On the origin of CO2-rich fluid inclusions in migmatites

Abstract Nearly pure CO₂ fluid inclusions are abundant in migmatites although H₂O-rich fluids are predicted from the phase equilibria. Processes which may play a role in this observation include (1) the effects of decompression on melt, (2) generation of a CO₂-bearing volatile phase by the reaction graphite + quartz + biotite + plagioclase = melt + orthopyroxene + CO₂-rich vapour, (3) selective leakage of H₂O from CO₂+ H₂O inclusions when the pressure in the inclusion exceeds the confining pressure during decompression, and (4) enrichment of grain-boundary vapour in CO₂ by subsolidus retrograde hydration reactions.     

Andalusite-bearing veins at Vedrette di Ries (eastern Alps, Italy): fluid phase composition based on fluid inclusions

Abstract Andalusite-bearing veins formed during contact metamorphism in the aureole of the Vedrette di Ries tonalite. In the veins, quartz crystals that are completely armoured by andalusite or that occur in strain shadow areas contain three generations of fluid inclusions: low-salinity H₂O-CO₂-CH₄ mixtures with CH₄/(CO₂+ CH₄) ± 0.35 (type A); low-salinity aqueous fluids (type B); H₂O-free, CO₂-CH₄ fluids with the same carbonic speciation as A (type C). Carbonic types A and C typically have a dark appearance, which is attributed to graphite coatings on inclusion walls. Microstructural analysis of the host quartz and calculated densities indicate that type A inclusions were likely trapped during vein formation. These inclusions underwent strain-assisted re-equilibration during cooling that resulted in density increases without change of composition. After the rocks had cooled below about 350 ° C, type C inclusions appear to have formed from one of the immiscible fractions after unmixing of the H₂O-CO₂-CH₄ fluid mixtures. Aqueous type B inclusions, apparently trapped between 225 and 350 ° C, could represent an independent fluid, or could be the H₂O-rich fraction of unmixed type A fluids. Taking account of the uncertainties, the composition and density of the complex type A inclusion fluids are in good agreement with the properties of primary fluids calculated from the petrological data. The fluid inclusion data support the model of vein formation by hydrofracturing as a result of dehydration of graphitic metapelites. These new results also demonstrate the importance of considering strain in the interpretation of metamorphic fluid inclusions.     

The nature of fluids during pegmatite development in metamorphic terrains: Evidence from Hamadan complex,Sanandaj-Sirjan metamorphic zone,Iran

In the Sanandaj-Sirjan zone of metamorphic belt of Iran, the area south of Hamadan city comprises of metamorphic rocks, granitic batholith with pegmatites and quartz veins. Alvand batholith is emplaced into metasediments of early Mesozoic age. Fluid inclusions have been studied using microthermometry to evaluate the source of fluids from which quartz veins and pegmatites formed to investigate the possible relation between host rocks of pegmatites and the fluid inclusion types. Host minerals of fluid inclusions in pegmatites are quartz, andalusite and tourmaline. Fluid inclusions can be classified into four types. Type 1 inclusions are high salinity aqueous fluids (NaCl_eq >12 wt%). Type 2 inclusions are low to moderate salinity (NaCl_eq <12 wt%) aqueous fluids. Type 3 and 4 inclusions are carbonic and mixed CO₂-H₂O fluid inclusions. The distribution of fluid inclusions indicate that type 1 and type 2 inclusions are present in the pegmatites and quartz veins respectively in the Alvand batholith. This would imply that aqueous magmatic fluids with no detectable CO₂ were present during the crystallization of these pegmatites and quartz veins. Types 3 and 4 inclusions are common in quartz veins and pegmatites in metamorphic rocks and are more abundant in the hornfelses. The distribution of the different types of fluid inclusions suggests that CO₂ fluids generated during metamorphism and metamorphic fluids might also contribute to the formation of quartz veins and pegmatites in metamorphic terrains.     

Genesis of Kanggur Gold Deposit in Eastern Tianshan Orogenic Belt, NW China: Fluid Inclusion and Oxygen and Hydrogen Isotope Constraints

Abstract. Primary fluid inclusions in quartz and carbonates from the Kanggur gold deposit are dominated by aqueous inclusions, with subsidiary CO₂-H₂O inclusions that have a constant range in CO₂ content (10–20 vol %). Microthermometric results indicate that total homogenization temperatures have a wide but similar range for both aqueous inclusions (120 to 310C) and CO₂-H₂O inclusions (140 to 340C). Estimates of fluid salinity for CO₂-H₂O inclusions are quite restricted (5.9∼10.3 equiv. wt% NaCl), whereas aqueous inclusions show much wider salinity ranging from 2.2 to 15.6 equivalent wt %NaCl.
The 6D values of fluid inclusions in carbonates vary from -45 to -61 %, in well accord with the published δD values of fluid inclusions in quartz (-46 to -66 %). Most of the δ¹⁸O and δD values of the ore-forming fluids can be achieved by exchanged meteoric water after isotopic equilibration with wall rock by fluid/rock interaction at a low water/rock ratio. However, the exchanged meteoric water alone cannot explain the full range of δ¹⁸O and δD values, magmatic and/or meta-morphic water should also be involved. The wide salinity in aqueous inclusions may also result from mixing of meteoric water and magmatic and/or metamorphic water.     

Characteristics of Mineralizing Fluids of the Darreh‐Zerreshk and Ali‐Abad Porphyry Copper Deposits,Central Iran,Determined by Fluid Inclusion Microthermometry

The Darreh‐Zereshk (DZ) and Ali‐Abad (AB) porphyry copper deposits are located in southwest of the Yazd city, central Iran. These deposits occur in granitoid intrusions, ranging in composition from quartz monzodiorite through granodiorite to granite. The ore‐hosting intrusions exhibit intense hydrofracturing that lead to the formation of quartz‐sulfide veinlets. Fluid inclusions in hydrothermal quartz in these deposits are classified as a mono‐phase vapor type (Type I), liquid‐rich two phase (liquid + vapor) type (Type IIA), vapor‐rich two phase (vapor + liquid) type (Type IIB), and multi‐phase (liquid + vapor + halite + sylvite + hematite + chalcopyrite and pyrite) type (Types III). Homogenization temperatures (Th) and salinity data are presented for fluid inclusions from hydrothermal quartz veinlets associated with potassic alteration and other varieties of hypogene mineralization. Ore precipitation occurred between 150° to >600°C from low to very high salinity (1.1–73.9 wt% NaCl equivalent) aqueous fluids. Two stages of hydrothermal activity characterized are recognized; one which shows relatively high Th and lower salinity fluid (Type IIIa; Th_(L‐V) > Tm_(NaCl)); and one which shows lower Th and higher salinity (Type IIIb; Th_(L‐V) < Tm_(NaCl)). The high Th_(L‐V) and salinities of Type IIIa inclusions are interpreted to represent the initial existence of a dense fluid of magmatic origin. The coexistence of Type IIIb, Type I and Type IIB fluid inclusions suggest that these inclusions resulted either from trapping of boiling fluids and/or represent two immiscible fluids. These processes probably occurred as the result of pressure fluctuations from lithostatic to hydrostatic conditions under a pressure of 200 to 300 bar. Dilution of these early fluids by meteoritic water resulted in lower temperatures and low to moderate salinity (<20 wt% NaCl equiv.) fluids (Type IIA). Fluid inclusion analysis reveals that the hydrothermal fluid, which formed mineralized quartz veinlets in the rocks with potassic alteration, had temperatures of ～500°C and salinity ～50 wt% NaCl equiv. Cryogenic SEM‐EDS analyses of frozen and decrepitated ore‐bearing fluids trapped in the inclusions indicate the fluids were dominated with NaCl, and KCl with minor CaCl₂.     

Fluid evolution during metamorphism of the Otago Schist, New Zealand: (I) Evidence from fluid inclusions

Fluid inclusion salinities from quartz veins in the Otago Schist, New Zealand, range from 1.0 to 7.3 wt% NaCl eq. in the Torlesse terrane, and from 0.4 to 3.1 wt% NaCl eq. in the Caples terrane. Homogenization temperatures from these inclusions range from 124 to 350  °C, with modal values for individual samples ranging from 163 to 229  °C, but coexisting, low-salinity inclusions exhibiting metastable ice melting show a narrower range of T  _h from 86 to 170  °C with modes from 116 to 141  °C. These data have been used in conjunction with chlorite chemistry to suggest trapping conditions of ≈350–400  °C and 4.1–6.0  kbar for inclusions showing metastable melting from lower greenschist facies rocks, with the densities of many other inclusions reset at lower pressures during exhumation of the schist. The fluid inclusion salinities and Br/Cl ratios from veins from the Torlesse terrane are comparable to those of modern sea-water, and this suggests direct derivation of the vein fluid from the original sedimentary pore fluid. Some modification of the fluid may have taken place as a result of interaction with halogen-bearing minerals and dehydration and hydration reactions. The salinity of fluids in the Caples terrane is uniformly lower than that of modern sea-water, and this is interpreted as a result of the dilution of the pore fluid by dehydration of clays and zeolites. The contrast between the two terranes may be a result of the original sedimentary provenance, as the Torlesse terrane consists mainly of quartzofeldspathic sediments, whilst the Caples terrane consists of andesitic volcanogenic sediments and metabasites which are more prone to hydration during diagenesis, and hence may provide more fluid via dehydration at higher grades.     

赣中大王山钨多金属矿床流体包裹体及 H-O-S 同位素特征

为确定赣中大王山钨多金属矿床成因类型及地质特征, 笔者对主成矿期石英和硫化矿物进行了流体包裹体、H-O-S 同位素研究。 结合野外矿体产出形态, 可以将研究区划分出3 期成矿作用, 早期以矿囊状为特征, 与围岩无明显的蚀变现象, 主成矿期为大脉状, 与围岩发生云英岩化, 成矿晚期可见含矿石英晶洞。 主成矿期包裹体岩相学和显微测温结果显示： 石英中主要发育气液二相包裹体、富气相包裹体、CO₂三相包裹体和气-液-固三相包裹体 ; 包裹体均一温度为 180 ℃ ～280 ℃（峰值为190 ℃ ～210 ℃）, 盐度为7.86% ～20.22% NaCl_eqv （峰值为11%～17% NaCl_eqv ）, 结合前人对赣中石英脉型黑钨矿中的黑钨矿测温结果, 推测大王山形成于中温、中高盐度;石英包裹体δD_V-SMOW 值介于- 93.1‰～-72.5‰, δ¹⁸O_H2O 值介于0.9‰～3.4‰, 石英包裹体的温度-盐度关系图显示成矿流体混入了低温、低盐度的流体相;δ³⁴S 值介于-1.3‰～+1.9‰之间, 表明成矿物质硫源主要来自深源岩浆。 结合前人研究显示, 黑钨矿较石英早结晶, 成矿流体以岩浆水为主, 大气降水参与成矿, 硫源与深部岩浆有关。 赋矿碱长花岗岩中见有W-Mo 多金属矿囊和细晶岩、伟晶岩脉, 其成岩时间和成矿时间一致。 指示了大王山钨多金属与围岩碱长花岗岩具有一定的亲源性, 并且岩浆-流体液态不混溶作用是导致W-Mo 多金属矿沉淀的主因。     

延边杨金沟大型白钨矿矿床流体包裹体特征及成因探讨

延边杨金沟大型白钨矿矿床的成矿过程可划分为黄铁矿-毒砂阶段、石英-粗粒白钨矿阶段、石英-多金属硫化物-细粒白钨矿阶段以及碳酸盐阶段,其中,石英-粗粒白钨矿阶段为主成矿阶段。与粗粒白钨矿共生的石英中主要发育4种类型流体包裹体。Ⅰ型包裹体的气相组分主要由CO₂、CH₄和N₂组成,均一温度为278.5～336.4℃,盐度（w(NaCl)）为3.53%～7.72%;Ⅱ型气液两相包裹体均一温度为144.7~345.9℃,多数为190～220℃,w(NaCl)为3.05%～9.34%;Ⅲ型CO₂包裹体中的气相组分均为CO₂,液相中尚含少量CH₄等组分;Ⅳ型含CO₂三相包裹体由液态CO₂、气态CO₂、盐水溶液三相组成,CO₂相占10%～15%,完全均一化温度为301.6～305.1℃。综合地质条件及矿床特征、包裹体显微测温和成分分析结果认为：杨金沟石英脉型白钨矿矿床的成矿流体为中高温、低盐度的NaCl-H₂O-CO₂（-N₂）体系,初始流体主要来自酸性岩浆热液,并有地层组分的加入。成矿过程中流体发生过不混溶,并对钨的富集起到了重要作用。     

Grain boundary migration of water and carbon dioxide during uplift of garnet-zone Alpine Schist, New Zealand

Abstract Deformed quartz veins in garnet-zone schist adjacent to the active Alpine Fault, New Zealand, have fluid inclusions trapped along quartz grain boundaries. Textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins. Many of the inclusions are empty, but some contain carbon dioxide with densities that range from 0.16 to 0.80 g cm⁻³. No water, nitrogen or methane was detected. The inclusions are considerably more CO₂-rich than either the primary metamorphic fluid (<5% CO₂) or fluids trapped in fracture-related situations in the same, or related, rocks (<50% CO₂). Enrichment of CO₂ is inferred to have resulted from selective migration (wicking) of saline water from the inclusions along water-wet grain boundaries after cooling-induced immiscibility of a water-CO₂ mixture. Inclusion volumes changed after loss of water. Non-wetting CO₂ remained trapped in the inclusions until further percolation progressively removed CO₂ in solution. This mechanism of fluid migration dominated in ductile quartz-rich rocks near, but below, the brittle-ductile transition. At deeper levels, hydraulic fracturing is also an important mechanism for fluid migration, whereas at shallower levels advection through open fractures dominates the fluid flow regime.     

Mobility and H2O loss from fluid inclusions in natural quartz crystals

Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples. Received: 17 November 1998 / Accepted: 16 April 1999     

Hydrothermal Quartz Vein Formation, Revealed by Coupled SEM-CL Imaging and Fluid Inclusion Microthermometry: Shuteen Complex, South Gobi, Mongolia

Abstract. Scanning electron microscopy-cathodoluminescence (SEM-CL) imaging of vein quartz in the Cu-mineralised, Shuteen Complex (South Gobi, Mongolia) has revealed a complex history of crystal growth, dissolution and microfracture healing, associated with several hydrothermal events that could not be detected using other observational techniques (e.g. transmitted/reflected light microscopy, back-scattered electron imaging, or secondary electron imaging).
The quartz initially grew as CL-bright/grey crystals in a 345±30C liquid reservoir, as inferred by the analysis of primary liquid fluid inclusions (average Th of 343C; 6.6∼7.7 wt% NaCl_eq). Quartz precipitation occurred at the edge of the crystals as reservoir fluids cooled to 260±25C, as indicated by micron-scale CL-dark/CL-bright quartz growth bands containing abundant fluid inclusions (with an average T_h values of 261C). Pressure fluctuations were the likely cause of dissolution, as SEM-CL imaging reveals the quartz have corroded or rounded crystal edges, and precipitation of later quartz into open space. SEM-CL imaging shows the quartz contains healed microfractures that trapped low salinity fluids (3.9 wt% NaC1_eq) with Th values of 173±15C.
SEM-CL imaging provides a means of deciphering the thermal and chemical evolution of the fossil Shuteen hydrothermal system, and the nature of hydrothermal quartz vein-forming processes, by facilitating the correlation of distinct fluid inclusion populations and their relative chronology, with specific hydrothermal events.     

Microthermometric Evidence for the Formation of Ca-rich Hypersaline Brine and CO2–rich Fluid in the Mori Geothermal Reservoir, Japan

Abstract: Fluid inclusions in hydrothermal quartz and anhydrite samples from the Mori geothermal field, southwest Hokkaido, have been studied microthermometrically using heating/freezing stages. Based on homogenization temperatures of fluid inclusions, salinities after correction of effect of freezing-point depression of CO₂ on ice melting temperatures of fluid inclusions, and previous geochemical data by Yoshida (1991), we discuss the geneses of various types of inclusion fluids in the Mori geothermal reservoir.     

Genesis and mineralization of gold-bearing quartz veins in the Xiao Qinling area, central China

Gold-bearing quartz veins of the Taihua Group consisting of Archean metavolcanic rocks are a main gold deposit type in the Xiao Qinling area,one of the three biggest gold production areas in China.The quartz veins experienced strong alteration characterized by a typical mesothermal hydrothermal altered mineral assemblage.The grade of gold is affected by the contents of sulphides,e.g.galena,pyrite and chalcopyrite.Results of minor elements analysis for the of gold-bearing quartz veins indicate higher contents of Au and high contents of Ag,Pb,Cu,Cd,W,and Mo.Abundant fluid inclusions were found in the gold-bearing quartz veins.Three types of fluid inclusions were identified:(1) aqueous inclusions;(2) CO 2-bearing inclusions;and(3) daughter crystal-bearing fluid inclusions.Homogenization temperatures ranged from 110 to 670℃ with low and high peaks appearing at 160 180℃ and 280 300℃,respectively.The salinity of aqueous inclusions varies between 1.8 wt% and 38.2 wt% NaCl.The homogenization temperature and salinity show a positive correlation.The H and O isotopes of fluid inclusions in the gold-bearing quartz veins indicate that magmatic solution and metamorphic hydrothermal solution,together with meteoric water,were involved in the formation of gold-bearing fluid.Mesozoic magma activities related to granite intrusions should be the main source of CO 2 fluid with higher temperature and salinity.     

Fluid inclusion studies of a new type of ore deposit: Porphyry tungsten occurrence in China

Lianhuashan mine in South China represents a new type of tungsten ore which can be described as a porphyry tungsten deposit. It is associated with a quartz porphyry stock of Yenshanian age (about 70–135 m. y.). The ore occurs in zone surrounding the contact of the quartz porphyry with Jurassic sandstone and extends into both rock bodies. The ore occurs either as the matrix of breccia or in the form of a very fine network of cross cutting veinlets. The major tungsten minerals are wolframite and scheelite associated with sulfide minerals of Mo, Fe, Cu, Pb and cassiterite. The minerals are fine-grained. There is zoned alteration in the wall rocks. From the center of the quartz porphyry toward the wall rocks one finds: potassic alteration, silicification-sericitization, and chloritization. All these features are similar to those of porphyry copper mineralization. Fluid inclusion studies show three types of inclusion: liquid-rich (Type I), gas-rich (Type II), and polyphase with daughter minerals (Type III) fluid inclusions. The homogenization temperatures of Type I range from 210° to 380°C, with a salinity of 2–15 wt.% NaCl equiv., those of Type II from 270° to 420°C, and those of Type III from 240° to 400°C with a salinity of 31–33 wt.% NaCl equiv. The closely associated group of gas-rich and daughter mineral-bearing fluid inclusions homogenized at almost the same temperatures. Such results indicate boiling of oreforming fluids. These fluid inclusion data indicate that low salinity (Type I) and high salinity fluids (Type III) responsible for porpb yry copper deposits are the same as those for porphyry tungsten ore deposits. These observations suggest that the Lianhuashan tungsten ore deposit is a porphyry tungsten deposit and was formed by hydrothermal fluids similar to those responsible for the well-known porphyry copper deposits.     

柴北缘阿日特克山斑岩型铜钼矿床流体包裹体、稳定同位素特征及其地质意义

阿日特克山铜钼矿床位于柴北缘中北段,为近年来新发现的隐伏斑岩型矿床,矿体产出于海西晚期—印支期花岗闪长（斑）岩和古元古代达肯大坂岩群接触部位。为探讨该矿床成矿流体特征和成矿机制,本文对矿床野外地质特征、流体包裹体及稳定同位素组成进行了系统的研究。根据不同类型矿脉之间的相互关系,可将热液成矿期次划分为成矿早期石英阶段、成矿期辉钼矿-多金属硫化物-石英阶段和成矿晚期石英-方解石阶段。流体包裹体岩相学研究表明,阿日特克山铜钼矿床流体包裹体以Ⅰ型（富液相L+V两相水溶液包裹体）、Ⅱ型（富气相L+V两相水溶液包裹体）和Ⅲ型（含子矿物三相水溶液包裹体）为主。显微测温及包裹体拉曼光谱分析结果显示,成矿流体体系为中高温、中低盐度、中高密度的NaCl-H₂O体系,至成矿晚期,流体性质变化为低温、低盐度、高密度流体,矿床形成深度为0.40~4.00 km。氢氧同位素分析测试结果显示,δD_V-SMOW值为-92.9‰~-78.4‰,δ¹⁸O_H2O值为-7.4‰~2.0‰,表明成矿流体以混合流体为主,随着成矿流体的演化,有更多的大气降水不断混入。矿石中金属硫化物δ³⁴S值处于9.4‰~11.7‰之间,平均值为10.2‰,表现出明显的地层硫特征,为岩浆热液与围岩地层相互作用所致。综上认为,阿日特克山铜钼矿床为矽卡岩型-斑岩型矿床,形成于海西晚期—印支期俯冲碰撞构造环境,混合成矿流体强烈的不混溶作用为斑岩型铜钼矿床形成的主要机制。     

青海东昆仑阿斯哈金矿Ⅰ号脉成矿流体地球化学特征和矿床成因

阿斯哈金矿位于东昆中隆起带东段,是东昆仑重要的金、铁多金属成矿带。金矿的容矿围岩为印支早期闪长岩和黑云母花岗岩,NNE向和NW向断裂为主要的容矿构造,Ⅰ号脉为该金矿主要的矿脉之一,云煌岩与金矿脉空间关系密切。流体包裹体主要有富CO₂三相和气液两相2种类型。流体盐度（w(NaCl)）为1.83%~8.13%,流体密度为0.69~0.87 g/cm³,成矿温度为155.3~425.6 ℃。成矿Ⅰ阶段流体为低盐度、富CO₂的高温流体;成矿Ⅱ阶段富CO₂型和气液两相流体包裹体共存,发生了以CO₂逸失为特征的不混溶或沸腾,致使残余流体盐度升高;成矿Ⅲ阶段为气液两相包裹体。激光拉曼光谱分析表明,流体气相成分主要有CO₂、CH4、N₂。结合氢、氧和硫同位素组成分析认为,成矿流体主要为幔源流体,晚期有大气水的加入。通过等容线图解法估算成矿压力为98~132 MPa,估算成矿深度为8.16~9.58 km。通过与典型造山型金矿特征对比,阿斯哈金矿为中成造山型金矿,矿床形成于早印支期陆内造山由挤压向伸展转换时期。     

赤城县梁家沟铅锌银多金属矿床流体包裹体特征及其意义

文章运用激光拉曼光谱和显微测温等方法,对赤城县梁家沟铅锌银多金属矿床矿石中的石英流体包裹体进行均一温度、盐度的测试分析。结果表明,矿物中的流体包裹体以气液2相为主,气相成分主要是CO2,液相成分主要是H2O和烃类液体;包裹体的均一温度为80.0~160.0℃,盐度w(NaCl)=2%~12%,说明矿床形成条件为低温低盐度,且富含烃类物质。结合矿床地质特征、矿床的构造位置、产出地层和该矿床中矿(岩)石的常量元素、微量元素和稀土元素的数据研究结果,初步厘定梁家沟铅锌银矿床属于密西西比河谷型(MVT)矿床。     

辽宁清原南龙王庙金矿流体包裹体研究

南龙王庙金矿位于华北克拉通北缘,产在清原群表壳岩的北东端.主要容矿岩石为新太古代的磁铁石英岩,控矿构造为葫芦头沟-大荒沟韧性剪切带.矿石以细脉-浸染状构造为主.主要蚀变类型有白云母化、硅化、绿泥石化、碳酸盐化和绿帘石化.对矿区细脉-浸染状矿石石英中的流体包裹体进行了系统的岩相学、显微测温分析.结果显示,矿石石英中存在两个不同阶段的流体包裹体：早阶段形成的包裹体主要为含子矿物的三相包裹体（I）;晚阶段形成的包裹体包括气液两相包裹体（II）、纯CO₂包裹体（III）和含CO₂三相包裹体（IV）三种类型.流体演化过程为：早阶段的中温、高盐度、中等密度的流体,萃取清原群表壳岩中的Au;晚阶段在剪切带韧性变形向脆性变形转化过程中,流体演化为中温、中低盐度、低密度的特征,Au成矿元素达到饱和,在有利的构造空间沉淀成矿.成矿作用的方式由早期的扩散交代逐渐转变为晚期的充填作用,分别形成细脉-浸染状矿体和含金黄铁矿石英脉型矿体.     

Primary carbonate/CO2 inclusions in sapphirine-bearing granulites from central Sri Lanka

High-density CO₂-rich fluid inclusions from a sapphirine-bearing granulite (Hakurutale, Sri Lanka) have been studied by microthermometry, Raman spectrometry and SEM analysis. Based on textural evidence, two groups of inclusions can be identified: primary, negative crystal shaped inclusions (group I) and pseudo-secondary inclusions, which experienced a local, limited post-trapping modification (group II). Both groups contain magnesite as a daughter mineral, occurring in a relatively constant fluid/solid inclusion volume ratio (vol_solid =0.15 total volume). CO₂ densities for group I and II differ only slightly. Both groups contain a fluid, which was initially trapped at peak metamorphic conditions as a homogeneous (CO₂+MgCO₃) mixture. Thermodynamic calculations suggest that such a fluid (CO₂+15 vol% MgCO₃) is stable under granulite facies conditions. After trapping, magnesite separated upon cooling, while the remaining CO₂ density suffered minor re-adjustments. A model isochore based on the integration of the magnesite molar volume in the CO₂ fluid passes about 1.5–2 kbar below peak metamorphic conditions. This remaining discrepancy can be explained by the possible role of a small quantity of additional water.