Intergranular coesite and coesite inclusions in dolomite from the Dabie Shan: Constraints on the preservation of coesite in UHP rocks

Intergranular coesite is extremely rare in, and bears crucial information on the formation and preservation of, ultrahigh‐pressure (UHP) rocks. Here, we report the first occurrence of intergranular coesite in a metasedimentary rock, which occurs in the Ganjialing area in the Dabie Shan, east‐central China, and contains abundant coesite inclusions in both garnet and dolomite. We investigated the content of structural water in these minerals with Fourier transform infrared spectroscopy. Our new results undermine the ubiquity of the “pressure‐vessel” model and highlight the role of reaction kinetics in preserving coesite due to the availability of water in UHP rocks.     

超高压变质矿物中的多相固体包裹体研究进展

大陆碰撞过程中熔/流体的组成和演化是研究大陆深俯冲动力学的重要内容,而超高压岩石记录了大陆俯冲和折返过程中的熔/流体-岩石相互作用,因而是研究大陆碰撞过程中熔/流体组成和演化的天然实验室。大陆俯冲带高压/超高压变质矿物中多相固体包裹体作为熔/流体活动的直接记录,为我们提供了揭示超高压变质过程中熔/流体演化的重要制约。近年来,围绕超高压岩石中多相固体包裹体的形成时间、演化过程及其所反映的俯冲带超高压变质熔/流体的组成和性质,进行了大量的研究工作。超高压岩石中多相固体包裹体的发现,为理解峰期超高压变质流体的组成和演化提供了重要制约,同时也为研究俯冲板片-地幔楔界面的熔/流体交代作用提供了新的途径。本文从多相固体包裹体形成机制、结构形态特征、矿物化学成分及其地质地球化学意义等方面,对于超高压变质岩中多相固体包裹体的研究现状和存在的问题进行系统地总结和探讨,以期促进多相固体包裹体的岩石学和地球化学研究。     

川西甲基卡花岗伟晶岩型锂矿床中熔体、流体包裹体固相物质研究

川西甲基卡二云母花岗岩和伟晶岩内发育大量原生熔体包裹体和富晶体流体包裹体。为了查明甲基卡成矿熔体、流体性质与演化特征,运用激光拉曼光谱和扫描电镜鉴定了甲基卡花岗伟晶岩型锂矿床中二云母花岗岩及伟晶岩脉不同结构带内的原生熔体、流体包裹体的固相物质。分析结果表明,甲基卡二云母花岗岩石英内熔体包裹体的矿物组合为磷灰石+白云母、白云母+钠长石、白云母+石墨;伟晶岩绿柱石内富晶体流体包裹体的矿物组合主要为刚玉、富铝铁硅酸盐+刚玉+锂辉石、锂辉石+石英+锂绿泥石;伟晶岩锂辉石内富晶体流体包裹体的矿物组合主要为磷灰石、锡石、磁铁矿、石英+钠长石+锂绿泥石、萤石、富钙镁硅酸盐+富铁铝硅酸盐+富铁硅酸盐+石英;花岗岩浆熔体与伟晶岩浆熔体(流体)具有一定的差异,成矿熔体、流体成分总体呈现出碱质元素(Na、Si、Al)、挥发分(F、P、CO_2)含量增高及基性元素(Fe、Mg、Ca)降低的特征;包裹体中子矿物与主矿物的化学成分具有一定的差别,揭示出伟晶岩熔体(流体)存在局部岩浆分异作用,具不混溶性及非均匀性。因此认为,伟晶岩熔浆(流体)为岩浆分异与岩浆不混溶共同作用的产物,挥发分含量的增高(F、P、CO_2)使伟晶岩能够与稀有金属组成各类络合物或化合物,这对于稀有金属成矿起到了至关重要的作用。     

矿物流体包裹体中稀有气体的保存能力初探

查明流体包裹体中稀有气体的保存能力,对于判断其初始组分特征是否因后生作用而发生改变具有重要意义.文章以Ar为例,从扩散动力学角度对稀有气体地球化学研究中常用的矿物中流体包裹体稀有气体的保存能力进行了定量分析和系统比较,计算了Ar在这些矿物中的封闭温度以及不同温度条件下的保存时间,得出相同条件下各矿物对Ar、He等保存能...     

Fluid inclusions in high-grade gneisses of the Kapuskasing structural zone,Ontario: metamorphic fluids and uplift/erosion path

Fluid inclusions in quartz grains from five samples of high-grade rocks (two paragneisses, an amphibolite, a mafic gneiss and a tonalite dike) from the 2.7 Ga Kapuskasing structural zone (KSZ), Ontario, were examined with petrographic, microthermometric and laser Raman techniques. Three types of fluid inclusions were observed: CO₂-rich, H₂O-rich and mixed CO₂-H₂O. CO₂-rich fluid inclusions are pseudosecondary or secondary in nature and are generally pure CO₂; a few contain varying amounts of CH₄·H₂O-rich fluid inclusions are secondary in nature, contain variable amounts of dissolved salts, and generally contain daughter crystals. Mixed CO₂-H₂O fluid inclusions occur where trails of H₂O-rich inclusions intersect trails of CO₂-rich inclusions. Isochores for high density (p=1.03 g/cm³) pseudosecondary, pure CO₂ inclusions intersect the lower pressure portion of the estimated P-T field for high-grade metamorphism, implying that pure CO₂ was the peak metamorphic fluid. The variable CH₄ content of CO₂ inclusions within graphite-bearing samples suggests that CH₄ was introduced locally after the formation of the CO₂ inclusions; however the origin of the CH₄ remains problematic. An aqueous fluid clearly penetrated the gneisses after the peak metamorphism (during uplift/erosion), forming secondary inclusions and contributing to the minor retrogressive hydration observed in these rocks. The presence of the pseudosecondary, high-density CO₂ inclusions in quartz crystals in the KSZ rocks constrains the uplift/ erosion path for the KSZ to one of simultaneous decrease in pressure and temperature.     

Platinum-group minerals and other solid inclusions in chromite of ophiolitic complexes: Occurrence and petrological significance

Summary Platinum-group mineral, silicate and other solid and fluid inclusions occur in disseminated and massive chromite in a variety of lithologies from ophiolitic and other mafic-ultramafic complex-types. The inclusions are small (<250 microns) and randomly distributed throughout their host. Silicate inclusions are modally more abundant than the other inclusion types. Platinum-group mineral phases are ruthenium-rich sulphides and PGE alloys are osmium-rich. Mafic silicates (olivine, pyroxenes, pargasitic-amphiboles, micas) are magnesium-, titanium-, and alkali-rich and felsic silicates are sodium-rich (albite, nepheline).The intimate association of these inclusions with chromite suggests that their origin must be considered within a chromite crystallization model. A hypothesis of origin is suggested wherein the platinum-group minerals and silicates are trapped as discrete, crystalline euhedral phases and silicate liquid during the precipitation of chromite. The similarity of physical characteristics, modal mineralogy and chemical compositions indicates that this model may be applicable to all mafic-ultramafic complex-types.

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Minerale der Platin-Gruppe und andere feste Einschlüsse in Chromiten aus Ophiolit-Komplexen: Vorkommen und petrologische Bedeutung

Zusammenfassung Minerale der Platin-Gruppe, Silikate und andere feste und flüssige Einschlüsse kommen in disseminierten und massiven Chromiten in einer Vielzahl von Gesteinen in ophiolitischen und anderen mafisch-ultramafischen Komplexen vor. Die Einschlüsse sind klein (<250 microns) und unregelmäßig im Chromit verteilt. Silikat-Einschlüsse sind modal weiter verbreitet als andere Arten von Einschlüssen. Minerale der Platin-Gruppe sind durch Ruthenium-reiche Sulfide und Osmium-reiche Legierungen vertreten. Mafische Silikate (Olivin, Pyroxen, pargasitische Amphibole, Glimmer) sind Magnesium-, Titan- und Alkali-reich; felsische Silikate sind Natrium-reich (Albit, Nephelin).Die ausgeprägte Assoziation dieser Einschlüsse mit Chromit weist darauf hin, daß ihre Herkunft im Zusammenhang mit einem Kristallisations-Modell für Chromit zu sehen ist. Ein genetisches Konzept wird vorgelegt, wobei die Platin-Gruppen-Minerale als gut ausgebildete, idiomorphe kristalline Phasen, und die Silikate als Silikatschmelze während des Ausfallens des Chromites eingeschlossen werden. Die Ähnlichkeit der physikalischen Eigenschaften, der modalen mineralogischen Zusammensetzung und der chemischen Zusammensetzung weisen darauf hin, daß dieses Modell auf alle mafisch-ultramafischen Komplexe anzuwenden ist.

     

Synthetic fluid inclusions - VII. Re-equilibration of fluid inclusions in quartz during laboratory-simulated metamorphic burial and uplift

ABSTRACT P-T conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations. These observations suggest that inclusions formed during early stages of regional metamorphism continue to re-equilibrate during burial and subsequent uplift in response to differential pressure. P-T conditions accompanying burial and uplift were experimentally simulated by initially forming pure H₂O inclusions in quartz at elevated temperatures and pressures, and then re-equilibrating the inclusions in the presence of a 20 wt% NaCl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re-equilibration. In all samples re-equilibrated at confining pressures below the internal pressure, some inclusions were formed that had compositions of 20 wt% NaCl and densities in accord with the final P-T conditions. Additionally, some inclusions were observed to contain fluids of intermediate salinities (between 0 and 20 wt% NaCl). Densities of these inclusions were also consistent with formation at the re-equilibration P-T conditions. The remainder of the fluid inclusions observed in these samples contained pure H₂O and their homogenization temperatures corresponded to densities intermediate between the initial and final P-T conditions. In short-term experiments (7 days) where the initial internal overpressure exceeded 1 kbar, no inclusions were found that contained the original density and none were found to have totally re-equilibrated. Instead, most H₂O inclusions re-equilibrated until their internal pressures were between ∼750 and 1500 bars above the confining pressure, regardless of the initial pressure differential. In a long-term experiment (52 days), inclusions re-equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar (i.e. total re-equilibration) and 1.2 kbar above the confining pressure. In experiments where the confining pressure during re-equilibration exceeded the initial internal pressure, densities of pure H₂O inclusions increased to values intermediate between the initial and final P-T conditions. Additionally, these inclusions were generally surrounded by a three-dimensional halo of smaller inclusions, also of intermediate density, resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure. In extreme cases where confining pressures were 4–5 kbar above the initial pressure, the parent inclusion almost completely closed leaving only the three-dimensional array of small (5 μm) inclusions, the outline of which may be several times the volume of the original inclusion. Groups of such inclusions closely resemble textures commonly observed in medium- to high-grade metamorphic rocks. Inclusions containing 10 and 42 wt% NaCl solutions trapped at 600 °c and 3 kbar were re-equilibrated at 600 °c and 1 kbar for 5 days in dry argon to evaluate the importance of H₂O diffusion as a mechanism of lowering the inclusion bulk density. Salinities of re-equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved. Density changes similar to those previously described were noted in these experiments, in inclusions showing no visible microfractures. Therefore, density variations observed in inclusions in this study, re-equilibrated under rapid deformation conditions, are considered to result from a change in the inclusion volume, without significant loss of contents by diffusion or leakage.     

First symposium of gas-liquid inclusions in minerals

This paper briefly reviews the highlights of the First Symposium on Gas-Liquid Inclusions in minerals, held at Moscow University in May 1963. The remainder of the paper 1) presents a historical background stressing the role of Soviet scientists in developing the science of the study of fluid inclusions; 2) reviews in detail the general status of this science in the Soviet Union, including shortcomings, goals, and recent advances; and 3) demonstrates, with examples, the application of fluid inclusion data to the solution of a variety of geologic problems.—R.D. DeRudder     

The microstructure of minerals in coarse-grained Ca-Al-rich inclusions from the Allende meteorite

The microstructure and microchemistry of minerals in Ca-Al-rich, coarse-grained inclusions (CAI) from the Allende meteorite have been investigated with transmission electron microscopy (TEM). Spinels contain only low to moderate dislocation densities and are characterized by a ubiquitous, fine black spotty texture believed to originate from a slightly non-stoichiometric composition. Ti-Al-pyroxenes are relatively featureless, but contain veins of secondary phases apparently deposited in unhealed cracks. Chromite has been identified in the veins, suggesting transport of oxidized iron during alteration. Melilites exhibit the greatest variety of microstructures and are the most heavily altered phase in CAI. High dislocation densities are common and crystals exhibit considerable internal strain, indicating that they have not been annealed. Alteration occurs both as veins along cracks and in fronts extending across several grains. Plagioclase is commonly twinned, but dislocations are rare. The size and morphology of antiphase domains suggest a high temperature of formation with significant low-temperature annealing. Submicron pyroxene precipitates are a ubiquitous and unusual feature of Allende plagioclase whose properties are most consistent with prolonged slow cooling and equilibration after plagioclase crystallization. The precipitates appear to be sufficiently abundant to contain the majority of Mg present in plagioclase but do not easily account for Na and Ti abundances. Wollastonite needles from a cavity in a “fluffy” Type A inclusion exhibit the growth habits and relatively perfect external surfaces indicative of direct condensation from a vapor. Alteration products are predominantly crystalline and alteration of melilite appears to have proceeded primarily by solid-state diffusion at a temperature of approximately 920°K. Overall, the TEM observations suggest that CAI formed under near equilibrium conditions characterized by slow cooling and that solid-state bulk diffusion was the major process affecting their post-crystallization history.     

蚌埠隆起区石榴辉石岩变质P-T轨迹的构建

蚌埠隆起区位于华北克拉通东南缘,胶—辽—吉造山带的最南端,主体由五河杂岩组成。前人对该地区的研究主要集中于同位素年代学和变质温压条件研究,其中变质P-T条件研究结果差异较大,以压力变化最为显著,对峰期变质P-T条件缺乏统一认识。本文对蚌埠隆起区石榴辉石岩进行了大量的岩相学、矿物化学成分分析,表明该岩石记录了3期变质作用,其中S-M1和S-M2的矿物组合类似为Grt+Cpx+Opx+Amp+Pl+Ilm,S-M3的矿物组合为Cpx+Amp+Pl+Grt （极边窄带）。结合变质温压条件分析和锆石U-Pb年代学分析,本次主要取得以下几点认识：1）石榴辉石岩WS047-1中记录的3期变质作用,温压条件分别为T-M1 = 616 ℃～647 ℃、P-M1 = 1.03～1.08 GPa,T-M2 = 721 ℃～837 ℃、P-M2 = 1.11～1.29 GPa和T-M3 = 531 ℃～607 ℃、P-M3 = 0.81～0.91 GPa,经历了由较高压力的角闪岩相→中-低麻粒岩相→角闪岩相的变质过程;2）据变质温压条件分析知,蚌埠隆起区具有顺时针的P-T轨迹特征,S-M1→S-M2和S-M2→S-M3分别为近等压升温和近等压降温的缓慢过程;3）石榴辉石岩锆石U-Pb年代学结果主要分为4组：1 839±13 Ma、1 925±31 Ma、2 041±55 Ma和2 762±14 Ma,其中峰值变质年代为1.93～1.84 Ga;4）结合温压条件和锆石U-Pb年代学分析结果,本文认为蚌埠隆起区的P-T轨迹与弗朗西斯科型俯冲或大陆碰撞环境的P-T轨迹较为类似,其应与1.93～1.84 Ga华北克拉通东、西陆块的碰撞拼合及胶—辽—吉造山带形成时限基本吻合。本次研究为深入理解华北克拉通的构造演化特征和蚌埠隆起区的变质作用及演化,提供了大量可靠的科学资料。     

Dehydration melting of ultrahigh‐pressure eclogite in the Dabie orogen: evidence from multiphase solid inclusions in garnet

Several types of multiphase solid (MS) inclusions are identified in garnet from ultrahigh‐pressure (UHP) eclogite in the Dabie orogen. The mineralogy of MS inclusions ranges from pure K‐feldspar to pure quartz, with predominance of intermediate types consisting of K‐feldspar + quartz ± silicate (plagioclase or epidote) ± barite. The typical MS inclusions are usually surrounded with radial cracks in the host garnet, similar to where garnet contains relict coesite. Barite aggregates display significant heterogeneity in major element composition, with total contents of only 57–73% and highly variable SiO₂ contents of 0.32–25.85% that are positively correlated with BaO and SO₃ contents. The occurrence of MS inclusions provides petrographic evidence for partial melting in the UHP metamorphic rock. The occurrence of barite aggregates with variably high SiO₂ contents suggests the coexistence of aqueous fluid with hydrous melt under HP eclogite facies conditions. Thus, local dehydration melting is inferred to take place inside the UHP metamorphic slice during continental collision. This is ascribed to phengite breakdown during ‘hot’ exhumation of the deeply subducted continental crust. As a consequence, the aqueous fluid is internally buffered in chemical composition and its local sink is a basic trigger to the partial melting during the continental subduction‐zone metamorphism.     

Fluid inclusions in Adirondack granulites: Implications for the retrograde P-T path

Investigation of fluid inclusions in granitic and cale-silicate gneisses from the Adirondack Mountains, New York, has revealed the presence of various types, including: (1) CO₂-rich, (2) mixed H₂O–CO₂±salt and (3) aqueous inclusions with no visible CO₂. Many, if not all, of these inclusions were trapped or modified after the peak of granulite facies metamorphism, as shown by textural relations or by the lack of agreement between the composition of the fluids found in some inclusions and the composition of the peak-metamorphic fluid as estimated from mineral equilibria. Many fluid inclusions record conditions attained during retrograde cooling and uplift, with minimum pressures and temperatures of 2 to 3 kbar and 200 to 300°C. The temperatures and pressures derived from the investigation of these inclusions constrain the retrograde P-T path, and the results indicate that a period of cooling with little or no decompression.     

Texturally-early fluid inclusions in garnets: evidence of the prograde metamorphic path?

Well-formed, texturally-early fluid inclusions in garnets from the Archean Pikwitonei granulite domain, Manitoba, Canada, have been analyzed using microthermometric methods. The mean CO₂ homogenization temperature (to liquid) for inclusions in 12 of 13 samples from the Cauchon Lake-Nelson River area is +15.2° C (n=125, 2σ=8.2° C), corresponding to a CO₂ density of 0.82 g/cm³. Inclusions in the remaining sample have somewhat lower CO₂ homogenization temperatures (mean=+5.4° C, n=24). The studied inclusions contain an estimated 10 to 20 vol. percent H₂O, with minor amounts of other fluid species such as CH₄, N₂, and/or H₂S. The fluid inclusions were probably trapped during early garnet growth at relatively low pressures (≤5 kbar if at 750° C), and appear to have undergone only limited or possibly no subsequent re-equilibration. This interpretation is consistent with the “anti-clock-wise” P-T-t path (heating before loading) determined for the Pikwitonei region by other workers. For such a prograde path, inclusions entrapped early, at high temperatures but at relatively low pressures, would experience internal underpressures during most of the subsequent prograde and retrograde phases of metamorphism. The texturally-early fluid inclusions in garnets from the Pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions (750° C and 7 kbar). However, the results obtained in this study suggest that texturally-early fluid inclusions in garnets may, in some cases, retain evidence of the prograde metamorphic path.     

Sulfide inclusions in diamonds: not monosulfide solid solution

Sulfide inclusions in diamonds, the most common of all inclusions, contain critical evidence about the timing and physical/chemical conditions prevailing during diamond formation. Typically, sulfide inclusions are encapsulated as a monosulfide solid solution (Mss) in the Fe-Ni-S system, with a minor amount of Cu. This Mss and the enclosing diamond have sufficiently different thermal expansion properties, so that, after encapsulation, the Mss creates a series of cracks in the diamond radiating from the sulfide. On cooling, this increase in volume permits the Mss to undergo exsolution to an assemblage of pyrrhotite + pentlandite + chalcopyrite + pyrite. The kinetics of this exsolution is so rapid that practically no Mss remains in nature. Instead, in recovered diamonds, all sulfides that originally were Mss now consist of this fine-grained assemblage. Chalcopyrite prefers to form around the edges of the inclusions and also migrates into the minute cracks in the diamonds. It is the bulk composition of the Mss as encapsulated that is important for interpretation of diamond petrogenesis (P- versus E-type diamonds) and to the commonly used Re-Os dating technique. However, this bulk composition is definitely not attainable with polished sections cut through the inclusions. The assumption that the kernel of the sulfide inclusion for Re-Os age dating represents the entire original Mss may also be incorrect, depending what has been lost, mostly chalcopyrite, which has migrated into the surrounding cracks within the diamond host.     

The conservation of an aqueous fluid in inclusions in minerals and their interstices at high pressures and temperatures during the decomposition of antigorite

An experimental study of serpentine decomposition at high pressure (4.5 GPa) was carried out to elucidate if water can be preserved in the system in the form other than structural admixtures in minerals. This problem is of interest because it is water that plays a leading role in the melting in a subducted slab and a mantle wedge. To estimate the possible content of an aqueous fluid in deep-seated rocks, a BARS pressless split-sphere apparatus was used in complex with thermobarogeochemistry and gas chromatography. It has been established that the serpentine decomposition is accompanied by the release of water, which concentrates in inclusions in the produced minerals (olivine and orthopyroxene) and their interstices. Chromatographic analysis with a stepwise heating of samples showed that most of the released water is localized in the interstices, and the rest is conserved in fluid inclusions in the minerals. The produced solid phases conserve 0.13 to 2.43 wt.% fluids as inclusions, with water amounting to 0.1–2.06 wt.%. The content of inclusions determined by microscopic examination falls in this region. Since the mobility of the fluid conserved as inclusions in the olivine and orthopyroxene is significantly lower than that in the interstices, this fluid might be better preserved in olivine-containing rocks subsided to depth.     

Volatile components of natural fluids: Evidence from inclusions in minerals: Methods and results

A database compiled by the author on volatile components in fluid inclusions (5300 analyses compiled from 300 publications) was used to compare destructive and nondestructive analytical techniques and thermal and mechanical methods for the extraction of volatiles in destructive techniques. Possible explanations are proposed for opposite conclusions published by various researchers. The paper summarizes the principal outcomes of the long-lasting discussion on the optimal methods able to provide the most reliable results. No unambiguous answer is provided. Analysis of extensive literature data indicates that each of the techniques is characterized by its own advantages and disadvantages, and an optimal solution should be selected with regard for the materials to be analyzed and formulated tasks. In any event, the results require careful interpretation. The average composition of natural fluids calculated from extensive statistical material is as follows (mol %): 70.3 H₂O, 21.4 CO₂, 6.3 CH₄, 2.0 N₂, and 0.07 H₂S. The distribution of volatile components was examined in minerals from hydrothermal ore deposits of various types (gold, tungsten, tin, and base-metal) and metamorphic rocks     

太白金矿流体包裹体中黄铁矿和铁白云石等子矿物的发现及成冈意义

太白金矿含金角砾岩带赋存于秦岭泥盆纪浅变质细碎屑岩系中,地质特征独特。金矿佛主要产于含铁白云石－黄铁矿等胶结物中,这些载金矿物中普遍有大量流体包裹体产出。应用扫描电镜、能谱分析和电子探针技术发现了石英和含铁白云石中的黄铁矿、毒砂和铁白云石等离子矿物,结合流体包裹体成分ＬＲＭ分析资料,对成矿流体特征有了新认识。     

西华山钨矿床共生透明矿物与不透明矿物中流体包裹体的对比研究

西华山钨矿床是一个产于燕山期花岗岩中的大脉型钨矿床。笔者利用红外显微镜、冷热台及其他相关设备对矿床中的透明矿物(石英、绿柱石和萤石)与不透明矿物(黑钨矿、黄铁矿)中的流体包裹体进行了对比研究。结果显示,共生透明矿物与不透明矿物之间,在包裹体均一温度等特征上既可基本相同又可出现很大差异。一般来说,黑钨矿能有效地保存原生流体包裹体(t_h=300～420℃;晶洞中为220～290℃),仅有少量次生包裹体(t_h=160～280℃),而与之共生的石英中原生包裹体则几乎被破坏殆尽,现在所见到的包裹体绝大多数是次生的或是在较晚结晶时捕获的(t_h=130～270℃)。只有未经后期应力作用和流体改造的晶洞水晶及与其共生的黑钨矿,二者获得的结果才相同或相似。绿柱石中通常有大量的次生包裹体和原生包裹体。黑钨矿与绿柱石中硅酸盐熔融包裹体的出现,表明西华山钨矿床的成矿作用始于岩浆-热液过渡阶段,其初始成矿流体是一种岩浆-热液过渡性流体,尔后才演变成单一的热水溶液。笔者认为,在进行金属矿床流体包裹体研究时,应强调共生透明矿物与不透明矿物的对比研究,在进行对比研究时,详尽的基础地质研究和包裹体岩相学观察必不可少;当单独利用透明矿物包裹体资料对金属矿床进行地质解释时,需慎之又慎。     

The effect of pressure on the solubility of minerals in water and seawater

The effect of presure on the solubility of minerals in water and seawater can be estimated from In

$\text{(}\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^0{}_{\mathrm{sp}}\text{) +}\text{(?ΔVP + 0.5ΔKP}{}^2\text{)}\text{RT}$

where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by

$\text{ΔV =}\text{V}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{V}\text{?}\text{[MX(s)]ΔK =}\text{K}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{K}\text{?}\text{[MX(s)]}$

Values of the partial molal volume ($\text{V}\text{?}$) and compressibilty ($\text{K}\text{?}$) in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10^?3 cm³ bar^?1 mol^?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In K_sp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of $\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{sp}}$ for the solubility of CaCO₃, SrSO₄ and CaF₂ in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered.