Primary Fluid Inclusions In Quartz Research Articles

Multiple Hydrothermal Processes in Footwall Units of the North Range, Sudbury Igneous Complex, Canada, and Implications for the Genesis of Vein-Type Cu-Ni-PGE Deposits

Systematic regional sampling along the contact zone of the 1.85 Ga age Sudbury Igneous Complex with the Archean Levack Gneiss footwall in the North Range of the Sudbury structure revealed textural, mineralogical, and fluid inclusion systematics of post-Sudbury Igneous Complex hydrothermal processes that affected the various lithologies. At late stages of emplacement of the Sudbury Igneous Complex and formation of magmatic Fe-Ni-Cu sulfide deposits a partial melt from the Levack Gneiss invaded the contact zone. This partial melt is revealed by small microdikes and irregular bodies of granophyric quartz-plagioclase with megacrysts of hornblende, clinopyroxene, and titanite. Plagioclase-hornblende equilibrium was established at 750° to 800°C and 1.10 to 1.55 kbars pressure, corresponding to about a 4- to 6-km depth under lithostatic conditions. F/Cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a Cl-rich fluid phase separated during the crystallization of the footwall granophyre: this is expressed as miarolites. The Cl-rich fluid (50 wt % NaCl equiv salinity) was trapped as primary fluid inclusions in quartz at around 480°C minimum temperature and around 1.1 kbars minimum pressure during supercooling. These inclusions are rich in Ca, Fe, Mn, and K, as well as Na chloride. This fluid may have interacted with earlier primary magmatic sulfide, causing remobilization and reprecipitation of Cu-Ni-platinum-group elements (PGE) in veins and disseminations in the footwall. These veins are parallel to the Sudbury Igneous Complex-footwall contact and are characterized by chalcopyrite, pentlandite, millerite, magnetite, stilpnomelane, ferropyrosmalite, epidote, and chlorite. Michenerite, moncheite, merenskyite, froodite, insizwaite, sobolevskite, gold, and Bi-Ni sulfides are associated with sulfides. Epidote, quartz, actinolite, and chlorite are common in the alteration selvages of the veins. Compositions and assemblages of platinum-group minerals (PGM) indicate their precipitation below 575° to 485°C. Primary, highly saline fluid inclusions (about 40 wt % NaCl equiv) in quartz indicate crystallization at 400° to 480°C and around 1.6 kbars minimum T and P, respectively. Late carbonate-epidote-actinolite-chlorite veins and alteration overprinted the earlier assemblages at about 300° to 400°C, with some bornite, millerite, native silver, and other Bi sulfides. The second stage of hydrothermal activity is characterized by regional carbonic-aqueous (NaCl-CO 2 -CH 4 -H 2 O-type) immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies. No mineralization is related to this stage along the North Range. Boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5- to 6- to a 3- to 4-km depth at 300° to 350°C. High- (20–26 wt % NaCl equiv) and low-salinity (6–12 wt % NaCl equiv) fluids coexisted with different carbonic species contents. The predominant north-south and northwest-southeast orientations of fluid inclusion planes reveal that mobilization of carbonic-aqueous solutions may be related to the northwesterly oriented thrusting in the Sudbury structure during the late stages (1.8–1.7 Ga) of the Penokean orogeny and to predominantly north-south faulting in the North Range. The third stage of fluid mobilization also took place mostly along northerly and northwesterly oriented fractures. Aqueous fluids were Ca-rich brines (20–40 wt % salinity) with temperatures between 150° and 250°C. Some of these fluids also circulated in fractures parallel to the Sudbury Igneous Complex-footwall contact (NE-SW); thus, they locally may have interacted with the earlier sulfide assemblages and are also responsible for formation of late veinlets with chalcopyrite-epidote-quartz-chlorite assemblages. Mobilization of these fluids took place under litho- and hydrostatic conditions at about a 4- to 6-km depth. This hydrothermal activity is related to a regional tectonothermal event during emplacement of northwesterly oriented Sudbury dikes (1.24 Ga). Regional-scale fluid inclusion studies along the North Range highlight the role of multiple hydrothermal processes in the metallogenic evolution of the Sudbury Igneous Complex and especially in the distribution of copper and precious metals in the footwall units.

Origin of the Gacun Volcanic-Hosted Massive Sulfide Deposit inSichuan, China: Fluid Inclusion and Oxygen Isotope Evidence

The Gacun polymetallic, Ag-rich, volcanic-hosted massive sulfide deposit occurs in a Triassic submarine calc-alkaline volcanic belt that forms part of the Yidun collisional orogenic zone of southwestern China. The deposit is hosted in felsic volcanic rocks associated with an underlying mafic unit (a bimodal suite), which formed in an intra-arc rift basin at about 1,000 m water depth. The volcanic rocks underwent regional lower greenschist facies metamorphism and related deformation during the Yanshan-Himalayan orogeny, resulting in folding and shearing of the ore lenses. The deposit is made up of three mineralized zones: a sheet-like upper massive sulfide zone with exhalite (barite, chert, and jasper), a middle stringer-stockwork strata-bound zone hosted in rhyolitic volcanic rocks, and an underlying lower stringer strata-bound zone in dacitic volcanic rocks. Fluid inclusion studies indicate that two-phase primary fluid inclusions in quartz in the lower stringer ore zone homogenized between 299° and 319°C (average temperature 308°C), whereas those in sphalerite yielded a temperature range from 185° to 260°C (average temperature 241°C). Homogenization temperatures of fluid inclusions in quartz from the middle stringer-stockwork zone ranged from 150°to 350°C and averaged 243°C. The homogenization temperature of fluid inclusions in quartz and sphalerite from the massive sulfide zone show a bimodal distribution corresponding to temperatures from 250° to 150°C for quartz and from 200° to 140°C for sphalerite. Fluid inclusions in barite fragments from an interpreted submarine vent recorded higher homogenization temperatures ranging from 208° to 358°C, whereas those in fined-grained barite from the upper gray-white massive baritic ore gave lower homogenization temperatures ranging from 98° to 125°C. Salinities of fluid inclusions show a wide range from 4.2 to 21.3 wt percent NaCl equiv in the three mineralized zones. Fluid inclusions in quartz from the lower stringer zone have the highest salinities (17.1–21.3 wt % NaCl equiv), whereas those in barite from gray-white massive baritic ores have the lowest salinity (average 4.0 wt % NaCl equiv), close to that of normal seawater. Salinities of fluid inclusions in sphalerite ranged from 5.1 to 14.5 wt percent NaCl equiv, and the high-salinity end member was found mainly in the massive sulfide zone. Preliminary laser Raman spectroscopic analysis of fluid inclusions from the three mineralized zones identified CO 2 , CH 4 , and H 2 S. Oxygen isotope compositions of eleven quartz samples separated from the stringer and stockwork ores and of two silica breccias in the basal sulfide massive ores yielded a limited range from 13.7 to 16.4 per mil. Fourteen host felsic volcanic rock samples and seven quartz samples separated from several alteration zones display a wide range in bulk rock δ 18 O values from 8.0 to 17.1 per mil. For the volcanic rocks in various alteration zones, a significant increase in δ 18 O value was recorded in the deposit outward from the orebodies and downward from upper to lower volcanic units. The most strongly altered quartz-hyalophane zone gave a bulk rock δ 18 O value of 11.3 to 14.4 per mil. The moderately altered sericite-quartz zone yielded slightly higher bulk rock δ 18 O values of 12.5 to 15.4 per mil. The weakly altered lower volcanic unit has much higher bulk rock δ 18 O values ranging from 15.1 to 17.1 per mil; these values are comparable to those measured for the zeolite zone in the Kuroko deposits of Japan. The hydrothermal system that formed the Gacun deposit was relatively high temperature (up to 350°C); it had a relatively high gas content and high salinity and was enriched in 18 O. These data suggest that the dominant 18 O-rich hydrothermal fluid was derived from a felsic magma chamber at depth. The high-salinity fluid inclusions in the massive sulfide zone suggest that ore formed in a sea-floor brine pool filled by episodic venting of mixed subsea-floor fluids. Fluid inclusions with salinities close to that of normal seawater and homogenization temperatures around 250°C in sphalerite and barite within the ore zone suggest that seawater was heated to that temperature by felsic intrusions. Near the mineralized center and main path of hydrothermal fluid discharge at Gacun, fluid inclusions in the strata-bound zone recorded that a minor amount of cold seawater mixed with magmatic fluid. In comparison, away from the mineralized center, a large amount of cold seawater mixed with magmatic-derived fluid and heated seawater in the strata-bound zone.

Thermal history during Mesozoic extension and Tertiary uplift in the Cameros Basin, northern Spain

AbstractDetailed structural cross‐sections, analysis of extensional structures and palaeotemperatures obtained from primary fluid inclusions in quartz and calcite veins from the extensional Cameros Basin (N Spain) allow an interpretation of its thermal evolution and its geometric reconstruction to be constrained. The Cameros Basin underwent an extensional stage during the Late Jurassic to Early Cretaceous, with a maximum preserved thickness of Mesozoic deposits of about 9000 m. During the Tertiary, the basin was inverted, allowing a large part of the sedimentary sequence to be exposed. Extensional deformation in individual beds created N120E‐striking tension gashes in the synrift sequence, parallel to the master normal faults limiting the basin and dipping perpendicular to bedding. The extensional strain calculated from tension gashes varies between 4 and 12%. The number and thickness of veins increases the lower their position in the stratigraphic section. Palaeotemperatures were obtained from samples along a stratigraphic section comprising a thickness of 4000 m synrift deposits. Homogenization temperatures range from 107 to 225 °C. Palaeothermometric data and geometric reconstruction give a geothermal gradient of 27–41 °C km−1 during the extensional stage and allow an eroded section of at least 1500 m to be inferred. Low‐grade metamorphic assemblages in lutitic rocks of the deepest part of the basin presently exposed at surface imply P–T conditions of 350–400 °C and less than 2 kbar, which implies a geothermal gradient of about 70 °C km−1. Since the metamorphic thermal peak is dated at 100 Ma, the P–T path indicates a heating event during the late Albian, probably linked to the reaching of thermal equilibrium of the continental crust after extension. The results obtained support the hypothesis of a synclinal basin geometry, with vertical superposition of Lower Cretaceous sedimentary units rather than a model of laterally juxtaposed bodies onlapping the prerift sequence.

Evidence for fluid phase separation in high-grade ore zones at the Porgera gold deposit, Papua New Guinea

Coexisting, liquid-rich and vapor-rich primary fluid inclusions in quartz provide direct evidence for fluid phase separation in high-grade quartz–roscoelite–gold veins and breccias from the Porgera alkalic-type gold deposit. Vapor-rich fluid inclusions are CO2-rich, and sometimes contain liquid CO2 at room temperature. The close spatial and paragenetic relationship between these “boiling assemblage” fluid inclusions and gold suggests that gold was precipitated by phase separation, at least locally. Additionally, the occurrence of carbonate and sulfate minerals in high-grade veins (reflecting pH increase and oxidation of the boiled fluid) and the appearance of hydrothermal breccias, are consistent with the process of fluid phase separation. Liquid CO2-bearing fluid inclusions are rare in near-surface epithermal deposits, and indicate that the Porgera vein system was formed at greater depths and pressures (our estimates suggest pressures between 250 and 340 bars). It is suggested that alkalic-type gold deposits may be distinguished from other epithermal deposit types by the more gaseous nature of the ore-forming fluids, in addition to their association with alkalic magmas.

High CO 2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids?

Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with the gold mineralisation contain a low salinity ( CO2 and low salinity ( ± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids.

Diffusional 18O loss from inclusion water in a natural hydrothermal quartz from the Kaneuchi tungsten deposit, Japan

In hydrothermal quartz from the Kaneuchi tungsten deposit of Honsyu island, Japan, the smaller primary fluid inclusions have the power δ18O values. This correlation is well accounted for by a quantitative model based on (isotropic or anisotropic) 18O diffusion through quartz. The model yields a room temperature 18O diffusivity that is close to the extrapolated diffusivity of water molecules measured by Cordier (1988) but much higher than the extrapolated diffusivity of structural oxygen measured by Farver and Yund (1991). The observed correlation between the size of primary fluid inclusions in quartz and their δ18O(water) is thus, well explained by relatively fast diffusion of oxygen as water molecules.

Fluid inclusion and phase equilibrium studies at the Cannivan Gulch molybdenum deposit, Montana, USA: Effect of CO 2 on molybdenite-powellite stability

The molybdenum deposit at Cannivan Gulch is characterized by both stockwork- and skarn type mineralization. The vein mineral assemblages, however, differ considerably between the various host rocks. In the Cannivan stock, molybdenite occurs in typical quartz + K-feldspar or quartz + muscovite veins. In the country rocks, molybdenite occurs in chlorite + pyrite + magnetite veins containing variable amounts of quartz, calcite, and epidote. Primary fluid inclusions in quartz and fluorite contain aqueous liquid, CO 2 liquid, and CO 2 vapor (average X CO 2 = 0.05). Microthermometric and Laser Raman microspectrographic analyses indicate CO 2 is the principal volatile phase. First melting temperatures in the aqueous portion indicate the dissolved salt is principally NaCl. Final CO 2-clathrate melting temperatures indicate NaCl contents ranging from 2 to 7 wt% relative to H 2O. Homogenization temperatures range from 196 to 272°C. Four chlorite temperatures from two samples range from 296 to 319°C. In P- T space, the four chlorite univariants intersect four fluid inclusion isochores (from the same samples) at temperatures of 300 ± 20° C and 1500 ± 300 bars, which are the inferred P and T of molybdenite formation. Mineral equilibria in vein assemblages from country rocks at Cannivan Gulch indicate f O 2 and f S 2 conditions of molybdenite formation between the pyrite-pyrrhotite-magnetite and pyrite-magnetite-hematite buffers. Formation of a calcite-molybdenite assemblage over powellite suggests that even small amounts of CO 2 ( X CO 2 = 0.05) in an ore fluid greatly extend the stability field of molybdenite to higher oxygen fugacities.

Duration of quartz cementation in sandstones, North Sea and Haltenbanken Basins

Evidence from fluid inclusions, petrography and burial history modelling is used to estimate the duration of quartz cementation in sandstones. The homogenization temperatures of primary fluid inclusions in quartz cements from samples from the Brent Group (North Sea) and Haltenbanken (offshore Norway) show variations (4σ) of 17.4 and 20.2°C. These are interpreted to reflect durations of less than approximately 9 and 17 Ma. Low variances are general features of such data sets and suggest that quartz cementation usually takes place as events with durations of the order of 10 Ma or possibly less. Confining the age of quartz cement growth using a combination of geological, petrographical and radiometric dating methods that are independent of fluid inclusions also suggests that quartz cements grow over periods substantially shorter than the age of the sandstone. It is not easy to reconcile this deduction with the suggestion that burial itself causes cementation.

Significance of fluid inclusions for determining the temperature gradients of hydrothermal solutions and their application to metallogenesis

Temperature gradients have been calculated using homogenisation temperatures of primary fluid inclusions in quartz, sphalerite and calcite of the Au-Ag and base-metal deposits in the Baia Mare metallogenetic province, Romania. Gradients ranging from 6 to 36°C/100 m are common. The steep dipping veins (e.g., main vein at Baia Sprie) are marked by high temperature gradients (19–36°C/100 m) and wide chloritisation aureoles (60–170 m). The shallow slope veins (40–45°N, Sofia vein at Nistru) have lower temperature gradients (6°C/100 m) and smaller chloritisation aureoles (10–40 m) in surrounding rocks. Normal temperature gradients (e.g., sphalerite of the Gutin vein at Cavnic yielding 12.5°C/100 m) correspond to normal Mn concentration gradients (0.023 wt.% Mn/100 m). The relationship between temperature gradient and concentration gradient of trace elements in ore deposits may be important in prospecting studies.

Fluid inclusion study on the Itaga tungsten deposit, Ashio district, Japan.

Fluid inclusion study on the Itaga tungsten deposit is carried out in order to characterize the hydrothermal solution responsible for this deposit. Polyphase fluid inclusions and vapor-rich ones as well as liquid-rich inclusions are found in quartz of the disseminated ore in the Itaga granite. Vapor-rich and liquid-rich inclusions are found in vein quartz, scheelite, and topaz from this deposit, but polyphase inclusions are not found in these minerals. Homogenization temperatures of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 518° to 261°C, from 388° to 265°C, from 336° to 301°C, and from 420° to 370°C, respectively. Salinities of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 45.1 to 0.9, from 21.0 to 8.3, from 7.9 to 5.3, and from 14.3 to 3.1 NaCl eq. wt%, respectively. The highest temperature and salinity reported in the present study are higher than any other data previously obtained for the Japanese tungsten deposits. Based on the plots of homogenization temperature against salinity, it is suggested that there were at least two hydrothermal solutions, i.e., very saline and dilute ones, responsible for the mineralization of the Itaea deoosit.

Toddlers' responses to the distress of their peers

In hydrothermal quartz from the Kaneuchi tungsten deposit of Honsyu island, Japan, the smaller primary fluid inclusions have the power δ18O values. This correlation is well accounted for by a quantitative model based on (isotropic or anisotropic) 18O diffusion through quartz. The model yields a room temperature 18O diffusivity that is close to the extrapolated diffusivity of water molecules measured by Cordier (1988) but much higher than the extrapolated diffusivity of structural oxygen measured by Farver and Yund (1991). The observed correlation between the size of primary fluid inclusions in quartz and their δ18O(water) is thus, well explained by relatively fast diffusion of oxygen as water molecules.

Sulfur isotopic compositions of ores from Mines Gaspe, Quebec: an example of sulfate-sulfide isotopic disequilibria in ore-forming fluids with applications to other porphyry-type deposits

Sulfur isotopic compositions of coprecipitated anhydrite, chalcopyrite, and pyrite from late stage porphyry-type ore mineralization at Mines Gaspe, Murdochville, Quebec, suggest isotopic disequilibria between sulfate and H 2 S in the ore-forming fluid. The delta 34 S sulfate-sulfide values range between 6.6 and 12.0 per mil, yielding apparent isotopic temperatures between 800 degrees and 550 degrees C. However, microthermometric measurements of primary fluid inclusions in quartz, anhydrite, and fluorite indicate depositional temperatures between 425 degrees and 200 degrees C. The delta 34 S pyrite-chalcopyrite values from nonanhydrite-bearing assemblages also yield a wide range of isotopic temperatures not in agreement with the fluid inclusion data. The delta 34 S pyrite-chalcopyrite values from anhydrite-bearing assemblages yield isotopic temperatures in general agreement with the fluid inclusion data. In addition, these delta 34 S pyrite-chalcopyrite values increase with increasing delta 34 S sulfate-sulfide values. Thus, it appears that the anhydrites and sulfides are in systematic isotopic disequilibria.Pyrite and chalcopyrite approach sulfur isotopic equilibrium with an H 2 S-bearing fluid more quickly than aqueous sulfate and H 2 S equilibrate isotopically. We therefore suggest that the sulfur isotopic compositions of chalcopyrite and pyrite in anhydrite-bearing assemblages were controlled by their relatively rapid approach to sulfur isotopic equilibrium, whereas the delta 34 S sulfate-sulfide values were controlled by the relatively slower rate of isotopic equilibration between aqueous sulfate and H 2 S. The sulfur isotopic compositions of the isotopically lightest anhydrite and isotopically heaviest chalcopyrite (smallest delta 34 S anhydrite-chalcopyrite value) are assumed to reflect the original disequilibrium isotopic compositions of sulfate and H 2 S in the ore-forming fluid, respectively. The changing isotopic compositions of pyrite and chalcopyrite precipitated from the solution, with time, were calculated from the inferred original delta 34 S values of sulfate and H 2 S. These calculated model isotopic values for pyrite and chalcopyrite are in agreement with the measured values.The consistent isotopic disequilibria between sulfates and sulfides places severe constraints on the temporal evolution of the ore-forming fluids at Mines Gaspe and has important implications for: redox disequilibrium in the fluid, mixing of sulfate- and H 2 S-rich fluids; hydrothermal dissolution, transport, and redeposition of earlier sulfides; and the preservation of earlier, higher temperature isotopic equilibria.Reexamination of the sulfur isotopic systematics of other porphyry-type ore deposits, most notably the El Salvador, Chile, deposit, suggests that sulfur isotopic disequilibria between aqueous sulfate and H 2 S may be an important feature of porphyry copper ore formation and may reveal remobilization of earlier precipitated ore constituents as well as record changes in the chemistry of the ore-forming fluid.If the rate constant for sulfur isotopic exchange equilibria between aqueous sulfate and H 2 S is known, sulfur isotopic disequilibria in porphyry-type systems may place limits on the residence times of sulfur species in solution. If the location of the source of the initial sulfur isotopic disequilibrium is known, these residence times may yield estimates of fluid flow rates in porphyry-type vein systems.