Geothermometry

Recent studies on the Uganda geothermal systems have focused on three geothermal prospects, Katwe, Buranga and Kibiro, all located in the tectonically active and Recent volcanic belt in the Western Rift valley along the border of Uganda and the Democratic Republic of Congo. Geothermal systems and saline and fresh water lakes characterize the Rift Valley. The three areas were chosen for study because of their volcanic and tectonic features that indicate a powerful heat source and high permeability. The objective is to develop geothermal energy as an alternative energy source to hydro and others to meet the energy demand of rural areas in sound environment. The geology and geochemistry results for the surface hot springs indicate that potential geothermal systems exist at depth. The subsurface temperatures of 160-200°C, 200°C, and above 200°C for the Katwe, Buranga and Kibiro prospects, respectively, have been inferred by geothermometry and mixing models. These temperatures are suitab...

Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study evaluates these hot springs based on surface geological information, radon emission measurements, hydro-geochemical and isotopic signatures and potential source mechanisms. Field observations reveal that the hot springs are located at the crest of the Tattapani anticline along the faulted contact of Cambrian carbonates with Paleocene siliciclastics. In addition, remnants of igneous intrusions in the Cambrian carbonates are commonly observed. Spatial distribution of radon emissions (ranging between 2.1 and 29.5KBq m-3) indicates an anomalous zone located over the Cambrian-Paleocene faulted contact. Hydro-geochemical data show sodium-bicarbonate affinity of hot springs. The highest surface temperature of these springs is recorded at 60.8oC. Average reservoir temperatures based on silica and cation geo-thermometers are 101oC and 115oC, respectively. Giggenbach ternary diagram (Na-K-Mg) sugge...

Temperature is a crucial factor influencing the effectiveness of metal smelting process. When studied in historical slags it provides information on the evolution of smelting technologies over time and how humankind approached metal recovery. Methodological approaches to temperature reconstruction using pyrometallurgical slags vary and this study serves as a critical review of the methods used so far with the complex historical smelting site used as an example of the application of the methods. The example includes silica-undersaturated, potassium-rich Cu slags from four sites in the Old Copper Basin (Stare Zagłębie Miedziowe), Poland, and is of particular interest because (a) K-rich slag compositions are not widely found and this provides additional challenge to temperature reconstruction approach and (b) the site provides material of different ages (18 th and 19 th century) and, therefore, gives insight into potentially different pyrometallurgical processes. Several methods are compared and include phase diagrams, geothermometry (Cpx-WR), thermodynamic modelling with MELTS software and temperature XRD analyses with the main implication that most of the methods have their merits, but modelling by MELTS software returns the most reliable estimates of liquidus temperature. In fact, MELTS is the only method that returns differences of 200 � C in reconstructed temperatures between the studied sites, which signifies a change in smelting technique probably related to the change in input material. More importantly , MELTS may also be used to estimate crystallization interval (temperature difference between solidus and liquidus) that together with liquidus temperature gives insight into metal extraction efficiency for a given site and provides information on society advancement in metallurgy. The software can also be used cost-effectively for a large number of samples and its combination with experimental approach (temperature XRD analyses) provides the most promising tool to reconstruct differences in smelting technologies of ancient and historical metallurgical sites.

Although potassium-related classical geothermometers have been widely used over the years to estimate the temperature of geothermal reservoirs, there are limitations regarding their practical applications. In order to obtain more reliable reservoir temperature estimates, the limitations and the advantages of classical geothermometers must be realized and understood prior to their selection and application. In this study, the hydrogeochemical data for 239 water samples from geothermal wells drilled into crystalline basement reservoirs across the world were collated and analyzed to obtain the applicability conditions of K-related classical geothermometers from the scientific literature. Of these samples, 44 are of special interest being unaffected by mixing and because their reservoir temperature is known. The study shows that generally, the Na-K geothermometer gives valid estimates of reservoir temperatures above 200 °C. However, that is not the case in lower-temperature reservoirs since the equilibrium between albite, K-feldspar, and the aqueous solution is not always achieved, and the Na-K ratio of the primary fluids in the host reservoirs may change due to mixing taking place during the ascent of these thermal waters which have relatively low Na and K concentrations. At high temperatures, especially above 250 °C, reservoir temperature calculations for the use of the K-Mg geothermometer showed relatively large deviations from the measured temperatures. The K-Mg geothermometer seems to work well for mid-low temperature reservoirs (below around 150 °C), and the deviations from the reservoir temperatures probably result from the low activities of clinochlore in chlorites. Moreover, the performance of the K-Mg geothermometer is negatively affected by mixing of the thermal waters with other kinds of groundwater. The Na-K-Ca geothermometer may play a complementary role for evaluating reservoir temperatures above 200 °C but should be applied with caution when calcite precipitation triggered by degassing of the thermal waters takes place.

Northern Thailand has 16 hot spring systems with surface temperatures near or greater than 80°C with potential for binary plant power generation. Presently only Fang system generates power from wells flowing a total of 8.3 1/s of 116°C water to a 300 kW single module Ormat binary plant. Current production is 150-250 KW, which potentially can be increased by constructing new wells and increasing flow by pumping. Of the other 15 systems, 4 are in national parks and not considered for development. Several of the hot springs systems have silica geothermometry >130°C suggesting significant undeveloped resources exist in northern Thailand. Certainly the San Kamphaeng hot springs have the greatest known potential (estimated ~5MW) but like most of the systems it is associated with high-angle faulting and drilling has yet to find permeable zones yielding high flows (>11 l/s). The current project of the Thailand Department of Energy Development and Efficiency (DEDE) will survey these prospects with the intention of installing a small plant of 2-10 MW.

The study aims to determine the radioactivity levels of thermal waters which have been used seasonally or permanently in spas for therapeutic intentions. Samples were collected from spas in different regions of Turkey. Some radionuclides (40K, 232Th, 226Ra, 137Cs), gross alpha (GA) and gross beta (GB) activities, and physical and some chemical parameters were measured. Gamma radiation measurements for 226Ra, 232Th and 40K radionuclides were performed by using a high purity germanium (HPGe) detector. The results of the gamma spectrometry ranged from 1.385 to 11.025 Bql−1 for 226Ra, <minimum detectable activity to 3.477 Bql−1 for 232Th and 9.679 to 36.989 Bql−1 for 40K. GA and GB activity concentrations were detected by using ultra-low level α/β counter. The GA and GB activity ranged from 43 to 3,182 mBql−1 and 54 to 1,950 mBql−1, respectively. Based on calculated annual effective dose equivalent, the total dose originated mostly from 226Ra and slightly from 40K. Furthermore, water...

Northern Thailand has 16 hot spring systems with surface temperatures near or greater than 80°C with potential for binary plant power generation. Presently only Fang system generates power from wells flowing a total of 8.3 1/s of 116°C water to a 300 kW single module Ormat binary plant. Current production is 150-250 KW, which potentially can be increased by constructing new wells and increasing flow by pumping. Of the other 15 systems, 4 are in national parks and not considered for development. Several of the hot springs systems have silica geothermometry >130°C suggesting significant undeveloped resources exist in northern Thailand. Certainly the San Kamphaeng hot springs have the greatest known potential (estimated ~5MW) but like most of the systems it is associated with high-angle faulting and drilling has yet to find permeable zones yielding high flows (>11 l/s). The current project of the Thailand Department of Energy Development and Efficiency (DEDE) will survey these prospects with the intention of installing a small plant of 2-10 MW.

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the *340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe-Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over *10-85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the ~340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe–Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over ~10–85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.

ABSTRACT The boron stable isotope ratio δ11B of twelve water samples representative of three chemical facies (fresh Na-bicarbonate, brackish Na-chloride, saline and brine Ca-chloride) have been analyzed. Interpretation of the δ11B data, along with the chemical compositions, reveals that Na-carbonate waters from the Northern Apennine are of meteoric origin, with boron contributions from clay-desorption and mixing with seawater-derived fluids of Na-chloride or Ca-chloride compositions. The comparison of our new results with the literature data on other sedimentary basins of Mediterranean, and worldwide, confirms the contribution of Na-bicarbonate waters to the genesis of mud volcano fluids. The Na-chloride sample of Salvarola (SAL), which may represent the end-member of the mud volcanoes, and the Ca-chloride brine water from Salsomaggiore (SM) indicate boron release from clays compatible with the diagenetic process. The empirical equation: δ11B = [5.1364 x ln(1/B)mg/l] + 44.601 relating boron concentration and the stable isotope composition of the fluids observed in this study and the literature is proposed to trace the effect of diagenesis in sedimentary basins. A geothermometer associated to the diagenetic equation is also proposed: T°C = [δ11B - 38.873 (± 1.180)] / [-0.164 (± 0.012)] The application of this equation to obtain reservoir temperatures from δ11B compositions of waters should be carefully evaluated against the results obtained from other chemical and isotopic geothermometers from other basins around the world.

An optical and electron microscope study has been made of inverted pigeonite from the Sjelset Igneous Complex, Rogaland, SW Norway. The inverted pigeonites reveal a Stillwater-type of microstructure: the pigeonite to orthopyroxene transformation has been pre-and postdated by two stages of augite exsolution (parallel to (001)pig and (100)opx respectively). In addition. two distinct microstructural domains have been recognized: (1) single and (2) clusters of inverted pigeonite crystals. Most clusters of pigeonite crystals have been replaced by single orthopyroxene crystals which exhibit domains of differently oriented (001)opx exsolution lamellae. The mechanism of exsolution is interpreted to be heterogeneous nucleation and growth, while the transformation of pigeonite to orthopyroxene is regarded as massive.

There is a paucity of suitable geothermometers for low temparature geological processes. Water-rock interactions at lower temperatures relavant to diagenesis, low-T hydrothermal process and low-T metamorphism can be studied if chlorite is present as a stable phase. However, this requires meticulous analytical data acquisition and complecated formula calculation protocols.  For a quick assessment of low-T events in sedimentary and metasedimentary rocks, Raman spectroscopic study of associated carbonaceous matter provides a convinient alternative.  Here we show the efficacy of this method (Kouketsu et al., 2014) and provide chlorite thermometric estimates (Bourdelle et al., 2013) for comparison from the Proterozoic Banganapalle Quartzite.  While Raman Spectroscopic study of carbonaceous matter, probably of organic nature, yielded the temperatures of 327, 357, 370, 400 and 413°C, the corresponding thermometers obtained from chlorite thermometry were 228, 322, 339 and 347°C.  Although the temperatures of 327 to 357°C overlap with the chlorite temperatures from 322 to 347°C, the carbonaceous matter  record still higher temperatures while the chlorites record still lower temperatures  indicating the irreversible change that occurs in the carbonaceous matter and the capability of the chlorites to re-equilibrate to lower temperatures, at least partially.

Abstract: Nisyros is characterised by a high enthalpy geothermal system. Numerous thermal springs are concentrated near the coastline with temperatures of 27°-43°C. Isotopic composition of Nisyros thermal water samples reveals mixing between seawater with magmatic water and geothermal steam and the possible involvement of groundwater and/or meteoric water. Combined silica and K2/Mg geothermometry indicates temperatures of 90°-140°C while deep geothermal fluids display temperatures of 245°C and steam heated samples approximately 210°C. We have calculated the initial temperature of the hot component of mixing using the diagram of dissolved SiO2 versus enthalpy. We propose that the geothermal system of Nisyros consists of two major reservoirs. A deeper one (1400-1800 m) with temperatures greater than 245°C which is the result of mixing between seawater and primary geothermal fluid and hosts hot waters of high enthalpy which cool adiabatically and ascend, due to separation of vapours, to the shallow reservoir (0-500m) of lower enthalpy. In this mixing occurs mixing between seawater and geothermal vapours and/or underground water or meteoric water with a hot water component of approximately 180°-220°C. The latter is derived from the ascent of the high enthalpy waters into the shallow reservoir which represents the mixing zone of the geothermal system and is characterised by lower enthalpy compared to the deeper reservoir displaying temperatures of 90°-140°C whilst the temperature of the separated vapours are approximately 225°C.