Latest revision as of 01:57, 25 January 2013

Sublevel Caving 1.png

Sublevel Caving is one of the most advanced mining methods. This method is usually undertaken when mining the orebody through an open pit is no longer economically viable. In Sublevel Caving, mining starts at the top of the orebody and develops downwards. Ore is mined from sublevels spaced at regular intervals throughout the deposit. A series of ring patterns is drilled and blasted from each sublevel, and broken ore is mucked out after each blast. Sublevel Caving can be used in orebodies with very different properties and is an easy method to mechanize. This method is normally used in massive, steeply-dipping orebodies with considerable strike length, and usually has a high amount of dilution and low recoveries. Thus Sublevel Caving is usually used to mine low-grade, low-value orebodies.

Ore Body Characteristics

•Strong and competent rock with few major structures:

- A competent rock mass allows for more drilling and blasting within each stope. This provides good fragmentation and leaves the caving above very coarse. This results in blasted material finer than the cave, making distinction between ore and waste easier.

• Steeply dipping orebody:

- Keeps the low grade waste further away from the current draw points, keeps dilution low.

•Massive deposit:
- Need a large footprint to minimize dilution levels as most dilution comes from the boundary between ore and waste. A massive deposit minimizes the dilution as a smaller proportion of material is being mined from these boundary areas.
• No weak or weathered materials:
- Can cause problems with muck rushes, over-compaction, and hang-ups.

• Preferably have mineralised waste:

- Keeps the dilution low and allows for overdrawing at drawpoints. The model (Figure 2) below shows the proportion of ore (below the line) and dilution (above the line) as the extraction increases. It can be seen that very high extractions can be achieved depending on the shape of the curve and the grade of the ore and waste. If the waste rock is mineralized more ore can be removed without increasing the dilution factor.

Advantages

• Inexpensive method that yields a large amount of muck
• Highly mechanized process:
- in most cases the drifts and tunnels are sufficiently large enough to introduce large trackless mining equipment
• High efficiency:
- with the repetitive nature of this mining method you can standardize all the mining activities
• High amount of flexibility with production rates
• Because all of the mining activities are executed in or from relatively small openings, sublevel caving is one of the safest mining methods

Disadvantages

• High level of dilution
• Low recovery
• Ore loss:
- when the extraction limit (point with maximum allowable dilution) is reached, the remaining diluted ore represents an ore loss
- Losses are larger as the inclination of the orebody and footwall is reduced
• Large amount of development required

Mine Development

Sublevel caving operations involve a large amount of development before the mine can go into production. The entire mine must be developed with the exception of the production headings on the lower sublevels. They will be developed after the mine has gone into production since the orebody is mined out from top to bottom.

F10.jpg

1. Production Shaft
2. Internal ramp
3. Sublevel extractions drifts
4. Production Headings
5. Orepasses
6. Main Haulage Level(s)
7. Mine Infrastructure

1.Production Shaft

• Usually Located in the footwall
• Sized based off of the production rate

2. Internal Ramp

• Developed in the footwall
• Grade of around 15% with flattening at sublevel access drifts
• Follows the dip of the orebody
• Allows equipment to travel freely from level to level without the use of the shaft
• Designed to be approximately 5 ft wider and higher than the largest piece of equipment

3. Sublevel Extraction Drifts

• Developed in footwall parallel to the strike of the orebody
• Designed to be approximately 5 ft wider and higher than the largest piece of equipment
• Usually developed every 100 ft

4. Production Headings

Drifts that run the width of the orebody from the sublevel extraction drifts in the footwall to the hangingwall.

Heading Width:
• Developed as wide as possible to get good draw coverage

Heading Spacing:
• Determined based off of the ellipsoid extraction width usually around 60% to 65% of the ellipsoid draw height
• Should be wide enough to provide some interactive draw between headings
• Should be no less than twice the heading width to limit development costs

Flat Back:
• Results in a level zone of moving material
• An arched back will cause more ore to be drawn from the middle of the stope resulting in more dilution from the caved waste rock

Heading Height:
• As low as possible to allow more room for loading blasts but high enough to allow equipment to enter

5. Orepasses

• Located every 100 ft to 200 ft in the sublevel extraction drift
• Used for transporting ore from the sublevels to the main haulage level
• Designed to have a dip of approximately 70° to 80°
• Sized based off of the production rate and orepass spacing
• Grizzlies and rock breakers should be installed at the top of each finger raise to prevent oversize from causing hang-ups

6. Main Haulage Level

• Track drift developed in the footwall parallel to orebody strike
• Used to tram ore from the orepasses to the crushing station and loading pocket for skipping to surface
• Sized based off of the size of the tramming equipment which is based off of the production rate for the mine

7. Mine Infrastructure

• Ventilation Raises – Sized based off of ventilation requirements( 100 CFM per brake horsepower)
• Equipment shops – Sized based off of equipment fleet
• Mine Dewatering system
• Pressurized air and water pipes
• Electrical System
• Refuge Stations

Ground Support

Standard ground support is used including rock bolts and screen. Shotcreting and cablebolting are used in areas of bad ground as determined by the rock mechanics engineer.

Production Rate

The production rate at sublevel caving mines is usually high tonnage due to the massive size of the ore body, the high degree of mechanization, the accuracy and speed of the production drills, and the number of draw points available to muck from. Production rates for various sublevel caving operations are shown below:

- Kiruna Iron Ore Mine, LKAB – 76,000 tpd

- Stobie-Frood Copper-Nickel Mine, Vale – 4,500 tpd

Equipment

Sub level caving operations involve a high degree of mechanization. Due to the nature of the mine method each equipment type is usually isolated in a specific level of the mine.
Lateral development is completed using drill-jumbos to drill off rounds while LHD’s are used for mucking the broken rock and bolters for providing ground support for the drift.
Production drilling is carried out by top hammer drills. The drills typically drill off an entire stope at once before any rings are blasted. Recent technology has been able to create faster and more accurate drilling allowing sublevel spacing to be increased decreasing development costs and increasing production rates.
Production Mucking is done by the use of LHD`s that transport the ore from the drawpoint to orepasses located in the sublevel extraction drift.
Drawpoints are considered mucked out when there is enough dilution to drop the grade of the ore below the cut-off grade. Drawpoints are usually mucked under geology control.

Material Handling

The following steps outline the material handling process in sub level caving operations following production blasting and sufficient drawpoint ventillation:

1. The ore is mucked out of a drawpoint and transported using a LHD to an orepass located in the sublevel extraction drift
2. The ore is dumped down the orepass to the main haulage level
3. The ore is pulled from chutes at the bottom of the orepass and transported by rail to the main crushing station located near the shaft
4. The ore is crushed, loaded into skips, and sent to surface for processing

Sublevel Caving Layout

Extensive research has been performed on layout parameters, using model experiments and theoretical applications. The use of models has proved to be the most constructive in determining layout parameters for a known ore as well as for gaining general knowledge of the principles involved. Any small change in recovery in a sublevel caving layout can have a significant impact on revenue. Therefore, it is essential to implement the most efficient possible layout and to have a good understanding of the process by the engineers, the supervisors and the operators in order to maintain a controlled draw that limits dilution.

Layout parameters include a choice between transverse or longitudinal production layouts, sublevel height, production drift spacing and pillar width, and the size and shape of the production drift.

Legitimate interrelation has been found between model tests and actual in mine behavior. It is, however, important to acknowledge the limitations present in model testing. The main difference between model tests and actual in mine results can be contributed to the consolidation that takes place in a mine when ore is blasted against broken muck. In a modeled scenario, the material is loose and does not account well for this phenomenon. Also, volume and weight are a cubic function which are often not properly represented in a model.

Sublevel Caving Safety

Sublevel caving is a relatively safe mining method since the operations take place in small areas at a time and are highly mechanized. The uniformly distributed nature of generally 5mx3.7m sublevel nature of drifts aids in the safety of this mining method. To increase the stability of drifts in competent rock is controlled by smooth blasting and shotcrete, whereas less competent rock is affected positively by reinforcement, smooth blasting, shotcrete, and rockbolts.

The Kiruna Mine

The Kiruna mine in Norbotten County, Lapland is a sublevel caving iron ore operation in Luossavaara-Kiirunavaara Aktiebolag (LKAB) begun in 1898. The ore body is 4km long, 80m thick and 2km deep and has yielded more than 950Mt of ore since opening. It is estimated that the original reserve is about 1,800Mt, with proven reserves being 602Mt at a grade of 48.5% iron and probably reserves of 82Mt at 46.7% iron. The measured, indicated, and inferred resources are about 328Mt.

F7.jpg

The sublevels are spaced at 28.5m vertically and have 3.0-3.5m burden per ring. The main haulage level is at 1,045m. The ore-handling systems are equipped to handle 26Mt/y of rock, moved by seven 500t shuttle trains that collect ore from ten groups of ore passes. The ore is then taken to one of four crushers, sampled to determine apatite and magnetite contents and processed in a sorting plant, two concentrators and two pellet plants. The main haulage system is to be moved to its 7th level at 1,365m in 2012. Using an estimated yearly production of 19Mt of finished product, the mine life of Kiruna will be increased to 2030.

F6.jpg

References

(1) Page, Chris. Sub-level Caving: Where is it Headed?. Retrieved on November 13, 2012 from https://www.minewiki.org/index.php/Sub-Level_Caving:_Where_Is_It_Headed%3F
(2) Sublevel Caving. Retrieved on November 15, 2012 from http://194.132.104.144/Websites%5CRDE%5Cwebsite.nsf/$All/DD6EE84F7D32F22F4125674D004C122B?OpenDocument
(3) Gertsch, R. and R. Bullock. Techniques in Underground Mining. Retrieved on November 10, 2012 from http://books.google.ca/books?id=s5bcuu3fQQsC&pg=PA621&lpg=PA621&dq=sublevel+caving+advantages&source=bl&ots=DbqJ-m-61S&sig=YqHesqPDROeaDzeW7aMEgzDtaLI&hl=en&sa=X&ei=UqaiUOiLMumgywGn9YDwAg&ved=0CCAQ6AEwAA#v=onepage&q=sublevel%20caving%20advantages&f=false
(4) Hartman, Howard L. SME Mining Engineering Handbook. 2nd Edition. Vol.2. Society for Mining, Metallurgy, and Exploration, Inc. Littleton, Colorado. 1992. Print.

(5) Kiruna, Sweden. Retrieved on November 12, 2012 from http://www.mining-technology.com/projects/kiruna/

(6) Kiruna. Mine Sites: Major Mining Operations Around the World (17 January 2007). Retrieved on November 12, 2012 from http://www.infomine.com/minesite/minesite.asp?site=Kiruna

(7) Sharma, Partha Das. Sublevel Caving Technique: Simplicity and Low Cost are the Essence. Retrieved on November 12, 2012 from http://miningandblasting.wordpress.com/2010/06/01/sublevel-caving-technique/

@@ Line 1: / Line 1: @@
-&nbsp;Sublevel Caving is one of the most advanced mining methods. This method is usually undertaken when mining the orebody through an open pit is no longer economically viable. In Sublevel Caving, mining starts at the top of the orebody and develops downwards. Ore is mined from sublevels spaced at regular intervals throughout the deposit. A series of ring patterns is drilled and blasted from each sublevel, and broken ore is mucked out after each blast. Sublevel Caving can be used in orebodies with very different properties and is an easy method to mechanize. This method is normally used in massive, steeply-dipping orebodies with considerable strike length, and usually has a high amount of dilution and low recoveries. Thus Sublevel Caving is usually used to mine low-grade, low-value orebodies.
+&nbsp;[[Image:Sublevel Caving 1.png|thumb|right|615x476px|Sublevel Caving 1.png]]Sublevel Caving is one of the most advanced mining methods. This method is usually undertaken when mining the orebody through an open pit is no longer economically viable. In Sublevel Caving, mining starts at the top of the orebody and develops downwards. Ore is mined from sublevels spaced at regular intervals throughout the deposit. A series of ring patterns is drilled and blasted from each sublevel, and broken ore is mucked out after each blast. Sublevel Caving can be used in orebodies with very different properties and is an easy method to mechanize. This method is normally used in massive, steeply-dipping orebodies with considerable strike length, and usually has a high amount of dilution and low recoveries. Thus Sublevel Caving is usually used to mine low-grade, low-value orebodies.&nbsp;
-[[Image:Sublevel Caving 1.png|thumb|center|509x449px]]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;''Figure 1: Sublevel caving development and production schematic''&nbsp;
+<br>
 = <br>&nbsp;Ore Body&nbsp;Characteristics&nbsp;  =
-•'''Strong and competent rock with few major structures:'''
+•'''Strong and competent rock with few major structures:''' [[Image:F2.jpg|thumb|right|387x316px]]
 - A competent rock mass allows for more drilling and blasting within each stope. This provides good fragmentation and leaves the caving above very coarse. This results in blasted material finer than the cave, making distinction between ore and waste easier.
@@ Line 18: / Line 18: @@
 - Keeps the dilution low and allows for overdrawing at drawpoints. The model (Figure 2) below shows the proportion of ore (below the line) and dilution (above the line) as the extraction increases. It can be seen that very high extractions can be achieved depending on the shape of the curve and the grade of the ore and waste. If the waste rock is mineralized more ore can be removed without increasing the dilution factor.<br>
-[[Image:Example.jpg]]
 = Advantages  =
@@ Line 29: / Line 27: @@
 '''• High level of dilution<br>• Low recovery<br>• Ore loss:<br>'''-&nbsp;when the extraction limit (point with maximum allowable dilution) is reached, the remaining diluted ore represents an ore loss<br>-&nbsp;Losses are larger as the inclination of the orebody and footwall is reduced'''<br>• Large amount of development required<br>'''
-= Mine Development  =
+= &nbsp;Mine Development  =
-Sublevel caving operations involve a large amount of development before the mine can go into production. The entire mine must be developed with the exception of the production headings on the lower sublevels. They will be developed after the mine has gone into production since the orebody is mined out from top to bottom.&nbsp;&nbsp; <br><br>'''1. Production Shaft<br>2. Internal ramp <br>3. Sublevel extractions drifts<br>4. Production Headings<br>5. Orepasses<br>6. Main Haulage Level(s)<br>7. Mine Infrastructure'''<br>
+Sublevel caving operations involve a large amount of development before the mine can go into production. The entire mine must be developed with the exception of the production headings on the lower sublevels. They will be developed after the mine has gone into production since the orebody is mined out from top to bottom.&nbsp;&nbsp; [[Image:F10.jpg|thumb|right|483x701px|F10.jpg]]<br> <br>'''1. Production Shaft<br>2. Internal ramp <br>3. Sublevel extractions drifts<br>4. Production Headings<br>5. Orepasses<br>6. Main Haulage Level(s)<br>7. Mine Infrastructure'''<br>&nbsp;
-== 1. Production Shaft  ==
+== 1.Production Shaft  ==
 • Usually Located in the footwall<br>• Sized based off of the production rate <br>
@@ Line 81: / Line 79: @@
 - Kiruna Iron Ore Mine, LKAB – 76,000 tpd
-- Stobie-Frood Copper-Nickel Mine, Vale – 4,500 tpd<br>
+- Stobie-Frood Copper-Nickel Mine, Vale – 4,500 tpd<br> [[Image:F3.jpg]]
-[[File:f3.jpg]]
 = Equipment  =
-Sub level caving operations involve a high degree of mechanization. Due to the nature of the mine method each equipment type is usually isolated in a specific level of the mine. <br>Lateral development is completed using drill-jumbos to drill off rounds while LHD’s are used for mucking the broken rock and bolters for providing ground support for the drift. <br>Production drilling is carried out by top hammer drills. The drills typically drill off an entire stope at once before any rings are blasted. Recent technology has been able to create faster and more accurate drilling allowing sublevel spacing to be increased decreasing development costs and increasing production rates.<br>Production Mucking is done by the use of LHD`s that transport the ore from the drawpoint to orepasses located in the sublevel extraction drift. <br>Drawpoints are considered mucked out when there is enough dilution to drop the grade of the ore below the cut-off grade. Drawpoints are usually mucked under geology control.&nbsp;&nbsp;&nbsp; <br>
+Sub level caving operations involve a high degree of mechanization. Due to the nature of the mine method each equipment type is usually isolated in a specific level of the mine. <br>Lateral development is completed using drill-jumbos to drill off rounds while LHD’s are used for mucking the broken rock and bolters for providing ground support for the drift. <br>Production drilling is carried out by top hammer drills. The drills typically drill off an entire stope at once before any rings are blasted. Recent technology has been able to create faster and more accurate drilling allowing sublevel spacing to be increased decreasing development costs and increasing production rates.<br>Production Mucking is done by the use of LHD`s that transport the ore from the drawpoint to orepasses located in the sublevel extraction drift. <br>Drawpoints are considered mucked out when there is enough dilution to drop the grade of the ore below the cut-off grade. Drawpoints are usually mucked under geology control.&nbsp;&nbsp;&nbsp; <br> [[Image:F4.jpg]]
-[[File:f4.jpg]]
 = Material Handling  =
@@ Line 91: / Line 89: @@
 The following&nbsp;steps outline&nbsp;the material handling process in sub level caving operations&nbsp;following production blasting&nbsp;and sufficient&nbsp;drawpoint&nbsp;ventillation:&nbsp;
-<br>1. The ore is mucked out of a drawpoint and transported using a LHD to an orepass located in the sublevel extraction drift<br>2. The ore is dumped down the orepass to the main haulage level <br>3. The ore is pulled from chutes at the bottom of the orepass and transported by rail to the main crushing station located near the shaft<br>4. The ore is crushed, loaded into skips, and sent to surface for processing<br>
+<br>1. The ore is mucked out of a drawpoint and transported using a LHD to an orepass located in the sublevel extraction drift<br>2. The ore is dumped down the orepass to the main haulage level <br>3. The ore is pulled from chutes at the bottom of the orepass and transported by rail to the main crushing station located near the shaft<br>4. The ore is crushed, loaded into skips, and sent to surface for processing<br> [[Image:F5.jpg]]
-[[File:f5.jpg]]
 = Sublevel Caving Layout  =
@@ Line 99: / Line 97: @@
 <br>Layout parameters include a choice between transverse or longitudinal production layouts, sublevel height, production drift spacing and pillar width, and the size and shape of the production drift.
-[[File:f8.jpeg]]
+[[Image:F8.jpeg]]
 <br>Legitimate interrelation has been found between model tests and actual in mine behavior. It is, however, important to acknowledge the limitations present in model testing. The main difference between model tests and actual in mine results can be contributed to the consolidation that takes place in a mine when ore is blasted against broken muck. In a modeled scenario, the material is loose and does not account well for this phenomenon. Also, volume and weight are a cubic function which are often not properly represented in a model.
-= Sublevel Caving&nbsp;Layout =
-Extensive research has been performed on layout parameters, using model experiments and theoretical applications. The use of models has proved to be the most constructive in determining layout parameters for a known ore as well as for gaining general knowledge of the principles involved. Any small change in recovery in a sublevel caving layout can have a significant impact on revenue. Therefore, it is essential to implement the most efficient possible layout and to have a good understanding of the process by the engineers, the supervisors and the operators in order to maintain a controlled draw that limits dilution.
-Layout parameters include a choice between transverse or longitudinal production layouts, sublevel height, production drift spacing and pillar width, and the size and shape of the production drift. <br>
-Legitimate interrelation has been found between model tests and actual in mine behavior. It is, however, important to acknowledge the limitations present in model testing. The main difference between model tests and actual in mine results can be contributed to the consolidation that takes place in a mine when ore is blasted against broken muck. In a modeled scenario, the material is loose and does not account well for this phenomenon. Also, volume and weight are a cubic function which are often not properly represented in a model.
-= Gravity Flow  =
-== Principles of Gravity Flow  ==
-== Factors that control Gravity Flow  ==
-== Specific Application to Sublevel Caving  ==
-== Practical&nbsp;Design Guidance  ==
-== Importance of Precise&nbsp;Sublevel Caving&nbsp;Geometry  ==
 = Sublevel Caving Safety  =
@@ Line 129: / Line 105: @@
 Sublevel caving is a relatively safe mining method since the operations take place in small areas at a time and are highly mechanized.&nbsp; The uniformly distributed nature of generally 5mx3.7m sublevel nature of drifts aids in the safety of this mining method.&nbsp; To increase the stability of drifts in competent rock is controlled by smooth blasting and shotcrete, whereas less competent rock is affected positively by reinforcement, smooth blasting, shotcrete, and rockbolts.&nbsp;
-= The Kiruna Sublevel Caving&nbsp;Operation  =
+= The Kiruna&nbsp;Mine&nbsp;  =
+The Kiruna mine in Norbotten County, Lapland is a sublevel caving iron ore operation in Luossavaara-Kiirunavaara Aktiebolag (LKAB) begun in 1898.&nbsp; The ore body is 4km long, 80m thick and 2km deep and has yielded more than 950Mt of ore since opening.&nbsp; It is estimated that the original reserve is about 1,800Mt, with proven reserves being 602Mt at a grade of 48.5% iron and probably reserves of 82Mt at 46.7% iron.&nbsp; The measured, indicated, and inferred resources are about 328Mt. [[Image:F7.jpg|thumb|right|265x394px|F7.jpg]]
-The Kiruna mine in Norbotten County, Lapland is a sublevel caving iron ore operation in Luossavaara-Kiirunavaara Aktiebolag (LKAB) begun in 1898.&nbsp; The ore body is 4km long, 80m thick and 2km deep and has yielded more than 950Mt of ore since opening.&nbsp; It is estimated that the original reserve is about 1,800Mt, with proven reserves being 602Mt at a grade of 48.5% iron and probably reserves of 82Mt at 46.7% iron.&nbsp; The measured, indicated, and inferred resources are about 328Mt.
+<br>&nbsp;
-[[File:f7.jpg]]
-The sublevels are spaced at 28.5m vertically and have 3.0-3.5m burden per ring.&nbsp; The main haulage level is at 1,045m.&nbsp; The ore-handling systems are equipped to handle 26Mt/y of rock, moved by seven 500t shuttle trains that collect ore from ten groups of ore passes.&nbsp; The ore is then taken to one of four crushers, sampled to determine apatite and magnetite contents and processed in a sorting plant, two concentrators and two pellet plants.&nbsp; The main haulage system is to be moved to its 7th level at 1,365m in 2012.&nbsp; Using an estimated yearly production of 19Mt of finished product, the mine life of Kiruna will be increased to 2030.
+The sublevels are spaced at 28.5m vertically and have 3.0-3.5m burden per ring.&nbsp; The main haulage level is at 1,045m.&nbsp; The ore-handling systems are equipped to handle 26Mt/y of rock, moved by seven 500t shuttle trains that collect ore from ten groups of ore passes.&nbsp; The ore is then taken to one of four crushers, sampled to determine apatite and magnetite contents and processed in a sorting plant, two concentrators and two pellet plants.&nbsp; The main haulage system is to be moved to its 7th level at 1,365m in 2012.&nbsp; Using an estimated yearly production of 19Mt of finished product, the mine life of Kiruna will be increased to 2030.&nbsp; [[Image:F6.jpg|thumb|center|630x440px|F6.jpg]]
-[[File:f6.jpg]]
-= References  =
+= &nbsp;&nbsp;References  =
 (1) Page, Chris. Sub-level Caving: Where is it Headed?. Retrieved on November 13, 2012 from https://www.minewiki.org/index.php/Sub-Level_Caving:_Where_Is_It_Headed%3F<br>(2) Sublevel Caving. Retrieved on November 15, 2012 from http://194.132.104.144/Websites%5CRDE%5Cwebsite.nsf/$All/DD6EE84F7D32F22F4125674D004C122B?OpenDocument<br>(3) Gertsch, R. and R. Bullock. Techniques in Underground Mining. Retrieved on November 10, 2012 from http://books.google.ca/books?id=s5bcuu3fQQsC&amp;pg=PA621&amp;lpg=PA621&amp;dq=sublevel+caving+advantages&amp;source=bl&amp;ots=DbqJ-m-61S&amp;sig=YqHesqPDROeaDzeW7aMEgzDtaLI&amp;hl=en&amp;sa=X&amp;ei=UqaiUOiLMumgywGn9YDwAg&amp;ved=0CCAQ6AEwAA#v=onepage&amp;q=sublevel%20caving%20advantages&amp;f=false<br>(4) Hartman, Howard&nbsp; L. SME Mining Engineering Handbook. 2nd Edition. Vol.2. Society for Mining, Metallurgy, and Exploration, Inc. Littleton, Colorado. 1992. Print.

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