Kiglapait Geochemistry II: Petrography

The mode of the Kiglapait intrusion carries 73 per cent feldspar,but average rocks near the base of the Upper Zone contain aslittle as 48 per cent feldspar. Olivine remained stable throughoutthe crystallization, but was locally suppressed by abundantcrystallization of augite and titano-magnetite. Red biotiteoccurs as rims on Fe–Ti oxide minerals and is probablyfluorine oxybiotite; its frequently similar occurrence in troctoliticrocks may, perversely, indicate dry magmas rather than dampones. Excluded modal components follow Rayleigh fractionation behaviour;their presence in trace amount permits estimation of residualporosity in the Lower Zone. This porosity diminishes directlywith accumulation rate from 0.14 to 0.03 over the first 80 percent of crystallization history. The saturation ratio of excludedmodal components is a well-behaved function of fraction solidified,and implies that the decrease in porosity continues above the80 per cent solidified level. The saturation ratio links withbulk composition, porosity, and F_L, allowing one of these parametersto be estimated from the others. The cumulus arrival of apatite is abrupt, but the earlier arrivalsof augite, oxide minerals, and sulfide each occur over an interval,followed by an interval of overproduction. This behaviour isattributed to feedback on concentration gradients generatedby a long history of plagioclase + olivine extraction, in theabsence of perfect stirring. Diffusion plays a role in the differentiationof large, slowly cooled magma systems because radial mixingby convection is inefficient. Inherited potential supersaturationis the inevitable result. This leads to modal irregularities,and to crystallization effectively on metastable extensionsof field boundaries. The track of the liquid in the Lower Zone is closely parallelto that in the system Fo–Di–An, but offset fromit by the combined effects of Ab and P (toward plagioclase)and Fa (away from plagioclase). The latter effect is important,with the result that the shedding of plagioclase by an ascendingmagma will be much less marked than predicted from iron-freeexperimental systems.     

Kiglapait Geochemistry IV: The Major Elements

The summed bulk composition of the Kiglapait intrusion is SiO₂ 47.46 (31). TiO₂ 0.81 (20), Al₂O₃ 19.46 (48), Fe₂O₃ 1.91 (46), FeO 9.36 (36), MnO 0.15 (01). MgO 8.04 (21), CaO 9.27 (46). Na₂O 3.13 (05), K₂O 0.22 (01), P₂O₅, 0.09 (01), and BaO 0.02 (01). total 99.98 wt% (estimated standard deviations of the last two decimals in parentheses). The CIPW norm isap 0.34, mt 2.78, il 1.52, or 1.11, ab 26.27, an 38.64, (fsp 66.47), di 5.38, hy 2.45, ol 21.58. Molar X_An is 0.58; molar x_fo is 0.65.The variation curves for oxides in calculated liquids are explained in detail by the petrographic variations shown in earlier papers of this series. The Kiglapait FeO + MnO:MgO:Alkalies (FMA) trend reaches higher iron concentrations than the Skaergaard liquid and constitutes a new limiting case of the Fenner trend of fractional crystallization, implying low oxygen fugacity and silica activity. The end-stage Kiglapait ferrosyenite lies on the FeO + MnO-Alkalies sideline, being essentially devoid of MgO.Except in$\text{K and K}\text{Rb.}$the Kiglapait composition is the same within experimental error as the chilled margin of the nearby Hettasch intrusion (BERG, 1980.), but slight systematic differences show that the Hettasch composition is slightly more fractionated or represents a smaller fraction of melting at the source. Both are low-augite troctolite compositions, and they require troctolitic parent liquids. Such liquids are related to common augite-rich basalts by addition of spinel, and they imply exhaustion of clinopyroxene in the source. Except for their low augite and high Al₂O₃, the Kiglapait and Hettasch compositions resemble modern MORB and suggest a depleted source.     

Kiglapait Geochemistry I: Systematics, Sampling, and Density

The Kiglapait intrusion affords many opportunities for evaluatingplutonic fractionation processes. Estimates of boundary conditionsinclude emplacement of anhydrous high alumina basaltic magmaat 4 kbar and about 1250 °C, initial crystallization nearthe WM buffer, and fractionation to Mg-free ferrosyenite whichcrystallized at 960°C, somewhat above the WM buffer. Thelast ferrosyenites represent fractionation to 0.01 per centof the initial volume. Plagioclase varies from An₆₇ to An₁₀, olivine from Fo₆₉ to Fo₀,and augite from En₇₃ to En₀. The specific gravity of the intrusionis 2.93, varying between 2.87 and 3.18 on smoothed models. Crystals accumulated chiefly at the floor. As they did so, themagma depth decreased as the square root of the volume fractionof liquid. The volume fraction solidified was roughly proportionalto time. Cooling was slower than the t relation because of hotsurroundings on one side. The crystallization time was about10⁶ yr, and the average accumulation rate was about 1 cm/yr.Average crystal concentrations of 3–300 ppm are impliedfor the nucleation zone. The cooling rate corresponds to crystallizationof 2 x 10⁷ kg/yr per km² roof area, about 550 times slower thana lava lake. Calculated liquid densities range from 2.67 to 2.88 g/cm³ athigh temperatures. Feldspar almost surely did not sink in themagma, but nevertheless it accumulated mainly on the floor.Cooperative sinking with mafics as proposed by Coats, combinedwith oscillatory nucleation as proposed by Wager, may accountfor this paradox. Oscillatory nucleation leading to feldspar-supersaturatedliquids is supported by laboratory evidence on the feldspar-likestructure of liquids and the concave-úp plagioclase liquidusin systems involving olivine. Both lines of evidence imply highpolymerization of feldspar-rich liquids, particularly in slowprocesses. Such polymerization can help to explain the genesisof primary Eu anomalies and anorthositic magmas in additionto the floor accumulation of feldspar and rhythmic layering.     

Kiglapait Mineralogy III: Olivine Compositions and Rayleigh Fractionation Models

Olivines, present throughout the layered cumulates of the KiglapaitIntrusion, record extreme iron enrichment during fractionalcrystallization. Mn is less compatible than Fe; the exchangecoefficient K_D for Mn/Fe (OL-LIQ) has values near 0.95 but theydrop to 0.7 near the Lower Zone-Upper Zone boundary. Ca is depletedby more than a factor of 30 relative to experimental valuesat 5 kbar pressure. Attempts to find a sink for Ca in the LowerZone without invoking liquid as a reactant are unconvincing,and questions of metastability arise. Cumulus olivines varysystematically to lower Fo contents with stratigraphic height.Using equilibrium values for the exchange coefficient K_D (Fe/Mg,OL-LIQ), and the observed mode of olivine and residual porosity,a Rayleigh fractionation calculation reproduces the observedLower Zone trend without recourse to multiple injections ofmagma. An anomalously Fe-rich region above the Main Ore Bandin the Upper Zone is ascribed to ponding of Fe-rich magma atthe floor of the intrusion until later, buoyant residual magmaentrained the Fe-rich residua. Such Fe-rich ponds probably accountfor the abnormal Feenrichment shown by some other Fenner-trendlayered intrusions. Summation over the observed crystal compositionsyields values of X_Mg that do not represent the equilibrium liquid,but that reduce to it by a simple multiplier p = 0.78. Thisresult means that if K_D is known, the high-temperature, liquidusolivine compositions can be retrieved, or vice versa. Becausethe observed olivine compositions are supported by realisticforward models, there is no need to invoke evolved boundary-layerliquids to explain the in situ crystallization of Kiglapaitcumulates. Classical cumulate theory suffices. KEY WORDS: olivine; Rayleigh fractionation; Kiglapait Intrusion; cumulative theory     

Kiglapait geochemistry V: Strontium

The Kiglapait intrusion contains 330 ppm Sr and has $\text{Sr}\text{Ca}\text{= 5 × 10}{}^{\mathrm{?3}}$ and $\text{Rb}\text{Sr}\text{= 3 × 10}{}^{\mathrm{?3}}$, as determined by summation over the Layered Group of the intrusion. Wholerocks in the Lower Zone contain 403 F_L^0.141 ppm Sr, where F_L is the fraction of liquid remaining; Sr drops to 180 ppm at the peak of augite production (F_L = 0.11) and rises to a maximum of 430 ppm in the Upper Zone before decreasing to 172 ppm at the end of crystallization. Feldspars in the Lower Zone contain 532 F_L^0.090 ppm Sr, increasing to 680 ppm in the Upper Zone before decreasing to 310 ppm at the end. Clinopyroxenes contain 15 to 30 ppm Sr and have a mineral-melt distribution coefficient D = 0.06 except near the top of the intrusion where D = 0.10.The calculated feldspar-liquid distribution coefficient has an average value near 1.75 but shows four distinct trends when plotted against X_An of feldspar. The first two of these are strongly correlated with the modal augite content of the liquid, on average by the relation D = 1.4 + 0.02 Aug^L. The third (decreasing) trend is due to co-crystallization of apatite, and the fourth (increasing) trend can best be attributed to a triclinic-monoclinic symmetry change in the feldspar at An₂₆, 1030°C. The compound feldspar-liquid distribution coefficient K_D for $\text{Sr}\text{Ca}$ bears out these deductions in detail and yields ΔG_r for the Sr-Ca exchange ranging from nearly zero at the base of the Lower Zone to ?26 kJ/gramatom at the end of crystallization. The compound feldspar-liquid distribution coefficient K_D for $\text{Rb}\text{Sr}$ varies from 0.3 in the Lower Zone to 1.1 at the end of crystallization.The ratio $\text{Ca}{}^{\mathrm{F}}\text{Ca}{}^{\mathrm{L}}$ is about 1.45 for troctolitic liquids containing 5% augite, for which K_D (Sr-Ca) = 1.0 and D_Ca = D_Sr. For common basaltic liquids containing 20% augite, the Kiglapait data predict $\text{solSr}{}^{\mathrm{F}}\text{Sr}{}^{\mathrm{L}}\text{= 1.8}$, as commonly found elsewhere. The strong dependence of D_sr on augite content of the liquid illuminates the role of liquid composition and structure in determining the feldspar-liquid distribution coefficient. Conversely, a discontinuous change in the trend of D_Sr when apatite arrives shows that the effect is due to apatite crystallization itself, not to the continuous variation of the liquid as it becomes enriched in apatite component.     

Kiglapait geochemistry VI: Oxygen isotopes

The Kiglapait layered intrusion is the first major intrusion found to have all whole rock and calculated liquid δ¹⁸O values close to a normal uncontaminated gabbroic value of 6.0. The intrusion experienced no detectable oxygen isotope exchange with its surrounding rocks and cooling of the magma was conductive. The δ¹⁸O values of average whole rocks vary smoothly from 6.0 at the base of the Lower Zone to 6.3 at the top of the Upper Zone. The calculated liquid δ¹⁸O values lie practically superimposed on the whole rock trend. The whole-rock data and the modelled δ¹⁸O of the magma and cumulates rigorously demonstrate that the effect of incoming cumulus phases such as magnetite and augite on the δ¹⁸O of the liquid and rocks during fractional crystallization is negligible. The cancelling effects of complementary modal variations among the mafic mineral phases and feldspar, keep the δ¹⁸O of the whole rocks constant to within ±0.1 %.. The minor change in δ¹⁸O that does occur with fractionation is consistent with the enrichment of residual liquids in feldspar component and the increasing fractionation factor δ Liquid-Fsp with falling temperature.The δ¹⁸O values of the country rocks bracket the estimated δ¹⁸O of the Kiglapait magma. Modelling with oxygen isotopes indicates that contamination of the intrusion, indicated by published radiogenic Sr and Nd isotopic data, was minor. The most probable contaminant had δ¹⁸O?7.7 and the contamination most likely occurred at >99% solidified. Subsolidus oxygen isotope exchange with an external source appears to have been very minor.     

Thermodynamics Phase Equilibria for the Salt- Water System of Potassium and Rubidium Ions

正1 Introduction Brines,containing a variety of useful components,such as alkali metal(IA),alkaline earth metal(type IIA),halogen elements(such as VIIA),are naturally occurring complex electrolyte solution.Although rubidium is not the main component of the brine,while in the brine exploiting process,rubidium ion is continuously enriched in the     

Preparation of Ammonium Tungstophosphate-Calcium Alginate Composite Adsorbent and the Separation of Rubidium and Potassium

正As a kind of rare metals,rubidium is often used to prepare special glass,photomultiplier tubes,thermoelectric converter,organic catalysts and antidepressants.Rubidium forms no minerals of its own,hence,it often coexists with     

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.     

Kiglapait Mineralogy I: Apatite, Biotite, and Volatiles

Electron microprobe analyses show that Upper Zone apatites inthe Kiglapait intrusion are fluorine rich and contain minorchlorine and hydroxyl (calculated). Apatite from the Outer BorderZone has a higher Cl content. The refractive indices of UZ apatites have the following ranges: = 1.6345–1.6379, = 1.6326–1.6352, and B = 0.0020–0.0028.The birefringence is low for apatites with these refractiveindices. Some Outer and Upper Border Zone apatites have higherindices of refraction and normal birefringence. Fractional crystallization of the basaltic Kiglapait magma producedcumulus apatite beginning at the 94 per cent solidified levelwhen P₂O₅ reached saturation in the liquid. The amounts of P₂O₅and modal apatite decreased gradually from the 94 per cent tothe 99.99 per cent solidified level as the liquid was depletedin P₂O₅. F and Cl appear to be equally partitioned between theliquid and apatite because no fractionation trends are notedbetween the two halogens. There is a slight decrease in thecalculated ratio OH/F in apatite which suggests possible depletionof OH in the liquid with fractionation. Kiglapait apatites appear to be stoichiometric, based on microprobechemistry, refractive index, and unit cell dimensions. However,infrared absorption analyses show no detectable water, whichleaves approximately 11 per cent of the monovalent anion siteunaccounted for. Anion deficiencies in apatites from low-H₂Oenvironments may be explained either by substitution of O forF, or domains of tetracalcium phosphate. Non-cumulus biotite occurs in minor quantities in the intrusion.Electron microprobe analyses of Upper Zone biotites show thatthey contain an average (by weight) pf 0.4 per cent F, 0.07per cent Cl, and 4.0 per cent H₂O (calculated). The volatile chemistry of the Kiglapait intrusion is calculatedfrom apatite and biotite chemistry. The intrusion contains anestimated 900 ppm P₂O₅, 166 ppm F, and 12 ppm Cl. There is amaximum of 68 ppm H₂O using calculated H₂O from microprobe data,or a minimum of 8 ppm using H₂O from infrared analysis. It isproposed that the anhydrous basaltic Kiglapait magma was a secondpartial melt of amphibole-bearing mantle rock.     

Kiglapait Mineralogy II: Fe-Ti Oxide Minerals and the Activities of Oxygen and Silica

Cumulus titanomagnetite and subordinate ilmenite first appearin the Upper Zone of the Kiglapait intrusion. They arrive graduallyand then reach abnormal abundances before falling to a sustainedcotectic mode near seven volume per-cent. The most Ti-rich titanomagnetites(to Usp ₆₆) are preserved in ore bands (layers) which solidifiedby adcumulus growth leading to the complete expulsion of interstitialsilicate liquid. Analyses from three of these ore bands, appliedto the solution model of Lindsley (1977), form a single lineararray in f_o2 versus 1/T ?K, with log f_o2 = (–28,283 ?89)/T + 11.03 ? 0.25. This array implies log f_o2 = –9.65at 1094 ?C, the model temperature of the Main Ore Band, consistentwith primary mineral compositions Ilm₈₉, Usp₇₉ and a weightmode of 18 per cent ilmenite. Silicate rocks yield another linear array, i.e. log f_o2 = (–37,910? 102)/T + 22.57 ? 0.61. This array is ascribed to closure ofsubsolidus reactions from initial compositions near Usp_79–80Ilm₉₀. The center of gravity of the data falling on this arraysuggests a primary mode of about 50 per cent ilmenite for thesilicate rocks, implying somewhat more reducing conditions ofcrystallization than for the ore bands. The modal overproductionrepresented by the ore bands is attributed to super-saturationin oxygen, which is demonstrated by the Al-depleted compositionsof titanomagnetite in ore bands, by direct evidence for elevatedf_o2 at the top of the Main Ore Band, and by abnormally magnesiansilicate mineral compositions in and near the ore bands. The primary titanomagnetite composition for average rocks isestimated at Usp₈₀ for the base, and Usp₇₃ for the top of theUpper Zone, from rock and mineral chemistry and observed textures.The idealized magma path for the Upper Zone runs from (T andlog f_o2) 1154 ?C, –9.0 to 960 ?C, –12.2. The orebands lie above this path and are interpreted as lying on themetastable extension of the Lower Zone path, which originatesat 1250 ?C, –8.1, on the WM buffer at 4 kbar total pressure. Silica activity is estimated from mineral compositions nearthe ore bands as applied to the FMQ equilibrium, and mappedfor the Lower Zone by an adjustment downward from the En-Fo-Silequilibrium, with resultant values near 0.55 relative to quartz= 1.0. The logarithmic oxygen/silica activity ratio (OSAR) coincideswith that of the Skaergaard intrusion in the Lower Zones. TheSkaergaard OSAR is offset downward from the Kiglapait trendduring MZ time, and remains below it at the end of crystallization.The more highly silicated Skaergaard magma was initially moreoxidized than the Kiglapait magma, but this relation was reversedafter the loss of olivine in the Skaergaard intrusion, as couldhave been predicted from theory and the mineralogy of the twointrusions.     

The Ordovician chondrite from Brunflo, central Sweden: III. Geochemistry of terrestrial alteration

The fossil H chondrite Brunflo, found in a slab of Ordovician limestone from central Sweden, is pervasively altered to an assemblage dominated by calcite and barite. The meteorite is surrounded by a 15–20 cm wide zone of lighter colors than the unaffected limestone due to dissolution of hematite. Here we present detailed geochemical analyses of two meteorite samples, 14 limestone samples at distances from 0 to 29 cm along two profiles from the meteorite, and a reference sample of Brunflo limestone. Element concentrations in Brunflo and surrounding bleached limestone have been strongly disturbed during two stages of alteration (early oxygenated and deep burial). In the meteorite, the Ni/Co ratio has changed from an initial value of 20 to 0.8 and redox sensitive elements like V, As, Mo, Re and U are strongly enriched. The sulfur isotope composition of barite from Brunflo (δ³⁴S=+35‰) indicates initial loss of meteoritic sulfide, followed by later accumulation of sea water sulfate as barite. During deep burial under more reducing conditions, reduction processes supported by an externally derived reductant possibly derived from alum shale underlying the limestone, were largely responsible for the observed redox phenomena. In spite of massive redistribution of many elements, concentrations of Pt, Ir and Au remain at chondritic levels. The geochemistry and mineralogy of alteration determined for Brunflo are similar to those in “reduction spots” in red beds, where accumulation of a similar suite of elements (except Mo, Re) occurred as a result of isolated reduction activity.     

Preface to Owen P. Bricker III Special Issue of Aquatic Geochemistry

This special volume of aquatic geochemistry is dedicated to the memory of Owen Peterson Bricker III (1936–2011) and serves as a tribute to his life and career. Owen had a distinguished and productive research career in both academics at Johns Hopkins University (Fig. 1) and as a public servant with the Maryland Geological Survey, the US Environmental Protection Agency, and the US Geological Survey. He was a pioneer and leader in aqueous geochemistry, who applied a study approach that quantified mineral weathering reactions and equilibrium thermodynamic relations to better understand the chemical evolution of stream water in small watersheds. He will be especially remembered for his efforts to establish rigorous field studies in small catchments around the United States as a means of quantifying the sources of acid-neutralizing capacity that affect the chemical status and biological health of natural waters.

Isotopic Studies of Processes in Mafic Magma Chambers: I. The Kiglapait Intrusion, Labrador

The initial Nd and Sr isotopic ratios of cumulate rocks andminerals of the Kiglapait intrusion are pertinent as indicatorsof the processes that affected the Kiglapair magma while itwas resident in the crust. A Sm–Nd mineral isochron indicatesthat the crystallization age of the intrusion is 1305?22 millionyears. The initial _Nd values range from—1?6 in the LowerZone to 6 in the Upper Zone and correlate with the anorthitecontent of plagioclase. The initial ₈₇Sr/⁸⁶Sr ratios are 0.70407to 0.70433 in the Lower Zone, and increase monotonically up-section(decreasing plagioclase anorthite content) to 0.7068 in theUpper Zone. These variations are attributed to assimilationof roof rock concurrently with crystallization. It is evidentthat replenishment of the chamber with uncontaminated magmawas important during the accumulation of the lower zone rocks,but did not occurduring crystallization of the Upper Zone. Amathematical model relating isotope ratio shifts to the relativerates of crystallization, assimilation, and replenishment ispresented. It is estimated that the rate of assimilation wasbetween 0.01 and 0.04 of the crystallization rate, and thatduring the accumulation of the Lower Zone, the rate of replenishmentwas about half of the crystallization rate. A formulation for‘assimilation efficiency’is presented that relatedthe actual amount of assimilation (determined from the isotopedata) to the thermodynamic maximum allowable amount. The assimilationefficiency of the Kiglapait intrusion is not tightly constrained,but appears to be of the order of 0.01 near the end of crystallizationand perhaps as high as 0.07 near the beginning. Further quantitativeestimates of assimilation efficiency in different intrusionsemplaced under different conditions may aid in understandingassimilation mechanisms and in assessing the role of assimilationin magmatic evolution in general. Many layered intrusions studiedto date have initial Nd isotope ratios close to the chondriticvalue (_Nd= 0), suggestive of mantle magma sources that are chemicallyundepleted, and thus different from the sources of mid-oceanridge basalt and island-arec basalt.     

金顶铅锌矿床地质-地球化学

金顶铅锌矿床的成矿作用发生在中－新生代沉积地层当中，且矿区内没有明显出露岩浆岩，矿体为板状，产在古新统统云龙组和下白垩统景星组的陆相碎屑岩中，但成矿并不受岩相地层控制，而受断裂和穹隆构造控制。铅同位素数据指示成矿金属主要为自地幔。硫同位素具有δ^34S黄铁矿＞δ^34S闪锌矿＞δ^34S方铅矿的趋势，硫主要来自地壳，闪锌矿及有关脉石矿物（石英，天青石，方解石和硬石膏）的流体包裹体研究表明，均一温度主要在110－150℃，盐度ω（NaCleq)5.09%-19.63%，成矿压力32.5-22.6MPa，所对应的成矿深度0.9-1.5km。     

Experimental Petrology of the Kiglapait Intrusion: Cotectic Trace for the Lower Zone at 5 kbar in Graphite

The inferred crystallization history of the troctolitic LowerZone of the Kiglapait Intrusion in Labrador is tested by meltingmineral mixtures from the intrusion, made to yield the observedcrystal compositions on the cotectic trace of liquid, plagioclase,and olivine. Melting experiments were made in a piston-cylinderapparatus, using graphite capsules at 5 kbar. Lower Zone assemblagescrystallized from 1245°C, 5% normative augite in the liquid,to 1203°C, 24% normative augite in the liquid at saturationwith augite crystals. This transit is consistent with modaldata and the large volume of the Lower Zone. The 1245°Ccotectic composition matches the average Inner Border Zone composition.Quenched troctolitic liquid from the Upper Border Zone, andothers from nearby Newark Island, plot on or near our experimentalcotectic, supporting a common fractionation history. Olivine–plagioclaseintergrowths from cotectic troctolitic melt show mosaic texturesreflecting the differing barriers to nucleation of these twophases. The linear partitioning of X_Ab in plagioclase–meltyields an intercept constant K_D = 0·524 for these maficmelts. Observed subsolidus exchange of Ca between plagioclaseand olivine elucidates the loss of Ca from plutonic olivines.The bulk composition of the intrusion is revised downward inFo and An. KEY WORDS: experimental; olivine; plagioclase; Kiglapait; partitioningAbbreviations: AP, MT, IL, OR, AB, AN, DI, HY, OL, FO, NE, Q, FSP, AUG: (Oxygen) Normative components; Ap, Aug, Ilm, Ol, Pl: Phases; Ab, An, Di, Fa, Fo, Or, Wo: Phase components; also ternary endmembers; BSE: Back-scattered electron; CaTs: Calcium Tschermak's component, CaAlAlSiO₆; D: Partition coefficient; f: Fugacity; F_L: Fraction of the system present as liquid = 1 – (PCS/100); FMQ: Fayalite = magnetite + quartz buffer; IBZ: Inner Border Zone; IW: Iron = wüstite buffer; kbar: kilobar, 10⁸ pascal; K_D: Exchange coefficient; KI: Kiglapait Intrusion; L: Liquid phase; LLD: Liquid line of descent; Ma: Mega-annum, age; Myr: Mega-year, time; OLHY: Normative OL + HY; OLRAT: The ratio OLHY/(OLHY + AUG); P: Pressure; P: Phosphorus; PCS: Percent solidified (volume); SMAR: South Margin average composition; T: Temperature, °C; UBZ: Upper Border Zone; WM: Wüstite = magnetite buffer; Wo: Wollastonite component of pyroxene; X: Mole fraction; X_Mg: Molar ratio Mg/(Mg + Fe²⁺); , X_Mg(0): Initial X_Mg before MT is formed in the norm calculation; X: Coordinate, horizontal axis; Y: Coordinate, vertical axis     

Ferricretes of Sriperumbudur: Micromorphology and Geochemistry

Earlier studies on the ferricrete of Sriperumbudur Formation were focused on their types of occurrences and mode of formation. However, in the present study, an attempt is made to understand the physico-chemical changes across seven saprolite-ferricrete profiles developed over sedimentary protolith after upliftment to decipher the paleoenvironmental conditions to which the Sriperumbudur Formation was exposed and to understand the processes of ferricretisation. For this purpose, the ferricrete exposures around Sriperumbudur were surveyed and mapped for their occurrences and types of ferricretes, collected samples were examined for various physio-chemical aspects. Geochemical and petrographic studies exhibit a relatively high percentage of iron content. The Fe₂O₃ content varies from 7.71% to 14.9% followed by the higher concentration of Al₂O₃ and SiO₂ as a result of deep weathering of the Sriperumbudur beds. Other major oxides such as CaO, MgO, Na₂O, K₂O, MnO and TiO₂ show lower concentrations. The bulk X-ray diffraction of the ferricrete samples shows the occurrence of tourmaline, muscovite and magnetite. SEM analysis of the ferricrete samples exhibits solution channels and pits in the matrix, on the limonite, quartz and magnetite revealing intense chemical weathering. Petrographic studies show the occurrence of quartz in a variety of shapes, sizes and sediment sorting, cemented by iron oxides in varying stages. It also reveals iron oxide mobilization due to the alteration of ferruginous sandstone forming a hard ferricrete crust. Iron oxide cementation is due to leaching and re-cementing from the parent sedimentary rock with subsequent re-deposition of the earlier material taking place in a near shore environment and in wetter conditions after the Sriperumbudur beds were exposed since the lower Cretaceous period.     

中国铷铯资源需求展望

铷和铯是高新技术产业发展不可或缺的关键矿产,全球资源相对丰富,中国铯资源相对短缺,其安全配置需要给予高度关注,同时需要解决未来中国铷和铯需求预测的科学问题。本文通过调研,从产业链分析入手,构建了铷和铯的数据基础,并尝试使用部门需求预测法和投入产出法,对我国铷和铯的需求做出了研判。结论是国内铷和铯消费进入快速增长期, 2025年我国铯需求1000～1100 t,铷需求约10 t。届时,我国铷和铯的市场规模也将有较大膨胀。     

Geothermometry in the Kiglapait Aureole: Part II. Evaluation of Exchange Thermometry in a Well-Constrained Thermal Setting

Previous determination of a well-constrained thermal profilerepresenting peak conditions of metamorphism for the contactaureole of the Kiglapait Intrusion, Labrador, provides the basisfor critical comparative geothermometry of cation exchange thermometersapplied to mafic and ultramafic granulites. Knowledge of theshape of the profile and constraints on the temperature of theintruding magma allow calculation of cooling rates which rangefrom 150?C/m.y. at the contact to 30?C/m.y. at 2500 m from thecontact. Substitution of these rates in diffusion equationspermits discrimination between geothermometers which are eitheradequately or poorly calibrated, as well as thermometers whichare probably inappropriate for use in metamorphic terranes.Our results suggest that the two-pyroxene thermometer (Lindsley& Andersen, 1983) is accurate from 950 to 750?C. Below 750?C,both limbs of the miscibility gap require at least minor recalibration,or the projection scheme of Lindsley & Andersen (1983) requiresadjustment. Results from the cpx-ilm thermometer are erraticand imply that the solution models for pyroxene and ilmenite,as presently formulated in this thermometer, are inadequate.Results from the opx-ilm, ol-ilm, and opx-ol thermometers areinconsistent. Theoretical calculations at both high and lowtemperatures show that these three thermometers cannot giveinternally consistent results. Results from Fe-Ti oxide thermometrysuggest that these minerals are easily re-equilibrated due tocation interdiffusion between grains. However some grain pairsappear to retain compositions appropriate to peak thermal conditions.     

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.