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This study evaluates the effect of organic matter impurities on pyrite Re-Os dating, using the giant Jinding sediment-hosted Zn-Pb deposit in China as an example. The Jinding deposit is hosted in a Paleocene evaporite dome that was a hydrocarbon reservoir before mineralization. Pyrite in Jinding formed in two stages: pre-ore (py1) and syn-ore (py2). Two types of py1 are recognized, organic matter-free and organic matter-bearing. The organic matter-free py1 contains homogeneously distributed low concentrations of Re (

The Angouran deposit is the second-largest Zn–Pb deposit in Iran with 4.7 Mt sulfide ore (27.7% Zn, 2.4% Pb, and 110 g/t Ag) and 14.6 Mt nonsulfide ore (28.1% Zn, 4.4% Pb). Various models have been proposed to explain the genesis of sulfide ore in this deposit. Moreover, the mineralization type of its primary sulfide ores remains controversial. The major and trace element concentrations and sulfur isotopic composition of the two stages of sphalerite have been analyzed to constrain mineralization conditions and the genesis. The Angouran deposit, which contains discordant orebodies, is hosted in a Neoproterozoic/Cambrian schist-marble sequence. Two stages of sphalerite have been distinguished: early-stage (S1) red-brown sphalerite and late-stage (S2) honey-yellow sphalerite. Our result shows that, relative to the S2 sphalerite, the S1 sphalerite has higher contents of Fe, Mn, Co, Cu, Ag, Sn, Ga, Sb and In, but lower contents of As and Tl. Time-resolved depth profiles in these sphalerites determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Fe, Cd, Co, Hg, Mn, Ge, and In are mainly present in solid solution and that Ag, Cu, Pb, As, Ni, Ga, Tl, Sb, and Sn are present in both solid solution and mineral inclusions. Correlation analyses reveal the occurrence of direct substitution mechanisms, such as Zn2+ ↔ (Fe2+, Cd2+) and 2Zn2+ ↔ Ge4++□ (vacancy) as well as coupled substitutions, such as 2Zn2+ ↔ Cu+ + Ga3+, 2Zn2+ ↔ (Cu+, Ag+) + Sb3+, 3Zn2+ ↔ Pb2+ + Tl+ + As3+, 4Zn2+ ↔ Pb2+ + 2As3++□(vacancy) or (Zn2+, Pb2+) ↔ Tl+ + As3+, and 4Zn2+ ↔ Cu+ + (Ga3+, In3+) + Sn4++□(vacancy). Geothermometer studies suggest that sphalerite in the Angouran deposit precipitated from a low-temperature (

Hydrous and anhydrous isothermal experiments on n-pentane and n-octadecane were conducted at 300–375℃ for durations up to 1094 h to evaluate the cracking and hydrolysis of hydrocarbons, using fused silica capillary capsules as micro-reactors. The chemical compositions of the gaseous products during cracking of n-octadecane at 350 and 375℃ were methane, ethane, propane, and n-butane. The aqueous product in the hydrolysis of n-pentane and n-octadecane at 300–375℃ was alcohol. Alkenes and hydrogen were not detected throughout all the isothermal experiments. Results showed that the gaseous yields were characterized by higher contents of wet gas than those in natural gas accumulations. Mechanisms regulating the enrichment of methane in reservoirs should be further studied. The hydrolysis and oxidation of hydrocarbon were relatively limited in the absence of iron-bearing mineral buffers, suggesting that hydrocarbons might be more stable in iron-poor reservoirs (e.g. carbonate and quartz arenite) than in iron-bearing-mineral-rich ones (e.g. mudstone and arkose) under deep burial conditions. The absence of hydrogen was ascribed to its high diffusion rate in fused silica than in gold tube; any hydrogen produced in the reaction tends to diffuse out of the fused silica capsule with no or limited hydrogen accumulation, similar to those in geological environment. The diffusion of hydrogen should be considered during calculating the volume and pressure changes in the thermal cracking of oil to gas in reservoirs, because the loss of hydrogen would result in a decrease in the conversion rate of oil to gas.

Fault zones control the locations of many ore deposits, but the ore-forming processes in such fault zones are poorly understood. We have studied the deformation and ore textures associated with fault zones that controlled the lead–zinc mineralization of the Dongmozhazhua deposit, central Tibet, ∼100 km southwest of Yushu City. Geological mapping shows that the structural framework of the Dongmozhazhua area is defined by NW–SE-trending reverse faults and superposed folds that indicate at least two stages of deformation. The first stage is characterized by tight nearly E–W-striking folds that formed during the closure of the Jinshajiang Paleo-Tethyan Ocean in the Triassic. The second stage of deformation produced NW–SE-trending reverse faults and related structures of the Fenghuoshan–Nangqian fold-and-thrust belt associated with India–Asia collision in the late Eocene to Oligocene. Scanline surveys along the ore-controlling fault zones show an internal structure that comprises a damage zone, a breccia zone with clasts that have become rounded, and a breccia zone with lenticular clasts, and this complex architecture was formed during at least two compressional substages of deformation. The Pb–Zn mineralization in the Dongmozhazhua area occurs exclusively close to NW–SE-trending reverse fault zones. Microtextural observations reveal that mineralization occurred as veinlets and disseminated blebs in limestone clasts, and as continuous bands and cements in fractured rocks. Cataclastic sulfide grains also can be seen in the matrix of some fault zones. The types of mineralization differ with structural position. The fillings of the ore-bearing veinlets typify the products of hydraulic fracture and both types of mineralization took place concurrently with regional contraction. We consider, therefore, that the ore-bearing fluids in the Dongmozhazhua deposit were concentrated in fault zones during regional compression and that the ore minerals were precipitated during hydraulic fracturing of host rocks. Subsequent fault activity pulverized some pre-existing sulfide material into cataclastic grains in the matrix of a tectonic breccia that developed in the same faults.

The Sanjiang metallogenic belt includes a variety of economically important carbonate-hosted Pb-Zn deposits that share some similarities with classic Mississippi Valley-type (MVT) ore deposits but are hosted within a thrust belt rather than an orogenic foreland. This study aims to clarify the origin of mineralizing fluids responsible for this style of mineralization. Fluid inclusions trapped in ore-stage carbonate and fluorite from these deposits have salinities of ~6 to 28 wt % NaCl equiv and homogenization temperatures of 70° to 370°C that extend to much higher values than are typical of MVT deposits. The majority of ore-stage samples have fluid inclusion molar Br/Cl ratios of between seawater (1.5 × 10 −3 ) and (2.86 ± 0.04) × 10 −3 , but low-salinity fluid inclusions in late calcite have lower Br/Cl of less than (0.55 ± 0.01) × 10 −3 . In contrast, fluid inclusion molar I/Cl ratios are uniformly greater than the seawater value of ~0.8 × 10 −6 and extend from (2.1 ± 1.1) × 10 −6 to (506 ± 12) × 10 −6 . This range of Br/Cl and I/Cl values is similar to what has been reported for fluid inclusions in other MVT districts and together with the fluid salinity implies the ore-forming fluids had a dominant origin from basinal brines (e.g., sedimentary formation waters) formed by the subaerial evaporation of seawater; all the fluids were influenced by addition of organic Br and I derived from the sedimentary host rocks and some fluids were locally modified by interaction with evaporites producing low Br/Cl ratios. The fluid inclusions have 40 Ar/ 36 Ar ratios of up to 441 that are higher than the atmospheric value of 296 and typical of carbonate sedimentary rocks. The fluid inclusions have high concentrations of atmospheric 36 Ar and variable 129 Xe/ 36 Ar and 84 Kr/ 36 Ar ratios that are outside the range expected from mixing air and air-saturated water. These data are likely to reflect a complex fluid history involving acquisition of atmospheric ( 36 Ar, 84 Kr, 129 Xe) and radiogenic (e.g., 40 Ar ✼ ) noble gases trapped in sedimentary rocks and fractionation of these gases between water and hydrocarbons. The 3 He/ 4 He ratios of fluorite fluid inclusions range from a typical crustal value of 0.061 ± 0.004 to values of >0.7 Ra, indicating a minor component of mantle-derived 3 He. The fluids with the highest 3 He/ 4 He also have 4 He/ 40 Ar ✼ close to the mantle value, suggesting the 3 He could have been introduced by a volumetrically minor fluid of either magmatic or deep metamorphic origin ( 40 Ar ✼ = radiogenic 40 Ar). The new halogen and noble gas data are consistent with a model in which regional Pb-Zn mineralization formed by mixing two modified basinal brines that were transported through independent aquifers and fluid pathways to the sites of mineralization. A low-temperature brine contained organic Br, I, and H 2 S, and a high-temperature metal-rich brine (>370°C) that included a volumetrically minor magmato-metamorphic component was channeled up deeply penetrating thrust structures.

Mississippi Valley type (MVT) Pb–Zn deposits can occur in orogenic thrust belts. However, the relationship between MVT ore-forming processes and thrusting is unclear. The 1500-km-long Sanjiang Metallogenic Belt in Tibetan Plateau is an important thrust-controlled MVT ore province with 860 Mt at 0.76–2.3% Pb, 0.3–6.1% Zn. The Zhaofayong MVT ore cluster in the Changdu area is a typical sample. The orebodies in this ore cluster are hosted in limestone, controlled by secondary faults to regional thrusts and forming along these faults. Two Pb–Zn mineralization stages in this cluster are recognized. Stage I is characterized by coarse and euhedral galena + sphalerite + calcite + fluorite + barite and Stage II by fine grained sphalerite + galena + pyrite + calcite. Sm–Nd isotopic dating of calcite forming in Stage I yields isochron ages of 41.1–38.1 Ma, suggesting the mineralization formed during extension following the first regional compression in the Changdu area. The connection between Stage I mineralization and the regional thrusting in the Changdu area can extend to the whole Sanjiang belt. Two stages of regional Pb–Zn mineralization are recognized between 65 Ma and 30 Ma and between 30 Ma and 16 Ma in the belt. The two Pb–Zn mineralization stages are consistent with those regional episodic thrusting activities and both of them immediately occurred after the episodic thrusting. An interpretation of the regional Pb–Zn mineralization is that regional compression forced the movement of hydrothermal fluids along regional thrust-nappe detachment faults and subsequent post-thrust extension caused the migration of hydrothermal fluids to the ore forming locations. The two mineralization stages in the Sanjiang Belt indicate complex processes related to India–Eurasia collision and the gradually younger mineralization ages from southeast to northwest indicate the collision follows the same direction.

Baiyangping Pb–Zn–Cu–Ag deposit is located in Lanping basin, northwestern Yunnan province. The deposit is composed of a few ore veins and can be divided into several ore blocks. The ore bodies are primarily hosted in Mesozoic carbonate, sandstone and siltstone along the north–south-striking, NWW-striking and NE–SW-striking fault zones. There are breccia, massive, vein like and disseminated ores. The main ore minerals are sphalerite, galena, gratonite, jordanite, tetrahedrite series minerals, chalcocite, chalcopyrite, realgar, orpiment, bournonite, cobalt-bearing arsenopyrite, argentite, kongsbergite, cobaltine, siegenite. The sizes of fluid inclusions in Baiyangping deposit are generally less than 10 μm and have the shape of round, oval, irregular, etc. The ore-forming fluid system is Ca 2+ –Na + –K + –Mg 2+ –Cl − –F − –NO 3 − brine system. The freezing temperature of fluid inclusions in mineral deposits ranges from −26.4 to −0.2 °C, average −14.6 °C; the homogenization temperature is concentrated in 120–180 °C, and the salinity is between 0.35 and 24.73 wt% (NaCl eq ), average 16.9 wt% (NaCl eq ). δ 13 C PDB and δ 18 O SMOW values of hydrothermal calcite range from −4.16‰ to 3‰ and −2.5‰ to 20.4‰, respectively. δ 34 S values of sulfide minerals range from −10.2‰ to 11.2‰, average 5.6‰. The sulfide samples yield 206 Pb/ 204 Pb values of 18.609–18.818, 207 Pb/ 204 Pb of 15.548–15.842 and 208 Pb/ 204 Pb = 38.514–39.556. C–O–S–Pb isotope compositions of the Baiyangping deposit indicate a homogeneous carbon source, and the carbon in hydrothermal calcite is derived from the dissolution of carbonate rock strata, the ore-forming fluid belongs to basin brine fluid system, which is mixed with the precipitate water, sulfur in sulfides and sulfosalts is derived from thermal chemical sulfate reduction, and the thermal decomposition of sulfur-bearing organic matter. The metal mineralization material is from sedimentary strata and basement. The late Pb–Zn polymetallic mineralization event superposed within early Cu–Co polymetallic mineralization event resulted in the differences of ore-forming elements for Baiyangping deposit.

A significant belt of carbonate-hosted Pb–Zn mineralization occurs in the Himalayan–Zagros collisional orogenic system. Three differing types of these Pb–Zn deposits within this belt have been identified based on variations in gangue mineral assemblages, leading to the classification of carbonate-, quartz- and fluorite-rich classes of Pb–Zn deposits. The third Pb–Zn mineralization (fluorite-rich) type is common in this orogenic system, but little research has been undertaken on it. Here, we focus on the Mohailaheng deposit, a large-sized fluorite-rich carbonate-hosted Pb–Zn deposit (> 100 Mt Pb + Zn ores with average grade of 2.18%–4.23%); the deposit is located in the Sanjiang Cenozoic thrust-fold belt, an important part of the Himalayan–Zagros collisional orogenic system and an area that formed during the early Tertiary India–Eurasia collision. The main orebodies in this deposit are stratabound and are hosted by Carboniferous limestones that are located along secondary faults associated with a regional thrust fault. The main assemblage is a sphalerite + galena + pyrite sulfide assemblage associated with a calcite + fluorite + barite + quartz + dolomite gangue assemblage. Detailed field and experimental work indicates that the deposit formed during three distinct phases of hydrothermal activity. Studies on fluid inclusion and stable isotopes of gangue minerals indicate that two dominant distinct fluids involving the deposit formation. They include (1) a low-temperature (130–140 °C), high-salinity (23–24 wt.% NaCl equivalent) basinal brine containing Na + –K + –Mg 2 + –Ca 2 + –Cl − ions and abnormally high SO 4 2 − concentrations, which probably derived from Tertiary basins in the regional district, and (2) a low- to moderate-temperature (170–180 °C) and moderate- to high-salinity (19–20 wt.% NaCl equivalent) metamorphic fluid containing Na + –K + –Mg 2 + –Cl – –SO 4 2 − ions and abnormally high F − and organic matter concentrations, that probably formed during regional metamorphism. Some evaporated seawaters and meteoric fluids were also identified in mixtures with these two dominant fluids. The Pb–Zn mineralization at Mohailaheng formed during three distinct stages, consistent with the regional tectonic history. The first stage involved the formation of favorable lithological and structural traps at Mohailaheng during regional thrusting, leading to the migration of compressed metamorphic waters at depth along a detachment zone, sequestering metals from sediments within the region. Basinal brines at the surface also began to infiltrate down along the secondary faults, dissolving gypsum from the underlying sediments. The second stage was associated with the cessation of thrusting and the onset of strike-slip movements along these thrust faults. Metamorphic fluids containing high concentrations of halogen ions, organic gases, and metals ascended into the structural traps at Mohailaheng along the reactivated thrust faults, causing fluorite, calcite, and some sulfide precipitation. Then, basinal brines rich in SO 4 2 − quickly descended into the structural traps along the reactivated faults, causing reduction of SO 4 2 − by organic matter, and producing significant amounts of H 2 S. The reduced sulfur then reacted with the metals in the fluids, causing significant sulfide precipitation. The third stage was associated with metal-depleted fluids, which only resulted in the precipitation of calcite from the diluted basinal brines. Combining these findings with research results on other fluorite-rich carbonate-hosted Pb–Zn deposits in the Himalayan–Zagros orogenic system suggests that this type of carbonate-hosted Pb–Zn deposits can also be classified as Mississippi Valley-type (MVT) deposits, and that the origin of the fluorite in these deposits may be related to multiple hydrothermal fluids involved in the mineralization evolution.

The Dongmozhazhua deposit, the largest Pb–Zn deposit in south Qinghai, China, is stratabound, carbonatehosted and associated with epigenetic dolomitization and silicification of Lower–Middle Permian—Upper Triassic limestones in the hanging walls of a Cenozoic thrust fault system. The mineralization is localized in a Cenozoic thrust-folded belt along the northeastern edge of the Tibetan plateau, which was formed due to the India–Asia plate collision during the early Tertiary. The deposit comprises 16 orebodies with variable thicknesses (1.5–26.3 m) and lengths (160–1820 m). The ores occur as dissemination, vein, and breccia cement. The main sulfide assemblage is sphalerite + galena + pyrite + marcasite ± chalcopyrite ± tetrahedrite, and gangue minerals consist mainly of calcite, dolomite, barite, and quartz. Samples of pre- to post-ore stages calcite yielded d13C and d18O values that are, respectively, similar to and lower than those yielded by the host limestones, suggesting that the calcite formed from fluids derived from carbonate dissolution. Fluid inclusions in calcite and sphalerite in the polymetallic sulfidization stage mostly comprise liquid and gas phases at room temperature, with moderate homogenization temperatures (100–140°C) and high salinities (21–28 wt% NaCl eq.). Micro-thermometric fluid inclusion data point to polysaline brines as ore-forming fluids. The dD and d18O values of ore fluids, cation compositions of fluid inclusions, and geological information suggest two main possible fluid sources, namely basinal brines and evaporated seawater. The fluid inclusion data and regional geology suggest that basinal brines derived from Tertiary basins located southeast of the Dongmozhazhua deposit migrated along deep detachment zones of the regional thrust system, leached substantial base metals from country rocks, and finally ascended along thrust faults at Dongmozhazhua. There, the base-metal-rich basinal brines mixed with bacterially-reduced H2S-bearing fluids derived from evaporated seawater preserved in the Permo–Triassic carbonate strata. The mixing of the two fluids resulted in Pb–Zn mineralization. The Dongmozhazhua Pb–Zn deposit has many characteristics that are similar to MVT Pb–Zn deposits worldwide.

Raman spectroscopy is a powerful method for the determination of CO 2 densities in fluid inclusions, especially for those with small size and/or low fluid density. The relationship between CO 2 Fermi diad split ( Δ , cm −1 ) and CO 2 density ( ρ , g/cm 3 ) has been documented by several previous studies. However, significant discrepancies exist among these studies mainly because of inconsistent calibration procedures and lack of measurements for CO 2 fluids having densities between 0.21 and 0.75 g/cm 3 , where liquid and vapor phases coexist near room temperature. In this study, a high-pressure optical cell and fused silica capillary capsules were used to prepare pure CO 2 samples with densities between 0.0472 and 1.0060 g/cm 3 . The measured CO 2 Fermi diad splits were calibrated with two well established Raman bands of benzonitrile at 1192.6 and 1598.9 cm −1 . The relationship between the CO 2 Fermi diad split and density can be represented by: ρ = 47513.64243 − 1374.824414 × Δ + 13.25586152 × Δ 2 − 0.04258891551 × Δ 3 ( r 2 = 0.99835, σ = 0.0253 g/cm 3 ), and this relationship was tested by synthetic fluid inclusions and natural CO 2 -rich fluid inclusions. The effects of temperature and the presence of H 2 O and CH 4 on this relationship were also examined.

The mesogenetic dissolution is well developed in the middle Ordovician Yijianfang formation (O2yj) limestone, and the dissolution pores are very important for petroleum accumulation in the south slope area of the Tahe oilfield which lies in the north of the Tarim basin, northwestern China. Mottled, dotted or laminar dissolution can be observed in the O2yj limestone. Under microscope, the grains, lime matrix and all stages of calcite cements (including oil-inclusion-bearing blocky calcite cements) can all be found dissolved ubiquitously. The stylolites in the limestone were enlarged and rounded because of dissolution. Some dolomite rhombs, precipitated along stylolites in burial environment, were found dissolved as well. The dissolution of the blocky calcite cements and dolomite rhombs and the enlarging of stylolites demonstrate that the dissolution took place in the mesogenetic environment. Concentration of trace elements, including REEs, of the eroded part of the O2yj limestone is intermediate between that of the uneroded part and that of the underlying lower Ordovician limestone hydrocarbon source rocks. Both δ13CPDB and δ18OPDB values of the eroded part are less than those of the uneroded part, respectively. The geochemical characteristics indicate that the eroding fluids are hydrocarbon-bearing fluids coming from the underlying hydrocarbon source rocks.

Considerable advances in our understanding of physicochemical properties of geological fluids and their roles in many geological processes have been achieved by the use of synthetic fluid inclusions. We have developed a new method to synthesize fluid inclusions containing organic and inorganic material in fused silica capillary tubing. We have used both round (0.3 mm OD and 0.05 or 0.1 mm ID) and square cross-section tubing (0.3 × 0.3 mm with 0.05 × 0.05 mm or 0.1 × 0.1 mm cavities). For microthermometric measurements in a USGS-type heating–cooling stage, sample capsules must be less than 25 mm in length. The square-sectioned capsules have the advantage of providing images without optical distortion. However, the maximum internal pressure ( P ; about 100 MPa at 22 °C) and temperature ( T ; about 500 °C) maintained by the square-sectioned capsules are less than those held by the round-sectioned capsules (about 300 MPa at room T , and T up to 650 °C). The fused silica capsules can be applied to a wide range of problems of interest in fluid inclusion and hydrothermal research, such as creating standards for the calibration of thermocouples in heating–cooling stages and frequency shifts in Raman spectrometers. The fused silica capsules can also be used as containers for hydrothermal reactions, especially for organic samples, including individual hydrocarbons, crude oils, and gases, such as cracking of C 18 H 38 between 350 and 400 °C, isotopic exchanges between C 18 H 38 and D 2 O and between C 19 D 40 and H 2 O at similar temperatures. Results of these types of studies provide information on the kinetics of oil cracking and the changes of oil composition under thermal stress. When compared with synthesis of fluid inclusions formed by healing fractures in quartz or other minerals or by overgrowth of quartz at elevated P – T conditions, the new fused-silica method has the following advantages: (1) it is simple; (2) fluid inclusions without the presence of water can be formed; (3) synthesized inclusions are large and uniform, and they are able to tolerate high internal P ; (4) it is suitable for the study of organic material; and (5) redox control is possible due to high permeability of the fused silica to hydrogen.

A 50 m thick diabase sill was found in the Paleogene black mudstone hydrocarbon source rocks in Xia38 well. Within heating aureola of the sill, optical changes of kerogen and signatures of extractable bitumens in the mudstones were investigated. Under effects of high heating rate associated with sill intrusion, the vitrinite reflectance (Ro) has an increasing tendency with decreasing distance to the sill both below and above the sill. However, only within a zone of about 15 m to the diabase sill, the vitrinite reflectance shows significant increase. Above the sill, the Ro values increase gradually from 0.6% to 1.0%, whereas below the sill, the Ro values increase dramatically from 0.8% to 3.8%. The contrasting Ro increasing patterns are attributed to the different heat transferring conditions, the relatively open system above the sill and the relatively close system below. The more mature signatures below the sill are also demonstrated by the n -alkane distribution, carbon predominance index and odd-to-even carbon number predominance of the extracted bitumens. Below the sill, the proportion of the saturated hydrocarbons in the extracted bitumens increases from 34% to 79% towards the sill contact. The bitumens in the two highest rank samples which are closest to the sill are dominated by saturated or saturated + aromatic hydrocarbons. The %20S, %αββ and %Ts biomarker parameters of the extracted bitumens are 46%, 58% and 54%, respectively, at Ro = 1.5%. At Ro = 2.6% or 3.0%, they reach to 52%, 71%, and 71%, respectively, still under or close to their corresponding equilibrium end-points. These samples of high rank, established on the basis of optical assessment (vitrinite reflectance), have less mature biomarker signatures. The remarkable disparities between optical and biomarker parameters can be ascribed to that the aromatization of kerogen to increase Ro was more favored than the isomerization of biomarker in the rapid heating scenario.

A unified equation has been derived by using all available data for calculating methane vapor pressures with measured Raman shifts of C–H symmetric stretching band (υ1) in the vapor phase of sample fluids near room temperature. This equation eliminates discrepancies among the existing data sets and can be applied at any Raman laboratory. Raman shifts of C–H symmetric stretching band of methane in the vapor phase of CH4–H2O mixtures prepared in a high-pressure optical cell were also measured at temperatures between room temperature and 200 °C, and pressures up to 37 MPa. The results show that the CH4 υ1 band position shifts to higher wavenumber as temperature increases. We also demonstrated that this Raman band shift is a simple function of methane vapor density, and, therefore, when combined with equation of state of methane, methane vapor pressures in the sample fluids at elevated temperatures can be calculated from measured Raman peak positions. This method can be applied to determine the pressure of CH4-bearing systems, such as methane-rich fluid inclusions from sedimentary basins or experimental fluids in hydrothermal diamond-anvil cell or other types of optical cell.

Reservoir rocks at the Tazhong 45 oil pool, central Tarim Basin, consist of fluoritized carbonate strata of Middle - Late Ordovician age. Petrological observations indicate that the fluorite replaces calcite. Several other hydrothermal minerals including pyrite, quartz, sphalerite and chlorite accompany the fluorite. Two generations of fluid inclusions are present in the fluorite. Homogenization temperatures (Th) for primary inclusions are mostly between 260°C and 310°C and represent the temperature of the hydrothermal fluid responsible for fluorite precipitation. Th for secondary inclusions range from 100°C to 130°C, and represent the hydrocarbon charging temperature as shown by the presence of hydrocarbons trapped in some secondary inclusions. The mineral assemblage and the homogenization temperatures of the primary fluid inclusions indicate that the precipitation of fluorite is related to hydrothermal activity in the Tazhong area. Strontium isotope analyses imply that the hydrothermal fluids responsible for fluorite precipitation are related to late-stage magmatic activity, and felsic magmas were generated by mixing of mafic magma and crustal materials during the Permian. Theoretical calculations show that the molecular volume of a carbonate rock decreases by 33.5% when calcite is replaced by fluorite, and the volume shrinkage can greatly enhance reservoir porosity by the formation of abundant intercrystalline pores. Fluoritization has thus greatly enhanced the reservoir quality of Ordovician carbonates in the Tazhong 45 area, so that the fluorite and limestone host rocks have become an efficient hydrocarbon reservoir. According to the modelled burial and thermal history of the Tazhong 45 well, and the homogenization temperatures of secondary fluid inclusions in the fluorite, hydrocarbon charging at the Tazhong 45 reservoir took place in the Tertiary.

Two Mesozoic continental basins in the Lower Yangtze Valley of Southeast China host a number of iron oxide and sulfide ore deposits that have been previously interpreted as magmatic-hydrothermal mineralization associated with prophyry intrusions. Our work indicates, however, that a significant part of the metallogenic history in this area prodated the sub-volcanic emplacement of the porphyry intrusive rocks. The ore-forming process is thought to have included an early event of massive sulfide formation in continental fault-bounded basins, which products were subsequently reworked and metal-enriched by the porphyry-related hydrothermal system. Detailed reconstruction of the geological relationships between the ores and their host-rocks, coupled with interpretation of the textural, mineralogical and paragenetic characteristics of the various types of ores in several different deposits in the area, collectively suggest asyngenetic, volcanic-exhalative origin for the lens-shaped, massive pyrite-anhydrite ores related to Mesozoic volcanic activity. Evidence for this includes synsedimentary structures and soft-sediment deformation features, widespread, siliceous, and anhydriterich chemical sediments (exhalites) associated with the massive sulfides, and iron sulfide-oxide replacement relationships.