Mining Methods

1. Topic 4: Mining Methods Hassan Z.Harraz hharraz2006@yahoo.com 2010- 2011 Prof. Dr. H.Z. Harraz Presentation

2. Outline of Topic 4:  Choice of mining and processing methods  Choice of mining method  What determines the type of mining?  Types of Mining  Processes and Considerations  Surface and underground mining: what’s the difference? We will explore all of the above in Topic 4. Prof. Dr. H.Z. Harraz Presentation The Mining Cycle 2 2 February 2016

3. Mining Geology • This is one of three employment centers for geologists, and it is presently enjoying a boom. The other boom employers are: • The Petroleum Industry • The Environmental Industry

4. Modern safety standards mean that most modern mines, at least those constructed by large corporations, are engineering marvels. They are expensive, and are not constructed unless the commodity sought is known to be present in profitable quantities and is recoverable.

5. Choice of mining and processing methods: “The simple aim in selecting and implementing a particular mine plan is always to mine a mineral deposit so that profit is maximized given the unique characteristics of the deposit and its location, current market prices for the mined mineral, and the limits imposed by safety, economy, environment” Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 5

6. Choice of mining method: The choice of mining method depends on many factors, including: 1) Shape of the orebody (i.e., tabular, cylindrical, spherical). 2) Orientation of the orebody (i.e., sub-horizontal, sub-vertical). 3) Continuity of the orebody. 4) Size of the orebody. 5) Depth to the orebody. 6) Ore-grade (i.e., high-grade, low-grade). 7) Distribution of ore-bearing minerals within the orebody {i.e., massive or disseminated (with a cut-off grade)}. 8) Depth of overburden. 9) Strength of the orebody and overburden/host-rocks. 10) Projected production rates. 11) Capital costs, rate of (financial recovery), cash-flow. 12) Area of land available for waste disposal (e.g., open-pit mines cover a larger surface area and generate a greater volume of wastes). 13) Safety concerns (e.g., surface mining methods have a better safety record). 14) Impacts on surface (i.e., environnemental, surface drainage and sub-surface aquifers, land-use changes, social). 15) Rehabilitation concerns. What determines the type of mining? Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 6

7. What determines the type of mining? Underground Mining v.s. Surface Mining v.s. Solution Mining ….??? Depth below surface Size of the ore body Shape of ore body Grade Type of Ore Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 7

8. Types of Mining Underground mining Surface mining Deep, small but rich: usually underground mining. Shallow, near surface: usually surface mining. Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 8

9. Types of Mining Traditional mining methods fall into two broad categories based on locale: 1) Surface mining 2) Underground mining: is usually classified in three categories of methods: unsupported, supported, and caving. Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 9

10. Figure shows morphology of surface(Open Pit) and Underground methods. Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 10

11. Comparison of waste production for surface and underground mining: Data are for USA in 1997 (from Hartman and Mutmansky, 2002), in million tons. Surface Underground All Mining Commodity Ore Waste Total Ore Waste Total Ore Waste Total (million tons) Metals Nonmetals Coal 1,290 2778 669 1863 449 10303 3,153 3,227 10,972 64 123 421 3 0 67 123 466 1,354 2,901 1,090 1,866 449 10,348 3,220 3,350 11,438 45 Total 4,737 12,615 17,352 608 48 656 5,345 12,663 18,008 Surface mining Waste = 73% of total rock tonnage extracted 266% of ore tonnage extracted Underground mining Waste = 7% of total rock tonnage extracted 9% of ore tonnage extracted Pit excavation initially generates huge volumes of waste rock that must be removed to allow access the orebody, and to allow stable pit slopes to be developed. Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 11

12. Processes and Considerations Surface mining Underground mining Scoop ore off surface of earth or dig big holes and scoop:  Disturbs large area (large amount environmental destruction).  Produces large amounts of waste rocks (spoil).  Relatively safe for miners (Safer working conditions and a better safety record than underground mining).  Cheaper (Low operating costs).  More efficient. Use adits and shafts to reach deeply buried ores: Dig a deep vertical shaft, blast underground tunnels to get mineral deposit, remove ore or coal and transport to surface Less resource recovered, more dangerous and expensive Disturbs less land and produces less waste: i) Disturbs much smaller surface area (Usually less environmental damage). ii) Waste rock (spoil) often left in mine. Dangerous (hazardous for miners; collapse, explosions (natural gas), and lung disease) Expensive (High operating costs). Less efficient. Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 12

13. Surface and underground mining: what’s the difference? Surface mining Underground mining The predominant exploitation method worldwide. Refers to two main types of mining: open-cast and open-pit. Does not require a surface pit but involves clearing rock space beneath the surface. Both open-cast and open-pit mining involves digging a large pit in the ground down from surface level. The main difference between the two is the direction of mining. In open-cast mining, the pit progresses across the landscape whereas an open-pit mine is deepened and widened but does not migrate laterally. Generally cheaper than underground mining, with higher productivity (i.e. a higher output rate of ore), lower operating costs, and safer working conditions. What does it involve? Likely to need less than one hectare at each site because there is no surface pit. Only seven percent of rock tonnage extracted is waste. If the mine waste is replaced back into the mined-out tunnels (‘backfilling’), there is also little need for surface dumping. Unfortunately, this is not very common practice because of the additional costs involved. Comparative benefits? Given these reduced surface impacts, the impact on communities, forest and biodiversity in the locality is also reduced. Without adequate attention paid to tunnel safety and the quality and strength of tunnel supports, mines can collapse. This can be dangerous both for the miners underground as well as human, plant and animal life on the surface. South Africa has one of the highest mining fatality rates in the world and of 220 deaths in 2007, more than half were caused by rock falls in undergroundmining. Environmental and social impacts are much greater because the large amount of land required– some are up to a kilometer deep and several kilometers in circumference. Frequently results in deforestation, communities, and removal of artisanal miners. relocation of Problems? Open pit mining, and to a lesser extent open-cast mining, creates a huge amount of rock waste compared to underground mining. Some analysts have estimated that 73 percent of rock tonnage extracted by surface mining is waste, which requires a great deal of space for storage and poses environmental risks of its own.133 2 February 2016 Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 13

14. US Mining Trends Prof. Dr. H.Z. Harraz Presentation Mining Geophysics, Introduction 2 February 2016 14

15. Mining Hazards Most hazardous activity in the US: Activity Deaths per 100,000 workers (1989) 43 40 Mining Agriculture Construction 32