Mineral Exploration Definitions

Mineral is a homogeneous inorganic substance that occurs naturally, usually in crystalline form with a definite chemical composition. The common rock-forming minerals (RFM) are quartz, orthoclase feldspar (KAlSi3O8), plagioclase feldspar (CaNaAlSi3O8), albite, mica group such as muscovite and biotite. The common ore-forming minerals (OFM) are hematite (Fe2O3), cassiterite (SnO2), chalcopyrite (CuFeS2), sphalerite (ZnS), galena...

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Twin Galaxy Stones

11 Black Opal  Twin Galaxy Stones - A stunning pair of nearly identical Lightning Ridge Black Opals. These rare stone are both more valuable than diamonds. Source Here...

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Gas Control (Underground Coal Mining)

Some mines do not have a gas problem of any type, the quantity of gas in the coal being so low that only small percentages (or even zero) are ever detected in the air. In such mines, other than continuously or regularly checking gas levels to ensure conditions have not changed, no special processes are required. Note that this comment refers to naturally occurring gas coming from the seam or surrounding strata. The ventilation system still has to deal with introduced gases such as diesel exhaust, shotfiring fumes and blackdamp (an atmosphere...

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Development Face Ventilation

To maintain a ventilation circuit it is necessary to have an intake and a return airway to the innermost point to be ventilated. As roadways are mined, the last section has only a single roadway so another arrangement has to be made. At one time this was done by erecting a temporary "wall" along one side of the roadway by hanging a flexible, airtight material known as brattice on timber props and extending the brattice across the last completed cut-through so air was forced to flow up to the face. This system works quite well and is still...

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VENTILATION Secondary or Panel Airways

Secondary or Panel Airways There is a tendency for development panels to be mined for longer distances, in order to maximize the length of longwall panels, without increasing the number of headings. At the same time production rates from longwall equipment have increased. The result, combined with increasing face lengths, is ever more arduous ventilation requirements and high ventilation pressures as noted previously. Airways around longwall face ends are also frequently obstructed by equipment, windrows of coal, brattice wings and secondary...

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VENTILATION Main Airways

As mines become larger and production rates increase the quantity of air flowing in the main intakes becomes large and ventilation effectiveness and cost is usually the main factor deciding the number of main airways required. For other purposes it would often be the case that only two intakes, one each for coal haulage and personnel/materials transport, and one return are necessary. Additional headings are to reduce the resistance to air flow and /or to reduce air velocities. For ventilation, the more airways the better, but after a point the...

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VENTILATION Main Fans

Note that the following is written using fan in the singular for the main ventilation. In fact where a large fan duty is required it is common to use 2 or 3 fans in parallel to provide the duty. The reasons for this are: Fan duties are becoming very large and the physical size of fans that could meet such duties singularly become impractical With multiple fans partial ventilation can be maintained in the event that one is stopped, a feature which is considered very beneficial. The main fans which ventilate large mines are major power consumers,...

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Common Operational Problems

Gate Roads Misaligned If the main and tailgates are driven off line far enough it is possible the longwall block is too wide or the space between the gate road pillar ribs is too narrow for the face equipment to fit. The only solution if this occurs is to strip coal off the rib(s) in question to allow the wall to fit and install additional support to cater for the extra width. It is best for such alignment problems to be identified early, preferably...

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Longwall Top Coal Caving

Longwall top coal caving (LTCC) is a special type of longwall mining applicable to very thick seams (greater than 4.5m) where good quality coal is being left because "conventional" longwall equipment has not yet been designed to operate successfully beyond around 5m mining height. It enables an increased recovery for only an incremental additional cost. The method originated in Europe but has been developed in China in more recent years and is used there quite extensively and successfully. The lower section of the seam is cut by a conventional longwall...

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Stress/Strata Control

Along the Longwall Face Along the face, the roof control function is a matter of providing sufficient resistance to control the dead load of the mass of strata which is breaking, or has broken, away from the bulk of the overlying strata. The chocks are not resisting the whole vertical stress field, most of which is redistributed to the solid coal ahead of the face (the "front abutment load") and to re-compacted material in the goaf behind the face (the "rear abutment load"). Provided the chock load capacity is sufficient to control the movement...

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Installation/Relocation

The initial installation of a set of longwall equipment and subsequent relocations, which involve recovery, transport and installation operations, are major logistical operations and require detailed planning in advance and close supervision during the exercise. The planning should start prior to development as cut-throughs need to be located at particular spacings around longwall start and finish points to assist recovery and installation operations. It can also be advantageous to mine additional access points (often referred to as "chutes")...

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Ventilation/Gas Control

The ability to provide adequate ventilation to a longwall panel can be a major factor in the success of an installation, especially in gassy conditions. Most gassy mines now use some degree of gas pre-drainage of the seam being worked which greatly reduces the gas to be dealt with during longwall extraction. However in many cases much of the gas make from a longwall panel comes from sources in the roof and/or floor and requires some form of post drainage of strata or goaf drainage, or otherwise must be handled by the mine ventilation network. The...

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Alternative Shortwall Mining Method – Gretley Colliery

Another shortwall mining method was developed in the 1980's as a means of realising the benefits of longwall mining in a shallow seam, partial extraction application where there were considerable subsidence constraints under a residential area. A short (approx 30m) longwall face was employed with a short, single ended shearer, and a "round the corner" AFC which eliminated the use of a stage loader. The face was operated blind off the two entry maingate, with an auxiliary fan being used to ventilate the face. The single drum BJD shearer was able...

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Punch Longwall Mining

This is a rather specialized type of mining which is only applicable where a seam is exposed at the highwall of an open cut mine which has reached the economic limit for open cut mining. It could also be applied where a seam has an extensive natural outcrop, but there are no instances of this in Australia known to the writer. Two roadways or sets of roadways are driven into the seam from the highwall (or outcrop) to the maximum practical distance to form gate roads and are then connected by driving the longwall installation roadway. The...

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Shortwall Underground Coal Mining

This method of mining was developed in the late 1960's to take advantage of the then recent development of suitable hydraulic longwall supports, coupled with the productivity and low capital cost of continuous miners and shuttle cars. In effect it gained some of the advantages of longwall mining without the cost of installing a complete set of longwall equipment An installation roadway was driven as for a normal longwall, but only supports were installed. A continuous miner was then utilised to cut 3.5m wide open ended lifts off the face, with...

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Cutting Machines - Coal Ploughes

Coal Ploughs have had little application in Australia, and their main use has been in Europe, particularly in Germany where they were first developed. Essentially a plough is a large mass of steel, usually of a more or less triangular shape when viewed from the coal face or goaf sides, fitted with large "picks" (more like small agricultural plough blade tips) angled from the steel body towards the coal face. The plough height is the working height...

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Cutting Processes

It has been stated that a longwall advances by cutting slices off the block. This is relatively simple for hand worked faces and with a coal plough, but with mechanized longwalls using shearers the means of doing this is not as straightforward as it would at first appear because of the complexity of the equipment. To start with, the cutting machine has to cut into the face after each slice is taken to line itself up to cut the next web. It is incapable...

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Advancing and Retreating Longwalls

Advancing Longwalls In this method, the face start point is close to the main headings, usually leaving a barrier pillar to protect them. Once the face equipment is installed, extraction commences working away from the main headings towards the block limit. Obviously the main and tailgates do not exist prior to the start of extraction and have to be formed at each end of the face as mining progresses. The gate roads are effectively in the goaf and a false rib has to be installed on one side, usually by constructing a small pillar, sometimes...

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LONGWALL MINING FOR UNDERGROUND COAL

Overview In the method of secondary extraction known as longwall mining a relatively long mining face (typically in the range 100 to 300m but may be longer) is created by driving a roadway at right angles between two roadways that form the sides of the longwall block, with one rib of this new roadway forming the longwall face. Once the longwall face equipment has been installed, coal can be extracted along the full length of the face in slices of a given width (referred to as a "web" of coal). The modern longwall face is supported by hydraulically...

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