Hydrothermal Alteration

The Tertiary Sivas Basin contains widespread, tectonically deformed deposits af massive OIigocene gypsum. This unit is one of the most important factors controlhg the tcctono-stratigraphic evolution of the basin insofnr as these deposits are interpreted as dlcollement levels. Sivas Basin also has remarkable structural expressions within these evaporite deposits, ES seen in satellite images aided by colour composites. Because of the arid climatic conditions of the region, the basin provides ease of interpretation geologically in terms of the synoptic-view capability of broad-band multispectral data sets, such as ASTER and Landsat ETM+. In this study, data fusion and decorrelation stretching methods were applied to highlight Oligocene gypsum deposits of the basiil. There continental deposits host celestite and barite mineralization of great industrial importance. These gypsum deposits also carry a geohazard impact, namely their propensi? to lead to collapses, particularly on the eastern side of the city of Sivas. Because the present study aids in the discrimination of these gypsum occurrences from other geological units, it may also lead to geohazard-risk reduction.

Variations in shape, metal content, alteration mineralogy, and volcanic host rocks of the ore deposits in the two major volcanic-hosted luassive sulfide (VHMS) districts of eastern Anstralia, the Cambrian Mount Read Volcanics and the Camhro-Ordovician Mount Windsor snbprovince, strongly reflect their volcanic environment, conditions of ore forination. and hvdrothermal alteration orocesses. prol,~l,ly iorn.rJ r t t l ~~r ,I. the sed flojr r ,:, Hrllvrr Qltc lli\.er or hy rcpl~crmrnt of pun,~ts volcnnicl~snc IIU,,+, Jirrzdv Irlo\r. thr s,u f.wr T e., H,n.l,cn . The, iounrull ulrrrdi<)n ~cs,ci~rrd unh rhccr nolvmrtrlllc . . \'HhlS Jc~>u\lts u,n\ controllrd I. ! hoit-rock pc;lllc.~l,rl~ty .r~d iroro\tty which arc it1 turn rr!,t+d n) n)lcxn>c Cicirs r\pv deucr oiir~zu.nl.c. 111d ~\ ? . v o I ~. t ~~i z ~~u ~r ~t r n l nrchitccturc Fucustneof llvurotllrrrnul fluids ihlno synvold&c sGctures has resurted in well-zoned chlorite-sericite footwall aheracon p;pes within footwall l a"; at Hellyer. On the other hand, diffnse fluid flow through veIy thick pninice breccia at RosebeIy and Hercules has resulted in strata-hound, sericite-dominated footwall alteration zones parallel to the paleosea floor and the ore lenses. Massive and disseininated, pyitic Cu-Au deposits, such as those in the Mount Lyell field and at Highway-Reward. formed by subsea-floor replacement and are associated with only minor nnc-lead massive sulfide ore. These deposits formed from higher temperature fluids (>30OeC), in which copper transport is enhanced, and are commonly located in felsic volcanic centers do~nh~ated by shallow porphyitic intrusions (e.g., Highway-Reward). The Cn-An ore lenses may be strata-bound (e.g., Mount Lyell) or crosscutting pipes (e.g., Highway-Reward) depending on the structure and permeability characteristics of the felsic volcanic host rocks. The presence of high-sulfidation alteration minerals (e.g., pyrophyllite, zunyite) in some of the Cu-An deposits (e.g., Mount Lyell field) indicates that fluids were relatively acidic and snggests the possibility of magmatic fluid input into the hydrothemal system. Alteration zonation associated with the Cu-An VHMS deposits is more symmetrical than that of the Zn-rich deposits, with sericite-rich alteration extending into the hanging wall, in keeping with the subsnrface replacement origin of these de osits J . ' Synvolcanic gold-rich deposits, with high gold/base met ratlos are less common than the Cu-Au and Znrich VHMS ore types. The gold-rich ores (e.g., Henty, South Hercules) are strata bonnd in nature, have low sulfide contents, and are associated with central zones of intense silicification, surrounded hy envelopes of sericite-pyite and carbonate alteration. Volcanological and geochemical studies at Hen? indicate the gold-rich ore formed by the replacement of particular volcanic units deposited in a relatively shallow water environment dominated by volcaniclastic facies, lavas, and limestones. This spectrum of Cu-Au, Zn-rich, and Au-only deposits in the Mount Read Volcanics and the Mount Windsor subprovince is interpreted to represent a continunm from classic sea-floor VHMS ores toward those with features more akin to porphry Cu-Au and cpithermal An-Ag deposits. This spectrum relates to the inte~play between factors in the snbn~arine volcanic environment and the character of the hydrothermal fluid as follows: (1) proportions of volcaniclastic, lava, and subvolcanic intrusive facies; (2) depth of seawater; (3) permeability and porosity of volcanic host rock;; (4) balance behveen magmatic components and seawater components in the ore fluid; and (5) temperature and acidity of the ore fluid. Mineralogical, lithogeochemical, and isotopic studies have revealed a range of alteration vectors usefnl in exploration for both the Zn-rich and Cu-An VHMS deposits. Carbonate and white mica compositional variations are highlighted as important mineralogical vectors; thallium and antimony halos may be nseful trace element vectors; and oxygen and sulfur provide important isotope vectors toward the center of the hydrothermal system. ' ( ~6 6 1 ' a % ~e l ) salnalaH qmos pue k + u a ~ Je saio qa!r-p102 punoq-aje~js pa$eu!mass!p pus 'plarj 1lad7 JunoR ayj u~ salo plo8-~addoa a q d d pa?eu!urassv pue an!ssem 'Xraqasou pue I a X n a ~ se qans salo q a u -a u ~ a![[ejaur -X[od aA!ssem a&s-~aaqs pue sual sapnpu! (1 . 2 ! * ) sa!uea -[OA peau junopq aqj u! q~sodap SNHA jo mmmads ar[L sa~ue310~ pean j m o ~ ayr u! s a a J ~s o d a a a10 jo urrujsadg asu+o~dq~ls raspuim .&w uadswj ~a s u a ~ sw a'l!~aaqs 6'0 ciz SO z-z a's 9'1 U ~O ~U O ! T aou+o~dqus LOSprr!M lyy rampard ased sasusl sw ay!iaa=~s PO 69 9.1 9.8 V8 9.9 a % u e ~~~ sa!uea[o~ peay ~" ~n p o ~d J S B ~ sasual SN aid!&[n~ 8 2 691 PO PS r PC s a p ~a ~ 1 3 ! ~t ~3 p ~ poaa ' 2 ~ au!m juaun3 waqs sw a r d g p ~ cz PI 9.0 PP CPT L'IC Xraqasay s a p q o ~ psaa .qq laanpard ]sea sw P ~P I O B PC wz 9.0 S.L 1 I'C 'an!~~ and S ~! U ~J I O A pea8 'IN ppasop a u ! ~ sual sw ale8~013 . r.z 091 PO CI z'sr la41an n3-qd-UZ u o g e o a ~ snle~s was (mdd) (add) (% W) (% W) (% W) (&w) acl(l ilsodaa nV % "3 'Id uz aluuql.

Surface sediment samples from the coastal zone of Qatar were collected and analyzed to determine the characteristics, and sources of anthropogenic and biogenic hydrocarbons. The main compounds in these surface sediments included n-alkanes, methyl n-alkanoates, diterpenoids, hopanes, steranes, phthalate esters, polycyclic aromatic hydrocarbons (PAHs) and unresolved complex mixture (UCM). Their total concentrations ranged from 18.7 ± 3.7-81.1 ± 7.5 ng/g (3.7 ± 0.6-10.4 ± 4.8%) for n-alkanes, 8.3 ± 2.3-51 ± 3.4 ng/g (3.0 ± 2.0-5.6 ± 2.0%) for methyl n-alkanoates, 1.8 ± 0.1-10.5 ± 1.0 ng/g (1.0 ± 0.5-0.4 ± 0.1%) for diterpenoids, 0.0-79.3 ± 7.4 ng/g (0.0-7.9 ± 0.6%) for hopanes, 0.0-32.9 ± 7.9 ng/g (0.0-6.5 ± 1.0%) for steranes, 0.7 ± 0.1-36.3 ± 3.4 ng/g (0.1 ± 0.1-1.9 ± 3.4%) for phthalates, 0.30 ± 0.2-7.8 ± 0.7 ng/g (0.02 ± 0.04-0.42 ± 0.72%) for PAHs, and 38 ± 9-609 ± 57 ng/g (38.5 ± 13.4-56.5 ± 13.4%) for UCM. The major sources of these lipids were anthropogenic petroleum residues and plasticizers (80-89%), with lesser amounts from natural higher plants and microbial residues (11-20%). Petroleum residues and plasticizer inputs to the coastal sediments of Qatar likely affect the marine ecosystems and associated species groups as well as shallow coastal nursery and spawning areas.

The development of high temperature geothermal systems in Kenya is partly due to the occurrence of shallow magma bodies under volcanoes in the axis of the rift. Drilling of geothermal wells presents a critical development activity of a geothermal project. However, drilling activityfaces numerous challenges which negatively affect drilling rates. The drilling costs are increased since drilling operations are run on tight schedules and any delays come at a high cost. Some of the most common drilling problems can be attributed to lithology and stratigraphy of the formations. This research assessed the effect of lithological characteristics and structural attributes on the drilling rate at Olkaria geothermal field. The study investigated the joint effect of lithostratigraphy, geological structures and hydrothermal alterations on the drilling rate usingwells OW 724B and OW 45V as case study. These wells experienced drilling challenges caused by severe formation problems leading to high n...

Cenozoic continental basalts from east-central China have been analysed for whole-rock major and trace elements, Sr-Nd-Hf isotopes, and mineral O isotopes. The basalts are alkalic to tholeiitic in composition, but are dominantly alkalic. They are characterized by OIB-like patterns of trace element distribution, with no depletion in Nb and Ta but with negative Pb anomalies on primitive mantle normalized diagrams. In addition, they have high Fe/Mn ratios and subchondritic Nb/Ta ratios. Sr-Nd-Hf isotope compositions indicate predominant contributions from young subcontinental lithospheric mantle (SCLM). Some phenocrysts of clinopyroxene and olivine have lower O isotope ratios than normal upper mantle, suggesting involvement of low δ 18 O melts derived from dehydrated oceanic basalt that experienced high-T seawater-hydrothermal alteration during MORB-type magma eruption. Such low δ 18 O melts are unlikely to be transported through the convective asthenosphere because of its rapid O isotope homogenization, but likely to directly metasomatize the overlying peridotite to form pyroxenite. Oxygen isotope disequilibrium between olivine and clinopyroxene suggests a maximum timescale of b 1 ka for melting, transport and eruption during basaltic magmatism. Therefore, we propose a model of oceanic crust-lithospheric mantle interaction for petrogenesis of the continental basalts, in that they were principally derived from near-solidus partial melting of pyroxenites in the juvenile SCLM. Low-angle subduction of the oceanic crust beneath the continental lithosphere during the Early Mesozoic would have not only delaminated the ancient SCLM into the asthenosphere to result in the mantle heterogeneity, but also transform the overlying mantle wedge to the juvenile SCLM beneath the thinned ancient SCLM. Partial melting of the dehydrated oceanic metabasalt and metasediment during the Late Mesozoic would generate adakitic and felsic melts, respectively, metasomatize the overlying juvenile SCLM peridotite to form isotopically depleted silica-deficient to enriched silica-excess pyroxenites. As a result, SCLM beneath the eastern China was stratified in the Cenozoic, with the juvenile SCLM underlying the ancient SCLM but overlying the pyroxenites. Lithosphere rifting during the Cenozoic would cause the melting of the pyroxenites, giving rise to the alkalic to tholeiitic basalts. Therefore, the Cenozoic continental basalts provide the petrological record of melt-peridotite reactions in response to the asthenosphere-lithosphere interaction during the Mesozoic thinning of continental lithosphere.

A Província Mineral de Carajás (PMC), no sudeste do Cráton Amazônico, possui diversos depósitos de Cu-Au de classe mundial distribuídos ao longo dos cinturões de cobre-ouro de Carajás. Os depósitos estão relacionados principalmente aos sistemas minerais IOCG neoarqueanos pré- a sin-tectônicos (2,72-2,55 Ga) e/ou sistemas IOCG e Cu-Au polimtálicos relacionados a granitos tipo A pós-tectônicos, da Suíte Serra dos Carajás (ca. 1,88 Ga). O Cinturão Norte do Cobre abriga importantes depósitos como Salobo, Igarapé Bahia-Alemão, Paulo Afonso, Furnas, GT-46 (Igarapé Cinzento) e Pojuca-Gameleira-Grota Funda, onde são reportadas mineralizações de ambas as épocas metalogênicas. O objetivo do trabalho é apresentar e discutir a ocorrência de adulária no Cinturão Norte do Cobre, até então restritas ao depósito Furnas, bem como correlaciona-las aos sistemas minerais conhecidos. A metodologia consiste na caracterização mineralógica, textural e estrutural com base em petrografia/calcografia detalhad...

Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8 km 3 Osceola Mudflow (5600 y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz-alunite, quartz-topaz, quartz-pyrophyllite, quartz-dickite/kaolinite, and quartz-illite (all with pyrite). Clasts of smectite-pyrite and steam-heated opal-alunite-kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite-pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite-pyrite assemblages, whereas the proximal Electron Mudflow and a b 100 y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite-pyrite alteration within 1 km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H 2 S in the unsaturated zone above the water table. Weakly developed smectite-pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal-mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (≥8 km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1-1.5 km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower west flanks are not intensely altered and probably have not significantly

Discussion 263 Leaching 264 Geochemical processes 265 Biochemical processes 267 Enrichment 270 Geochemical processes 270 Biochemical processes 272 Estimation of the Carbon Budget in the Supergene Environment... 27S Conclusions 276 ^"Ar/^'Ar GEOCHRONOLOGY OF SUPERGENE MINERALIZATION IN THE MORENCI PORPHYRY COPPER DEPOSIT LIST OF FIGURES -Continued FIGURE 67. Schematic cross sections through Metcalf and Western Copper FIGURE 68. Schematic cross sections through Coronado and Northwest Extension FIGURE 69. Morenci landscape evolution and supergene cycles 338

The Clifton-Morenci map area includes four 7.5’ USGS quadrangles: Coronado Mountain, Copperplate Gulch, Clifton, and Mitchell Peak. Descriptions of the Precambrian, Paleozoic, and Mesozoic rocks are primarily from Lindgren (1905a,b). The early Tertiary (Laramide) intrusive rock units are also described in detail by Bennett (1975), Menzer (1980), Preece and Menzer (1992), Griffin, Ring and Lowery (1993), Walker (1995), Phelps Dodge (1996), and Wright (1997). Hydrothermal alteration of the rocks of the Morenci porphyry copper deposit is well described in Lindgren (1905a), Reber (1916), Bennett (1974), Preece, Stegen and Weiskopf (1993), and Walker (1995). Descriptions of the Tertiary volcanic and sedimentary rocks are primarily derived from recent mapping by Ferguson and Enders (this report). Many of the unit names were derived from work in adjacent areas by Richter et al. (1983), Houser et al. (1985), Ratté and Brooks (1995), and Schroeder (1996).

The formation and stabilization of reduced silver species in the regularly interstratified clay minerals, trioctahedral smectite/chlorite (tri-Sm/Ch) and dioctahedral smectite/mica (di-Sm/M), have been studied by electron paramagnetic resonance (EPR) spectroscopy. Both minerals loaded with Ag + cations after degassing and dehydration were γ-irradiated at 77 K and monitored by EPR as the temperature increased. Some samples were exposed to water or methanol vapor after dehydration. In both hydrated and dehydrated samples only the doublets assigned to Ag 0 atoms were observed with no evidence of the formation of Ag clusters. However, the EPR parameters of silver atoms in both matrices are different. In tri-Sm/Ch the narrow anisotropic EPR lines overlap with the broader isotropic lines, whereas in di-Sm/M only broad lines are recorded. The hyperfine splitting -A iso (Ag 0 ) is larger in tri-Sm/Ch than in di-Sm/M. Also the stability of Ag 0 in both clay minerals is distinctly different. Ag 0 doublet in di-Sm/M disappears completely above 230 K, whereas in tri-Sm/Ch it is still recorded at 310 K. It is proposed, basing on the EPR results that Ag 0 atoms appear at different sites in both matrices:in tri-Sm/Ch in the middle of smectite interlayer and in hexagonal cavities in the silicate sheets of tetrahedron layer and in di-Sm/M in hexagonal cavities only. When samples had been exposed to methanol before irradiation, the silver clusters become stabilized in the interlayer sites. In tri-Sm/Ch matrix the silver dimer Ag 2 + formed by γ-irradiation at 77 K is transformed to tetrameric cluster, Ag 4 3+ at 150 K. In di-Sm/M the radiation-induced silver agglomeration proceeds in a similar way, but with a slower rate and Ag tetramer is formed only above 190 K. In both clay minerals, Ag 4 3+ clusters decay above 250 K.

The Okpella region in southwestern Nigeria’s Precambrian Basement Complex holds significant gold (Au) mineralization potential but remains underexplored due to its complex lithostructural evolution. The terrain comprises diverse metasedimentary and granitoid rocks, including granite gneiss (GGN), garnet-biotite schist (GBS), calc-silicate gneiss (CGN), quartzite (Qs), banded iron formation (BIF), charnockite (Ch), granite (G), and minor pegmatite and basic dykes. This study presents a novel integration of geological, geochemical, and high-resolution aeromagnetic and radiometric data—including magnetic derivatives, optimized radiometric indices, potassium deviation analysis, Au prospectivity modeling, and magnetic depth-to-source estimations—to delineate lithological units, characterize hydrothermal alteration, identify Au-bearing zones, and estimate the depths of mineralized structures. The Ch-dominated southern domain shows low to moderate magneto-radiometric responses, while the central to northern zones (GGN, GBS, CGN, BIF, G) exhibit higher signals—with magnetic intensities reaching up to 105.6 nT—interspersed with localized lows. Enhanced magnetic derivatives, optimized radiometric indices, and Au prospectivity mapping refine auriferous targeting by highlighting structurally reactivated contacts, particularly GBS–G, CGN–G, GGN–CGN–G, and GBS–CGN–G, dominated by NE–SW and NW–SE structures. Three structurally controlled hydrothermal belts with exploitable depths from <37 to 125 m are delineated, while deeper magnetic models resolve reactivated crustal blocks down to ~3.5 km. The resulting framework provides a transferable exploration strategy, integrating geophysical, geochemical, and geological insights to support sustainable mineral development and national resource-based economic growth.

Weathering process of rocks leads continuous changes in their physico-chemical state which affects their use in engineering applications. Many tests are used to identify the grade of weathering for classification purposes. Numerous descriptive engineering classifications are developed on weathering of rock and rock masses. These classifications include five or six grades of weathering schemes with crisp boundaries and linguistic terms. The transitions between grades are naturally ambiguous and gradual. Further, the engineering grades of a classification scheme are not suitable for all rock types due to the difference on weathering process of each rock type. Applications of artificial intelligence methods became a practical instrument in the solution of this kind of complex problems in rock mechanics and engineering geology. This study proposes implementation of artificial neural network (ANN) to evaluate weathering properties of Sancaktepe granite crops out around Gebze District in Kocaeli Province in Turkey. For this purpose, uniaxial compressive strength, bulk density, ultrasonic velocity, quick absorption, and point load tests are conducted on drill cores, road cuts and field exposure samples of different weathering grades of Sancaktepe granite. Since the relationship between the rock properties and the weathering index value is nonlinear, an ANN classification model is developed-based on the description of weathering grades using a database consisting of 60 dataset. It is concluded that implication of ANN provides higher performance in classifying than it does in classical method.

Introduction: The Simlipal Basin consists of a 2-3 km-thick sequence of supracrustal rocks deposited on 3.44 Ga TTG gneisses, and 3.3 to 3.12 Ga granites and greenstone belts of the Archean Singhbhum Craton, in NE Odisha, Eastern India [1,2]. Lithologically, the Simlipal Basin is made up mainly of basaltic lavas and pyroclastics interbedded with three quartzite units, the lowest of which also contains conglomerates [1,2]. The basin outcrops in the form of a concentric ring structure (centered on 21°52’07.66” N; 86°20’08.75” E), with a diameter of c. 45 km, situated within a NNE-SSW trending plateau with a long axis of about 70 km (Fig. 1A). The beds within the ring structure dip inwards at angles varying from 18 to 76° towards the centre. Three topographic rings are defined by the resistant quartzites (Fig. 1B). The centre of the Simlipal Structure is occupied by an 800m-thick differentiated ultramafic-mafic intrusion, the Amjori Sill, covering an area of 130 km. The layers consist,...

Spectral Identification and Analysis of
Trace Elements and Minerals in Rock Samples using EDS and FTIR

Andrew M. Appaji1* and N. Joseph John2

1*Research Scholar, Dept of Physics, Kamarajar Govt Arts College, Surandai, India                                   
2Assistant Professor, Dept of Physics, Kamarajar Govt Arts College, Surandai, India
1,2Affiliated to Manonmaniam Sundaranar University, Tirunelveli-627859, Tamil Nadu,India
*andrew.appaji@gmail.com

Abstract: Elements like oxygen, silicon, iron, aluminum, calcium, potassium, sodium, magnesium, titanium, and hydrogen among the naturally occurring elements account for over 99% of Earth’s crust by mass. The other elements that form less than 0.5% by mass together are known as trace elements. They do not play a fundamental role in the makeup of Earth’s crust. Still, their significance in the economy, ecology, agriculture, medicine, toxicology, health, and many other areas is vital and disproportional to their low crustal abundances. In Crystal Analysis by spectroscopic methods, the presence of elements is analyzed along with the trace elements. This paper gives an account of trace elements found in rock crystals. Their qualitative behavior and quantitative presence in the crystal samples are analyzed. EDS and powder FTIR are taken for the samples. The results show the presence of trace elements along with other elements and minerals.

Keywords: EDS, FTIR, trace elements, rock crystals, crystal analysis

The Bosumtwi impact structure, Ghana, is one of the few craters known on Earth that retains a tektite strewn field and fallout suevites. In addition, ICDP borehole LB-07A has intersected three suevite packages ranging from 12.65 m to 21.89 m thick, and centimeter-thick intercalations within monomict breccias and basement rocks from within the crater. These suevites differ from the fallout suevite in having significantly less melt and a different clast population. No evidence for a meteoritic component has been found. Introduction: The 10.5 km diameter, 1.07 Ma Bosumtwi impact structure, Ghana, is the youngest wellpreserved complex impact structure known on Earth; it is associated with the Ivory Coast tektite strewn field. Bosumtwi was excavated in 2.1-2.2 Ga Birimian metasediments and metavolcanics [1,. The Bosumtwi structure was the subject of an interdisciplinary drilling effort by the International Continental Scientific Drilling Program (ICDP) from July to October 2004, which led to the recovery of a series of cores through the sedimentary crater fill as well as two cores through the impact breccia fill and underlying crater basement (LB-07A and LB-08A) [3]. First results on cores LB-07A and LB-08A were reported at LPSC in 2006. This study: In borehole LB-07A a number of suevitic breccia units were identified in addition to polymict lithic and monomict breccias; these have been compared geochemically and petrographically. Ten samples of suevites and country rocks (with variable siderophile contents) were analyzed for their PGE contents using ICP-MS after Ni-sulfide fire assay with Te coprecipitation, using signal intensity calibration [4]. Revised stratigraphy of LB-07A: Following initial results [5], the LB-07A borehole was revisited and re-logged [6]. The core has been divided [6] into upper and lower impactite sections, and a predominantly metasedimentary basement. The upper impactites (333.38 -415.67 m) consist of alternating suevites and lithic breccias, which are similar in breccia characteristics (e.g., clast content, size) but differ by the presence or absence of melt particles. The lower impactites (415.67-470.55 m) represent monomict impact breccia after both metagreywacke and shale (metagreywacke >> shale). Two intercalations of suevite are found in this section, one of which contains significantly more melt fragments than the other suevite samples studied

Introduction: Initial lithologic characterization of core material recovered from the 2016 joint International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364 has produced exemplary evidence for postimpact hydrothermal alteration of the Chicxulub peak-ring [1–4]. The impact melt-bearing breccias and melt rocks of the upper peak-ring are pervasively altered and preserve a diverse suite of clay minerals and zeolites, in addition to carbonates, sulfides and other phases. The conditions under which these minerals form within impact settings on both Earth and Mars remains unclear due, in part, to a lack of detailed studies of terrestrial craters, and the large range of possible conditions that could lead to their development. Additional geochemical and isotopic datasets are needed to provide environmental constraints, particularly for such phases present on the surface of other terrestrial bodies (e.g., Mars), for which there is ...

Introduction: The sequence of events recorded by the continuing sedimentation in the central and annular depressions of complex impact structures is valuable for preserving the history of lake formation and the evolution of such structures’ host environment. At the Ries impact structure, southern Germany, studies of the post-impact lacustrine deposits have had a similar focus [e.g. 1, 2, 3]. Hydrothermal modification of the Ries’ lacustrine deposits is also preserved by the sedimentary record [4, 5], providing an opportunity to study the Ries hydrothermal system and possibly its interaction with the overlying lake environment. Lake environments with input from underlying hydrothermal systems could provide suitable habitats for life [6, 7]. This is especially relevant in Martian environments that would otherwise be less habitable. Jezero Crater, the landing site of the Mars 2020 sample return mission, hosts rover-accessible deltaic deposits and possible lacustrine carbonates [8, 9]. ...

Introduction: The Curiosity rover first observed high-silica (&gt;75 wt.% SiO2) with the ChemCam instrument in outcrops in the Murray formation at Marias Pass on sol 991 [1]; the Buckskin drill target provided mineralogy with the CheMin instrument [2]. High silica was also found associated with fractureadjacent diagenetic halos of the Stimson formation in the Bridger Basin [1] up to sol 1155. The Meeteetse area in Bridger Basin may provide a critical link between the high-silica diagenetic features of the Murray and Stimson formations. Murray strata explored thus far has been interpreted as a lacustrine mudstone [3], while Stimson is a (mostly eolian) sandstone unit [4] that unconformably overlies the Murray [5]. Fig 1 shows an area just to the east of the Meeteetse area, within an area of bedrock in Bridger Basin (Fig 1, inset) between Marias Pass and the Bagnold Dunes of Gale Cater. The area has been characterized by Curiosity’s Alpha Particle X-ray Spectrometer (APXS), ChemCam, M...

Introduction. The Arctic Mars Analogue Svalbard Expeditions (AMASE) enable in situ measurements of environmental chemistry relevant to habitability and biosignature detection using instruments that are under development or study for future Mars surface missions. More detailed subsequent characterization of samples by laboratory instruments allows the strengths and limitations of the suite of field instruments to be evaluated. AMASE field studies are also able to address sample collection, caching, and contamination issues that are relevant to future sample return missions. Two experiments employed during the AMASE-2009 campaign, X-ray diffraction (XRD) and evolved gas analysis (EGA) closely mimicked similar experiments that are planned for the 2011 Mars Science Laboratory (MSL). These 2 MSL investigations are SAM (Sample Analysis at Mars) and CheMin (the Chemistry and Mineralogy experiment). Additional 2009-AMASE field instruments employed are similar to those under development for the ESA ExoMars or other rover missions. These provided imaging, spectroscopic, and subsurface sounding data. A variety of microbiology and field life detection techniques rounded out the AMASE-2009 analytical tools. Here we focus on data obtained from the EGA analyses of carbonate rocks from a site in the Bockfjord Volcanic Complex (BVC).

Carbonate analyses show that SAM evolved gas analysis will complement CheMin X-ray diffraction by supporting volatile-bearing mineral identification and providing information about trace phases below the XRD detection limit or amorphous phases.

Publisher&#39;s copyright statement: NOTICE: this is the author&#39;s version of a work that was accepted for publication in Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be re ected in this document. Changes may have been made to this work since it was submitted for publication. A de nitive version was subsequently published in Geochimica et Cosmochimica Acta, Volume 96, 1 November 2012, 10.1016/j.gca.2012.08.016.

Publisher&#39;s copyright statement: NOTICE: this is the author&#39;s version of a work that was accepted for publication in Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be re ected in this document. Changes may have been made to this work since it was submitted for publication. A de nitive version was subsequently published in Geochimica et Cosmochimica Acta, Volume 96, 1 November 2012, 10.1016/j.gca.2012.08.016.

Movement within the Earth's upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K-Ar and Rb-Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as ''Kristallgranit'') at 325 ± 7 Ma, whereas the K-Ar and Rb-Sr ages of two illite fractions \2 lm (266-255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the ''Kristallgranit'' was already at or near the Earth's surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U-Th)/He thermochronology of two single fluorite grains from a fluorite-quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50-80°C) in the fault zone during the Cretaceous.

Afrika kıtası, nadir metallerle zenginleştirilmiş pegmatitler açısından zengindir. Kıtadaki birçok bölge, önemli nadir element pegmatit yataklarıyla tanınır. Bunlar arasında, en zengin tantal ve lityum kaynaklarından biri olan Demokratik Kongo Cumhuriyeti, tantal, berilyum ve lityum içeren pegmatit yatakları bulunan Ruanda, niyobyum, tantal ve kalay yatakları bulunan Burundi ve yaklaşık 100 yıllık kalay ve tantal üretimi bulunan Uganda gibi Orta Afrika ülkeleri bulunur. Diğer kaynaklar ise Mısır, Etiyopya (tantal bakımından zengin pegmatitler), Somali, Mozambik, Madagaskar, Namibya, Zimbabve ve Güney Afrika'da bulunur.

The Kopuz Fe skarn deposit in the eastern Sakarya Zone is genetically associated with the 44-45 Ma Kopuz granitoid. The Fe ores are hosted within the contact zone between this granitoid and Jurassic Lower Cretaceous limestone. The deposit is characterized by both endo-and exoskarn zones, which exhibit a diverse range of minerals including clinopyroxene, plagioclase, amphibole, biotite, garnet, epidote, phlogopite, magnetite, hematite, pyrite, quartz, calcite, actinolite, limonite, and goethite. Magnetite and hematite, accompanied by small amounts of pyrite, are primarily ore minerals. Pyroxene types observed in the mineralization include diopsidic hedenbergite in the endoskarn zone and diopside in the exoskarn zone. Plagioclase in the endoskarn zone vary from oligoclase to Labrador in composition, which transition towards Na-rich plagioclase and orthoclase in the ore-bearing exoskarn zone. Amphiboles, primarily calcic in nature, are classified as Mg-hornblende and actinolite, with low F and Cl contents, indicating minimal F enrichment during Fe-skarn formation. Garnet is characterized by andradite in the exoskarn zone close to the endoskarn and grossular-andradite in the distal exoskarn zone. The increase of Ad/Gr ratios in zoned garnet indicate an increasing ƒO 2 value outward from it. Considering that rare pyrite occur together with magnetite and hematite, we suggest that the deposit formed under conditions of low ƒS 2 and high ƒO 2 conditions. The homogenization temperature and salinity of the fluid inclusions in quartz from the exoskarn zone vary from 224 • C to 349 • C and 4.18 % (wt% NaCl equiv.), respectively. The oxygen isotope composition (5.10 ‰ to 7.86 ‰) of the fluids in equilibrium with magnetite and quartz minerals in the exoskarn zone supports a magmatic fluid origin. The oxygen isotopic signatures of epidote and amphibole further indicate a minor interaction with an additional source, likely meteoric waters. The sulfur isotope composition of pyrite (2.3 ‰) is consistent with a magmatic sulfur source. In summary, the middle Eocene-aged Kopuz Fe skarn deposit occurred a shallow depth within a magmatic arc, where oxidized conditions predominated. ☆ This article is part of a special issue entitled: 'Iron and critical metals' published in Journal of Asian Earth Sciences.

The Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabound volcanogenic Cu-Zn-(Pb) ± Au-bearing massive sulphide deposits and associated zones of hydrothermal alteration. Here, we use major and trace element analyses of massive sulphides, gossans, and hydrothermally altered and least altered metamorphosed host rock (schist) from two of the deposits (Shaib al Tair and Rabathan) to interpret the geochemical and petrological evolution of the host rocks and gossanization of the mineralization. Tectonic interpretations utilize high-field-strength elements, including the rare earth elements (REE), because they are relatively immobile during hydrothermal alteration, low-grade metamorphism, and supergene weathering and therefore are useful in constraining the source, composition, and physicochemical parameters of the primary igneous rocks, the mineralizing hydrothermal fluid and subsequent supergene weathering processes. Positive Eu anomalies in some of the massive sulphide samples are consistent with a high temperature (>250°C) hydrothermal origin, consistent with the Cu contents (up to 2 wt.%) of the massive sulphides. The REE profiles of the gossans are topologically similar to nearby hydrothermally altered felsic schists (light REE (LREE)-enriched to concave-up REE profiles, with or without positive Eu anomalies) suggesting that the REE experienced little fractionation during metamorphism or supergene weathering. Hydrothermally altered rocks (now schists) close to the massive sulphide deposits have high base metals and Ba contents and have concave-up REE patterns, in contrast to the least altered host rocks, consistent with greater mobility of the middle REE compared to the light and heavy REE during hydrothermal alteration. The gossans are interpreted to represent relict massive sulphides that have undergone supergene weathering; 'chert' beds within these massive sulphide deposits may be leached wallrock gossans that experienced silicification and Pb-Ba-Fe enrichment from acidic groundwaters generated during gossan formation.

Ultramafik kayaçlar, okyanus litosferinin önemli bir bileşenidir ve genellikle yavaş ancak geniş olarak yayılan sırtların yakınında ve sırtlar boyunca ve diğer aktif tektonik ortamlarda yüzeylenirler.
Manto malzemesinin serpantinleşmesi, küresel deniz sistemi ve dalma-batma zonu ortamları için önemli jeofiziksel, jeokimyasal ve biyolojik öneme sahip temel bir süreçtir.
Mineral toplulukları ve dokuları genellikle karmaşık olup; yerleşme, hidrotermal alterasyon ve ayrışma sırasında oluşan süreçlerin tümünü yansıtır.
Bu makalede, farklı tektonik ortamlardaki okyanusal üst manto dizilerindeki serpantinleşme süreçlerinin mineralojik ve jeokimyasal sonuçları incelenmekte ve serpantinleşme ile akışkan kimyası arasındaki ilişki tartışılmaktadır.

Ekwueme federal university Ndufu-Alike Ikwo Gossans, the weathered and oxidized remnants of sulfide-rich ore bodies, are among the most important natural indicators in mineral exploration. These ferruginous caps, often associated with supergene enrichment zones, provide valuable clues to the type, location, and economic potential of underlying mineralization. This article reviews the geological characteristics of gossans, their significance as exploration guides, color and texture indicators for ore types, and their integration with modern geochemical, geophysical, and remote sensing techniques. Case studies from Canada, Australia, and Turkey demonstrate the enduring importance of gossan analysis in identifying economically significant ore deposits, while also highlighting its role in planetary geology as an analogue for Martian surficial process.-Key words: (deposits, enrichment zones, supergene).

The Sefidrud sub-basin, extending from Kurdistan to the southern Caspian Sea, is the main drainage basin of the Kurdistan Province. Based on previous works and new field investigations, potentially contaminated areas were identified, and approximately sixty groundwater samples were collected from wells and springs during the dry (October 2020) and wet (April 2021) seasons, along with 40 rock and soil samples. After analyzing the samples by coupled plasma mass spectrometry and modeling in ArcGIS software, we present a new dataset of toxic element contamination in the water resources of Kurdistan Province. Higher toxic element concentrations include arsenic, antimony, and lead, of which 80%, 28%, and 13.3% of samples had concentrations higher than WHO guidelines, respectively. The severely contaminated sites mainly include east Qorveh, north and northeast Dehgolan, and south and southwest Bijar, which, based on the data of rock and soil samples, are associated with geological phenomena. A review of published research and comparison of the geology of northwest Iran with that of western and southern Iran implies that the high incidence of gastric and esophagus cancers in northwest Iran is mainly linked to the geology of the contaminated areas, which increases exposure to the toxic elements through drinking and irrigation water. Results indicate that the main sources of toxic elements are geogenic, and are primarily related to geothermal processes and contributions from altered young acidic rocks (mainly resulted
from Miocene-Quaternary volcanic activities) of northwest Iran.

Geochemical cycling of the redox-sensitive trace elements arsenic (As) and vanadium (V) was examined in shallow pore waters from a marsh in an interdistributary embayment of the lower Mississippi River Delta. In particular, we explore how redox changes with depth and distance from the Mississippi River affect As and V cycling in the marsh pore waters. Previous geophysical surveys and radon mass balance calculations suggested that Myrtle Grove Canal and the bordering marsh receive fresh groundwater, derived in large part from seepage of the Mississippi River, which subsequently mixes with brackish waters of Barataria Bay. Additionally, the redox geochemistry of pore waters in the wetlands is affected by Fe and S cycling in the shallow subsurface (0-20 cm). Sediments with high organic matter content undergo SO 4 2reduction, a process ubiquitous in the shallow subsurface but largely absent at greater depths (~3 m). Instead, at depth, in the absence of organic-rich sediments, Fe concentrations are elevated, suggesting that reduction of Fe(III) oxides/oxyhydroxides buffers redox conditions. Arsenic and V cycling in the shallow subsurface are decoupled from their behavior at depth, where both V and As appear to be removed from solution by either diffusion or adsorption onto, or coprecipitation with, authigenic minerals within the deeper aquifer sediments. Pore water As concentrations are greatest in the shallow subsurface (e.g., up to 315 nmol kg -1 in the top ~20 cm of the sediment) but decrease with depth, reaching values < 30 nmol kg -1 at depths between 3 and 4 m. Vanadium concentrations appear to be tightly coupled to Fe cycling in the shallow subsurface, but at depth, V may be adsorbed to clay or sedimentary organic matter (SOM). Diffusive fluxes are calculated to examine the export of trace elements from the shallow marsh pore waters to the overlying canal water that floods the marsh. The computed fluxes suggest that the shallow sediment serves as a source of Fe, Mn, and As to the surface waters, whereas the sediments act as a sink for V. Iron and Mn fluxes are substantial, ranging from 50 to 30,000 and 770 to 4300 nmol cm -2 yr -1 , respectively, whereas As fluxes are much less, ranging from 2.1 to 17 nmol cm -2 yr -1 . Vanadium fluxes range from 3.0 nmol cm -2 yr -1 directed into the sediment to 1.7 nmol cm -2 yr -1 directed out of the sediment

The A-type Paleoproterozoic Bannach Granite belongs to the Jamon Suíte and cross-cut the Archean units of the Rio Maria Domain in the Carajás Province. It comprises eight facies with varied mafic content and texture: even-grained cumulate granite (CG), even coarse-grained biotite-amphibole monzogranite (cBAMz), even coarse-grained amphibole-biotite monzogranite (cABMz), porphyritic biotite monzogranite (pBMz), even coarse-grained leucomonzogranite (cLMz), early even medium-grained leucomonzogranite (EmLMz), late even medium-grained leucomonzogranite (LmLMz) and even fine-grained leucomonzogranite (fLMz). In the less evolved facies, the dominant amphibole is Fe-hornblende passing to Fe-edenite or hastingsite, with associated cummingtonite/grunerite originated from the destabilization of clinopyroxene. Biotite has ferroan composition and approaches annite in the late-emplaced leucomonzogranite. Plagioclase varies from andesine to oligoclase or from oligoclase to albite. Titanite, magnetite, and ilmenite are found in all granite facies showing magmatic origin. The near liquidus temperatures vary between 943ºC and 795ºC and the estimated emplacement pressure is 300 ± 50 MPa (~11.1 ± 1.9 km). Amphibole Fe/(Fe + Mg) ratios together with magmatic magnetite and titanite indicate that these granites crystallized at moderately oxidizing conditions, similar to those admitted for the Jamon granite and magnetite series granites of Laurentia. However, the composition of biotite suggests a more reduced character close to NNO to NNO -0.5. The late leucomonzogranite facies is an exception because it displays high Fe/(Fe + Mg) ratios in biotite and approaches to the reduced granites of Carajás, Laurentia and Fennoscandia in this regard. It derived from a more reduced source than the other facies of Bannach Granite.

The 572 Ma Guarany stock consists of magmatic epidote-bearing hornblende monzodiorite to biotite granite that intruded Paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern Brazil. Co-magmatic diorite enclaves and dikes are abundant throughout the pluton. The monzodiorite-granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams. They display chemical and isotopic characteristics of crustal melts, such as enrichment in incompatible elements, high back-calculated initial 87 Sr/ 86 Sr ratios (avg. 0.71253), negative εNd (0.57Ga) values (avg. -14.58), as well as high and variable (+9.1 to + 11.1‰ VSMOW ) δ 18 O (zircon) values. Correlations between O-isotope and whole-rock silica contents, as well as initial 87 Sr/ 86 Sr ratios with 1/Sr concentrations, suggest hybridization of a lower continental crustal melt with more felsic crustal rocks, concomitant with fractional crystallization. Amphibole chemistry and whole rock Zr, TiO 2 and P 2 O 5 contents suggest magma solidification at a pressure ~7 kbar and near liquidus temperature ~900 °C. The parental magma was likely formed by partial melting of old (tDM = 2.0 Ga) amphibolitic lower continental crustal rocks, in a post-collisional setting, probably triggered by underplating of mantle-derived mafic magma during the period of relaxation after collision.

This paper comprises a comparison between the vegetation response in ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) multispectral optical imagery and possibly equivalent bedrock/regolith/soil response in airborne gamma-ray spectrometry grids, employing a tropical rainforest area in the Brazilian Amazon as a control. The applied technique comprised band ratios using a fixed near infrared band (numerator) divided by individual visible and shortwave infrared bands (denominator). These band ratios were subsequently submitted to principal component analysis, and the high frequency information is smoothed by low pass filtering. The colour compositions selected for interpretation were sharpened by the first principal component of the original ASTER bands through an IHS transform in order to add albedo/texture information -lost through band rationing -back to the imagery. The products show a plausible coherence with airborne gamma-ray data and field observations, proving that the proposed processing strategy applied to low cost multispectral data can provide useful geologic information in inaccessible vegetated areas.

The intermediate-sulfidation epithermal Strauss deposit is part of the Drake Goldfield of north-eastern NSW, Australia. The mineralization is gold dominant with minor silver and significant zinc, copper and lead. Strauss has a combined total resource of 2.66 Mt @ 1.5 g/T Au and 1.9 g/T Ag. Petrographic analysis has shown the deposit to be hosted by varying layers of dacitic ash flow tuffs and a cross-cutting lamprophyre dyke though previous authors classified some of the tuffs as intrusive andesites. Mineralization mainly occurs in the form of vein stockworks of three main orientations. Structural analysis indicates that these resulted from two fault system events and one conjugate fault system. Petrographic and SEM analysis shows that there are two different mineralization styles, a pyrite dominant and chalcopyrite dominant assemblage, with three main mineralization events. Correlation analysis for the assay data indicates that Au has a strong relationship with Ag and a moderate co...

Extensive drilling at the Hellisheiði geothermal field within the Hengill volcanic complex in SW-Iceland has yielded vast amount of data on hydrothermal alteration and alteration zones within an active rift-zone. The majority of rock formations in the area are of olivine-tholeiite composition and are mostly hyaloclastite formations formed subglacially. Basalt lava flows from interglacial periods and from the Holocene occupy the lowlands and are therefore less common in the volcanic centre. This study involved characterising the clinopyroxene in the Hellisheiði geothermal wells and their subsequent alteration by electron microprobe analyses. The intention was to compare the progressive alteration of buried lava flows, where temperatures have risen with increased burial depth, with the alteration of intrusive rocks that should record the primary alteration of the prevailing temperature conditions in their surroundings. The results suggest that the geothermal alteration of primary pyro...

The petrology and geochemistry of Icelandic basalts have been studied for more than a century. The results reveal that the Holocene basalts belong to three magma series: two sub-alkaline series (tholeiitic and transitional alkaline) and an alkali one. The alkali and the transitional basalts, which occupy the off-rift volcanic zones, are enriched in incompatible trace elements compared to the tholeiites, and have more radiogenic Sr, Pb and He isotope compositions. Compared to the tholeiites, they are most likely formed by partial melting of a lithologically heterogeneous mantle with higher proportions of melts derived from recycled oceanic crust in the form of garnet pyroxenites compared to the tholeiites. The tholeiitic basalts characterise the mid-Atlantic rift zone that transects the island, and their most enriched compositions and highest primordial (least radiogenic) He isotope signature are observed close to the centre of the presumed mantle plume. High-MgO basalts are found scattered along the rift zone and probably represent partial melting of refractory mantle already depleted of initial water-rich melts. Higher mantle temperature in the centre of the Iceland mantle plume explains the combination of higher magma productivity and diluted signatures of garnet pyroxenites in basalts from Central Iceland. A crustal component, derived from altered basalts, is evident in evolved tholeiites and indeed in most basalts; however, distinguishing between contamination by the present hydrothermally altered crust, and melting of recycled oceanic crust, remains non-trivial. Constraints from radiogenic isotope ratios suggest the presence of three principal mantle components beneath Iceland: a depleted upper mantle source, enriched mantle plume, and recycled oceanic crust. The study of glass inclusions in primitive phenocrysts is still in its infancy but already shows results unattainable by other methods. Such studies reveal the existence of mantle melts with highly variable compositions, such as calcium-rich melts and a low-18 O mantle component, probably recycled oceanic crust. Future high-resolution seismic studies may help to identify and reveal the relative proportions of different lithologies in the mantle.

The Geological Survey of Italy, the Società Geologica Italiana and the Editorial group are not responsible for the ideas, opinions and contents of the guides published; the Authors of each paper are responsible for the ideas, opinions and contents published. Il Servizio Geologico d'Italia, la Società Geologica Italiana e il Gruppo editoriale non sono responsabili delle opinioni espresse e delle affermazioni pubblicate nella guida; l'Autore/i è/sono il/i solo/i responsabile/i.

Epidote/allanite-fluorapatite coronae around monazite and xenotime are investigated in Permian pegmatites deformed under greenschist-facies conditions during Alpine tectonometamorphism in the Austroalpine basement, Eastern Alps. The aim was to evaluate the replacement reactions involved in the formation of a corona microstructure, its age and relation to deformation. In the corona core, monazite and xenotime single crystals show domains with different composition and age. Monazite (Mnz1) and xenotime (Xen1) dating by electron microprobe (EPM) reveals an age of 250-287 Ma, consistent with the Permian magmatic age of the pegmatites. These are partly replaced by secondary monazite (Mnz2) and xenotime (Xen2) compositions yielding younger Mesozoic (170-210 Ma) and Alpine (30-120 Ma) ages. The same crystallographic orientation of the primary and secondary monazite and xenotime indicates interface-coupled dissolution-precipitation reactions. Allanite U-Th-Pb dating by laser ablation inductively coupled mass spectrometry in the corona revealed an age of 60 ± 6 Ma, interpreted as the age of corona formation. The coronae around monazite consist of an inner zone of equant fluorapatite grains surrounded by prismatic allanite, which are surrounded by epidote enriched in heavy rare earth elements (HREEs) and REE-poor epidote grains. Compared to coronae around monazite, fluorapatite has higher REE contents and no allanite occurs in the coronae surrounding the xenotime. General reactions for monazite and xenotime breakdown can be written as follows: The amount of replacement (judged by the relative proportions of monazite and fluorapatite) is low for monazite included in tourmaline but high within the mylonitic foliation. This dependence on the degree of replacement on the local surrounding microfabric indicates that fluid availability along grain boundaries in the matrix and cracks controlled reaction advancement, allowing the elementary mass transfer required for corona formation (e.g. input of Ca, Al, Si, Fe, F). The oblate shape of the coronae aligned within the foliation of the pegmatites and the deflected foliation around the coronae, without an outer rim of prismatic epidote showing signs of deformation, indicate that the main stage of corona formation took place during deformation and reactions were still ongoing after the main stage of deformation. The corona microstructure documents replacement reactions of a single reactant into multiple distinct mineral growth zones by dissolution and precipitation processes at nonisostatic, greenschist-facies conditions, which prevailed in the area to the north of the Defereggen-Antholz-Vals shear zone between the middle Cretaceous and the Oligocene. These reactions ceased before being completed, and REE gradients within single grains within the corona and on the thin-section scale are preserved, which suggests restricted and/or episodic transport of REE in the fluid phase and/or availability of fluid.

A metapelitic sequence with Silurian protolith from the Horváthertelend Unit (Tisza Mega-unit, Hungary) has a K-white mica + chlorite + quartz + albite + anatase ± tourmaline mineral assemblage. Moderately developed disjunctive and welldeveloped continuous foliations are present. Geochemical results reflect a dominantly felsic source of the protoliths, suggesting an intermediate to acidic volcanic arc in the provenance area. Metasandstone pebbles in the metaconglomerate indicate a recycled sedimentary source. Raman spectroscopy of carbonaceous material indicates a ~ 350-370 °C peak metamorphic temperature. The Kübler Index (KI Basel ) values of the phengitic K-white mica indicate epizonal metamorphism (0.22 ± 0.04 Δ°2θ). The Chlorite 'Crystallinity' Index (ChC CIS ) suggests metamorphic alteration near to the anchizone-epizone boundary (0.31 ± 0.06 Δ°2θ). K-Ar ages of K-white mica are interpreted as a result of Variscan metamorphism (c. > 310 Ma) and post-Variscan uplift (c. 290 Ma). The predominance of lydite and slate of Llandoverian age and the overlying coarse-grained metagreywacke and metaconglomerate beds of the Szalatnak Slate Formation show strong lithological similarities with the proximal Silurian sequences in the Małopolska Massif (Kielce Region, Holy Cross Mountains, Poland). The original position of the Horváthertelend Unit is presumably to the northeast from the Bohemian Massif, next to the Upper Silesian Block (Moravo-Silesian Zone) and the Małopolska Terrane.

The Middle Triassic shallow marine carbonates of the SE Pannonian Basin (Szeged Dolomite Formation) show evidence for multistage dolomitization and a complex diagenetic history. In first stage the whole sequence was completely dolomitized by reflux of slightly evaporated seawater. This process took place from the near surface till shallow burial realms and resulted in the formation of both fabric-preserving and fabric-destructive dolomite types. In the following stage nonplanar matrix dolomite and saddle dolomite cement were formed in the intermediate and/or deep burial realm. These later dolomite phases are likely generated by invasion of exotic fluids at relatively high temperature evidenced from the fluid inclusion homogenization temperatures, and stable isotope compositions. Vuggy, fracture, and solution enhanced porosity are also related to this local hydrothermal event. Microthermometry performed on saddle dolomite-hosted primary fluid inclusions confirm the presence of hot (138-235 °C) and moderately saline brines (4.1-8.7 mass% NaCl equivalent). The calculated δ 18 O water and the measured δD water values of the fluid inclusions from the saddle dolomite cement together with the relatively low salinity values indicate a metamorphogenic (and/or magmatic) origin of the hydrothermal fluid that probably was channeled along the Upper Cretaceous subhorizontal overthrust zones. The pores formed by the leaching effect of these hydrothermal fluids were subsequently partly occluded by meteoric calcite during the Paleogene-Middle Miocene subaerial exposure but a remarkable part was preserved, and currently serves as reservoir space. Such an integrated study of the different dolomite and porosity types, the understanding of their genesis, and timing relative to hydrocarbon maturation and migration could aid in exploration and development.