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By M J. Pejovic, S BoÜevski, I Miljanovic, M Hudej, A Milutinovic, A Petrovski

The paper deals with the problem of managing the supplies of consumables (energy resources, lubricants, explosives, explosive supplies, tires, spare parts, etc) in mines. After the introductory remarks and comments, a general stochastic model of supply, relating in general to the dynamic programming method is presented. A selection of stochastic supply model for experiments and research by the authors of this paper is not a coincidence, based on of their long experience, showing that this type of model is the most suitable to provide support for decision-making and management of supplies of consumables in mines.In order for the problem?of?consumables?supply?management to be reviewed, in whole and objectively from the aspect of risk, experimental tests of the stochastic model in real conditions were performed at the limestone open pit mine æZelenikovecÆ near Skopje, the capital of Macedonia. The scope of the experimental research enabled reliable analysis. The results obtained confirm the efficiency and reliability of the stochastic model and two separate manipulative-operational positions regarding its application, which may have an important influence on the optimisation of supplies.

Sep 26, 2011

By M Araos, I Onederra

A novel explosive formulation that substitutes the use of ammonium nitrate (AN) with hydrogen peroxide (HP) as the main oxidising agent has been developed and tested as part of an Australian Coal Industry Research Program (ACARP) project. The main objective was to provide a step-change solution that has the potential to completely eliminate NOx fumes in blasting. The development of this HP/fuel-based explosive started with a comprehensive detonation characterisation program, consisting of unconfined velocity of detonation (VOD) measurements of samples at different diameters, densities and void sensitisation techniques. VOD results showed that the HP/fuel-based explosive mixtures behaved similarly to non-ideal commercial explosives; in that way mixtures could be tailored to achieve specific detonation performance targets. The next stage of testing in this development involved preliminary confined tests to evaluate the rock breakage potential of the HP/fuel-based explosive mixtures. Fully instrumented single-hole tests were conducted in a limestone quarry. Results from these preliminary trials confirmed the rock breakage performance of HP/fuel-based explosive mixtures. The confined VOD measured in one of the tests was 5100 m/s in a 102 mm diameter blasthole at a density of 0.96 g/ml. The corresponding borehole pressure measurement of this HP charge was 2.61 GPa with a detonation temperature of 2921°C. Based on near-field accelerations, both HP and ANFO charges displayed similar attenuation characteristics in the test conditions. Post-blast observations indicated that the breakage performance of the HP mixtures clearly reflected the in-hole detonation performance measurements obtained, confirming the ability of these explosive mixtures to both fragment and effectively displace the rock mass under evaluation. Further research work continues with the future commissioning of a prototype mixing and delivery unit, the successful completion and analysis of data from multiple-hole trials, and further characterisation work associated with product stability, reliability and performance under different geotechnical conditions.CITATION:Onederra, I and Araos, M, 2015. Detonation and breakage performance of a hydrogen peroxide-based explosive formulation, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 565–574 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

There are many compelling reasons why correct sampling schemes should be standard practice in the mining industry, yet there are numerous examples where poor sampling practices are known to exist in the business yet permitted to continue. It is not just technical issues that can be ascribed to the reasons for the continued use of incorrect methods. This paper proposes non-technical reasons why incorrect sampling practices continue, and identifies potential ways to overcome them.

Mar 1, 2010

By R McIlwraith, B Breul

"This paper discusses the successful use of bituminous geomembranes (BGMs) in mining applications since their development in 1974. It explains and illustrates the structure of a BGM composite, which is a geomembrane manufactured by impregnating a polyester geotextile with a compound of bitumen, elastomer and filler. Examples of applications of BGMs in the mining industry are also presented in the following contexts.Storage of solid waste: storage of mining waste at mines in Canada heap leach pads in France, Peru, Chile and Turkey at the base of a mining waste landfill in Brazil capping of solid mining waste in Chile and Canada temporary capping of mining stockpiles in Australia (with possible reuse of the BGM for other works).Examples of the application of BGMs for the storage of liquid waste in mining containment reservoirs in Canada, Guatemala and Peru will also be given.For each example given, reasons are supplied that supported the choice of BGMs by the clients and consultants, drawn from the following advantages of the BGM:BGMs have excellent puncture strength, due to the internal polyester reinforcement, as well as excellent ultraviolet resistance. This often eliminates the need for a cushion geotextile or cover soil over the BGM.BGMs have a very long life expectancy, in excess of 300 years, in subsoil conditions (Breul et al, 2004).BGMs can be installed in very harsh climatic conditions. They are suitable for high wind environments as their heavy mass per square metre makes them resistant to wind uplift. The low coefficient of thermal expansion means that BGMs are suitable for installation in mines where very low or very high temperatures are expected. This reduces construction delays and allows for a quicker use of the mining facility.The fact that the BGM can be installed by the mine’s own workforce, after appropriate training from the BGM manufacturer, allows for a more flexible construction sequence on the mine.Ability of the BGM to connect to other materials such as concrete, steel, rock and other geomembranes that may be on the mine site.The technical advantages of a BGM enabled the engineering consultants to prepare solutions for their mining clients that had a lower environmental risk, had a faster completion schedule and were overall a cheaper option than with a polymeric geomembrane.CITATION:Breul, B and McIlwraith, R, 2015. Bituminous geomembranes in mine construction, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 289–296 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 27, 2015

By D Bruce, D Cox

The main access decline at Carrapateena mine was excavated through two different underground aquifers. In these areas of decline, pressurised water finds the path of least resistance through the rock and into the excavation. In some locations the ground water would upwell underneath the roadway resulting in rapid deterioration of the running surface. The deterioration of the road was so rapid that the two areas of decline required significant roadworks every single shift or it would become impassable by mine traffic. With a full fleet of underground trucks hauling to the surface, managing these sections of roadway was impractical and unproductive. The site team resolved this issue by installing Roller Compacted Concrete (RCC) to the affected sections of decline. RCC is a specialist concrete product that is delivered to the site near dry and is installed using a grader and roller similar to road base. This product can be installed quickly and be trafficked within hours of installation, making it ideal for mines with single access declines and unfavourable road conditions. RCC roadways were successfully installed at Carrapateena mine in conjunction with under-road drainage. These roadways have proved to be a very effective solution which requires minimal maintenance and are resistant to water ingress from the aquifer. This paper discusses the technical aspects of the RCC, as well as the practical implementation of the solution as a whole.

Mar 15, 2021

By J MacNeil, R Dimitrakopoulos

As open pit mining of a deposit deepens, the cost of extraction may increase up to a threshold where transitioning to mining through underground methods is more profitable. This paper provides an approach to identifying an optimal depth at which a mine should transition from open pit to underground mining. The value of a set of candidate transition depths is investigated by optimising the production schedules for each depth’s unique open pit and underground operations. By considering the sum of the open pit and underground mining portions’ value along with the cost of transitioning corresponding to each candidate transition depth, the optimal transition depth can be identified. The optimisation model presented is based on a stochastic integer program that integrates geological uncertainty. As an input, the stochastic integer program utilises a set of several stochastic simulations that represent equally probable scenarios of the mineral resource. This group of simulations describes the uncertainty in the deposit, while the optimiser aims to maximise value based on discounted profits of both the open pit and underground components of the deposit.CITATION:MacNeil, J and Dimitrakopoulos, R, 2014. A stochastic optimisation formulation for the transition from open pit to underground mining within the context of a mining complex, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014, pp 363–368 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 24, 2014

This paper describes techniques that have been used at RixÆs Creek Colliery to control blast vibration from throwblasts that face a residential area 4 km in front of the face. The paper describes blast design, face control including laser profiling, selective loading of blastholes after borehole camera surveys, and techniques used to assess the effect of burden variation, the cumulative effect of drilling and delay sequence, and the effects of meteorology.

Jan 1, 2001

By S Mitra, T Singh, D O’Dea, T Honeyands

Permeability and air flow rate in the bed during iron ore sintering is crucial to controlling the sinter quality and productivity of a sinter plant due to its influence on the flame front speed. In the present work, the permeability of the bed during sintering was analysed by means of measured pressure drop and temperature at multiple points in the bed during sintering. Three different zones were categorised, ie humidified (green) bed, region of maximum resistance (high temperature zone) based on temperature, and sintered bed. Previous work has shown that the maximum pressure drop during sintering was due to several concurrent physico-chemical processes including dehumidification, calcination of fluxes, dehydroxylation of goethite, combustion of coke and melting of granules (>1200°C). To quantify the effect of the different process, sintering experiments were conducted in a milli-pot (diameter 53 mm, height 400 mm) with pressure and temperature measured at same location in bed. The milli-pot was fitted with four equidistant (80 mm apart) taps. Overall, five sections in the milli-pot were analysed for pressure drop at different times during sintering. It was found that in region of maximum resistance, coke combustion and flux calcination were highest contributors with ~35 per cent of the pressure drop when compared to other processes like de-humidification and goethite dehydroxylation which contributed to ~20 per cent and 25 per cent each respectively. The pressure drop contribution of the coke combustion region increased with increasing coke addition rate.

Nov 8, 2021

Two main aspects need to be considered when analysing a potential petroleum development project. Firstly, an estimate of the recoverable reserves must be made, and in many instances, these reserves must serve as collateral to finance development if outside capital is required. Secondly, the likely production profile and cash flow has to be established, and this cash flow then must meet debt service require- ments and in addition generate the required profits. In making these crucial deter- minations, the impact on the project of a wide variety of risks has to be analysed. A computer model, which represents the project in its entirety, is a great aid in determining project viability. Such a model requires imput from geologists, engineers and economists, and interpretation of the model must also be a joint effort. Communications, and inter react ion amongst individuals and disciplines is essential if the best answers are to be obtained

Jan 1, 1983

By Holcombe R. J, Dobos S. K, Little T. R

Blue amphibole-bearing rocks in the North D'aguilar Block of southeast Queensland occur either as relict pods and lenses within regionally extensive greenschist facies phyllites and schists or as blocks entrained in serpentinite-matrix melange. Epidote + crossite-bearing varieties predominate and formed under conditions consistent with underplating and high P:T metamorphism in a subduction-related tectonic environment. Neither lawsonite nor jadeite has been observed and metamorphic conditions are estimated at 380-4500C for pressures of 0.5-0.8 GPa. High P:T metamorphism occurred during the earliest stages of deformation and was superimposed upon protoliths of inferred Late Devonian - Early Carboniferous age, including mafic volcanics, tuffs and coarse volcaniclastic breccias as well as pelagic and henipelagic sediments, all of which have undergone varying degrees of over-printing to the greenschist facies. Greenschist facies metamorphism occurred during the second phase of deformation and was associated with the formation of mainly flat-lying or subhorizontal structures; it followed the cessation of subduction and occurred in response to either thermal relaxation during uplift or the imposition of regional heating induced by crustal thickening and/or synkinanatic granite emplacement. Uplift and cooling of the high P:T rocks was completed by 260-265 Ma and may have occurred in response to the same extensional processes which gave rise to the onset of rifting in the adjacent Esk Trough.

Jan 1, 1990

By M J. Nugus

The structural models developed by exploration and mining geologists are most commonly concerned with the ‘main structures’ or key constituents that pertain to the associated mineralisation. To this end, it is recognised that the geological and exploration models, which are developed, are essentially ‘fit for task’ and the scale-related variances are not always realised at an early stage. In fact, in many cases anomalous intercepts along different trends and of variable apparent continuity have often been neglected as ‘back scatter’ and not important. Recognition of the importance of subordinate structures as mineralising hosts suggests that additional opportunities exist outside the primary and main structures. History shows that opportunities are often not realised where gold is hosted in orientations not parallel to the predominant trend of the schistosity, main fault or shear zone.Another reason for the importance of subordinate structures can be understood from their roles in a percolation network. Subordinate structures can access the large fluid fluxes provided by backbone elements, but, as dangling elements, they provide greater opportunities for gold precipitation mechanisms and hence may constitute essential parts of the resource. Therefore, the role, understanding and consideration of the smaller-scale and orthogonal structures should be considered during all facets of exploration, resource development, delineation and mining.

Aug 22, 2011

By R Robinson

Modem occupational health practice can be described as the fitting of work to the individual and each individual to his job; perhaps a non-traditional way to view occupational health. This two-component description is achieved through the development of programs to implement and monitor specific job procedures, from the monitoring of unwanted exposures to contaminants to the auditing of mine sites. This paper is about such programs. Some attempt must be made to evaluate the effectiveness of the program and several performance indicators which are intended to measure the effectiveness of such a program are offered.

Jan 1, 1994

By H Askari-Nasab, E Torkamani, M M. Badiozamani, S P. Upadhyay, M Tabesh

"Decision-making in mining is a challenging task. Optimal decisions regarding shovel and truck allocations, aligned with the optimal short-term production schedules, are crucial in keeping the operations in line with the company’s long-term objectives. In this paper, we present two main modelling components as the means to achieve near-optimal operational plans: a mixed integer linear goal programming model to allocate trucks and shovels to mining faces over a shift-by-shift basis so that operating costs are minimised and resource utilisations are maximised through the planning horizon a discrete-event simulation model to investigate the behaviour of a truck-and-shovel haulage system in the presence of uncertainty within mining operations. The goals integrated into the mathematical model are to: maximise production minimise deviations from the target head grade minimise deviations in tonnage feed to the processing plants from the desired feed minimise operating cost.The mathematical model provides shovel assignments and the target productions as an input to the discrete event simulation model while meeting the desired goals and constraints of the mining operation. We illustrate the applications of the discrete event simulation model by presenting a large-scale oil sands case study. The main contribution of this work thus far is the development, implementation and verification of a simulation model with a link to optimal short-term mine schedule and extraction sequence of mining faces, which assists in achieving a high level of mine plan compliance across short-term planning and operational planning time horizons.CITATION:Askari-Nasab, H, Upadhyay, S P, Torkamani, E, Tabesh, M and Badiozamani, M M, 2014. Simulation optimisation of mine operational plans, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014, pp 299–312 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Nov 24, 2014

By J C. Koppe, L Vieira

One common problem for blasting in iron ore mines with significant weathering is the occurrence of large blocks of hard rock mixed with softer material. This situation causes a problem for blasting design and sometimes produces large boulders of rock that require a secondary blasting, as well as excavation difficulties. To minimise this situation, geophysical techniques were used to identify the hardest material amid the weathered material. To study the problem, seismic, ground penetrating radar (GPR), electrical resistivity and induced polarisation (IP) methods were used in an intensely weathered Brazilian iron ore deposit. The methods of GPR combined with IP, resistivity and seismic showed to be effective in modelling the contrast among hard, friable materials and soil. The results were used to improve the geological model and create more favourable conditions for the subsequent blast design. The blast design based on geophysical/geological models resulted in significant improvement in the fragmentation of the iron ore. This was achieved by the adoption of a specific drilling pattern for a given geological situation. With the new specialised blasting design the formation of boulders was eliminated.CITATION:Vieira, L and Koppe, J C, 2015. Geophysical techniques applied to blasting design, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 289–294 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By C Preston, T Williams, D Roy

The easiest way to mine valuable orebodies is through the use of explosives and well-planned blasting layouts that produce fragmentation profiles designed specifically for conveyance equipment in underground mines. The design of blasting patterns is specific to not only the explosives being used but also the rock or ore type being fragmented. Many blasting designs are based solely on the experience of those developed for similar orebodies in terms of properties and orientation or individuals that have some blasting experience.The primary technical objective of this paper is to outline a unique methodology for determining underground blasting methodologies (developing specific blasting parameters) commensurate with explosive energies and rock/ore equations of state for a narrow-vein gold property located in Northern Quebec and for underground mines in general.The procedures developed are to define the desired fragmentation specification so that a specific thermodynamic break is generated, taking into account powder factor, energy factor, tonnages, explosive energies and distribution along with blasthole diameter and orebody orientation for a specific set of explosive and dynamic rock/ore properties. Determining dynamic modulus values for the ore using seismic sensors to measure P- and S-wave velocities, the aforementioned parameters will be utilised to set the design constraints to maximise recovery and minimise overbreak and dilution.New underground blasting software (AEGIS) will use thermodynamic break in conjunction with defined fragmentation profiles to create an array of blasting parameters used to design and plan ring layouts. This software will also allow mining planners, prior to drilling and loading a production blast, to appraise future intended blasting patterns to minimise the potential of diluting ore with host rock and the likelihood of damaging mine support structures.CITATION:Roy, D, Williams, T and Preston, C, 2015. Underground stope drill and blast designs optimisation program, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 137–148 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By Khosrowshahi S

The objectives of grade control remain unchanged but new methods are being developed to attain them. Since the early-1990s, an improvement in the power of mine site computers has made the geostatistical tools of conditional simulation more accessible. Optimisation of the grade control process on mine sites now involves two stages: optimisation of the sampling regime and optimisation of the interpretation of ore and waste boundaries. Optimisation of the sampling regime first requires an understanding of the nature of the mineralisation and in particular the impact of particle size on the sampling precision. This relationship, termed the Fundamental Error of sampling, enables an optimum subsampling protocol to be defined for the sample preparation and assaying. However, the actual sample collection method, whether drilling or trenching, must be correctly selected and the sampling grid should be optimised. The relative costs and benefits of various alternative sampling methods and grids can be determined using the method discussed. The use of the grade control data can also be optimised. In the past ore and waste boundaries were often defined using a linear interpolation algorithm that smoothed the data (such as polygonal, sectional, inverse distance squared or even kriging methods). Frequently the relative impact of ore loss and dilution could not be estimated. Conditional simulation to generate equiprobable alternative maps (realisations) can now be adopted to address these issues. A transfer function is then used to evaluate the similarities and differences between the maps. The Ore Block Optimisation (OBO¬) process is a transfer function that produces a three-dimensional model of the optimal ore block outlines. This provides a clear guide for the mining geologist to refine and mine. The nature of the transfer function and the inputs and outputs are discussed. In the past, reconciliation has been the `acid test' for any grade control system. Any ore blocking method based on conditional simulation can make use of the exhaustive data set to ensure that reconciliation between prediction and production will improve significantly. The OBO¬ method provides a guide to the mining geologist to ensure that the best ore blocks are mined. Misclassification between ore and waste is reduced, ore loss and dilution are minimised (and are measurable) and ore is optimally assigned to stockpiles of various cut-off grades. These advantages significantly enhance mine profitability and control of the mined grade.

Jan 1, 1997

By M Nagarajan, S Esen

This paper presents three case studies from three surface coalmines. The first case study is from a coalmine where a dragline operates in 60 m wide and 1 km long strips. Typical overburden height ranges from 30 m to 50 m. The base case blast was modelled using an advanced blasting model (Distinct Motion Code – DMC) to establish the baseline using the blasting parameters in use before optimisation. DMC was used to model the alternative blasting scenarios to obtain the following key objectives:the post-blast muck pile profile was required to have an optimum height of ~28 moptimise cast percentageachieve a well-fragmented muck pile for the draglinethe muck pile profile should be appropriate for the dragline entry into the strip.Achieving these objectives would optimise the dragline performance through reducing rehandle and improving advance along the strip. DMC modelling resulted in the following outcomes:the required muck pile profile could be achievedthe cast percentage increased from 21.1 to 25.1 – a four per cent increaserehandle volumes were reduced.Establishing a good quality assurance / quality control (QA/QC) process was essential to delivering a blast that could achieve these outcomes. The blast was fired successfully and the dragline completed the strip approximately two weeks ahead of the time taken for the previous strip.The second case study is from a coalmine where D11 dozers are used to move the blasted material to the spoil. An optimum profile was required for the dozers for this low-cost mining operation. To achieve this, an electronic blasting system (uni tronicTM 600) was introduced to optimise the muck pile profiles being delivered. The new muck pile profiles showed improved cast percentage from 10.6 per cent to 17.8 per cent. The changes in the muck pile centre of mass displacement improved dozer efficiency as a result of pushing material shorter distances to its final position. Dozer productivity (bcm/h) statistically did not change but coal was being exposed at a faster rate.The third case study summarises the results from a site where dozers are used to minimise the total mining cost. Traditionally, excavators had been used on-site with conventional blast designs. After firing the first cast shot, the blasted material was found reasonably well-fragmented. Although dozing productivity hasn’t been quantified on-site, operators were providing positive feedback (easier push) due to the reasonably good muck pile profile suiting to the dozers. This site also realised significant savings with the dozing as compared to their truck/shovel operation.CITATION:Esen, S and Nagarajan, M, 2015. Muck pile shaping for draglines and dozers at surface coalmines, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 409–416 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By X L. Liu, W Huang, J M. Zhu, S L. Wu

The shape, position and thickness of the cohesive zone have a great influence on the operational performance of the blast furnace. Many researchers have found that the high temperature properties of iron ores determine the formation of the cohesive zone. The results of this work show that sinter of high basicity interacts with lump ores and acid pellets due to the difference in chemical compositions. The softening and melting properties and the primary slag formation behaviours in the cohesive zone are improved by the high temperature interactions. The high temperature interaction is mainly influenced by the chemical compositions, porosity, interfaces and so on. Although the softening and melting properties and primary slag formation behaviours of lump ore A (a typical limonite lump ore from Australia) is the poorest of the iron ores studied, the high temperature properties of integrated burden A (consisting of sinter and lump ore A) is no worse than the other integrated burdens due to the high interaction between the sinter and lump ore A. It is useful to apply the results in the optimisation of blast furnace burden.CITATION:Liu, X L, Wu, S L, Huang, W and Zhu, J M, 2015. High temperature interactivity of iron ores in the cohesive zone of the blast furnace, in Proceedings Iron Ore 2015, pp 363–366 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By D M. Brady

Underground coal mines in Australia have embraced the use of various inertisation techniques both proactively and reactively. The use of such techniques can have a significant influence on ratios and trends used to monitor the status of the underground environment. Whilst control strategies should never be ignored in favour of preserving the integrity of ratios, the influence and significance of the changes likely to be seen should be anticipated and understood for reliable interpretation of the situation. This paper looks at the influence inertisation techniques can have on results and subsequent interpretation.CITATION:Brady, D M, 2013. The influence of inertisation techniques on gas interpretation, in Proceedings The Australian Mine Ventilation Conference , pp 259-264 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By J Rutter, E Amini, D La Rosa, N Beaton, M Scott, F Faramarz, L Keeney

Anglo American’s Los Bronces copper mine in Chile has been conducting detailed assessments investigating value adding options for their asset. The mine has conducted several detailed Mine-to- Mill and Grade Engineering studies to investigate increased throughput and head grade and to quantifying the impact of these approaches across the life of mine. CRC ORE has two key technologies namely Grade Engineering and the Integrated Extraction Simulator. These two technology suites have been combined to understand the technological landscape and associated value drivers suitable for application at Los Bronces. Detailed ore characterisation test work was conducted to:  measure and spatially model the propensity of ores to naturally deport and  develop customised blast models for Mine-to-Mill and Grade Engineering evaluation The outputs of this work were utilised to develop a block model populated with a range on new Grade Engineering and blasting parameters suitable for scenario analysis. To facilitate scenario analysis a high-fidelity value chain model of the Los Bronces operation from blasting to concentrate production was built in IES. IES was combined with sophisticated analytical tools such as Neural Networks to develop and reconcile a fully integrated value chain. The value chain model made it possible to simulate in IES all available blocks in the block model to predict throughput and grade changes for different strategic scenarios. The scenario analysis was run across 24 strategic combinations of Mine-to-Mill and Grade Engineering and comprised several million simulations. The scenarios investigated each technology independently and jointly to provide an attributed block model that can feed forward into technoeconomic modelling to determine optimal execution strategies for the mine. This paper presents the first published study combining Grade Engineering and IES to provide mass simulation capability to investigate strategic options for a mining asset.

Nov 10, 2020