Journal articles: 'Lithogeochemical alteration'

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Mokhtari, Ahmad Reza. "Hydrothermal alteration mapping through multivariate logistic regression analysis of lithogeochemical data." Journal of Geochemical Exploration 145 (October 2014): 207–12. http://dx.doi.org/10.1016/j.gexplo.2014.06.008.

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Byrne, Kevin, Guillaume Lesage, Sarah A. Gleeson, Stephen J. Piercey, Philip Lypaczewski, and Kurt Kyser. "Linking Mineralogy to Lithogeochemistry in the Highland Valley Copper District: Implications for Porphyry Copper Footprints." Economic Geology 115, no. 4 (June 1, 2020): 871–901. http://dx.doi.org/10.5382/econgeo.4733.

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Abstract The Highland Valley Copper porphyry deposits, hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera, are unusual in that some of them formed at depths of at least 4 to 5 km in cogenetic host rocks. Enrichments in ore and pathfinder elements are generally limited to a few hundred meters beyond the pit areas, and the peripheral alteration is restricted to narrow (1–3 cm) halos around a low density of prehnite and/or epidote veinlets. It is, therefore, challenging to recognize the alteration footprint peripheral to the porphyry Cu systems. Here, we document a workflow to maximize the use of lithogeochemical data in measuring changes in mineralogy and material transfer related to porphyry formation by linking whole-rock analyses to observed alteration mineralogy at the hand specimen and deposit scale. Alteration facies and domains were determined from mapping, feldspar staining, and shortwave infrared imaging and include (1) K-feldspar halos (potassic alteration), (2) epidote veins with K-feldspar–destructive albite halos (sodic-calcic alteration), (3) quartz and coarse-grained muscovite veins and halos and fine-grained white-mica–chlorite veins and halos (white-mica–chlorite alteration), and two subfacies of propylitic alteration comprising (4) prehnite veinlets with white-mica–chlorite-prehnite halos, and (5) veins of epidote ± prehnite with halos of chlorite and patchy K-feldspar. Well-developed, feldspar-destructive, white-mica alteration is indicated by (2[Ca-C] + N + K)/Al values <0.85, depletion in CaO and Na2O, enrichment in K2O, and localized SiO2 addition and is spatially limited to within ~200 m of porphyry Cu mineralization. Localized K2O, Fe2O3, and depletion in Cu, and some enrichment in Na2O and CaO, occurs in sodic-calcic domains that form a large (~34 km2) nonconcentric footprint outboard of well-mineralized and proximal zones enriched in K. Water and magmatic CO2-rich propylitic and sodic-calcic–altered rocks form the largest lithogeochemical footprint to the mineralization in the Highland Valley Copper district (~60 km2). Calcite in the footprint is interpreted to have formed via phase separation of CO2 from a late-stage magmatic volatile phase. Several observations from this study are transferable to other porphyry systems and have implications for porphyry Cu exploration. Feldspar staining and shortwave infrared imaging highlight weak and cryptic alteration that did not cause sufficient material transfer to be confidently distinguished from protolith lithogeochemical compositions. Prehnite can be a key mineral phase in propylitic alteration related to porphyry genesis, and its presence can be predicted based on host-rock composition. Sodic-calcic alteration depletes the protolith in Fe (and magnetite) and, therefore, will impact petrophysical and geophysical characteristics of the system. Whole-rock loss on ignition and C and S analyses can be used to map enrichment in water and CO2 in altered rocks, and together these form a large porphyry footprint that extends beyond domains of enrichment in ore and pathfinder elements and of pronounced alkali metasomatism.

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Grunsky, E. C. "Recognition of alteration in volcanic rocks using statistical analysis of lithogeochemical data." Journal of Geochemical Exploration 25, no. 1-2 (March 1986): 157–83. http://dx.doi.org/10.1016/0375-6742(86)90012-9.

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Halley, Scott, John H. Dilles, and Richard M. Tosdal. "Footprints: Hydrothermal Alteration and Geochemical Dispersion Around Porphyry Copper Deposits." SEG Discovery, no. 100 (January 1, 2015): 1–17. http://dx.doi.org/10.5382/segnews.2015-100.fea.

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ABSTRACT Whole-rock lithogeochemical analyses combined with short-wave infrared (SWIR) spectroscopy provide a rapid and cost-effective method for prospecting for porphyry-type hydrothermal systems. Lithogeochemistry detects trace metals to average crustal abundance levels and allows vectoring via gradients of chalcophile and lithophile elements transported by magmatic-hydrothermal ore and external circulating fluids that are dispersed and trapped in altered rocks. Of particular use are alkalis in sericite and metals such as Mo, W, Se, Te, Bi, As, and Sb, which form stable oxides that remain in weathered rocks and soils. SWIR mapping of shifts in the 2,200-nm Al-OH absorption feature in sericite define paleofluid pH gradients useful for vectoring toward the center of the buoyant metal-bearing magmatic-hydrothermal plume.

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Barker, Shaun L. L., Shawn Hood, Rosie M. Hughes, and Shannon Richards. "The lithogeochemical signatures of hydrothermal alteration in the Waihi epithermal district, New Zealand." New Zealand Journal of Geology and Geophysics 62, no. 4 (August 26, 2019): 513–30. http://dx.doi.org/10.1080/00288306.2019.1651345.

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Honarpazhouh, Jamal, Ali Asghar Hassanipak, and Kumars Seifpanahi Shabani. "Integration of Stream Sediment Geochemical and Aster Data for Porphyry Copper Deposit Exploration in Khatun Abad, North West of Iran / Integracja geochemicznych danych o osadach dennych oraz danych pozyskanych z systemu aster do poszukiwań geologicznych w rejonie złóż miedzi porfirytowej w khatun abad, w północno-zachodniej części iranu." Archives of Mining Sciences 58, no. 1 (March 1, 2013): 37–54. http://dx.doi.org/10.2478/amsc-2013-0003.

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Urumieh-Dokhtar magmatic belt is the host of large porphyry copper deposits in Iran. Khatun Abad area is located in north west part of this belt, so in this study, the stream sediment geochemical survey and hydrothermal alteration zones extracted from ASTER data were used to generation new target for future lithogeochemical survey. In this study after a brief discussion on descriptive statistics, principal component analysis (PCA) and hierarchical cluster analysis were used to compress the information to a few maps and to assist in determining multi-element associations. Then C-A fractal method was used for map classification. In order to extraction hydrothermal zones ASTER data were used. ASTER SWIR bands are most useful for the identification of alteration minerals such as Alunite, Pyrophylite, Kaolinite, Sericute and Carbonates. In this paper based on spectral analysis of ASTER SWIR data six maps of alteration zones were prepared. Geochemical study and spectral analysis of ASTER data showed that mineralization and alteration are limited to E1lb and gr lithological units and have NW-SE trends from east of Khatun Abad to Ghezeljeh-Gheshlaghi.

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Murphy, D. M. K., and C. R. Stanley. "Lithogeochemical constraints on the host rock, hydrothermal alteration and weathering of the Groundrush gold deposit." Geochemistry: Exploration, Environment, Analysis 7, no. 4 (November 2007): 363–75. http://dx.doi.org/10.1144/1467-7873/07-143.

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Darabi-Golestan, F., R. Ghavami-Riabi, and H. Asadi-Harooni. "Alteration, zoning model, and mineralogical structure considering lithogeochemical investigation in Northern Dalli Cu–Au porphyry." Arabian Journal of Geosciences 6, no. 12 (October 12, 2012): 4821–31. http://dx.doi.org/10.1007/s12517-012-0689-0.

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Hollis, Steven P., Sabri Foury, Stefano Caruso, Sean Johnson, Vitor Barrote, and Andrew Pumphrey. "Lithogeochemical and Hyperspectral Halos to Ag-Zn-Au Mineralization at Nimbus in the Eastern Goldfields Superterrane, Western Australia." Minerals 11, no. 3 (February 28, 2021): 254. http://dx.doi.org/10.3390/min11030254.

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With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration.

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Pazand, Kaveh, Ardeshir Hezarkhani, and Mohammad Ataei. "The application of lithogeochemical and alteration index for copper mineralization in the Sonajil area, NW Iran." Arabian Journal of Geosciences 6, no. 5 (November 16, 2011): 1447–56. http://dx.doi.org/10.1007/s12517-011-0453-x.

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Bonnet, Anne-Laure, Louise Corriveau, and Marc R. La Flèche. "Chemical imprint of highly metamorphosed volcanic-hosted hydrothermal alterations in the La Romaine Supracrustal Belt, eastern Grenville Province, Quebec." Canadian Journal of Earth Sciences 42, no. 10 (October 1, 2005): 1783–814. http://dx.doi.org/10.1139/e05-098.

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The La Romaine Supracrustal Belt and the southeastern end of the Wakeham Group in the eastern Grenville Province, Canada, host a series of Pinwarian, 1.50 Ga felsic-dominated volcanic centres metamorphosed at amphibolite to granulite facies during the Grenville orogeny. The centres are interpreted as being related to the emergence of rhyolitic domes in shallow-marine intra-arc basins within the active Pinwarian continental magmatic arc. High-grade metamorphosed hydrothermal alteration zones are intimately associated with pyroclastic deposits composing these volcanic centres and an overlying composite amphibolite unit. They comprise layers of rhyolitic metatuff bearing networks of aluminous nodules and veins, migmatized garnetbiotitesillimanite gneiss with well-preserved volcanic fragments, and mottled quartzcordierite gneiss with textures similar to those of vuggy silica facies. Alteration zones of ironstone, carbonate and calc-silicate rocks, garnetite, diopsidite, epidosite, and sulphide mineralization collectively cut across the internal contacts of a composite amphibolite unit inferred to be a mafic lava and sill complex. Lithogeochemical analysis of inferred metamorphosed altered rocks and precursors highlights chemical changes typical of metamorphosed sericitic zones, advanced argillic and silicic zones, and discharge zones characterized by calcic alterations and copper mineralizations. Such zones involve the interaction of hot, very acidic to neutral fluids. Medium to heavy rare-earth elements (REE) and Zr behave as mobile elements in the hydrothermal system as a result of the presence of F-rich fluids. The chemical changes recorded by the various alteration zones share similarities with those observed in high-sulphidation, volcanic-hosted massive sulphide deposits occurring in proximal, shallow-marine, volcanic sequences.

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Hokka, Janne. "Geology, alteration and lithogeochemistry of the Paleoproterozoic Korpela VMS occurrence in Eastern Finland." Mineralium Deposita 55, no. 8 (February 7, 2020): 1581–604. http://dx.doi.org/10.1007/s00126-020-00954-0.

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Abstract Korpela is a Cu-Zn-Au VMS occurrence hosted by bimodal, sub-alkaline, volcanic and volcaniclastic rocks. It is part of a Svecofennian supracrustal sequence 1.93–1.91 Ga in age. In this study, lithogeochemical evidence is used to assess the VMS-prospectivity in the Korpela area to serve regional-scale exploration and provide detailed information on chemostratigraphy and hydrothermal alteration within the Korpela succession. Korpela is understood to have been formed in an evolved arc rift, possibly in a continental back-arc environment. The felsic rocks of the sequence are FII-FIIIa, HFSE-enriched (A-type) rhyolites overlain and, locally cross-cut, by mafic rocks with MORB/BABB signatures and felsic synvolcanic porphyry dykes. In the vicinity of Korpela, tonalitic subvolcanic intrusions intrude the supracrustal rocks which share textures common with local shallow VMS-related intrusion complexes. The Korpela area comprises a volcanic succession where primary volcanic textures are completely destroyed by multiple deformation, metamorphism and alteration. Using detailed volcanic chemostratigraphy established from downhole geochemical profiles, 12 chemostratigraphic units and 21 chemical rock types could be identified ranging from basalt to rhyolite. Several metamorphic mineral assemblages were identified which were further classified into six alteration types, i.e. Mg-Fe-S, K-Al-Fe-(± S), K-Al-Mg-Fe-S, K, Si-K-Ca-(± S) and Ca-(± Na), using a combination of mineralogy and geochemistry. The chemostratigraphy and alteration studies help in understanding the volcanic stratigraphy and in recognising a potential VMS-related alteration.

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Buschette, Michael J., and Stephen J. Piercey. "Hydrothermal alteration and lithogeochemistry of the Boundary volcanogenic massive sulphide deposit, central Newfoundland, Canada." Canadian Journal of Earth Sciences 53, no. 5 (May 2016): 506–27. http://dx.doi.org/10.1139/cjes-2015-0237.

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The Boundary volcanogenic massive sulphide deposit (0.50 Mt at 3.5% Cu, 4.0% Zn, and 1.0% Pb, 34 g/t Ag) is hosted by the Tally Pond group (∼510 Ma), Victoria Lake supergroup, central Newfoundland, Canada, and represents a subseafloor replacement-style massive sulphide deposit. The deposit is hosted by rhyolitic lapilli tuff of the Bindons Pond formation. The rhyolites have immobile element signatures consistent with the formation of felsic rocks through the melting of juvenile-weakly evolved crust within an extensional rift environment (rifted peri-continental arc). The host rocks of the Boundary deposit contain elevated alteration indices, including high Ba/Sr, Hg/Na2O, chlorite–carbonate–pyrite index, and Ishikawa alteration index values. The mobile element geochemistry effectively differentiates between three distinct hydrothermal alteration styles: intense chlorite, chlorite-sericite, and quartz-sericite. Intense chlorite alteration exhibits mass gains in MgO and Cu and depletions in K2O and Ba. Chlorite-sericite alteration contains variable gains and losses of SiO2, K2O, Ba, MgO, and Fe2O3 depending on the dominant matrix mineral phase (i.e., chlorite vs. sericite). The quartz-sericite assemblage has mass gains in SiO2, K2O, Ba, and Fe2O3. Short-wave infrared spectroscopic data, particularly AlOH and FeOH absorption hulls, differentiate alteration styles and correlate with lithogeochemical results: AlOH absorption features increase in length (>2208 nm) proximal to Zn mineralization and wavelength variations correspond to relative abundances of sericite and chlorite. Electron probe microanalyses indicate that increasing short-wave infrared wavelengths correlate with increasing Mg–Fe and Fe contents in sericite and chlorite, respectively. Collectively, these data have been used to develop a three-dimensional alteration model of the Boundary deposit.

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Schetselaar, Bellefleur, and Hunt. "Elucidating the Effects of Hydrothermal Alteration on Seismic Reflectivity in the Footwall of the Lalor Volcanogenic Massive Sulfide Deposit, Snow Lake, Manitoba, Canada." Minerals 9, no. 6 (June 25, 2019): 384. http://dx.doi.org/10.3390/min9060384.

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The integrated analysis of seismic rock properties, lithogeochemical data, and mineral compositional data, estimated via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), provides insight into the effects of hydrothermal alteration on seismic reflectivity in the footwall of the Lalor volcanogenic massive sulfide (VMS) deposit, Manitoba, Canada. The effects of hydrothermal alteration on variations in acoustic impedance are secondary in magnitude and superimposed on the dominant acoustic impedance contrast between felsic and mafic volcanic protoliths. This secondary effect is due to an increase in P-wave velocity with increasing intensity of hydrothermal alteration, as measured by the Ishikawa and Carbonate-Chlorite-Pyrite alteration indices. Mixture modeling of the seismic rock properties and mineral percentages suggests that the increase in seismic velocity is due to an increase in abundance of cordierite, which is one of the diagnostic aluminum silicates for hydrothermally-altered volcanic rocks metamorphosed in the upper almandine amphibolite facies. The synthetic seismic data of a simple VMS model consisting of mafic-felsic host rock contacts, a sulfide ore lens, and a discordant hydrothermal conduit, consisting of the amphibolite-facies mineral assemblage (600 °C, 6 kbar) encountered at Lalor, show enhanced seismic reflections at conduit-host rock contacts, in comparison to its greenschist facies equivalent (350 °C, 2.5 Kbar). This zone of enhanced seismic reflectivity in the footwall of the massive sulfide ore zone is also recognized on the Lalor seismic data suggesting that high-grade terrains hosting VMS deposits possess enhanced potential for the seismic detection of their footwall hydrothermal alteration zones.

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Maciąg, Łukasz, Dominik Zawadzki, Maciej J. Kotarba, Adam Piestrzyński, Ryszard A. Kotliński, Rafał Wróbel, and Hieronim Zych. "Thermal Properties and Burial Alteration of Deep-Sea Sediments: New Indicators of Oxic−Suboxic Diagenesis." Minerals 10, no. 10 (October 11, 2020): 901. http://dx.doi.org/10.3390/min10100901.

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The application of thermal methods, such as Rock−Eval 6 pyrolysis or differential thermal analysis, provides complex information about sediment and rock properties, including thermal behaviour, degree of maturity, alteration of organic matter, and high temperature combustion synthesis mineral products. In this study, thermal methods included experiments on the thermokinetics of modern deep-sea sediments of the Northeast Pacific Basin. For experimental the procedure, twelve samples of siliceous clayey silts collected from the Clarion−Clipperton Fracture Zone (CCFZ), Interoceanmetal claim area, were analysed. CCFZ is highly prospective as a giant marine polymetallic deposit which contains several economically valuable metals, such as Ni, Cu, or Co. Hydrocarbon potential, thermal maturity, and roasting products were investigated. Mineralogical characteristics of thermal products were investigated. The obtained results of thermal experiments were compared with sedimentological, mineralogical, and geochemical data of bulk sediments. The total enthalpy ΔHTot. and activation energy Ea were proposed as a new lithogeochemical proxies of oxygen depletion during oxic−suboxic diagenesis. The distinctive increase in positive enthalpy (or heat transmission) was observed with the burial depth, where pelagic sediments showed strong oxygen depletion and consumed more energy during phase transformations.

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Lotfi, Mohammad, Mansoureh Shirnavard Shirazi, Nima Nezafati, and Arash Gourabjeripour. "MINERALOGY AND GEOCHEMISTRY STUDY OF REE MINERALS IN HOST ROCKS IN IIC IRON DEPOSIT, BAFGH MINERAL AREA, CENTRAL IRAN." Geosaberes 11 (January 8, 2020): 51. http://dx.doi.org/10.26895/geosaberes.v11i0.909.

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The IIC deposit area to the east of the Bafq region exposes rocks that comprise the part of the Central Iran continental terrane. The IIC deposit iron orebodies are magmatic-related hydrothermal deposits that, when considered collectively display a vertical zonation from high-temperature, magmatic ± hydrothermal deposits emplaced at moderate depths (~1–2 km) to magnetite-dominant IOCG deposits emplaced at an even shallower subvolcanic level. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, and synsedimentary (exhalative) ironstone deposits. Alteration associated with the IOCG mineralizing system within the host volcanic, plutonic, and sedimentary rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. Our data suggest that hydrothermal magmatic fluids contributed to formation of the primary sodic and calcic alterations. The aim of this study is to delineate and recognize the different iron mineralized zones, based on surface and subsurface study. However, the data do not discriminate between a magmatic-hydrothermal source fluids resolved from Fe-rich immiscible liquid or Fe-rich silicate magma. Iron ores, occurring as massive-type and vein-type bodies are chemically different. Minor pyrite occurs as a late phase in the iron ores. The REE patterns of the mineralized metasomatites show LREE enrichment and strong Eu negative anomalies. The strong negative Eu anomaly probably indicates near-surface fractionation of alkali rhyolites involving feldspars. Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the IIC deposit.

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Brueckner, Stefanie M., Gregory Johnson, Stephanie Wafforn, Harold Gibson, Ross Sherlock, Christina Anstey, and Ken McNaughton. "Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry." Minerals 11, no. 8 (August 11, 2021): 867. http://dx.doi.org/10.3390/min11080867.

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The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, X-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

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McQueen, Kenneth G., and Michael A. I. Whitbread. "An integrated lithogeochemical approach to detecting and interpreting cryptic alteration around the Elura Zn-Pb-Ag deposit, New South Wales, Australia." Geochemistry: Exploration, Environment, Analysis 11, no. 3 (August 2011): 233–46. http://dx.doi.org/10.1144/1467-7873/09-011.

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Smith, E. J., S. E. Kesler, and E. H. P. Van Hees. "Relationship of fluid inclusion geochemistry to wall-rock alteration and lithogeochemical zonation at the Hollinger-McIntyre gold deposit, Porcupine District, Canada." Journal of Geochemical Exploration 29, no. 1-3 (January 1987): 434. http://dx.doi.org/10.1016/0375-6742(87)90121-x.

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Vasilopoulos, Mikael, Ferenc Molnár, Hugh O’Brien, Yann Lahaye, Marie Lefèbvre, Antonin Richard, Anne-Sylvie André-Mayer, Jukka-Pekka Ranta, and Matti Talikka. "Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland." Mineralium Deposita 56, no. 6 (January 19, 2021): 1195–222. http://dx.doi.org/10.1007/s00126-020-01039-8.

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AbstractThe Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

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Rozendaal, A. "Wall rock alteration and lithogeochemical haloes associated with the sediment-hosted Rosh Pinah Zn-Pb-Ag deposit in the Pan African Gariep Belt, southwestern Namibia." South African Journal of Geology 108, no. 1 (March 1, 2005): 119–34. http://dx.doi.org/10.2113/108.1.119.

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Bierlein, Frank P., Warren Potma, Federico Cernuschi, Carl Brauhart, Jamie Robinson, Chris J. Bargmann, Warwick Bullen, Jose F. Henriquez, Ian Davies, and Allen Kennedy. "New Insights into the Evolution and Age of the Neoproterozoic Jebel Ohier Porphyry Copper Deposit, Red Sea Hills, Northeastern Sudan." Economic Geology 115, no. 1 (January 1, 2020): 1–31. http://dx.doi.org/10.5382/econgeo.4691.

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Abstract New SHRIMP U-Pb data from dioritic to granodioritic synmineral intrusions associated with the Jebel Ohier porphyry copper deposit (mineral inventory, including NI43-101-compliant total inferred and indicated resources, of 593 million tonnes [Mt] at 0.33% Cu and 0.05 ppm Au, for 1.953 Mt of contained Cu and 933,600 oz of Au at 0.15% Cu cutoff) in the Red Sea Hills of northeastern Sudan have bracketed the age of mineralization to ca. 816 to 812 Ma. This age range, as well as constraints from new and existing lithogeochemical data, is consistent with the deposit’s formation from a productive parental magma source during the early stages in the evolution of an intra-Mozambique Ocean island arc. The Jebel Ohier porphyry copper deposit bears many similarities to well-documented Phanerozoic analogues elsewhere in terms of (1) the mapped style and zonation of hydrothermal alteration (i.e., proximal K-silicate–dominated, to sericitic, to distal propylitic alteration), (2) the occurrence of intense Cu-bearing A- and B-type vein stockwork, as well as sulfide-only C-type veins, anhydrite veins, and younger, peripheral D-type veins, and (3) the geochemical fingerprint of the associated porphyry, which is akin to those of ore-related Tertiary porphyries in the Escondida area in northern Chile. The multiphase intrusion hosting the Jebel Ohier porphyry copper deposit has been intruded by several generations of mafic to felsic postmineralization dikes and voluminous plutons, with a peak in magmatic activity coinciding with the suturing of the Gebeit terrane at ca. 724 Ma. In spite of, or perhaps because of, the occurrence of extensive postmineralization magmatism, and regardless of subsequent deformation, regional metamorphism, uplift, and erosion, the deposit has remained remarkably intact. The discovery of a relatively ancient, yet well-preserved porphyry copper deposit in the Neoproterozoic Arabian-Nubian Shield has major implications for the exploration potential of this resource-rich geologic terrain.

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Theart, H. F. J., R. Ghavami-Riabi, H. Mouri, and P. Gräser. "Applying the box plot to the recognition of footwall alteration zones related to VMS deposits in a high-grade metamorphic terrain, South Africa, a lithogeochemical exploration application." Geochemistry 71, no. 2 (May 2011): 143–54. http://dx.doi.org/10.1016/j.chemer.2010.09.002.

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Caté, Antoine, Ernst Schetselaar, Patrick Mercier-Langevin, and Pierre-Simon Ross. "Classification of lithostratigraphic and alteration units from drillhole lithogeochemical data using machine learning: A case study from the Lalor volcanogenic massive sulphide deposit, Snow Lake, Manitoba, Canada." Journal of Geochemical Exploration 188 (May 2018): 216–28. http://dx.doi.org/10.1016/j.gexplo.2018.01.019.

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Rezaei, Somayeh, Mohammad Lotfi, Peyman Afzal, Mohammad Reza Jafari, Mojtaba Shamseddin Meigoony, and Masoumeh Khalajmasoumi. "Investigation of copper and gold prospects using index overlay integration method and multifractal modeling in Saveh 1:100,000 sheet, Central Iran." Gospodarka Surowcami Mineralnymi 31, no. 4 (December 1, 2015): 51–74. http://dx.doi.org/10.1515/gospo-2015-0038.

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Abstract This study aims at prospecting copper and gold promising areas in Saveh 1:100,000 sheet, situated in Urumieh-Dokhtar magmatic belt (Central Iran). Geographic information system (GIS) is effective in recognition of probable mineral resources by collecting, processing, exploration layer weighting and integrating thematic maps. As there is no certainty in different geological phenomena, modeling and integrating information layers are used to obtain suitable results for determining potential areas. In this study, index overlay method, which is a combination of software processing and expertise knowledge, was used. The survey layers consist of the lithologic units, geophysical data, mineralization, faults and structures and alteration. For more exact survey, concentration-area (C-A) fractal modeling was applied to the map of results obtained from integration. Applying fractal model to this map, the results of the original map were prioritized and became more limited. In the end for assessing the validity of determined promising areas, the results were compared with geochemical anomaly maps of stream sediments and also field observation was performed. Areas with high exploration priority with limited extend exist in center, west and some parts of NW, conformed to granodiorite intrusives and also next priority exists in center, west, NE and NW conformed to granite, diorite, and also subvolcanic rocks respectively. These prioroties are related to fault systems. In order to perform X-ray Diffraction (XRD), Inductively Coupled Plasma – Mass Sepctrometry (ICP-MS) analyses and microscopic studies, lithogeochemical samplings were done. All investigations indicate the possibility of pyrite, chalcopyrite and galena epithermal mineralizations resulted from post magmatic fluids, and also secondary products like hematite, goethite, and malachite as a result of oxidation processes in these areas.

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Whitbread, M. A., and C. L. Moore. "Two lithogeochemical approaches to the identification of alteration patterns at the Elura Zn–Pb–Ag deposit, Cobar, New South Wales, Australia: use of Pearce Element Ratio analysis and Isocon analysis." Geochemistry: Exploration, Environment, Analysis 4, no. 2 (May 2004): 129–41. http://dx.doi.org/10.1144/1467-7873/03-031.

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Wang, Xiaochen, Qinglin Xia, Tongfei Li, Shuai Leng, Yanling Li, Li Kang, Zhijun Chen, and Lianrong Wu. "Application of fractal models to delineate mineralized zones in the Pulang porphyry copper deposit, Yunnan, southwestern China." Nonlinear Processes in Geophysics 26, no. 3 (August 20, 2019): 267–82. http://dx.doi.org/10.5194/npg-26-267-2019.

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Abstract. The aim of this study is to delineate and identify various mineralized zones and barren host rocks based on surface and subsurface lithogeochemical data from the Pulang porphyry copper deposit, southwestern China, utilizing the number–size (N-S), concentration–volume (C-V) and power-spectrum–volume (S-V) fractal models. The N-S model reveals three mineralized zones characterized by Cu thresholds of 0.28 % and 1.45 %: <0.28 % Cu represents weakly mineralized zones and barren host rocks, 0.28 %–1.45 % Cu represents moderately mineralized zones, and > 1.45 % Cu represents highly mineralized zones. The results obtained by the C-V model depict four geochemical zones defined by Cu thresholds of 0.25 %, 1.48 % and 1.88 %, representing nonmineralized wall rocks (Cu<0.25 %), weakly mineralized zones (0.25 %–1.48 %), moderately mineralized zones (1.48 %–1.88 %) and highly mineralized zones (Cu>1.88 %). The S-V model is used by performing a 3-D fast Fourier transformation of assay data in the frequency domain. The S-V model reveals three mineralized zones characterized by Cu thresholds of 0.23 % and 1.33 %: <0.23 % Cu represents leached zones and barren host rocks, 0.23 %–1.33 % Cu represents hypogene zones, and >1.33 % Cu represents supergene enrichment zones. All the multifractal models indicate that high-grade mineralization occurs in the central and southern parts of the ore deposit. Their results are compared with the alteration and mineralogical models resulting from the 3-D geological model using a log-ratio matrix. The results show that the S-V model is best at identifying highly mineralized zones in the deposit. However, the results of the C-V model for moderately and weakly mineralized zones are also more accurate than those obtained from the N-S and S-V models.

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Idrus, Arifudin, Fadlin Fadlin, and Hill Gendoet Hartono. "Eksplorasi Geokimia untuk Menentukan Daerah Prospek Mineralisasi Emas Tipe Urat Epitermal: Studi Kasus di Daerah Tompaso, Kabupaten Minahasa Selatan, Sulawesi Utara." EKSPLORIUM 42, no. 1 (May 31, 2021): 13. http://dx.doi.org/10.17146/eksplorium.2021.42.1.6230.

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ABSTRAK Sulawesi Utara termasuk daerah Tompaso, Kabupaten Minahasa Selatan merupakan jalur magmatik yang potensial menghasilkan endapan bijih hidrotermal. Penelitian ini bertujuan menentukan daerah prospek mineralisasi emas khususnya tipe urat epitermal berdasarkan eksplorasi geokimia meliputi geokimia batuan dan sedimen sungai, khususnya metode BLEG (Bulk Leach Extractable Gold). Metode penelitian meliputi pemetaan geologi, alterasi dan jalur urat, percontoan (bijih/batuan dan sedimen sungai), dan analisis geokimia. Sampel bijih dianalisis dengan metode FA/AAS untuk emas dan metode AAS untuk unsur lain, sedangkan analisis sampel sedimen sungai dilakukan dengan metode cyanide leach dan AAS. Hasil penelitian menunjukkan batuan induk mineralisasi berupa lava andesit dan intrusi diorit. Batuan ini mengalami alterasi silica-clay, argilik, dan propilitik. Perpaduan antara pemetaan geologi, zona alterasi, dan jalur urat dengan eksplorasigeokimia batuan dapat menentukan daerah prospek mineralisasi yaitu Prospek Asam dan Polangkok. Pada Prospek Asam, sampel bijih memiliki kandungan emas sampai 0,03 ppm dengan anomali emas pada sampel BLEG menunjukkan nilai threshold 13,52 ppb Au. Pada Prospek Polangkok ditemukan 2 jalur urat (P1 dan P2) berarah baratlaut-tenggara dengan lebar sampai 5 m. Urat P1 memiliki kadar Au mencapai 0,31 ppm dan pada urat P2 mencapai 0,16 ppm Au. Mineralisasi pada Prospek Polangkok didukung oleh anomali Ag pada sampel BLEG dengan nilai threshold 67,18 ppb. Kedua daerah prospek tersebut direkomendasikan untuk eksplorasi lanjut (follow-up exploration). ABSTRACT North Sulawesi, including the Tompaso region, South Minahasa district, is a part of the magmatic belts hosting potential hydrothermal ore deposits. This study is aimed to determine the prospect area for epithermal vein-type gold mineralization, based on geochemical exploration including rock and BLEG (Bulk Leach Extractable Gold) stream sediment geochemistry. Mapping of geology, alteration and vein direction, sampling (ore/rock and stream sediment), and geochemical analysis were performed. Gold in rock samples was analyzed by FA/AAS, and other elements were detected by AAS, while BLEG samples were analyzed using the cyanide leach and AAS methods. The study area is occupied by andesitic lava and diorite, which are suffered by silica-clay, argillic and propylitic alteration. An integration of geological mapping, alteration zones and vein direction with lithogeochemical survey enables to determine the prospect areas, which consist of Asam and Polangkok prospects. At the Asam prospect, the ore sample contains gold up to 0.03 ppm, where the gold anomaly in BLEG samples show a threshold of 13.52 ppb Au. At the Polangkok prospect, two NW-SE trending veins (P1 and P2 Veins) were discovered with a width of up to 5 m. Vein P1 and P2 contains of up to 0.31 and 0.16 ppm Au, respectively. Mineralization at the Polangkok prospect coincides with Ag anomaly of BLEG samples with a threshold of 67.18 ppb. The two prospect areas are recommended for follow-up exploration.

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Adams, Cameron, Christabel Brand, Michael Dentith, Marco Fiorentini, Stefano Caruso, and Manasvi Mehta. "The use of pXRF for light element geochemical analysis: a review of hardware design limitations and an empirical investigation of air, vacuum, helium flush and detector window technologies." Geochemistry: Exploration, Environment, Analysis 20, no. 3 (January 27, 2020): 366–80. http://dx.doi.org/10.1144/geochem2019-076.

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Light element data are required for robust and accurate lithogeochemical interpretations and are important components in the study of hydrothermal alteration and mineralization processes. In this contribution we review the latest available portable energy dispersive X-Ray Fluorescence (pXRF) technologies exclusively in the context of light element analysis, with focus on the acquisition of data for Na, Mg, Al and Si. We discuss pXRF hardware design limitations, quantify variables that attenuate X-ray energies through numerical modelling, including common pXRF configurations, and empirically investigate modern pXRF technologies used to mitigate X-ray attenuation and improve light element analysis.The void between the sample and detector is a key issue regarding the success of pXRF light element analysis. Dry-air (normal conditions), vacuum purge and helium flush systems are evaluated. Modelled data that use a nominal sample-detector void of 10 mm show that using helium in lieu of air improves X-ray transmission effectiveness from ≈2% to ≈99% for Na and ≈10% to ≈100% for Mg. Modelled detector window data show that using a graphene detector window in lieu of a traditional beryllium detector window improves X-ray transmission effectiveness for Na from ≈38% to ≈64% and ≈57% to ≈77% for Mg. Progressive X-ray transmission effectiveness equates to ≈63% Na and ≈76% Mg when using a helium-graphene pXRF configuration v. ≈1% for Na and ≈6% Mg when using a traditional in-air beryllium pXRF arrangement (i.e. without sample or X-ray entrance window media).Empirically determined improvements of the resolved signal are more modest than those of modelled X-ray transmission effectiveness data. Instrument noise, spectral overlaps and random counting errors are unavoidable and inherent with the limitations of modern detector technologies. However, the employment of helium with graphene detector window technology allows very precise data to be obtained at significantly shorter scan times (i.e. 20 s, instead of the traditional 60–180 s, i.e. 3–9 times faster): a scan time of 20 s can achieve a precision of ≈18% @ ≈0.4% Na and ≈8% @ ≈0.3% Mg for elemental interference-free samples. Precision will improve with increasing analyte concentration.

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Nouri, Reza, Mohammadreza Jafari, Mehran Arian, Faranak Feizi, and Peyman Afzal. "PROSPECTION FOR COPPER MINERALIZATION WITH CONTRIBUTION OF REMOTE SENSING, GEOCHEMICAL AND MINERALOGRAPHICAL DATA IN ABHAR 1:100,000 SHEET, NW IRAN / POSZUKIWANIA ZASOBÓW RUD MIEDZI Z ZASTOSOWANIEM ZDALNYCH TECHNIK WYKORZYSTUJĄCYCH DANE GEOCHEMICZNE I MINERALOGICZNE W POKŁADZIE GEOLOGICZNYM ABHAR 1:100,000 W PÓŁNOCNO-ZACHODNIM IRANIE." Archives of Mining Sciences 58, no. 4 (December 1, 2013): 1071–84. http://dx.doi.org/10.2478/amsc-2013-0074.

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Abstract Abhar 1:100,000 sheet is located within the Cenozoic Tarom volcano-plutonic belt, NW Iran. The present study is based on the integration of remote sensing techniques on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), geochemical data analysis consisting of stream sediment and lithogeochemical samples, within geological field observations and mineralographical studies to identify Cu prospect. On ASTER data; using a number of selected methods including band ratio, Least Square Fit (LS-Fit) and Minimum Noise Fraction (MNF) distinguished alternation zones. These methods revealed that three types of alterations: argillic, phyllic, and iron oxide zones occurring at the NE and SE of Abhar sheet, while the propylitic and silica zones are developed in NW and SW of the studied area. Lineaments were identified by aid of false color composite, high pass filters and hill-shade DEM techniques that two NW-SE and NE-SW major trends were determined. Geochemical anomalies were separated by number-size (N-S) method. Interpretation of N-S log-log plots of Cu in the area may be a result of the three steps of enrichment, i.e., mineralization and later dispersions. Field checks and Mineralgraphical studies also confirm the existence of suitable copper mineralization.

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Jansson, Nils F., Rodney L. Allen, Göran Skogsmo, and Thomas Turner. "Origin of Palaeoproterozoic, sub-seafloor Zn-Pb-Ag skarn deposits, Sala area, Bergslagen, Sweden." Mineralium Deposita, September 9, 2021. http://dx.doi.org/10.1007/s00126-021-01071-2.

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AbstractUnravelling the genesis of metamorphosed mineral deposits can be complicated due to difficulties in separating between primary features and features that formed during the metamorphic overprint. Such uncertainty exists for stratabound and dolomite- and skarn-hosted Zn-Pb-Ag sulfide deposits in 1.89 Ga rocks in the Bergslagen lithotectonic unit (BLU) of Sweden, where a metasomatic vs. regional metamorphic origin for skarns has long been discussed. By integrating geological mapping with new lithogeochemical, mineralogical, and stable isotope data (C, O, S), we show that complexly zoned garnet and clinopyroxene skarns in the Sala area of the central BLU predate mineralization. Sphalerite-galena mineralization formed after the deposition of a younger, more Mn-rich ferroan diopside and andradite-grossular garnet, and is associated with phlogopite, tremolite-actinolite, chlorite, serpentine, and calcite. Mineralization in conjunction with a transition from high-T metasomatism to hydrolytic alteration is inferred. An average δ34SV-CDT of 1.6 ± 1.9‰ in sulfides is consistent with a primordial sulfur source. Trends defined by negative shifts in δ18OV-SMOW and δ13CV-PDB in dolomite and calcite are consistent with fluid infiltration at 300–500 °C. The alteration system is sharply truncated by unaltered, c. 1.89 Ga calc-alkaline granite and porphyritic intrusions, which along with F1 folding of the alteration zones and mineralization suggest that mineralization predate regional metamorphism. The Sala deposits are interpreted as Zn skarn deposits formed in conjunction with the emplacement of intrusions into penecontemporaneous marine volcanic and dolomitized limestone strata. The unusually Mg-rich mineralogy in relation to Zn skarns worldwide most likely reflects the dolomitic precursor.

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Journal articles on the topic 'Lithogeochemical alteration'

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