Unit 4 ch 16 s2 mineral exploration & miningPresentation Transcript
Mining & Mineral ResourcesChapter 16, Section 2: Mineral Exploration & Mining Standards: SEV4a, b, e
What are the steps in harvesting minerals? Prospecting- finding places where ores occur Mine exploration & development- learn whether ore can be extracted economically Mining- extract ore from ground Extraction- separate ore minerals from other mined rock Smelting & refining- extract pure mineral from ore mineral (get the good stuff out of waste rock) Transportation- carry mineral to market Marketing & sales- find buyers & sell the mineral
How do we know where mineral deposits are located? Airplanes can carry instruments that detect Patterns of gravity Images of the Saline Valley in California. Magnetism Left picture- red indicates trees, white Radioactivity indicates snow Data is collected, satellite images are Middle picture- short wavelengths used taken, and a geologic map is created. to identify types of rocks Right picture- thermal infrared used to Rock samples are taken & analyzed for identify types of rocks that contain their content & grade valuable minerals. Red indicates quartz Test holes are drilled to create a 3D estimate of the extent of the ore This will tell the driller if the amount and grade of ore is high enough to warrant the cost of opening a mine. How Much Does a Mine Cost?
3 Types of MiningA. Subsurface miningB. Surface miningC. Placer mining
A. What is subsurface mining? Mining of ore deposits 50m or more below Earth’s surface. (This is as long as an Olympic size pool) 3 types of subsurface mining: 1. Room & Pillar mining 2. Longwall mining 3. Solution mining
1. Room & Pillar Mining Coal & Salt can be mined this way “Rooms” are cut into a coal seam. Coal seam is a long, wide, layer of coal. The “walls” of the room act as pillars to prevent collapse. After all rooms of coal removed, the pillars are taken down starting with farthest away.
2. Longwall mining A shearer machine moves back and forth along the coal seam. Sheared coal drops onto a conveyor belt and exits the mine Hydraulic roof supports are used to prevent collapse
3. Solution Mining Potash, salt, sulfur are soluble in water Hot water is injected into ore Ore is dissolved Removal of ore from water: Compressed air pumped into dissolved ore and ore trapped in air bubbles that rise to surface… or… Water evaporates from dissolved ore leaving ore behind.
B. What is surface mining? Used when ore deposits are located close to Earth’s surface 3 types 1. Open Pit Mining 2. Quarrying 3. Solar Evaporation
1. Open Pit Mining Soil & rock (overburden) are removed from top of ore deposit Use explosives or heavy machinery AKA- mountain top removal Loaders remove the exposed coal Pit is then refilled with overburden & covered with soil. Some types of ore are taken to heap leaching ponds where mineral is removed from the ore rock. Gold miners used to use mercury to extract gold but proved very poisonous to animals & plants Now gold is extracted from ore rock using cyanide. Cyanide is also very poisonous. Bottom picture: Open pit gold mine with heap leaching cyanide ponds down below.
Machine used in open pit miningBucket Wheel Excavator- cost $184,400,000Takes 5 people to operate it, moves 10 meters per minute, power lines have to be removed whenmoving it.
2. Quarrying Open pit mine that is used to harvest Granite Marble Granite quarry in Elberton, GA Sand Gravel Crushed rock (aggregates) LaFarge Granite Clay Quarry in Gypsum Douglasville, GA Talc
3. Solar Evaporation Place sea water into shallow ponds Water evaporates and leaves crystallized salt behind 30% of world’s salt produced this way Used largely in developing countries Salt evaporation ponds in San Francisco Bay. The beautiful colors are a result of harmless bacteria and brine shrimp that live among the salt. The colors vary depending on the “age” of the pond.
C. What is placer mining? Rock with minerals weathers & disintegrates Minerals carried by water in streams As streams bend, the water slows, minerals fall out of slower water and accumulate as placer deposits Can also occur along coastline where waves keep minerals from moving out to sea. Use dredging to remove minerals Bucket system that scoops sediment with minerals from bottom of body of water. Minerals are separated from sediment Scoop placer deposits in bucket, deposit on barge, barge takes to refinery for separation.
How is mineral removed from ore? Smelting Crushed ore heated to high temps. Impurities are trapped by a material called flux & create slag that forms a layer on top of the melted metal which is easily removed (but toxic) Purified molten metal falls to the bottom of the furnace and is harvested. Heap Leaching Using chemicals to dissolve mineral from ore Ex: cyanide used to remove gold Ex: sulfuric acid used to remove copper Copper can be extracted thru smelting (top) OR thru heap leaching (bottom).