These waters may deposit their dissolved minerals in openings in the rock, thus filling the cavities, or they may replace the rocks themselves to form so-called replacement deposits. The two processes may occur simultaneously, the filling of an opening by precipitation accompanying the replacement of the walls of the opening.
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Conditions necessary for the formation of hydrothermal mineral deposits include 1 presence of hot water to dissolve and transport minerals, 2 presence of interconnected openings in the rock to allow the solutions to move, 3 availability of sites for the deposits, and 4 chemical reaction that will result in deposition.
Deposition can be caused by boiling, by a drop in temperature, by mixing with a cooler solution, or by chemical reactions between the solution and a reactive rock. Although hydrothermal mineral deposits may form in any host rock, deposition is preferentially influenced or localized by certain kinds of rock.
For example, lead-zinc-silver ores in some parts of Mexico occur in dolomitic rather than pure limestone; the reverse is true at Santa Eulalia, where massive sulfide deposits end abruptly at the limestone-dolomite contact. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions.
Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. See Article History. Learn More in these related Britannica articles:. Hydrothermal mineral deposit s are those in which hot water serves as a concentrating, transporting, and depositing agent. They are the most numerous of all classes of deposit. Replacement deposit , in geology, mineral deposit formed by chemical processes that dissolve a rock and deposit a new assemblage of minerals in its place.
See metasomatic replacement. History at your fingertips. Sign up here to see what happened On This Day , every day in your inbox! By signing up, you agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. More About Hydrothermal mineral deposit 3 references found in Britannica articles Assorted References gold In gold: Properties, occurrences, and uses ore deposits In mineral deposit: Hydrothermal solution volcanic deposits In geology: Volcanology.
Help us improve this article! It can also come from the washing of the underlying series or by the thermochemical reduction of the marine sulfate. Generally take the form of stratiform lenses with maximum thicknesses in the range of just 5 to 20 m.. In contrast, sphalerite tends to be concentrated in the lower grade outer portions of the ore bodies. The deposits are hosted in limestone or dolomite that was deposited on shallow marine platforms in a tectonically stable intraplate environment.
As expected in such an environment, volcanic rocks, folding and regional metamorphism are absent as a general rule. Deposits are discordant to bedding on a deposit scale, and are confined to specific stratigraphic horizons. Ore-hosting structures are most commonly zones of highly brecciated dolomite — these structures may be more or less vertical, crossing bedding at high angles, or they may be lensoid in shape extending in the same direction as bedding.
Ore-hosting structures are most commonly zolinknes [ clarification needed ] of highly brecciated dolomite. These structures may be more or less vertical, crossing bedding at high angles, or they may be lensoid in shape extending in the same direction as bedding. As many as individual deposits occur within the upper Mississippi Valley mining district alone. Iron sulfides are commonly minor, although pyrite and chalcopyrite can be present and are even abundant in a few deposits. Mississippi Valley-type deposits can be compared with the Red Sea deposits, which are modern analogues of ancient sedex deposits, some differences can be made: .
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Please introduce links to this page from related articles ; try the Find link tool for suggestions. November Main article: Porphyry copper deposit. Main article: Volcanogenic massive sulfide ore deposit. Main article: Sedimentary exhalative deposits. Nature Geoscience. Bibcode : NatGe Exploration and mining geology. Second edition. January American Mineralogist. The geology of ore deposits. Waveland Pr.
Submarine Hydrothermal Mineral Systems
Bibcode : Natur. Understanding mineral deposits. Kluwer academic. Bibcode : Geo March The Geographical Journal. June Economic Geology. Bibcode : Sci Astronomische Nachrichten.
Society of Resource Geology. Government Printing Office. Seafloor massive sulfide deposits: Continuing efforts toward a global estimate of seafloor massive sulfides. Ore Geology Reviews. Mineralium Deposita. Professional Paper. Categories : Ore deposits.
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These deposits are commonly stratiform and are typically hosted in shale. MVT deposits are hosted in carbonate rocks, whereas sedex deposits are found within marine shales.
Hydrothermal Processes and Mineral Systems
Average age of 13 million years, continental and oceanic arcs of Tertiary and Quaternary age. Amongst the largest in the world, especially porphyry-type deposits. The 25 biggest porphyry deposits are found in the southwest Pacific and South America. Ore is associated with one or more subvolcanic intrusions of felsic to intermediate composition such as granite, granodiorite or diorite. In island arc settings where the host plutons are typically andesitic in composition, the elements of economic interest are mainly copper and gold.
Commonly low in grade and have relatively low dollar value . Ore minerals are generally confined to small veinlets and less common larger veins that formed as fracture fillings in the host rocks . The wallrock on both sides of each veinlet is typically altered to varying degrees. Relatively small, they tend to be less than 10 million tonnes, although a few large ones exist such as the Mission mine in Arizona, million tonnes. Tungsten, tin, molybdenum, copper, iron, lead- zinc and gold ores. Nonfoliate rock textures created by contact metamorphism such as hornfels and marble .
Close proximity to a felsic to intermediate pluton of relatively large size. Therefore, shallow depths. Ore zones may grade laterally into calcic or dolomitic marble.
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Equidimensional geometries are most common. Many orebodies are elongate along structural weaknesses such as faults and bedding planes The largest and thickest orebodies tend to occur where carbonate beds lie immediately above gently inclined pluton contacts. Grasberg and Ertsberg Mines are part of a single mining complex in the glacier-capped mountains of Irian Jaya , Indonesia. Individual lenses that are a hundred meters thick and extend hundred meters along strike.
The median deposit size is only about 70, tonnes. There are three of types of sulfide ore that can be found in these mineral deposits. Massive sulfide ore locally shows primary stratiform features such as lamination and grading. Breccia ore is common near the top of the ore, with sulfide fragments as large as 10 m or more in diameter.
Although the breccia may be the result of hydrofracturing or slumping in a seafloor smoker, a tectonic origin such as faulting, cannot be discounted. The ore is Zn-rich at the top and Cu-rich at the base. Typically tabular to lensoid , and range from less than 1 to more than million tonnes. They often occur in clusters.
Chalcopyrite Cu , sphalerite Zn , galena Pb , silver and gold.