Hypogene Processes Research Articles

Late-stage evolution of hypogene caves at Tyuya-Muyun (Kyrgyzstan): Quantitative insights from mineral deposits

The Tyuya-Muyun massif in SW Kyrgyzstan hosts a number of caves some of which contain Ra- and U-bearing minerals that were extensively mined in the early 20th century. Previous studies have suggested that the caves of the Tyuya-Muyun have experienced a complex speleogenetic history, including epigene and hypogene processes. Here, we reconstruct the late stages of hypogene processes by studying subaqueous (calcite and barite spars, cave clouds), near-water table (rafts, folia) and vadose (flowstone) mineral deposits in Great Barite and Surprise caves. We determined the chronology (230Th dating), stable isotope composition (δ18O, δ13C and Δ47), and formation temperature (fluid inclusion microthermometry and Δ47) of these minerals and reconstructed the oxygen isotopic composition of the paleo-water (δ18Ow). In contrast to previous hypotheses about cave evolution, we found no evidence of an initial epigenic karst phase. The earliest mineral deposits suggest already hydrothermal conditions, with calcite and barite forming at ~40–50 °C prior to 600 ka. Cave clouds in Great Barite Cave mark the beginning of the lowering of the groundwater table and also record a decrease in water temperature from 29.7 ± 8.3 °C to 12.7 ± 5.6 °C, as shown by Δ47 thermometry. The latter temperature remained stable, within analytical uncertainties, during the past 600 ka, as indicated by Δ47 results of near-water table and vadose speleothems in Surprise Cave. At the same time, the decrease in δ18Ow suggests a reduced contribution of thermal water and an increased input of colder meteoric water. By around 540–450 ka Surprise Cave emerged from the phreatic zone, as indicated by 230Th ages of the highest folia and flowstone. This lowering of the water table continued until 84 ka and may have been related to the final uplift phase of the Tyuya-Muyun massif and the concomitant incision of the Aravan River forming the Dangi Gorge.

Revealing the ongoing speleogenetic processes in an underwater cave through the application of natural radionuclides and stable isotopes: case study from the hypogene Buda Thermal Karst

The underwater Molnár János Cave in the hypogene Buda Thermal Karst system (Budapest, Hungary) provides a unique site to study the effects of flowing groundwater and the interplay of fluids of different origin. The aim of the present study is to characterize the groundwater in different parts of the cave with temporal resolution, hence describe the recent speleogenetic processes within the cave. This study uses natural radioisotopes (uranium, radium, and radon) besides stable isotope ratios of oxygen and hydrogen to identify the different fluid components. The results show that the majority of the cave is situated in the flow path of the intermediate flow system, discharging in the Boltív Spring. Thus, the dominant recent speleogenetic processes are connected to this lukewarm groundwater. In contrast to previous views, typical hypogene processes, such as mixing corrosion involving thermal waters, are restricted to a narrower area in the cave, to the contact zone of lukewarm waters and the warmer upper water layer around the largest partially air-filled chamber (Kessler Hall). The warmer water layer is the result of free convection. In the air-filled chambers condensation-corrosion might be active. However, its effect is limited to the largest room (Kessler Hall), as it is open to surface conditions. More active mixing corrosion probably occurs deeper, in the area of the Northeastern Margin Fault, which is indicated by the radon content in the Boltív Spring. Regarding the temporal processes, the main driving force can be linked to the water level fluctuations of the Danube, which regulates the discharge of the regional flow-related thermal water upwelling, thus affecting the mixing ratio of the lukewarm waters transported by the intermediate flow systems and the thermal waters, representing the regional flow path, including basinal components.

Role of hypogenesis in the evolution of karst in the Taurus Mountains Range, Turkey

Field observations and laboratory data collected from the Taurus Mountains Range, Turkey during the last two decades provided evidence for the link between the evolution of hypogene karst and the geodynamic history. Major evidence includes; carbonate-hosted secondary ore deposits that are converted from primarily hypogene minerals by epigene, oxygen-rich groundwater circulating at local to intermediate depths. Another piece of evidence of hypogene karst in the Tauride is the Kırkgöz springs’ huge submerged cave/conduit system, which formed the Antalya Travertine Plateau, which is the world’s largest deposit precipitated by cool karst groundwater. The obruks in central Tauride are giant collapse dolines formed by ascending hypogene fluids in the upper continental crust, rich in volcanogenic carbondioxide. The groundwater’s noble gas and carbon isotope data are helpful in determining the existing but asymptomatic hypogene activity in the upper crust. Hypogene karst development seems common in parts of the world with current or past geodynamic activity. However, a hydrogeological overview of the geodynamic history is essential to assess the hypogene processes and their reflections on the land surface.

Klimchouk’s Impact on the Development of Speleogenetic Models for Castile Evaporites: West Texas and Southeastern New Mexico, USA

Due to the pioneering work of Alexander Klimchouk (2007), hypogene karst is now recognized as being complex and extensive throughout Permian strata of the greater Delaware Basin in West Texas and southeastern New Mexico (USA). Klimchouk heavily influenced our current understanding of hypogene speleogenesis in the Permian Ochoan Castile Formation where we now recognize diverse hypogene manifestations that include vertically-extensive breccia pipes, laterally-extensive blanket breccias, morphologically-varied caves, diagenetically-altered sulfates, and unique venting structures. Underlying Bell Canyon strata provide the transmissive zone for delivery and removal of solutionally aggressive fluids to the conformably overlying Castile evaporites. Current speleogenetic models indicate that hypogene karstification in Castile evaporites began in the early Neogene in conjunction with regional uplift and tilting. Since that time, hypogene processes have shifted eastward across the Delaware Basin in conjunction with the eastward migration of the Pecos River. Surface denudation has exposed updip regions of the Castile Formation to the west creating the Gypsum Plain where hypogene karst is exposed to epigene processes and associated overprinting. Today, the Gypsum Plain continues to evolve with both hypogene and epigene processes still active within the Delaware Basin.

Guano-derived morphologies and associated minerals found in Cova de sa Guitarreta, Llucmajor, Balearics

Cova de sa Guitarreta is located in the southern part of Mallorca Island (western Mediterranean). It was formed presumably by hypogenic processes in Upper Miocene reefal calcarenites. The cave hosts an important breeding colony of bats during the end of spring and early summer. Its microclimate is influenced by the presence of a thermal phreatic water table (27.7ºC) as well as by bat populations remaining in the cave along the reproductive season. The morphological bat-related features include bat claws and thumb marks scratches, together with several morphologies linked to bat excreta and aggressive leachates from guano. From the mineralogical point of view, this cave outstands regarding the presence of cave minerals linked to guano: nine phosphates have been identified, comprising three of them that are reported for the first time in Mallorcan caves (newberyite, struvite and whitlockite). Particularly interesting is the dichotomy between struvite and newberyite: the first one occurs when the cave is occupied by bat colonies (spring-summer), whereas in the colder seasons would occur the transformation of metastable struvite into a more stable newberyite. Caves with seasonal cyclical occupation of bat colonies could provide a new arena for the study of the guano-related mineral assemblages.

Epigenic vs. hypogenic speleogenesis governed by H2S/CO2 hydrothermal input and Quaternary icefield dynamics (NE French Pyrenees)

Hypogenic caves, linked to carbonate rock dissolution due to CO2- and H2S-rich ascending deep waters, represent more than 10% of karstic networks worldwide; a proportion that increases as these systems are better constrained. However, interaction between hypogenic and epigenic processes is still poorly understood, especially since the subsequent invasion of surface water often obliterates the morphological and mineral markers of hypogenic activities. The Ariège Valley (French Pyrenean foothills) hosts significant karstic networks epigenically reworked by several episodes of glacier meltwater penetration during the successive coverage of Quaternary icefields. Among these karstic systems, the Vapeur and Ermite caves were probably initiated by a hypogenic component during the Miocene. In particular, multiple-S, Sr, H, C, and O isotopes of thermo-mineral waters and calcite-sulfate speleothems confirm that hydrothermal fluids reached the caves, and subsequently interacted with Quaternary glacial epigenic phases. Deep fluids conveyed CO2 and H2S, both produced from the thermochemical reduction of Triassic evaporites at depth. H2S oxidation and CO2 hydration in the cave atmosphere, above the water table, created sulfuric and carbonic acids responsible for an intense karstification. Interpretation of isotopic data, together with a geomorphological, mineralogical and textural study of cave minerals, allow us to propose a speleogenetic model in which the respective impact of epigenic and hypogenic processes was driven by base-level changes during successive Quaternary glacial/interglacial epochs: (i) during glacial periods, invasion of glacier meltwater within the karst led to the dilution of the hydrothermal water, and was responsible for an “epigenic mechanical-dominant” speleogenesis through water-related abrasion; (ii) interglacial epochs were marked by base-level drops and the establishment of a vadose domain in caves, favoring the widening of karstic conduits through carbonic and sulfuric acid condensation-corrosion during thermal water degassing. This “hypogenic chemical-dominant” speleogenesis was active until a new advance of glaciers, and this cycle occurred several times.

Hypogenic Versus Epigenic Origin of Deep Underwater Caves Illustrated by the Hranice Abyss (Czech Republic)—The World's Deepest Freshwater Cave

AbstractExtremely deep freshwater filled cave systems are common in karst systems globally. The origin and evolution of such caves are usually attributed to hypogenic (bottom‐up) processes, in which acidic groundwater dissolves limestone from below. However, these deep cave systems can form by epigenic (top‐down) processes, with meteoric waters descending from the surface underground. The Hranice Abyss (Czech Republic), with a reached depth of 473.5 m, is the deepest mapped extent of such a system globally, although its maximum depth is unknown. Multiple geophysical data sets (gravity, electrical resistivity tomography, audiomagnetotellurics, and seismic refraction and reflection) are used to investigate the extent and formation of the Hranice Abyss. The geophysical results suggest the Hranice Abyss extends to depths of ~1 km. Further, we identify structures within the karst, including buried cockpit karst towers with several NW‐SE‐oriented valleys. The new geophysical results from the Hranice Abyss, considered in combination with geological constraints of the region (tectonic evolution and morphology of karst structure), suggest an epigenic formation process, rather than the traditionally invoked hypogenic origin. Formation by epigenic rather than hypogenic processes has implications for local and regional karst history associated with areas hosting deep karst systems.

Genesis of giant sinkholes and caves in the quartz sandstone of Sarisariñama tepui, Venezuela

Quartz sandstone of the Sarisariñama massif in Venezuela hosts the world biggest collapse dolines in quartz-rich lithologies, with volumes up to some millions of cubic meters. Due to extremely complex logistics required to reach the massif, the genesis of these depressions and of the underlying caves has never been studied in detail. The lack of field campaigns and extended data has fostered a decade-long scientific debate on whether their origin was due to epigenic or hypogenic processes. This study integrates petrological, structural and hydrochemical observations, including analyses of silica concentration, pH, conductivity of surface and cave waters (EC), to investigate the speleogenetic processes acting underground.Petrographic and compositional analyses of the host rock (Matauí Formation) show that in the Sarisariñama region quartz sandstones are regularly characterized by clay interlayers with significant content of pyrophyllite and kaolinite and minor amount of iron hydroxides. Compared to surface waters, subsurface infiltration along vertical fractures and fault planes show enrichment in silica, higher pH and lower EC, confirming that chemical weathering is effective underground provoking intergranular silica dissolution along structural discontinuities. The weathering of the clay and iron hydroxide interlayers guides the speleogenesis, weakening specific stratigraphic levels and causing the collapse and fragmentation of the more resistant quartz sandstone strata. The initial void, created by piping of the loose sand released by quartz sandstone weathering, can migrate upwards by means of roof and wall breakdown; this chain of events eventually triggers a collapse at the surface, which generates a circular or squared sinkhole. The weathering acts mainly along the dominant fracture networks, showing a clear guidance by regional tectonics. These speleogenetic controls rule out the hypothesis of a hypogenic origin of the simas, suggesting a primary role of long-term epigenic chemical weathering and mechanical erosion guided by joints, weak clay and iron hydroxide interlayers, followed by subsequent massive collapses.

Relict Pleistocene calcareous tufa of the Chlupáčova sluj Cave, the Bohemian Karst, Czech Republic: A petrographic and geochemical record of hydrologically-driven cave evolution

The tufas of the presently shallow Chlupáčova sluj Cave document an unusual history of deeper to shallower hydrologic processes in cave evolution. The wider geological context of the cave, along with fluid inclusion and stable isotope (C and O) analyses of calcite from tectonic veins cutting through its wallrock, are evidence of the origin of the cave in the deeper subsurface, under the influence of ascending 25–70 °C warm, saline (2.0–22.3 wt% eq. NaCl) waters driven by regional hypogene processes. The formation of calcite veins, which occurred at 700–400 ka, was probably coeval with the early stages of cave development. However, two generations of tufa formed in the later Pleistocene during the mature shallow-subsurface stage of cave development when daylight and cold meteoric waters penetrated the cave through ceiling windows and tectonic fractures.The first-generation tufa, which consists of cauliflower-like aggregates of hollow, outward-radiating carbonate tubules covered with isopachous banded calcite cements, is interpreted as ancient bryophyte tufa that was deposited about 620 ± 140–530 ± 110 ka. The presence of microscopic biomorphic fabrics resembling micro-stromatolites, calcareous algal chambers, calcite crystals with cloudy cores and clear sparitic rims, and specific biomarkers identified in tufa extracts suggest that, in addition to mosses, algae and bacteria may have also been instrumental in promoting the deposition of tufa. Tufa stable isotope (C and O) characteristics and fluid inclusion contents point to deposition of this first-generation tufa from fresh water with a minor admixture of higher hydrocarbons at the surface temperature.Post-dating the first-generation tufa, minute grains of exotic minerals (e.g. stibnite, gothic-arch calcite, gypsum, Mn-minerals, opaline silica) and sparry calcite were precipitated in the tufa moulds and between carbonate tubules as cements. These minerals suggest at least one event in which hydrothermal waters entered the cave from below after deposition of the first tufa from cool meteoric waters. In this hydrothermal phase, the cave may have been a hot spring.The second-generation tufa originated during the Riss – Würm Interglacial at 121 ± 2.1–107 ± 2.6 ka, following a period of intense water erosion that partly erased older spelean deposits from cave walls. This tufa consists of highly porous, friable, crudely laminated carbonate sediments with floral and molluscan remains, characteristic of common cold-water karstic tufa. This and the earlier tufa were, in turn, covered by later fine-grained cave sediments, contributing to the preservation of Pleistocene tufa that records an alternation of deep and shallow waters in the cave over at least the last 500,000 years.

The Hizeh‐Jan Kaolin Deposit of NW Iran: the Tetrad Effect in REE Distribution Patterns

AbstractThe Hizeh‐Jan kaolin deposit (northwest of Varzeghan, East‐Azarbaidjan Province, NW Iran) is a product of the alteration of Eocene andesitic rocks. Based on mineralogical examinations, kaolinite, quartz, smectite, pyrophyllite, muscovite‐illite, alunite, calcite, diaspore, goethite and hematite are the most abundant mineral phases in this deposit. The geochemical indicators, such as Y/Ho and Zr/Hf, indicate the non‐CHARAC (non‐Charge‐radius control) behavior of these pairs, which are likely to be due to the occurrence of the tetrad effect phenomenon in this deposit. Simultaneous concave and convex shapes in the chondrite‐normalized REE distribution patterns are a remarkable feature of the kaolin samples. Bivariate diagrams of the size of the third tetrad effect (T3) versus geochemical parameters such as Y/Ho, Nb/Ta and Zr/Hf ratios display two distinct populations for the kaolin samples. The first population is characterized by high T3 values (>0.13), which are near or on the fault zone. The second population is characterized by low T3 values (<0.13), and are farther from the fault zone. The obtained results from the geochemical data have furnished compelling evidence that fluid‐rock interaction, overprint of hypogene processes by supergene ones, and structural control, are key controlling factors for the occurrence of tetrad effects in REE distribution patterns in the Hizeh‐Jan kaolin deposit.

Rare-earth elements in groundwater of the abandoned Levikha copper mine (Middle Urals, Russia)

The distribution of REE in groundwater of the catchments, which were formed during the long-term operation of copper mines in the Middle Urals (Russia), was studied. The groundwater composition reflects a significant removal of REE from water-bearing rocks, which leads to their enrichment by several orders of magnitude relative to the oceans, surface water and groundwater. Maximum REE values (up to 15 mg/L) were recorded in groundwater discharged to the surface in the collapse zone (pH=3.5). In mine shafts REE values do not exceed 0.3 mg/L. Water of mine wastes occupy an intermediate position: here REE content varies from 0.5 to 6.5 mg/L. The degree of REE fractionation in mine waters is lower than in oceanic, surface and underground waters of the active water exchange zone at much higher contents. The chemical composition of groundwater of the abandoned copper mine is determined by hypogene processes and structure of the mineralized supergene zone, its mineralogical composition, and oxidation-reduction conditions.

Quantitative comparison of structural and alteration genesis relations of Masahim and Bidkhan-volcano calderas: Located in northern strip of Dehej-Sardu'ieh, Kerman, Iran

The origin of hydrothermal alterations in different facies of calderas can be exogenous or endogenous, depending on the age of volcanism and the kind of structures in an area. Naturally, most alterations have proportion with faults and fractures which facilitate fluid penetration. Comparing different locations of areas with high concentration of fractures in studied volcanic areas of Masahim and Bidkhan calderas and investigating the alterations of central facies within current study suggests that there is the strong relation between argillic alteration (as supergenic and exogenous alteration) and lineaments whereas phylic alterations as more endogenous genesis alteration have less general relation with lineaments. In Masahim caldera, with younger volcanism age, the origin of clay minerals is mostly related with meteoric waters and its major mineral is kaolin. According to XRD experiments, minerals such as pyrophyllite and dickite (as endogenous clays) are not very common in Masahim caldera; most alterations in Masahim volcanic area are argillic with exogenous origin. On the other hand in Bidkhan caldera, as older volcano than Masahim caldera, despite the argillic presence, phylic alterations (with endogenous origin) are significantly observed as well. Conformity matrix of alteration map and upper bound of the lineament-index map in Masahim and Bidkhan areas shows conformity coefficients of 37.8 and 29 percent for argillic and 1.1 and 10.7 for phylic alterations, respectively. Positive relation between argillic alteration and lineament-index, and weaker relation between phylic alteration and the factor of lineaments in center of Masahim and Bidkhan calderas, alongside with closer relation between general alterations regime of Masahim area (mostly exogenous) and lineament-index, indicates and confirms stronger effects of faults in supergenic processes compared with hypogenic processes within these areas. Also, due to older age of volcanism activity in Bidkhan caldera (longer time of erosion action) and younger age of Masahim volcanism (shorter time of erosion action), current surface observable facies are deeper facies in Bidkhan caldera with more endogenous phylic alterations, while in Masahim caldera, more surface facies are mostly argillic exogenous alterations.

The South Um Mongul Cu-Mo-Au prospect in the northern Eastern Desert of Egypt: Tonian porphyry-style mineralization with an Ediacaran hydrothermal iron oxide overprint

The South Um Mongul prospect is occupied by Tonian porphyritic dacite (773 ± 6.9 Ma) intruded by Ediacaran post-collisional hornblende gabbro (603 ± 3.5 Ma) and monzogranite (558 ± 4.6 Ma). The dacite porphyry was formed in a continental arc and hosts a weakly mineralized porphyry system. The earliest veinlet stockwork contains mainly chalcopyrite and molybdenite, which is associated with biotite-rich potassic alteration. The sulfide-bearing system evolved to intermediate sulfidation veins and hosts chalcopyrite and tetrahedrite with minor sphalerite and cobaltite, while the alteration evolved to sericitic-argillic assemblages.A younger iron oxide-rich hydrothermal system is associated with the monzogranite overprinting the previous sulfide-bearing one. The iron oxide-rich system evolved from quartz-magnetite veins with potassic selvages to quartz-specularite and barite-specularite veins associated with more pervasive sericite-chlorite alteration. The sulfur isotopic signature of the barite indicates mainly a magmatic-hydrothermal origin with a limited involvement of meteoric water. The sulfur source may have been mafic melts accompanying the monzogranite, while the Ba was most likely leached from the host rocks, especially the varieties that were affected by potassic alteration. The magnetite hosts chalcopyrite inclusions. The monzogranite was probably derived from melting of an amphibolitic lower crust related to the formation of the earlier Tonian porphyry copper-hosted dacite porphyry. The earlier Tonian melting might have caused the low sulfide contents in the hydrous lower crust, which became fertile for Au-rich magmas during later remelting process, which caused the formation of monzogranite. This model is substantiated by the close association between the native gold and the supergene oxidation products of the chalcopyrite inclusions in the magnetite rather than the oxidation assemblages of the sulfides of the earlier Tonian porphyry system in the prospect.Supergene oxidation occurred under near-neutral to mildly alkaline conditions due to the scarcity of pyrite in the prospect. It is manifested by the formation of atacamite and chrysocolla in association with goethite and widespread incipient argillic alteration, which resulted in plagioclase alteration to clay minerals. Only the sericitic alteration, which is related to the early porphyry copper systems, contains jarosite, alunite and svanbergite, which indicate more acidic conditions during the formation of such argillic alteration. This reflects pyrite oxidation which is related to either supergene processes or hypogene processes accompanying the younger iron oxide-rich hydrothermal system.

Micro- to nano-scale characterization of martite from a banded iron formation in India and a lateritic soil in Brazil

The pseudomorphic transformation of magnetite into hematite (martitization) is widespread in geological environments, but the process and mechanism of this transformation is still not fully understood. Micro- and nano-scale techniques—scanning electron microscopy, focused ion bean transmission electron microscopy, and Raman spectroscopy—were used in combination with X-ray diffraction, Curie balance and magnetic hysteresis analyses, as well as Mössbauer spectroscopy on martite samples from a banded iron formation (2.9 Ga, Dharwar Craton, India), and from lateritic soils, which have developed on siliciclastic and volcanic rocks previously affected by metamorphic fluids (Minas Gerais, Brazil). Octahedral crystals from both samples are composed of hematite with minor patches of magnetite, but show different structures. The Indian crystals show trellis of subhedral magnetite hosting maghemite in sharp contact with interstitial hematite crystals, which suggests exsolution along parting planes. Grain boundary migrations within the hematite point to dynamic crystallization during deformation. Dislocations and fluid inclusions in hematite reflect its precipitation related to a hydrothermal event. In the Brazilian martite, dislocations are observed and maghemite occurs as Insel structures and nano-twin sets. The latter, typical for the hematite, are a transformation product from maghemite into hematite. For both samples, a deformation-induced hydrothermally driven transformation from magnetite via maghemite to hematite is proposed. The transformation from magnetite into maghemite comprises intermediate non-stoichiometric magnetite steps related to a redox process. This study shows that martite found in supergene environment may result from earlier hypogene processes.

Supergene and Hypogene Halloysite in a Porphyry-Epithermal Environment at Cerro la Mina, Chiapas, Mexico

Abstract Halloysite, a phyllosilicate clay mineral chemically similar to but structurally different from kaolinite, occurs in a variety of mineral deposit types. It is, however, difficult to identify and dehydrates quite readily. When identified in a porphyry or epithermal environment, halloysite is often interpreted to be a low-temperature polymorph of kaolinite and an indication of supergene processes. The occurrence of halloysite in the Cerro la Mina Au (Cu-Mo) prospect, Chiapas, Mexico, was investigated to determine if halloysite in porphyry-epithermal deposits might also be the product of hypogene processes. The prospect consists of Quaternary volcaniclastic breccias intruded by monzodiorites and trachyandesites crosscut by a volcanic-hydrothermal breccia pipe. Gold-copper-molybdenum mineralization at Cerro la Mina is structurally and lithologically controlled by matrix-rich breccia pipes hosting all of the significant alteration and mineralization drilled to date. Average grades within the prospect are 0.4 ppm Au, 0.16% Cu, and 131 ppm Mo. A total of 100 samples were obtained from 22 diamond drill holes over a range of stratigraphic levels. X-ray diffraction (XRD) and SWIR techniques were employed to identify the different clay minerals found within these samples, including halloysite, kaolinite, dickite, and illite. Identification of halloysite and kaolinite were facilitated by the use of formamide intercalation to produce distinctive peaks for the two minerals in X-ray diffractograms. Halloysite and kaolinite were found to occur from the current erosional surface to depths of over 800 m. Halloysite occurs as both the hydrated 10Å and dehydrated 7Å forms within the deposit. The morphology of the halloysite present is that of well-developed tubes and spheroids. Results of the study show that halloysite associated with gypsum and jarosite is of supergene origin, whereas halloysite occurring with quartz, alunite, dickite, kaolinite, and pyrite is of hypogene origin.

Hypogene Processes of the Gypsum Beds in Sangaw Sinkholes, Kurdistan Region, NE-Iraq

The Sangaw region is located at the western part of Zagros orogenic belt at the boundary between Low and High Folded Zones, Sulaimani governorate in Kurdistan region. The area characterized by low amplitude folds that are trending northwest southeast and arranged in en echelon pattern. The exposed formations are Eocene Pila Spi (limestone), middle Miocene Fat`ha(lagoon) and Upper Fars (clastics) formations. Many large and small sinkholes are found around Ashdagh anticline; some of them about 50 m in diameter and about 30 m deep. Some are developed into complicated cave systems with collaps blocks and breccias in addition to narrow passages and fissures. The largest of them is located directly to the west of Darzilla village at the southeastern plunge of Ashdagh anticline. The sinkholes occur in Fat`ha and in the Pila Spi Formations. The walls of the sinkholes are covered by secondary gypsum, sulfur, bitumen and secondary calcite. Inside the cave collapse, breccias and blocks with lensoidal stratified clayey sediments as weathering product could be seen. The water is acidic (pH=4) inside the caves and discharges as large spring (200L/S) with white milky color; it is called in the local Kurdish language, “Awa Spi “which means white stream. The weathering of the carbonate rocks is intense inside the cave and appears as honeycombs and rills mark which have very rough surface with dull color. The sinkholes were produced from the dissolution of thick gypsum and limestone beds. The origin of these caves has been proposed to be hypogenic speleogenesis due to the presence of gypsum and bitumen. These materials with the aid of bacteria enrich the water with H2S which aciditfies the water and precipitates the sulfur and secondary gypsum on the cave wall. The formation of H2SO4 by oxidaton of H2S is the main reason that aid the sinkhole hypogene generation in Sangaw area. A realistic model is drawn to interpret and connect the following:1- The stratigraphy and structure of the area encourage the generation of underground stagnant pond suitable for reacting with the emanating H2S necessary for the hypogene generation of the sinkholes and precipitation of secondary native sulfur and gypsum.2- dissolution of gypsum and its reduction by bacteria. 3- upward migration of bitumen from nearby oil traps(hydrocarbon accumulation).

Sources of matter for the Il’meno-Vishnevogorsky alkaline complex: Evidence from Lu—Hf isotopic data for zircons

The composition of hafnium isotopes in zircons iscurrently an important instrument for reconstructionof the source of magmatic rocks. Zircon is stable inmany hypogene and hypergene processes. Metamictization and later processes of alteration practically donot affect the composition of Hf isotopes in zircon[12]. The relative stability of Hf isotopes in zirconsmakes them a powerful instrument for the study of thesource age, as well as the origin and isotopic evolutionof various rocks [6, 11]. The combination of dating ofan individual zircon grain by the U–Pb method withthe study of Hf isotopes of the same grains (with application of local isotopic methods, such as SHRIMP,SIMS, and laser ablation) is the most effective. Such acombination provides important information on therock source even in the case when other isotopic systems are significantly disturbed.We obtained the first Lu–Hf isotopic data (in combination with the U–Pb isotopic data) by the methodof laser ablation for zircons from carbonatite and alkaline rocks of the Il’menoVishnevogorsky Complex inorder to study the age of rocks and the source of theirmaterial. Since the Sm–Nd and Rb–Sr isotopic systems were disturbed to various degrees during the Hercynian collision [5, 9], we considered application ofthe Lu–Hf isotopic system as the most stable andinformative to be especially important.The Il’menoVishnevogorsky Complex occurs atthe boundary between the Middle and Southern Uralsand is located within the Sysert–Ilmeny Precambrianblock, which has a twolevel structure and a long history of the formation. The core of the block is composed of granulitic gneiss and migmatite of the Selyankino Series (the U–Pb age of its zircons is 1820 ±70 Ma), as well as plagiogneiss and amphibolite of theVishnevye Gory Series (PR

Statistical analysis of geochemical data: a tool for discriminating between kaolin deposits of hypogene and supergene origin, Patagonia, Argentina

AbstractThe numerous kaolin deposits located in Patagonia, Argentina, have been formed by hypogene or supergene processes. The primary origin has been established from O18 and D isotopic composition of the main minerals, kaolinite and/or dickite, and from the behaviour of certain elements during the alteration. The aim of this paper was to find if there is a tool, other than oxygen-deuterium data, to establish the origin of the Patagonian kaolin deposits. To handle the large number of variables per sample, a statistical multivariate study was used. The Principal Component method defines, on one hand the variables that better characterize each deposit and, on the other hand, the correlation between them. Fifty seven elements were considered and those that were not explained using these two components (which represent 75% of the total variance of the model) were discarded. As a result, the contents of Fe2O3, P2O5, LOI, Sr, Y, Zr, V, Pb, Hf, Rb, S and REE were used and the results show that the two components separate the deposits into two fields that are consistent with the process of formation. The first component indicates that Fe2O3, Y, Rb, U and HREE are more abundant in the supergene deposits, whereas, Sr, Pb, S and V are more abundant in the hypogene deposits. The second component shows that S, P2O5 and the LREE are enriched in the hydrothermal deposits, whereas Zr is more abundant in those formed under weathering conditions.

Accessory minerals of fluorite and their implication regarding the environment of formation (Nabburg–Wölsendorf fluorite district, SE Germany), with special reference to fetid fluorite (“Stinkspat”)

The Nabburg–Wölsendorf vein-type fluorites in SE Germany which are characterized by a pronounced timebound variation in mineral color (blue → black → green → white/colorless → yellow → brown) were investigated for their accessory minerals included in or associated with these different fluorite types. Nabburg–Wölsendorf is not a unidirectional fluorite mineralization but a polyphase mineralizing process with several repetitions of the various color types during the vein mineralization event. Accessory minerals of the fluorite mineralization include silicates, sulfates, oxide/hydroxides, phosphates, sulfides and carbonates. These minerals are intimately intergrown with fluorite in the vein-type mineralization and are efficient tools to broaden knowledge on the depositional environment of fluorite that is otherwise poor in marker minerals for redox conditions, temperature, alkalinity/acidity and fluid viscosity. Pyrite, galena and cinnabar, are indicative of hypogene processes, while uranyl phosphates and APS minerals furnish evidence for supergene mineralizing processes. Some minor constituents may be used as marker minerals of redox conditions (hematite, galena, and goethite) or held to be characteristic for the changing pH regime (kaolinite and smectite). Oxidizing conditions prevailed during fluorite mineralization, excluding some phases when fetid and white fluorite precipitation ran through a maximum. Yellow-brown honey spar marks the oxidizing physical–chemical conditions by its brown mineral color at the end of fluorite mineralization. Oxidizing conditions prevailed also during supergene mineralization. The pH of the mineralizing fluids of the hypogene stages was greater than pH 7. During the supergene stage, Eh fluctuated, but was mainly > 0; the pH of fluids ranged between 7 and 4. The black color of fetid fluorite and its pungent odor resulted from the U present primarily in its tetravalent state. Incomplete haloes recognized in some fetid fluorites reflect “frozen” uranium disequilibria and an early phase of supergene alteration. In this respect, the fetid fluorite (“Stinkspat”) plays an important part and held to be a marker for the radioactive “hot spot” as well as “ghost” uranium mineralization. Fetid fluorite is defined as to its mineral color, morphology and characteristic spectral features so as to allow for a precise distinction from other dark blue or green fluorite varieties by its outward appearance and easy-to-handle methods. The accessory minerals under study are indicative of the depocentre of the fluids which lies close to an unconformity but does not, however, deliver information on the source of the mineralizing fluids. The nearness to the potential source rock of the fluids can only concluded from the presence of cerite-(Ce) which formed prior to fluorite. This REE silicate is cast as a marker of the root zone of the fluorite veins which fade out into late Variscan granites. Cerium is assumed to have been derived from monazite an accessory mineral largely found outside the fluorite veins, proper, in the late Variscan granites. In the waning stages of fluorite mineralization different types of REE-bearing phosphates, belonging to the rhabdophane solid solution series, and some APS minerals (aluminum–phosphate–sulfate solid solution series) evolved.

Metamorphic-hosted pyrophyllite and dickite occurrences from the hydrous Al-silicate deposits of the malatya-Pütürge region, central eastern Anatolia, Turkey

AbstractHydrous Al-silicate deposits are found to the south of Pütürge in Malatya city, Turkey. The surrounding rocks consist of mylonitic granitic gneiss overlain by muscovite gneiss with kyanite-bearing metabasic schist lenses on top which are cut by silica veins containing prismatic tourmaline and speculante. Pyrophyllite is found within kyanite gneisses overlying the granitic gneisses. Fibrous, platy pyrophyllite is developed along the edges and cleavage planes of kyanite, whereas platy bunches of dickite occur as replacements of the relict kyanites as well as crack- and pore-fillings. Rocks forming the hydrous Al-silicate deposit contain 2M1 pyrophyllite, alunite, topaz, paragonite, dravite, dumortierite, chlorite and epidote as early hypogene minerals, and 2M1 dickite, diaspore, gibbsite, speculante, goethite and crandallite/goyazite as late hypogene minerals. On the basis of fluid inclusion and stable isotope data, it is estimated alterations to pyrophyllite and kaolinite occurred at temperatures are of 150 and 100°C, respectively, the minerals being formed by meteoric waters interacting with metamorphic rocks. Trace and REE variations are highly distinctive in terms of enrichment of most trace elements in pyrophyllite, whereas REEs are clearly abundant in dickite, indicating different conditions during formation such as early and late hypogene processes. The pyrophyllitic alteration took place in the late Cretaceous (69–71 Ma), whereas kaolinization occurred later.