Homogenization Temperatures Of Fluid Inclusions Research Articles

Pervasive early diagenetic dolomitization, subsequent hydrothermal alteration, and late stage hydrocarbon accumulation in a Middle Triassic carbonate sequence (Szeged Basin, SE Hungary)

Abstract The Middle Triassic shallow marine carbonates of the SE Pannonian Basin (Szeged Dolomite Formation) show evidence for multistage dolomitization and a complex diagenetic history. In first stage the whole sequence was completely dolomitized by reflux of slightly evaporated seawater. This process took place from the near surface till shallow burial realms and resulted in the formation of both fabric-preserving and fabric-destructive dolomite types. In the following stage nonplanar matrix dolomite and saddle dolomite cement were formed in the intermediate and/or deep burial realm. These later dolomite phases are likely generated by invasion of exotic fluids at relatively high temperature evidenced from the fluid inclusion homogenization temperatures, and stable isotope compositions. Vuggy, fracture, and solution enhanced porosity are also related to this local hydrothermal event. Microthermometry performed on saddle dolomite-hosted primary fluid inclusions confirm the presence of hot (138–235 °C) and moderately saline brines (4.1–8.7 mass% NaCl equivalent). The calculated δ18Owater and the measured δDwater values of the fluid inclusions from the saddle dolomite cement together with the relatively low salinity values indicate a metamorphogenic (and/or magmatic) origin of the hydrothermal fluid that probably was channeled along the Upper Cretaceous subhorizontal overthrust zones. The pores formed by the leaching effect of these hydrothermal fluids were subsequently partly occluded by meteoric calcite during the Paleogene–Middle Miocene subaerial exposure but a remarkable part was preserved, and currently serves as reservoir space. Such an integrated study of the different dolomite and porosity types, the understanding of their genesis, and timing relative to hydrocarbon maturation and migration could aid in exploration and development.

Fluid P-T-X characteristics and evidence for boiling in the formation of the Phoenix uranium deposit (Athabasca Basin, Canada): Implications for unconformity-related uranium mineralization mechanisms

The Phoenix uranium deposit in the southeastern Athabasca Basin (Canada) is a typical unconformity contact-hosted uranium deposit, characterized by an association with reactivated basement faults, graphite-rich rocks in the underlying basement, and a pervasive clay alteration halo surrounding the mineralized zones. Petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events. Uraninite and clay-size minerals (tourmaline, kaolinite, illite and minor chlorite) mainly precipitated in the desilicification periods whereas hydrothermal quartz (mainly drusy quartz) formed during the silicification periods. Primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore-forming fluids even though quartz did not co-precipitate with uraninite. The coexistence of multiple types of fluid inclusions (liquid-dominated biphase, vapor-dominated biphase, vapor-only and halite-bearing triphase) within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping. Bulk fluid inclusion volatile analysis by mass spectrometry indicates H2O as the dominant species, with less than 1 mol% non-aqueous volatiles that show a compositional trend typical of fluid boiling. Microthermometric and cryogenic Raman spectroscopic analyses indicate that the mineralizing fluids are of H2O-NaCl-CaCl2 ± MgCl2 composition, with salinities ranging mainly from 23.4 to 31.1 wt%. The liquid-dominated biphase inclusions (excluding those interpreted to have resulted from heterogeneous trapping) have homogenization temperatures from 90 to 157 °C. These data are generally consistent with the classical diagenetic-hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults, and precipitated uraninite near the unconformity through reaction with reducing agents. However, the relatively low fluid inclusion homogenization temperatures documented in this paper, together with fluid boiling inferred from fluid inclusion assemblages, suggest that the deposit may have formed in a shallower environment (∼2.5 km) than assumed in the conventional diagenetic-hydrothermal model (>5 km). Abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling (flash vaporization) changing the fluid pH and promoting uraninite precipitation, with the alternating liquid-vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively.

Characteristics and origin of the major authigenic minerals and their impacts on reservoir quality in the Permian Wutonggou Formation of Fukang Sag, Junggar Basin, western China

Abstract This research is focused on the characteristics and origin of major authigenic minerals and the influences on the reservoir quality of the Permian Wutonggou Formation sandstones in the eastern slope of Fukang Sag, Junggar Basin, Western China. Authigenic cements were observed and described from thin sections, scanning electron microscopy, fluorescence, and cathodoluminescence. The elemental concentrations of the authigenic minerals were measured by electron probe microanalysis. Additional characterizations were obtained from O and C stable isotope ratios and from the homogenization temperature of aqueous fluid inclusions. The results show that the sandstones in the Wutonggou Formation are dominated by volcanic lithic fragments. Carbonates and laumontites are the major authigenic minerals in the study area. Authigenic quartz and kaolinite can also be observed. Two types of carbonate cements are identified. The first type is calcite with yellow fluorescent hydrocarbon inclusions. The carbon and oxygen isotopes in the calcites are highly C-depleted and O-depleted. The homogenization temperatures of the aqueous fluid inclusions in the calcite cements are higher than the highest paleogeotemperatures during the burial history. Combined with the presence of authigenic fibrous illites and the illitization of kaolinites, it is determined that the precipitation of the calcites is related to the upwelling of deep fluids and was impacted by the CO 2 from the thermal decarboxylation of organic matters during the middle-late Jurassic. The second type is ferroan calcite with blue fluorescent hydrocarbon inclusions and higher contents of Fe, Mn, Cr, and Mg than in the calcites. The ferroan calcites in the Beisantai uplift are rich in 13 C (δ 13 C (V-PDB) values are +22.10‰ and +22.16‰). The precipitation of these ferroan calcites was impacted by the CO 2 from crude oil biodegradation after the late Jurassic. Two types of laumontites are identified. The first type is partially dissolved and is characterized by a high Ca/Na ratio and low Fe contents. The second type is hardly dissolved, has hydrocarbon inclusions with yellow and blue fluorescence, and is characterized by a low Ca/Na ratio and high Fe contents. The first type of laumontite was precipitated prior to hydrocarbon charging and the second type was formed after hydrocarbon charging and meteoric water leaching. The hydration of the volcanic debris provided the source materials for both types of laumontite. The authigenic quartz and kaolinite were formed by the alteration of feldspars, laumontites, and volcanic materials. The evolution of the reservoir properties was impacted by various degrees of cementation and dissolution; as a result, the reservoir quality in the Beisantai uplift was better than in the Shaqiu area.

Mineralogy of the Tumanny Au-Ag-Te-Hg epithermal veins, Western Chukchi Peninsula, Russia

The Tumanny Au-Ag-Te-Hg epithermal prospect, Chukchi Peninsula, Russia is located in the near contact zone of the large Vuknei pluton, part of the Early Cretaceous Egdykgych Complex, which is related to the Peschanka porphyry copper deposit and the Nakhodka porphyry-epithermal ore district located 45 km north of Tumanny. Mineralization at Tumanny is characterized by an early carbonate-base metal and a late gold-silver-sulfosalt mineral assemblage. Pyrite of the first assemblage is unzoned and As-poor, and tennantite-tetrahedrite solid solutions (Ttrs) are characterized by a weak oscillatory zoning caused by variable contents of Sb and As, low Ag content, and the widely variable Sb/(Sb + As) values. Pyrite of the second assemblage is zoned and As-rich (up to 5.2 wt%) and Ttrs is weakly zoned and Ag-rich (up to 10.35 apfu) and has a comparatively narrow range of Sb/(Sb + As) value. Electrum, Au-Ag alloy (“küstelite”), Au-Ag-S phases, hessite, polybasite, and imiterite recognized at the prospect belong to the second mineral assemblage. The homogenization temperature of primary fluid inclusions in quartz ranges from 340 to 210 °C and decreased during the mineralizing process; fluid salinity varying from 0.8 to 5.2 wt% NaCl equiv is not evolved during the process. Cores of quartz crystals formed from a boiling fluid, whereas crystal rims appear to have formed from a lower temperature non-boiling liquid. LogfS2 decreased from −8 at the formation of carbonate-base metal assemblage to −16 at the deposition of gold-silver-sulfosalt assemblage as temperature decreased from 340 to 200 °C. Bulk ICP-OES analysis of mineralized samples indicated up to: 38 ppm Au, 908 ppm Ag, 154 ppm Mo, 106 ppm Te, 53 ppm Se, 9246 ppm As, 1284 ppm Sb, and 23 ppm Bi. Cluster analysis of the data obtained identified three geochemical associations corresponding the carbonate-base metal the gold-silver-sulfosalt, and to the overlapped mineral assemblages. The whole-ore composition is controlled by mineralogy of these assemblages. Taking into account the geological setting, mineralogy, composition of minerals, and fluid inclusion data, the Tumanny Au-Ag-Te-Hg prospect is characterized as intermediate sulfidation epithermal style.

Rb–Sr Dating of Gold‐Bearing Pyrite in the Jinchang Porphyry Cu–Au Deposit, Heilongjiang Province, NE China

AbstractThe Jinchang Cu–Au deposit in Heilongjiang Province, NE China, is located in the easternmost part of the Central Asian Orogenic Belt. Rb–Sr analyses of auriferous pyrite from the deposit yielded an isochron age of 113.7 ±2.5 Ma, consistent with previously reported Re–Os ages. Both sets of ages represent the timing of Cu–Au mineralization because (i) the pyrite was separated from quartz–sulfide veins of the mineralization stage in granite porphyry; (ii) fluid inclusions have relatively high Rb, Sr, and Os content, allowing precise measurement; (iii) there are no other mineral inclusions or secondary fluids in pyrite to disturb the Rb–Sr or Re–Os decay systems; and (iv) the closure temperatures of the two decay systems are ≥500°C (compared with the homogenization temperatures of fluid inclusions of 230–510°C). It is proposed that ore‐forming components were derived from mantle–crust mixing, with ore‐forming fluids being mainly exsolved from magmas with minor amounts of meteoric water. The age of mineralization at Jinchang and in the adjacent regions, combined with the tectonic evolution of the northeast China epicontinental region, indicates that the formation of the Jinchang porphyry Cu–Au deposit was associated with Early Cretaceous subduction of the paleo‐Pacific Plate.

Using integrated in-situ sulfide trace element geochemistry and sulfur isotopes to trace ore-forming fluids: Example from the Mina Justa IOCG deposit (southern Perú)

The Cretaceous Mina Justa iron oxide copper-gold (IOCG) deposit in southern Perú is an important deposit in the Central Andean IOCG mineralization belt. At Mina Justa, Stage I alteration is represented by albite-actinolite, followed by Stage II K-feldspar-magnetite alteration. Stage III alteration is composed mainly of prismatic actinolite, and Stage IV of specular hematite. In-situ SIMS sulfur isotope and LA-ICP-MS trace element analyses were conducted on the major sulfide phases, i.e., pyrite from the magnetite-pyrite-K-feldspar alteration (Stage V) and chalcopyrite from the Cu mineralization (Stage VI). Results show that the δ34S values of Stage V pyrite range from −0.5 to +6.4‰, indicating that the sulfur is mainly magmatic and has possible late external fluid incursion. Co/Ni (0.1 to 209) and Se/S (0.3 to 1.4 × 10−4) ratios show clear coupling with the δ34S values, which is also indicative of external fluid incursion during Stage V pyrite formation. Two distinct fluid sources were identified for Stage V: One shows magmatic affinity with low δ34S (<+2.5‰) and Co/Ni (<1) but high Se/S (1.2 to 1.4 × 10−4), and the other shows non-magmatic fluid (e.g., basinal brine) affinity with high δ34S (>+2.5‰, up to +6.4‰) and Co/Ni (>10, up to 209) but low Se/S (as low as 0.3 × 10−4). The Stage VI chalcopyrite grains that did not replace Stage V pyrite have δ34S values clustering around +1.0‰, suggestive of a magmatic-like origin. Given the low homogenization temperature of fluid inclusions (∼88 to 220 °C, mode ∼130 °C) and Ca-rich nature of the fluids in Stage VI, the ore-forming materials may have derived from the andesitic host rocks, although derivation via mixing with magmatic fluids may have also been possible. For the Stage VI chalcopyrite grains that replaced Stage V pyrite, both their δ34S values and trace element patterns show inheritance of the replaced pyrite. In summary, Stage V ore-forming fluids was likely magmatic initially, with external fluid incursion occurring later in this stage; whereas the fluids of Cu mineralization stage may have come mainly from the external fluids that leached the andesitic wall rocks, during which the external fluids had inherited certain sulfur isotope and trace element signatures of the pyrite they replaced.

Tectono–Thermal Evolution, Hydrocarbon Filling and Accumulation Phases of the Hari Sag, in the Yingen–Ejinaqi Basin, Inner Mongolia, Northern China

This work restored the erosion thickness of the top surface of each Cretaceous formations penetrated by the typical well in the Hari sag, and simulated the subsidence burial history of this well with software BasinMod. It is firstly pointed out that the tectonic subsidence evolution of the Hari sag since the Cretaceous can be divided into four phases: initial subsidence phase, rapid subsidence phase, uplift and erosion phase, and stable slow subsidence phase. A detailed reconstruction of the tectono–thermal evolution and hydrocarbon generation histories of typical well was undertaken using the EASY Ro% model, which is constrained by vitrinite reflectance (Ro) and homogenization temperatures of fluid inclusions. In the rapid subsidence phase, the peak period of hydrocarbon generation was reached at c.a. 105.59 Ma with the increasing thermal evolution degree. A concomitant rapid increase in paleotemperatures occurred and reached a maximum geothermal gradient of about 43–45°C/km. The main hydrocarbon generation period ensued around 105.59–80.00 Ma and the greatest buried depth of the Hari sag was reached at c.a. 80.00 Ma, when the maximum paleo–temperature was over 180°C. Subsequently, the sag entered an uplift and erosion phase followed by a stable slow subsidence phase during which the temperature gradient, thermal evolution, and hydrocarbon generation decreased gradually. The hydrocarbon accumulation period was discussed based on homogenization temperatures of inclusions and it is believed that two periods of rapid hydrocarbon accumulation events occurred during the Cretaceous rapid subsidence phase. The first accumulation period observed in the Bayingebi Formation (K1b) occurred primarily around 105.59–103.50 Ma with temperatures of 125–150°C. The second accumulation period observed in the Suhongtu Formation (K1s) occurred primarily around 84.00–80.00 Ma with temperatures of 120–130°C. The second is the major accumulation period, and the accumulation mainly occurred in the Late Cretaceous. The hydrocarbon accumulation process was comprehensively controlled by tectono–thermal evolution and hydrocarbon generation history. During the rapid subsidence phase, the paleo temperature and geothermal gradient increased rapidly and resulted in increasing thermal evolution extending into the peak period of hydrocarbon generation, which is the key reason for hydrocarbon filling and accumulation.

Cathodoluminescence, fluid inclusions, and trace element data for the syntaxial quartz cementation in the sandstones of the Ora Formation, northern Iraq

Quartz cements of the quartz arenitic sandstones from the Chalky Nasara and Ora sections of the (Devonian-Carboniferous) Ora Formation in northern Iraq have been studied. A combination of hot cathodoluminescence, LA-ICP-MS, and fluid inclusion microthermometry revealed three syntaxial quartz cement generations (Q1, Q2, and Q3). The early Q1 cementation has gray to slightly brown luminescences, postdated compaction, and reduced intergranular porosity associated with illite formed during eogenesis. Q2 is characterized by dark brown luminescence overgrowths and is more voluminous in the thinly bedded sandstones than in the thickly bedded sandstones filling most of the remaining pore space during mesogenesis. Q3 was formed during the early telogenesis stage fully cementing the sandstones and the fractures were filled by hydrothermal chlorite and sulfides. Significant amounts of trace elements Al, Li, Ge, and Fe have been detected in quartz overgrowths. Al varies consistently between each cement with averages of 7125, 4044, and 2036 ppm for the Q1, Q2, and Q3 generations, respectively. A strong linear correlation between Al and Li in the three quartz cements with an average Li/Al of ~0.02 in Q1 and Q2 indicates sufficient availability of both Al and Li where Li is most likely to be found in high-saline pore waters. Illite is the most probable origin of Li since high salinities favor the mobilization of Li during diagenesis. Germanium concentrations in quartz cements are slightly less than that in the detrital quartz of the Ora Formation, indicating that the pressure dissolutions of quartz and feldspar are the dominant sources of cementation in the Ora Formation. Homogenization temperatures of fluid inclusions indicate precipitation of the Q1, Q2, and Q3 cement generations at temperature ranges of 155-160 °C, 160-166 °C, and 168-178 °C, respectively, with salinities ranging between 5.0 and 6.4 wt.% NaCl equiv., as an indication of hydrothermal burial conditions for Q3 cement, which was affected by the major Zagros Thrust Zone faulting.

Fahlore and Sphalerite from the Darasun Gold Deposit in the Eastern Transbaikal Region, Russia: II. Fe and Zn Partitioning, Fluid Inclusions, and Formation Conditions

The partitioning of Fe and Zn between coexisting fahlore and sphalerite and fluid inclusions in sphalerite from the Darasun gold deposit have been studied. These data were used to estimate the formation temperature of the minerals by the sphalerite–fahlore geothermometer. The calculated crystallization temperature of 175–355°С is close to the homogenization temperature of fluid inclusions in sphalerite of 225–385°С.The estimated pressure for fluid inclusion trapping ranged from 340 to 1420 bar. The sulfur fugacity obtained from the FeS content in sphalerite associated with pyrite and the calculated temperature ranges from 10–5.5 to 10–11 bar.

In situ geochemical characterization of pyrite crystals in burial dolomites of St. George Group carbonates

Secondary ion mass spectrometry (SIMS) was used to measure the δ34S of pyrite disseminated in burial dolomite matrix of Boat Harbour formation at Main Brook and Daniel’s Harbour (about 130 km apart). At Main Brook, δ34S values for the pyrite grains show wide variation (–15 to +20‰ (n = 20)), but are mostly negative. Combined with a paucity of two-phase fluid inclusions in the host burial dolomite, the depleted δ34S values suggest that the pyrite is a direct product of bacterial sulfate reduction (BSR). Predominantly negative δ34S values were also obtained for sampled pyrite at Daniel’s Harbour and Port au Choix; however, relatively high homogenization temperatures (&gt;100 °C) of two-phase fluid inclusions in the host dolomite is incompatible with a BSR process for pyrite formation. More so, Daniel’s Harbour is a site for main stage sulfide mineralization (Mississippi Valley-type (MVT) system), hosted in similarly burial dolomite and that has been previously constrained to be associated with thermochemical sulfate reduction (TSR). A relative proximity of the currently studied pyrite samples to this MVT system deposit is thus inconsistent with an in-situ BSR for these pyrites. The analyzed pyrite grains are commonly encased in bitumen, and they postdate their host burial dolomite and predate deep burial saddle dolomite. Taken together, the depleted δ34S signature in the pyrite was likely inherited from migrated hydrocarbons in the reservoir. Incursion of an initial pulse of hot sulfate-rich brine into the formation can cause thermal cracking of hydrocarbons, thereby releasing its low δ34S. Thus the inherited low δ34S signature was likely a product of an earlier BSR that occurred in the kerogen or source organic materials in source rock. Subsequently, the main stage sulfide mineralization (MVT deposit) occurred via in-situ TSR. These findings have an implication for the paragenetic history of sulfide minerals precipitated during MVT mineralization episode.

Nature and evolution of fluid inclusions in the Cenozoic Beiya gold deposit, SW China

The Beiya Au deposit in the Sanjiang metallogenic belt, SW China, is a porphyry-skarn deposit that formed in an intracontinental setting. Three stages of hydrothermal veins, namely quartz veins (Stage 1), quartz-pyrite veins (Stage 2), and Au-rich sulfide-quartz veins (Stage 3) were identified on the basis of field relationship and petrography under scanning electron microscopy cathodoluminescence (SEM-CL). Intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) have been identified in both Stage 1 and Stage 2 veins. Only liquid-rich fluid inclusions (L3) were found in Stage 3 veins. Raman spectroscopy revealed that all the inclusions contain abundant CO2. H2S was identified in ID2 and V2 inclusions. Salinities and homogenization temperatures of the intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) are 7.4 ± 1.1–11.9 ± 2.2, 33.6 ± 0.5–39.2 ± 1, and 1.6 ± 0.7–5.8 ± 0.8 (wt% NaCl equiv.) and 400 ± 35–440 ± 37, 395 ± 20–414 ± 6, and 386 ± 5–416 ± 4 °C, respectively. Salinities and homogenization temperatures of the L3 inclusions range from 4.9 ± 1.6 to 9.8 ± 0.7 (wt% NaCl equiv) and from 301 ± 28 to 398 ± 4 °C, respectively. Initial intermediate density aqueous fluid inclusions contain 2000–10,000 ppm Fe, 2000–4000 ppm Cu, 200–600 ppm Zn, 200–500 ppm Pb, 17–89 ppm Mo, 1–8 ppm Ag, and 0.9–5.9 ppm Au, comparable to that of intermediate density inclusions in subduction-related porphyry deposits. Brine inclusions are rich in metals and have 9000–24600 ppm Fe, 3400–11,000 ppm Cu, 1200–5200 ppm Pb, 500–3000 ppm Zn, hundreds of ppm Mo, and tens of ppm Ag. The corresponding vapor inclusions contain lower metal concentrations: 400–6000 ppm Fe, 1700–4700 ppm Cu, 50–270 ppm Pb, 100–500 ppm Zn, and minor Mo and Ag. Low to intermediate density fluids are abundant and are inferred to have been the main metal transporting medium. A temperature decrease to approximately 350 °C during Stage 3 triggered metal precipitation.

Genesis of the Bianbianshan Cu-polymetallic deposit of the Xilamulun Cu-Mo metallogenic belt, Inner Mongolia, China: A fluid inclusion and O–H–S–Pb isotope study

The Bianbianshan Cu-polymetallic deposit is located in the Xilamulun Cu-Mo belt of Inner Mongolia, NE China, and occurs within Late Jurassic andesite, rhyolite and tuff. Cu mineralization is observed in various types of hydrothermal disseminated veins exhibiting siliciification, sericitization and chloritization. The ore-forming process occurred in four stages: (1) chalcopyrite-pyrite-quartz, (2) pyrite-chalcopyrite-quartz-vein, (3) sphalerite-galena-quartz-vein, (4) and quartz-calcite-vein. Three types of fluid inclusions were identified in the deposit, including C-type (CO2-NaCl-H2O) as well as V- and L-type (NaCl-H2O) inclusions, where only L-type inclusions are observed in the fourth stage. Homogenization temperature of fluid inclusions in the four stages are 325–365 °C, 282–335 °C, 268–312 °C, and 195–259 °C, respectively, all of which exhibit salinities lower than ∼ 13 wt% NaCl equiv. Trapping pressure estimated from C, V- and L-fluid inclusions are between 550 and 900 bars, corresponding to minimum depths of 2.5–3.7 km. Hydrogen and oxygen isotopic compositions of quartz from different stages (δD = −109.7 ~ –107.6‰, δ18O = 7.6–9.6‰, V-SMOW) suggest that the mineralizing fluid gradually evolved from a magmatic to a meteoric origin. Sulfur (δ34SV-CDT = −0.7 to 0.4‰) and lead isotopes (208Pb/204Pb = 37.746–38.137‰; 208Pb/204Pb = 15.52–15.56%; 206Pb/204Pb = 17.75–18.36%) indicate that ore-forming materials were derived from mantle with minor additional participation of crustal reservoirs. Our data suggests the ore-forming fluids of the Bianbianshan Cu-polymetallic deposit are attributed to a moderate temperature, moderate-low salinity, and moderate density system, where decreases in pressure, phase separation and local mixing with meteoric water drove precipitation of metals.

Ore facies, mineral chemical and fluid inclusion characteristics of the Hossein-Abad and Western Haft-Savaran sediment-hosted Zn-Pb deposits, Arak Mining District, Iran

The Arak basin in the northern part of the Malayer-Esfahan metallogenic belt (MEMB) of Iran hosts 9 Zn-Pb sulfide deposits within a Jurassic sedimentary succession of black, fine-grained sandstone, siltstone and shale. This succession was deposited in an extensional back-arc environment between the Sanandaj- Sirjan Zone (SSZ) and the Central Iranian microcontinent. Two of the 9 deposits (Western Haft-Savaran and Hossein-Abad) are the focus of study. Here, three ore facies can be distinguished, based on the morphology of the orebodies and the sulfide mineralogy and textures: (a) stockwork, (b) massive, and (c) bedded mineralization. The stockwork and massive mineralization are interpreted to have formed in the subsurface, whereas bedded mineralization was sedimented on the seafloor. The Fe contents of sphalerites from massive and stockwork mineralization from the two deposits, together with the presence of pyrrhotite inclusions, indicate that sphalerite precipitated from relatively low fS2 (<10−11) fluid. Homogenization temperatures of fluid inclusions in sphalerite, quartz and siderite in massive mineralization range from 105 to 309 °C, and average 208 °C, with salinities between 4.03 and 11.1 wt% NaCl eq., and averaging 5.77 wt% NaCl eq. These widely ranging salinities and homogenization temperatures reflect mixing of shallow connate water with venting metalliferous fluid that is of deep basinal origin, and deposition of mineralization predominantly below the seafloor. Collectively, the host rock types, ore facies and textures, deposition in an reduced ambient environment, fluid inclusion temperatures and salinities, and mineralizing fluid behaviour at the seafloor are all compatible with a vent-proximal sedimentary exhalative (SEDEX) origin for the Western Haft-Savaran and Hossein-Abad deposits.

Characteristics and formation mechanisms of silicified carbonate reservoirs in well SN4 of the Tarim Basin

High-yield natural gas was discovered in well SN4 in the Ordovician Yingshan Formation in the Tarim Basin. The gas is found in unusual, silicified, carbonate reservoirs. According to the degree of silicification, the silicified reservoirs can be divided into a lower section of silicified carbonates, a middle section of limestone, and an upper section of silicified carbonates. The silicified carbonates are mainly composed of quartz and calcite, in which the reservoir space mostly occurs as vugs, inter-crystalline pores of quartz, and partial fractures. Porosity varies widely, ranging from 3 to 20.5% with strong heterogeneity. The homogenization temperatures of fluid inclusions in quartz and calcite show that the silicification temperatures were 150–190°C, with characteristics of high temperature/low salinity and low temperature/high salinity. The 87Sr/86Sr ratios of secondary calcite are 0.709336–0.709732, which are significantly higher than that of concurrent seawater, indicating that the hydrothermal fluid originated from the deep clastic strata or the basement (sialic rock). The δ13C values of the secondary calcite are similar to that of the surrounding limestone, indicating that the carbon in the secondary calcite is derived from the limestone strata, and that the secondary calcite is the product of dissolution and re-precipitation resulting from interaction between the silica-bearing hydrothermal fluids and surrounding limestones. The silicification of silica-bearing hydrothermal fluid was significantly controlled by strike-slip faults. The fluids ascending along the fault zone and branch faults interacted with the surrounding limestone in the Yingshan Formation. As a result, a large amount of quartz and secondary calcite were formed together with various types of secondary pores, resulting in excellent reservoirs.

Fluid evolution and ore genesis of the Dalingshang deposit, Dahutang W-Cu ore field, northern Jiangxi Province, South China

The Dalingshang W-Cu deposit is located in the North section of the Dahutang ore field, northern Jiangxi Province, South China. Vein- and breccia-style tungsten-copper mineralization is genetically associated with Mesozoic S-type granitic rocks. Infrared and conventional microthermometric studies of both gangue and ore minerals show that the homogenization temperatures for primary fluid inclusions in wolframite (~ 340 °C) are similar to those in scheelite (~ 330 °C), but about 40 °C higher than those of apatite (~ 300 °C) and generally 70 °C higher than those in coexisting quartz (~ 270 °C). Laser Raman analysis identifies CH4 and N2 without CO2 in fluid inclusions in scheelite and coexisting quartz, while fluid inclusions in quartz of the sulfide stage have variable CO2 content. The ore-forming fluids overall are characterized by high- to medium-temperature, low-salinity, CH4, N2, and/or CO2-bearing aqueous fluids. Chalcopyrite, muscovite, and sphalerite are the most abundant solids recognized in fluid inclusions from different ores. The H-O-S-Pb isotope compositions favor a dominantly magmatic origin for ores and fluids, while some depleted δ34S values (− 14.4 to − 0.9‰) of sulfides from the sulfide stage are most likely produced by an increase of oxygen fugacity, possibly caused by inflow of oxidized meteoric waters. The microthermometric data also indicate that a simple cooling process formed early scheelite and wolframite. However, increasing involvement of meteoric waters and fluid mixing may trigger a successive deposition of base metal sulfides. Fluid-rock interaction was critical for scheelite mineralization as indicated by in-situ LA-ICP-MS analysis of trace elements in scheelite.

The Bairendaba silver polymetallic deposit in Inner Mongolia, China: characteristics of ore-forming fluid and genetic type of ore deposit

Bairendaba silver-polymetallic deposit is located in the middle south of the Xing Meng orogenic belt, and in the silver-polymetallic metallogenic belt on the west slope of the southern of Great Xing’an Range. Based on studying of the fluid inclusion, we discuss the characteristics of ore-forming fluid and the metallic genesis of the Bairendaba silver-polymetallic deposit. By means of the analysis of the fluid inclusions, homogenization temperature, salinity and composition were studied in quartz and fluorite. The result is as the follows: with homogenization temperatures of fluid inclusions in quartz veins being 196∼312 °C, the average 244.52 °C, and fluid salinity 2.90∼9.08 wt%NaCl; with homogenization temperatures of fluid inclusions in fluorite being 127∼306 °C, the average 196.92 °C, and fluid salinity 2.90∼9.34 wt% NaCl. The ore-forming fluid is mainly composed of water and the gas. The results of laser Raman analysis show that the gas phase is mainly CH4. It shows that the ore-forming fluid is characterized by medium-low temperature and low-salinity system. The temperature of ore-forming fluid is from high to low, and the salinity from high to low, and the meteoric water or metamorphic water is added during deposit. According to the geological characteristics of the mining area, it is considered that the genetic type of the ore deposit should be the fault-controlled and the medium-low temperature hydrothermal deposit related to magmatic hydrothermal activities.

Evidence of high-temperature rock salt transformations in areas of occurrence of borate minerals (Zechstein, Kłodawa salt dome, Poland)

Occurrences of borate minerals in the Zechstein salt-bearing deposits of the Klodawa salt dome (central Poland), and the manner of their development, suggest that the minerals were formed at high temperatures, that considerably exceed the temperature estimated from the thermal gradient (~180°C). Research on rock salt and potassium-magnesium salts containing congolite and boracite, respectively, are consistent with high-temperature processes of transformations affecting the salt rocks in certain sections of the salt dome. The chemical composition of, and daughter minerals occurring in, primary fluid inclusions in halite, originating from the congolite zone, indicated a very high proportion of potassium and magnesium in the brines from which the halite crystallised. The thermal transformations observed in inclusions indicate a halite crystallisation temperature exceeding 420°C. Anhydrite crystals, co-occurring with borate minerals, represent unique features as to the distribution and composition of solid and fluid inclusions. These features indicate crystallisation or recrystallisation in conditions that differed considerably from those typical of the salt dome, with the involvement of solutions of changing chemical compositions. The crystals contain multiple solid inclusions of transparent and non-transparent minerals, among which we have focused on carnallite. The relationships of carnallite with liquid and gaseous phases indicate, as in the congolite zone, migration of very highly concentrated brines with respect to potassium and magnesium, or even transport of carnallite in the form of melt (liquid). Measurements of fluid inclusion homogenization temperatures, within the range from 197.8 to 473.8°C, supported a high-temperature origin for these minerals in hydrothermal conditions.

Genesis of the Nanyangtian scheelite deposit in southeastern Yunnan Province, China: evidence from mineral chemistry, fluid inclusions, and C–O isotopes

The Nanyangtian skarn-type scheelite deposit is an important part of the Laojunshan W–Sn polymetallic metallogenic region in southeastern Yunnan Province, China. The deposit comprises multiple scheelite ore bodies; multilayer skarn-type scheelite ore bodies are dominant, with a small amount of quartz vein-type ore bodies. Skarn minerals include diopside, hedenbergite, grossular, and epidote. Three mineralization stages exist: skarn, quartz–scheelite, and calcite. The homogenization temperatures of fluid inclusions in hydrothermal minerals that formed in different paragenetic phases were measured as follows: 221–423 °C (early skarn stage), 177–260 °C (quartz–scheelite stage), and 173–227 °C (late calcite stage). The measured salinity of fluid inclusions ranged from 0.18% to 16.34% NaCleqv (skarn stage), 0.35%–7.17% NaCleqv (quartz–scheelite stage), and 0.35%–2.24% NaCleqv (late calcite vein stage). Laser Raman spectroscopic studies on fluid inclusions in the three stages showed H2O as the main component, with N2 present in minor amounts. Minor amounts of CH4 were found in the quartz–scheelite stage. It was observed that the homogenization temperature gradually reduced from the early to the late mineralization stages; moreover, δ13CPDB values for ore-bearing skarn in the mineralization period ranged from − 5.7‰ to − 6.9‰ and the corresponding δ18OSMOW values ranged from 5.8‰ to 9.1‰, implying that the ore-forming fluid was mainly sourced from magmatic water with a minor amount of meteoric water. Collectively, the evidence indicates that the formation of the Nanyangtian deposit is related to Laojunshan granitic magmatism.

渤海石臼坨凸起古近系沙河街组砂岩成岩作用特征

渤海石臼坨凸起古近系沙河街组砂岩储层的发育主要受成岩作用的控制。利用普通薄片、铸体薄片、X衍射分析、扫描电镜和物性分析等实验测试资料，分析了渤海石臼坨凸起古近系沙河街组砂岩成岩作用和孔隙演化特征。研究表明，砂岩储层孔隙类型主要为粒间孔、粒内溶孔；不同类型的砂岩压实差异较大，分选较好、粒度较粗的砂岩压实较弱；自生矿物主要为(铁)方解石、(铁)白云石、高岭石，其他胶结物(如自生石英、伊利石等)较少；经历的最晚成岩阶段为中成岩B期，大部分砂岩储层目前处于中成岩A期。根据成岩作用类型及其相互关系、包裹体均一温度等资料，建立了成岩演化序列；通过对压实作用、自生矿物和溶蚀的定量估算，反演了砂岩储层的孔隙演化特征。对砂岩储层发育有利的成岩作用主要是整体压实作用不强、早期油气充注以及长石颗粒的溶蚀，方解石胶结物对储层的破坏较显著。 The sandstone reservoirs are mainly controlled by diagenesis in the Eogene Shahejie Formation of the Shijiutuo Uplift in Bohai Sea. Using petrographic thin sections, casting thin sections, X-ray dif-fractometry, scanning electron micrograph observations, physical properties data and other analysis materials, diagenesis and porosity evolution characteristics are analyzed in the the Eogene Shahejie Formation Sandstone in Bohai Sea. The sandstone reservoir pores mainly consist of the intergranular pores and intragranular secondary pores. Compaction levels are incoordinate in different sandstones and the well-sorting and fairly coarse sandstones present relatively weak compaction. Calcite, ferrocalcite, dolomite, ferrodolomite and kaolinite are the major cements and other cements like authigenic quart and illite are rarely observed in microscope. The latest di-agenetic stage of the sandstones is the stage B of mesogenetic diagenesis and the most is evolved to the stage A of mesogenetic diagenesis. The sandstone diagenetic evolution sequence is established based on different diagenesis phenomena and relationship among them and fluid-inclusion homogenization temperatures. The sandstone porosity evolution features are inverted through quantitatively estimating the compaction intensity and the contents of authigenic minerals and dissolution. The relatively weak compaction, early hydrocarbon filling and feldspar dissolution benefit for the sandstone reservoir development, and the carbonate cements obviously damaged the sandstone reservoir.

Testing clumped isotopes as a reservoir characterization tool: a comparison with fluid inclusions in a dolomitized sedimentary carbonate reservoir buried to 2–4 km

Abstract Constraining basin thermal history is a key part of reservoir characterization in carbonate rocks. Conventional palaeothermometric approaches cannot always be used: fluid inclusions may be reset or not present, while δ 18 O palaeothermometry requires an assumption on the parent fluid composition. The clumped isotope palaeothermometer, however, is a promising technique for constraining the thermal history of basins. In this study, we test if clumped isotopes record temperatures of recrystallization in deeply-buried dolomitic reservoirs, through comparison with fluid-inclusion data. The studied reservoir is the Cretaceous Pinda Formation, offshore Angola, a deeply-buried dolomitized sedimentary carbonate hydrocarbon reservoir. It provides an ideal test case as samples from industry wells are available over a relatively wide burial depth range of c. 2000–4000 m below seafloor (mbsf) and the constituent dolomites are relatively homogeneous. Across this depth range, fluid-inclusion homogenization temperatures for the Pinda Formation record a range of temperatures from c. 110 to 170°C, increasing with depth. These closely match present-day ambient well temperatures, indicating recent resetting of the fluid inclusions. Clumped isotopes, however, record temperatures significantly ( c. 20–60°C) below fluid-inclusion and well temperatures for the seven samples analysed. The deepest five samples ( c. 2800–3700 mbsf) record clumped isotope temperatures of around 100–120°C, interpreted to represent a deep burial recrystallization event responsible for a massive (re)dolomitization of the reservoir. The lower clumped isotope temperatures (65 and 82°C) of the shallower (2055 and 2740 mbsf) samples are interpreted to represent physical mixing of two dolomite generations due to incomplete burial recrystallization of an early shallow dolomite. Determination of temperature through clumped isotopes allows calculation of the parent fluid δ 18 O values. In the five deepest samples, the fluid δ 18 O values of 3.7–6.5‰ cluster around the modern-day porewater composition (5‰), suggesting that burial dolomitization occurred in the presence of evolved brine. Mineral δ 18 O values of c . −7 to −4.5‰ are lower than pristine Cretaceous marine dolomite and are in accordance with burial recrystallization. Clumped isotopes are therefore interpreted to record temperatures corresponding to open-system burial recrystallization events. This study shows that clumped isotopes are a valuable tool in characterizing the thermal history of deeply-buried (&gt;2000 m) carbonate hydrocarbon reservoirs.