REE distribution in the resin-asphaltene fractions as a geochemical criterion for identification of sources of trace elements in oil

This paper reports REE data on resin-asphaltene components of oil from six oil-gas-bearing provinces and on bitumoids from inferred oil-source rocks (domanikites and bazhenites). It was shown that, regardless of geological-tectonic structure of the regions, oil composition, depth of reservoirs, and host lithologies, oil exhibits significant REE fractionation, and, unlike bitumoids, positive Eu anomaly. The (Eu/Sm)_n ratio increases from asphaltenes to resins and further to oils. Based on REE distribution in oil, source rocks, and bitumoids, it was concluded that deep-seated fluids were one of the possible sources that defined the trace element composition of oil.     

Petrology and geochemistry of mafic and ultramafic cumulate rocks from the eastern part of the Sabzevar ophiolite (NE Iran): Implications for their petrogenesis and tectonic setting

The Late Cretaceous Sabzevar ophiolite represents one of the largest and most complete fragments of Tethyan oceanic lithosphere in the NE Iran. It is mainly composed of serpentinized mantle peridotites slices; nonetheless, minor tectonic slices of all crustal sequence constituents are observed in this ophiolite. The crustal sequence contains a well-developed ultramafic and mafic cumulates section, comprising plagioclase-bearing wehrlite, olivine clinopyroxenite, olivine gabbronorite, gabbronorite, amphibole gabbronorite and quartz gabbronorite with adcumulate, mesocumulate, heteradcumulate and orthocumulate textures. The crystallization order for these rocks is olivine ​± ​chromian spinel → clinopyroxene → plagioclase → orthopyroxene → amphibole. The presence of primary magmatic amphiboles in the cumulate rocks shows that the parent magma evolved under hydrous conditions. Geochemically, the studied rock units are characterized by low TiO₂ (0.18–0.57 ​wt.%), P₂O₅ (<0.05 ​wt.%), K₂O (0.01–0.51 ​wt.%) and total alkali contents (0.12–3.04 ​wt.%). They indicate fractionated trends in the chondrite-normalized rare earth element (REE) plots and multi-element diagrams (spider diagrams). The general trend of the spider diagrams exhibit slight enrichment in large ion lithophile elements (LILEs) relative to high field strength elements (HFSEs) and positive anomalies in Sr, Pb and Eu and negative anomalies in Zr and Nb relative to the adjacent elements. The REE plots of these rocks display increasing trend from La to Sm, positive Eu anomaly (Eu/Eu1 ​= ​1.06–1.54) and an almost flat pattern from medium REE (MREE) to heavy REE (HREE) region [(Gd/Yb)_N ​= ​1–1.17]. Moreover, clinopyroxenes from the cumulate rocks have low REE contents and show marked depletion in light REE (LREE) compared to MREE and HREE [(La/Sm)_N ​= ​0.10–0.27 and (La/Yb)_N ​= ​0.08–0.22]. The composition of calculated melts in equilibrium with the clinopyroxenes from less evolved cumulate samples are closely similar to island arc tholeiitic (IAT) magmas. Modal mineralogy, geochemical features and REE modeling indicate that Sabzevar cumulate rocks were formed by crystal accumulation from a hydrous depleted basaltic melt with IAT affinity. This melt has been produced by moderate to high degree (~15%) of partial melting a depleted mantle source, which partially underwent metasomatic enrichment from subducted slab components in an intra-oceanic arc setting.     

The geochemistry of Archaean shales derived from a Mafic volcanic sequence, Belingwe greenstone belt, Zimbabwe: provenance, source area unroofing and submarine versus subaerial weathering

Shales of the ∼2.7 Ga Zeederbergs Formation, Belingwe greenstone belt, Zimbabwe, form thin (0.2-2 m) horizons intercalated with submarine lava plain basalts. Shales of the overlying Cheshire Formation, a foreland basin sedimentary sequence, form 1-100 m thick units intercalated with shallow-water carbonates and deep-water, resedimented basalt pebble conglomerates. Zeederbergs shale is characterized by high contents of MgO and transition metals and low concentrations of K₂O and LILE as compared to average Phanerozoic shale, indicative of an ultramafic to mafic source terrain. Cheshire shales have similar major and trace element contents, but MgO and transition metals are less enriched and the LILE are less depleted. Zeederbergs shales have smoothly fractionated REE patterns (La_N/Yb_N = 2.84-4.45) and no significant Eu anomaly (Eu/Eu* = 0.93-0.96). REE patterns are identical to those of the surrounding basaltic rocks, indicating local derivation from submarine reworking. Cheshire shales have rather flat REE patterns (La_N/Yb_N = 0.69-2.19) and a small, negative Eu anomaly (average Eu/Eu* = 0.85), indicative of a mafic provenance with minor contributions of felsic detritus. A systematic change in REE patterns and concentrations of transition metals and HFSE upwards in the sedimentary succession indicates erosion of progressively more LREE-depleted basalts and ultramafic volcanic rocks, followed by unroofing of granitoid crust. Weathering indices confirm the submarine nature of Zeederbergs shale, whereas Cheshire shale was derived from a source terrain subjected to intense chemical weathering.     

Nature of the crust in Maine,USA: evidence from the Sebago batholith

 Neodymium and lead isotope and elemental data are presented for the Sebago batholith (293±2 Ma), the largest exposed granite in New England. The batholith is lithologically homogeneous, yet internally heterogeneous with respect to rare earth elements (REE) and Nd isotopic composition. Two-mica granites in the southern/central portion of the batholith (group 1) are characterized by REE patterns with uniform shapes [Ce_N/Yb_N (chondrite normalized) = 9.4–19 and Eu/Eu* (Eu anomaly) = 0.27–0.42] and ɛ _Nd(t) = −3.1 to −2.1. Peripheral two-mica granites (group 2), spatially associated with stromatic and schlieric migmatites, have a wider range of total REE contents and patterns with variable shapes (Ce_N/Yb_N = 6.1–67, Eu/Eu* = 0.20–0.46) and ɛ _Nd(t) = −5.6 to −2.8. The heterogeneous REE character of the group 2 granites records the effects of magmatic differentiation that involved monazite. Coarse-grained leucogranites and aplites have kinked REE patterns and low total REE, but have Nd isotope systematics similar to group 2 granites with ɛ _Nd(t) = −5.5 to −4.7. Rare biotite granites have steep REE patterns (Ce_N/Yb_N = 51–61, Eu/Eu* = 0.32–0.84) and ɛ _Nd(t) = −4.6 to −3.8. The two-mica granites have a restricted range in initial Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 18.41–18.75; ²⁰⁷Pb/²⁰⁴Pb = 15.60–15.68; ²⁰⁸Pb/²⁰⁴Pb = 38.21–38.55), requiring and old, high U/Pb (but not Th/U) source component. The Nd isotope data are consistent with magma derivation from two sources: Avalon-like crust (ɛ _Nd>−3), and Central Maine Belt metasedimentary rocks (ɛ _Nd<−4), without material input from the mantle. The variations in isotope systematics and REE patterns are inconsistent with models of disequilibrium melting which involved monazite. Received: 8 December 1995 / Accepted: 29 April 1996     

REE Geochemical Characteristics of Apatite,Sphene and Zircon from Alkaline Rocks

The accessory minerals apatite and sphene are the main carriers of REE in alkaline rocks.Their chondrite-normalized REE patterns decline sharply to the right as those of the host rocks,In the patterns an obvious negative Eu anomaly and a positive Ce anomaly can be seen in apatite and sphene,respectively.Zircon from alkaline rocks is different in REE pattern,I,e,. a nearly symmetric“V“-shaped pattern with a maximum negative Eu anomaly.Compared with the equivalents from granites,apatite,sphene and zircon from alkaline rocks are all characterized by higher (La/Yb)N ratio and less Eu depletion,As to the relative contents of REE in minerals,apatite,sphene and zircon are enriched in LREE,MREE and HREE respectively,depending on their crystallochemical properties.     

Experimental Study on the Effects of Organic Acids on the Dissolution of REE in the Weathering Crust of Granite

The results of REE leached by some organic acids with various concentrations and water/rock ratios for different durations from a mixed samples of the weathering crust of a granite in Gonghe,Guangdong,China,showed that:1)the contents of REE leached increase with increasing concentrations of the organic acids;2) the contents of REE leached by 0.01mol/L organic acids increase with increasing water/rock ration;3) the interaction between the organic acids and the samples enhances the pH value of the medium and the contents of REE leached tend to increase with decreasing pH value;and 4) compared with those leached by ammonia sulfate,the REE leached by the organic acids are characterized by a weaker negative C e anomaly,a stronger negative Eu anomaly,and lower(La/Sm)N and (Gd/Yb)N ratios,indicating that the organic acids have made contributions to the fractionation of REE in the weathering crust.     

Geochemistry of clastic sediments from Sargur supracrustals and Bababudan group,Karnataka: Implications on Archaean Proterozoic Boundary

The sediments from three stratigraphic levels in the Bababudan schist belt of Dharwar craton exhibit great diversity in major, trace and rare earth element (REE) geochemistry and thus interpreted to represent significant compositional variation in the source rocks. Detailed geological and geochemical studies have been carried out on clastic rocks constituting the Archaean Sargur supracrustals and the Bababudan belt of Dharwar craton (DC), southern India for understanding the geochemical characteristics and to define the Archaean-Proterozoic Boundary (APB/QPC) in southern India. There is significant contrast in the geochemical signatures for the sediments from these stratigraphic levles. The Sargur enclave population is characterised by slight LREE enrichment with (La/Sm)_N ranging from 1.45 to 3.58, almost flat HREE with (Gd/Yb)_N ranging from 0.65 to 1.29 with Eu/Eu* ranging from 0.49 to 0.91 suggesting mafic-ultramafic source rocks in the provenance. On the other hand, the Post QPC (PQPC) rocks are characterised by LREE enrichment with (La/Sm)_N ranging from 2.66 to 7.07, nearly flat HREE with (Gd/Yb)_N ranging from 0.58 to 0.95 and significant depletion of Eu with Eu/Eu* ranging from 0.34 to 0.85, indicating felsic province in the source area. The conglomerates and quartzites representing the QPC are showing mixed nature of these, reflecting the transitional character in depositional environment. Increase in abundance of REE, K₂O/Na₂O, Th/Sc, La/Sc, Th/U, Hf/Ta and Zr/Y ratios are characteristic of the QPC. The PQPC sediments are enriched in Th, U and HFSE like Hf, Nb, Zr and Y, and depleted in Co and Eu than their older counterparts. These geochemical signatures signify the dominance of mafic-ultramafic rocks in the source area for Sargur rocks and the existence of granite-granodiorite for PQPC clastics. Thus, the unconformity related oligomictic quartz pebble conglomerates (QPC) and quartzites at the base of Bababudan Group resembling the QPC of Witswaterand, South Africa signifies that a stable continental crust had already developed in southern India prior to ∼3.0Ga.     

Petrology,geochemistry and geodynamic setting of Eocene-Oligocene alkaline intrusions from the Alborz-Azerbaijan magmatic belt,NW Iran

The Kaleybar, Razgah and Bozqush (KRB) intrusions were studied to better understand subduction-related Eocene-Oligocene alkaline magmatism in NW Iran. The bulk of intrusions mainly consist of Si-undersaturated rocks including foid-bearing monzonite and syenite (nepheline syenite, pseudoleucite syenite) with some foid-bearing diorite and gabbro. In addition, they are spatially associated with Si-saturated rocks ranging in composition from monzo-diorite to syeno-granite. The main mafic rock-forming minerals of the studied rocks are olivine (Fo₄₄Fa₅₆), clinopyroxene (diopside to augite), biotite (Mg-biotite through Fe-biotite), amphibole (ferro-pargasite and magnesio-hastingsite with Mg#<0.55), and garnet (Ti-andradites). Based on whole rock geochemistry, the foid-syenites and associated rocks show mildly alkaline (shoshonitic) affinity. The content of SiO₂, K₂O?+?Na₂O, and K₂O/Na₂O ratio ranges from 47.8 to 60.7?wt.%, 5.31 to 16.33?wt.%, and 0.6 to 3.2, respectively. The intrusions are commonly metaluminous, with an aluminum-saturation index (ASI) ranging from 0.66 to 1.01. Almost all the rocks display similar arc-related geochemical features characterized by the enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) together with the depletion in high field strength elements (HFSE). The chondrite-normalized REE patterns show no to marked negative Eu anomaly (Eu/Eu*?=?0.55 to 1.12), (La/Yb)_N?=?8.16 to 31, (La/Sm)_N?=?2.80 to 10.59, and (Tb/Yb)_N?=?0.84 to 2.40. The evaluation of the REE patterns for the KRB magmas and the comparison of the trace element ratios with experimental studies indicate a chemically enriched lithospheric mantle source composed of garnet-spinel-lherzolite that have underwent a low degree of partial melting <5% to generate the KRB intrusions. Based on the present data, we infer that the mantle source was contaminated by a subduction component and the melting of the mantle lithosphere occurred by local extension in an overall convergent regime in NW Iran. The extension regime during the Eocene is proposed to be the result of the Neo-Tethys slab roll-back and the Sevan-Akera-Qaradagh (SAQ) slab break-off.     

Rare earth element geochemistry of South Atlantic deep sea sediments: Ce anomaly change at ~54 My

The geochemistry of the REE (rare earth elements) in oceanic sediments is discussed, based mainly on samples from DSDP Holes 530A and 530B, Leg 75, and Hole 525A, Leg 74. The proposed mechanisms for incorporation of the REE into the marine carbonate phases are adsorption, chiefly onto the carbonate minerals and on Sc, Hf, and Ta-rich Fe-Mn hydroxide flocs as carbonate coatings.The Ce anomaly of marine carbonate was used as an indicator of paleo-ocean water redox conditions: the bottom water of the Angola Basin was in a reducing condition in the Cretaceous. At ca. 54 My, the South Atlantic water condition became oxidizing, similar to the present seawater redox condition. This change was related to the improvement of circulation due to the widening of South Atlantic and the subsidence of water circulation barriers such as the Walvis Ridge and perhaps the Romanche Fracture Zone.The younger (Eocene-Recent) and older (Albian-Santonian) argillaceous sedimentary rocks from 530A (denoted as YSAB and OSAB respectively) show different degrees of Eu depletion with a transition period in between. The REE patterns of OSAB suggest a basaltic origin. The possible sources are Kaoko basalt in Southwest Africa or Namibia and the basaltic Walvis Ridge itself. The decrease in the area covered by Kaoko basalt due to erosion, the subsidence of the Walvis Ridge, and the improvement of water circulation led to changes in the Eu anomaly from Campanian to Paleocene, and resulted in the YSAB REE pattern. Changes in the Sm/Eu, La/Th, Th/Yb, Ti/Al₂O₃, FeO/Al₂O₃, and Hf/Al₂O₃ ratios suggest changes of average source rock composition from and esite to granodiorite.The REE abundances and patterns of younger sediments in the Angola Basin (YSAB) are very similar to those observed in NASC, PAAS, and ES sediments. The YSAB REE abundances and patterns may represent the average REE distribution of the exposed African continental crust. The strong resemblance of REE distributions of YSAB, NASC, PAAS and ES suggests thorough REE mixing from different sources and the uniformity of the average crustal compositions of different continents: Africa, North America, Australia, and Europe     

Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China： Petrochemical evidence for partial melting of the mantle-crust transition zone

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2=52%–62%, Al2O3>15%, Na2O/K2O>1 and MgO<3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10–13, (La/Yb)N=15–19, and show a weak negative Eu anomaly with δEu=0.71–0.89. The close relationship between Mg# and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.23–3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.     

Geochemistry of black shales from the Lower Cretaceous Paja Formation,Eastern Cordillera,Colombia: Source weathering,provenance, and tectonic setting

The major and trace element characteristics of black shales from the Lower Cretaceous Paja Formation of Colombia are broadly comparable with those of the average upper continental crust. Among the exceptions are marked enrichments in V, Cr, and Ni. These enrichments are associated with high organic carbon contents. CaO and Na₂O are strongly depleted, leading to high values for both the Chemical Index of Alteration (77–96) and the Plagioclase Index of Alteration (86–99), which indicates derivation from a stable, intensely weathered felsic source terrane. The REE abundances and patterns vary considerably but can be divided into three main groups according to their characteristics and stratigraphic position. Four samples from the lower part of the Paja Formation (Group 1) are characterized by LREE-enriched chondrite-normalized patterns (average La_N/Yb_N = 8.41) and significant negative Eu anomalies (average Eu/Eu¹ = 0.63). A second group of five samples (Group 2), also from the lower part, have relatively flat REE patterns (average La_N/Yb_N = 1.84) and only slightly smaller Eu anomalies (average Eu/Eu¹ = 0.69). Six samples from the middle and upper parts (Group 3) have highly fractionated patterns (average La_N/Yb_N = 15.35), resembling those of Group 1, and an identical average Eu/Eu¹ of 0.63. The fractionated REE patterns and significant negative Eu anomalies in Groups 1 and 3 are consistent with derivation from an evolved felsic source. The flatter patterns of Group 2 shale and strongly concave MREE-depleted patterns in two additional shales likely were produced during diagenesis, rather than reflecting more mafic detrital inputs. An analysis of a single sandstone suggests diagenetic modification of the REE, because its REE pattern is identical to that of the upper continental crust except for the presence of a significant positive Eu anomaly (Eu/Eu¹ = 1.15). Felsic provenance for all samples is suggested by the clustering on the Th/Sc–Zr/Sc and Gd_N/Yb_N–Eu/Eu¹ diagrams. Averages of unmodified Groups 1 and 3 REE patterns compare well with cratonic sediments from the Roraima Formation in the Guyana Shield, suggesting derivation from a continental source of similar composition. In comparison with modern sediments, the geochemical parameters (K₂O/Na₂O, La_N/Yb_N, La_N/Sm_N, Eu/Eu¹, La/Sc, La/Y, Ce/Sc) suggest the Paja Formation was deposited at a passive margin. The Paja shales thus represent highly mature sediments recycled from deeply weathered, older, sedimentary/metasedimentary rocks, possibly in the Guyana Shield, though Na-rich volcanic/granitic rocks may have contributed to some extent.     

Mafic forearc cumulates and associated rocks in the central high-pressure belt of the Acatlán Complex of southern México: geochemical constraints

The high-pressure (HP) Piaxtla Suite at Tehuitzingo contains peridotites, gabbros, and serpentinized peridotites, as well as granitoids and metasedimentary rocks. The HP mafic rocks are characterized by low SiO₂ (38–52 wt.%) and high Mg# (～48–70), Ni (100–470 ppm), and Cr (180–1750 ppm), typical of cumulate compositions. Trace elements and rare earth element (REE) primitive mantle-normalized patterns display generally flat profiles, indicative of derivation from a primitive mantle with two distinct patterns: (1) gabbroic patterns are characterized by a positive Eu anomaly, low REE abundances, and slightly depleted high REE (HREE) relative to low REE (LREE), typical of cumulus olivine, pyroxene, and plagioclase; and (2) mafic-intermediate gabbroic patterns exhibit very flat profiles characteristic of olivine and clinopyroxene as cumulus minerals. Their Nb/Y and Zr/TiO₂ ratios suggest a subalkaline character, whereas low Ti/V ratios indicate that the Tehuitzingo cumulates are island arc tholeiitic basalts that resemble modern, immature oceanic, forearc magmas. These cumulates have high values of ? _Nd(t) = 5.3–8.5 and ¹⁴⁷Sm/¹⁴⁴Nd = 0.18–0.23, which renders calculations of model ages meaningless. Our data are consistent with the Tehuitzingo arc rocks being part of a tectonically extruded Devonian–early Carboniferous arc developed along the west margin of Gondwana.     

Rare earth geochemistry in the dissolved, suspended and sedimentary loads in karstic rivers, Southwest China

The watershed in the central Guizhou Province (Guizhou Province is called simply Qian) (CQW) is a karstic area. Rare earth elements (REEs) of dissolved loads, suspended particulate material (SPM) and sediments of riverbed are first synthetically reported to investigate REE geochemistry in the three phases in karstic watershed during the high-flow season. Results show that the low dissolved REE concentrations in the CQW are attributed to these rivers draining carbonate rocks. The dissolved REE have significant negative Eu anomaly and coexistence of middle and light REE (MREE??PAAS-normalized La _N /Sm _N and Gd _N /Yb _N ; LREE??PAAS-normalized La _N /Yb _N )-enrichment, which are due to the dissolution of impure Triassic carbonates. REE concentrations in most of SPM exceed that of sediments in the CQW and the average continental crust (UCC). The SPM and the sediments show some common features: positive Eu, Ce anomalies, and MREE enrichment. The controls on the patterns seem to be from weathering profiles: the oxidation state, the REE-bearing secondary minerals (cerianite, potassium feldspar and plagioclase), which are also supported by the evidence of Y/Ho fractionations in the three phases.     

Origin of natural sulfur-metal chimney in the Tangyin hydrothermal field,Okinawa Trough: constraints from rare earth element and sulfur isotopic compositions

For the first time, we present the rare earth element (REE) and sulfur isotopic composition of hydrothermal precipitates recovered from the Tangyin hydrothermal field (THF), Okinawa Trough at a water depth of 1206 m. The natural sulfur samples exhibit the lowest ΣREE concentrations (ΣREE= 0.65×10^–6–4.580×10^–6) followed by metal sulfides (ΣREE=1.71×10^–6–11.63×10^–6). By contrast, the natural sulfur-sediment samples have maximum ΣREE concentrations (ΣREE=11.54×10^–6–33.06×10^–6), significantly lower than those of the volcanic and sediment samples. Nevertheless, the δEu, δCe, (La/Yb)_N, La/Sm, (Gd/Yb)_N and normalized patterns of the natural sulfur and metal sulfide show the most similarity to the sediment. Most hydrothermal precipitate samples are characterized by enrichments of LREE (LREE/HREE=10.09–24.53) and slightly negative Eu anomalies or no anomaly (δEu=0.48–0.99), which are different from the hydrothermal fluid from sediment-free mid-oceanic ridges and back-arc basins, but identical to the sulfides from the Jade hydrothermal field. The lower temperature and more oxidizing conditions produced by the mixing between seawater and hydrothermal fluids further attenuate the leaching ability of hydrothermal fluid, inducing lower REE concentrations for natural sulfur compared with metal sulfide; meanwhile, the negative Eu anomaly is also weakened or almost absent. The sulfur isotopic compositions of the natural sulfur (δ³⁴S=3.20‰–5.01‰, mean 4.23‰) and metal sulfide samples (δ³⁴S=0.82‰–0.89‰, mean 0.85‰) reveal that the sulfur of the chimney is sourced from magmatic degassing.     

Significance of quartz REE geochemistry, Shihu gold deposit, western Hebei Province, North China, using LA-ICP-MS

Rare earth element (REE) geochemistry on monomineral has been widely used in various fields of geosciences to reveal the origin of ore-forming materials and fluid. Quartz are ubiquitous mineral in the Shihu gold deposit that is situated in central shear zone of mesocenozoic Fuping metamorphic core complex in the middle-northern part of Taihang Mountains. Gold-bearing quartz veins are their most important industrial orebodies. Rare earth element abundances in quartz from the Shihu gold mine, as determined by laser ablation-indutively coupled plasma-mass spectrometry (LA-ICP-MS) analysis, are shown to be sensitive to identify barren quartz and mineralized quartz. Amounts of REE concentrations in barren quartz and mineralized quartz are 97 × 10⁻⁹ and 85 × 10⁻⁹, respectively. The average (La/Yb)_N and (La/Sm)_N ratios for the barren quartz are 0.25 and 0.13, and the ratios for mineralized quartz are 0.28 and 0.19, respectively. There is a pronounced positive correlation between (La/Yb)_N and (La/Sm)_N ratios. There is no obvious correlation between REE characteristics and sampling sites. The mineralized quartz show the most pronounced negative Ce anomalies, whereas weak negative Ce anomalies are typical of barren quartz vein. A negative Eu anomaly becomes more significant in mineralized quartz than barren quartz. δCe have a broadly positive correlation with δEu. Y/Ho ratio of barren quartz and mineralized quartz are ranging from 2.14–28.75, and from 1.28–9.92, respectively. The REE characteristics of quartz indicate that the ore-forming fluids of the gold deposit were derived from the deep fluid and its formation was dually controlled by Precambrian metamorphic basement and Mesozoic granitoids. The results significantly enhance the usefulness of quartz in tracing the sources of ore-forming fluid to discuss the genesis of the gold deposit, and as an indicator mineral in mineral exploration in Taihang mountain region.     

Pressure-Dependence of Rare Earth Element Distribution in Amphibolite- and Granulite- Grade Garnets. A LA-ICP-MS Study

Using an excimer (KrF) laser ablation ICP-MS system, we studied the distribution of REE in garnets from metapelites and metabasites from Ivrea-Verbano (Western Alps, Italy) and from the Peña Negra Anatectic Complex (Central Iberia), finding systematic variations that correlate well with the metamorphic grade. Chondrite-normalized REE patterns of garnets from amphibolite-grade metapelites have lower-than-chondrite levels from La to Sm, a very small or no Eu anomaly, and a steep rise in the abundance of heavy REE as the atomic number increases. Metapelitic garnets from the amphibolite-granulite transition have a marked Eu negative anomaly and are enriched in MREE such that Sm is 10-15 times chondrite and the pattern is almost flat from Dy to Yb-Lu. In garnets from granulite-grade metapelites, the intensity of the Eu anomaly and the relative concentration of Nd, Sm, Gd and Tb increase, with almost flat chondrite-normalized patterns from Sm to Lu. Garnets from mafic granulites are remarkably similar to those of metapelitic garnets equilibrated at the same pressure, except for the Eu anomaly. The apparent paradox of enhanced uptake of larger REE ions with increasing pressure is attributed to the 3M²⁺ 2REE³⁺+ vacancy substitution, which produces a net decrease in the dimensions of the unit-cell of garnet. Variations in REE patterns depend essentially on the pressure and have little dependence on either temperature, bulk-composition of garnet, or REE whole-rock composition, so they could represent a new approach for geobarometric studies. The best numerical parameter to express pressure-related variations of REE distribution in garnets is the Gd/Dy ratio which does not seem perceptibly affected by disequilibrium partitioning. The regression equation between GASP pressure and the average Gd/Dy^garnet is P = 3.6 + 5.6 Gd/Dy. This equation seems to be reliable for garnets: (1)equilibrated within a pressure range of 4-9 kbar, (2) coexisting with modal monazite; and (3) with unit-cell dimensions under 11.46 Å.     

Kiglapait geochemistry VII: Yttrium and the rare earth elements

Based on 51 wholerock analyses by XRF and summation over the layered group, the Kiglapait Intrusion contains 4.7_?1.6^+1.2 ppm Y, which resides principally in augite and apatite. Using liquid compositions calculated by summation, the partition coefficient D^AUG/L_Y is 0.95 ± 0.12 from 84 to 97 PCS (percent solidified) and 1.5 ± 0.4 above 97 PCS. For feldspar, the most likely value for D is 0.028 ± 0.02 (N = 6).REE analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs PCS. Summations over the rocks of the layered group gave La = 2.5, Ce = 5.8, Nd = 3.9, Sm = 1.0, Eu = 0.8, Tb = 0.17, Yb = 0.37, and Lu = 0.06 ppm, with 2 s.d. errors near ± 30%. All these elements are highly incompatible until the arrival of augite, which affects chiefly the HREE, and apatite, which affects all (but more strongly, the LREE). The net result is that after apatite arrival at 94 PCS, the liquid compositions are nearly constant, hence D^WR/L_REE ≈ 1.0. These results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar, olivine, augite, apatite, and Fe-Ti oxide minerals. For pre-apatite liquids, D^FSP/L_REE vary regularly with the normative di content of the liquid and change by an order of magnitude, hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids.The Eu anomaly at first decreases in Kiglapait liquids due to plagioclase fractionation, but then increases due to removal of augite and apatite with negative Eu anomalies. The features dominantly responsible for Eu partitioning are liquid structure and, for monoclinic ternary feldspars, crystal structure. The former is best monitored by the augite or diopside content of the liquid and the latter, by the K content of the feldspar.The chondrite-normalized REE pattern for the intrusion has La_N = 7.4, Lu_N = 1.6, (Ce/Yb)_N = 3.6, and Eu/Eu* = 2.4, indicating its feldspar-rich nature. The chilled margin of the nearby Hettasch Intrusion has a similar but more evolved pattern, corresponding roughly to the Kiglapait liquid at 70 PCS. As with other data, those for the REE suggest source differences for the two intrusions rather than a relationship due to fractionation.     

Petrologic significance of rare earths distribution in granites

Granitic rocks of various ages and composition are found in the Schwarzwald region of West Germany. These granites range in age from Upper Devonian to Upper Carboniferous (370-280 m.y.) and in composition from granodiorites to alkali feldspar granites. 14 representative samples of twelve different types were analysed for their La, Ce, Nd, Sm, Eu, Tb, Dy, Yb, Lu by instrumental neutron activation. The studies reveal that there are characteristic differences between the different types of granitic rocks both as regards to their total REE content as well as the distribution pattern of these elements. These differences can not be directly related to the variations in the major element chemistry or the mineralogy of the granites. On the other hand, a relationship is found between the age of the granitic rocks and the total REE as well as their distribution pattern. In general the ΣREE varies from 22 to 215 ppm in different types. The ΣLa-Lu increases gradually in the direction Upper Devonian→Lower Carboniferous, however, in the granitic rocks of the Upper Carboniferous this trend is reversed and there is again a marked depletion in the content of REE. The chondrite normalised patterns of all the older types give a smooth concave curve with decrease of concentration from La to Lu. All the Upper Carboniferous granites on the other hand are characterised by a progressive pronounced negative Eu anomaly. The gradual increase of the ΣREE in the older granites is related to their evolution by progressive anatexis, whereas, the decrease in the total REE content in case of the younger Upper Carboniferous granites is due to processes of magmatic differentiation. The depletion of Eu in these K-feldspar rich types of granite is probably related to the breakdown of biotite in the anatectic starting material.     

The Bovedy meteorite; mineral chemistry and origin of its Ca-rich glass inclusions

The Bovedy meteorite fell on 25 April 1969 in Northern Ireland; the main mass of 4·94 kg was found at Bovedy (54°57′N, 06°37′W). It is an L3 chondrite with abundant chondrules clearly visible in hand specimen. Bulk chemical analyses are presented, the total Fe content being 22·5%. The olivines are homogeneous (Fa₂₄) but the pyroxenes are not equilibrated (Fs_8–28). Brown glass is common within chondrules but a clear glass of composition An₈₅ is present interstitially in a few orthopyroxene-rich (Fs_17–28) chondrules. A bleb, 2 mm across, of clear glass, again of composition An₈₅ was found in one stone of the meteorite and in the glass five REE (rare earth elements), (La, Sm, Eu, Yb, Lu) were determined. The low REE abundances coupled with a large positive Eu anomaly are characteristic of plagioclase, but the finer details of the pattern suggest that this glass has a closer affinity to the lunar anorthosites than to plagioclases from lunar mare basalts or eucritic meteorites. There is also evidence that the magnitude of the Eu anomaly for plagioclases and anorthosites from extra-terrestrial sources is inversely related to trivalent REE content. The existence of anorthositic material and, as a consequence, a differentiated planetary body prior to the formation of the Bovedy meteorite is suggested.     

Geochemical Constraints of Sediments on the Provenance, Depositional Environment and Tectonic Setting of the Songliao Prototype Basin

The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settings have distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances, depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of the clastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin are enriched in silica (SiO2=66.48-80.51 %), and their ΣREE are 30-130 dmes of that of chondrite with remarkable Eu anomalies. In discriminating diagrams of Eu/Eu vs eeeeeREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/ Eu=l, on the right of the line Eu/Eu/ΣREE=1 and under the line La/Yb)N/eeeeeREE=1/8, which indicates that the depositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3, FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments