What is the difference between vein deposits and disseminated deposits

This was a period characterized by a rapid rise of resource consumption and increasing diversification of products made by metalworking.

Perhaps the most significant advancement in metal use was the discovery of how to make bronze, an alloy created by melting and combining the metals copper and tin. The map in Figure 9. Even today, a great deal of copper mining takes place in Cyprus, although most operations have moved underground.

Although some copper and other metals came from mines on Cyprus and on the Asian mainland, tin deposits were generally small or hard to produce.

The scarcity of tin in the Middle East and other areas of the Mediterranean region, meant that tin ores came from as far away as the British Isles, which the Greeks named the Cassiterides , that translates to Tin Islands.

A key property that allowed humans to work with bronze is that, after pouring the molten bronze into stone molds and allowing the liquid to cool to a solid, the copper-tin alloy could be formed and shaped using hammers at room temperature, a process called cold working.

And, because bronze is much stronger than copper, people could make many improved products, including knives, shields and swords, and tools that led to more productive agriculture. Their technological breakthrough was to add a small amount of charcoal carbon to rocks that contained iron. The Hittites also figured out that iron-carbon alloys could not be cold-worked like bronze but had to be hammered and shaped while hot.

Thus, they invented the art of modern blacksmithing. The iron and alloys produced, once cooled, were much stronger and harder than bronze was. After the time of the Hittites, it took another to 1, years for the iron age to reach central and northern Europe Figure 9. The source of iron used by the Hittites was metallic meteorites.

Meteorites also contained a small amount of nickel that improved metal properties. Because iron-rich meteorites were not in abundance, the Hittites carefully guarded their invention of iron metal working for several centuries. During those centuries, the Hittites exercised military superiority over much of the Middle East and Egypt, where the weaker bronze was used in battle.

However, by BCE, iron metal working technology had spread across the Middle East, North Africa, Europe, and to Asia; people discovered new sources of iron; and the Hittite empire disappeared. Egyptians mined native metals, including gold, silver, and copper, from stream beds as early as to BCE.

By the Middle Ages, mining was common in Europe. Georgius Agricola Figure 9. Mineral resources literally put places on the map of the ancient world. If a region contained abundant amounts of copper, silver, tin, or gold, and later iron, it soon became populated and prosperous. Civilizations established trade routes and developed commercial systems, shipping commodities over increasingly longer distances.

If resource supplies became depleted in one location, people sought new sources. Thus, exploration was needed to sustain production and consumption of valuable resources. These same dynamics operate today: when new mineral deposits are discovered, new communities and industries may appear. When old deposits become depleted, communities and industries wane. And, always, mining companies are exploring to find new sources of economically viable minerals. Copper, tin, iron, and nickel were all important during the early ages of humans, and they are equally important today.

Those same metals — and many others — are key parts of a seemingly infinite number of products. For example, Figure 9. Tin is used to make the liquid crystal display LCD screen and to solder electrical connections that transmit digital information.

Iron is combined with the metals neodymium and boron to make magnets that are part of the microphone and speaker. And those are not the only elements in a smartphone; there are about 75 elements in all. Without any one of these elements, smartphones would not exist as they do. Nearly everything that we manufacture contains mineral resources, and the sources for these resources are mineral deposits. An ore deposit is a mineral deposit that can be produced to make a profit.

Thus, all ore deposits are mineral deposits, but the reverse is not true. Many factors control the profitability of an ore deposit. We call the amount of known ore in a deposit the reserves. When calculating the profitability, amount of reserves and ore grade are the most significant geological factors, although economic factors such as extraction costs, processing costs, and market price are often more decisive.

A high-grade ore deposit may be uneconomical to mine if the reserves are low, because start-up costs could consume all profits. A large high-grade deposit may be uneconomical to mine if it is in a remote area. Even large, developed deposits can become uneconomical if the market price falls, perhaps due to the discovery of a better deposit somewhere else.

Mining operations have many guises. Surface mining involves uncovering resources by removing overburden. This is done in several ways but, for metal deposits, open pit mining is most common. The Bingham Canyon Mine Figure 9.

It is 4. Since mining began just over years ago, the Bingham Canyon open-pit mine has produced 24 million tons of copper, tons of gold, 6, tons of silver, and , tons of molybdenum.

To put these numbers in perspective, consider that, in total, the people of the world consume about 30 million tons of newly mined copper, 2, tons of newly mined gold, 30, tons of newly mined silver, and , tons newly mined molybdenum every year.

When open pit mining cannot get to valuable resources, mining may move underground. Underground mining involves digging tunnels and shafts to reach buried ore bodies. This takes on many forms depending on the nature of an ore deposit. The Mponeng Gold Mine Figure 9.

Its deepest workings are more than 3. After mining, processing separates and concentrates valuable minerals from the ore. This involves crushing the ore rock, followed by gravity and chemical separation.

Any unwanted rock and minerals, called waste rock and gangue , respectively, are usually discarded in tailings piles. This photo Figure 9. Besides piling discarded material on the surface, sometimes miners return wastes to abandoned portions of a mine to fill voids left by ore removal. Mining commonly comes with some significant environmental costs because disposal of mine waste can lead to significant problems.

And, abandoned mines also pose environmental problems. Runoff from waste piles or mine sites may create soil, groundwater, or surface water contamination. Many ore bodies, for example, are rich in sulfide minerals. After mining ceases, sulfur from the minerals can react with water and air to create acid mine drainage Figure 9. The resulting sulfuric acid may kill vegetation and fish in nearby lakes and streams.

Contamination may also occur because of non-natural chemicals used during mineral production. And, there may be terrain costs.

After mining ceases it is often impossible to restore the mined land to anything like its pre-mining condition. Open pits remain forever and so do tailings piles. Mining sometimes also leads to increased erosion or the formation of sinkholes. Most mining companies are responsible and do their best to reduce impacts while mining takes place, but eliminating them all is impossible.

And, many mining companies do a good job of cleaning up after they are done. The photo seen in Figure 9. The area was restored and is now used for picnicking, walking and cycling. The United States, like many other countries, has enacted laws to limit the damage caused by mining.

These laws, however, are often controversial because they may drive up the price of mined commodities. Communities that rely on mining for employment, in particular, worry that regulations may lead eventually to loss of jobs. Mining, especially public land mining, is sometimes a controversial environmental issue.

For example, the Mining Law gives U. Miners pay no royalties, in contrast with those who develop coal, oil, or gas on public lands. So, the law is a federal subsidy for mining. Many environmental groups want to see Congress change the law. They argue that public lands are for the public, not mining corporations, and they point out that mining is incompatible with other uses such as wildlife habitat, hiking, and camping. Furthermore, mining leaves scars on the land and may cause long-term environmental degradation.

The mining industry argues that we need the law to ensure a flow of mineral resources to our citizens. They point out the importance of mining to some local western economies and say they can mine in an environmentally friendly way. The mining industry is correct when they argue that we need mineral resources and they have to come from somewhere.

A visit to active or abandoned mines confirms this. Besides scars on the land, less obvious problems include air, water, and soil pollution. All these problems can be limited, but not eliminated, by following the best mining practices. The real questions are where are they going to come from and how much are we willing to pay?

Those who seek reform of the law argue that some areas should be off limits to mining, that mining companies should pay more in royalties, and that there should be strict antipollution and land reclamation requirements.

If enacted by Congress, these changes might affect the price of mineral commodities, but most economists think the effect would be very small. We saw a histogram of this distribution in Figure 2.

It is no wonder, then, that humans have developed ways to use these elements in industry, agriculture, and manufacturing. Less abundant elements have also become important to modern society. These include metals, radioactive elements such as uranium or thorium, and fertilizer components including, most importantly, nitrogen and phosphorous.

The economical concentration factor listed in the table above is the ratio of typical minimum economical ore concentration to average crustal concentration. For example, the average crustal abundance of chromium is about 0. The necessary concentration factor is therefore nearly 3, — chromium must be concentrated at least 3, times to create profitable ore. The table compares economical concentration factors for a dozen different metals.

They are ordered from those most abundant top to those that are rare bottom. Concentration factors range from 4 for aluminum and iron, to nearly 3, for tin, chromium and lead. Elements that occur in high abundance do not need a high concentration factor to make mining economical. In contrast, less common chromium, lead, tin, and zinc require great concentrations to be profitably mined see the table above.

We mine relatively common elements, such as iron and aluminum, in many places worldwide; we mine rarer elements, including tin, chromium, or lead, in far fewer places. Although the table does not include prices, there is a correlation between the economical ore grades and the price of a given resource. Gold, for example, is much more expensive than the metals listed, although the demand for gold is less than for the others.

This price difference exists because the natural processes that concentrate most commonly used metals are much more common than the processes that concentrate gold, so there are fewer high-quality gold deposits than there are other kinds of deposits. Many gold mines can remain profitable even if the ore contains less than 0. The gold flakes are small — the entire photo is less than 2 cm across. The market for metals can be extremely volatile. Geopolitics, wars, economic sanctions, and other things may cause major market disruptions.

But, trends in technology may, over the long run, be even more significant. For example, beginning about 5 years ago, many predicted that the demand for electric vehicles EV was going to skyrocket. A growing EV industry means that demand for lithium-ion batteries will increase. So, in , the average market price for lithium began rising and doubled in two years. But, lithium-ion batteries also include other key metals besides lithium, for example cobalt.

Why did this happen? Several things are undoubtably important. Perhaps most significant is that the projected increase in EV sales and demand for lithium-ion batteries did not occur as rapidly as predicted. At the same time, smaller independent operators started new mines. So now we have a market surfeit of cobalt, and prices are about the lowest they have been in a decade.

Still, market prognosticators say that with the inevitable increase in demand for EVs, and for rechargeable batteries in general, prices for cobalt, nickel and graphite, and other key components of lithium-iron batteries can be expected to increase soon.

Geological processes that concentrate minerals are not unusual. But, the processes that create economically productive ore deposits are rare. If they were not, market prices would fall, decreasing profits and putting some mines out of business. The largest and most easily produced mines control market prices. Old mines shut down and new mines open up when new discoveries are made. Today, however, new discoveries are generally smaller than in the past because the largest deposits, which are more easily found than smaller deposits, have already been developed.

Because the geology of Earth varies, the distribution of ore deposits around the globe is uneven, and the minerals industry flourishes in some places and not in others. Some regions of the world contain most of the supply of certain commodities; this can affect international politics.

This mine has historically been the largest producer of molybdenum in the world. Production started in , but the mine temporarily shut down between and due to low molybdenum prices.

Nonetheless, the US has sufficient supply of molybdenum. Unfortunately, many other important minerals are not produced in the United States. We call these minerals critical minerals , or strategic minerals See Box Additionally, we import many mineral commodities, that we might produce ourselves, because it would cost too much to mine them in our own country; tungsten is a good example.

The largest pillow structure is about 65 cm in long dimension. Most South African ore deposits are associated with regions called Precambrian greenstone belts , ancient volcanic terranes.

Figures 9. Various other types of geological terranes are associated with ore deposits, too. Most economical metal and semimetal deposits are found near margins of continents, or the former margins of continents, where mountain building and igneous activity have occurred.

Still, other types of deposits are found in continental interiors. We use many different minerals and metals to maintain our lifestyles and provide military security.

Some of these commodities are not found or produced in the United States in sufficient quantities to meet demand. Consequently, we must import them from other nations. And sometimes supplies are problematic. During the Cold War, for example, the former Soviet Union and its allies stopped exporting minerals commodities to the Untied States. So, sources of strategic metals are controlled by politics as well as geology.

Consider the push to expand the use of electric vehicles EVs. The Netherlands, United Kingdom, France and some other countries have announced ambitious plans to completely eliminate gasoline and diesel vehicles. China is moving in that direction as well. But EVs need batteries and, although battery technology continues to evolve, lithium and cobalt are key components. Only eight countries produce lithium, and most of it comes from only three countries. Cobalt supplies are even more limited.

The last functioning rare earth mine in North America closed for financial reasons in Figure 9. Thus, the United States is heavily reliant on just a few countries if we are to expand electric vehicle technology and keep up with the rest of the world. Further complicating the picture is that the United States is both an importer and an exporter of some key metals and minerals. Today, the US relies entirely on imports for the following important element and mineral commodities:.

The United States is partially reliant on imports to meet needs for these element and mineral commodities:. Ores and ore minerals vary greatly in quality. Such ores do not exist, but some come close. Native copper, for example, is an ideal copper ore mineral. Ideal ore minerals are, however, uncommon. The most commonly mined ores are not ideal.

Instead they are rich in ore minerals that can be processed relatively inexpensively to isolate desired components. The table seen here lists common ore minerals for various metals. The minerals include the native metals copper and gold, and many sulfides, oxides, and hydroxides. Minerals in these groups are generally good ore minerals because they contain relatively large amounts of the desired elements. Furthermore, processing and element extraction are usually straightforward and relatively inexpensive.

That is why we mine Cu and Cu-Fe sulfides for their copper content and iron oxides for their iron content. Silicate minerals, although common, are generally poor ore minerals and are not included in the table. For example, although aluminum is found in many common silicates, tight bonding makes producing metallic aluminum from silicates uneconomical.

We obtain most aluminum from Al-hydroxides found in bauxite deposits. We discussed igneous and sedimentary minerals in previous chapters. In the following section, we focus on economic minerals that belong to other groups. Native elements have high value because they may require no processing before being used in manufacturing, as currency, or for other purposes.

The first metals ever used by humans were native minerals. Only later did humans develop refining techniques for the extraction of elements from more complex minerals. We conveniently divide native elements into metals, semimetals, and nonmetals based on their chemical and physical properties. The table to the right includes the most common minerals of each group. Within the metal group, the principal native minerals are gold, silver, copper, and platinum.

These four minerals all contain weak metallic bonds. Gold, silver, and copper have further commonality in their chemical properties because they are in the same column of the periodic table. Gold and silver form a complete solid solution; we call compositions containing both gold and silver electrum.

But, because copper atoms are smaller than gold and silver atoms, solutions are limited between copper and the precious metals. Native gold, silver, and copper may contain small amounts of other elements. For example, native copper frequently contains arsenic, antimony, bismuth, iron, or mercury.

Native platinum is much rarer than gold, silver, or copper. It typically contains small amounts of other elements, especially palladium. The native semimetals arsenic, antimony, and bismuth are also rare. Native copper, gold, silver, and platinum have atomic structures with atoms arranged in a cubic pattern Figure 9.

Iron does, too, although native iron is rare, except in meteorites, and the atomic arrangement in native iron is not quite the same as in the other metals. Nonetheless, euhedral crystals of any of these minerals may be cubic or, as we will explain in the next chapter, octahedral. More typically, however, these minerals crystallize in less regular shapes. Native zinc, a very rare mineral, has a hexagonal atomic arrangement and so forms crystals of different shapes.

The photos below Figures 9. Gold, sometimes mined as nuggets or flakes see the example in Figure 9. Large, visible specimens, like the one seen below in Figure 9. Most gold and other precious metal ores contain very fine subhedral metal grains, often microscopic. Silver sometimes occurs in a wire-like or arborescent tree-like form Figure 9. It also easily tarnishes and so has a gray color in this photo. Most bedrock gold and silver deposits are in quartz-rich hydrothermal veins.

Besides hard-rock deposits, gold and silver are also found in placers accumulations in river, stream, or other kinds of sediments , and native silver is found in several other types of deposits. Box below describes the Witwatersrand gold deposits, the largest gold deposits in the world. Section 9. The sample is 4 cm tall. The largest are about 2 mm across.

Copper is found as branching sheets, plates, and wires, and as massive pieces. In Figure 9. We mine native platinum primarily from ultramafic igneous rocks, but platinum is also found in placers — Figure 9. Platinum is also a secondary product of Cu- or Ni-sulfide refining. Native antimony in Figure 9. It is usually in solution with arsenic and may contain small amounts of other metals.

Untarnished specimens are metallic and silvery, but antimony typically tarnishes to a gray color as seen in this photo. Graphite, diamond, and sulfur are examples of nonmetallic native elements. Figure 3. Sulfur deposits are associated with volcanoes, often concentrated at fumaroles. Sulfur is also found in veins in some sulfide deposits and in sedimentary rocks where it is found with halite, anhydrite, gypsum, or calcite. Most of the rest is separated from sulfides during processing to recover metals.

Both graphite and diamond consist only of carbon. We discussed the nature of the two minerals in Box of Chapter 3. Graphite is common as a minor mineral in many kinds of metamorphic rocks, including marbles, schists, and gneisses.

The origin of the carbon is usually organic material in the original sediments. Graphite also occurs in some types of igneous rocks and in meteorites. Diamond only forms at very high pressures associated with the lowermost crust or mantle of Earth.

We mine it from kimberlite pipes, where rapidly moving, sometimes explosive, mafic magmas have carried it up to the surface. After formation, diamond sometimes concentrates in river and streambeds where we mine it from placer deposits. Although some diamonds are of gem quality, most are not. We call lower-quality diamonds industrial diamonds or bort if the diamonds are small and opaque.

See section 9. Gold occurs in many different ore deposits. The yellow grains are gold, and the black material is uraninite. This ore, like many Witswatersrand ores, is quite radioactive. The Witwatersrand deposits are paleoplacer deposits, meaning that they were placers when originally deposited. They occur in an area about km by 40 km. The origin of the Witwatersrand deposits is a bit of a mystery.

The fluid can be meteoric water that has moved downward toward a heat source, been heated, and ascended, leaching metals along its path. The sulfides are later deposited a considerable distance from the heat source.

Some of the richest gold and silver deposits in the world are hydrothermal veins. Disseminated deposits are those in which the metal is evenly distributed in generally low concentrations throughout large masses of rock.

An important type of disseminated deposit is the porphyry copper deposit , in which copper and molybdenum are found in porphyritic intrusive rocks.

Hot springs deposits are minerals that formed in response to hot spring activity at the surface of the earth. These can be rich in gold, silver, antimony, arsenic, and mercury. Ore deposits can form also by other processes at the earth's surface. These deposits are common in the central United States over relatively stable crust and may be one of the few deposit types not related to some kind of igneous heat source.

The ore minerals in most of the world's iron and manganese reserves were chemically precipitated in the ocean and accumulated on the sea floor. Placer deposits are heavy metallic minerals, such as iron or titanium minerals, or native gold or diamonds, that have been concentrated by wave or water action in a river or beach environment.

The source of the minerals may be far upstream and contain very low amounts of these minerals. The weathering, erosion, downstream transport, and deposition result in concentrations of the minerals that can be profitably mined. Lateritic weathering results in residual deposits that became enriched through the chemical breakdown and removal of most of the elements of the rock.

Water sources : Derived from cooling magma Circulating groundwater E. Deposit geometry : Vein deposits : precipitation concentrated in fractures through which water percolated. Vein deposits often yield metal ores including: iron sulfide pyrite gold Disseminated deposits : in which minerals are precipitated in a dissuse three-dimensional region near a water source. Common example: copper sulfide chalcopyrite Metamophic mineral deposits : Contact and regional metamorphism can concentrate valuable minerals.

Examples include: asbestos minerals graphite marble. Of course, metasomatism is also a means of concentrating minerals. Magmatic igneous mineral deposits : Some igneous minerals are economically valuable. These form in three ways: Fractional crystallization : We've seen how fractional crystallization of large magma intrusions can concentrate mineral in distinct layers.

One such economically significant mineral is chromite , a source of chromium used in the making of steel. Pegmatites : As a pluton cools and fractionally crystallizes, certain exotic substances become concentrated in the remaining melt. Also, as the solidified pluton cools and contracts, joints form in it. The remaining exotic materials typically fill these fractures and crystallize there, forming vein-like deposits with very large crystals, called pegmatites.

Common pegmatite minerals may include gems like corundum. Kimberlites : Remember diatremes? The magma erupted through these ancient volcanic pipes is called kimberlite , and contain material brought up from great depths. The volcanic necks of ditremes are called kimberlite pipes. Because diatreme eruptions were more common earlier in Earth's history, kimberlite pipes are more common in ancient continental cratons, such as those of southern Africa and northwestern Canada.

They are our only natural source of diamonds. Sedimentary deposits : Economic minerals are concentrated in sedimentary rocks by four processes. Evaporites : Non-biogenic chemical sediments concentrate minerals such as: halite gypsum right sodium bicarbonate potassium salts Biochemically catalyzed precipitates : Interactions of sea water and living organisms has been known to concentrate: apatite calcium phosphate Iron oxides in banded iron formations right can be economically recoverable.

Placer deposits : Currents of flowing water such as streams or longshore currents tend to segregate heavier clasts.

Often, metal nuggets and ores are concentrated in this way. The 49ers panning for gold in 19th century California were mining placer deposits in the process of forming.

Placer deposits often yield: gold platinum chromite uranite uranium oxide For info on a really weird placer deposit, follow this link. Residual mineral deposits : The percolation of groundwater, especially in the zone of leaching of laterite soils, can concentrate relatively insoluble minerals.

We've already mentioned that laterites are rich in iron ore.