These were based mostly on visual and binocular microscope observations of cut, wet surfaces, and specific alteration minerals were only distinguished where it was considered that unequivocal identification could be made. These equilibrium relationships have been systematized and alteration assemblage and paragenetic zoning relationships are now routinely used as guides to ore. Hydrothermal fluids chemically attack the mineral constituents of the wall rocks, which tend to re equilibrate by forming new mineral assemblages that are in equilibrium with the new conditions. Compared with carbonaceous schist, the modal mineralogy of hydrothermal alteration in bif is characterized by higher contents of quartz and, to a minor extent, chalcopyrite. Maps of hydrothermal alteration in the basin and range. It is commonly measured as changes in the amount of an element moved per unit volume or mass of rock relative to its initial content.
Hydrothermal alteration, also referred to as wallrock alteration, is a general term that encompasses many processes by which rockforming minerals are altered due to reactions accompanying the flow of heated aqueous fluids along fractures and grain boundaries meyer and hemley, 1967. Pdf hydrothermal alteration of a saponitic bentonite. The list of minerals and mineral groups formed by hydrothermal alteration comprises 68 names and doubtless will be expanded as research continues. Two varieties of alteration, naca and na, can be defined by mineralogic and compositional changes. Hydrothermal alteration of andesitic lava domes can lead to. Ideally these two methods should yield the same results, but a comparison of data shows that there are major discrepancies between these types of estimates e. The theoretical basis of mass transfer and alteration mineralogy associated with hydrothermal systems have been given by, e. Hydrothermal alteration of andesitic lava domes can lead. Evolution of jasperoid and hydrothermal alteration at veteran extension in the robinson ely porphyry copper district, nevada page count. The present study investigates commonly observed phenomena of hydrothermal alteration and observations at the. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. The lithogeochemical signatures of hydrothermal alteration in the waihi epithermal district, new zealand article pdf available in new zealand journal of geology and geophysics.
The mineralogical characteristics of the hydrothermal. The individual principal components pc images generated by dpca reveal the distribution of individual alteration minerals such as sericite, illite, kaolinite, chlorite, and epidote. Hydrothermal alteration follows a concentric model that phyllic zone located in the center. Metamorphism does not contribute to the formation and localization of porphyry copper deposits, although metamorphosed rocks are host rocks in some districts. Hydrothermal alteration varies widely from district to district and among individual deposits, and the literature on this topic is voluminous. The interaction of hydrothermal fluids with rockwalls, the hydrophere and the biophere, together with changes in their composition through time and space, contribute to the formation of a wide range of mineral deposit types and associated wallrock alteration. The nature of the process of hydrothermal alteration is such that zones of alteration are a normal result. Alterationmineralization and veinstructure descriptions for each hole are found in the core descriptions contents list. Hydrothermal alteration of the oceanic crust is widespread and locally thorough in oceanic crust. Geochemistry of hydrothermal alteration associated with cenozoic. Hydrothermal alteration, mineralization, and structural. Physical description of deposit dimensions in plan view singer and others 2008 tabulated the dimensions, including the area of hydrothermal alteration, orebodies, and sulfide. Importance of hydrothermal alteration and mineral exploration. Get file pdf atlas ofintelalteration a field and petrographic guide to hydrothermal alteration minerals.
The zoning of the type hydrothermal alteration, mineralogical composition and. In this report, we assigned various geochemical data to one of the. The significance of hydrothermal alteration zones for the. Hydrothermal alteration an overview sciencedirect topics. The hydrothermal alteration of oceanic basalts by seawater. Geochemical behavior of trace and rareearth elements in. The present paper conducts an investigation on the significance of hydrothermal alteration in the granite of the geothermal site in soultzsous.
Learn vocabulary, terms, and more with flashcards, games, and other study tools. Hydrothermal alteration assemblage maps were com piled from the following sources. Hydrothermal alteration and mineralization in the faina. Available to purchase and download in shapefile and kmz vector formats. The extent of the alteration may be measured in millimeters or kilometers. These areas were differentiated in order to characterize and contrast the geochemical signatures of solids and waters in a variety of mineralized areas. Pdf hydrothermal alteration is proximal to many base and precious metal deposits, and its products can provide insights into the characteristics of. Hydrothermal alteration in cijulang area, hydrothermal alteration is associated with pyriteenargitegold mineralization and covers over an area of approximately 2 km long and 1 km wide northsouth trending elongate zone figure 2. During hydrothermal alteration, plagioclase is generally albitised, sometimes with the formation of epidote, and albite may be subsequently a1tered to chlorite. The mineralogical characteristics of the hydrothermal types. A series of hydrothermal alteration maps, which identify the potential locations of hydrothermal silicarich, propylitic, argillic, and phyllic rocks on landsat thematic mapper tm band 7 orthorectified images, and shape files of hydrothermal alteration units are provided. Sodiumrich hydrothermal alteration is widely developed in permian to jurassic arc igneous rocks of the western united states, but it is rare in younger rocks. To view and print portable document format pdf files you will need adobe reader software. An explorers guide to hydrothermal alteration in the yilgarn.
Application of principal component analysis and spectral. Hydrothermal synthesis offers many advantages over conventional and non conventional synthesis methods. The formation of these hydrothermal alteration minerals is usually dependent on the temperature, permeability, pressure, fluid composition, initial composition of. Honnorez4 abstract major, trace, and rare earth element ree analyses of 57 samples of altered and relatively fresh basalts from four different. The desirable distribution of alteration zones around the limited borders of an ore body facilitates narrowing down the exploration activities into smaller targets pirajno, 2008. Hydrothermal solutions in high temperature hydrothermalmagmatic systems of modern volcanism areas are saturated and often oversaturated owing to alteration of conditions when hydrothermae are overflowing to different hypsometric levels and from certain hydrogeological structures to others. Small scale fractures large scale large surrounding area. Hydrothermal alteration is a very complex process involving mineralogical, chemical and textural changes, resulting from the interaction of hot aqueous fluids with the rocks through which they pass, under evolving physicochemical conditions. The permeability of a dome exerts a control on the outgassing efficiency of the underlying magma.
In some occurrences, minerals can be extracted at a profit by mining. The types of hydrothermal alteration were separated by the minerals assemblages formed through reaction of the wall rocks heat solutions with different chemical composition. Satellite image processing shows the presence of four hydrothermal alteration zones, characterized by a mineral assem blage constituted mainly by clay minerals. Generally, hydrothermal alteration processes lead to emanation of clay and other silicate minerals. Third, hydrothermal alteration can provide key information on the origin of metallic elements in vms deposits. Maps and data showing the geographic distribution of surficial minerals likely produced by hydrothermal alteration, which may indicate areas permissive of gold and copper mineral deposits. The lithogeochemical signatures of hydrothermal alteration. Arcrelated sodic hydrothermal alteration in the western. Aug 26, 2019 the lithogeochemical signatures of hydrothermal alteration in the waihi epithermal district, new zealand article pdf available in new zealand journal of geology and geophysics august 2019. In order to display hydrothermal alteration areas that show both phyllic and argillic alteration, an image was produced by the addition of pc3 phyllic alteration image and pc3 argillic alteration image.
Oct 16, 2014 the occurrence of hydrothermally altered zones is a commonly observed phenomenon in brittle rock. In ore exploration, alteration minerals form zones that are used to evaluate the geometry of the deposit, understand the mineralization processes, and observe the spatial relationships between the. Hydrothermal alteration of bif encompasses distal and proximal alteration zones that grade towards sulfiderich, intensely deformed bands fig. Fluid evolution of the magmatic hydrothermal porphyry copper. Using aster image processing for hydrothermal alteration. Figure 6 exhibits hydrothermal alteration map of sarkuh area. Hydrothermal alteration exhibits significant development in the sarkuh area. Pdf atlas of alteration a field and petrographic guide to hydrothermal alteration minerals get file pdf atlas ofintelalteration a field and petrographic guide to hydrothermal alteration minerals exe x c941f1f125b34df583e6888c51a1aab6 nl 822 my in hand works with at tgo phone sim. Based on sam results and laboratory studies, phyllic zone is divided into two parts. Hydrothermal alteration data based on aster satellite images. The sar cheshmeh deposit is estimated to contain approximately 1. Hydrothermal alteration the wallrock on both sides of each veinlet is typically altered to varying degrees. The lithogeochemical signatures of hydrothermal alteration in. The alteration is usually restricted to small regions characteristic of contact metamorphism where new minerals, clay minerals, zeolites, and hydroxides form in.
Hydrothermal alteration usgs publications repository. Characterization and mapping of hydrothermal alteration minerals are important procedures in evaluating ore deposits and geothermal systems. This image reveals the distribution of alteration haloes related to hydroxyl. Early in the investigation of epigenetic mineral deposits it was recog nized that hot solutions were important and that wallrocks were commonly highly altered. Hydrothermal alteration zones associated with porphyry copper deposit. On earth, sites of hydrothermal activity support varied ecosystems based on a range of. Unlike many advanced methods that can prepare a large variety of forms, the respective costs for instrumentation, energy and precursors are far less for hydrothermal methods. Sericitic alteration is confined to the western portion of the virginia city area and it is often associated with stockwork quartz veins. Dec 29, 2016 hydrothermal alteration zones can be recognized upon the spectral characteristics of main mineral assemblages.
Geothermal exploration is commonly separated into phases a set of techniques that the developer will use to determine if a location is worth investigating further. When using alteration mineralogy, however, care alteration are distinguished from their primary must be taken to. Application of airborne geophysical and aster data for. The dissolution and transformation of primary minerals and the precipitation of secondary minerals affect rocks in terms of mechanics, stress conditions, and induced seismicity. It is widely accepted that hydrothermal alteration plays a significant role in mineral exploration. The alteration may appear to be simply a color change or it may involve major textural, mineralogical andor chemical changes. Hydrothermal fluxes can be independently determined by analyzing the composition of hydrothermal fluids or by analyzing the alteration related chemical changes in the oceanic crust. Olivine is pseudomorphed by chlorite, and clinopyroxene alters to actinolite. Download pdf hydrothermal processes and mineral systems. The mineral components of bentonite are stable below. Hydrothermal alteration institute for mining geology.
Hydrothermal alteration definition, mineral exploration. Jun 01, 2019 hydrothermal activity produced pervasive silicic and advanced argillic alteration assemblages that are zoned from a central, massive quartz alteration domain, outward to massive quartzdickite, disseminated quartzalunite dickite, and disseminated quartzmuscovitedickite zones. Narich alteration reflects both paleogeographic and igneous compositional controls. Application of spectral analysis in mapping hydrothermal. The primary silicate minerals such as feldspar and amphibole are replaced by hydrothermal minerals stable at temperatures of about 400 c or less such as chlorite, epidote, muscovite and quartz. Geochemistry of hydrothermal ore deposits pdf free download. Contact details this course will run from 7 to 8 february, 20. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore. Any alteration of rocks or minerals by chemical reaction of heated fluids and a preexisting solid. Small zones of alunitic alteration are usually surrounded by kaolinitic andor.
The solid and solution phases were sep arated by centrifugation, and the solutions were ana. Application of xray diffraction to hydrothermal alteration. Early hydrothermal alteration was predominantly potassic and propylitic, but followed later by phyllic, silicic and argillic alteration 33. Figure 6 color composite rgb showing abundance of hydrothermal alteration that is. The most characteristic minerals include sericite, quartz, chlorite, sulfides, epidote, zoisite, clinozoisite, leucoxene, clay. Byrappa in 2001 propose to define hydrothermal reaction as any heterogenous chemical reaction in the presence of a solvent whether aqueous or nonaqueous above room temperature and at pressure greater than 1 atm in a closed system.
Several hydrothermal alteration assays have been carried out in teflon reactors at 45, 60, 90, 120, 175 and 200c for periods of up to 1 y. Download suggestion for portable document format pdf files recommended download procedures due to large file sizerightclick pc or controlclick macintosh and save file to hard drive. Metals tend to concentrate in the most intensely altered rocks. Pdf atlas of alteration a field and petrographic guide to hydrothermal alteration minerals. Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in earths crust through fractures. The darrehzar porphyry cumo deposit is located in southwestern iran 70 km southwest of kerman city. They eventually create richmetallic fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. Major styles of mineralization and hydrothermal alteration. The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Using aster image processing for hydrothermal alteration and key alteration minerals mapping 1mohamad boloki, 2rashed poormirzaee 1 islamic azad university ahar branch, 2 sahand university of technology tabriz iran rashed. It is the replacement of one rock by another of different mineralogical and chemical composition.
Examples of how to use hydrothermal in a sentence from the cambridge dictionary labs. The authors investigate the role of hydrothermal alteration on this process in the laboratory and. Maps of hydrothermal alteration in the basin and range province of the us. These are not uniform but naturally depend on the composition of the wallrock and of the solutions, with changes in the solutions during the process having a strong influence. Alteration may occur through dissolution, ion exchange. The zoning of the type hydrothermal alteration, mineralogical composition and spatial position within the ore body has permitted. The occurrence of hydrothermally altered zones is a commonly observed phenomenon in brittle rock.
The best results, in terms of mapping the distribution of alteration, were. The porphyries occur as tertiary quartzmonzonite stocks and dikes, ranging in composition from microdiorite to diorite and granodiorite. Hydrothermal exploration there are a number of exploration techniques used to explore for both visible and hidden or blind hydrothermal systems. At the end for hydrothermal alteration mapping a rgb composite images e. The most characteristic minerals include sericite, quartz, chlorite, sulfides, epidote, zoisite, clinozoisite, leucoxene, clay minerals, calcite, and other carbonates. Hydrothermal alteration maps of the central and southern.
The term hydrothermal overprint is employed in the following text also in such cases and for such rocks where mineral alteration is not a major feature, but where the geochemical element distribution pattern points to important postmagmatic hydrothermal fluid interaction and chemical alteration. Hydrothermal alteration and mineralization at darrehzar are centered on the stock and were broadly synchronous with its emplacement. Hydrothermal alteration of volcanic host rocks involves the replacement of primary igneous glass and minerals pla gioclase, orthoclase, quartz, biotite, muscovite, amphibole, pyroxene, titanomagnetite with alteration minerals stable at the conditions of alteration, generally in the temperate range of 150400 c. Geochemical changes during hydrothermal alteration of basement in the stockwork beneath the active tag hydrothermal mound 1 susan e. Hydrothermal alteration economic geology geoscienceworld. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a pdf plugin installed and enabled in your browser. Map showing the geology and hydrothermal alteration of the cijulang area, west java, indonesia. Hydrothermal alteration, fumarolic deposits and fluids from. Alteration mineralization and veinstructure descriptions for each hole are found in the core descriptions contents list. Plagioclase, in association with skeletal clinopyroxene, alters to chlorite and epidote. The present study investigates commonly observed phenomena of hydrothermal alteration and observations at the geothermal. Infotierra also offers existing alteration maps for most of the arid and super arid zones of south america.
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