Lithogeochemical approaches in geothermal system characterization: An application to the Reykjanes geothermal field, Iceland

Libbey, R.B.; Williams‐Jones, Anthony E.

doi:10.1016/j.geothermics.2016.05.001

Cited by 10 publications

(6 citation statements)

References 62 publications

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“…Copper is strongly depleted, whereas Sb is highly enriched. These trends broadly follow alteration-associated element re-distribution in Reykjanes reservoir rocks 51 , despite the Reykjanes fluids having much higher Cl-contents. 1).…”

Section: Resultsmentioning

confidence: 54%

The behaviour of metals in deep fluids of NE Iceland

Saby

Hinsberg

Pinti

et al. 2022

Sci Rep

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In this contribution, we present some of the first data on the elemental signature of deep crustal fluids in a basalt-hosted, low-chloride magmatic-hydrothermal system. Down-hole fluid samples (850–1600 m) from wells in the Theistareykir and Krafla geothermal fields in the Northern Volcanic Zone of Iceland were combined with well-head samples of condensed vapor, cuttings of altered rock, and fresh basalt (being some of the first concentration data for volatile and semi-volatile elements (Sb, Tl, Bi, Cd and As) for this area of Iceland). Results show that the deep fluids are relatively enriched in base metals and (semi)-volatile metals (in particular Te, Hg, Re and Tl) compared to local basalt. We interpret this enrichment in volatile metals to reflect a significant element input from magma degassing. Boiling of this deep fluid results in a well-head fluid composition that is significantly depleted in most elements. This well-head fluid has a distinct elemental signature, including a depletion in Sb that is mirrored in the altered rocks, and a depletion in the base metals that shows their selective sequestration in scale minerals, likely sulphides. As expected, the element content and patterns in surface fluids can thus not be interpreted to directly reflect that of the deep reservoir fluid. The behaviour of elements in Theistareykir and Krafla fluids is consistent, and largely agrees with similar data obtained for the Reykjanes geothermal system in SW Iceland. We therefore posit that our results are representative for this geological setting and indicate a significant magmatic degassing cation input to deep fluids, variably modified by water–rock interaction.

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Section: Resultsmentioning

confidence: 54%

The behaviour of metals in deep fluids of NE Iceland

Saby

Hinsberg

Pinti

et al. 2022

Sci Rep

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“…The methodology used in this prospection study is based on a novel and fundamental diagram of water-rock interaction (WRI) and chemical partitioning processes associated with geothermal environments, which was originally described by Libbey and Williams-Jones (2016). A simplified diagram showing some tracing paths of these processes (applied to the present study) is shown in Figure 4.…”

Section: Methodsmentioning

confidence: 99%

“…Reactive (Na, K, Ca, Mg, SO 4 , SiO 2 , F, among others) and conservative (Cl, Br, the 'Rare Alkalis': Li, Rb, Cs, among other) elements were used for finding out some geochemical signatures of the fluids produced in the reservoir (Giggenbach, 1991). The use of bulk-rock components as geochemical tracers of fluid paths contributes to a comprehensive understanding of element mobility and reactivity in these geothermal systems (Libbey and Williams-Jones, 2016…”

Section: Methodsmentioning

confidence: 99%

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Chemical and isotopic signatures of hot springs from east-central Sonora State, Mexico: a new prospection survey of promissory low-to-medium temperature geothermal systems

et al. 2018

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A promissory low-to-medium temperature geothermal system located in Sonora (Mexico) has been studied. In the present work, a detailed geochemical survey was carried out to understand the hydrogeochemical signatures of hot spring waters. A field work campaign was conducted for collecting water samples from twelve hot springs placed in four major zones (NW, NE, C, and S). The collected samples were analysed by chemical and isotopic methods for determining their chemical (major and trace elements) and isotopic (18O/16O and D/H) compositions. Using geochemometric analyses of the fluid composition and fractionation, depletion and enrichment processes exhibited by major and trace elements were analysed. Hydrogeochemical classification was used to indicate the presence of sodium-sulphate (Na-SO4) waters in the North (NW and NE) and South hydrothermal zones; whereas calcium-magnesium-bicarbonate (Ca-Mg-HCO3) waters were identified for the Central zone. Some hot spring waters located in the NE zone were also typified as sodium-bicarbonate (Na-HCO3). In relation to the isotopic signatures of 18O/16O and D/H, four water samples from NE and C zones lie near to the global meteoric water line; whereas the remaining eight samples showed a shift for both oxygen and deuterium isotopes. A mixing line with a small shift of δ18O was identified and used as a proxy to discriminate waters with different isotopic signatures. After applying a geochemometric outliers detection/rejection and an iterative ANOVA statistical test, the mean temperature inferred from the most reliable solute geothermometers was 149±40 °C, which suggests to be considered as the minimum value of the reservoir temperature. As most of the hot spring waters fall outside of the full equilibrium curve, the original reservoir conditions were corrected by using a mixing conductive model, which predicted a deep equilibrium temperature of 210±11 °C. As this temperature is considerably higher than the mean temperature inferred from the geothermometers, it was suggested as an optimistic maximum reservoir temperature of the Sonora geothermal system. Using 150 °C and 200 °C as rounded-off reservoir temperatures (or min-max estimates), geochemical equilibria modelling based on fluid-mineral stability diagrams was carried out. An equilibrium process among local hydrothermal waters and albite-potassium feldespar and muscovite-prehnite-laumontite mineral assemblages was found. These minerals were proposed as representative mineral assemblages of low-grade metamorphism, which seems to indicate that the geothermal fluid equilibria were probably reached within the intermediate to acidic volcanic rocks from the Tarahumara Formation.

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“…In addition, these correlation relationships are less influenced by primary depositional features compared to raw lithogeochemical data, and thus provide insights into the mechanisms that govern metasomatic reactions and metal distribution (Libbey and Williams-Jones, 2016).…”

Section: Correlation Relationships Among Mass Change Valuesmentioning

confidence: 99%

The use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the Malartic district, Québec

Gaillard

Williams‐Jones

Clark

et al. 2020

Ore Geology Reviews

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The Canadian Malartic world-class low grade, large tonnage gold deposit is located in the southeastern Superior Province of Canada. With reserves estimated at 6.38 Moz Au grading 1.10 g/t Au, it is currently the largest open pit mine in the Abitibi gold camp. The deposit is hosted predominantly by Pontiac Group metasedimentary rocks, Piché Group metavolcanic rocks, and quartz monzodiorite porphyritic intrusions. Stockwork-disseminated gold mineralization generally consists of a low-grade envelope of disseminated pyritic ore (0.35 to 1 g/t Au) grading inwards into higher grade (>1 g/t Au) stockwork and breccia zones. Hydrothermal alteration in the metasedimentary rocks displays a consistent zonation with distance from the main fluid pathways. Proximal alteration is characterized by a microcline±albite-quartz replacement-type assemblage, with lesser phlogopite, calcite±Fe-dolomite, pyrite and rutile. The distal alteration assemblage is dominated by biotite, microcline±albite, phengite, quartz, calcite, pyrite and rutile. In this study, a lithogeochemical approach is used to assess the magnitude and distribution of fluid-rock interaction in the metasedimentary rocks of the Malartic district. The metaturbidites are separated into four sub-lithologies according to grain size characteristics to reduce the effects of primary depositional processes on mass change calculations. Despite the variability in protolith compositions, the metasedimentary rocks define a geochemically consistent, cogenetic sequence. The results of the mass transfer calculations indicate progressive gains in C-S-K2O and LOI, as well as Au-Te-W-Ag±(As-Be-Sb-Bi-Mo-Pb) from background, through distal to proximal alteration zones (relative to least altered samples). Molar element ratio analysis (alkali/aluminium) indicates an increase in alkali metasomatism (K and Na) adjacent to the fluid pathways, which is manifested by the progressive stabilization of microcline and albite (at the expense of biotite and white mica). Ore-associated pathfinder elements delineate broad enrichment patterns around the deposit, and can be used to outline hydrothermal fluid circulations in the Malartic district. A statistical approach based on the comparison of the mass balance results with the background composition provides robust constraints on the magnitude and extent of the lithogeochemical haloes. Most alteration envelopes extend along the S2 fabric, and the largest lithogeochemical anomalies (e.g., Au, W, Te and Ag) reach up to 10 kilometers in length, and 2 kilometers in width. These observations demonstrate that whole-rock lithogeochemistry provides a valuable vectoring tool toward gold mineralization in a regional exploration context.

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Lithogeochemical approaches in geothermal system characterization: An application to the Reykjanes geothermal field, Iceland

Cited by 10 publications

References 62 publications

The behaviour of metals in deep fluids of NE Iceland

The behaviour of metals in deep fluids of NE Iceland

Chemical and isotopic signatures of hot springs from east-central Sonora State, Mexico: a new prospection survey of promissory low-to-medium temperature geothermal systems

The use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the Malartic district, Québec

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