Mineral-fluid interactions in the Broadlands-Ohaaki geothermal system, New Zealand

Lonker, Steven W.; FitzGerald, John; Hedenquist, Jeffrey W.; Walshe, John L.

doi:10.2475/ajs.290.9.995

Cited by 37 publications

(18 citation statements)

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“…Sample VF-4 is a quartzose sandstone (Hutcheon, 1990). The third sample, despite containing 0.25 mole proportion of "Al-chlorite," does not coexist with kaolinite, but apparently is found is a very quartzose (acidic) volcanic rock sequence (Lonker et al, 1990). Figure 8 shows that a relatively good positive correlation exists between Zv~ and temperature for the suite of samples considered here.…”

Section: Discussion: Comparison Of Chlorite Geothermometersmentioning

confidence: 66%

“…Scotian Shelf (Lower Cretaceous, quartzose to feldspathic sandstones; see Hutcheon, 1990); 4) the Salton Sea geothermal field (SS), California (hydrothermally altered recent feldspathic sandstones and feldspathic argillaceous sandstones: McDowell and Elders, 1980); 5) the Los Azufres geothermal field (LA), Mexico (hydrothermally altered recent andesites: see Cathelineau and Nieva, 1985;Cathelineau, 1988;and Cathelineau and Izquierdo, 1988); and 6) the Broadlands-Ohaaki geothermal field (BO), New Zealand (hydrothermally altered Quaternary quartzitic volcanic rocks and sedimentary rocks: see Lonker et aL, 1990). The chlorites selected for this comparison cover a broad range of compositions, coexist with a variety of mineral assemblages, and formed at temperatures ranging from 25 ~ to 322~ The various compositional chlorite geothermometers discussed in this paper were applied to this selection of chlorite analyses.…”

Section: Discussion: Comparison Of Chlorite Geothermometersmentioning

confidence: 99%

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Chlorite Geothermometry: A Review

Caritat

Hutcheon

Walshe

1993

Clays and clay miner.

317

210

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Abstract--Chlorite minerals, found in a great variety of rocks and geological environments, display a wide range of chemical compositions and a variety of polytypes, which reflect the physicochemical conditions under which they formed. Of particular importance for studies dealing with ore deposit genesis, metamorphism, hydrotherrnal alteration or diagenesis is the paleotemperature of chlorite crystallization. However, in order to understand the relationship between chlorite composition and formation temperature and hence use chlorite as a geothermometer, one must determine how other parameters influence chlorite composition. These parameters may include fO2 and pH of the solution and Fe/(Fe + Mg) and bulk mineral composition of the host rock.Four approaches to chlorite geothermometry, one structural and three compositional, have been proposed in the past: 1) a polytype method based on the (largely qualitative) observation that structural changes in chlorite may be partly temperature-dependent (Hayes, 1970); 2) an empirical calibration between the tetrahedral aluminum occupancy in chlorites and measured temperature in geothermal systems (Cathelineau, 1988), which has subsequently been modified by several workers; 3) a six-component chlorite solid solution model based upon equilibrium between chlorite and an aqueous solution, which uses thermodynamic properties calibrated with data from geothermal and hydrothermal systems (Walshe, 1986); and 4) a theoretical method based on the intersection of chlorite-carbonate reactions and the CO2-H20 miscibility surface in temperature-XCO2 space, which requires that the composition of a coexisting carbonate phase (dolomite, ankerite, Fe-calcite or siderite) be known or estimated (Hutcheon, 1990). These four approaches are reviewed and the different calculation methods for the compositional geotherrnometers are applied to a selection of chlorite analyses from the literature. Results of this comparative exercise indicate that no single chlorite geothermometer performs satisfactorily over the whole range of natural conditions (different temperatures, coexisting assemblages, Fe/(Fe + Mg), fO2, etc.).. Therefore, chlorite geothermometry should b e used with caution and only in combination with alternative methods of estimating paleotemperatures.

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Section: Discussion: Comparison Of Chlorite Geothermometersmentioning

confidence: 66%

Section: Discussion: Comparison Of Chlorite Geothermometersmentioning

confidence: 99%

Chlorite Geothermometry: A Review

Caritat

Hutcheon

Walshe

1993

Clays and clay miner.

317

210

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“…It has, however, become apparent that earlier bulk chemical analyses did not resolve single illite crystals (Ransom and Warren, 1989). Indeed, recent ATEM studies of natural illite samples have shown that: (1) individual crystals from geothermal basins are compositionally homogenous (e.g., Lonker et al, 1990) and (2) the overall compositional range appears to be more limited than previously presumed (Figure 2). Where differences in compositions have been observed for samples from different sandstone formations, they reflect differences in the chemistry of the coexisting pore fluids (Warren and Curtis, 1989).…”

Section: Clay Compositional Variationmentioning

confidence: 93%

The Thermodynamic Status of Compositionally-Variable Clay Minerals: A Discussion

Aja

Rosenberg

1992

Clays and clay miner.

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Abstract--According to Lippmann (1977Lippmann ( , 1982 wide compositional variations and excess enthalpies of mixing calculated with electrostatic models imply that clay minerals of variable composition are disequilibrium solids. However, recent ATEM analyses ofillite samples indicate compositional homogeneity of single illite grains and limited compositional variations in sedimentary basins. Moreover, Lippmann's electrostatic model may be inadequate inasmuch as it neglects polarization energy which is known to be a significant component of lattice energy even in dominantly ionic structures. Contrary to the assumptions of Lippmann, I/S minerals have also been shown to undergo Ostwald ripening. May et al. (1986) reported that smectites do not reversibly control equilibria and further argued that conceptual and experimental deficiencies inherent in the solubility method prevent the attainment and demonstration of equilibrium in experiments with complex aluminosilicates of variable composition. However, equilibrium may be assumed if: (1) steady states are approached from both under-and oversaturation, (2) the slopes of univariant lines representing mineral-solution equilibria are rational over a wide range of solution compositions and temperature, and (3) results are reproducible in experiments of long duration. Recent solubility studies of smectites, chlorites, and illites meet these criteria indicating that clay minerals of variable composition are true phases capable of attaining equilibrium.

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“…Chlorite is a ubiquitous product of fluid-rock interaction in fossil hydrothermal systems associated with metal ores. Its use helps to constrain the temperature and fugacities of oxygen and sulfur of the hydrothermal regime associated with the mineralization and alteration Lonker et al, 1990Lonker et al, , 1993Cathelineau, 1988;Barton et al, 1977). Epidote is one of the most common minerals observed in hydrothermal systems (Shikazono 1984;Cho et al, 1988;Charles et al, 1988;Bird et al, 1988;Caruso et al, 1988;Bird and Spieler, 2004) and exhibits octahedral substitution of Al 3+ for Fe 3+ , which can be used to estimate the temperature, composition and oxygen fugacity of the mineralizing fluid (Bird and Spieler, 2004 and references therein).…”

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confidence: 99%

Reconstructing physico-chemical parameters of hydrothermal mineralization of copper at the Malanjkhand deposit, India, from mineral chemistry of biotite, chlorite and epidote

et al. 2008

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Mineral chemistry of biotite, chlorite and epidote associated with the granitoid ore body of the Malanjkhand coppermolybdenum deposit have been studied to constrain temperature, oxidation and sulfidation states as well as fugacity ratios of HF, HCl and H 2 O of the hydrothermal mineralizing fluid. Calculated mineralizing temperatures from biotite, chlorite and epidote are mutually consistent and agree well with earlier estimates derived from fluid inclusion studies. Major element chemistry of biotite indicates low oxidation state (FMQ-NNO) and re-equilibrated nature (~300°C). However, exchange of Cl-F-OH between biotite and the fluid continued to lower temperatures. Subtle differences between the Malanjkhand deposit and known porphyry copper deposits have been evidenced by the fugacity ratios of halogens and water. Chlorite registers equilibrium with fluid down to 200°C and, together with biotite composition, indicates that copper was transported as chloride complex in the fluid. Sulfide deposition occurred during a prompt rise in fugacity of H 2 S at 300°C, possibly resulting from a coupled oxidation of Fe 2+ and reduction of SO 4 2-. Interaction of ore fluid with epidote in the wall-rock favored the deposition of chalcopyrite, enhanced the Ca 2+ activity in the fluid and inhibited a fall in pH and a subsequent acid alteration of K-feldspar in the wall-rock. These physicochemical characteristics of the mineralized fluid suggest that the Malanjkhand deposit represents an ancient granitoid-associated geothermal system rather than a classic porphyry copper ore deposit.

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Mineral-fluid interactions in the Broadlands-Ohaaki geothermal system, New Zealand

Cited by 37 publications

References 0 publications

Chlorite Geothermometry: A Review

Chlorite Geothermometry: A Review

The Thermodynamic Status of Compositionally-Variable Clay Minerals: A Discussion

Reconstructing physico-chemical parameters of hydrothermal mineralization of copper at the Malanjkhand deposit, India, from mineral chemistry of biotite, chlorite and epidote

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