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33-520: Minerals of interest are generally oxides , sulfides , silicates , or native metals such as copper or gold . Ore bodies are formed by a variety of geological processes generally referred to as ore genesis and can be classified based on their deposit type. Ore is extracted from the earth through mining and treated or refined , often via smelting , to extract the valuable metals or minerals. Some ores, depending on their composition, may pose threats to health or surrounding ecosystems. The word ore

66-756: A placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer , meaning " alluvial sand". Placer mining is an important source of gold , and was the main technique used in the early years of many gold rushes, including the California Gold Rush . Types of placer deposits include alluvium , eluvium , beach placers, aeolian placers and paleo-placers. Placer materials must be both dense and resistant to weathering processes. To accumulate in placers, mineral particles must have

99-462: A specific gravity above 2.58. The separation of the valuable minerals from the most common non-economic mineral, quartz , depends on the difference in specific gravity / density .The weathering process allows for the accumulation of placer minerals, while less dense material such as quartz are swept away. Hardness allows placer minerals to resist mechanical breakdown and loss of mass from abrasion during transport. A hardness greater than quartz

132-524: A cement like substance in which material like gold are found. Wind action blows sand and dirt away leaving the deposits close to the surface. Historically, aeolian placers have been mined by hand with simple tools by miners due to the proximity to the surface, and small concentration. Aeolian placers are common in Australia and the Western United states, where the climate is arid and the ground

165-457: A centimeter over several million years. The average diameter of a polymetallic nodule is between 3 and 10 cm (1 and 4 in) in diameter and are characterized by enrichment in iron, manganese, heavy metals , and rare earth element content when compared to the Earth's crust and surrounding sediment. The proposed mining of these nodules via remotely operated ocean floor trawling robots has raised

198-416: A direct result of metamorphism. These are the leading source of copper ore. Porphyry copper deposits form along convergent boundaries and are thought to originate from the partial melting of subducted oceanic plates and subsequent concentration of Cu, driven by oxidation. These are large, round, disseminated deposits containing on average 0.8% copper by weight. Hydrothermal Hydrothermal deposits are

231-565: A large body of water. Materials collect as beach placers by continuous wave action and currents. Some important examples of beach placers include black sands of Oregon, gold deposits in Nome, Alaska , zircon sands in Brazil and Australia as well as diamond marine gravel in South Africa. Gold bearing beach placers consist of large strips of black sands and are typically constantly changing as

264-445: A large source of ore. They form as a result of the precipitation of dissolved ore constituents out of fluids. Laterites form from the weathering of highly mafic rock near the equator. They can form in as little as one million years and are a source of iron (Fe), manganese (Mn), and aluminum (Al). They may also be a source of nickel and cobalt when the parent rock is enriched in these elements. Banded iron formations (BIFs) are

297-640: A number of ecological concerns. The extraction of ore deposits generally follows these steps. Progression from stages 1–3 will see a continuous disqualification of potential ore bodies as more information is obtained on their viability: With rates of ore discovery in a steady decline since the mid 20th century, it is thought that most surface level, easily accessible sources have been exhausted. This means progressively lower grade deposits must be turned to, and new methods of extraction must be developed. Some ores contain heavy metals , toxins, radioactive isotopes and other potentially negative compounds which may pose

330-412: A placer deposit, the particles desired must show a marked density contrast with the gangue material, which is able to be transported away from the trap site. Only if the deposit is winnowed in this way can the minerals be concentrated to economic levels. Beach placers are formed in sand and gravel deposited along the edge of large bodies of water and are typically found where streams or rivers flow into

363-972: A result of storms or sporadic wave action. Typically beach placers are populated by ilmenite and magnetite , however gold, platinum and chromite are found in varying amounts. Some of the most productive beach placers are considered ancient beaches that are now far inland from the water, these placers no longer shift with storms and tidal action but with wind and rainfall. Eluvial placers are deposits of metal formed on hillsides and slopes weathered by rainfall and wind. Lighter materials are carried away and weathered leaving concentrations of valuable metals. Eluvial placers are typically not large enough to support large scale mining, however in one case in Nevada there has been large scale gold mining operations based on placer deposits at Round Mountain . Aeolian placers are valuable minerals found in arid regions freed from their source rock by wind actions. Wind erosion leaves

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396-819: A risk to the environment or health. The exact effects an ore and its tailings have is dependent on the minerals present. Tailings of particular concern are those of older mines, as containment and remediation methods in the past were next to non-existent, leading to high levels of leaching into the surrounding environment. Mercury and arsenic are two ore related elements of particular concern. Additional elements found in ore which may have adverse health affects in organisms include iron, lead, uranium, zinc, silicon, titanium, sulfur, nitrogen, platinum, and chromium. Exposure to these elements may result in respiratory and cardiovascular problems and neurological issues. These are of particular danger to aquatic life if dissolved in water. Ores such as those of sulphide minerals may severely increase

429-552: A sizeable portion of international trade in raw materials both in value and volume. This is because the worldwide distribution of ores is unequal and dislocated from locations of peak demand and from smelting infrastructure. Most base metals (copper, lead, zinc, nickel) are traded internationally on the London Metal Exchange , with smaller stockpiles and metals exchanges monitored by the COMEX and NYMEX exchanges in

462-613: A specific gravity above 2.58. Placer environments typically contain black sand , a conspicuous shiny black mixture of iron oxides, mostly magnetite with variable amounts of ilmenite and hematite . Valuable mineral components often occurring with black sands are monazite , rutile , zircon , chromite , wolframite , and cassiterite . Early mining operations were probably a result of placer deposits as they were easily accessible and potential size. The events known as gold/diamond rushes were caused by placer deposits and have proved to be plentiful. Placer minerals are defined as having

495-480: Is a mineral deposit occurring in high enough concentration to be economically viable. An ore deposit is one occurrence of a particular ore type. Most ore deposits are named according to their location, or after a discoverer (e.g. the Kambalda nickel shoots are named after drillers), or after some whimsy, a historical figure, a prominent person, a city or town from which the owner came, something from mythology (such as

528-407: Is considered alluvial if formed via river, colluvial if by gravity, and eluvial when close to their parent rock. Polymetallic nodules , also called manganese nodules, are mineral concretions on the sea floor formed of concentric layers of iron and manganese hydroxides around a core. They are formed by a combination of diagenetic and sedimentary precipitation at the estimated rate of about

561-413: Is considered an ancient alluvial placer. Substances commercially mined from placer deposits include: Kimberlites are a major source of diamonds. Kimberlites are long "pipes" of lava brought up from the mantle where diamonds form at high temperatures and pressures. These diamonds are then weathered from the source and swept away by alluvial processes (transported by water) to a source that becomes

594-530: Is desired, however substances such as gold typically deform and create irregularly shaped nuggets when subject to mechanical stress. Chemical stability is important for a placer mineral to resist chemical breakdown such as oxidation , Minerals lacking chemical stability will form less desirable alteration when subject to chemical breakdown. Alluvial placers are those formed in river or stream sediments. Another name for alluvial placers are stream placers. Typical locations for alluvial gold placer deposits are on

627-614: Is of Anglo-Saxon origin, meaning lump of metal . In most cases, an ore does not consist entirely of a single mineral, but it is mixed with other valuable minerals and with unwanted or valueless rocks and minerals. The part of an ore that is not economically desirable and that cannot be avoided in mining is known as gangue . The valuable ore minerals are separated from the gangue minerals by froth flotation , gravity concentration, electric or magnetic methods, and other operations known collectively as mineral processing or ore dressing . Mineral processing consists of first liberation, to free

660-466: Is relatively level leaving wind as the primary erosion force. Paleo-placer deposits are deposits of minerals from all of the above placer types that occurred millions of years ago. These deposits are typically very far underground in ancient riverbeds, beaches, or slopes. The Witwatersrand Basin, South Africa is the largest gold deposit in the world and is considered a paleo-placer, it has produced over 1.5 billion ounces of gold. The Witwatersrand Basin

693-520: The US and Japan. For detailed petrographic descriptions of ore minerals see Tables for the Determination of Common Opaque Minerals by Spry and Gedlinske (1987). Below are the major economic ore minerals and their deposits, grouped by primary elements. [REDACTED] Media related to Ores at Wikimedia Commons Oxide mineral The oxide mineral class includes those minerals in which

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726-751: The United States and the Shanghai Futures Exchange in China. The global Chromium market is currently dominated by the United States and China. Iron ore is traded between customer and producer, though various benchmark prices are set quarterly between the major mining conglomerates and the major consumers, and this sets the stage for smaller participants. Other, lesser, commodities do not have international clearing houses and benchmark prices, with most prices negotiated between suppliers and customers one-on-one. This generally makes determining

759-549: The acidity of their immediate surroundings and of water, with numerous, long lasting impacts on ecosystems. When water becomes contaminated it may transport these compounds far from the tailings site, greatly increasing the affected range. Uranium ores and those containing other radioactive elements may pose a significant threat if leaving occurs and isotope concentration increases above background levels. Radiation can have severe, long lasting environmental impacts and cause irreversible damage to living organisms. Metallurgy began with

792-410: The direct working of native metals such as gold, lead and copper. Placer deposits, for example, would have been the first source of native gold. The first exploited ores were copper oxides such as malachite and azurite, over 7000 years ago at Çatalhöyük . These were the easiest to work, with relatively limited mining and basic requirements for smelting. It is believed they were once much more abundant on

825-456: The highest concentration of any single metal available. They are composed of chert beds alternating between high and low iron concentrations. Their deposition occurred early in Earth's history when the atmospheric composition was significantly different from today. Iron rich water is thought to have upwelled where it oxidized to Fe (III) in the presence of early photosynthetic plankton producing oxygen. This iron then precipitated out and deposited on

858-434: The inside bends of rivers and creeks ; in natural hollows; at the break of slope on a stream; the base of an escarpment , waterfall or other barrier. Stream placers are the most economical and common types of placers and have provided many with riches in the past. Alluvial placers are formed by the deposition of dense particles at a site where water velocity remains below that required to transport them further. To form

891-620: The main tin source, began. Some 3000 years ago, the smelting of iron ores began in Mesopotamia . Iron oxide is quite abundant on the surface and forms from a variety of processes. Until the 18th century gold, copper, lead, iron, silver, tin, arsenic and mercury were the only metals mined and used. In recent decades, Rare Earth Elements have been increasingly exploited for various high-tech applications. This has led to an ever-growing search for REE ore and novel ways of extracting said elements. Ores (metals) are traded internationally and comprise

924-524: The name of a god or goddess) or the code name of the resource company which found it (e.g. MKD-5 was the in-house name for the Mount Keith nickel sulphide deposit ). Ore deposits are classified according to various criteria developed via the study of economic geology, or ore genesis . The following is a general categorization of the main ore deposit types: Magmatic deposits are ones who originate directly from magma These are ore deposits which form as

957-578: The ocean floor. The banding is thought to be a result of changing plankton population. Sediment Hosted Copper forms from the precipitation of a copper rich oxidized brine into sedimentary rocks. These are a source of copper primarily in the form of copper-sulfide minerals. Placer deposits are the result of weathering, transport, and subsequent concentration of a valuable mineral via water or wind. They are typically sources of gold (Au), platinum group elements (PGE), sulfide minerals , tin (Sn), tungsten (W), and rare-earth elements (REEs). A placer deposit

990-400: The ore from the gangue, and concentration to separate the desired mineral(s) from it. Once processed, the gangue is known as tailings , which are useless but potentially harmful materials produced in great quantity, especially from lower grade deposits. An ore deposit is an economically significant accumulation of minerals within a host rock. This is distinct from a mineral resource in that it

1023-540: The oxide anion (O ) is bonded to one or more metal alloys. The hydroxide -bearing minerals are typically included in the oxide class. Minerals with complex anion groups such as the silicates , sulfates , carbonates and phosphates are classed separately. IMA -CNMNC proposes a new hierarchical scheme (Mills et al., 2009). This list uses it to modify the Nickel–Strunz classification ( mindat.org , 10 ed, pending publication). Placer deposit In geology ,

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1056-430: The price of ores of this nature opaque and difficult. Such metals include lithium , niobium - tantalum , bismuth , antimony and rare earths . Most of these commodities are also dominated by one or two major suppliers with >60% of the world's reserves. China is currently leading in world production of Rare Earth Elements. The World Bank reports that China was the top importer of ores and metals in 2005 followed by

1089-466: The surface than today. After this, copper sulphides would have been turned to as oxide resources depleted and the Bronze Age progressed. Lead production from galena smelting may have been occurring at this time as well. The smelting of arsenic-copper sulphides would have produced the first bronze alloys. The majority of bronze creation however required tin, and thus the exploitation of cassiterite,

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