四川雪宝顶W-Sn-Be矿床中矿物化学组成及矿床成因

雪宝顶矿床位于四川省的松潘甘孜造山带中,以出产大颗粒含W-Sn-Be-F-P的矿物而闻名,前人对该矿床已经开展了大量的研究,但缺乏对粗粒矿物的主次痕量元素研究.本次研究采用X射线荧光光谱(XRF)、电子探针(EMPA)和电感耦合等离子体质谱(ICP-MS)技术对矿床中各矿物的主次痕量元素进行测试分析.结果显示,雪宝顶矿...     

Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks

Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks from the island of Syros (Greece) were studied, using secondary ion mass spectrometry, inductively coupled plasma optical emission spectrometry and prompt gamma neutron activation analysis. Partitioning between coexisting mineral phases was found to be rather constant and independent of element concentrations. For several mineral pairs, apparent partition coefficients vary in a narrow range, while concentrations vary by more than an order of magnitude. Hence, it was possible to establish sets of inter-mineral partition coefficients for Li, Be and B among 15 different high-pressure minerals. This data set provides important information on the behaviour of the light elements in different lithologies within subducting slabs from the onset of metamorphism to the eclogite stage. It is essential for modelling trace-element and isotope fractionation during subduction and dehydration of oceanic crust.     

富锂氟含稀有矿化花岗质岩石的对比和成因思考

Li-F花岗质岩石以超酸性、过铝、富含H2O、F、B、P等挥发性组分和富含Li、Rb、Cs、Be、Ta、Nb、Sn、W等亲石稀有金属元素为主要特征，以黄玉－锂云母－钠长石花岗岩为典型代表。从该类岩石地质产状的多样性和可对比性、空间分布的规律性、矿物岩石的结构构造、硅酸盐－熔体包裹体特征以及实验岩石学的研究成果等方面，综合论证该类岩石主要是从经过分异演化而形成的残余熔浆中直接结晶而在的；充分的分离结晶作用，是产生这种残余熔浆的主要机制；岩体的空间分带特征和各带之间的渐变过渡关系，为分离结晶作用的途径和演化方向提供了重要信息；熔体中挥发性组分的大量存在，是分离结晶作用能充分进行的关键因素；亲石稀有金属元素在流／熔配分中倾向于进入熔体相，是残余熔体中逐步富集这些稀有金属元素的主要原因；岩浆－热液过渡阶段出溶的流体相与已晶出的共存固相之间的相互作用，造成了广泛的交代蚀变现象；残余熔浆在不同地质和物理化学环境中的侵位、结晶和演化，造成了Li-F花岗质岩石在产状、结构构造和矿物组合等方面的多样性。     

The Lithium, Boron and Beryllium content of serpentinized peridotites from ODP Leg 209 (Sites 1272A and 1274A): Implications for lithium and boron budgets of oceanic lithosphere

Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 μg g⁻¹) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 μg g⁻¹), depleted in Li (most values below 1 μg g⁻¹) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 μg g⁻¹), H₂O and Cl contents and to lower Li contents (0.07-3.37 μg g⁻¹) of peridotites, implying that—contrary to alteration of oceanic crust—B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at 1 and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of 1 m × 1 m × thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li.     

Implications of the serpentine phase transition on the behaviour of beryllium and lithium-boron of subducted ultramafic rocks

The Totalp-Platta-Malenco ophiolites in the Eastern Central Alps offer a unique opportunity to study the behaviour of Li, Be and B in ultramafic rocks in response to serpentinization and to progressive Alpine metamorphism. These units represent the remnants of a former ocean-continent transition that was intensely serpentinized during exposure on the Jurassic seafloor of the Ligurian Tethys. From north to the south, three isograd reactions (lizardite⇒antigorite+brucite;lizardite+talc⇒antigorite;lizardite+tremolite⇒antigorite+diopside) have been used to quantify the evolution of the light element content of metamorphic minerals. We determined the Li, Be and B concentrations in major silicate minerals from the ultramafic bodies of Totalp, Platta and Malenco by secondary ion mass spectrometry. Mantle minerals have Be concentrations (e.g. <0.001-0.009 μg/g in olivine) similar to the metamorphic minerals that replace them (e.g. <0.001-0.016 μg/g in serpentine). The mantle signature of Be is thus neither erased during seafloor alteration nor by progressive metamorphism from prehnite-pumpellyite to epidote-amphibolite facies. In contrast, the Li and B inventories of metamorphic minerals are related to the lizardite-to-antigorite transition. Both elements display higher concentrations in the low-temperature serpentine polymorph lizardite (max. 156 μg/g Li, max. 318 μg/g B) than in antigorite (max. 0.11 μg/g Li, max. 12 μg/g B). Calculated average B/Li ratios for lizardite (∼1395) and antigorite (∼115) indicate that Li fractionates from B during the lizardite-to-antigorite transition during prograde metamorphism in ultramafic rocks. In subduction zones, this signature is likely to be recorded in the B-rich nature of forearc fluids.Relative to oceanic mantle the Be content of mantle clinopyroxene is much higher, but similar to Be values from mantle xenoliths and subduction-related peridotite massifs. These data support previous hypothesis that the mantle rocks from the Eastern Central Alps have a subcontinental origin. We conclude that Be behaves conservatively during subduction metamorphism of ultramafic rocks, at least at low-temperature, and thus retains the fingerprint of ancient subduction-related igneous events in mantle peridotites.     

Trace element partitioning between type B CAI melts and melilite and spinel: Implications for trace element distribution during CAI formation

Calcium- and aluminum-rich inclusions (CAIs), occurring in chondritic meteorites and considered the oldest materials in the solar system, can provide critical information about the environment and time scale of creation of planetary materials. However, interpretation of the trace element and isotope compositions of CAIs, particularly the light elements Li, Be, and B, is hampered by the lack of constraint on melilite-melt and spinel-melt partition coefficients. We determined melilite-melt and spinel-melt partition coefficients for 21 elements by performing controlled cooling rate (2 °C/h) experiments at 1 atmosphere pressure in sealed platinum capsules using a synthetic type B CAI melt. Trace element concentrations were measured by secondary ion mass spectrometry (SIMS) and/or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Melilites vary only slightly in composition, ranging from Åk_31-43. Results for the partitioning of trace elements between melilite and melt in three experiments and between spinel and melt in two experiments show that partition coefficients are independent of trace element concentration, are in good agreement for different analytical techniques (SIMS and LA-ICP-MS), and are in agreement with previous measurements in the literature. Partition coefficients between intermediate composition melilites and CAI melt are the following: Li, 0.5; Be, 1.0; B, 0.22; Rb, 0.012; Sr, 0.68; Zr, 0.004; Nb, 0.003; Cs, 0.002; Ba, 0.018; La, 0.056; Nd, 0.065; Sm, 0.073; Eu, 0.67; Er, 0.037; Yb, 0.018; Hf, 0.001; Ta, 0.003; Pb, 0.15; U, 0.001; Th, 0.002. Site size energetics analysis is used to assess isovalent partitioning into the different cation sites. The Young’s modulus deduced from +2 cations partitioning into the melilite X site agrees well with the bulk modulus of melilite based on X-ray diffraction methods. The changes in light element partitioning as melilite composition varies are predicted and used in several models of fractional crystallization to evaluate if the observed Li, Be, and B systematics in Allende CAI 3529-41 are consistent with crystallization from a melt. Models of crystallization agree reasonably well with observed light element variations in areas previously interpreted to be unperturbed by secondary processes [Chaussidon, M., Robert, F., McKeegan, K.D., 2006. Li and B isotopic variations in an Allende CAI: Evidence for the in situ decay of short-lived ¹⁰Be and for the possible presence of the short-lived nuclide ⁷Be in the early solar system. Geochim. Cosmochim. Acta70, 224-245], indicating that the trends of light elements could reflect fractional crystallization of a melt. In contrast, areas interpreted to have been affected by alteration processes are not consistent with crystallization models.     

川西同德和沙坝麻粒岩及其退变质岩石之间的元素迁移

利用川西麻粒岩的全岩化学组成与岩石中特征矿物的化学性质,研究了麻粒岩退变质作用的元素迁移。对紫苏辉石、普通辉石和普通角闪石的电子探针分析表明,随着麻粒岩退变质作用程度的加深,矿物的化学组成与全岩的元素迁移同步变化。由于矿物组合和岩相的转变以及地壳流体的作用,同德二辉麻粒岩在退变质至黑云角闪斜长片麻岩过程中,K,Rb,Cs,K／Na,Fe^3+和Fe3+／Fe^2+增加,Fe^2+,V,Co,Ba,Sr和Pb降低;在沙坝二辉麻粒岩退变质为含绿帘石角闪斜长片麻岩过程中,Na,Ca,Fe^3+,Zr,Hf,Nb,Ta,Rb,U,Th,REE和Fe^3+／Fe^2+增加,Fe^2+,Mg,K,Co,Zn,Cs,Pb和K／Na降低。麻粒岩退变质过程中制约不同元素迁移的主要矿物相是普通角闪石等退变质新生矿物。同德和沙坝两个麻粒岩块退变质作用中,个别元素迁移性状并不相同,这可能与原岩的性质和变质流体的成分等环境地质条件有关。     

Light lithophile elements in martian basalts: Evaluating the evidence for magmatic water degassing

Whether water has played a role in the petrogenesis of martian basalts remains a subject of significant debate. Estimates of pre-eruptive water concentrations in martian magmas are impeded by the effects of degassing and shock. However, zoning trends of light lithophile elements (LLE) in pyroxene have been interpreted as evidence for the degassing of magmatic water, on the basis of the soluble behavior of these elements in hydrothermal fluids. We provide ion microprobe analyses of LLE in pyroxene in the Zagami and Shergotty martian basalts, complemented by detailed electron microprobe analyses and major-element X-ray maps, to independently verify the zoning of LLE and its relationship to texture and major-element variations. Our results corroborate previous results; specifically, that Li concentrations are lower in rims than cores of Shergotty and Zagami pyroxene. In contrast, we see no evidence for a core-to-rim decrease in B. In the absence of further data, we interpret the decrease in Li as reflecting either loss after crystallization of pyroxene cores, consistent with magmatic degassing, or the diffusive preferential loss of Li from pyroxene rims, possibly as a result of shock. Because the partitioning behavior of Li between hydrous fluid, minerals, and melt under relevant conditions of pressure, temperature, and melt composition is unknown, the viability of the water degassing hypothesis depends on experiments establishing the compatibility of Li in hydrous fluid associated with martian basaltic melt and the incompatibility of Li in pyroxene at elevated pressures.     

Reference Minerals for the Microanalysis of Light Elements

The quantitative determination of light element concentrations in geological specimens represents a major analytical challenge as the electron probe is generally not suited to this task. With the development of new in situ analytical techniques, and in particular the increasing use of secondary ion mass spectrometry, the routine determination of Li, Be and B contents has become a realistic goal. However, a major obstacle to the development of this research field is the critical dependence of SIMS on the availability of well characterized, homogeneous reference materials that are closely matched in matrix (composition and structure) to the sample being studied. Here we report the first results from a suite of large, gem crystals which cover a broad spectrum of minerals in which light elements are major constituents. We have characterized these materials using both in situ and wet chemical techniques. The samples described here are intended for distribution to geochemical laboratories active in the study of light elements. Further work is needed before reference values for these materials can be finalized, but the availability of this suite of materials represents a major step toward the routine analysis of the light element contents of geological specimens.     

Determination of Lithium, Beryllium and Boron at Trace Levels by Laser Ablation-Inductively Coupled Plasma-Sector Field Mass Spectrometry

The analytical capabilities of laser ablation (LA)-ICP-MS in determining Li, Be and B at trace levels in geological samples have been tested on a series of glass reference materials and natural samples. The LA-ICP-MS instrument used consisted of a sector-field ICP-MS coupled with a laser ablation microprobe operating at either 266 or 213 nm wavelength. Reference glasses from NIST (SRM 612, 614 and 616) and MPI-DING (KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, T1-G and ATHO-G) were selected to develop the analytical method and to assess the best instrumental configuration. A series of calcic amphiboles with different Li, Be and B concentrations were also analysed using both LA-ICP-MS and SIMS to test the applicability of the method to natural minerals. Results indicated that with a spot size of 40 μm the agreement between measured and reference values of Li, Be and B is generally better than 10% for NIST SRM 612 and 20% for NIST SRM 614. Average reproducibility at the 2s level was 10% for Li, 20% for Be and 15% for B. Limits of detection were approximately 100 ng g^-1 for Be and B and 200 ng g^-1 for Li. These results were confirmed by analyses carried out on natural amphiboles and compared well in terms of precision and accuracy with those commonly achieved by SIMS.     

冀东迁西—迁安地区紫苏花岗岩的地球化学特征及其成因

本文根据地质和地球化学的研究提出本区紫苏花岗岩主要是由英云闪长质、花岗闪长质岩浆侵位之后经麻粒岩相变质而形成的。根据地球化学特征,本区的紫苏花岗岩可分为大离子亲石元素亏损的北区(太平寨—三屯营)和大离子亲石元素较富集的南区(水厂—松汀),它们的地球化学差异反映了其形成时构造条件的不同。     

乌兰图嘎富锗煤中微量元素在不同密度级煤中的分布特征

煤系关键金属的开发利用对于缓解我国战略性矿产资源紧缺具有重要意义。内蒙古胜利煤田乌兰图嘎低阶煤中除富集关键金属Ge以外,同时富集有害元素Be、F、As、Hg、Sb和W,出于对关键金属的提取利用及环境保护2个方面考虑,须对研究区煤炭进行洗选处理。基于前期研究认识,浮选对于乌兰图嘎煤中As、Sb和W脱除效果相对较好,对于F和Hg的脱除效果较差,基于此,采用浮沉实验(重选法)以及XRD、XRF、SEM-EDS和EMPA等实验方法和测试手段,研究关键金属Ge以及Be、F、As、Hg等有害元素在不同密度级煤中的分布特征,结果表明:(1) 乌兰图嘎煤中矿物主要包括石膏、石英、黄铁矿、高岭石等,矿物含量随煤密度级增大而增加,电子探针分析结果表明,Co、As、Sb和Hg赋存在黄铁矿中。(2) 经过重选,低密度精煤中Ge元素富集,表明Ge主要以有机态存在,Be、F、As等可能与有机质相关,或者赋存在嵌布于有机质中的微细粒矿物中,煤中Hg和大部分亲石性元素在高密度级煤中含量较高,表明其赋存在矿物中。(3) 重选对于Hg元素的脱除效果较好,对Be、F、As和一些亲硫或亲铁性元素浮选脱除效果优于重选。建议乌兰图嘎低阶煤使用重选?浮选联合脱除法进行有害元素的脱除。      

The Geochemistry of Scapolite: Part II. Trace Elements, Petrology, and General Geochemistry

Fifty scapolites have been analysed spectrographically for numerouselements. Average concentrations (p.p.m.) were as follows: B25, Be 9–3, Ga 33, Ti 82, Li 56, Cu 4–4, Zr 59,Mn 57, Sr 1,800, Pb 45, Ba 120, Rb 20. The following were seldomor never detected: Cr, Ni, Co, Mo, Sn, V, Sc, Ag, Y, La. Themajor elements Ca, Na, K were also determined. The distributionof the trace elements can be explained by isomorphous substitution,but no detailed correlation of trace elements with each otheror with major elements was found. Refractive indices were determined and the relation betweenaverage index and per cent Me was examined: correlation waspoor, which may in part be attributed to analytical error. Examination of scapolite parageneses shows that scapolite characteristicallyoccurs in the upper amphibolite facies or the pyroxene hornfelsfacies: it is not restricted to these and may occur in any faciesfrom zeolitic to granulitic and in any hornfels facies. Theelements generally concentrated in scapolite include Ca, Na,C, Cl, S, H, B, Be, Li, Sr, Pb. The presence of C, Cl, S, Htestify to genesis in the presence of high partial pressureof CO₂, Cl₂, SO₃, H₂O (or related compounds), that is in pneumatolytic,pegmatitic, or hydrothermal environments. The concentrationof B, Be, Li can also be attributed to these conditions. The source of the elements concentrated in scapolite must inpart be common rocks. In a limited contact zone, the nearbymagma supplied some elements, but where regional scapolitizationhas taken place the presence of magma is less clear. Many commonrocks or rock series contain all the necessary constituents,but some particular conjunction of conditions is necessary forscapolite to form, or it would be more common.     

Volatile (S,Cl and F) and fluid mobile trace element compositions in melt inclusions: implications for variable fluid sources across the Kamchatka arc

Volatile element, major and trace element compositions were measured in glass inclusions in olivine from samples across the Kamchatka arc. Glasses were analyzed in reheated melt inclusions by electron microprobe for major elements, S and Cl, trace elements and F were determined by SIMS. Volatile element–trace element ratios correlated with fluid-mobile elements (B, Li) suggesting successive changes and three distinct fluid compositions with increasing slab depth. The Eastern Volcanic arc Front (EVF) was dominated by fluid highly enriched in B, Cl and chalcophile elements and also LILE (U, Th, Ba, Pb), F, S and LREE (La, Ce). This arc-front fluid contributed less to magmas from the central volcanic zone and was not involved in back arc magmatism. The Central Kamchatka Depression (CKD) was dominated by a second fluid enriched in S and U, showing the highest S/K₂O and U/Th ratios. Additionally this fluid was unusually enriched in ⁸⁷Sr and ¹⁸O. In the back arc Sredinny Ridge (SR) a third fluid was observed, highly enriched in F, Li, and Be as well as LILE and LREE. We argue from the decoupling of B and Li that dehydration of different water-rich minerals at different depths explains the presence of different fluids across the Kamchatka arc. In the arc front, fluids were derived from amphibole and serpentine dehydration and probably were water-rich, low in silica and high in B, LILE, sulfur and chlorine. Large amounts of water produced high degrees of melting below the EVF and CKD. Fluids below the CKD were released at a depth between 100 and 200 km due to dehydration of lawsonite and phengite and probably were poorer in water and richer in silica. Fluids released at high pressure conditions below the back arc (SR) probably were much denser and dissolved significant amounts of silicate minerals, and potentially carried high amounts of LILE and HFSE. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sc- and REE-bearing ixiolite and associated minerals from the Sosedka pegmatite vein in the Malkhan pegmatite field, central Transbaikal region

Composition and localization of REE mineralization in miarolitic pegmatites and its role in the pegmatite formation were studied at the Malkhan gem deposit (jewel-quality tourmaline, morganite, danburite, and hambergite) in the central Transbaikal region. The chemical composition of Ti-, Ta-, Nb- and REE-bearing minerals, their relationships with rock-forming and accessory minerals indicate that two geochemically specialized stages of pegmatite formation are distinguished. The early stage gave rise to the crystallization of quartz-feldspar aggregates including K-feldspar block zone with Sc and REE mineralization. The rare-metal (Li, Cs, F, B, Be) albite-lepidolite-cleavelandite complex with pockets of gem mineralization was formed at the late stage.     

Trace elements in minerals as indicators of the evolution of alkaline ultrabasic dike series: LA-ICP-MS data for the magmatic provinces of northeastern Fennoscandia and Germany

In this paper we report the results of the analysis of rare earth (REE), large-ion lithophile (LILE), and high field strength (HFSE) elements in minerals from the alkaline lamprophyre dikes of the Kola region and the Kaiserstuhl province by the local method of laser ablation inductively coupled plasma mass spectrometry. The contents of Y, Li, Rb, Ba, Th, U, Ta, Nb, Sr, Hf, Zr, Pb, Be, Sc, V, Cr, Ni, Co, Cu, Zn, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu were measured in olivine, melilite, clinopyroxene, amphibole, phlogopite, nepheline, apatite, perovskite, and the host fine-grained groundmass. The obtained data on trace element partitioning among the mineral phases of the alkaline ultrabasic rocks of the dike series indicate that the main mineral hosts for the HFSEs and REEs in alkaline picrites, olivine melanephelinites, and melilitites are perovskite and apatite comprising more than 90% of these elements. Among major rock-forming minerals, melilite, clinopyroxene, and highly magnesian amphibole make a significant contribution to the balance of REEs during the evolution of melanephelinite melts. The partition coefficients of Ni, Co, Cu, Zn, Sc, V, Cr, Ga, Y, Li, Rb, Ba, Th, U, Ta, Nb, Sr, Hf, Zr, Pb, Be, and all of the REEs were calculated for olivine, clinopyroxene, amphibole, phlogopite, nepheline, perovskite, and apatite on the basis of mineral/groundmass ratios. Variations in the composition of complex zoned clinopyroxene phenocrysts reflect the conditions of polybaric crystallization of melanephelinite melt, which began when the magmas arrived at the base of the lower crust and continued during the whole period of their ascent to the surface. The formation of green cores in clinopyroxene is an indicator of mixing between primary melanephelinite melts and phonolite magmas under upper mantle conditions. The estimation of the composition of primary melts for the rocks of the alkaline ultrabasic series of the Kola province indicated a single primary magma for the whole series. This magma produced pyroxene cumulates and complementary melilitolites, foidolites, and nepheline syenites.     

The Geochemistry of Scapolite Part II. Trace Elements, Petrology, and General Geochemistry

Fifty scapolites have been analysed spectrographically for numerouselements. Average concentrations (p.p.m.) were as follows: B25, Be 9-3, Ga 33, Ti 82, Li 56, Cu 4-4, Zr 59, Mn 57, Sr 1,800,Pb 45, Ba 120, Rb 20. The following were seldom or never detected:Cr, Ni, Co, Mo, Sn, V, Sc, Ag, Y, La. The major elements Ca,Na, K were also determined. The distribution of the trace elementscan be explained by isomorphous substitution, but no detailedcorrelation of trace elements with each other or with majorelements was found. Refractive indices were determined and the relation betweenaverage index and per cent Me was examined: correlation waspoor, which may in part be attributed to analytical error. Examination of scapolite parageneses shows that scapolite characteristicallyoccurs in the upper amphibolite facies or the pyroxene hornfelsfacies: it is not restricted to these and may occur in any faciesfrom zeolitic to granulitic and in any hornfels facies. Theelements generally concentrated in scapolite include Ca, Na,C, Cl, S, H, B, Be, Li, Sr, Pb. The presence of C, Cl, S, Htestify to genesis in the presence of high partial pressureof CO₂, Cl₂, SO₃, H₂O (or related compounds), that is in pneumatolytic,pegmatitic, or hydrothermal environments. The concentrationof B, Be, Li can also be attributed to these conditions. The source of the elements concentrated in scapolite must inpart be common rocks. In a limited contact zone, the nearbymagma supplied some elements, but where regional scapolitizationhas taken place the presence of magma is less clear. Many commonrocks or rock series contain all the necessary constituents,but some particular conjunction of conditions is necessary forscapolite to form, or it would be more common.     

Lithium, boron and chlorine as tracers for metasomatism in high-pressure metamorphic rocks: a case study from Syros (Greece)

High-pressure metamorphic (HPM) rocks (derived from igneous protoliths) and their metasomatised rinds from the island of Syros (Greece) were analysed for their B and Cl whole-rock abundances and their H₂O content by prompt-gamma neutron-activation analysis (PGNAA) and for their Li and Be whole-rock abundances by ICP-OES. In the HPM rocks, B?/Be and Cl?/Be ratios correlate with H₂O contents and appear to be controlled by extraction of B and Cl during dehydration and prograde metamorphism. In contrast, samples of the metasomatised rinds show no such correlation. B?/Be ratios in the rinds are solely governed by the presence or absence of tourmaline, and Cl?/Be ratios vary significantly, possibly related to fluid inclusions. Li/Be ratios do not correlate with H₂O contents in the HPM rocks, which may in part be explained by a conservative behaviour of Li during dehydration. However, Li abundances exceed the vast majority of published values for Li abundances in fresh, altered, or differentiated oceanic igneous rocks and presumably result from metasomatic enrichment of Li. High Li concentrations and highly elevated Li/Be ratios in most metasomatised samples demonstrate an enrichment of Li in the Syros HP mélange during fluid infiltration. This study suggests that B and Cl abundances of HPM meta-igneous rocks can be used to trace prograde dehydration, while Li concentrations seem to be more sensitive for retrograde metasomatic processes in such lithologies.     

华南某地浸染型锯、钽花岗岩原生晕找矿的探讨

勘查地球化学作为一种找矿手段在寻找硫化多金属矿床方面日臻完善,应用愈益广泛并取得了令人满意的效果。然而对于浸染型铌、钽花岗岩矿床的地球化学找矿论述较少。事实上,此类矿床Nb、Ta矿物的颗粒细小,肉眼无法看到,除直观的地球化学找矿标志外,岩石地球化学找矿法和重砂法(即矿物晕法)是寻找和评价这类矿床的重要手段。     

Light lithophile elements in pyroxenes of Northwest Africa (NWA) 817 and other Martian meteorites: Implications for water in Martian magmas

Zoning patterns of light lithophile elements (the LLE: Li, Be, and B) in pyroxenes of some Martian basaltic meteorites have been used to suggest that the parent basalts were saturated in water and exsolved an aqueous fluid phase. Here, we examine LLE zoning in the augites of a quickly cooled Martian basalt that was not water-saturated—the Northwest Africa (NWA) 817 nakhlite. Analyses for LLE were by secondary ion mass spectrometry (SIMS), supported by EMP analyses of major and minor elements. In NWA 817, zoning of Be and B is consistent with igneous fractionations while Li abundances are effectively constant across wide ranges in abundance of other incompatible elements (Be, B, Ti, and Fe*). The lack of strong zoning in Li can be ascribed to intracrystalline diffusion, despite the rapid cooling of NWA 817. Most other nakhlites, notably Nakhla and Lafayette, cooled more slowly than did NWA 817 [Treiman, A.H., 2005. The nakhlite Martian meteorites: augite-rich igneous rock from Mars. Chem. Erde65, 203-270]. In them Li abundances are constant across augite, as are abundances of other elements. In Nakhla pyroxenes, all the LLE have effectively constant abundances across significant ranges in Fe* and Ti abundance. Lafayette is more equilibrated still, and shows constant abundances of LLE and nearly constant Fe*. A pyroxene in the NWA480 shergottite has constant Li abundances, and was interpreted to represent mineral fractionation coupled with exsolution of aqueous fluid. A simple quantitative model of this process requires that the partitioning of Li between basalt and aqueous fluid, ^LiD_aq/bas, be 15 times larger than its experimentally determined value. Thus, its seems unlikely that the Li zoning pattern in NWA480 augite represents exsolution of aqueous fluid. Late igneous or sub-solidus diffusion seems more likely as is suggested by Li isotopic studies [Beck, P., Chaussidon, M., Barrat, J.-A., Gillet, Ph., Bohn, M., 2005. An ion-microprobe study of lithium isotopes behavior in nakhlites. Meteorit. Planet. Sci.40, Abstract #5118; Beck, P., Chaussidon, M., Barrat, J.-A., Gillet, Ph., Bohn, M., 2006. Diffusion induced Li isotopic fractionation during the cooling of magmatic rocks: the case of pyroxene phenocrysts from nakhlite meteorites. Geochim. Cosmochim. Acta70, in press]. Pyroxenes of the Shergotty and Zagami meteorites have nearly constant abundances of B, and Li that decreases core-to-rim. Applying the quantitative model to the constant B in these pyroxenes requires that ^BD_aq/bas be 25 times larger than experimentally constrained values. Li abundances in pigeonite can be fit by the model of crystal fractionation and fluid loss, but only if ^LiD_aq/bas is 30 times the experimentally constrained value. The Li abundance pattern in augite cannot be modeled by simple fractionation, suggesting some strong crystal-composition effects. Thus, Li and B distributions in Shergotty and Zagami pyroxenes cannot be explained by igneous fractionation and exsolution of aqueous vapor. Intracrystalline diffusion, complete for B and incomplete for Li, seems more consistent with the observed zoning patterns.