Influence Of Hydrothermal Fluids Research Articles

Fluid–rock interaction controlled by integrated hydrothermal fluid and fault: Implications for reservoir development

Hydrothermal activity is prevalent in petroliferous basins, particularly in fractured reservoirs. Hydrothermal fluids enter the reservoirs and cause significant fluid–rock interaction, which ultimately controls reservoir development. The Mahu Sag in western China is a hydrocarbon-rich region where hydrothermal fluids and faults control the reservoirs, making it challenging to understand the development mechanism of the shale reservoirs. This study focused on the Fengcheng Formation in the Mahu Sag. Based on a range of previous lithological test results, numerical models of hydrothermal fluid charging were established to explore differences in fluid–rock interactions under varying temperature, fluid, and flow rates. Results revealed that within a specific range, increasing temperature and Mg2+ concentration promoted hydrothermal processes. The hydrothermal flow rate influenced ion accumulation on the fluid-rock contact surface, thus controlling mineral dissolution rates. In a certain range, when the flow rate is increased by 3 times, the growth rate of dolomite content is increased by more than 15 times. Hydrothermal fluid flowing near the fault underwent chemical action more readily than in other areas. The influence of hydrothermal fluid and fault on reservoir development was both constructive and destructive. The decrease and increase of porosity are 30 % and 25 %, respectively. This study could provide a theoretical basis for identifying factors influencing shale reservoir development.

Mixed sources and complicated petrogenetic processes of the Himalayan granites recorded by apatite in-situ geochemistry of the Eocene Yardoi-Lhunze complex, southeast Tibet

The Cenozoic Himalayan granites are widely accepted as the anatectic products of crustal rocks. However, previous geochemical studies on their petrogenesis are mainly based on whole-rock analyses. Here we conducted a detailed petrographic, trace elemental and Sr isotopic investigations of apatite from the Middle Eocene (44–40 Ma) two-mica granites and subvolcanic porphyritic leucogranites of the Yardoi-Lhunze complex from the Tethyan Himalayan Sequence in the southeast Tibet, with the aim to constrain their magma sources and petrogenetic processes. The results show that apatites from the Quedang and Dala two-mica granites are characterized by euhedral to subhedral crystal shape, and have a wide range of initial 87Sr/86Sr ratios (0.7016–1.0088). They show significant negative Eu anomaly and varied concentrations of Sr and Y, indicating they are typical magmatic apatites. Apatites from the Qiaga porphyritic leucogranites can be divided into two groups based on Eu anomaly. Group-I apatites with positive Eu anomaly mainly display euhedral to subhedral crystal shape but with alteration rim, suggesting from the influence of hydrothermal fluids. Group-II apatites with negative Eu anomaly also have euhedral to subhedral crystal shape but they exhibit patchy or oscillatory zones, consistent with a magmatic origin. However, both group-I and II apatites have comparable initial 87Sr/86Sr ratios, 0.7198–0.9966 and 0.7174–0.9999, respectively. Previous studies based on whole-rock petrology and geochemistry have suggested that the Quedang and Dala two-mica granites and the Qiaga porphyritic leucogranites represent cumulates and fractionated melt-rich magmas, respectively. This is evidenced by systematic variations between Sr, Y, (La/Sm)N and Eu/Eu* in magmatic apatites from Quedang and Dala, consistent with the fractionation crystallization of plagioclase and monazite.Apatite has a wide range of initial 87Sr/86Sr ratios (0.7016–1.0088), far exceeding the range of whole-rock records (0.7011–0.7204). Notably, most of the analyzed apatites show lower range of initial 87Sr/86Sr ratios consistent with locally exposed amphibolites (0.7109–0.7332). The remaining small portion of apatites have initial 87Sr/86Sr ratios falling within the data range of the locally exposed metapelites (0.8517–0.9527). Therefore, the investigated granites have mixed magma sources dominated by amphibolites with subordinate metapelites. This can be inferred by apatite Sr isotopes alone, but not by whole-rock Sr isotopes alone. Our investigations highlight that in-situ geochemistry of apatite can provide a powerful means to unravel the mixed magma sources and complicated magmatic processes for granites.

Особенности сульфидной минерализации гидротермальной системы мыса Фиолент (юго-западный Крым)

As a result of generalization of geophysical studies, petro-paleomagnetic and structural-geomorphological analyses, as well as thermodynamic modeling, some features of ore formation in the hydrothermal system of Cape Fiolent (southwestern Crimea) under island arc conditions were revealed. It has been established that the main transformations of rocks of the Middle Jurassic igneous complex of Cape Fiolent occurred under the influence of hydrothermal fluids during the introduction of felsic intrusions during 168–140 Ma. The zones contain sulfide mineralization, the main minerals of which are pyrite, sphalerite, pyrrhotite, galena, chalcopyrite and arsenic pyrite. In the central parts of the hydrothermal alteration zone, massive sulfides are strongly weathered; these zones contain many secondary sulfates. In the marginal parts of hypergenic limonite, yellow-brown goethite prevails in the oxidation zone, yellow jarosite in the center, which is probably due to the large amount of pyrite in the center of the system, which gave more sulfuric acid during oxidation. The presence of native sulfur in the section testifies to the mixing of the acidified hydrothermal solution with seawater. Complex petro-paleomagnetic and magnetometric studies have shown that contact changes and transformation of the contrasting basalt-rhyolite formation occurred along the NNW-trending faults.

Mineralogical Characteristics of No. 3 Coal in the Jurassic Coalfield of Northern Shaanxi

This study investigates the mineralogical characteristics of No. 3 coal seam in the Mahuangliang Coal Mine, located within the Jurassic coalfield of northern Shaanxi Province, China. Utilizing techniques such as low-temperature ashing (LTA), X-ray diffraction (XRD), scanning electron microscopy with energy- permissive spectroscopy (SEM-EDS), and Siroquant software, we examined the distribution and composition of the minerals present in the coal, partings, and roof and floor strata. The results reveal a rich assemblage of minerals, including quartz, kaolinite, and carbonates. The primary geological factors controlling the distribution of minerals and trace elements are the input of detrital materials from the depositional source area and the influence of hydrothermal fluids.

Influence of multistage hydrothermal fluids on dolomite reservoirs: A case study from the Lower Ordovician Yeli-Liangjiashan Formation in the Chengdao-Zhuanghai area, Jiyang subbasin, Bohai Bay Basin, China

It remains controversial whether the influence of hydrothermal fluids on dolomite reservoirs is dominated by dissolution or precipitation. In this study, the influence of multistage hydrothermal fluids on the dolomite reservoirs of the Lower Ordovician Yeli-Liangjiashan Formation in the Chengdao-Zhuanghai area was investigated based on petrographic observations and geochemical analyses, with an emphasis on the temporal relationships among dolomitization, pore formation, and multistage hydrothermal fluid activities determined by in situ U-Pb dating. The δ18O, δ13C, and 87Sr/86Sr data indicate that the genesis of pre-hydrothermal dolomites and the earliest-formed dolomite cement (Cd1) closest to the edges of pores were related to coeval seawater. The U-Pb age of pre-hydrothermal dolomites is 427 ± 11 Ma, representing the time when early dolomitization occurred. The original pore formation predates the precipitation of Cd1 with a U-Pb age of 391 ± 12 Ma. Stage I and stage II hydrothermal fluids were derived from the Precambrian basement and the mantle, respectively, as evidenced by differences in δ18Ofluid values and rare earth element characteristics. Stage I and II hydrothermal fluids occurred at 161 ± 12 Ma and 81 ± 16 Ma, respectively. Therefore, early dolomitization and pore formation are not correlated with the two stages of hydrothermal fluids. Stage II hydrothermal fluids contained a relatively higher amount of H2S than stage I hydrothermal fluids. H2S-related dissolution caused by stage II hydrothermal fluids mainly occurred in the dolomite reservoirs adjacent to major faults, and H2S was gradually consumed as the distance from the major faults increased. The two stages of hydrothermal minerals successively filled most of the spaces in pores and fractures. The influence of multistage hydrothermal fluids on dolomite reservoirs was found to be dominated by precipitation.

Barremian to Aptian Os isotopic record of a pelagic deep-sea chert (Goshikinohama-bedded chert) in a Japanese accretionary complex

The early Aptian oceanic anoxic event (OAE) 1a was one of the largest OAEs in the Cretaceous, and the organic-rich sediments have been reported from various sedimentation depths worldwide. Because the sedimentation age of this organic-rich interval corresponds to the radiometric ages of the Ontong Java Nui (OJN) basalts, their causal linkage has been debated. The Goshikinohama-bedded chert is a Cretaceous sedimentary sequence deposited at depths deeper than the carbonate compensation depth (∼4000 m) in the pelagic Pacific. Although it covers the Barremian to Aptian, its stratigraphic relation to the OAE1a has not been fully constrained. Here, we present the 187Os/188Os record of the Goshikinohama-bedded chert to further constrain the OAE1a interval. As a result, 187Os/188Os showed several shifts to unradiogenic values, which may be correlated to the early Aptian OAEs. However, the 187Os/188Os values of the Goshikinohama-bedded chert are less radiogenic than the previously reported Barremian to Aptian 187Os/188Os values. The less radiogenic trend may represent the high contribution of extraterrestrial Os in the sediments or the influence of hydrothermal fluid from the underlying Valanginian basaltic rocks. Because of such unknown factors, there remain uncertainties in the stratigraphic correlations between the Goshikinohama-bedded chert with other sections.

Diagenetic and hydrothermal fluid influence on tight sandstone reservoir quality: Gravity-flow deposits from the Huangliu Formation, Ledong area, Yinggehai Basin, South China Sea

The tight sandstone of gravity-flow deposits in Miocene Mbr 2 of the Huangliu Fm, Ledong area is one of the focuses future exploration in the Yinggehai Basin. Reservoirs have complex sedimentary and diagenesis processes, experienced multi-stage fluid influence. However, the influence of different diagenesis on reservoir quality, and distribution patterns of different diagenetic facies in Mbr 2 of the Huangliu Fm are still short in research. In this paper, a variety of methods, such as thin sections analysis, electron microscopy (SEM), electron probe micro-analyzer (EPMA), cathode luminescence (CL), x-ray diffraction measurement (XRD), in situ carbon and oxygen isotopes composition of cements (SIMS), fluid inclusion homogenization temperature, and high-pressure mercury injection (HPMI), are used to analyze reservoir quality, diagenetic evolution stages, diagenesis, fluid filling processes, etc. Studies have shown that there are obvious differences in diagenetic evolution process, including carbonate cementation, organic acid and hydrothermal dissolution, etc. Which ultimately leads to large differences in physical properties. Although sandstone texture has an impact on reservoir quality, strong compaction and early carbonate cementation were the main reasons for reservoir densification. Early calcite was precipitated in alkaline seawater, and later ferrocalcite was formed by the recrystallization of calcite and polyframboidal pyrites and euhedral pyrites formed under organic acid charged. After hydrothermal fluid charged, dolomite, iron dolomite, cement pyrites and dispersed granular pyrites precipitated. Besides, illite filled the throat. The dissolution of organic acids and late CO2-rich hydrothermal fluids improved the quality of reservoirs. According to the difference of diagenetic process and the quality of the reservoirs, Mbr 2 of the Huangliu Fm is divided into 4 types of diagenetic facies. High-quality reservoirs are mostly developed in H2-Ⅰ, H2-Ⅱ, and H2-Ⅴ sand formation near faults. Early carbonate cements were less developed, which could support primary intergranular pores. Feldspar, rock fragments, and early carbonate cements were strongly dissolved. It includes two diagenetic facies, low cementation - strong dissolution reservoirs and slightly cementation - weaken dissolution reservoirs. On the contrary, tight reservoirs mostly develop in H2-Ⅲ, H2-IV, and H2–V sand formation far away from faults, including late compacted tight reservoirs and early carbonate cementation tight reservoirs. The research results are helpful to analyze the diagenetic evolution of tight sandstone reservoirs, and conducive to the study of similar gravity-flow reservoir quality with the influence of hydrothermal fluids.

Diagenesis and reservoir quality of Cambrian carbonates in the Tarim Basin, northwestern China

Quantitative petrographic analysis revealed the diagenetic controls on the reservoir quality of deep (>5,000 m) carbonate reservoirs in the Tarim Basin. Dolostones were formed by the extensive dolomitization of originally low-energy (siliciclastic mudrocks, calcimudstones, and wackestones) and moderate-to-high-energy (peloidal, intraclastic, and/or bioclastic packstones to grainstones, rarely microbialites) deposits. Replacement of primary and diagenetic constituents by dolomite occurred in multiple phases. Eogenetic dolomitization precipitated microcrystalline to finely crystalline dolomite, followed by dolomite overgrowth during shallow mesogenesis. Saddle, coarse, and radial undulose dolomite precipitated during deep mesogenesis under increasing temperature and pressure and were locally replaced by microcrystalline quartz. Primary porosity is absent, but these carbonates can display vuggy, intercrystalline, and fracture porosity due to dolomite dissolution and local fracturing. Secondary porosity can be partially or totally filled by saddle dolomite and/or quartz. Petrological and fluid-inclusion data indicated that three ascending fluids considerably influenced the diagenetic evolution and quality of the Cambrian reservoirs, namely, organic acid-rich fluids from the maturation of source rocks, SO2-rich fluids derived from the dissolution of calcium sulfate and hydrothermal fluids. The structurally controlled percolation of SO2-rich fluids was the main process responsible for creating porosity in deep carbonate reservoirs in the Tarim Basin. The influence of hydrothermal fluids is not ubiquitous, and it had a dual impact on reservoir quality, i.e., the hydrothermal fluids enhanced the porosity through dolomite dissolution and decreased the porosity through dolomite and quartz precipitation.

Lanthanum Diffusion in Fluorapatite at 400 °C, 50 MPa and 4–16 wt %

Apatite is an important carrier of rare earth elements (REEs) and phosphorite is a potential REEs resource. However, the influence of hydrothermal fluids on the migration and enrichment of REE in apatite remains controversial. The experimental study of the interaction between REE-bearing fluid and apatite is one of the essential ways to understand the chemical behavior of rare earth elements in apatite. In this study, we conducted the fluid–mineral reaction experimental study (at 400 °C, 50 MPa and 4–16 wt %) between high lanthanum (La) content hydrothermal solution and low REE content to reveal the influence of different salinities on the diffusion of rare earth elements in fluorapatite. Based on in situ geochemical analyses of experimental products, we show that the diffusion coefficients of La in fluorapatite are between 3.24 × 10−15 and 5.88 × 10−15 m2/s. The salinity of the fluid has a great influence on the diffusion coefficient, with the increase of salinity, the diffusion coefficient increase.

The influence of magmatic-hydrothermal activities on porosity and permeability of sandstone reservoirs in the Linxing area, Ordos Basin, Northern China

The eastern margin of the Ordos Basin in the Linxing area has great potential for exploration of natural gas. However, the intrusion of the Zijinshan igneous pluton and associated hydrothermal activities have affected the sandstone reservoirs. Through the data analyses of rock thin sections, cathodoluminescence, X-ray diffraction, vitrinite reflectance, fluid inclusions, and reservoir physical property, this paper aims to clarify the influences of magmatic-hydrothermal activity and to explore the response characteristics of reservoir porosity and permeability. From the outer zone to the inner zone, the closer to the pluton, the closer the contact between the reservoir clastic particles, which confirms the compression caused by magma intrusion. The differences in feldspar dissolution and alteration, siliceous cementation, clay mineral content, vitrinite reflectivity, homogenization temperature and salinity of fluid inclusions, confirmed that magmatic-hydrothermal activity affected fluid properties and evolution of strata temperature. Combined with the vertical distribution characteristics of feldspar dissolution-alteration and the abnormal conversion of clay minerals, it is considered that the influence of hydrothermal fluid was limited to the reservoir under the thick mudstone of the Xiashihezi Formation. Magma intrusion causes the development of reservoir fractures, thus the permeability of the reservoir decreases from the inner zone to the outer zone, and the porosity presents the distribution pattern of “high-low-slightly high”. The reservoir porosity and permeability genetic model was established to provide references about favorable areas for oil and gas exploration and development in the Linxing area and areas with similar geological history.

PETROLOGICAL CHARACTERISTICS OF CLASTIC SEDIMENTARY ROCKS FROM THE ST. BARBARA ORE MINE IN RUDE NEAR SAMOBOR

In the scope of this research, the petrographic and geochemical analyses of clastic sedimentary rocks from the St. Barbara, copper and iron ore mine in Rude near Samobor, have been made, aiming to classify and determine the provenance and environment of formation of clastic sedimentary rocks, as well as the influence of hydrothermal fluids on their properties. Eight samples were collected in total from different locations in the mine. Six of those samples have been studied in detail. The results showed structural and geochemical variability and uneven hydrothermal alteration intensity in the samples. Based on petrographic analyses, three rocks are classified as sublithoarenite, quartz arenite and quartz greywacke. Three of the samples are classified as ore breccia, ore sandstone, and ore silt-sandstone due to the pronounced hydrothermal alterations and ore mineralisation. Comprehensively, petrographic and geochemical analyses indicate that the source rocks of the investigated clastic sedimentary rocks were felsic (La/Sc = 0.9-6.2; Th/Sc = 1.3-2.4), most probably sedimentary, possibly resedimented rocks. The extent of source rock weathering was very high (Chemical Index of Alteration CIA = 52.1 - 81.3 %) and the geotectonic position of the sedimentary basin was very likely to be at the passive continental margin.

The Influence of Hydrothermal Fluids on the REY-Rich Deep-Sea Sediments in the Yupanqui Basin, Eastern South Pacific Ocean: Constraints from Bulk Sediment Geochemistry and Mineralogical Characteristics

Rare earth elements (REEs) and yttrium (Y), together known as REY, are extremely enriched in deep-sea pelagic sediments, attracting much attention as a promising new REY resource. To understand the influence of hydrothermal processes on the enrichment of REY in deep-sea sediments from the eastern South Pacific Ocean, we conducted detailed lithological, bulk sediment geochemical, and in situ mineral geochemical analyses on gravity core sample S021GC17 from the Yupanqui Basin of eastern South Pacific. The REY-rich muds of S021GC17 are dark-brown to black zeolitic clays with REY contents (ΣREY) ranging from 1057 to 1882 ppm (average 1329 ppm). The REY-rich muds display heavy rare earth elements (HREE) enriched patterns, with obvious depletions in Ce, and positive anomalies of Eu in Post-Archean Australian Shale (PAAS)-normalized REE diagrams. In contrast, the muds of S021GC17 show light rare earth elements (LREE) enriched patterns and positive anomalies of Ce and Eu in the seawater-normalized REE diagrams. Total REY abundances in the core show positive correlations with CaO, P2O5, Fe2O3, and MnO concentrations. In situ analyses of trace element contents by laser ablation-inductively coupled plasma–mass spectrometry (LA-ICP-MS) demonstrate that bioapatite fossils contain high REY concentrations (998 to 22,497 ppm, average 9123 ppm), indicating that they are the primary carriers of REY. The in situ Nd isotope values of bioapatites are higher than the average values of seawater in Pacific Ocean. Fe–Mn micronodules are divided into hydrogenetic and diagenetic types, which have average REY concentrations of 1586 and 567 ppm, respectively. The high contents of Fe-Mn-Ba-Co-Mo, the positive correlations between ΣREY and Fe-Mn, the ratios of Fe/Ti and Al/(Al + Fe + Mn), and the LREE-enriched patterns in the REY-rich muds, combined with high Nd isotope values shown by bioapatite fossils, strongly indicate that the hydrothermal fluids have played an important role in the formation of the REY-rich sediments in the eastern South Pacific Ocean.

High environmental stress and productivity increase functional diversity along a deep-sea hydrothermal vent gradient.

Productivity and environmental stress are major drivers of multiple biodiversity facets and faunal community structure. Little is known on their interacting effects on early community assembly processes in the deep sea (>200m), the largest environment on Earth. However, at hydrothermal vents productivity correlates, at least partially, with environmental stress. Here, we studied the colonization of rock substrata deployed along a deep-sea hydrothermal vent gradient at four sites with and without direct influence of vent fluids at 1,700-m depth in the Lucky Strike vent field (Mid-Atlantic Ridge [MAR]). We examined in detail the composition of faunal communities (>20μm) established after 2 yr and evaluated species and functional patterns. We expected the stressful hydrothermal activity to (1) limit functional diversity and (2) filter for traits clustering functionally similar species. However, our observations did not support our hypotheses. On the contrary, our results show that hydrothermal activity enhanced functional diversity. Moreover, despite high species diversity, environmental conditions at surrounding sites appear to filter for specific traits, thereby reducing functional richness. In fact, diversity in ecological functions may relax the effect of competition, allowing several species to coexist in high densities in the reduced space of the highly productive vent habitats under direct fluid emissions. We suggest that the high productivity at fluid-influenced sites supports higher functional diversity and traits that are more energetically expensive. The presence of exclusive species and functional entities led to a high turnover between surrounding sites. As a result, some of these sites contributed more than expected to the total species and functional β diversities. The observed faunal overlap and energy links (exported productivity) suggest that rather than operating as separate entities, habitats with and without influence of hydrothermal fluids may be considered as interconnected entities. Low functional richness and environmental filtering suggest that surrounding areas, with their very heterogeneous species and functional assemblages, may be especially vulnerable to environmental changes related to natural and anthropogenic impacts, including deep-sea mining.

Hydrogeochemistry, circulation path and arsenic distribution in Tahlab aquifer, East of Taftan Volcano, SE Iran

The geochemical composition of waters from wells fed by Taftan aquifer located east of Taftan volcano, mainly focusing on the distribution of arsenic, was investigated in order to provide insights into the geochemical processes controlling the chemistry of the shallow aquifer and the possible influence of hydrothermal fluids from the volcano on groundwater quality. For this purpose, 16 water samples were collected and analyzed for the determination of selected trace elements, major ions and stable isotopes (18O and 2H). The chemical and isotopic features of the investigated groundwater samples suggest that they are significantly affected by fluids originated from Taftan volcano driven toward the surface by local and regional fault systems. The volcanic source is also responsible for the relatively high concentrations of As, U and V, which pose severe concerns for the quality of the water resource in the area. Distribution of As seems to be independent of pH values and the concentrations of Fe, the latter commonly forming As-adsorbing minerals, likely due to the precipitation of siderite and the occurrence of As colloids. Lack of correlation between As and SO4 seems to exclude a significant As contribution from sulfide minerals.

Influence of non-marine fluid inputs on potash deposits in northeastern Thailand: evidence from δ37Cl value and Br/Cl ratio of halite

Late Cretaceous evaporite in the Khorat Plateau (KP) is one of the largest potash deposits in the world. Previous researches reported that the origin of potash deposits in the KP is controversial; however, recent studies emphasized non-marine fluids (hydrothermal fluid or meteoric water) influenced geochemical behaviors of potash deposits. Eleven halite samples from halite and potash layers in a drilling core (NS007) in southwestern KP were collected and analyzed for δ37Cl values, Br− and Cl− concentrations in this study. The results show that (1) low δ37Cl values (− 1.31‰ ~ + 0.14‰) of halite from halite layer, combining with reported isotopic (δD and δ18O) values of fluid inclusions in halite in corresponding layer, suggest possible influence of hydrothermal fluid; (2) positive correlation between δ37Cl values and Br × 103/Cl ratios, high δ37Cl values (− 0.48‰ ~ + 0.41‰) and previous high 87Sr/86Sr values of halite from potash layer indicate meteoric water inputs into this layer. These comparisons demonstrate that hydrothermal or meteoric waters (non-marine fluids) influenced potash deposits in northeastern Thailand.

Ta-Nb mineralization in rare-metal pegmatite from north-western frame of Lypniazhka granite-migmatite structure

The three type of rare-metal pegmatites are know in Stankuvatske ore field (Ingul megablock, the Ukraianian Shield), such as: Li-bearing, Bi-As-U and Ta-Nb pegmatites. For the first time Ta-Nb mineralisation from Ta-Nb bearing albite-K-Feldspar rare metal pegmatite have been described. Investigated pegmatite is located on the Norh-West frame of the Lypnazky granitemigmatite massive among hosted amphibolites. Rare-metal pegmatite doesn’t have obvious zonality and consist of alkaline feldspar, biotite, muscovite, dark to black colour quartz, blue-greenish apatite, nigerite, gachnite, tourmaline, monazite. The primary ferrocolumbite and Nb-rutile-II have undergone strong hydrothermal alteration. Thus primary rutile-II decomposed with formation of skeletal intergrowths of secondary cassiterite and rutile-III with a much lower volume of Nb and Ta under the influence of hydrothermal fluid. Primary homogenous Nb-rutile-I (Nb2O5+Ta2O5 from 33,5 to 42,9 wt.%) exsolved a fine trellis-like pattern and lamellar of Nb-pure rutile-III, cassiterite and Mn-rich ilmenite. The Nb-rutile-II is occurred in tabular grains with unclear internal zonation. Primary ferrcolumbite breakdown to Ti-ixiolite and Nb-rutile-III. Primary oscillatory zonality is transformed into irregularly patchy and veinlety. Recrystallized ferrotantalite is secondary and uncommon mineral. Ferrocolumbite contains 2.93 to 4.74 wt.%TiO2, and titanian ixiolite 7,33-10,76 wt.%. The (Ti,Nb)>Ta mineral assemblages, and compositional trend of columbite with very low Ta/(Ta+Nb) and Mn/ (Mn+Fe) imply a general low level of fractionation in comparison with typical beryl-columbite rare-metal pegmatites.

A Multi–fluid Constrain for the Forming of Potash Deposits in the Savannakhet Basin: Geochemical Evidence from Halite

AbstractThe Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re‐define the evaporation processes of the study area. Geochemical analyses of halite from various borehole‐derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11B indicated that ore deposits formed primarily due to evaporation of seawater, although non‐marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite‐ and sylvite‐rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermal fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages: (1) an initial marine evaporation at the beginning of the deposit's formation, where seawater (and minor fresh water) trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine‐derived evaporites; (2) a transgression stage, where seawater recharged the basin; (3) a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and (4) a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non–marine fresh water and hydrothermal fluids.

Origin of halogens and their use as environmental tracers in aquifers of Thriassion Plain, Attica, Greece

The processes that control halide concentrations in coastal aquifers of the Thriassion Plain in Greece include both natural and anthropogenic factors as follows: evapotranspiration, dissolution of evaporites, domestic sewage as well as dissolution of minerals containing fluoride. Groundwater monitoring data indicate that the Cl−/Br− mass ratio ranges between 43 and 1510. Ratios ranging round the value 292 are attributed to sea intrusion; 300–600 to domestic sewage; and 900–1510 to dissolution of evaporites. The evaporation of irrigated water plays an important role as well. Fluoride concentrations ranging from 0.1 up to 9.94 mg/l possibly originate from Holocene as well as Plio–Pleistocene sediments which contain organic material. It is also likely that fluoride originates from fluorite dissolution or comes from Palaeozoic-Middle Triassic volcano-sedimentary rocks which occur around the wider area and constitute the basement of the study area. In those rocks, the alteration of biotite to chlorite takes place under the influence of hydrothermal fluids, as the Thriassion Plain is close to South Aegean volcanic arc where volcanic activity exists.

Mechanisms of granite alteration into grus, Karkonosze granite, SW Poland

Granitic gruses are usually considered as a product of deep weathering, but the influence of hydrothermal fluids was also noticed. In this work, a wide range of mineralogical and chemical methods performed on 43 samples from three representative outcrops and a reference site is used to determine the influence of hydrothermal and weathering fluids on the development of granitic gruses from the coarse grained Karkonosze granite. Four types of altered granites have been distinguished, including compact and friable granite, typical grus, and localized heavy altered zones. Mineralogical observations such as complete albitization of plagioclase and crystallization of secondary quartz revealed an important role of hydrothermal alteration at the early stage of grusification. The origin of smectite and alteration of biotite into muscovite are likely to be connected with circulation of hydrothermal fluids too. Grusification sensu stricto was primarily caused by vermiculitization of biotite which resulted in volumetric expansion and the development of transmineral microcracks with non-accordant pore surfaces. Thus, it requires hydrothermal alteration to be relatively minor, confined to postmagmatic changes, since more advanced alteration of biotite into muscovite rather than vermiculite arrests further development of microcracks and leads to the development of friable granite.

Sedimentary Environment of Ediacaran Sequences of South China: Trace Element and Sr-Nd Isotope Constraints

Post-Marinoan sedimentary rocks from the Yangtze block in South China were investigated to seek constraints on their provenance, genetic relationship with paleoclimate, depositional environment, and changes. Sedimentary rocks from the Doushantuo Formation in the Jiulongwan section of the Yangtze block were collected for whole-rock trace elements and Sr-Nd isotopic analyses. Flat-to-slightly middle rare earth element (REE)–enriched REE-plus-yttrium patterns, negative-to-positive Ce anomalies (Ce/Ce* of 0.86–1.40), positive La anomalies (La/La* of 1.02–1.42), and suprachondritic Y/Ho ratios (36.8–49.5) obtained for the Doushantuo cap carbonates indicate their deposition in a fluctuating inner-shelf setting where freshwater and seawater mixed together and the influence of hydrothermal fluid from the seafloor is absent. All Doushantuo carbonates and shales have variable Sr isotopic compositions, with initial Sr isotopic ratios (0.704030–0.712720) that support significant river-water contribution during the deposition of the Doushantuo Formation. Samples of the Doushantuo Formation collected across sedimentary profiles show distinct variations in Nd isotopic compositions and diagnostic trace elemental ratios (Th/Sc). The cap carbonates received significant input from a broad continental area undergoing extensive weathering immediately after the cease of the glaciation era. In contrast, the upper Doushantuo Formation sediments received more mature detritus from the nearby Archean Kongling complex, reflecting receding sea levels. In contrast to the negative Ce anomalies observed in lower Doushantuo rocks, negligible Ce anomalies in upper Doushantuo rocks suggest an anoxic setting, in agreement with the growth of phosphatic concretions and the presence of framboids of pyrite and a higher concentration of organic matter.