Interpretation Of Fluid Inclusion Data Research Articles

Fluid Origin and Evolution of the Roc Blanc Silver Deposit (Jebilet Massif, Variscan Belt, Morocco): Constraints from Geology and Fluid Inclusions

The Roc Blanc Pb-Zn-Ag-Au vein deposit is located in the NW of Marrakech, in the Central Jebilet massif. It is spatially related to Bramram-Tabouchennt-Bamega (BTB) granodioritic pluton (ca. 330 Ma) metamorphism aureole. The main veins hosted in black shales are oriented N-S to NNW-SSE. Pb-Zn-Ag-Au ore is associated with quartz, chlorite, sericite, and carbonate gangue minerals. Two major stages of ore deposition were distinguished. The preore stage (stage I) comprises two quartz-mineralised vein generations with Fe, As, Zn, and Cu ores (vg1 and vg2). The main ore stage (stage II) consists mainly on Ag, Au, Pb, Zn, Cu, and Sb ores, which is hosted by carbonaceous vein (vg3) and by two late quartz generations veins (vg4 and vg5 with a geodic quartz). Three types of fluid inclusions have been recognized in silver mineralisation bearing quartz veins according to petrographic investigations, microthermometry, and Raman spectroscopy studies: (i) liquid-rich H2O-N2-CH4±CO2-(salt) fluid inclusions (type 1), (ii) vapour-rich H2O-CO2-CH4-N2-(salt) fluid inclusions (type 2), and (iii) aqueous H2O-(salt) fluid inclusions (type 3). The interpretation of fluid inclusion data shows a mixing of two fluids that are metamorphic and surface to subsurface origin, trapped at boiling state. The first mineralised stage was deposited at 350 ± 20 ° C (this temperature of ore deposition was supported also by chlorite geothermometry) with salinity of 13.7 wt% NaCl equiv., while the deposition of the argentiferous stage, which consists of the main economic mineralisation of the Roc Blanc deposit, occurs during decreasing temperature at 150°C with a salinity of 12.1 wt% NaCl equiv. The all-mineralised ore was deposited at relatively low pressure, below ~1-1.1 kbar. So, fluid dilution and cooling are probably the main factor for silver deposition in the Roc Blanc polymetallic vein deposit. In addition, fluid inclusion studies reveal that the mineralising fluid corresponds to a mixture of metamorphic fluid (H2O-CH4-N2-CO2) with surface to subsurface aqueous gas-free fluids (H2O-salt, meteoric, or brine).

Geology, geochemistry, fluid inclusion and genesis of the Guijeh Qaleh IOA-type iron ore deposit, north of Takab district, Northwestern Iran

The Guijeh Qaleh iron deposit, located in the Takab district of northwestern Iran contains ca. 0.3 million metric tons (Mt) of ore at 48 wt. % Fe. The host rocks are Eocene to Oligocene volcano-sedimentary sequences consisting of andesite, trachy-andesite to basaltic andesite flows intruded by granites to granodiorite intrusions. The hydrothermal alterations include argillic, sericitic, silicified, carbonate, and hematitic zones. Silicified and hematitic alteration zones are spatially associated with the mineralization and occur proximal to ore bodies, whereas sericite, carbonate, and argillic alteration zones are distal to main ore bodies.Iron mineralization occurred as several quartz-hematite-specularite veins, 0.5- to 5-m wide and 10- to 20-m long, which were formed within and along normal and strike-slip fault zones. The mineralogy of ore bodies consists of hematite, specularite, pyrite, subordinate magnetite and apatite together with minor malachite (after chalcopyrite) with open space-filling, disseminated, massive, and breccia textures. Geochemical analyses of high-grade ore bodies show that Fe concentration is strongly correlated with Mo, Zn, Mn, Pb, SiO2, MgO, TiO2, and P2O5. The chondrite-normalized REE patterns of the altered and mineralized ore bodies displays with LREE/HREE ratio with a negative Eu anomaly and low Eu/Eu* values characteristic of the Kiruna-type IOA deposits.Fluid inclusion studies from quartz occurring with the mineralization characterized mineralizing fluids with homogenization temperatures ranging from 133 to 464 °C, and apparent salinities between 0.2 to 23.2 wt. % NaCl equ. Interpretation of fluid inclusion data suggest that mixing of magmatic and meteoric fluids and cooling caused ore precipitation. Geology, mineralogy, ore textures, geochemistry, and fluid inclusion data suggest that iron mineralization in the Guijeh Qaleh deposit is similar to Kiruna-type IOA deposits. The presented data show that the Takab district has the potential for hosting Kiruna-type IOA mineralization in the northwest of Iran.

Fluids in metamorphic rocks

Basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated. A major problem relates to the number of inclusions, possibly formed on a wide range of P– T conditions, having also suffered, in most cases, extensive changes after initial trapping. The interpretation of fluid inclusion data can only be done by comparison with independent P– T estimates derived from coexisting minerals, but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host. The three essential steps in any fluid inclusion investigation are described: observation, measurements, and interpretation. Observation, with a conventional petrographic microscope, leads to the identification and relative chronology of a limited number of fluid types (same overall composition, eventually changes in fluid density). For the chronology, the notion of GIS (Group of synchronous inclusions) is introduced. It should serve as a systematic basis for the rest of the study. Microthermometry measurements, completed by nondestructive analyses (mostly micro-Raman), specify the composition and density of the different fluid types. The major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms, allowing elimination of a great number of inclusions having suffered late perturbations. Finally, the interpretation is based on the comparison between few isochores, representative of the whole inclusion population, and P– T mineral data. Essential is a clear perception of the relative chronology between the different isochores. When this is possible, as illustrated by the complicated case of the granulites from Central Kola Peninsula, a good interpretation of the fluid inclusion data can be done. If not, fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur.

The thermal and geochemical structure of geothermal and epithermal systems: A framework for interpreting fluid inclusion data

Fluid inclusions are often formed during mineral growth in hydrothermal systems. They may be studied in geothermal systems, where comparing the results with directly measured temperatures and fluid compositions allows short time scale variations in the system to be assessed. Insight into the interpretation of fluid inclusions is obtained from such comparisons, which can be applied to the interpretation of fluid inclusion data from extinct systems, e.g., epidermal ore deposits. The interpretation of fluid inclusion data from extinct systems is often much more difficult than for active systems, due to constraints imposed by the mineral record, which only preserves a partial history of a system, and uncertainty of the water level during activity. A good paragenetic control on timing of inclusion formation is also necessary, particularly where there are several overprinting events. Fluid inclusion data need to be integrated with all relevant geochemical and geological constraints to develop an internally consistent model of the systems; internal consistency is sometimes the only assurance that our conclusions are realistic. The fluid inclusion data reviewed here include T h and T m measurements and the composition of extracted gases from liquid-dominated hydrothermal systems of neutral pH and relatively low salinity. The deep fluids in many systems boil in the uppermost 1 to 2 km of ascent, though mixing with cooler waters on the margins and very close to the surface will quench boiling. These processes can be recognized from the interpretation of paragenetically-controlled T h and T m data; furthermore, the temperatures and compositions of the end-member fluids can be estimated, and the total gas content of a fluid inferred. However, the extraction and analysis of gases provides a more quantitative estimate of the total concentration while determining the species and relative amounts of gases. Gases may be used in studies of mineral-fluid equilibria, and as independent geothermometers (CO 2 , CH 4 , H 2 S and H 2 ); combined with Th data, this information helps to estimate the temperature of first boiling as well as the initial gas content of a fluid, while variation in gas ratios between samples may be evidence for boiling and vapour loss. Comparison of gas composition with the host mineral assemblages allows post-entrapment changes and analytical artefacts to be recognized (e.g., H 2 ), which are topics for further study before gases can be confidently used to their full potential. Relatively non-reactive gases (N 2 , Ar, He, as well as gas isotopes such as 3 He/ 4 He) can be used as tracers of sources

Mixing diagrams for hydrothermal solutions: Applications to interpretation of fluid inclusion data of hydrothermal ore deposits in Japan.

Temperature-chloride mixing diagrams at 500 and 1000 bars, and at vapor-saturated pressures, are calculated in order to demonstrate the mixing behavior of saline (up to 40 NaCl wt%) high-temperature solutions with 1 wt% low-temperature solutions, with the results applied to interpreting fluid inclusion data. The temperature of the initial saline solutions is 450°C at 500 bars, 600°C at 1000 bars, or 300°C at vapor-saturated pressures. The temperature of the diluent is 100° or 300°C at 500 and 1000 bars, and 100°C at the vapor-saturated pressure. Mixing diagrams at 500 and 1000 bars are recast onto the relation between homogenization temperature and chloride concentration of fluid inclusion using densities of NaCl solutions. Temperature-chloride mixing diagrams indicate that mixing of 40 wt% fluids with dilute solutions at 1000 bars is not linear, but shows a greater decrease in temperature with up to 3 wt% NaCl deviation. The deviations are larger (up to 9 wt%) with respect to homogenization temperature versus concentration relations. In contrast, mixing lines for 30 to 10 wt% initial fluids at 1000 bars and those for 40 to 10 wt% fluids at 500 bars are nearly linear with respect to temperature (or homogenization temperature) and NaCl concentration, within ±3 wt% deviations. At vapor-saturated pressures, 300°C and 25 to 5 wt% initial solutions show nearly linear mixing relationships under the condition that vapor/liquid volume ratios are less than 1. Potassium chloride solutions show almost identical temperature-chloride relations with sodium chloride solutions, up to 325°C, 500 bars, and 6 mole/kg, when the molalities of saline and dilute solutions are same for both solutes. The relations between homogenization temperature and concentration for KCl solutions show slightly smaller slopes than those for NaCl solutions. Application of these results to fluid inclusion data of the Ohe, Toyoha, and Fujigatani-Kiwada deposits in Japan indicates that high temperature and high salinity fluids (335°C and 6.3 wt% for the Ohe deposit; 325°C and 4.6 wt% for the Toyoha deposit; 360°C and 7.4 wt% for the Fujigatani-Kiwada deposits) mixed with low temperature and low salinity solutions (221°C and 1.6 wt% for the Ohe deposit; 209°C and 0.0 wt% for the Toyoha deposit; 250°C and 1.9 wt% for the Fujigatani-Kiwada deposits).

P- V- T properties of fluids in the system H 2O ± CO 2 ± NaCl: New graphical presentations and implications for fluid inclusion studies

Understanding the role of fluids in geologic processes requires a knowledge of the P- V- T properties of fluids over a wide range of conditions. Comparisons of several published equations of state with available experimental data for fluids composed of H 2O and CO 2 lead to the conclusion that the hard-sphere modified Redlich-Kwong equation of state of Kerrick and Jacobs (1981) most accurately predicts the P- V- T properties in this binary system. To model the volumetric properties in the H 2OCO 2NaCl system a formulation is presented involving a linear (ideal) interpolation between a pure-CO 2 isochore predicted by the equation of state of Kerrick. and Jacobs (1981) and an H 2O-NaCl isochore predicted by an empirical equation derived from the regression of available P- V- T data for the H 2O-NaCl system. This formulation is applicable over a wide range of temperatures (>350°C) and pressures (2–10 kbars) and is especially suitable for high pressures and low-to-moderate temperatures (fluid densities ≥ 1.0 cm 3). Determination of the appropriate isochore for an H 2OCO 2NaCl fluid inclusion requires (1) the relative salinity (NaCl/H 2O + NaCl), (2) bulk density of the combined gas and liquid CO 2 phases, and (3) volume percent estimate of the aqueous p the total homogenization temperature. The commonly encountered problem of estimating the volume percents of phases in inclusions may be avoided in some applications, and several new P- X(CO 2) diagrams have been constructed and contoured with (a) the solvi in the mixed volatile system and (b) the measured density of the CO 2 phase. The effects of H 2OCO 2 clathrates during microthermometric observations in the laboratory are evaluated and in most instances can be minimized or avoided. Application of these results to fluid inclusion studies have led to improved determinations of (1) pressures and temperatures of fluid entrapment in a variety of geologic settings and (2) pressures and temperatures of cooling and uplift following the peak of metamorphism. Proper interpretation of fluid inclusion data (from the literature) for two granulite fades terranes suggests that the uplift P- T- t path is more nearly initially isobaric than has sometimes been presented.

The application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs

Fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history. Temperature, pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration. Cements in petroleum reservoirs contain both oil and aqueous fluid inclusions. Fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil. The lifetime of fluorescence induced by a pulsed laser is related to the API gravity of entrapped oil. Interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment. Those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments. Examples of how fluid inclusions are used to determine the physico-chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the Wealden Basin, England, the Mishrif Formation, Dubai, the Smackover Formation, Gulf Coast, U.S.A. and Jurassic sandstones, offshore Norway. In the Wealden Basin, temperature data from fluid inclusions are used to determine that oil migration occurred in the Cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration. Distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin. The geochemistry of oil inclusions in calcite cements from the Mishrif Formation, Dubai, are used to determine the type and maturity of entrapped oil. Temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil. In deep Smackover reservoirs oil contains H 2S. The origin of the H 2S is examined by study of fluid inclusions containing H 2S. In Jurassic sandstones, offshore Norway, fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid.

Fluid immiscibility in natural processes: Use and misuse of fluid inclusion data: II. Interpretation of fluid inclusion data in terms of immiscibility

Phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility (in Part I). Following from that point, the major limits on the accuracy, and even the validity, of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed. The practical implications of the general constraints (temperature, pressure, topology of the fluid systems) are envisaged. Emphasis is laid on some important consequences such as: the use of isochore intercepts (and the possible resulting interpretation of fluid mixing rather than unmixing), the case of highly saline inclusions, the identification and interpretation of heterogeneous trapping. The composition and density constraints on coexisting fluids are presented, and illustrated by natural examples. Taking into account all the measurable parameters in fluid inclusions (volume, temperature and nature of phase transitions, more or less complete individual spectroscopic analyses), all the available experimental data, and all the theoretical constraints, may be long and difficult. However, it is most generally very informative and productive although part of these data is often sufficient to deny unmixing. Nevertheless, a final example on metamorphic fluids demonstrates how such an approach can “prove”; and also characterize a fluid unmixing during a geologic process.

Fluid immiscibility in natural processes: Use and misuse of fluid inclusion data: I. Phase equilibria analysis — A theoretical and geometrical approach

Many occurrences of fluid immiscibility in natural geologic systems have been reported recently, most often from fluid inclusion studies. However, the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary, insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology (in the TPX space) of natural fluid systems. For such reasons some authors have been misled to erroneous interpretations. The term “chemical immiscibility” is unambiguously redefined as a multiphase multicomponent equilibrium. The consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters (temperature, pressure, volumes, compositions) to each other. These equations already put constraints on the topology of the phase equilibria in fluid systems. A particular expression of the phase rule is proposed, which takes into account the multiphase-constant bulk volume-constant bulk composition constraints in fluid inclusions. The consequences of such an expression are of major importance in fluid inclusion studies. The phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed: H 2ONaCl, CO 2CH 4, H 2OCO 2, H 2OCO 2NaCl. The effects of these topologies and of the supplementary constraints (constant bulk composition and constant bulk volume) assumed for fluid inclusions (isopleth-isochoric systems) are discussed.