme heat that spalls the surrounding rock to a strategically located drill hole, as an alternative to traditional blasting. This paper creates a net present value (NPV) model of a mining method using thermal fragmentation, as well as for an existing method used for narrow vein mining; comparisons and evaluations were made regarding the feasibility of the new technology. It was found that while overall costs for thermal fragmentation were relatively high, reductions in wages, haulage and processing costs, as well as increased productivity and ore recovery, meant that the new method would improve the financial performance of any operation. These results identify that there is an opportunity to introduce the thermal fragmentation technology to narrow vein mines within Australia, in order to lower costs and increase profit.

Application of Thermal Fragmentation in Australian Hard Rock Underground Narrow-Vein Mining

This paper presents the results from the investigation of the application of thermal fragmentation in Australian hard rock underground narrow-vein mining. Two geologically similar samples from an underground narrow-vein hard rock gold mine were collected to obtain a measure of the technology’s ability to recover ore by the creation of large thermal openings to assess the applicability of the thermal method. Particle size distribution showed a higher generation of fine product, − 2 mm, by thermal fragmentation compared with selective blasting by 31%. The Bond work index for thermal ore (12.62 kWh/t) is half to that of the blasted ore value (25.32 kWh/t). The average grindability obtained for the thermal ore sample was greater than the blasted sample by a factor of 2.44, a higher value indicating a decrease in the energy required to grind. The thermal fragmentation method generates product with higher dissolution of gold in cyanide, by 14% for the − 9.5 + 2 mm size fraction samples. Additionally, the thermal fragmentation results in higher production of − 9.5 + 2 mm material by 15 % compared with selective blasting.

Factors Influencing Stope Hanging Wall Stability and Ore Dilution in Narrow-Vein Deposits: Part 1

Unplanned ore dilution negatively affects overall mine profitability by increasing operating costs (e.g., mucking, haulage, crushing, hoisting, milling, waste treatment, and low-grade ore upgrading). Eliminating ore dilution requires identifying and controlling the major causal factors, which are related to in-situ stress regimes, depth of stope undercut, ore dip/orientation, stope geometry, and quality of the host rock mass. In-situ stress regimes and depth of stope undercut were examined in a previous publication (see Part I). The results showed that the stability of the stope hanging wall significantly deteriorates when in situ stress regimes and depth of stope undercutting of the access drift increase. Conversely, the extent of plastic zones increases with such an increase. Also, the depth of stope undercutting has no impact on the deformation development of the rock mass. The objective of this paper is to assess stope hanging wall (HW) stability and ore dilution with respect to ore inclination and stope geometry in sublevel, open stoping, narrow-vein mines. A series of two-dimensional elasto-plastic numerical models was built to examine the effect of ore dip angle and stope geometry (height and width) on stope HW stability and ore dilution in a highly stressed environment (in-situ stress ratio = 2.5). The results are presented, discussed, and compared in terms of depth of relaxation zones, extent of plastic failure zones, and total displacement with respect to four stope dip angles (45°, 60°, 75°, and 85°), three stope widths (5, 7.5, and 10 m), and three stope heights (20, 30, and 40 m). Results show that stope HW stability improves when ore dip angle increases (i.e., steeply dipping ore deposits) because the depth of relaxation zones and extent of failure zones decreases. Dip angle had a negligible effect on HW deformation. Less dilution occurred at very steep (85°) inclination angles. At different ore dip angles, stope HW stability greatly deteriorated with increasing stope width and improved with decreasing stope height.

Cemented Paste Backfill Geomechanics at a Narrow-Vein Underhand Cut-and-Fill Mine.

Underhand cut-and-fill mining has allowed for the safe extraction of ore in many mines operating in weak rock or highly stressed, rockburst-prone ground conditions. However, the design of safe backfill undercuts is typically based on historical experience at mine operations and on the strength requirements derived from analytical beam equations. In situ measurements in backfill are not commonplace, largely due to challenges associated with instrumenting harsh mining environments. In deep, narrow-vein mines, large deformations and induced stresses fracture the cemented fill, often damaging the instruments and preventing long-term measurements. Hecla Mining Company and the Spokane Mining Research Division of the National Institute for Occupational Safety and Health (NIOSH) have worked collaboratively for several years to better quantify the geomechanics of cemented paste backfill (CPB), thereby improving safety in underhand stopes. A significant focus of this work has been an extensive in situ backfill instrumentation program to monitor long-term stope closure and induced backfill stress. Rugged and durable custom-designed closure meters were developed, allowing measurements to be taken for up to five successive undercuts and measuring closures of more than 50 cm and horizontal fill pressures up to 5.5 MPa. These large stope closures require the stress-strain response of the fill to be considered in design, rather than to rely solely on traditional methods of backfill span design based on intact fill strength. Furthermore, long-term instrument response shows a change in behavior after 13-14% strain, indicating a transition from shear yielding of the intact, cemented material to compaction of the porosity between sand grains, typical of uncemented sand fills. This strain-hardening behavior is important for mine design purposes, particularly for the use of numerical models to simulate regional rock support and stress redistribution. These quantitative measurements help justify long-standing assumptions regarding the role of backfill in ground support and will be useful for other mines operating under similar conditions.

A feasibility study on confinement effect on blasting performance in narrow vein mining through numerical modelling

Due to the limited free face in narrow-vein stoping, blasting is usually subjected to excessive confinement effect that often result in difficulties in ore loss and dilution. The aim of this study is to analyze the blasting confinement mechanism in narrow-vein mining, and to quantitatively define the confinement effect. The PFC and LS-DYNA numerical modelling programs are combined to investigate the effect of blasting-induced stress waves and detonation gas effects. A confinement coefficient in narrow-vein mining is introduced and defined as the ratio of the blasting crater volume or area formed in an infinite free face to that in a confined face. The blasting confinement coefficient is used to rate the confinement severity. On this basis, the effects of minable width and burden on the confinement coefficient are analyzed. The numerical simulation results indicate that the confinement coefficient decreases with increasing minable width for a given burden. The relationship between the minable width and the confinement coefficient can be described by a first-order exponential decay function. For a given minable width, the confinement coefficient increases with increasing burden. The relationship between the burden and the confinement coefficient can be expressed by a first-order exponential growth function. Based on the numerical modelling results, a design chart for the blasting confinement effect in narrow-vein mining is introduced as a guide for preliminary design of narrow vein blasting to optimize production by reducing overbreak (dilution) and underbreak (ore loss).

MATCHING MACHINE DESIGN TO THE PRODUCTION PROCESS: A CASE STUDY IN THE INTEGRATED DESIGN OF MOBILE EQUIPMENT AND MINING METHODS

Underground mining imposes very rigid constraints on mobile equipment design. The choice of a particular mining “method” – i.e. the specific mix of techniques for excavation, ground support, and materials handling – is greatly influenced by the nature of the ore body being exploited. Mining methods tend to be fairly conservative, relying upon well established and proven equipment designs. In order to improve worker safety and productivity, South African platinum mines have increasingly turned to mechanization. An added benefit of these mechanization efforts is that the nature of the mining can be modified based on the feasible equipment designs. These efforts have resulted in changes to the mining methods employed in South Africa’s narrow-reef platinum group metal (PGM) ore bodies, as well as the development of a suite of mobile equipment which enables implementation of the new production processes. This paper focuses on the design and development of one of these machines - a narrow-reef bulldozer suited to selective mining. The resulting machine is a miniature unmanned bulldozer and multipurpose crawler platform designed for narrow-vein mining applications, with integrated mechatronics and remote control capabilities. This paper will discuss the development of the machine and the applications for which it was designed.

Development of benchmark stoping widths for longhole narrow-vein stoping

In narrow vein mining it is often not possible to limit stope width to the vein width when utilising blasting for rock breakage. A probabilistic benchmarking method is used to estimate benchmark stability stoping widths and benchmark average stoping width for three commonly used narrow vein longhole blast patterns. Average stoping widths for inline, staggered and dice-5 blast patterns have been estimated at 1˙3, 1˙5 and 1˙7 m respectively. Average stoping width can be used to assess planned and unplanned dilution. Additionally, a concept termed the benchmark stability stoping width has been defined and quantified for the three blasting patterns. Stability stoping widths for inline, staggered and dice-5 have been estimated at 1˙6, 2˙0 and 2˙1 m respectively. Narrow vein stopes within these limits after blasting can be regarded as stable.

Practical aspects of mineral resources and ore reserves measurement and accounting

Mineral resources and ore reserves estimation, mine planning, measurement of mine and plant performance and the reconciliation of production results with original expectations are continuous processes during the operation of a mine. These activities involve members of several disciplines over an extended period. Although operating conditions, policies and personnel may change, estimating and reporting practices must be applied consistently to achieve accuracy in periodic evaluations and reconciliation.Operational practices are considered against the background of refinement of the definitions of 'resources' and 'reserves' in an effort by mining and regulatory institutions to achieve conformity. The examples relate to underground gold mining, but the principles are adaptable to other situations. Many elements of the systems described are in place at some operations, but may not be consistently used. At other mines systems may be modified on an ad-hoc basis, with the result that not everyone understands them or some may misinterpret the data. This may have serious consequences when ownership or key staff changes occur or third parties have to interpret inconsistently stated resources, reserves and production data—for example, during due-diligence studies.The monitoring of resources and reserves estimation efficiency and the effective reporting of trends are discussed. Some standard terms and ratio definitions are noted that can be adapted for most situations, and the verified mineral resource estimate is suggested for use as an internal tool to provide an ultimate mineral resource check from observations made immediately before mining takes place. The importance of realistic planning and tracking of both stoping and development material and their contributions to production is stressed, especially in narrow-vein mines, where planning and control of development ore output and quality can have a major effect on extractive performance. The translation of resources to reserves, the treatment of 'not-in-reserve' ore and the accounting of remnant ore reserves are discussed, as are shaft call and plant call factors, which combine to create the more familiar mine call factor. Ore-reserve reconciliation procedures are outlined that comprise two stages: the results of the ongoing resources and reserves estimation and monitoring, followed by the accounting of additions and depletions from the reserves due to exploration, mining and changing conditions. Procedural flowcharts and suggestions for reporting formats are included.

Narrow vein mining 1 - steep veins: T. Brewis, Mining Magazine, 173(3), 1995, pp 116–130

Narrow vein mining 1 - steep veins: T. Brewis, Mining Magazine, 173(3), 1995, pp 116–130

Narrow vein mining 2 - flat-lying veins: ANON, Mining Magazine, 173(3), 1995, pp 131–133

Narrow vein mining 2 - flat-lying veins: ANON, Mining Magazine, 173(3), 1995, pp 131–133

Blasthole stoping in narrow vein mining : Lizotte, Y CIM BullV84, N945, Jan 1991, P35–41

Blasthole stoping in narrow vein mining : Lizotte, Y CIM BullV84, N945, Jan 1991, P35–41

Alimak narrow vein mining at the Dome Mine : Robertson, B E; Vehkala, J T; Kerr, S S CIM BullV83, N938, June 1990, P63–66

Alimak narrow vein mining at the Dome Mine : Robertson, B E; Vehkala, J T; Kerr, S S CIM BullV83, N938, June 1990, P63–66

Application of longhole drilling methods for narrow vein mining : Larsen, P; Cyr, R; Quesnel, W CIM BullV83, N937, May 1990, P35–40

Application of longhole drilling methods for narrow vein mining : Larsen, P; Cyr, R; Quesnel, W CIM BullV83, N937, May 1990, P35–40

Alimak narrow vein mining at the Dome mine : Robertson, B E; Vehkala, J T; Kerr, J S Min MagNov 1989, P393–395

Alimak narrow vein mining at the Dome mine : Robertson, B E; Vehkala, J T; Kerr, J S Min MagNov 1989, P393–395