what is open-pit mining? (with picture)

what is open-pit mining? (with picture)

Just like the name suggests, open-pit mining is a type of mining operation that involves the digging of an open pit as a means of gaining access to a desired material. This is a type of surface mining that involves the extraction of minerals and other materials that are conveniently located in close proximity to the surface of the mining site. It differs from other types of mining processes that may require the digging of underground tunnels a long distance from the surface in order to reach the material. One of the advantages of the open-pit mining system is the fact that it is not as capital or labor intensive as the underground method of mineral or precious metal and stone extraction.

The process of open-pit mining is precipitated by the analysis of the area in order to determine the presence of the desired material that may be coal or ore. If it is determined that the desired materials are present in the area, the next step would be to calculate the stripping ratio of the mining process, meaning that even though ore, coal or another desired material may be present, the profitability of mining it has to be ascertained. This may be done by calculating how much of the surface material obstructing the mineral of choice has to be moved in order to reach the desired material. Generally, the less effort it takes to extract whatever material is in the sites, the more the mining company stands to gain in terms of profit as a consequence of the fact that the material and labor investments will be reduced. The stripping ratio in open-pit mining is important because the profitability of that particular mining venture hinges on the ability of the company to gain more from the extraction process than what it expends in order to obtain access to the material.

Usually, the open pit-mining system is one that is based on simplicity due to the fact that it merely requires the shifting of whatever material is covering the deposit. This process may be expedited if the top material is made up of easily maneuverable material, such as coarse sand, as opposed to rocks that may require more specialized equipment to break down and move them from the site. After a while, the profitability of such mines will decrease since the materials that are closest to the surface will have been mined.

@pastanaga - There are advantages and disadvantages in every kind of mining process, but I'm not sure in a lot of cases that mining is necessary at all. That's the best means of ensuring that no one gets sick or that the environment maintains its integrity, after all.

@browncoat - Actually, open pit mining can be better than the alternative, as long as it's done well. For one thing, it isn't always done on pristine forested glades and usually there is a condition in the planning that the company involved has to fill in the pit when they're done and plant over it. So the land could end up being better than it was when they started. And mining is extremely dangerous when you dig down under the ground instead of into it. Open pit mining might not be completely safe, but it's safer than having deep tunnels that will probably never be filled and may contain dangerous gases or become unstable over time.

And mining is extremely dangerous when you dig down under the ground instead of into it. Open pit mining might not be completely safe, but it's safer than having deep tunnels that will probably never be filled and may contain dangerous gases or become unstable over time.

Open pit mining is just so destructive and awful I don't know how it can be allowed anywhere, let alone in the places it's often done. They basically just strip off huge chunks of land so that nothing can grow there and in the process they end up polluting nearby water supplies and disrupting every other local natural process, since they use loud, obtrusive machinery. The pollution tends to be heavy metals that take forever to leave the ecosystem and cause all kinds of problems in any creature that encounters them. Basically, it's the kind of exploitative resource gathering that ensures our grandkids are going to think we were complete idiots with no regard for our own health and wellness.

The pollution tends to be heavy metals that take forever to leave the ecosystem and cause all kinds of problems in any creature that encounters them. Basically, it's the kind of exploitative resource gathering that ensures our grandkids are going to think we were complete idiots with no regard for our own health and wellness.

twechar | coal mining

twechar | coal mining

A mining community was established in Twechar in the 1860s with the sinking of two main pits, Twechar and Gartshore, by the somewhat infamous William Baird & Co. The village developed as a result of its position at the northern limit of the vast Lanarkshire coalfield, with 12 shafts eventually being sunk. Mining continued in Twechar until the 1960s, and miners from the area then travelled to other local pits until the closures which followed the miners strike of 1984-5. While much of Twechars history is typical of the situation across Scotland, there is also much that is unique. Bairds had their huge headquarters here, which trained apprentices and contained workshops for most of the trades that manufactured and supplied the whole organisation. Those trades included engineering, blacksmithing, joinery, electricians, painters, slaters, chimney sweeps and transport. To increase transport speed and efficiency, Bairds created their own railway network that spread out from Twechar across Lanarkshire. Notably, the Bevin Boys came here, from across the whole of Scotland, to learn about mining in a training pit that was linked to the local school. Through the housing that was made available for miners, managers, and the administrative and clerical staff, the village was and still is a microcosm of the social class system of its day.

Whilst there is a commonality of cultural traditions and social conditions in coal mining communities across Scotland, Twechar was distinctive because it was home to the headquarters of one of the largest mining companies working in the Lanarkshire coalfield, and because it employed a huge number of people across a wide diversity of trades, which is not typical of most mining villages. However, when the industry that utilised all these skills suddenly disappeared, the resulting mass unemployment is shared with mining communities throughout Scotland and many parts of the UK.

Small scale coal mining has existed in Scotland since the 12th century, though it was James Watts development of the steam engine, in the 18th century, that boosted demand for coal and accelerated moves towards industrialisation. Together with other railway and industry developments in the 19th century, the demand for coal further increased, which eventually led to the exhaustion of shallow seams and necessitated extraction from deeper deposits.

It was not unusual to find whole families working down the pit. Hewers were the most skilled workers and were paid by the amount of coal carried to the surface. They often paid their wives and children to carry the coal to the pit top so that they could concentrate on digging it out. Everyone who worked in the pits laboured hard and worked long hours. The Mines Act of 1842 ostensibly put an end to women and children under the age of 10 from working under ground and introduced the first pit inspectors. Yet mining remained a notoriously dangerous occupation and fatalities, injuries and dust-related diseases were not uncommon.

Mining provided common employment throughout East Dunbartonshire, where mines extended from Baljaffray in the west, to Twechar in the east. Coal was the most common mineral extracted locally, but limestone and ironstone were also extensively mined, and the presence of alum shale led to the building of a chemical processing works at Campsie to process the alum for use in the textile industry. The 'Secret Works', as it was known, was a major employer in Lennoxtown for most of the nineteenth century.

Early mines followed an angled seam from its protrusion on the surface; miners then excavated the mineral seams at progressively deeper locations. Perpendicular pit shafts were also sunk from an early date, with crude winding mechanisms used to lift the elements to the surface. Modern collieries were established during the second half of the nineteenth century, some of them employing many hundreds of men.

The most important coal-owner was the firm of William Baird & Company, which came to the Twechar area about 1860 and developed extensive mining operations to supply coal and coke to its Gartsherrie iron-smelting works at Coatbridge.

Twechars proximity to the Forth and Clyde Canal, as well as the abundant seams of coal, were also key factors in Bairds decision to sink pits in the area. Twechar No.1 Pit, was sunk on the north bank of the canal, to the east of Twechar Bridge, with 12 shafts eventually being sunk. With the arrival of Bairds and due to its location at the northern limit of the vast Lanarkshire coalfield, a mining community was firmly established in Twechar.

While much of Twechars history is typical of the situation across Scotland, there is also much that is distinctive. Bairds established their huge headquarters here, which trained apprentices and contained workshops for most of the tradesmen that manufactured, maintained and repaired supplies for the whole organisation. Those trades included engineers, blacksmiths, joiners, electricians, painters, slaters, chimney sweeps and transport workers. Notably, the Bevin Boys came here during WWII, from across the whole of Scotland, to learn about mining in a training pit that was linked to the local school.

Despite bringing much employment to the area, Bairds was very much disliked by mining communities, who deplored its treatment of workers and their families, particularly when those folk fell on hard times. The animosity towards Bairds continues to this day, even though the National Coal Board took over all the pits in 1947, and was perhaps most noticeably observed when Twechar folk petitioned hard against plans to name a village street after William Baird.

Nonetheless, industrialised mining activity continued in and around Twechar for almost a century. Twechar No.1 Pit closed in 1964, while Gartshore 9/11, the very last colliery in the area, was shut in 1968. Following this closure some Twechar men travelled each day to collieries such as Bedlay and Cardowan in Lanarkshire, until those pits, too, were closed, during the early 1980s.

Many reminders of the mining industry can be seen today, from bings (spoil heaps) to fenced-off shafts. Unfortunately, subsidence of the ground above former mine workings sometimes occurs, as at Grampian Way, Bearsden, in 1982, when a huge hole appeared in the ground above a former mining works.

how is coal mined and extracted? | plante nergies

how is coal mined and extracted? | plante nergies

Depending on the depth of the depositAn accumulation of natural resources, such as oil, natural gas, coal, uranium, metal ore or another commodity... , coalCoal is ranked by its degree of transformation or maturity, increasing in carbon content from... is extracted from underground or open-pit mines. In underground mines, vertical shafts are sunk and then galleries excavated horizontally. In open-pit mines, benches are drilled to allow trucks to circulate.

Conveyors or cars (railway wagons) transport the coal to vertical shafts for removal from the mine. After the coal is brought up to the surface by conveyors, it undergoes a process thatremoves sand and mud by immersing the coal in a solution of water and tiny magnetite particles. The different elements separate naturally. The coal floats while the other ores, called tails, sink to the bottom.

There are hazards, however. Galleries can flood or collapse, or fine particles of coal dust in the right concentration can explode and produce intense radiant heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... . Fire damp explosions can also occur. They are caused by undetectable pockets of methane (ch4)The main component of natural gas deposits and oil deposit gas caps. Methane is produced naturally by landfills... , mixed with the air in the galleries, that are highly combustible. Almost 1,800 miners have died in France in coal mining disasters since 1876. More than 6,000 miners died in China in mining accidents in 2004, while 301 were killed in a mining accident in Soma, Manisa province, Turkey on May13,2014. And between February 25 and 28, 2016, 36 miners were killed by a series of methane explosions in a coal mine in Vorkuta, Russia, more than 100 kilometers north of the Arctic Circle.

An open-pit coal mine is a huge hole in the ground with terraces along which earth-moving vehicles excavate seams. It looks a bit like a sports stadium. The largest open-pit mines are several kilometers long and hundreds of meters deep.

First of all, the layer of earth overburden above the first coal seam has to be removed. (The seam can be up to 200 meters below the surface.) All the earth around the base of the seam is removed before extraction begins. When the hole is large enough, the miners dig down to the next layer of coal. Each layer is called a bench.

Huge excavators extract the coal. The biggest of these machines is 240meterslong (longer than two soccer stadiums) and 96 meters high (equivalent to a 38-story building). The buckets on the excavators can hold up to 300metrictonsofrock.

Open-pit mining costs less than underground mining and is therefore more profitable in terms of productivity. Working conditions in these mines are also much safer. However, open-pit mining is less acceptable from an environmental standpoint, because it disfigures the landscape and causes dust pollution.

phase planning for open pit coal mines through nested pit generation and dynamic programming

phase planning for open pit coal mines through nested pit generation and dynamic programming

Xiaowei Gu, Qing Wang, Xiaochuan Xu, Xiaoqian Ma, "Phase Planning for Open Pit Coal Mines through Nested Pit Generation and Dynamic Programming", Mathematical Problems in Engineering, vol. 2021, Article ID 8219431, 8 pages, 2021. https://doi.org/10.1155/2021/8219431

This paper presents a phase planning method specially designed for coal deposits with nearly horizontal, bedded coal seams. The geology of this type of deposit is modeled into a column model, instead of a block model, to avoid coal-rock mixing in blocks. A nested pit generation algorithm is developed for producing a series of nested, least-strip ratio pits with a column model as its input. The algorithm completely overcomes the troublesome gap problem. Taking the least-strip ratio pits as possible phase states, a dynamic programming formulation is proposed to simultaneously optimize the number of phases, the phase-pits, and the ultimate pit, with an objective of maximizing the net present value. The merits and capability of the proposed method are demonstrated through a case study on a large coal deposit.

Large open pit mines are often mined in a number of phases, with intermediate pits for the phases referred to as phase-pits or pushbacks. The phases must be carefully planned since they provide a long-term strategic guide for the sequential development of a mine and for detailed production scheduling. In designing the phases, three elements must be determined: the number of phases, the phase-pits, and the ultimate pit. These elements are interrelated and should be simultaneously optimized to maximize the net present value (NPV) of an open pit project.

Phase optimization, unlike production scheduling, has not been an extensively studied topic in open pit planning in recent years, and most of the research work had been done before the turn of the century. Lerchs and Grossmann first introduced the parametric analysis approach, where the block values of the block model are systematically changed and a pit optimization algorithm is executed repeatedly to obtain an optimal pit each time after the block values are changed, producing a series of nested pits [1]. These pits can then be evaluated to choose the appropriate phase-pits. Technical parameterization of reserves is another method for nested pit generation, with an objective of finding the family of technically optimal pits. A technically optimal pit for a total volume, V, and ore quantity, Q, is the pit that has the highest quantity of mineral of interest among all pits of the same V and Q. A number of authors have elaborated on the mathematical formulations and solution algorithms for technical parameterization of reserves [27]. Dagdelen and Johnson formulated the pushback optimization problem into an integer programming (IP) model and used Lagrangian relaxation for solution [8]. All these methods have an inherent gap problem; that is, the size increment between two consecutive pits can be very large. Big gaps can inflict serious difficulties when the pits are used for phase planning or production scheduling, with the resulting solution far from the optimal or with no feasible solution at all. To overcome the gap problem, Wang and Sevim proposed a heuristic algorithm using a cone eliminating process [9]. The algorithm is capable of finding a series of nested, maximum-metal pits with a pit increment almost the same as the user specified value and, thus, completely eliminates the gap problem. Meagher et al. formulated the pushback optimization problem as an IP model [10]. To facilitate the solution process and to overcome the gap problem, they solved the linear programming relaxation version of the IP model first and, then, applied a method known as pipage rounding to convert a fractional solution into an integral solution. The authors claimed that their approach completely overcomes the gap problem.

One of the most significant developments in the related and wider area of open pit planning, over the last two decades, is probably the incorporation of geological uncertainty in planning schemes. Conditional geostatistical simulation techniques have been developed that are capable of generating multiple, equally probable, realizations of an orebody [1114]. These realizations show the possible variations of the mineral content and corresponding tonnages of a deposit and provide the basis for quantifying geological uncertainty. Based on simulated orebody realizations, stochastic open pit planning techniques can be used to integrate geological uncertainty into planning processes, so as to allow some sort of geological risk management while maximizing the expected NPV. Several authors have incorporated geological uncertainty in their pushback/phase-pit optimizing approaches. Goodfellow and Dimitrakopoulos applied the simulated annealing algorithm to pushback design based on simulated orebody realizations [15]. Their goal was to modify an existing pushback design to better account for the joint local uncertainty in metal grades and material types, while remaining similar to the original design in terms of pushback tonnages and the tonnages sent to various destinations. Their case study on a copper mine showed that the approach achieved a 3561% reduction in variability in terms of material quantities sent to the processes, leading to a reduced level of risk in the economic value of the design. Asad and Dimitrakopoulos presented a stochastic parametric maximum flow algorithm for pushback design under uncertainties in both metal content and commodity price [16]. They used Lagrangian relaxation together with subgradient method to accommodate knapsack constraints for ore quantities in the pushbacks and addressed the gap problem by introducing a modification in the subgradient method to minimize the size difference between consecutive pushbacks. The authors applied the algorithm to a gold mine and compared the outcome with that from the conventional (deterministic) nested pit approach [17]. The case study demonstrated that the stochastic approach gave 30% more discounted cash flow, a 21% larger ultimate pit, and about 7% more metal than the conventional approach. Asad et al. later expanded the formulation to include multiple ore processing streams [18].

As mentioned above, the number of phases, the phase-pits, and the ultimate pit should be optimized simultaneously. However, few approaches are capable of providing simultaneous solutions to the three elements, especially, for coal mines. Asad and Dimitrakopoulos algorithm solves the phase-pits and ultimate pit simultaneously, but the gap problem is not completely overcome and the algorithm is for metal mines [16]. Gu et al. proposed a method capable of providing simultaneous solutions to the three elements [19]. It consists of a heuristic algorithm for generating a series of geologically optimal pits and a dynamic programming (DP) formulation for sequencing the pits, but the method is also for metal mines.

Based on the basic framework from a previous research for metal mines [19], we have developed a phase planning method particularly for open pit coal mines with nearly horizontal and bedded coal seams, with the objective of simultaneously optimizing the number of phases, the phase-pits, and the ultimate pit.

Almost all open pit optimization formulations and solution algorithms take 3D block models of deposits as their geological inputs. However, most coal deposits consist of nearly horizontal (inclination angle smaller than 15 or so), bedded coal seams. As depicted in Figure 1, blocks at the coal-rock interfaces contain a mixture of coal and rock (e.g., the blocks outlined by the dotted lines), and such blocks constitute a significant portion of all the blocks containing coal. This will cause large errors in coal quantity calculation and subsequent economic evaluation, since whole blocks are classified as coal or waste. The problem is more pronounced in cases of multiple coal seams and/or the coal seams are thin.

In this study, we model this type of coal deposit into a column model, where the whole deposit is divided into vertical columns instead of blocks, with all columns having a square horizontal cross section of the same size. Figure 1 illustrates a vertical cross section of a column model with the columns numbered from 1 to 23. Each column in such a model is assigned a group of attributes defining the physical and chemical properties of all the coal seams along the column. The attributes generally include floor elevation and thickness of each coal seam and the unconsolidated layer at the central line of the column, and heat value, ash content, and sulfur content of each coal seam along the column. These attributes may be estimated based on drill hole data using a method such as Kriging or inverse distance interpolation. With a column model, the coal quantity in any given volume (e.g., a pit or a cone) is calculated based on the thickness of each seam falling inside the volume on each column. The resulting coal quantity is much more accurate than that based on whole blocks with a block model. The reduction in coal-rock mixing with a column model, as compared with a block model, depends on the geometries of the coal seams (especially, their thicknesses) and the block and column sizes. For the coal deposit model used in the case study, we estimated that the reduction is at least 50% in terms of the total amount of rock mixed in coal and coal classified as waste.

The basic idea of phase optimization is first generating a candidate series of nested pits with a specified size increment and, then, selecting the best phase-pits (including the ultimate pit) from the series that maximize the NPV. The best candidate pits are the least-strip ratio pits, referred to as least-SR pits hereafter. A least-SR pit for a given coal quantity, Q, is defined as the pit that has the lowest strip ratio of all pits having the same Q. To overcome the gap problem, a cone eliminating algorithm is applied on a column model to generate a series of nested, least-SR pits. The basic logic of the algorithm is briefly described as follows.

Suppose that a series of n nested, least-SR pits, denoted as , is to be generated with a specified coal quantity increment of Q, where P1 is the smallest pit and Pn the largest. Let Qi denote the coal quantity in Pi. The algorithm starts with the largest pit, Pn, which is created by projecting the pit walls from a closed surface boundary outline down to the lowest floor elevation of the lowest coal seam, according to the pre-determined slope angles in different directions or in different zones. The pit slope angles are determined beforehand through rock stability studies and are inputs to the algorithm. The surface boundary could be the boundary that encloses all exploration drill holes, or the property boundary for which the mining company has acquired the right of mining, or any boundary that is large enough to enclose the optimal ultimate pit within the acquired property. Within Pn, the algorithm searches for a portion that contains a coal quantity of Q and has the highest strip ratio, and then eliminates this portion from Pn. The remaining part of Pn after eliminating such a portion constitutes the next smaller pit, Pn1, in the series, which has a coal quantity of QnQ. To make Pn1 feasible with respect to pit slope constraints, the eliminated portion is constructed by combining upward cones (whose apexes point upwards) with shell inclination angles equal to the pit slope angles. From Pn1, the same cone eliminating process is repeated to generate the nest smaller pit, Pn2. The process continues until the coal quantity in the remaining part is equal to or below the coal quantity, Q1, specified for the smallest pit in the series, thus, resulting all the pits in the series.

With a column model, a pit is outlined by the bottoms and the tops of all the columns inside the pit, as depicted in Figure 2 for pit Pi, where the bottom elevation of each column is equal to the elevation of the pit wall or pit bottom at the column center, and the top elevation of each column is equal to the elevation of ground surface at the column center. Without losing generality, suppose we have come to the point of generating Pi1 from pit Pi. The cone eliminating process is outlined as follows.

Place the cone apex on the central line of a column at an elevation that is z higher than the bottom elevation of the column, as shown by Cone 1 in Figure 2. Calculate the quantities of coal, rock, and unconsolidated material in the cone inside pit Pi. The cones coal quantity is denoted as qc. If qc is not greater than the coal quantity increment, Q, specified for the pit series, compute the cones strip ratio and put the cone in an array. Then, move the cone apex upwards along the central line of the same column by a distance of z, and do the same as for the previous cone. Continue the process of moving the cone upwards along the same column, until the cones coal quantity, qc, is greater than Q, or the cones apex is above the ground surface, as depicted by the upward arrow and the dot lined cones in Figure 2. Then, the cone is moved horizontally to another column inside pit Pi, as shown by the horizontal arrow in Figure 2, and the entire process for the previous column is repeated. The above process continues until all the columns inside pit Pi are traversed.

At the end of the above cone moving process, an array of J cones, each having a coal quantity qc Q, is obtained. Sort the cone array in order of descending strip ratio. A union of the first K cones in the sorted cone array is sought, such that the total coal quantity of the union is closest to Q and not greater than 1.1Q. In a cone union, the overlapping part between two or more cones is accounted only once. Such a union is obtained by sequentially combining the cones in the sorted array one at a time, starting with the first cone. The cones in the union are eliminated from pit Pi and the remaining part is pit Pi1, whose coal quantity is about Q smaller than Pi. Eliminating a cone from a pit is simply done by raising the bottom elevation of each column traversed by the cone up to the cone shell elevation at the column center.

The algorithm outlined above is a heuristic one and does not guarantee that the resulting pit is the true least-SR pit. However, since the eliminated cones are the ones having the highest strip ratios, their union constitutes a volume whose strip ratio should be very close to the highest strip ratio of all volumes with the same coal quantity. Thus the remaining part should be very close to the true least-SR pit for its coal quantity.

In the above algorithm, each and every cone kept in the array has a coal quantity not greater than the specified increment, Q, and the coal quantity of the eliminated cone union is controlled by an upper limit of 1.1Q. Thus, the coal quantity increment between any consecutive pits in the generated pit series may be smaller than Q, but cannot exceed 1.1Q. The gap problem is, therefore, completely overcome.

The up-moving step size, z, can affect the quality of the resulting pits: a smaller z generally gives better result (i.e., the resulting pits are closer to the true least-SR pits), but consumes more time and memory. z is an input parameter to the developed software and different values can be tried if necessary. From our experiments on different coal deposits using different z values, bench height, h (usually 10m15m), is a good choice for z, and smaller values (e.g., h/2, h/4) make insignificant improvement on the resulting pits, but substantially increase the computing time. The column size has a similar effect.

Once a series of nested, least-SR pits, {P}n, is generated, the pits can then be sequenced using a DP model to optimize the phase plan. Figure 3 is a schematic illustration of the DP model, and for clarity of illustration, {P}n is assumed to contain 6 pits (in real-life instances, the number would be much larger). The horizontal axis represents the stage variable t with each stage corresponding to a phase, and the maximum stage number is the number of pits in {P}n. The vertical axis represents the state variable P with each state corresponding to a pit in {P}n, depicted by a circle in Figure 3. The states (pits) of a given stage (phase) are the possible phase-pits for that phase. An arrow represents a state transition from a pit of a phase to a pit of the next phase. Since any phase-pit of phase t is the result of expansion (through mining) of a smaller phase-pit of the preceding phase, t1, a state transition can only go upwards from a pit of a stage to one of the larger pits of the succeeding stage. That is why the starting (lowest) state of stage t corresponds to pit Pt in {P}n (t=1, 2,,n), and the lower-right half of the diagram is void.

A path starting with the origin and ending at any pit in Figure 3 is a possible phase plan scenario. For example, path 0P2P4P6, as shown by the thick arrows, represents such a phase plan: the number of phases is 3 (since the path ends at phase 3); the phase-pits for phases 1, 2, and 3 are pits P2, P4, and P6, respectively; and the ultimate pit is P6. The path with the highest NPV is the optimal phase plan, which can be found by economically evaluating all the paths. The following is a DP formulation for finding the best path.

In general, suppose that pit Pi of stage t is being evaluated. Pi can be transited from those smaller-than-Pi pits of the preceding stage, t1. When pit Pi of stage t is transited from pit Pj of stage t1 (t1ji1), the quantities of coal, rock, and unconsolidated material mined in phase t, denoted as Qt,i (t1, j), Wt,i (t1, j), and Ut,i (t1, j), respectively, are calculated aswhere Qi, Wi, and Ui are the quantities of coal, rock, and unconsolidated material that can be mined from pit Pi, respectively. They are quantities after coal recovery and waste mixing incurred in mining operations are taken into account.

Suppose that the mining company has a coal processing plant and the salable product is clean coal. Such a transition brings a total revenue of Vt,i (t1, j) and cost of Ct,i (t1, j) for phase t.where rp is the coal recovery rate of the processing plant; p is the coal price; and cm, cp, , and cu are the unit costs of coal mining, coal processing, rock mining, and unconsolidated material stripping, respectively.

Let yt,i (t1, j) denote the time (in years) required to make such a transition, and assume that the coal mining, waste removing, and coal processing capacities match one another. Then,where A is the annual coal mining capacity.

yt,i (t1, j) may not be an integer number of years, and let Lt,i (t1, j) be the integer part of it. The average annual revenue and cost for each of the Lt,i (t1, j) years, denoted by and ct,i (t1, j), respectively, are

Following the transition, the cumulative time to arrive at pit Pi of stage t after finishing mining phase t, denoted by Yt,i (t1, j), iswhere Yt1,j is the cumulative time to arrive at pit Pj of the preceding stage, t1, following the best path. Yt1,j has been calculated in evaluating the states of the preceding stage, t1.

Therefore, when pit Pi of stage t is transited from pit Pj of stage t1, the cumulative NPV realized at pit Pi of stage t, after t phases of production, is given by NPVt,i (t1, j) aswhere NPVt1,j is the cumulative NPV at pit Pj of stage t1, following the best path, which has been calculated in evaluating the states of the preceding stage, t1; p and c are the escalation rates of coal price and production cost, respectively; and d is the discount rate.

As stated before, pit Pi of stage t may be transited from all the smaller-than-Pi pits of the preceding stage, t1. Obviously, when pit Pi of stage t is transited from a different pit of stage t1, the quantities mined and processed in phase t will be different, and the revenue, cost, and time length will also be different. Consequently, different transitions (decisions in DP) give different cumulative NPVs at pit Pi of stage t. The transition with the highest cumulative NPV is the best transition (optimal decision in DP) and, thus, the recursive objective function is

Starting from the first stage, the pits are evaluated forwards stage by stage, until all the pits of all stages are evaluated. The best transitions and the associated cumulative NPVs are obtained for all the pits of all stages. Then, find the pit that has the highest cumulative NPV of all pits of all stages. This pit is the best ultimate pit, and the stage at which it is found indicates the best number of phases. Then, starting from the best ultimate pit and tracing the best transitions backwards to the first stage, the optimum path (optimal policy in DP) is found, and the pits along this path indicate the best phase-pits of the corresponding phases. Thus, the number of phases, the phase-pits, and the ultimate pit are simultaneously optimized. This is a forward and open-ended DP formulation.

A software package has been developed based on the above model and algorithm and was used in a case study on a large coal deposit in northern China. The topography of the coal field is nearly flat with a maximum relief of less than 20m. The surface boundary of the planning area is about 7800m long and 4500m wide. From drill hole information, 8 coal seams were identified, with thicknesses varying from around 1m to around 40m and densities between 1.28 and 1.31t/m3. The deposit was modeled into a column model having around 39000 columns, each having a horizontal cross section of 30m30m. The attributes of each column, mainly the thickness and elevation of each coal seam along the column, were estimated based on drill hole data using an inverse distance interpolation method particularly designed for this study.

The coal reserve within the planning boundary was estimated to be some 900Mt. For a deposit of this scale, the annual coal mining rate was assumed to be 20Mt of run-of-mine coal. The coal is to be sold without processing. The time span of a single phase is generally more than 5 years to avoid complications associated with frequent transitions between phases. Therefore, in generating the least-SR pits, the coal quantity of the smallest pit, Q1, was set to 100Mt (5-year production), and the coal quantity increment, Q, to 20Mt. A maximum pit slope of 25 was used. With these parameter values and the column model as inputs, 40 nested pits were generated by applying the cone eliminating algorithm described above. The coal quantity increment between any two consecutive pits in the generated pit series has a very small variation (20.00Mt to 20.17Mt), indicating that the algorithm has produced an evenly spaced series of nested pits with increments virtually equal to the specified value. This is a verification of the algorithms capability of completely overcoming the gap problem.

The phase plan was optimized with the generated pit series and the parameter values in Table 1 as inputs to the DP model. The best (highest-NPV) phase plan consists of 4 phases and Table 2 summarizes the major quantities to be mined in the phases. With an annual coal production of 20Mt, each of the first three phases has a time span of 10 years and the fourth phase 11 years, giving a total mine life of 41 years. The average strip ratio increases from phase 1 to phase 4. Since maximizing NPV implies postponing waste removal as much as possible, the increasing strip ratio with time is a verification of the rationality of the proposed method.

Figure 4 is a 3D view of the four phase-pits of the optimized phase plan, where phase-4 pit is also the best ultimate pit. Figure 5 is a vertical cross section of the phase-pits superimposed on the coal seams in the column model. The direction of phase expansion can be clearly seen from these figures. One can also see the rationality of the optimization results from the spatial relationship between the phase-pits and the coal seams (Figure 5).

The developed software provides an option of keeping and outputting a specified number of best phase plan scenarios. For the case study, we found five other scenarios with virtually the same NPVs as the one given in Table 2, but with different numbers of phases, and/or phase-pits (including the ultimate pit). Since it is very difficult, if not impossible, to incorporate all relevant practical considerations in any optimization model and algorithm, these phase plan scenarios, which are equally good economically, provide valuable options for further evaluation with respect to certain practical considerations to arrive at the final phase plan.

We also analyzed the effects of certain input parameters, such as coal price, production costs, and their escalation rates, on the phase planning outcome for the case study, with the above phase plan as the base case for comparison. The planning outcome was found to be sensitive with respect to these parameters. When the coal price was lowered by 20%, the size of the optimum ultimate pit decreased by 30%, and the number of phases decreased from 4 to 3. Increasing the production costs by 20% had similar effects. Increasing the coal price (or lowering the production costs) had reverse effects on the planning outcome, as expected. Setting the annual escalation rates of coal price and production costs to 2.0% and 1.5%, respectively, resulted in a 7% larger ultimate pit, the same number of phases, but larger phase-pits. Based on the outcomes of these experiments, we suggest that the phases should be updated periodically (e.g., toward the end of each phase) in a real-life operation, as the relevant economic and technical conditions change over time. The optimization method presented herein and the developed software can be a handy tool for updating phase plans.

The phase planning method presented herein is specially designed for open pit coal mines with nearly horizontal and bedded coal seams. The major merits of the method include the following: it simultaneously optimizes the number of phases, the intermediate phase-pits, and the ultimate pit; it eliminates the gap problem in generating a series of nested pits; and the column model has a clear advantage over the commonly used block model in the accuracy of coal quantity computation with nearly horizontal and bedded coal seams. The method is capable of handling large real-life instances and produces rational results, as demonstrated by the case study. The method can also be used to analyze the effects of relevant input parameters on the phase planning outcome, providing useful scenarios for decision-making in strategic planning of open pit coal mines.

The proposed method in its current form has two major shortcomings. One is that the total cost of mining a phase is averaged over the years of the phases time span while, in actuality, the quantities of rock and unconsolidated material mined each year fluctuate within a phase, causing fluctuations in annual cost. Another shortcoming concerns the transition from one phase to the next. Transition takes place sometime before a phase is completely mined out. During the transition period, the upper benches of the next phase are mined and some working benches may traverse the boundary between the two phase-pits. Phase transitions are not incorporated in our current formulation and should be dealt with in a more detailed scheduling process. Overcoming these shortcomings will be the focus of our future research on this topic.

The authors acknowledge the National Natural Science Foundation of China (51674062, 51974060, and 51474049), National Science Foundation for Young Scientists of China (51604061), and Liaoning Province Key Research and Development Project (2019JH2/10300051), for their financial supports in the course of the research work presented in this paper.

Copyright 2021 Xiaowei Gu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

tent mountain open-pit coal mine designated for federal impact assessment

tent mountain open-pit coal mine designated for federal impact assessment

Federal Environment and Climate Change Minister Jonathan Wilkinson said the project could potentially impact cross-border environments in Alberta and British Columbia, Indigenous people, and fish and their habitats.

"Both provincial regulatory regimes provide for a duty to consult with Indigenous peoples to consider potential effects on their rights and related concerns. However, in part because of the project's cross-border location, neither province requires consultation with all potentially affected groups on both sides of the border," the minister said in a statement.

Australian company Montem Resources hopes to resume operations and expand the original pits to allow daily production of 4,925 tonnes of raw coal, over a lifespan of 14 years. It would also include a factory to handle and process coal and a rail-loading facility.

Wilkinson said earlier this month that the federal government will review any new coal project that could release selenium, which is toxic to fish and difficult to remove once it is introduced into groundwater.

"This process would allow the federal government to understand the full risks of the project and make an informed decision on whether it is in Canadians' best interests to let the Tent Mountain coal project proceed," he said in a news release.

Coal mining has been controversial in Alberta for more than a year, since the province's United Conservative government revoked a 1976 policy that protected the eastern slopes of the Rocky Mountains from open-pit coal mines.

Police are asking for the public's help after two men were found dead on a road near Good Spirit Lake in Saskatchewan on Monday. RCMP said the bodies of 29-year-old Bryton Lawrason and 20-year-old Seth Hildebrand were found on Tiny Grid Road near Burgis Beach, about 190 kilometres northeast of Regina. Both men were from Edmonton. Their families have been notified. Police say the deaths are being considered homicides, but that the causes of death are not being released because they are part of an

TORONTO Ontario will move to the third stage of its reopening plan next Friday several days ahead of schedule allowing gyms and restaurants to open indoor operations and larger gatherings to take place. The government said high vaccination rates and improvements in other pandemic metrics had allowed for the early move to Step 3. It said positive trends are expected to continue up until the July 16 reopening date. Premier Doug Ford thanked Ontarians who have been administering and receiving

Europe's drug regulator has found a possible link between very rare heart inflammation and COVID-19 vaccines from Pfizer-BioNTech and Moderna, it said on Friday, stressing that the benefits of the shots outweighed any risks. The conditions, myocarditis and pericarditis, must be listed as side-effects of the two mRNA vaccines, the safety committee of the European Medicines Agency (EMA) said, adding that such cases primarily occurred within 14 days of inoculation. EMA's safety panel also advised that people with a history of the rare blood disorder capillary leak syndrome (CLS), must not be vaccinated with Johnson & Johnson's shot.

This column is an opinion from Andrew Leach, an energy and environmental economist at the University of Alberta. Alberta Premier Jason Kenney has done many things in government that would come as a great surprise to the Jasons Kenney of the past, but perhaps none so much as the decision to purchase a 50 per cent interest in the Sturgeon Refinery. According to Energy Minister Sonya Savage, the near-billion-dollar deal was the best we could hope for as taxpayers, seeing as it would limit ongoing l

Canada's announcement that fully vaccinated Canadian travellers can skip quarantine upon their return has inspired some people to start making travel plans. But before packing your bags, take note that the pandemic isn't over and there are still travel rules in place that could affect your trip. "Travel isn't quite the same as pre-COVID, and that's just the reality moving forward for the foreseeable future," said Claire Newell, owner of Travel Best Bets, a travel agency based in Burnaby, B.C.

LONDON (AP) A British police officer pleaded guilty Friday to murdering a 33-year-old woman Sarah Everard, who was abducted as she walked home from a friends house in south London. Wayne Couzens previously admitted kidnapping and raping Sarah Everard, a marketing executive who went missing on March 3. Couzens entered a guilty plea to murder during a hearing at Londons Central Criminal Court, appearing by video link from Belmarsh high-security prison. A major police investigation was launched

BEIJING (AP) China sent a flight to bring home 210 of its nationals from Afghanistan, state media reported Friday, as the U.S. military prepares to leave the country and the security situation grows increasingly fraught. The Global Times newspaper published by the ruling Communist Party said the Xiamen Airlines flight departed July 2 from the Afghan capital, Kabul, and landed in the central province of Hubei. The airline confirmed the report in a post on its Twitter-like Weibo account but offe

Alberta's provincial government is vowing to add and replace more than 6,000 continuing care beds in the next four years. Health Minister Tyler Shandro announced Friday that $400 million in operational funding will be devoted to a new version of the Affordable Supportive Living Initiative to create new beds or upgrade existing spaces in publicly funded facilities in the province. The minister estimated 2,200 of those would be new spaces and an additional 3,800 would be replacements. "Taking inno

Highly-trained Colombian soldiers left at a loose end after retirement have frequently been tempted by opportunities to ply their trade abroad as private military contractors from Iraq to Yemen, military officials and experts said on Friday. At least 17 ex-members of Colombia's military are among the suspects in this week's assassination of Haitian President Jovenel Moise https://www.reuters.com/world/americas/colombian-suspects-haiti-presidents-killing-arrived-via-dominican-republic-2021-07-09, who was shot early on Wednesday at his home by what officials said was a group of foreign mercenaries. But for those want to hire mercenaries, Colombia is a popular choice.

NB Power has warned property owners along the Mactaquac headpond that water levels are expected to drop by two feet ahead of a weekend storm, an indication the utility is changing its policy. Earlier this year, the water unexpectedly dropped about four feet without any warning from NB Power, leaving motorboats beached on rocks and sailboats stuck in the mud. But after CBC News reported on the issue this week, a notice went out warning that headpond waters are expected to drop by two feet before

WARNING: This story contains details some readers may find distressing. Three Quebec-based religious orders that staffed residential schools in the rest of Canada have earned millions of dollars from property sales in recent years, even as the Catholic Church said it couldn't raise enough money to pay its share of a settlement meant for survivors. In a class-action settlement with Indigenous survivors of the schools reached in 2006, Catholic entities involved in residential schools pledged, amon

P.E.I. will no longer test Atlantic Canadian residents who have a PEI Pass when they come to the Island and vaccinated people will not be required to wear masks in most indoor spaces. P.E.I. implemented rapid testing at the border for everyone when it opened its borders to non-essential travellers from Atlantic Canada on June 27, though there have been busy times when Islanders with passes have been waved through without a swab. During a COVID-19 briefing on Friday, P.E.I. Premier Dennis King

Thirty-two percent of Russians support the extremism ban on jailed Kremlin critic Alexei Navalny's political network while 27% oppose it, according to an opinion poll by the Moscow-based Levada Centre published on Friday. Levada, which polled 1,630 people on June 24-30, said 38% had voiced indifference over last month's ruling that designated Navalny's groups as "extremist". It also said that support for Navalny's activities had dipped to 14% from 20% last September.

Body camera video of a mass shooting in Toledo show two officers running toward the sound of gunfire as they yell at people to "stay down" and "find cover" while dozens of rounds are being fired. (July 9)

Afghan Air Force Major Dastagir Zamaray had grown so fearful of Taliban assassinations of off-duty forces in Kabul that he decided to sell his home to move to a safer pocket of Afghanistan's sprawling capital. Instead of being greeted by a prospective buyer at his realtor's office earlier this year, the 41-year-old pilot was confronted by a gunman who walked inside and, without a word, fatally shot the real estate agent in the mouth. At least seven Afghan pilots, including Zamaray, have been assassinated off base in recent months, according to two senior Afghan government officials.

Ask the B.C. government if they've done a good job handling the pandemic, and you'll often hear a very specific answer. "The data is overwhelmingly supportive," said Premier John Horgan last week. "The next closest of the jurisdictions of our size, of five million people in North America, the next closest to the low mortality rate is Ontario, and their mortality rate is twice what ours is." Horgan, Health Minister Adrian Dix and government news releases have all mentioned B.C.'s official death c

Just days after a report on allegations of bullying and harassment against Chief RoseAnne Archibald was leaked and hours after she was elected the new national chief of the Assembly of First Nations Archibald said today she would support the implementation of a whistleblower policy at the AFN. "I have been the victim of workplace harassment and I know what that feels like," she told a morning press conference. "For too long, organizations like AFN have allowed this kind of behaviour to conti

The Quebec government may introduce COVID-19 vaccination passports in September that would give only people who are fully vaccinated access to non-essential services like gyms and cinemas if cases skyrocket once again. Lockdown measures throughout the pandemic closed entertainment venues, bars and restaurants in an effort to curb the spread of the coronavirus. Pumping iron alongside strangers and dining with friends became a distant memory. But if the virus starts spreading once again, vaccinati

SURFSIDE, Fla. (AP) The death toll in the collapse of a Miami-area condo building rose to 79 on Friday, a number the mayor called heartbreaking as recovery workers toiled for a 16th day to find victims in the rubble. Another 61 people remain unaccounted for. Miami-Dade Mayor Daniella Levine Cava said the work to recover victims was moving forward with great urgency in order to bring closure to the families of victims who have spent an agonizing two weeks waiting for news. This is a stagge

A Taliban delegation in Moscow said on Friday that the group controlled over 85% of territory in Afghanistan and reassured Russia it would not allow the country to be used as a platform to attack others. Foreign forces, including the United States, are withdrawing after almost 20 years of fighting, a move that has emboldened Taliban insurgents to try to gain fresh territory in Afghanistan. That has prompted hundreds of Afghan security personnel and refugees to flee across the border into neighbouring Tajikistan and raised fears in Moscow and other capitals that Islamist extremists could infiltrate Central Asia, a region Russia views as its backyard.

sustainability | free full-text | environmental sustainability of open-pit coal mining practices at baganuur, mongolia | html

sustainability | free full-text | environmental sustainability of open-pit coal mining practices at baganuur, mongolia | html

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mining | britannica

mining | britannica

mining, process of extracting useful minerals from the surface of the Earth, including the seas. A mineral, with a few exceptions, is an inorganic substance occurring in nature that has a definite chemical composition and distinctive physical properties or molecular structure. (One organic substance, coal, is often discussed as a mineral as well.) Ore is a metalliferous mineral, or an aggregate of metalliferous minerals and gangue (associated rock of no economic value), that can be mined at a profit. Mineral deposit designates a natural occurrence of a useful mineral, while ore deposit denotes a mineral deposit of sufficient extent and concentration to invite exploitation.

When evaluating mineral deposits, it is extremely important to keep profit in mind. The total quantity of mineral in a given deposit is referred to as the mineral inventory, but only that quantity which can be mined at a profit is termed the ore reserve. As the selling price of the mineral rises or the extraction costs fall, the proportion of the mineral inventory classified as ore increases. Obviously, the opposite is also true, and a mine may cease production because (1) the mineral is exhausted or (2) the prices have dropped or costs risen so much that what was once ore is now only mineral.

Archaeological discoveries indicate that mining was conducted in prehistoric times. Apparently, the first mineral used was flint, which, because of its conchoidal fracturing pattern, could be broken into sharp-edged pieces that were useful as scrapers, knives, and arrowheads. During the Neolithic Period, or New Stone Age (about 80002000 bce), shafts up to 100 metres (330 feet) deep were sunk in soft chalk deposits in France and Britain in order to extract the flint pebbles found there. Other minerals, such as red ochre and the copper mineral malachite, were used as pigments. The oldest known underground mine in the world was sunk more than 40,000 years ago at Bomvu Ridge in the Ngwenya mountains, Swaziland, to mine ochre used in burial ceremonies and as body colouring.

Gold was one of the first metals utilized, being mined from streambeds of sand and gravel where it occurred as a pure metal because of its chemical stability. Although chemically less stable, copper occurs in native form and was probably the second metal discovered and used. Silver was also found in a pure state and at one time was valued more highly than gold.

According to historians, the Egyptians were mining copper on the Sinai Peninsula as long ago as 3000 bce, although some bronze (copper alloyed with tin) is dated as early as 3700 bce. Iron is dated as early as 2800 bce; Egyptian records of iron ore smelting date from 1300 bce. Found in the ancient ruins of Troy, lead was produced as early as 2500 bce.

One of the earliest evidences of building with quarried stone was the construction (2600 bce) of the great pyramids in Egypt, the largest of which (Khufu) is 236 metres (775 feet) along the base sides and contains approximately 2.3 million blocks of two types of limestone and red granite. The limestone is believed to have been quarried from across the Nile. Blocks weighing as much as 15,000 kg (33,000 pounds) were transported long distances and elevated into place, and they show precise cutting that resulted in fine-fitting masonry.

One of the most complete early treatments of mining methods in Europe is by the German scholar Georgius Agricola in his De re metallica (1556). He describes detailed methods of driving shafts and tunnels. Soft ore and rock were laboriously mined with a pick and harder ore with a pick and hammer, wedges, or heat (fire setting). Fire setting involved piling a heap of logs at the rock face and burning them. The heat weakened or fractured the rock because of thermal expansion or other processes, depending on the type of rock and ore. Crude ventilation and pumping systems were utilized where necessary. Hoisting up shafts and inclines was done with a windlass; haulage was in trucks and wheelbarrows. Timber support systems were employed in tunnels.

Great progress in mining was made when the secret of black powder reached the West, probably from China in the late Middle Ages. This was replaced as an explosive in the mid-19th century with dynamite, and since 1956 both ammonium nitrate fuel-blasting agents and slurries (mixtures of water, fuels, and oxidizers) have come into extensive use. A steel drill with a wedge point and a hammer were first used to drill holes for placement of explosives, which were then loaded into the holes and detonated to break the rock. Experience showed that proper placement of holes and firing order are important in obtaining maximum rock breakage in mines.

The invention of mechanical drills powered by compressed air (pneumatic hammers) increased markedly the capability to mine hard rock, decreasing the cost and time for excavation severalfold. It is reported that the Englishman Richard Trevithick invented a rotary steam-driven drill in 1813. Mechanical piston drills utilizing attached bits on drill rods and moving up and down like a piston in a cylinder date from 1843. In Germany in 1853 a drill that resembled modern air drills was invented. Piston drills were superseded by hammer drills run by compressed air, and their performance improved with better design and the availability of quality steel.

Developments in drilling were accompanied by improvements in loading methods, from handloading with shovels to various types of mechanical loaders. Haulage likewise evolved from human and animal portage to mine cars drawn by electric locomotives and conveyers and to rubber-tired vehicles of large capacity. Similar developments took place in surface mining, increasing the volume of production and lowering the cost of metallic and nonmetallic products drastically. Large stripping machines with excavating wheels used in surface coal mining are employed in other types of open-pit mines.

Water inflow was a very important problem in underground mining until James Watt invented the steam engine in the 18th century. After that, steam-driven pumps could be used to remove water from the deep mines of the day. Early lighting systems were of the open-flame type, consisting of candles or oil-wick lamps. In the latter type, coal oil, whale oil, or kerosene was burned. Beginning in the 1890s, flammable acetylene gas was generated by adding water to calcium carbide in the base of a lamp and then released through a jet in the centre of a bright metal reflector. A flint sparker made these so-called carbide lamps easy to light. In the 1930s battery-powered cap lamps began entering mines, and since then various improvements have been made in light intensity, battery life, and weight.

Although a great deal of mythic lore and romance has accumulated around miners and mining, in modern mining it is machines that provide the strength and trained miners who provide the brains needed to prevail in this highly competitive industry. Technology has developed to the point where gold is now mined underground at depths of 4,000 metres (about 13,100 feet), and the deepest surface mines have been excavated to more than 700 metres (about 2,300 feet).

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