Homogenization Temperatures Of Inclusions Research Articles

A topaz- and amazonite-bearing leucogranite pluton in eastern Xinjiang, NW China and its zoning

The highly evolved Baishitouquan (BST) beryl-mineralised and topaz-bearing amazonite granite pluton is situated in the eastern Tianshan orogen of northwestern China. This pluton exhibits five well-exposed lithological zones, which, gradational from the lowest level, are leucogranite (zone-a), amazonite-bearing granite (zone-b), amazonite granite (zone-c), topaz-bearing amazonite granite (zone-d) and topaz albite granite (zone-e). The rocks are composed mainly of quartz, albite, and K-feldspar with varying amounts of topaz and amazonite. Quartz and topaz phenocrysts are the earliest phases that crystallised from the melt. Amazonite which replaced albite and K-feldspar was formed at the late magmatic stage or during the magmatic-hydrothermal transition. Geochemically, this pluton is characterised by high F (>2 wt.%) and Rb (499.5–1087.04 ppm), low P 2O 5 (⩽0.06 wt.%), Na 2O > K 2O, A/NKC = 1.00–1.11, low ratios of K/Rb, Al/Ga, Y/Ho, Zr/Ha and Nb/Ta, Σ14 REE = 28.6–231.9 ppm with gull wing-shaped distribution patterns (La CN/Lu CN = 0.11–0.68, Eu/Eu * = 0.0005–0.0110) and tetrad effects, and δ 18O = 9.75–7.32‰. Melt and fluid-melt inclusions coexist with liquid and vapour inclusions. The rocks were originated from a highly evolved granitic magma. The BST pluton exhibits transition in the following aspects from zone-a to zone-e: (1) As quartz and topaz phenocrysts progressively increase in size and crystal euhedral shape, rock textures change from equigranular to porphyritic. (2) Amazonite begins to appear in zone-b and becomes most concentrated in zone-c, whereas topaz begins to appear in zone-d becoming highly concentrated in zone-e. (3) Li and (Al + Ti) increase in white mica. (4) Petrochemically, there are general trends of increasing F, Al 2O 3 and Na 2O, and decreasing SiO 2, (Fe 2O 3 + FeO + MgO + MnO) and K 2O. Plots of normative compositions on the Qz–Ab–Or diagram move gradually towards the Ab apex. (5) Overall, Cr, Ni, Co, V, W, Nb, Zr, U, Th and Y decrease, while F, Li, Rb, Hf, Ta, Sn, Sc, Ga and Zn increase. (6) K/Rb, Al/Ga, Nb/Ta, Zr/Hf and Y/Ho decrease, and K/Cs, Th/U (La/Lu) CN and TE 1,3 (quantification factor of REE tetrad effect) increase. (7) There is a general decrease in whole-rock δ 18O from 9.25‰ to 9.75‰ in zone-a to 7.32‰ in zone-e. (8) Homogenization temperatures of melt inclusions in quartz decrease from about 860 °C for zone-a to about 660 °C for zone-e. It is interpreted that crystallisation of the magma started from zone-a and proceeded upwards to zone-e, and the vertical zoning is produced by fractional crystallisation accompanied by fluid-melt interaction. Some of the distinctive features of zone-e were caused by influx and reaction of meteoric fluid at the post-magmatic stage. Turbulent structures and co-magmatic deformation textures are well recorded in the rocks, and are ascribed to reduced viscosity and enhanced flow rate of the F- and H 2O-rich magma.

Late-stage rapid accumulation of the PL19-3 giant oilfield in an active fault zone during Neotectonism in the Bozhong depression, Bohai Bay

Late-stage is defined here as the period when Neotectonism occurred since 5.1 Ma. Most petroliferous basins in China lie in the areas where Neotectonism occurred intensively. In recent years, Chinese petroleum geologists have paid much attention to late-stage petroleum accumulation. The PL19-3 giant oilfield is situated where faulting activities occurred violently during Neotectonism. To understand the mechanism of lat-stage rapid accumulation, we discussed the most important aspects responsible for the formation of the giant oilfield, including oil generation, active oil-source rock occurrence, fault activity and fault conduits, late-stage rapid oil injection as well as the distinguishing indicators. This study shows that: (1) sufficient oil was supplied to the PL19-3 field since 5.1 Ma because the PL19-3 structure was surrounded by four sags in which three intervals of high-quality source rocks remained active during Neotectonism; (2) densely distributed faults and high porosity/permeability sandstone carrier beds comprised the effective conduit system for oil migration and injection; (3) oil migrated along the faults and charged the PL19-3 structure rapidly by means of seismic pumping which was triggered by frequent earthquakes during Neotetonism. It is documented that elevated reservoir temperature, abnormal geothermal gradients and abnormally high homogenization temperatures of the fluid inclusions are the indicators for late-stage rapid oil accumulation.

Granitic Pegmatite of the Umanotani-Shiroyama Quartz-Feldspar Mine, Shimane Prefecture, Southwest Japan

The pegmatite deposits at the Umanotani-Shiroyama mine, the largest producer of K-feldspar and quartz in Japan and characterized by a simple mineralogy, dominated by quartz and K-feldspar with minor muscovite and plagioclase, are hosted in the ilmenite-series Masago Granite.The ore zones are classified into the following three zones based on the distance from the host granite inwards: (1) marginal; (2) transitional; and (3) central ore zones. Crystal grain size increases in this order with the resultant occurrence of gigantically grown crystals of quartz in the central ore zone. The evidences presented here reveal that the pegmatite deposits were formed during the latest stage of crystallization and differentiation of the granitic magma being responsible for the Masago Granite. They include:(1) close temporal and spatial association of the granite and the pegmatite deposits (about 95 to 90 Ma), (2) common occurrence of macroscopic “graphic intergrowth" displayed by quartz and K-feldspar in orebodies, (3) common occurrence of melt inclusions trapped in “ore quartz" and “ore K-feldspar", (4) common occurrence of perthites observed in “ore K-feldspar" and (5) inheritance of oxygen isotopic signature, especially of quartz, from the surrounding biotite granite. The δ18O values of quartz, whether in the related igneous rocks or in ores, are almost the same, around +12 ‰, while those of K-feldspar in the igneous rocks is around +11‰ and those in ores are significantly depleted in 18O, about +7 to +8 ‰. It might be due to the difference in the exchange reaction rate of oxygen between quartz and K-feldspar. Abundant two-phase (liquid+gas) fluid inclusions are trapped in “ore quartz" and “ore K-feldspar", as well as in the related igneous rocks. Their presence strongly indicates that hydrothermal fluids, possibly admixture of magmatic fluids released from the Masago Granite and circulating meteoric water, entered to the magmatic-hydrothermal system and circulated through the orebodies mainly during the later phase of the pegmatite formation. Measured homogenization temperatures of two-phase inclusions trapped in “ore quartz" are in the following ranges: 250 to 400 ℃ in the marginal ore zone; 230 to 370 ℃ in the transitional ore zone; 240 to 340 ℃ in the central ore zone. Also suggested is that late circulation of hydrothermal fluids lasted for not so long time as to affect the δ18O values of quartz within the magmatic-hydrothermal system, resulting in escape of the fluids from the system through ubiquitously observed quartz±muscovite veins and fissures.

Fault fluid composition from fluid inclusion measurements, Laramide age Uinta thrust fault, Utah

The Laramide age (Late Cretaceous to Early Oligocene) Uinta thrust fault exposed on the northeast flank of the Uinta Mountains provides a fluid conduit for hydrocarbons that enter the Jurassic–Triassic age Nugget Sandstone, chemically reduce the red ferric oxide coloring minerals and bleach the sandstone. Mass spectrometric analyses of gases released from fluid inclusions during crushing of fault-associated calcite veins show fault fluids trapped in inclusions contain substantial CH 4 in addition to CO 2, N 2, Ar, H 2S, and C 2–C 6 hydrocarbons. The abundance of CO 2, CH 4, and other hydrocarbons is used to establish fault fluid redox conditions. Fluid inclusion temperature measurements together with gas analysis show fluids were trapped in inclusions over a range of temperatures and pressures. Temperature and salinity of the Uinta fault fluids determined by fluid inclusion homogenization temperatures corrected for hydrostatic pressure (350–850 bar) and ice melting are 95 to 217 °C and 0 to 11.8 eq. wt.% NaCl (average 3.8%). Vitrinite reflectance temperature estimates are 87 to 152 °C and temperature estimated from overburden thickness and thermal gradient are 142 to 202 °C. Log a H2(aq) ranges from − 5.3 to−5.7 estimated from CO 2/CH 4 equilibria at 160 °C. N 2/Ar ratios in excess of air-saturated water are consistent with derivation of N 2 from thermal decomposition of organic matter, and carbon and oxygen isotopic compositions of vein calcite suggest involvement of formation water. The Nugget Sandstone exposed in the fault footwall on the flanks of the Uinta Mountain uplift has been bleached from the moderate reddish brown color produced by hematite that coated the sand grains during early diagenesis to cream and nearly white colors, similar to bleached outcrops that have been observed in the correlative Navajo Sandstone on the Colorado Plateau. Geochemical modeling suggests that ample CH 4 and other hydrocarbons are available to reduce ferric oxide, bleach the sandstone, and precipitate disseminated pyrite and siderite.

Fluid inclusions as constraints in a three‐dimensional hydro‐thermo‐mechanical model of the Paris basin, France

ABSTRACTFluid inclusion homogenization temperatures and three‐dimensional hydro‐thermo‐mechanical modelling were combined to constrain fluid flow, solute and heat transport in the Paris basin, France, focusing on the two main petroleum reservoirs i.e. the Dogger and the Triassic (Keuper) formations. The average homogenization temperatures of two‐phase aqueous inclusions in different samples range from 66 °C to 88 °C in the Dogger calcite cement, from 106 °C to 118 °C in the Keuper dolomite cement and from 89 °C to 126 °C in the Keuper quartz and K‐feldspar cements. The maximum homogenization temperatures for inclusions in the Keuper quartz and K‐feldspar cements were 17–47 °C higher than present‐day temperatures in the boreholes at similar depths. Processes that might explain higher temperatures in the past were examined through numerical simulations and sensitivity tests. A warmer climate in the Late Cretaceous–Early Tertiary resulted in a temperature rise of only 8 °C. Late Cretaceous chalk had a thermal blanketing effect that resulted in simulated temperatures as high as 15–20 °C above the present day ones. An additional 300 m deposition and subsequent erosion of chalk, not taken into account so far, has to be considered to simulate the high palaeo‐temperatures recorded by fluid inclusions in both reservoirs. In view of the simulated thermal history of the basin, in the Keuper, an age of about 85 Ma is consistent with quartz/K‐feldspar temperatures and an age of about 65 Ma is in agreement with the precipitation temperature of the dolomite cement. Our models suggest an age of about 50 Ma for the Dogger calcite cementation.

Indications for the past redox environments in deep groundwaters from the isotopic composition of carbon and oxygen in fracture calcite, Olkiluoto, SW Finland

In paleohydrogeological studies, the geochemical and isotope geochemical composition of fracture calcites can be utilised to gain information about the evolution of the composition of deep groundwaters in crystalline bedrock. The aim of our study was to investigate the latest hydrogeochemical evolution of groundwaters in the crystalline bedrock at Olkiluoto, which is the planned site for deep geological disposal of spent nuclear fuel. Samples were collected from drill cores intercepting water-conducting fractures at the upper ∼ 500 m of the bedrock. The latest fracture calcite generations were identified using optical microscopy and electron microprobe. They occur as thin ∼ 10–200 μ m crusts or small euhedral crystals on open fracture surfaces. These latest calcite fillings were carefully sampled and analysed for the isotopic composition on carbon and oxygen. In addition, fluid inclusion homogenisation temperatures were determined on selected calcite samples. Fluid inclusion data indicated a low temperature of formation for the latest fracture calcite fillings. The δ18O values of calcite in these fracture fillings vary only slightly, from−7.3 to−11.5 ‰ (Vienna Pee Dee Belemnite, VPDB), whereas the δ13C values fluctuate widely, from−30 to+31 ‰ (VPDB). The δ13C values of latest calcite fillings show a systematic pattern with depth, with high and variable δ13C values below 50 m. The high δ13C values indicate active methanogenesis during the formation of the latest calcite fillings. In contrast, the present-day methanic redox environment is restricted to depths below 200–300 m. It is possible that the shift in the redox environment at Olkiluoto has occurred during infiltration of -rich marine waters, the latest of such events being the infiltration of brackish waters of the Littorina Sea stage of the Baltic Sea at ∼ 8000–3000 BP.

Chemical composition, volatile components, and trace elements in the magmatic melt of the Kurama mining district, Middle Tien Shan: Evidence from the investigation of inclusions in quartz

Melt and fluid inclusions were investigated in six quartz phenocryst samples from the igneous rocks of the extrusive (ignimbrites and rhyolites) and subvolcanic (granite porphyries) facies of the Lashkerek Depression in the Kurama mining district, Middle Tien Shan. The method of inclusion homogenization was used, and glasses from more than 40 inclusions were analyzed on electron and ion microprobes. The chemical characteristics of these inclusions are typical of silicic magmatic melts. The average composition is the following (wt %): 72.4 SiO2, 0.06 TiO2, 13.3 Al2O3, 0.95 FeO, 0.03 MnO, 0.01 MgO, 0.46 CaO, 3.33 Na2O, 5.16K2O, 0.32 F, and 0.21 Cl. Potassium strongly prevails over sodium in all of the inclusions (K2O/Na2O averages 1.60). The average total of components in melt inclusions from five samples is 95.3 wt %, which indicates a possible average water content in the melt of no less than 3–4 wt %. Water contents of 2.0 wt % and 6.6 wt % were determined in melt inclusions from two samples using an ion microprobe. The analyses of ore elements in the melt inclusions revealed high contents of Sn (up to 970 ppm), Th (19–62 ppm, 47 ppm on average), and U (9–26 ppm, 18 ppm on average), but very low Eu contents (0.01 ppm). Melt inclusions of two different compositions were detected in quartz from a granite porphyry sample: silicate and chloride, the latter being more abundant. In addition to Na and K chlorides, the salt inclusions usually contain one or several anisotropic crystals and an opaque phase. The homogenization temperatures of the salt inclusions are rather high, from 680 to 820°C. In addition to silicate inclusions with homogenization temperatures of 820–850°C, a primary fluid inclusion of aqueous solution with a concentration of 3.7 wt % NaCl eq. and a very high density of 0.93 g/cm3 was found in quartz from the ignimbrite. High fluid pressure values of 6.5–8.3 kbar were calculated for the temperature of quartz formation. These estimates are comparable with values obtained by us previously for other regions of the world: 2.6–4.3 kbar for Italy, 3.7 kbar for Mongolia, 3.3–8.7 kbar for central Slovakia, and 3.3–9.6 kbar for eastern Slovakia. Unusual melt inclusions were investigated in quartz from another ignimbrite sample. In addition to a gas phase and transparent glass, they contain spherical Feoxide globules (81.2 wt % FeO) with high content of SiO2 (9.9 wt %). The globules were dissolved in the silicate melt within a narrow temperature range of 1050–1100°C, and the complete homogenization of the inclusions was observed at temperatures of 1140°C or higher. The combined analysis of the results of the investigation of these inclusions allowed us to conclude that immiscible liquids were formed in the high-temperature silicic magma with the separation of iron oxide-dominated droplets.

Organic geochemical and fluid inclusion evidence for filling stages of natural gas and bitumen in volcanic reservoir of Changling faulted depression, southeastern Songliao basin

Recently, volcanic gas reservoirs in Yaoyingtai (腰英台) and Daerhan (达尔罕) tectonic belts in Changling (长岭) faulted depression of southeastern Songliao (松辽) basin have been discovered. Based on the compositions and isotopic values, the natural gas is characterized by high content of methane, low content of C2 +, and C1/C1–5 beyond 0.95. Also, the natural gas contains nonhydrocarbons including carbon dioxide with the content from 20% to 40% and minor amount of N2. Combined with the isotopic values, the natural gas is generated by humic kerogen and coal-derived type, but in Daerhan, the natural gas is probably mixed by oil type gas. From the measurement of lithology and fluid inclusions in volcanic rocks, the bitumen, liquid hydrocarbon, and gas hydrocarbon inclusions are present. Through the analysis of the single gas inclusion in volcanic reservoir, the content of carbon dioxide is low, so the carbon dioxide and hydrocarbon gas of the reservoirs are not accumulated at the same time. In addition, minor amount of bitumen in the reservoirs is formed by thermal evolution of the crude oils sourced from the Yingcheng (842557CE) Formation mudstones through the characterizations of the biomarkers. The distribution of homogenization temperatures presents two peaks, one with the liquid hydrocarbon filling stage, and the other with gas filling stage. However, in Daerhan tectonic belt, the second peak is gas and carbon dioxide mixed filling period probably. Combined with the homogenization temperatures of salt water inclusions, the oil and gas filling period is from Qingshankou (青山口) Formation to Nenjiang (嫩江) Formation in the research area. During the charging period, minor amount of inorganic carbon dioxide filled into the trap, but plenty of inorganic carbon dioxide from the end of Sifangtai (四方台) to Eogene periods was related with the structural movement.

Timing of petroleum accumulation and the division of reservoir-forming assemblages, Junggar Basin, NW China

Abstract Timing of petroleum accumulations and distribution of vertical basin-scale sealing beds are important in the study of superimposed basins. This information can be used to divide petroleum accumulations of different times into different petroleum-forming assemblages vertically so as to reconstruct the petroleum accumulation process and distribution more accurately. The Mahu-West Well Pen 1 combination petroleum system in the Junggar Basin is taken as the case study. By isotopic K-Ar dating of authigenic illite, optical feature of organic inclusions, and fluid inclusion homogenization temperature, combined with burial and thermal history analysis, timing of petroleum accumulations is defined, i.e., P 2–3 , T 3 , J 2 —K 1 and N. According to the vertical sealing mudstones of T 3 b, J 1 s 1 , and K 1 tg, four petroleum-forming assemblages were divided including C—T 3 , T 3 —J 1 , J 2 —K 1 , and K-N.

Hydrothermal recrystallization of the Lower Ordovician dolomite and its significance to reservoir in northern Tarim Basin

Discovered in S15 and some other wells, the Lower Ordovician in the northern Tarim Basin consists mainly of brown gray-dark gray very fine-fine crystalline dolomite, with a minor portion of locally light gray-white medium-coarse crystalline dolomite. Silicification can be observed in the medium-coarse dolomite, and some euhedral drusy quartz can also be found in pores and fractures of the dolomite. The homogenization temperature of the fluid inclusions in the medium-coarse dolomite is between 110 and 200°C with maximum between 140 and 190°C, and the salinity is between 10.7 and 18.5 wt.% NaCl Eq. The homogenization temperature and salinity of the fluid inclusions in the medium-coarse dolomite are similar to those in the drusy quartz. Compared with the very fine-fine dolomite, the medium-coarse phase contains relatively high Fe and Mn. The average concentration of FeO and MnO in the medium-coarse dolomite is 1.917% and 0.323%, respectively. The medium-coarse dolomite has a remarkable negative Eu anomaly, consistent with the REE pattern of the intermediate-felsic igneous rocks in the Tarim Basin. The oxygen isotopic composition of the medium-coarse dolomite is relatively lighter than that of the very fine-fine dolomite. The δ18OPDB values of the medium-coarse dolomite are between −10.35‰ and −7.31‰. The δ18OSMOW values of the fluid associated with the medium-coarse dolomite can be calculated according to homogenization temperature and oxygen isotope fractionation factor between dolomite and fluid, and the calculated values are between +4‰ and +10‰, consistent with those of the hydrothermal fluid. The medium-coarse dolomite has relatively high 87Sr/86Sr ratios as well, indicating an origin associated with intermediate-felsic igneous rock. The homogenization temperature, element composition, REE pattern, oxygen and strontium isotopes demonstrate that the medium-coarse dolomite is the result of recrystallization of very fine-fine dolomite under hydrothermal environment. The hydrothermal dolomite recrystallization is a special event but exists extensively in the Tarim Basin. The recrystallized dolomite becomes well reservoir bed for many intercrystalline pores and dissolution pores are produced in this event, so that more attention should be paid to the altered dolomite during the petroleum exploration in the lower Paleozoic in the Tarim Basin.

Fluid inclusion evidence for a coupling response between hydrocarbon charging and structural movements in Yitong Basin, Northeast China

For this study 145 fluid inclusion samples from 19 wells have been analysed to unravel the relationship between the complex charging history and tectonic evolution of the Yitong Basin, Northeast China. Fluid inclusion petrography, microthermometry, transmitted light microscopy and micro fluorescence observation methods were employed to systematically obtain information on fluorescent colors of hydrocarbon inclusions, homogenization temperatures of oil inclusions and their coeval aqueous inclusions. The results indicate three events of oil charging and one gas charging event for the Paleogene reservoirs. The oil charging events have been reconstructed at 38.1–27 Ma, 19.5–10 Ma and 1–0 Ma, while the gas charging event most likely occurred at 1–0 Ma. When combining the known information on hydrocarbon charging history and structural evolution, two intermittent periods of hydrocarbon migration and accumulation are likely to have occurred at 27–19.6 Ma and 10–2 Ma, coupling to two structural events. It is suggested that these events caused the termination of hydrocarbon supply or destruction of the previously accumulated hydrocarbons.

High density methane inclusions in Puguang Gasfield: Discovery and a T-P genetic study

Based on measurement of homogenization temperature of inclusions and Raman spectral analysis, high density methane inclusions were discovered in the Triassic reservoirs of Puguang Gasfield. The methane inclusions show a homogenization temperature Th = −117.5–−118.1°C, a corresponding density of 0.3455–0.3477 g/cm3, and a Raman scatter peak v 1 shift varying between 2911–2910 cm−1, which signifies a very high density of methane inclusions. The salt water inclusions paragenetic with methane inclusions show a homogenization temperature Th=170–180°C. Based on the composition of methane inclusions as determined by Raman spectra, PVTsim software was used to simulate the trapping pressure for high density methane inclusions in geologic history, and the trapping pressure was found to be as high as 153–160 MPa. Even though Puguang Gasfield is currently a gas pool of normal pressure, and the fluid pressure for the gas pool ranges between 56–65 MPa. However, data from this study indicates that remarkable overpressure may be generated at the stage of mass production of gas cracked from oils in Cretaceous, as high density methane inclusions constitute key evidence for overpressure in gas pool in geologic history. Meanwhile, discovery of small amounts of H2S, CO2 or heavy hydrocarbon in part of the high density methane inclusions indicates that the geochemical environment for trapping of inclusions may be related to formation of H2S. Therefore, the observation results can help to explore the thermochemical sulfate reduction (TSR) conditions for oil cracking and H2S formation.

The effect of fluid inclusion size on determination of homogenization temperature and density of liquid-rich aqueous inclusions

Homogenization temperature variations of several degrees Celsius or more are often observed within a group of fluid inclusions that appear to have all trapped the same homogeneous fluid at the same time and presumably at the same PTX conditions. For inclusions that homogenize at T≤ ≈230 °C, much of the observed variation can be attributed to the size of the inclusions. Larger inclusions homogenize at higher temperatures compared to smaller inclusions with the same density. The relationship between inclusion size and observed homogenization temperature is predicted by the Young-Laplace equation that relates the stability of a vapor bubble to the surface tension and pressure differential across the vapor-liquid interface. Vapor bubbles instantaneously collapse when the vapor bubble radius becomes less than the critical radius. During heating the critical radius of the vapor bubble is achieved at a lower temperature in the smaller inclusions. The critical vapor bubble radius varies from about 0.01 to ∼3 μm for low-temperature aqueous fluid inclusions. The Gibbs surface free energy associated with the growth and collapse of vapor bubbles in pure H 2 O inclusions with critical radii ranging from 0.01 to 1 μm ranges from about 10 -18 to 10 -13 J/m 2 and increases with both increasing critical vapor bubble radius and homogenization temperature. As a result of surface tension effects, the highest measured homogenization temperature, obtained from the largest inclusion in the group of coeval inclusions, most closely approximate the homogenization temperature that would be expected based on the inclusion density. For inclusions ranging from a few to several tens of micrometers in diameter and having densities such that the homogenization temperatures are approximately <230 °C, homogenization temperatures may vary by about 1-3 °C, depending on the inclusion size.

An investigation of cathodoluminescence in albite from the A-type Georgeville granite, Nova Scotia

Cathodoluminescence (CL) reveals red and blue colors within single, non-turbid albite (Ab 98–99) grains from the Georgeville granite, Nova Scotia. A 720 nm X-ray excited optical luminescence (XEOL) peak characterizes red CL regions, while a 280 nm XEOL feature dominates blue CL regions. Synchrotron X-ray fluorescence results indicate that red CL and the 720 nm XEOL peak intensities relate to total Fe concentrations. The relationship between red CL and Fe content is confirmed by electron microprobe (EMPA) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS). The XEOL technique is used to exclude the Fe K-edge as the cause of red CL. X-ray absorption spectroscopy results indicate that Fe in both the red and blue CL regions is Fe 3+, and that red CL activation may relate to the Si–Al order of the feldspar and to the distribution of Fe on tetrahedral sites. The CL textures, combined with EMPA and LA-ICPMS analyses, indicate that blue CL albite (Ab 98) regions contain higher concentrations of Ca, Ti, Pb and rare earth elements, and were replaced, in part, by a more Fe-rich, trace element depleted albite (Ab 99) which displays red CL. Complex diffraction contrasts and amorphous deposits identified in transmission electron microscope images suggest that aqueous fluids have reacted with both red and blue CL regions. Fluid inclusion homogenization temperatures of up to 430 °C provide a lower estimate of the fluid temperature.

FILLING HISTORY OF THE MAUI B FIELD, NEW ZEALAND: NEW INFORMATION FROM OIL INCLUSIONS IN AUTHIGENIC MINERALS FROM THE OIL LEG IN THE MAUI‐B1 WELL F SANDS

A study of the molecular composition of oil inclusions in the Maui field, Taranaki Basin, New Zealand, reveals compositional variation in oil during the filling history of the Paleocene reservoir. The homogenization temperatures of aqueous inclusions in quartz suggest that oil in genetically associated inclusions first reached the proto‐Maui structure about 7.0–7.5 Ma ago, and that an effective trap was present at the Paleocene F‐sands level, given the abundant oil inclusions. This date coincides with what is believed to represent the early stages of structural development of the trap. The Maui or Pihama sub‐basin appears the most likely kitchen for this early charge. The quartz‐included oil exhibits a biomarker distribution with a slightly more marine‐influenced signature than an oil stain from the same core plug, oil included in authigenic feldspar, and oil‐production samples from the overlying Eocene D sands as well as the F sands. The greater similarity of the feldspar‐included oil to the production oils together with its possibly slightly lower maturity suggest that the feldspar inclusions formed later than the quartz inclusions. Otherwise, all oil samples examined (inclusion oil, oil / bitumen in sandstones and producible oil) are of similar maturity.

The Qiyugou gold-bearing breccia pipes, Xiong'ershan region, central China: fluid-inclusion and stable-isotope evidence for an origin from magmatic fluids

Gold ores of the Qiyugou deposit in the eastern part of the Xiong'ershan region are hosted in breccia pipes within a Mesozoic granitic porphyry. Three stages of hydrothermal alteration activity are recognized within the Qiyugou breccias. The first stage of hydrothermal metasomatism produced extensive K-feldspar alteration. The second stage is associated with deposition of gold and base metal sulphides. The third stage is defined by fine quartz–calcite ± pyrite veinlets containing minor gold. Four types of fluid inclusions are present in quartz and calcite within the breccia matrix and veins. Type I are solid(s)-bearing high-salinity fluid inclusions, with homogenization temperatures up to 420°C and high salinities of 31–47 wt% NaCl equivalent. Type II are two-phase, vapour-rich fluid inclusions that homogenized between 265 and 476°C, with low to moderate salinities (7.2–19.8 wt% NaCl equivalent). Homogenization of Type III two-phase, liquid-rich fluid inclusions takes place at temperatures between 109 and 253°C, with salinities of 3.9–14.3 wt% NaCl equivalent. Type IV two/three-phase carbonic fluid inclusions are only found in calcite–quartz veins cutting wall rocks in the upper parts of the pipes or in adjacent country rocks, with homogenization temperatures that range from 239 to 315°C and salinities between 9.2 and 12.2 wt% NaCl equivalent. The coexistence of Types I and II in the middle parts of the breccia pipes suggests that these fluid inclusions either resulted from trapping of boiling fluids or represented immiscible fluids, most likely derived from a granitic magma. The fluid history, reflected in the fluid-inclusion characteristics, was complex, involving variable amounts of boiling, cooling and mixing in the breccia pipe system. values ( − 101.7 to − 60.1‰) and values (0.3–7.5‰) calculated from inclusion water in quartz on the basis of mean-to-maximum fluid inclusion homogenization temperatures are intermediate between magmatic water and surface-derived fluids (meteoric water). Ranges for δ34S values of ore sulphides ( − 3.0 to 0.8‰) suggest that sulphur originated directly from a magmatic (mantle) source or indirectly from leaching/desulphidation of primary magmatic sulphide minerals. The combined fluid-inclusion and stable-isotope data support previous proposals for a genetic relationship between the Qiyugou ores and magmatic fluids.

Fluid inclusions in halite from the Röt (lower triassic) salt deposit in central Germany: Evidence for seawater chemistry and conditions of salt deposition and recrystallization

The study of fluid inclusions in Lower Triassic Rot halite from the Rockensussra 2/83 borehole in northern Germany showed the presence of primary and secondary gas-liquid inclusions. The gas phase in inclusions indicates their stretching due to salt overheating at some postsedimentary stage. The homogenization temperature of inclusions indicates the overheating temperature of about 60–70°C. The overheating is additionally indicated by trails of migration of large secondary inclusions occurring inside chevrons. The major-ion (K, Mg and SO4) composition of inclusion brines was established with the use of ultramicrochemical analysis (UMCA). The results of chemical analyses of brines of primary inclusions in halite from the Rockensussra 2/83 borehole confirm the earlier results for the Rot halite from the Netherlands and Poland. The bromine content in halite is 78–107 ppm, supporting thus marine origin of halite. Brines of primary gas-liquid inclusions are thus representative samples of trapped evaporite water and they may be used for the reconstruction of the composition of Early Triassic seawater. The comparison of our analytical data with the earlier published data and models of chemical composition of seawater during the Phanerozoic which were constructed with the use of the HMW computer program makes it possible to conclude that the Early Triassic seawater was of the SO4-rich type and considering the ratios of major ions it fully corresponded to the Early Permian (Asselian-Sakmarian) seawater. It differed from the present seawater by a slight decrease of Na and Mg ions, a considerable decrease of SO4 ion (by 31%) and an increase of Ca ion (by 36%).

Effects of oil inclusion homogenization temperatures and their geological meanings

Effects of oil inclusion homogenization temperatures and their geological meanings

Relationship between CO2-dominated fluids, hydrothermal alterations and gold mineralization in the Red Lake greenstone belt, Canada

Abstract The Red Lake greenstone belt is one of the foremost Au mining camps in Canada and hosts the world-class Campbell-Red Lake Au deposit. Belt-scale hydrothermal alteration is characterized by proximal ferroan dolomite zones associated with Au mineralization surrounded by distal calcite zones, both being accompanied by potassic alterations (sericite, muscovite, and biotite). At the Campbell-Red Lake and Cochenour deposits Au mineralization (in particular high-grade ore) is associated with silica and sulfides (especially arsenopyrite) that replace carbonate ± quartz veins and the host rocks. The prevalence of carbonic fluid inclusions and rare occurrence of aqueous-bearing inclusions in carbonate–quartz–Au veins in the Campbell-Red Lake deposit, and the consistency of homogenization temperatures of carbonic inclusions within individual fluid inclusion assemblages (FIA), have been interpreted to indicate that H2O-poor, CO2-dominated fluids were responsible for the carbonate veining and Au mineralization. Further studies of fluid inclusions in carbonate–quartz veins within and outside the deformation zone hosting the Campbell-Red Lake deposit (the Red Lake Mine trend) including the Cochenour Au deposit, the Redcon Au prospect, and outcrops in the distal calcite zone also reveal the dominance of carbonic fluid inclusions in vein minerals. These studies indicate that CO2-dominated fluids were flowing through fractures during carbonate vein formation and Au mineralization both within and outside major structures. The carbonic fluid may have been initially undersaturated with water, or it may have resulted from phase separation of an H2O–CO2–NaCl fluid. In the latter case, phase separation modeling indicates that the initial fluid likely had X CO 2 values larger than 0.8. Calculations based on hydrothermal mineral assemblages indicate X CO 2 values in the host rocks from 0.025 to 0.85, reflecting a change from CO2-dominated fluids in the fractures (veins) to H2O-dominated fluids in the host rocks away from the fractures. The CO2-dominated fluids were likely advected from granulite facies in the deeper crust, whereas the H2O-dominated fluids were derived from the ambient host rocks of amphibole to greenschist facies. Calculations based on CO2 requirements and source constraints indicate that the mineralizing fluids were likely two orders of magnitude more enriched in Au than the commonly assumed values of a few μg/L, which may explain why the Campbell-Red Lake deposit has a very high-grade of Au (average 21 g/t for the whole deposit and 81 g/t for the Goldcorp High-Grade zone). Fluid inclusion data suggest that the carbonate veining and Au mineralization likely took place at depths from 7 to 14 km. The development of crustiform–colloform structures in the carbonate ± quartz veins, which was previously interpreted to indicate relatively shallow environments, may alternatively have been related to extremely high fluid pressures and the CO2-dominated nature of the fluids, which could have enhanced the brittle properties of the rocks due to their high wetting angles.

Mesozoic Multi-phase Magmatism and Gold Mineralization in the Early Precambrian North China Craton, Eastern Hebei Province, China: SHRIMP Zircon U-Pb Evidence

The early Precambrian North China craton (NCC) in eastern Hebei Province (also known as the Jidong area) was intruded by granitic batholiths and plutons spatially associated with gold deposits. No consensus has been reached regarding timing and tectonic setting of the gold deposits, chiefly due to the lack of reliable geochronological data. The gold deposits in the district are localized by NE-striking faults within granite plutons and/or nearby Archean amphibolites, as well as in Proterozoic sedimentary rocks. Gold mineralizations in the area are characterized by quartz (± albite) veinand sulfide-disseminated styles; both types of ores have relatively low sulfide contents (<10 vol%) and similar sulfide mineral assemblages dominated by pyrite + chalcopyrite + pyrrhotite + galena + sphalerite, locally with molybdenite, tellurides, and bismuthinoids. The alterations around the gold lodes include K-feldspathization, sericitization, silicification, chloritization, and sulfidation. Previous fluid inclusion data from all the deposits of the district show that the mineralizing fluids are characterized by relatively high salinities (3 to 17 wt% NaCl equiv.), H2O-CO2 ± CH4, N2 solutions, with CO2 contents in the inclusions ranging from 5 to 40 mol%. Fluid inclusion homogenization temperatures are between 240 and 400°C, and estimates of the trapping pressures vary significantly from 0.5 to 3.7 kbar. Stable isotope (O, H, S, C, and Pb) data from these deposits indicate a major magmatic component in the mineralizing fluids and the ore-forming materials, with a partial contribution by Archean host rocks, suggesting that these deposits are basically intrusion-related. SHRIMP zircon U-Pb geochronology of the gold-hosting granitic intrusions, in combination with previous Ar-Ar and Rb-Sr dates on hydrothermal minerals (e.g., sericite), indicates that there was no Archean gold mineralization, but instead suggests that at least three episodes of granitic magmatism and associated gold mineralization took place during the Mesozoic. The first episode occurred in the Late Triassic at ∼222 Ma, with emplacement of the Dushan granite batholith (223 ± 2 Ma), Sanjia granite porphyry (222 ± 4 Ma), and the Baizhangzi granite (222 ± 3 Ma). This episode of magmatism and gold mineralization was coeval with collision of the NCC with the South Mongolian block in the north along the Solonker suture and with the Yangtze craton in the south along the Dabie-Sulu suture. The second episode took place in the Early Jurassic, with emplacement of the Qingshankou granite (199 ± 2 Ma), and the third episode occurred in the Middle Jurassic, with intrusion of the Yuerya (∼ 175 Ma) and Niuxinshan (172 ± 2 Ma) and granites. These two events are about 25 and 45 Ma later than the collision of the NCC with other continental blocks in a post-collisional environment.