The generally accepted hydrothermal model of lode deposition posits that metals dissolved in hydrothermal solutions (hot spring fluids) deposit the gold or other metallic minerals inside the fissures in the pre-existing rocks.[3] Lode deposits are distinguished primarily from placer deposits, where the ore has been eroded out from its original depositional environment and redeposited by sedimentation.[4] A third process for ore deposition is as an evaporite.
A stringer lode is one in which the rock is so permeated by small veinlets that rather than mining the veins, the entire mass of ore and the enveined country rock is mined. It is so named because of the irregular branching of the veins into many anastomosis stringers, so that the ore is not separable from the country rock.[5]
One of the largest silver lodes was the Comstock Lode in Nevada,[6] although it is overshadowed by the more recently discovered Cannington Lode in Queensland, Australia.[7][8] The largest gold lode in the United States was the Homestake Lode.[9] The Broken Hill Lode in South Australia is the largest lead-zinc lode ever discovered.[10]
See also
Lodestone known just as lode in the 16th and 17th centuries.[11][2]
↑ Fournier, R.O. (1999). "Hydrothermal processes related to movement of fluid from plastic into brittle rock in the magmatic environment". Economic Geology and the Society of Economic Geologists. 18: 486–497.
↑ Wood, George McLane, ed. (1916). Suggestions to authors of papers submitted for publication by the United States Geological Survey with directions to typewriter operators. Washington, DC: United States Geological Survey. p.35. OCLC7678360.
↑ Walters, Stephen; Bailey, Andrew (1998). "Geology and mineralization of the Cannington Ag-Pb-Zn deposit; an example of Broken Hill-type mineralization in the eastern succession, Mount Isa Inlier, Australia". Economic Geology. 93 (8): 1307–1329. Bibcode:1998EcGeo..93.1307W. doi:10.2113/gsecongeo.93.8.1307.
↑ Yarrow, Andrew L. (9 August 1987). "Beneath South Dakota's Black Hills". The New York Times. Retrieved 2008-01-11. Homestake, which is the largest, deepest and most productive gold mine in North America, has yielded more than $1 billion in gold over the years.
↑ Staff (February 2007). "Curnamona Geology". Department for Manufacturing, Innovation, Trade, Resources and Energy, Government of South Australia.
Ore is natural rock or sediment that contains one or more valuable minerals concentrated above background levels, typically containing metals, that can be mined, treated and sold at a profit. The grade of ore refers to the concentration of the desired material it contains. The value of the metals or minerals a rock contains must be weighed against the cost of extraction to determine whether it is of sufficiently high grade to be worth mining and is therefore considered an ore. A complex ore is one containing more than one valuable mineral.
Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver.
The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada, which was the first major discovery of silver ore in the United States and named after American miner Henry Comstock.
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical composition, excluding volatile components. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name. In later stages, circulating meteoric fluids may interact with the magmatic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals in often stockwork-forming hairline fractures and veins. Because of their large volume, porphyry orebodies can be economic from copper concentrations as low as 0.15% copper and can have economic amounts of by-products such as molybdenum, silver, and gold. In some mines, those metals are the main product.
Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.
In the United States, gold mining has taken place continually since the discovery of gold at the Reed farm in North Carolina in 1799. The first documented occurrence of gold was in Virginia in 1782. Some minor gold production took place in North Carolina as early as 1793, but created no excitement. The discovery on the Reed farm in 1799 which was identified as gold in 1802 and subsequently mined marked the first commercial production.
Silver mining in the United States began on a major scale with the discovery of the Comstock Lode in Nevada in 1858. The industry suffered greatly from the demonetization of silver in 1873 by the Coinage Act of 1873, known pejoratively as the "Crime of 73", but silver mining continues today.
Silver mining in Colorado has taken place since the 1860s. In the past, Colorado called itself the Silver State.
Silver mining in Nevada, a state of the United States, began in 1858 with the discovery of the Comstock Lode, the first major silver-mining district in the United States. Nevada calls itself the "Silver State." Nevada is the nation's second-largest producer of silver, after Alaska. In 2014 Nevada produced 10.93 million troy ounces of silver, of which 6.74 million ounces were as a byproduct of the mining of gold. The largest byproducers were the Hycroft Mine, the Phoenix Mine, the Midas Mine and Round Mountain.
Uranium ore deposits are economically recoverable concentrations of uranium within Earth's crust. Uranium is one of the most common elements in Earth's crust, being 40 times more common than silver and 500 times more common than gold. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge for commercial uranium extraction is to find those areas where the concentrations are adequate to form an economically viable deposit. The primary use for uranium obtained from mining is in fuel for nuclear reactors.
Gold mining in Nevada, a state of the United States, is a major industry, and one of the largest sources of gold in the world. In 2018 Nevada produced 5,581,160 troy ounces, representing 78% of US gold and 5.0% of the world's production. Total gold production recorded from Nevada from 1835 to 2017 totals 205,931,000 troy ounces (6,405.2 t), worth US$322.6 billion at 2020 values. Much of Nevada's gold production comes from large open pit mining using heap leaching recovery.
The Admiralty mining district is a mining area in the U.S. state of Alaska which consists of Admiralty Island. Silver and base metals are mined, with gold recovered as a by-product.
An ore shoot is a hypogenic mass that is deposited in veins within a planar channel or lode, found in a shear or fault zone, fissure or lithologic boundary. The ore shoot is the area of concentration which contains a primary ore along the veins present in the rock, and consists of the most valuable part of the deposit.
Mars may contain ores that would be very useful to potential colonists. The abundance of volcanic features together with widespread cratering are strong evidence for a variety of ores. While nothing may be found on Mars that would justify the high cost of transport to Earth, the more ores that future colonists can obtain from Mars, the easier it would be to build colonies there.
Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually produce metallic-rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted for a profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. The presence of a known but unexploited mineral deposit implies a lack of evidence for profitable extraction.
An orogenic gold deposit is a type of hydrothermal mineral deposit. More than 75% of the gold recovered by humans through history belongs to the class of orogenic gold deposits. Rock structure is the primary control of orogenic gold mineralization at all scales, as it controls both the transport and deposition processes of the mineralized fluids, creating structural pathways of high permeability and focusing deposition to structurally controlled locations.
The epithermal vein deposit (EVP) is a type of mineral deposit that forms in the shallow subsurface, typically at depths of less than 1,500 meters below the Earth's surface. These deposits are formed by hot, mineral-rich fluids that circulate through fractures and cracks in rocks. As the fluids cool, they deposit minerals, such as gold, silver, copper, lead, and zinc, into the veins. EVP are typically small in size, but they can be very high-grade, meaning that they contain a high concentration of valuable minerals.
Confidence Reef is a historical gold-bearing quartz vein situated within the Kloofendal Nature Reserve, in close proximity to Roodepoort, South Africa.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
