Prospecting

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Prospector and burro, western Colorado, USA, circa 1900 Prospector&Burro.jpg
Prospector and burro, western Colorado, USA, circa 1900
Schoolchildren learn to pan for gold, Denver, 1972 THE DENVER P.T.A. SPONSORED A WEEK-LONG ECOLOGY WORKSHOP TO INTRODUCE SCHOOL CHILDREN TO THE NATURAL ENVIRONMENT.... - NARA - 543681.jpg
Schoolchildren learn to pan for gold, Denver, 1972
Rich specimen from a 2009 gold discovery by a prospector in southeastern Yukon Territory. The gold, deposited along a fracture, appears rusty-orange in this photo. Yukon Gold Discovery.jpg
Rich specimen from a 2009 gold discovery by a prospector in southeastern Yukon Territory. The gold, deposited along a fracture, appears rusty-orange in this photo.

Prospecting is the first stage of the geological analysis (followed by exploration) of a territory. It is the search for minerals, fossils, precious metals, or mineral specimens. It is also known as fossicking.

Contents

Traditionally prospecting relied on direct observation of mineralization in rock outcrops or in sediments. Modern prospecting also includes the use of geologic, geophysical, and geochemical tools to search for anomalies which can narrow the search area. Once an anomaly has been identified and interpreted to be a potential prospect direct observation can then be focused on this area. [1]

In some areas a prospector must also make claims, meaning they must erect posts with the appropriate placards on all four corners of a desired land they wish to prospect and register this claim before they may take samples. In other areas publicly held lands are open to prospecting without staking a mining claim.

Historical methods

Example of a prospecting pickaxe. Prospecting Pickaxe with rock.jpg
Example of a prospecting pickaxe.

The traditional methods of prospecting involved combing through the countryside, often through creek beds and along ridgelines and hilltops, often on hands and knees looking for signs of mineralisation in the outcrop. In the case of gold, all streams in an area would be panned at the appropriate trap sites looking for a show of 'colour' or gold in the river trail.

Once a small occurrence or show was found, it was then necessary to intensively work the area with pick and shovel, and often via the addition of some simple machinery such as a sluice box, races and winnows, to work the loose soil and rock looking for the appropriate materials (in this case, gold). For most base metal shows, the rock would have been mined by hand and crushed on site, the ore separated from the gangue by hand.

Often, these shows were short-lived, exhausted and abandoned quite soon, requiring the prospector to move onwards to the next and hopefully bigger and better show. Occasionally, though, the prospector would strike it rich and be joined by other prospectors and larger-scale mining would take place. Although these are thought of as "old" prospecting methods, these techniques are still used today but usually coupled with more advanced techniques such as geophysical magnetic or gravity surveys.

In most countries in the 19th and early 20th century, it was very unlikely that a prospector would retire rich even if he was the one who found the greatest of lodes. For instance Patrick (Paddy) Hannan, who discovered the Golden Mile, Kalgoorlie, died without receiving anywhere near a fraction of the value of the gold contained in the lodes. The same story repeated at Bendigo, Ballarat, Klondike and California.

The gold rushes

In the United States and Canada prospectors were lured by the promise of gold, silver, and other precious metals. They traveled across the mountains of the American West, carrying picks, shovels and gold pans. The majority of early prospectors had no training and relied mainly on luck to discover deposits.

Other gold rushes occurred in Papua New Guinea, Australia at least four times, and in South Africa and South America. In all cases, the gold rush was sparked by idle prospecting for gold and minerals which, when the prospector was successful, generated 'gold fever' and saw a wave of prospectors comb the countryside.

Modern prospecting

Modern prospectors today rely on training, the study of geology, and prospecting technology.

Knowledge of previous prospecting in an area helps in determining location of new prospective areas. Prospecting includes geological mapping, rock assay analysis, and sometimes the intuition of the prospector.

Metal detecting

Metal detectors are invaluable for gold prospectors, as they are quite effective at detecting gold nuggets within the soil down to around 1 metre (3 feet), depending on the acuity of the operator's hearing and skill.[ citation needed ]

Magnetic separators may be useful in separating the magnetic fraction of a heavy mineral sand from the nonmagnetic fraction, which may assist in the panning or sieving of gold from the soil or stream.

Prospecting pickaxe

Prospecting pickaxes are used to scrape at rocks and minerals, obtaining small samples that can be tested for trace amounts of ore. Modern prospecting pickaxes are also sometimes equipped with magnets, to aid in the gathering of ferromagnetic ores. Prospecting pickaxes are usually equipped with a triangular head, with a very sharp point.

Electromagnetic prospecting

The introduction of modern gravity and magnetic surveying methods has greatly facilitated the prospecting process. Airborne gravimeters and magnetometers can collect data from vast areas and highlight anomalous geologic features. [2] Three-dimensional inversions of audio-magnetotellurics (AMT) is used to find conductive materials up to a few kilometres into the Earth, which has been helpful to locate kimberlite pipes, as well as tungsten and copper. [3] [4]

Another relatively new prospecting technique is using low frequency electromagnetic (EM) waves for 'sounding' into the Earth's crust. These low frequency waves will respond differently based on the material they pass through, allowing for analysts to create three-dimensional images of potential ore bodies or volcanic intrusions. This technique is used for a variety of prospecting, but can mainly be for finding conductive materials. [5] So far these low frequency EM techniques have been proven for geothermal exploration as well as for coal bed methane analysis. [6] [7]

Geochemical prospecting

Geochemical prospecting involves analyzing the chemical properties of rock samples, drainage sediments, soils, surface and ground waters, mineral separates, atmospheric gases and particulates, and even plants and animals. Properties such as trace element abundances are analyzed systematically to locate anomalies. [8]

See also

Related Research Articles

Geophysical survey (archaeology) Non-invasive physical sensing techniques used for archaeological imaging or mapping

In archaeology, geophysical survey is ground-based physical sensing techniques used for archaeological imaging or mapping. Remote sensing and marine surveys are also used in archaeology, but are generally considered separate disciplines. Other terms, such as "geophysical prospection" and "archaeological geophysics" are generally synonymous.

A telluric current, or Earth current, is an electric current which moves underground or through the sea. Telluric currents result from both natural causes and human activity, and the discrete currents interact in a complex pattern. The currents are extremely low frequency and travel over large areas at or near the surface of the Earth.

Mining engineering Engineering discipline that involves the practice, the theory, the science, the technology, and applicatIon of extracting and processing minerals from a naturally occurring environment

Mining in the engineering discipline is the extraction of minerals from underneath, above or on the ground. Mining engineering is associated with many other disciplines, such as mineral processing, exploration, excavation, geology, and metallurgy, geotechnical engineering and surveying. A mining engineer may manage any phase of mining operations, from exploration and discovery of the mineral resources, through feasibility study, mine design, development of plans, production and operations to mine closure.

Gold prospecting

Gold prospecting is the act of searching for new gold deposits. Methods used vary with the type of deposit sought and the resources of the prospector. Although traditionally a commercial activity, in some developed countries placer gold prospecting has also become a popular outdoor recreation.

Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs.

Magnetotellurics

Magnetotellurics (MT) is an electromagnetic geophysical method for inferring the earth's subsurface electrical conductivity from measurements of natural geomagnetic and geoelectric field variation at the Earth's surface. Investigation depth ranges from 300 m below ground by recording higher frequencies down to 10,000 m or deeper with long-period soundings. Proposed in Japan in the 1940s, and France and the USSR during the early 1950s, MT is now an international academic discipline and is used in exploration surveys around the world. Commercial uses include hydrocarbon exploration, geothermal exploration, carbon sequestration, mining exploration, as well as hydrocarbon and groundwater monitoring. Research applications include experimentation to further develop the MT technique, long-period deep crustal exploration, deep mantle probing, and earthquake precursor prediction research.

Geophysical survey is the systematic collection of geophysical data for spatial studies. Detection and analysis of the geophysical signals forms the core of Geophysical signal processing. The magnetic and gravitational fields emanating from the Earth's interior hold essential information concerning seismic activities and the internal structure. Hence, detection and analysis of the electric and Magnetic fields is very crucial. As the Electromagnetic and gravitational waves are multi-dimensional signals, all the 1-D transformation techniques can be extended for the analysis of these signals as well. Hence this article also discusses multi-dimensional signal processing techniques.

Aeromagnetic survey

An aeromagnetic survey is a common type of geophysical survey carried out using a magnetometer aboard or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger areas of the Earth's surface to be covered quickly for regional reconnaissance. The aircraft typically flies in a grid-like pattern with height and line spacing determining the resolution of the data.

Transient electromagnetics,, is a geophysical exploration technique in which electric and magnetic fields are induced by transient pulses of electric current and the subsequent decay response measured. TEM / TDEM methods are generally able to determine subsurface electrical properties, but are also sensitive to subsurface magnetic properties in applications like UXO detection and characterization. TEM/TDEM surveys are a very common surface EM technique for mineral exploration, groundwater exploration, and for environmental mapping, used throughout the world in both onshore and offshore applications.

Induced polarization (IP) is a geophysical imaging technique used to identify the electrical chargeability of subsurface materials, such as ore.

The following outline is provided as an overview of and topical guide to geology:

Geologist Scientist who studies geology

A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes the Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, although backgrounds in physics, chemistry, biology, and other sciences are also useful. Field work is an important component of geology, although many subdisciplines incorporate laboratory work.

Magnetic survey (archaeology) Magnetic detection of archaeological artefacts and features

Magnetic surveying is one of a number of methods used in archaeological geophysics. Magnetic surveys record spatial variation in the Earth's magnetic field. In archaeology, magnetic surveys are used to detect and map archaeological artefacts and features. Magnetic surveys are used in both terrestrial and marine archaeology.

The Turam method is one of the oldest geophysical electro-magnetic methods used for mineral exploration, devised by Erik Helmer Lars Hedstrom in 1937. Its name is derived from Swedish "TU" (two) and "RAM" (frame), referring to the two receiving coils.

Near-surface geophysics Geophysics of first tens of meters below surface

Near-surface geophysics is the use of geophysical methods to investigate small-scale features in the shallow subsurface. It is closely related to applied geophysics or exploration geophysics. Methods used include seismic refraction and reflection, gravity, magnetic, electric, and electromagnetic methods. Many of these methods were developed for oil and mineral exploration but are now used for a great variety of applications, including archaeology, environmental science, forensic science, military intelligence, geotechnical investigation, treasure hunting, and hydrogeology. In addition to the practical applications, near-surface geophysics includes the study of biogeochemical cycles.

Outline of geophysics Topics in the physics of the Earth and its vicinity

The following outline is provided as an overview of and topical guide to geophysics:

Dan Hausel a polymath of martial arts, geology, writing, astronomy, art, and public speaking. Hall-of-Fame 10th degree black belt grandmaster of Shorin-Ryu Karate and Kobudo, mineral exploration geologist who made several gold, colored gemstone, and diamond deposit discoveries in Alaska, Colorado, Montana and Wyoming, author of more than 600 publications including books, maps, professional papers and magazine articles, public speaker, artist, former astronomy lecturer for the Hansen Planetarium in Utah, and former rock musician.

Primary mineral

A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In ore deposit geology, hypogene processes occur deep below the earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.

EMIGMA is a geophysics interpretation software platform developed by Petros Eikon Incorporated for data processing, simulation, inversion and imaging as well as other associated tasks. The software focuses on non-seismic applications and operates only on the Windows operating system. It supports files standard to the industry, instrument native formats as well as files used by other software in the industry such as AutoCAD, Google Earth and Oasis montaj. There is a free version of EMIGMA called EMIGMA Basic developed to allow viewing of databases created by licensed users. It does not allow data simulation nor modeling nor data import. The software is utilized by geoscientists for exploration and delineating purposes in mining, oil and gas and groundwater as well as hydrologists, environmental engineers, archaeologists and academic institutions for research purposes. Principal contributors to the software are R. W. Groom, H. Wu, E. Vassilenko, R. Jia, C. Ottay and C. Alvarez.

Decennial Mineral Exploration Conferences

The Decennial Mineral Exploration Conferences (DMEC) is a Canadian voluntary association dedicated to the advancement of geoscience applied to exploration for mineral resources. The inaugural 1967 conference "Canadian Centennial Conference on Mining and Groundwater Geophysics", held in Ottawa, Canada, was organized by the Geological Survey of Canada as part of the Canadian Centennial. While the original session focussed on mining and groundwater geophysics, the purpose of subsequent conferences expanded to include geochemistry, and other geoscience disciplines as they are applied in mineral exploration.

References

  1. "Mining - Prospecting and exploration". Encyclopedia Britannica. Retrieved 2020-02-29.
  2. Dobrin, Milton B. (1960). Introduction to Geophysical Prospecting .
  3. Farquharson, Colin; Craven, James (August 2009). "Three-dimensional inversion of magnetotelluric data for mineral exploration: An example from the McArthur River uranium deposit, Saskatchewan, Canada". Journal of Applied Geophysics. 68 (4): 450–458. Bibcode:2009JAG....68..450F. doi:10.1016/j.jappgeo.2008.02.002.
  4. Shi, Yuan (January 2020). "Three-dimensional audio-frequency magnetotelluric imaging of Zhuxi copper-tungsten polymetallic deposits, South China". Journal of Applied Geophysics. 172: 103910. Bibcode:2020JAG...17203910S. doi: 10.1016/j.jappgeo.2019.103910 .
  5. Singh, Anand; Sharma, S.P. (2015). "Fast imaging of subsurface conductors using very low-frequency electromagnetic data". Geophysical Prospecting. 63 (6).
  6. Wang, Nan (2017). "Passive super-low frequency electromagnetic prospecting technique". Frontiers of Earth Science. 11: 248–267.
  7. Van Der Kruk, J (2002). "An apparent-resistivity concept for low-frequency electromagnetic sounding techniques". Geophysical Prospecting. 48 (6).
  8. Fletcher, W.K. Analytical Methods in Geochemical Prospecting.