Mining

Underground Storage and Distribution of Hydraulic Fill

Many factors, some of which are not easily defined or described, must be considered in the design of a hydraulic backfill system. After participating in the design of several plants, I have a conviction that future refinements in sandfill systems must come in large part, from the merging of good design ideas and information from existing operating plants. It is important then, that we document and publish information on existing plant designs and their operating characteristics. This information will then be available for use by our successors and later innovators in hydraulic fill placement.

Pump Plant

The pump selected for the Mayflower Plant is a Gardner-Denver 5×6 FXG-FG duplex power pump, fitted with 3-½ inch diameter pistons and liners. It is being operated at a main shaft speed of 56 rpm. The sand slurry described is being pumped into the mine at 48 to 51% solids. Dry solid density is approximately 3.0 grams per cubic centimeter. The fluid flow from the pump to the mine is approximately 55 gallons per minute and operates at a pump discharge pressure of 500 psi. The capacity of the system is 9.7 tons of solids per hour.

As indicated in our original Plant schematic, slurry

Secondary Breakage in Taconite Open Pit Mining

The mining of taconite, to provide feed for a processing plant, requires that the flow of material continue uninterrupted. This means first, that the crude must be of a size acceptable to the primary crusher in order to reduce the delays caused by plugging the crusher with chunks. Secondly, elimination of oversize in the pit will reduce costs of all wear parts used in the mining and processing of taconite. Savings in wear parts is readily recognized in dipper teeth, bases, buckets, truck boxes, and crusher parts, both primary and secondary.

During the early days of taconite mining, it was soon recognized at reserve mining company’s Babbitt operations that experience in mining other ores was not always (or “necessarily”?) applicable to excavating taconite. This was especially true in drilling and blasting. Blasting of small tonnages in single or double rows simply filled the pit with scattered chunks and provided very shallow banks for shovel loading. It also created problems for the jet piercers, since all drilling had to be performed in fractured areas. drilling efficiency suffered and costs were extremely high. Shovel and truck efficiencies were also low and again costs were high.

The diesel track mounted crane, equipped with a drop

Use of Rocket Jet Burners in Quarrying of Granite

The first step in the quarrying of granite, following removal of any overburden material, involves the freeing of large blocks from the formation. For many years the use of explosives was the accepted method of obtaining these blocks. Even today there are operations where this is considered to be the most economical method even though it does result in a high percentage of damaged stone. In more recent times the preferred procedure at most quarries has been to produce a continuous vertical cut or slot completely around the block to be separated. Originally, this was done by drilling a series of closely spaced holes around the block and breaking the web between the holes with a chisel-like tool known as a broaching bar. The machine used in this mechanical method of producing the relief slot is known as the channel bar.

The Thermal Spalling Process

The application of a thermal device on rock depends upon a characteristic of the rock termed “spallability”. In its simplest terms spalling is considered as decrepitation resulting from differential expansion of rock crystals due to thermally induced stresses. The individual rock properties influencing the spalling characteristic are so numerous and their interaction so complex that

Priming and Boostering Anfo with Slurry Explosives

Following the wide-spread acceptance of ANFO as a useful, low cost blasting agent, studies have been made to adequately describe the physical and explosive properties of this material. As the quality of the AN blasting prill improved, reliability and sensitivity to initiation were greatly increased and many methods of priming were chosen from the standpoint of economics with little appreciation for the need to initiate so as to obtain the most efficient detonation. Under certain conditions, ANFO could be initiated with primers no more powerful than a No. 8 blasting cap.

It is the nature of ANFO to demonstrate transient velocities upon initiation from any primer or booster. These transients are a function of the primer performance and in order to obtain the most efficient use of ANFO the principles involved in priming should be considered. The principles involve not only power output but also geometry and can be summarized as follows:

A primer or booster for ANFO should have:

  1. High detonation pressure
  2. No dual or low order velocity
  3. Adequate diameter and length

Ammonium nitrate-fuel oil mixtures are extremely susceptable to transient velocities upon initiation from a primer. Initial velocities in ANFO over the range of 2,000 to 20,000 fps have been observed

Laser Alignment Underground

Accurate and economic control of line and grade on long tunnels, large structures, excavations and waterways, has been a problem to surveyors and engineers for decades. The conventional method of surveying, incorporating a level, transit, and a number of surveying technicians, has proven, in the past, to be a very expensive and time-consuming operation.

Operation of the laser is extremely simple. The laser head is connected to the power supply, and when “line” and “high voltage” indicator lights blink on (after a thermal relay delay has been 3 energized automatically), the operator merely presses the start control and the laser lights. The Construction Laser is normally supported by an optional laser stand for convenient pointing. Set-up can be done by an unskilled operator in a matter of minutes, and only one man is required.

The laser emits a 0.8 inch-diameter collimated red beam that is centered within the 2.2498-inch outer diameter of the laser housing and is parallel to the mechanical axis of the housing. Beam diameter at 3000 feet is 3 inches. Compact and rugged, it is designed specifically to withstand typical field environments. A metal bellows seal protects the laser’s cavity from dirt and moisture.

While low in power, its extreme

Predicting the Block Caving Behavior of Orebodies

Block caving is an efficient mass-production method for the underground mining of large orebodies. However, the block-caving method requires a substantial investment in developmental works, based on the assumption that the rock will cave.

Efficient block caving is prevented if the rock forms stable arches or breaks into fragments that are too large to pass easily through the finger raises. Under these conditions, the cost of the additional labor, drilling, and blasting required to assist caving may be sufficient to make marginal orebodies uneconomic or alternative mining methods more attractive.

The purely geological aspects of block caving were studied by means of geological indices. These are easily measured and reproducible, numerical properties of the rock mass. Relationships between the various indices and such rock mechanics parameters as compressive or tensile strength and deformation moduli can be established by correlation with test results. The aim of this part of the study was to determine which of the many possible geological indices was most highly correlated with some independent measure of block caving behavior. Clearly, the first step was to set up a measurement of block-caving behavior or “cavability.”

At the beginning of the study, there was considerable feeling that a composite index of cavability

Hydrofracing Mining

Hydraulic fracturing was developed as a method of stimulating production of oil from oil producing formations. The primary paper by Clark in 1949, describes the process of placing a hydrostatic pressure of sufficient strength on the producing formation of an oil well that the rock apparently cracked, and then, on allowing the well to flow back, a higher rate of recovery of oil was enjoyed.

Horizontal Fracture Field Experiments

Our first detailed study of horizontal fracturing possibilities was done in the Sacatosa Field, Maverick County, Texas. The oil horizon in this field was a tight well consolidated sandstone, average porosity of 23%, but with a permeability of 0.1 to 10 milidarcy and median value of 2.3 milidarcy. This was much too low to yield an economical quantity of oil. The depth was only 1,000 to 1,500 feet. It was proven that large horizontal fractures would increase the productivity. The geology and core data were presented at the Society of Petroleum Engineers Meeting, October, 1960.

The Natural Gas and Gas Products Division of Conoco needed inexpensive storage near to their pipe line complex running out of the Western Oklahoma gas fields. A convenient location was found near Medford, Oklahoma, which was the

Hydraulic Mining Techniques

The practice of transporting an ore or matrix from a pit area to the plant process area by means of a hydraulic pipeline has long been used by the mining industry. The industries which have classically used hydraulic transportation of ore to the plant include the phosphate mining industry, the heavy minerals mining industry, the clay mining industry, and the sand mining industry. As the advantages of this method become better known throughout the mining industry as a whole, and as techniques and expertise improve, its use will undoubtedly spread.

The widely recognized advantages of hydraulic transportation of ore from the pit area to the mines are:

  1. Its relatively low initial capital costs.
  2. Its speed of relocation at the mine site.
  3. The washing and scrubbing action given to the ore by its hydraulic passage into the pit pump and the subsequent trip through booster pumps down the pipeline to the plant.

The average hydraulic mining pit in use today consists of a dragline used for removing the matrix from its in situ location and depositing it in a well or pit. Around this pit are stationed high pressure hydraulic monitors which are used for the dual purpose of slurrying the material in

Electrical Fragmentation of Magnetic Iron Ores

Today’s increasing needs for rapid excavation have stimulated efforts to break rocks without explosives. The application of electric energy for this purpose has been studied by a number of investigators. Following principles have been used in electrical rock breaking:

  1. induction heating
  2. high frequency heating
  3. microwave heating
  4. contact resistance heating
  5. resistance heating
  6. electron beam heating
  7. plasma jet heating
  8. arc heating
  9. condensor discharge energy

This technique uses electrical heating of rock by electrode contact resistance and resistance heating phenomena. The electrically induced stresses inside of rock generate forces which break up the material. The fracturing of ore takes place by tensile stresses instead of compressive forces. The electric energy merely creates fractures in the rock and the separation of fractured material takes place by subsequent mechanical handling.

Energy requirements in secondary breaking of iron ores have been about one to two kilowatt-hours per ton of ore. Power requirement is a function of the degree of fragmentation.

The fact that rock is a heterogeneous material consisting of electrically conductive and nonconductive components sets special requirements for electrode design. By nature, the contact resistance of electrodes is much higher than the resistance of the rock electrodes. Therefore, very high temperatures can be expected of the electrodes when

Mine Ventilation

The language concerning ventilation in many sections of the Act could very well deprive or limit the mining engineer in planning the ventilation for new mines, since the Act requires federal approval of all ventilation plans. Dependent upon approval and of course application of the law, this could, due to economics, prohibit the opening of new mines in some cases.

Planning

The importance of ventilating principles are widely known and taught at all institutions of higher learning. There is very little that has not been published on this subject. Our biggest operating problem in respect to ventilation systems are ventilating practices. No matter how well a mine is planned in respect to ventilation, if the ventilating practices are not adhered to, you can expect and will have many complex problems.

In planning a new shaft operation, the most critical calculation is that of shaft size. This determination requires the consideration of many factors; for example:

  1. The acreage involved in the area;
  2. Adequate quantities of air per machine at the extreme development from the shaft;
  3. Adequate number of intakes and returns in the shaft bottom areas;
  4. Long angled arches at shaft bottoms to reduce shock losses;
  5. Shaft losses due to extreme velocities

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