Rock and Mineral Resources

Importance of Rock and Mineral Resources


·      Modern society requires a wide range of and large amount of mineral and rock resources.

·      Average American house contains 250,000 pounds of minerals, one mile of Interstate highway uses 170 million pounds of earth materials, and U.S. has ~4 million miles of roads.

·      Mineral resources are nonrenewable, because nature produces them very slowly.


Nature of Rock and Mineral Resources


·      Many rock resources (e.g., limestone, shale, slate, marble, granite, and pumice) can be used with little change.

·      Ore is earth material with profitable enrichment of minerals (photo #1, #2, #3); ore deposits contain abundant ore (world map with selected ore deposits for 14 mineral resources). Al ore minerals include Al(OH)3 and AlO(OH) and many metallic sulfide minerals are ore such as galena (PbS) and sphalerite (ZnS). Ore depends on: a) World demand - increasing demand raises price and increases amount of ore; b) Accessibility of ore - easy access to ore increases amount of ore; c) Form of metal - easily extracted metals increase amount of ore.

·      Mineral and rock resources are classified by abundant and scarce metals vs. non-metals, for industry and agriculture, construction, ceramics, abrasives, and gems. 

·      Enrichment factor is ratio of metal concentration for economic ore deposit over average abundance in Earth’s crust. Some metals (aluminum and iron) are profitable at small concentration factors and others (lead and mercury) are profitable at large concentration factors. Iron production creates little waste rock and gold production creates large amount of waste rock.


Origins of Ore Deposits


·       (a) Hydrothermal (most common) - hot, salty water dissolves metallic elements from large area and precipitates ore minerals (copper, lead, zinc, mercury, and silver sulfide, S2-) in small area along fractures (Fig. 12.7). Molten rock often provides heat and water is from groundwater, ocean, or magma. Hydrothermal vents discharge hot mineral-rich waters from cracks in oceanic crust and precipitate dark metallic sulfide minerals (black smokers, Fig. 12.8, photo). Hydrothermal vents occur commonly at oceanic ridges, where new ocean crust is produced and other settings with molten rock (map of hydrothermal vents).

·      (b) Igneous crystallization - molten rock cools to form igneous rock forming granite, pegmatite (granite with very large crystals with lithium, boron, beryllium, and uranium ore, Fig. 12.6), gemstones, sulfur, and metallic ores, where dense chromium or platinum minerals sink in magma (Fig. 12.5). Diamonds form in kimberlite (Mg-rich igneous rock) where deep magma moves quickly to surface and erupts explosively in narrow pipe (kimberlite mine photo).

·      (c) Metamorphism forms in very high temperature and pressure, producing marble, slate, asbestos, talc, and graphite.

·      (d) Sedimentary - rivers concentrate sand and gravel, dense gold, and diamonds (placer deposits); deep ocean floor with manganese and cobalt; and evaporated lakes or seawater with halite and other salts.

·      (e) Biological - action of living organisms, e.g., pearls in oysters and phosphorous in bird feces and fish bones and teeth

·      (f) Weathering - tropical rain forest where soil water concentrates insoluble elements (aluminum) by dissolving away soluble elements.


Mining and Processing Ore


·      Surface mines and underground mines; mine choice depends on ore quality (mineral concentration and distance from surface.

·      Surface mines = open-pit mines - large, semicircular holes extract low-grade metallic ore (photo), strip mines - extract horizontal ore or rock layers, solution mines (a in-situ leaching) - leaching solution pumped through fractured rock, and placer mines - gold or diamonds extracted from sediment by scooping it and density separation. Large, open-pit mines create huge piles of ore for processing and overburden.

·      Underground mines used when high-grade ore is deep, involve tunnel network to extract ore (photo).

·      Processing metallic ore involves crushing, grinding, separating ore minerals by density, and chemically separating metal using smelting (heating ore minerals with different chemicals) and heap leaching (using chemicals to dissolve metal). Fine-grained waste from processing ore = tailings. Slag = glassy by-product of smelting ore (photo - slag pile). Many nonmetallic minerals and rocks do not require chemical separation.


Environmental Issues of Rock and Mineral Resources - include impacts of mining and processing ore and mineral depletion.


Hazards of Ore Mining

·      Metallic ore mines produce much waste because ore is small part of mined material. Large surface mines and piles of overburden (photo) and tailings must be reclaimed, which is required in USA but often not in underdeveloped countries.

·      Hydraulic mining - high pressure hoses cut into landscape (photo, Fig. 12.21) of placer ore deposits can destroy natural settings, accelerate soil erosion, and fill river channels with sediment causing them to flood.

·      Heap leaching - sulfuric acid or cyanide-rich water flows through ore and slowly dissolves metal; water is treated to remove metal, Fig. 12.22). Heap leaching allowed recovery from very low-grade ore and waste ore tailings, but leaching solution can pollute environment, e.g., cyanide spill occurred in Romania due to gold tailings pond collapse (map, photo of dead fish from spill).

·      Underground mines are hazardous for miners due to cave-ins and lung disease from dust particles. Metallic ore mines are safer than coal mines due to stronger rock. Mine roof collapse can damage surface due to subsidence (photo). Large, deep surface mines can experience landslides such as 2013 landslide at Bingham Canyon mine in Utah (satellite photos-before, after; photo set); it was the largest non-volcanic incident in modern North American history (scientific discussion #1; #2). 


Hazards of Ore Processing


·      Unreclaimed and active surface mines and tailings can pollute environment. Metallic ore minerals often contain sulfide, which oxidizes quickly at surface producing acid mine drainage that pollutes surface water with toxic acid and heavy metals (photo). Plants die and soils erode. Underground mines are easier to reclaim; produce little acid drainage.

·      Metal smelting can cause air pollution from SO2 gas (causing acid rain), particulates, and heavy metals. Smelting for >100 years at Sudbury, Canada (photo) has polluted and devegetated huge area and created ~7,000 acid-damaged lakes. Metal smelting can cause air pollution from SO2 gas (causing acid rain), particulates, and heavy metals. Smelting for >100 years at Sudbury, Canada has polluted and devegetated huge area and created ~7,000 acid-damaged lakes.


Depletion of Rock and Mineral Resources


·      With rising world population and prosperity, demand for rocks and minerals will rise, depleting mineral deposits faster and requiring new deposits (Fig. 12.25). Table 4 gives estimated life of reserves (known amount of ore in world) of important and strategic minerals (essential to country but must be imported to meet demand). Estimated life = 800 - 20 years. Won’t totally run out but will use all “cheap” deposits.

·      Looming problem with rare earth elements, produced mainly by China, threatening to limit their exports.

·      More complex analysis predicts 20 of 23 minerals studied will experience permanent shortfall in global supply by 2030 i.e., peak mineral reached (Table 5). Most serious depletion for cadmium, gold, mercury, tellurium, and tungsten; serious depletion for cobalt, lead, molybdenum, platinum group metals, phosphate rock, silver, titanium, and zinc - they are likely at or near their global production peak and there is a very high probability that there will be a permanent global supply shortfall by 2030; depletion for chromium, copper, indium, iron ore, lithium, magnesium compounds, nickel, and phosphate rock; and no depletion for bauxite, rare earth minerals, and tin.

·      Prediction of future mineral shortages = difficult and controversial. Life for mineral reserves decreases if demand increases, but mineral reserve life increases if new deposits are found or if unprofitable deposits become profitable from price increase or technological improvements. Mineral resources = total amount of mineral with some economic potential (Fig. 12.3).


Sustainable Solutions for Rock and Mineral Resources


Hazards of Ore Mining and Processing


·      Need laws and good engineering to ensure mine reclamation and pollution reduction. Reclamation of rock and mineral mines is controlled by state and local laws, which can vary. For extreme pollution, unreclaimed surface mines are remediated through Superfund, federal program to identify and clean worst abandoned hazardous waste sites (photos).

·      Commonly reclamation is well done in USA but not everywhere, especially in underdeveloped countries with no laws or lax enforcement.


Extending the Mineral Supply


·      Mineral “sustainability” should emphasize conservation. We must explore for new mineral resources but minimize environmental impact.

·      Mineral conservation includes improved efficiency, substitution, and reduce, reuse, and recycle. Improved efficiency during mining, processing, and creating mineral products. Substituting rare mineral resource with more common or renewable resource helps, e.g., glass fiber optic cables for copper in telephone wires.

·      Difficult to < global mineral demand especially for growing economies of China, India, and Brazil. In theory, easier for affluent USA to < its mineral demand. Technology can < mineral demand, e.g., digital cameras eliminated photographic demand for silver in film development. More durable goods help. Resource reuse at yard sales.

·      Recycling extends mineral reserve life, especially metals (photo). Pure metal easy to recycle, metal mixtures, complex goods (computers), and nonmetals (fertilizer) are difficult. Recycling is easier for wealthy country. Mineral conservation = reductions in pollution, environmental degradation, energy use, and waste production.

·      Search for new minerals must continue using advanced technologies such as geophysics (seismic, gravity, magnetic, and electrical measurements, and remote sensing, i.e., satellite-based measurements), geochemistry (chemical enrichments in soil, water, air, and plants), and geology such as plate tectonics theory. We should explore and mine unconventional areas such as continental margins, ocean floor (for manganese ore), and oceanic ridges (with copper, zinc, and lead ore).

·      Biotechnology may provide solutions to metal extraction, e.g., biooxidation (microbial metal enrichment), bioleaching (microbial metal dissolution), biosorption (attaching metals to cells), and genetic engineering of microbes (create microorganisms specialized in extracting metal from ore).