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1.
In the Pyrenees, in association with the rotation of the Iberian plate around Europe during the Mid-Cretaceous, a Na–Ca metasomatism is recognized as a complementary record of the hydrothermal activity that led to Na-metasomatism (albitization) and talc–chlorite mineralization. It affected metasedimentary rocks as well as Hercynian granites. In situ laser ablation ICP-MS U–Pb analyses of titanite grains formed in albitites during metasomatism date the Na–Ca metasomatism between 110 and 92 Ma. The temperature of the Na–Ca metasomatism is estimated to be approximately 550 °C. Both the time constraints and temperature estimates suggest that the Na–Ca metasomatism is related to the low-P high-T North Pyrenean metamorphism.  相似文献   

2.
Geochemical responses in weathered and oxidized surface metasedimentary rocks associated with stratiform lead-zinc mineralization at Stirling Hill (6 km west of Broken Hill) are compared with the geochemical responses in fresh drill core from an equivalent lithostratigraphic section with stratiform lead-zinc mineralization at the Pinnacles Mine (8 km south of Stirling Hill). Mineralization is interpreted as being volcanic exhalative and it lies within highly metamorphosed (sillimanite grade) rocks of the Willyama Supergroup.Surface rocks were classified into groups by discriminant analysis using drill core data from the Pinnacles Mine as the initial training set. The behaviour of elements in surface rocks varies with the rock group but Zn, Pb, Mn, Fe, and Co are leached from all surface rocks relative to fresh drill core.Nothwithstanding the leaching effects of weathering, common geochemical responses to mineralization have been identified in drill core and surface rocks. Coincident positive anomalies for Zn/Ba and Fe/(Na × Ba) ratios and negative anomalies for Na/(Mn × Ca) ratios uniquely define mineralization in both weathered surface rocks and in fresh drill core.The results demonstrate that the pattern of geochemical responses to Pinnacles-type stratiform volcanic-exhalative mineralization in surface rocks has survived the intensive weathering regime in the Broken Hill region.  相似文献   

3.
The geological position, composition of mineral assemblages, and typomorphism of major minerals from garnet-bearing rocks at the Berezitovoe gold-base-metal deposit in the Upper Amur Region have been studied in detail. These are ore-bearing metasomatic rocks and metamorphosed porphyritic dikes. The garnet-bearing metasomatic rocks reveal zoning, which is caused by various degrees of metasomatic transformation of the Paleozoic porphyritic granodiorite that hosts the ore zone. The metasomatic replacement of granodiorite was accompanied by loss of Na, Ca, Ba, Sr and gain of K, Mn, and Rb. Garnet-bearing metamorphosed intermediate dikes occur within the metasomatic zone. The PT conditions of metamorphism and metasomatism are similar and estimated at 3.9 kbar and 500°C from various mineral equilibria. The results of physicochemical simulation of garnet-bearing mineral assemblages carried out by minimizing the Gibbs free energy and the geological data show that garnet-bearing mineral assemblages arose at the Berezitovoe deposit as a result of local high-temperature thermal metamorphism of previously formed low-temperature metasomatic rocks close in composition to classic beresite. In this connection, we propose considering garnet-bearing metasomatic rocks as high-temperature metamorphosed beresites.  相似文献   

4.
Summary Skuppesavon represents a uranium mineralisation emplaced within a sequence of metavolcanics dominated by rocks of rhyolitic to trachytic composition. Uraniferous solutions have penetrated along zones previously opened by Na-Ca-rich mineralising fluids which caused albitisation of potassium feldspar, the partial to complete removal of quartz and the crystallisation of new mineral phases. Uranium, which has been transported mostly as uranyl carbonate complexes, has precipitated as uraninite which occurs as impregnations and only very rarely forms fracture infillings. The introduction of Ca-and Ti-bearing solutions, coeval and subsequent to uraninite precipitation, has resulted in the association of uraninite and sphene. The hydrothermal fluids responsible for the observed mineral parageneses have been activated during metamorphism. During the passage of these fluids through the volcano-sedimentary country rocks, elements such as Ca, Na, U and Ti were mobilised, concentrated and transported. Access through the rocks was facilitated by structural weaknesses and rock permeability variations.  相似文献   

5.
白云鄂博REE-Nb-Fe矿床的富钠岩石类型析及成因分   总被引：4，自引：1，他引：4  
白云鄂博稀土-铌-铁矿是世界最大的稀土多金属矿床之一,主要产于中元古界富钠岩石、白云岩和富钾板岩中。富钠岩石与含矿碳酸岩、富钾板岩一起在白云鄂博广泛分布,特别是在主矿和东矿南侧分布广泛,也产在含矿围岩和底盘围岩中。富钠岩石包括富钠长石岩、含钠闪石钠长岩脉、钠闪石岩脉及钠闪石碳酸岩脉和钠闪石化蚀变白云岩。富钠岩石在一个地质单元内出现,但成分略有不同,其岩石化学分析表现出富钠特征,大部分样品的w(Na2O)在6%以上,w(Na2O+K2O)>8%,w(Na2O)>w(K2O)。富钠长石岩的里特曼指数δ为2.96~8.56,n(A l)/n(K+Na)>1,n(A l)/n(K+Na+Ca)<1,表明为弱碱性偏铝质岩石。富钠岩石以富集地壳不相容元素、亏损地幔元素为特征,其稀土总量低于矿化白云岩,但轻稀土元素高度富集,具弱负铕异常,与含矿白云质火山岩一致。根据岩石产状、组构及化学成分分析,富钠长石岩属于富钠火山岩,而其他含钠闪石岩脉则属于岩浆分异侵入的岩脉与岩浆热液充填岩脉。钠化交代以霓石化、钠铁闪石化和钠长石化出现为特征。另外,富钠流体与白云岩反应形成了钠铁闪石化白云岩,强烈的钠化蚀变作用主要出现在稀土强烈富集的主矿和东矿。比较蚀变与未蚀变岩石的化学成分,表明蚀变作用引起稀土的重新分配和弱负铕异常。钠铁闪石化白云岩的w(S iO2)、w(TiO2)、w(K2O)和w(Na2O)升高,w(P2O5)降低。钠化蚀变前的碳酸岩中稀土元素已经富集,热液蚀变引起稀土元素的活化和重新分配,但是没有提供新的稀土来源。  相似文献   

6.
发源于唐古拉山山脉的河流在青藏高原地区具有流域面积大、径流距离长以及流量大等特点,与喜马拉雅山地区河流共同组成全球河源区最高的水流系统。它们的物理与化学侵蚀在很大程度上代表了在全球气候变化的条件下,大陆的侵蚀作用所发生的变化,即大陆与海洋的物质运移和平衡。发源于唐古拉山北坡的长江源头主要支流楚玛尔河与沱沱河的物理化学特点是溶解的化学成分含量较高,一般为10.66～410.81mmol/L,主要阳离子为Na+、Ca2+和Mg2+,占阳离子总量的97%以上。Ca2+/Na+、Mg2+/Na+、K+/Na+的比值较低,87Sr/86Sr值为(0.708954±0.000020)～(0.711860±0.000011),表明唐古拉山北坡的河水成分以蒸发岩类溶解为主。发源于唐古拉山南坡的怒江源头以及雅鲁藏布江及其支流等的主要阳离子为Ca2+、Mg2+、Na+,占阳离子总量的97%以上。Ca2+/Na+、Mg2+/Na+、K+/Na+的比值较高,87Sr/86Sr值为(0.705534±0.000016)～(0.722856±0.000014),表现为以碳酸盐岩和硅酸盐岩的溶解为主。长江河源区河水中主要化学成分来自蒸发岩,其中Na+和Cl-在河流水化学成分中占比例最大,经计算,唐古拉山北坡长江源头地区的物理侵蚀率为77kg/(km.2a),蒸发岩的化学侵蚀率为49～72.7t/(km.2a),碳酸盐岩的化学侵蚀率为15～20t/(km.2a),硅酸盐岩的化学侵蚀率为2～5t/(km.2a);南坡物理侵蚀率为34kg/(km.2a),碳酸盐岩的化学侵蚀率为25～30t/(km.2a),硅酸盐岩的化学侵蚀率为7～10t/(km.2a)。这些特征反映出北坡高寒干旱环境下河流蒸发岩的化学侵蚀作用较强,南坡碳酸盐岩和硅酸盐岩的化学侵蚀作用大于北坡。  相似文献   

7.
以五龙金矿为例，在同一剖面上采集了不同成矿阶段的含金石英脉和近矿蚀变岩样品，．根据矿物流体包裹体和蚀变岩成分地的测定结果，系统地讨论了不同成矿阶段流体包裹体成（K^ 、Na^ 、Ca^＋、CO2等）和不同蚀变岩成分（K2O、Na2O、CaO1、MgO、CO2等）的变化规律，结果表明，从第二成矿阶段到第四成矿阶段，流体中的Na^ 、Ca^ 、Mg^ 含量有明显的升高的趋势，K^ 含量降低，蚀变岩中，K2O由远离矿体的原岩到靠近矿体的蚀变岩其含量增加，而Na2O、CaO、MgO逐渐降低，这种流体包裹体和蚀变岩中的某些相应成分的变化特征，应该是流体－岩石相互作用的结果。  相似文献   

8.
Whole-rock major element chemical analyses of progressively metamorphosed impure carbonate rocks and pelitic schists, collected from the same metamorphic terrain, reveal similarities and differences in the chemical response of these rock types to the metamorphic event. Relative to a constant aluminum reference frame, both schist and carbonate exhibit no detectable change in their contents of Fe, Mg, Ti, Si, and Ca with change in metamorphic grade. Carbonate rocks become progressively depleted in K and Na with increasing grade of metamorphism, while schists exhibit no statistically significant change in their contents of K and Na. Both rock types become depleted in volatiles (principally CO2 and H2O) with increasing grade.Whole-rock chemical data permit two mechanisms for migration of K and Na from the carbonate rocks during metamorphism: (a) diffusion of alkalis from carbonate to adjacent schist; (b) transport of alkalis by through-flowing metamorphic fluid (infiltration). Mineral equilibria in schist and metacarbonate rock from the same outcrops allow calculation of the affinity for cation exchange between the two rock types during metamorphism. Measured affinities indicate that if mass transport of K and Na occurred by diffusion, chemical potential gradients would have driven the alkalis from schist into carbonate rock. Because diffusion cannot produce the observed chemical trends in the metacarbonates, K and Na are believed to have been removed during metamorphism by infiltration.The disparity in chemical behavior between the pelitic schists and metacarbonate rocks may be a result of enhanced fluid flow through the carbonates. The carbonate rocks may have acted as metamorphic aquifers; the greater flow of fluid through them would then have had a correspondingly greater effect on their whole-rock chemistry.  相似文献   

9.
The south-east Reynolds Range, central Australia, is cut by steep north-west-trending Alice Springs age ( c. 334  Ma) shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement. Amphibolite facies (550–600  °C, 500–600  MPa) shear zones cut metapelites, while greenschist facies shear zones (420–535  °C, 400–650  MPa) cut metagranites. The sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow. Altered granites within greenschist facies shear zones have gained Si and K but lost Ca and Na relative to their unsheared counterparts, suggesting that the fluid flowed down-temperature (and hence probably upward) through the shear zones. Time-integrated fluid fluxes calculated from silica addition are up to 2.1×1010 mol  m−2 ( c. 4.2×105  m3  m−2). Similar time-integrated fluid fluxes are also estimated from changes in K and Na. The sheared granitic rocks locally have δ18O values as low as 0 which is much lower than the δ18O values of the adjacent unsheared granites (7 to 9), implying that the fluid which flowed through these shear zones was derived from the surface. For the estimated time-integrated fluid fluxes, the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres. The flow of surface-derived fluids into the ductile middle crust, with subsequent expulsion upwards through the shear zones, may have been driven by seismic activity accompanying the Alice Springs deformation.  相似文献   

10.
河北省赤城县独石口沸石岩矿物学特征及其性能研究   总被引：2，自引：0，他引：2  
王先琼  孙善平 《现代地质》1993,7(3):317-325
独石口沸石岩共生矿物组合为斜发沸石、蒙脱石、α-方石英和少量丝光沸石。斜发沸石呈微晶产于玻璃质岩屑和火山尘中,也呈板状产于玻屑和珍珠岩溶解形成的孔洞中,沸石总量大于70％;化学成分显示高Si、高Al、富K、富Ca、贫Na的特征;阳离子交换容量高,交换性阳离子以Ca为主,其次为K,Na,Mg;阳离子选择交换顺序为NH_4~+>K~+>Ca~(2+)>Na~+>Mg~(2+);不同阳离子类型的沸石岩其热稳定性和吸附性有差异,K型和Na型沸石岩可稳定至700℃,而Ca型沸石岩在500℃时结构被破坏;Ca型沸石岩吸附性好,而K型差。  相似文献   

11.
Amphiboles represent a crucial phase of the ultra-high-pressure (UHP) metamorphic rocks as their solid solution behavior reflects both bulk compositional and P–T changes. Three different types of amphibole have been reported from the UHP metamafic rocks of the Tso Morari Crystalline Complex, NW Himalayas: Na-rich (glaucophane); Na–Ca-rich (barroisite, taramite, winchite) and Ca-rich (tremolite, magnesio-hornblende, pargasite). The Na-amphibole is presented as a core of the zoned amphibole with Na–Ca-rich rim; Na–Ca-amphibole is presented as inclusion in garnets as well as in matrix, and Ca-amphibole is generally found in the matrix. The Na–Ca-amphibole is observed at two different stages of metamorphism. The first is pre-UHP, and the second is post-garnet–omphacite assemblage though with a significant difference in composition. The pressure–temperature estimations of the formation of these two sets of Na–Ca-amphiboles corroborate their textural associations. Ca-rich amphiboles are generally present in the matrix either as symplectite with plagioclase or as a pseudomorph after garnet along with other secondary minerals like chlorite and biotite. Two different types of zoning have been observed in the amphibole grains: (1) core is Na-rich followed by Na–Ca rim and (2) core of Na–Ca-amphibole is followed by Ca-rich rim. The pre-UHP (or the prograde P–T path) and post-UHP stages (or the retrograde P–T path) of Tso Morari eclogites are defined by characteristic amphibole compositions, viz. Na/Na–Ca-amphibole, Na–Ca-amphibole and Ca-amphibole and thus indicate their utility in inferring crustal evolution of this UHP terrain.  相似文献   

12.
天然高压矿物研究的新进展及其在地幔矿物学中的意义   总被引：4，自引：0，他引：4  
对地表陨石坑岩石和陨石的冲击变质效应的研究, 是以往发现天然高压矿物的主要途径。α-PbO2 超斯石英、(Na,K,Ca)AlSi3O8-锰钡矿以及磷灰石高压同质多像变体等是几个近期在陨石中发现的天然高压相,这些高压相很可能存在于地幔之中。天然高压矿物的发现对地幔矿物学研究和发展起了推动作用。  相似文献   

13.
Clinopyroxenes from pyroxenite, ijolite and nepheline syenite from the main intrusion of the Alnö complex define two sub-parallel compositional trends with respect to Na, Ca and FeTOT plotted against alkali-pyroxene fractionation index (Na–Mg). Both trends define a smooth fractionation of increasing Na and FeTOT and decreasing Ca with increasing Na–Mg, but one set of samples contain clinopyroxenes that constantly plot at higher Na and lower FeTOT and Ca (at similar Na–Mg) than the rest of the samples. Clinopyroxenes with higher Ca and FeTOT and lower Na (trend 1) co-exist with substantial amounts of Ti-andradite (up to 70 vol.%), while the sample set defining the more Na-rich trend (trend 2) lack co-existing Ti-andradite. Clinopyroxenes from both trends show fractionated REE patterns with a distinct difference in HREE content, reflecting the content of co-existing Ti-andradite. The rocks of the first Ti-andradite-bearing trend crystallized slightly prior to the rocks of the second trend, probably from a primitive, Ca- and Ti-rich nephelinitic magma. Crystallisation of pyroxenite and melteigite occurred under low aSiO2 and high aCaO and aTiO2 as evidenced by the presence of perovskite and sometimes substantial amounts of magnetite. Subsequent increase in aSiO2 is evidenced in the overgrowth of perovskite by titanite, which in turn is overgrown by Ti-andradite. Nepheline syenitic residuals crystallized under higher aSiO2 and aNa2O and lower aCaO and aTiO2, which reduced Ti-andradite into an accessory phase and produced more Si- and Na-rich clinopyroxenes. Some of these residuals probably also mixed with new primitive magma producing a hybrid magma that crystallised the more Na-rich and Ca- and FeTOT-poor clinopyroxenes of trend 2. The complete lack of Ti-andradite in these rocks indicates different crystallisation conditions and also a different magma composition.  相似文献   

14.
We report petrological, cathodoluminescence (CL), major and trace element analyses and fluid inclusion studies on scheelite (W)-mineralized granodiorite porphyries from Dongyuan and Zhuxiling, southern Anhui Province (China). In Dongyuan, the larger part of the granodiorite porphyry body is mineralized with W concentrations up to 1140 g/t (total WO3 reserves >140 000 tonnes), whereas in Zhuxiling mineralization is spatially more limited. All mineralized rocks are strongly altered, containing abundant calcite and no fresh plagioclase. W-mineralized rocks show higher K, Pb and lower Na, Sr, Ti contents compared to the non-mineralized ones. Co-variations between mobile elements (K, Na, Pb, Sr, Rb, etc.) and W, combined with petrological observations, demonstrate that fluid alteration must have controlled the mineralization. In quartz from both deposits 4 types of fluid inclusions have been recognized, i.e., aqueous-carbonic (WC-type), aqueous (W-type, subdivided into Wm-type containing minor detected CO2 and Wn containing no CO2), carbonic (pure CO2, C-type) and late secondary aqueous inclusions (LW-type). WC- and LW-type inclusions represent the original magmatic fluids and meteoric waters, respectively. The other inclusions represent evolved magmatic fluids which are closely related to alteration and mineralization. WC-, Wm- and Wn-type inclusions show higher salinity and lower homogenization temperatures, indicating fluid immiscibility with CO2 effervescence. Additionally, during plagioclase alteration and precipitation of K-feldspar and sericite the K/Na ratio is lowered and Ca released. The precipitation of scheelite must have been promoted by increasing Ca contents in the fluid and also by increasing pH due to CO2 loss. The present study demonstrates that for granitic rocks without calcareous wall rock, plagioclase breakdown must have been the key factor for scheelite mineralization. The presence of CO2-rich fluid indicates that both deposits formed in the same intracontinental extension setting as those in the Nanling region. Thus, the Yanshanian granites from southern Anhui Province may have a great potential for W mineralization, especially the blind ones in deep levels.  相似文献   

15.
The detailed hydro-chemical study of meltwater draining from Khangri glacier Arunachal Pradesh has been carried out to evaluate the major ion chemistry and weathering processes in the drainage basin. The investigative results shows that the meltwater is almost neutral to slightly acidic in nature with Mg–HCO3-dominated hydro-chemical facies. In glacial meltwater, Ca+?2 is the most dominated cation followed by Mg+2, Na+, and K+, while HCO3? is the most dominant anion followed by SO42?, NO3?, and Cl?. The dominant cations such as Ca+2 and Mg+2 show a good relation with the minerals abundance of the rocks. Calcite (CaCO3) and biotite [K(Mg,Fe)3AlSi3O10(F,OH)2] are the most abundant minerals in the deformed carbonate-rich metasedimentary rocks near to the snout with some K feldspar (KAlSi3O8) and quartz (SiO2). This suggests Ca+2 have definitely entered into the water due to the dissolution of calcite and Ca feldspar (CaAl2Si2O8), while one of the source of Mg+2 is biotite. Na feldspar (NaAlSi3O8) has contributed towards the availability of sodium ion, while potassium ion is derived from the chemical weathering of K feldspar and biotite. The chemical weathering is the foremost mechanism controlling the hydro-chemistry of the Khangri glacier because of the least anthropogenic interferences. The mineralogy of surrounding rocks is studied to understand better, the rock–water interaction processes, and their contribution towards ionic concentration of meltwater. The meltwater discharge and individual ion flux of the catchment area have also been calculated, to determine the ionic denudation rate for the ablation season. The high elemental ratio of (Ca?+?Mg)/(Na?+?K) (7.91?±?0.39 mg/l) and low elemental ratio of (Na?+?K)/total cations (0.11?±?0.004) indicate that the chemical composition of meltwater is mainly controlled by carbonate weathering and moderately by silicate weathering. The scatter plot result between (Ca?+?Mg) and total cations confirms that carbonate weathering is a major source of dissolved ions in Khangri glacier meltwater. In addition, the statistical analysis was also used to determine the correlation between physical parameters of glacier meltwater which controlled the solute dynamics.  相似文献   

16.
High-Na slag-like rocks (paralava) with 4.5–11 % Na2O from the Altyn-Emel mud volcanic field, Kazakhstan, are the products of melting of sediment + salt mixtures by methane flares associated with mud extrusion. The main minerals of the paralavas are diopside and wollastonite which have quench morphologies. Other high-temperature phases (crystallizing from melt and vapour phase) are tridymite, cristobalite, chlorapatite, alkali feldspar, pyrrhotite, native iron and silicon, iron phosphides, titanite, rutile, and carbon. The paralavas lack the Na–Ca silicates devitrite and combeite, but have high-Na and Na–K glasses that have not been homogenized despite low viscosities of <10?3.5 Pa s. The large number of ignition foci in the Altyn-Emel mud volcano field indicates gas venting from small, shallow reservoirs. The methane flares are inferred to have been small and the fire events short-lived. Fires were extinguished once overpressure released during eruption, methane venting stopped and melted rocks rapidly quenched. The periodicity of eruptions and methane flaring most likely depends on the recurrence of earthquakes (M < 5) which are frequent in this tectonically active area.  相似文献   

17.
渝东北黑色页岩元素迁移特征及化学风化程度   总被引：1，自引：0，他引：1       下载免费PDF全文
黑色页岩是富含有机质和硫化矿物的特殊沉积岩,但人们对其风化过程的元素活动性及矿物风化机制关注较少.为探讨不同地形位置的黑色页岩化学风化过程,采集了渝东北城口某山脊 (A)、近山顶 (B) 和沟谷 (C) 的下寒武统水井沱组黑色页岩风化剖面岩样,利用XRD、XRF和化学分析手段对采集样品的矿物成分、主量元素进行测定分析.元素和矿物的质量迁移系数 (τ) 和质量迁移通量 (Mj, flux) 的计算结果表明,黑色页岩风化过程中Ca、Mg和Na元素具有明显的贫化现象,近地表处存在Al元素的富集现象;矿物成分方面,黄铁矿和有机质氧化后形成的酸性水环境,造成方解石、白云石、斜长石等不稳定矿物溶解,并生成含水石膏、铁质氧化物、黏土矿物等次生矿物.不同赋存位置的黑色页岩风化程度有所差异,Na/K-CIA、K/Ca*-Al/Na、A-CN-K和A-CNK-FM图解显示:A剖面处于脱Ca过程的初级风化阶段,B剖面处于脱Ca、Na初期的初等-中等风化阶段,C剖面已发生脱Ca、Na过程,并伴随脱Si作用的中等-强烈风化阶段,结合不同风化指数 (如:CIA、CIW、PIA、MWPI等),得出各剖面的化学风化强弱程度依次为C＞B＞A.   相似文献   

18.
Skarns composed predominantly of Ca pyroxene, Ca amphibole, and biotite occur locally in the Grenville metamorphic terrain of the Canadian pre-Cambrian Shield. The enclosing rocks are Grenville gneisses and limestones, gabbroic rocks, veined gneisses, and granitic rocks. The metamorphic grade of the skarns is identical to that of the enclosing rocks, namely the upper region of the amphibolite facies.

Twelve skarn specimens were selected for chemical study. An investigation is made of the concentrations of Al, Fe, Mg, Mn, Ti, Ca, Na, K, Ba, V, Cr, Zr, Y, and Sc in eleven Ca pyroxenes, ten Ca amphiboles, and eleven biotites.

Consideration is given to the distribution of elements among coexisting minerals. Regular relationships appear when

1. (1) the concentration of an element in a mineral is related to the concentration of the element in a coexisting mineral by a linear or non-linear function

2. (2) the linear or non-linear function is itself a function of the concentration of another element in one or both of the coexisting minerals. These relationships indicate that, for the most part, minerals within each skarn specimen closely approached a state of chemical equilibrium.

A preliminary attempt is made to explain the distribution relationships in terms of crystal chemistry.  相似文献   


19.
采用微波消解白云石样品，电感耦合等离子体发射光谱法测定其中铁、铝、钙、镁、钾、钠、硫的氧化物，对微波消解条件和等离子体发射光谱仪的工作条件进行了选择，克服了常规化学分析方法步骤繁琐、耗时长、工作量大的不足。利用所建立的方法快速分析了白云石中铁、铝、钙、镁、钾、钠、硫的含量，结果与标准值或化学法相符，10次测定的相对标准偏差（RSD）7种元素均小于1％，可以满足生产和科研的要求。  相似文献   

20.
《Geochimica et cosmochimica acta》1999,63(13-14):1939-1953
Accessory calcite, present at concentrations between 300 and 3000 mg kg−1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57–98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering.The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport-limited weathering. These results indicate that the weathering of accessory calcite may strongly influence Ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces.  相似文献   

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