Reconstruction of deep fluid chemical constituents for estimation of geothermal reservoir temperature using chemical geothermometers

This paper elaborates the chemical constituent change principles of deep geothermal fluid during the process of upward movement. It summarizes research methods of hydrochemistry, isotope and numerical modelling technique for the physiochemical processes such as decreasing temperature, shallow groundwater infusion, and degassing. The multi-component chemical geothermometry methods including gas geochemical method are discussed. High-temperature geothermal fields in China are mostly located in the southwest with frequent new tectonic movements, especially in Tibet high-temperature geothermal areas. Therefore the paper also focuses the status of high-temperature geothermal fluid research. At last, it's pointed out in the paper that in the future we can start from typical high-temperature geothermal zones and geothermal fields to explore optimization of the multi-component geothermometry method and use it in the reconstruction and analogue of the formation mechanism and internal relevancy of regional geothermal systems.

Geochemistry, mineral paragenesis and geothermal conditions of oreforming fluids from the Ain El Bey Cu–Fe deposit: potential occurrence of native gold and precious metal traces (North African orogenic belt, Northern Tunisia)

The Ain El Bey abandoned mine, in North-West Tunisia, fits into the geodynamic context of the European and African plate boundary. Ore deposit corresponds to veins and breccia of multiphase Cu–Fe-rich mineralization related to various hydrothermal fluid circulations. Petromineralogical studies indicate a rich mineral paragenesis with a minimum of seven mineralization phases and, at least, six pyrite generations. As is also the case for galena and native silver, native gold is observed for the first time as inclusion in quartz which opens up, thus, new perspectives for prospecting and evaluating the potential for noble metals associated with the mineralization. Scanning Electron Microscope--Energy Dispersive Spectroscopy and Transmission electron microscopy analyses show, in addition, a large incorporation of trace elements, including Ag and Au, in mineral structures such as fahlores(tetrahedrite-tennantite) and chalcopyrite ones. The mineral/mineral associations, used as geothermometers, gave estimated temperatures for the mineralizing fluids varying from 254 to 330 ℃ for phase Ⅲ, from 254 to 350 ℃ for phase Ⅳ, and from 200 to 300 ℃ for phases Ⅴ and Ⅵ. The seventh and last identified mineralization phase, marked by a deposit of native gold, reflects a drop in the mineralizing fluid’s temperature(< 200 ℃) compatible with boiling conditions. Such results open up perspectives for the development of precious metal research and the revaluation of the Cu–Fe ore deposit at the Ain El Bey abandoned mine, as well as at the surrounding areas fitting in the geodynamic framework of the Africa-Europe plate boundary.

The use of hydrogeochemical analyses and multivariate statistics for the characterization of thermal springs in the Constantine area, Northeastern Algeria

This paper deals with the results of a hydrogeochemistry study on the thermal waters of the Constantine area, Northeastern Algeria, using geochemical and statistical tools. The samples were collected in December2016 from twelve hot springs and were analyzed for physicochemical parameters(electric conductivity, p H,total dissolved solids, temperature, Ca, Mg, Na, K, HCO_3,Cl, SO_4, and SiO_2). The waters of the thermal springs have temperatures varying from 28 to 51 °C and electric conductivity values ranging from 853 to 5630 l S/cm. Q-mode Cluster analysis resulted in the determination of two major water types: a Ca–HCO_3–SO_4 type with a moderate salinity and a Na–K–Cl type with high salinity. The plot of the major ions versus the saturation indices suggested that the hydrogeochemistry of thermal groundwater is mainly controlled by dissolution/precipitation of carbonate minerals, dissolution of evaporite minerals(halite and gypsum), and ion exchange of Ca(and/or Mg) by Na. The Gibbs diagram shows that evaporation is another factor playing a minor role. Principal Component Analysis produced three significant factors which have 88.2% of totalvariance that illustrate the main processes controlling the chemistry of groundwaters, which are respectively: the dissolution of evaporite minerals(halite and gypsum), ion exchange, and dissolution/precipitation of carbonate minerals. The subsurface reservoir temperatures were calculated using different cation and silica geothermometers and gave temperatures ranging between 17 and 279 °C. The Na–K and Na–K-Ca geothermometers provided high temperatures(up to 279 °C), whereas, estimated geotemperatures from K/Mg geothermometers were the lowest(17–53 °C). Silica geothermometers gave the most reasonable temperature estimate of the subsurface waters overlap between 20 and 58 °C, which indicate possible mixing with cooler Mg groundwaters indicated by the Na–K–Mg plot in the immature water field and in silica and chloride mixing models. The results of stable isotope analyses(δ^(18) O and δ~2 H) suggest that the origin of thermal water recharge is precipitation, which recharged from a higher altitude(600–1200 m) and infiltrated through deep faults and fractures in carbonate formations. They circulate at an estimated depth that does not exceed 2 km and are heated by a high conductive heat flow before rising to the surface through faults that acted as hydrothermal conduits.During their ascent to the surface, they are subjected to various physical and chemical changes such as cooling by conduction and change in their chemical constituents due to the mixing with cold groundwaters.

Establishing geothermometric constraints on the local geothermal gradients:Case study of the Eastern Cordillera Basin,Colombia

Geochemical analyses were performed on 170 coal bed-trapped groundwater samples from 97 underground mines located in the Eastern Cordillera Basin, Colombia. The waters analyzed in this paper are from exploited coal beds, located up to 0.73 km deep, which emerge along with the local fault systems.The hydrochemical facies were classified based on the concentration of major ions by inferring the equilibrium state and rock water source. The main hydrochemical facies presented in the groundwater study are SO_4-Ca-Mg, HCO_3-Ca, HCO_3-Ca-Mg, and SO_4-HCO_3 mixed waters. We used geothermometric equations to estimate the most probable temperature under in-situ conditions and the propagation of errors theory to test the results. The geothermal gradient in the study area is close to 30℃/km, which is consistent with measurements from oil wells within the study area. Principal Component Analysis was used to explain factors affecting formation water composition and hydrogeochemical evolution of aquifers.

A Report on a Biotite-Calcic Hornblende Geothermometer

This paper presents a biotite-calcic hornblende geothermometer which wasempirically calibrated based on the garnet-biotite geothermometer and thegarnet-plagioclase-hornblende-quartz geobarometer, in the ranges of 560-800 deg C (T) and 0.26-l.4GPa (P) using the data of metadolerite, amphibolite, metagabbro, and metapelite collected from theliterature. Biotite was treated as symmetric Fe-Mg-Al^VI-Ti quaternary solid solution, and calcichornblende was simplified as symmetric Fe-Mg binary solid solution. The resulting thermometer mayrebuild the input garnet-biotite temperatures well within an uncertainty of + - 50 deg C. Errors of+- 0.2 GPa for input pressure, along with analytical errors of = - 5 percent for the relevantmineral compositions, may lead to a random error of + - 16 deg C for this thermometer, so that thethermometer is almost independent of pressure estimates. The thermometer may clearly discriminatedifferent rocks of lower amphibolite, upper amphibolite and granulite facies on a high confidencelevel. It is assumed that there is a ferric iron content of 11.6 percent in biotite, and that theiron content in calcic hornblende may be calculated according to the method of Dale et al. (2000).This thermometer can be used for medium- to high-grade metabasites and metapelites.

Free Radicals in Organic Matter for Thermal History Reconstruction of Carbonate Succession

Geothermometer is one of the most useful methods to reconstruct the thermal history of sedimentary basins. This paper introduces the application of free radicals concentration of organic matter as a thermal indicator in the thermal history reconstruction of carbonate succession, based on anhydrous thermal simulation results of type I and H1 kerogen. A series of free radicals data are obtained under thermal simulation of different heating temperatures and times, and quantitative modds between free radical concentration （Ng） of organic matter and time-temperature index （TTI） for types I and type H1 kerogen are also obtained. This Ng.TTI relation was used to model the Ordovician thermal gradients of Well TZ12 in the Tarim Basin. The modeling result is corresponding to the results obtained by apatite fission track data and published data. This new method of thermal history reconstruction will be benefit to the hydrocarbon generation and accumulation study and resource assessment of carbonate succession.

ORIGIN ANALYSIS OF GEOTHERMAL WATER AND EVALUATION OF GEOTHERMAL RESERVOIR TEMPERATURE IN THE HENJING AREA, SOUTH JIANGXI PROVINCE, CHINA

The studies of water, gas and isotope chemistry indicate that the formation of geothermal water in the Henjing area is not related to the magmatic and volcanic sources. The geothermal water mainly derives from the meteoric source, and the gas components originate from the mixing of meteoric, crustal and mantle sources. Moreover, the geothermal water is in a low to moderate temperature geothermal reservoir. The results calculated by the quartz geothermometer and the silicaenthalpy diagram demonstrate that the lowest temperature of geothermal reservoir is in the range 78℃ to 134 ℃ and the highest temperature is in the range 95℃C to 155℃. Based on isotopic data, the possible elevation of recharge water is about 337. 5 m to 743. 6 m, which corresponds to the Wunizhang area.

An Experimental Calibration on the Sphalerite-Galena Sulfur Isotope Geothermometer

A new experimental calibration was undertaken in this study to get a more reliable sphalerite-galena sulfur isotope geothermometer. The experimental conditions selected in study were very similar to those of natural hydrothermal solution. The high-precision SF6 method was used in sulfur isotope analyses. The obtained calibration curve for sulfur isotope fractionation between sphalerite and galena can be expressed with the equation 10001nαSp-Gn= 0.74×106T-2+0.08.

Quartz-Ferberite Oxygen Isotope Geothermometer and Its Geological Applications

Experiments for oxygen isotope exchange between ferberite and water were carried out and the followingequation on oxygen isotope fractionation between ferberite and water against temperature was obtained:Combining this equation with the equation of Clayton et al. (1972) on oxygen isotope fractionation be-tween quartz and water, an equation on oxygen isotope fractionation between quartz and ferberite was ob-tained:The Bigeleison-Mayer function method was used to calculate the oxygen isotope fractionation betweenquartz and ferberite. The theoretical curve obtained agrees with the experimental calibration results quite wellin the temperature range of study.The above calibrated equation has been used in 5 world famous tungsten deposits to determine their tem-peratures of formation. The results show that the temperature range for an idividual deposit determined by thisgeothermometer agrees with those obtained from fluid inclusion determination and other isotopegeothermometers.

Effect of Temperature upon Fe-Mg Composition of Garnet in Pelitic System

Garnet is an essential phase in a wide range of metamorphic grades. Ratios of Fe and Mg concentrations in garnet have been widely used as a geothermometer for the crystallization, cooling rate and tectonic uplift rate because garnets in natural rocks always show a variety of Fe-Mg compositional partition. Normally, Fe-Mg concentrations of natural garnets vary widely and the Fe-Mg exchange reactions usually occur in a complex chemical system. Effect of pressure and temperature on Fe-Mg compositions of garnet in natural pelitic system was studied experimentally at temperatures of 700 to 780 ℃ and pressures from 21 to 29.4 kbar. The concentrations of FeO and MgO of garnet in the run products showed a linear relation with experimental temperatures. The result provided experimental evidence of Fe-Mg partition trend with temperature in a complex natural rock and therefore improved our understanding in the determinations of metamorphic temperature calculated by garnet geothermometer. Although the accurate geological application of our results requires the knowledge of the effects of other components upon [D(Mg)] and [D(Fe)] which is largely unknown currently, the data provided in this study are useful to build the relation between FeO-MgO contents and temperature, which is useful in the metamorphic temperatures determine of rocks with pelitic composition.

Geochemical genesis of geothermal waters from the Longling hydrothermal area, Yunnan, Southwestern China

Longling is characterized by a wide distribution of hydrothermal areas, among which the Banglazhang hydrothermal system is the most geothermally active. Banglazhang is marked by intensive hydrothermal activities including hot springs, geysers, fumaroles and hydrothermal explosions. The geothermal waters from the Longling region are mainly HCO3-Na type with low but comparable SO4 and Cl concentrations. Calculations based on a variety of chemical geothermometers and a K-Ca geobarometer indicate that the Banglazhang hydrothermal system has much higher subsurface temperature and CO2 pressure compared to the other systems such as Daheba, Dazhulin and Huangcaoba. However, geothermal water samples collected from all these alternative hydrothermal areas are either partially equilibrated with reservoir minerals or are immature. The silica-enthalpy relationships of Banglazhang geothermal waters indicate the presence of a deep geothermal fluid with an enthalpy value and silica concentration of 945 J/g（up to around 220 °C） and 339 mg/L. Our work indicates the Banglazhang area is a promising source in terms of long-term utilization of hydrothermal resources.

Thermal History of Cambrian Burgess Shale-Type Deposits:New Insights from the Early Cambrian Chengjiang and Qingjiang Fossils of South China

Burgess Shale-type deposits provide a wealth of information on the early evolution of animals.Questions that are central to understanding the exceptional preservation of these biotas and the paleoenvironments they inhabited may be obscured by the post-depositional alteration due to metamorphism at depth and weathering near the Earth’s surface.Among over 50 Cambrian BST biotas,the Chengjiang and Qingjiang deposits are well known for their richness of soft-bodied taxa,fidelity of preservation,and Early Cambrian Age.While alteration via weathering has been well-investigated,the thermal maturity of the units bearing the two biotas has not yet been elucidated.Here we investigate peak metamorphic temperatures of the two deposits using two independent methods.Paleogeotemperature gradient analyses demonstrate that the most fossiliferous sections of the Chengjiang were buried at a maximum depth of∼8500 m in the Early Triassic,corresponding to∼300°C,while the type area of the Qingjiang biota was buried at a maximum depth of∼8700 m in the Early Jurassic,corresponding to∼240°C.Raman geothermometer analyses of fossil carbonaceous material demonstrate that peak temperatures varied across localities with different burial depth.The two productive sections of the Chengjiang biota were thermally altered at a peak temperature of approximately 300°C,and the main locality of the Qingjiang biota experienced a peak temperature of 238±22°C.These results from two independent methods are concordant.Among BST deposits for which thermal maturity has been documented,the Qingjiang biota is the least thermally mature,and therefore holds promise for enriching our understanding of BST deposits.

U-Pb zircon geochronology and Hf isotope study of metamorphosed basic-ultrabasic rocks from metamorphic basement in southwestern Zhejiang:The response of the Cathaysia Block to Indosinian orogenic event

A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geothermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the metamorphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and metamorphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The ε Hf (t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (T DM2 LC ) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recycling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260–230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720°C, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study provided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.

Metamorphic Temperature Investigation of Coexisting Calcite and Dolomite Marble Examples from Nikani Ghar Marble and Nowshera Formation,Peshawar Basin,Pakistan

Using marble samples from the Nikani Ghar marble and Nowshera Formation from Northern Pakistan the determination of the temperature of metamorphism was undertaken with the help of calcite-dolomite solvus geothermometer. Two types of marbles, that is, calcite-dolomite marble and quartz-bearing calcite-dolomite marble were selected. Petrographic and scanning electron microscope analysis of dolomite samples indicated different grain sizes. X-ray diffraction technique indicated the calcites MgCO3 content up to 7.93 mol.%. Nikani Ghar marble samples have shown lower contents of MgCO3 as compared to samples from Nowshera Formation. The calcite-dolomite-quartz marble has also showed relatively lower MgCO3 content and hence rather low temperature （-500 ℃）. The temperature reached during peak metamorphism of the investigated marble occurrence, based on calcitedolomite solvus was 628 ℃. Metamorphic temperatures derived from the present study were shown as a linear graph and values were in good agreement with the published literature.

CALCULATION OF RESERVOIR TEMPERATURE USING A SiO_2 MIXING MODEL, ZHANGZHOU GEOTHERMAL FIELD, SE CHINA

Reservoir temperature is an essential parameter in geothermal exploration, which is usually obtained by using chemical geothermometers. There are more than a dozen of conventional geothermometers, each of which has its own limitation for application. Zhangzhou Geothermal Field is a saline water field, the thermal water chemistry of which

Occurrence of mixed-layer illite/smectite at temperature of 285℃ in an active hydrothermal system and its significance

THE progressive transformation of smectite into illite via mixed-layer illite/smectite (I/S) phases occurs during hydrothermal alteration, burial diagenesis and regional metamorphism. The proportion of illite or smectite (also indicated by their expandability) and ordering of I/S, interpreted by X-ray powder diffraction (XRD) profiles, have long been used as geothermometers in sedimentary basins. It is found that R=1 ordering mixed-layer I/S still exists