Sulfur-poor intense acid hydrothermal alteration: A distinctive hydrothermal environment

Kreiner, Douglas C.; Barton, Mark D.

doi:10.1016/j.oregeorev.2017.04.018

Cited by 17 publications

(9 citation statements)

References 30 publications

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“…This saline brine could become acidic as the result of adding CO 2 to form carbonic acid through the reaction: CO 2 + H 2 O → H 2 CO 3 [56]. Alternatively, the brine could become acidic through a reaction in which iron chlorides react with H 2 O to form magnetite and hydrochloric acid (3FeCl 2 + 4H 2 O → Fe 3 O 4 + 6HCl + H 2 O) [57], consistent with the dominant magnetite-rich alteration stage present in this sample.…”

Section: Characterization Of Metasomatic Fluidsmentioning

confidence: 99%

Geology, Apatite Geochronology, and Geochemistry of the Ernest Henry Inter-lens: Implications for a Re-Examined Deposit Model

et al. 2018

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The Ernest Henry Iron-Oxide-Copper-Gold deposit is the largest known Cu-Au deposit in the Eastern Succession of the Proterozoic Mount Isa Inlier, NW Queensland. Cu-Au mineralization is hosted in a K-feldspar altered breccia, bounded by two major pre-mineralization shear zones. Previous research suggests that Cu-Au mineralization and the ore-bearing breccia formed simultaneously through an eruption style explosive/implosive event, facilitated by the mixing of fluids at ~1530 Ma. However, the preservation of a highly deformed, weakly mineralized, pre-mineralization feature (termed the Inter-lens) within the orebody indicates that this model must be re-examined. The paragenesis of the Inter-lens is broadly consistent with previous studies on the deposit, and consists of albitization; an apatite-calcite-quartz-garnet assemblage; biotite-magnetite ± garnet alteration; K-feldspar ± hornblende alteration; Cu-Au mineralization and post-mineralization alteration and veining. Apatite from the paragenetically early apatite-calcite-quartz-garnet assemblage produce U–Pb ages of 1584 ± 22 Ma and 1587 ± 22 Ma, suggesting that the formation of apatite, and the maximum age of the Inter-lens is synchronous with D2 deformation of the Isan Orogeny and regional peak-metamorphic conditions. Apatite rare earth element-depletion trends display: (1) a depletion in rare earth elements evenly, corresponding with an enrichment in arsenic and (2) a selective light rare earth element depletion. Exposure to an acidic NaCl and/or CaCl2-rich sedimentary-derived fluid is responsible for the selective light rare earth element-depletion trend, while the exposure to a neutral to alkaline S, Na-, and/or Ca-rich magmatic fluid resulted in the depletion of rare earth elements in apatite evenly, while producing an enrichment in arsenic. We suggest the deposit experienced at least two hydrothermal events, with the first event related to peak-metamorphism (~1585 Ma) and a subsequent event related to the emplacement of the nearby (~1530 Ma) Williams–Naraku Batholiths. Brecciation resulted from competency contrasts between ductile metasedimentary rocks of the Inter-lens and surrounding shear zones against the brittle metavolcanic rocks that comprise the ore-bearing breccia, providing permeable pathways for the subsequent ore-bearing fluids.

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Section: Characterization Of Metasomatic Fluidsmentioning

confidence: 99%

Geology, Apatite Geochronology, and Geochemistry of the Ernest Henry Inter-lens: Implications for a Re-Examined Deposit Model

et al. 2018

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“…However, no clear evidence of fluid mixing was presented in these works. The local wall rock alterations, including silicic and kaolinite, indicate that the hydrothermal fluids were acidic and may have reacted with the wall rocks at Madiu (Constantopoulos, ; Kreiner & Barton, ). At Madiu, feldspars in the host rocks were strongly altered and partially replaced by fluorite, which reflects that the feldspars were altered by the acidic hydrothermal fluids via the following reaction (Frengstad, Banks, & Siewers, ):…”

Section: Discussionmentioning

confidence: 99%

Section: Timing Of Fluorite Mineralization and Implication For Earlmentioning

confidence: 99%

Formation timing and genesis of Madiu fluorite deposit in East Qinling, China: Constraints from fluid inclusion, geochemistry, and H–O–Sr–Nd isotopes

Pei

Zhang

et al. 2019

Geological Journal

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The Heyu fluorite ore district is newly discovered in the East Qinling metallogenic belt (EQMB), central China. In this district, the large Madiu fluorite deposit contains five Mesozoic granite‐hosted orebodies. The deposit may have formed at shallow depth and occurred as continuous veins controlled by a series of N‐S‐ or NE‐trending, steeply dipping faults. The fluorite mineralization can be divided into two stages (I and II). Fluid inclusions in stage I fluorite homogenized at 132.2°C to 342.5°C (peak at 170°C–210°C) with salinities of 0.18 to 4.43 wt% NaCl equiv, whilst those in stage II fluorite homogenized at 122.2°C to 305.7°C (peak at 130°C–170°C) and salinities of 0.18 to 3.71 wt% NaCl equiv. Raman spectroscopic analysis of the fluid inclusions reveals that they comprise predominantly H2O. The rare earth element (REE) characteristics indicate that the deposit is of hydrothermal origin. The δ18OH2O (−8.8‰ to −0.5‰) and δDH2O (−69.0‰ to −61.9‰) values show a subhorizontal trend, suggesting that the oxygen isotopic compositions were modified by fluid–rock interactions. Fluid inclusion and stable isotopic data suggest that the ore‐forming fluids belong to a meteoric water‐sourced, medium–low temperature, and low salinity NaCl–H2O system. Initial fluorite 87Sr/86Sr ratios (0.708879–0.709682) resemble those of the Heyu batholith. The water–rock reaction, which leached Ca from the host rock and increased the fluid pH, was likely causative to the ore precipitation. Geochemical and mineralization features suggest that the Madiu fluorite deposit is best classified as a fault‐controlled hydrothermal vein‐type fluorite deposit. The Sm–Nd isochron age of 118.9 ± 7.8 Ma and its regional age correlation suggest that the fluorite mineralization occurred under regional extension or lithospheric thinning setting and that the fluorite mineralization was an important component of the Early Cretaceous mineralization event in the EQMB.

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“…As shown schematically in Figure 1 for magmatichydrothermal systems developed in volcanic arcs, the locations of these different acidic environments correspond to distinct spatial domains with respect to associated ore deposits. Five environments have been examined here, although others may be possible in different magmatic settings (e.g., Kreiner and Barton, 2017).…”

Section: μMmentioning

confidence: 99%

Exploration Implications of Multiple Formation Environments of Advanced Argillic Minerals

Hedenquist

Arribas

2022

Economic Geology

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Advanced argillic minerals, as defined, include alunite and anhydrite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite, zunyite, and topaz), and diaspore. One or more of these minerals form in five distinctly different geologic environments of hydrolytic alteration, with pH 4–5 to <1, most at depths <500 m. (1) Where an intrusion-related hydrothermal system, typical of that associated with porphyry Cu ± Au deposits, evolves to white-mica stability, continued ascent and cooling of the white-mica–stable liquid results in pyrophyllite (± diaspore) becoming stable near the base of the lithocap. (2) A well-understood hypogene environment of formation is vapor condensation near volcanic vents, where magmatic SO2 and HCl condense into local groundwater to produce H2SO4 and HCl-rich solutions with a pH of 1–1.5. Close to isochemical dissolution of the host rock occurs because of the high solubility of Al and Fe hydroxides at pH <2, except for the SiO2 component, which remains as a siliceous residue because of the relatively low solubility of SiO2. This residual quartz, commonly with a vuggy texture, is largely barren of metals because of the low metal content in high-temperature but low-pressure volcanic vapor. Rock dissolution causes the pH of the acidic solution to increase, such that alunite and kaolinite (or dickite or pyrophyllite at higher temperatures) become stable, forming a halo to the residual quartz. This initially barren residual quartz, which forms a lithocap horizon where permeable lithologic units are intersected by the feeder structure, may become mineralized if a subsequent white-mica–stable liquid ascends to this level and precipitates copper and gold. (3) Boiling of a hydrothermal liquid generates vapor with CO2 and H2S. Where the vapor condenses above the water table, atmospheric O2 in the vadose (unsaturated) zone causes oxidation of H2S to sulfuric acid, forming a steam-heated acid-sulfate solution with pH of 2–3. In this environment, kaolinite and alunite form in horizons above the water table at <100°C. Silica derived within the vadose zone will precipitate as amorphous silica at the water table, as the condensate follows the hydraulic gradient, causing opal replacement above and at the aquifer. (4) By contrast, where condensation of this vapor occurs below the water table, the CO2 in solution forms carbonic acid (H2CO3), leading to a pH of 4–5. This marginal carapace of condensate, with temperatures up to 150°–170°C, commonly acts as a diluent of the ascending parental NaCl liquid. This steam-heated liquid forms intermediate argillic alteration of clays, kaolinite, and Fe-Mn carbonates; this kaolinite, which can be present at depths of several hundreds of meters, can potentially be mistaken as having been caused by a steam-heated acid-sulfate or supergene overprint. (5) The final setting is supergene, caused by posthydrothermal weathering and oxidation of mainly pyrite, locally creating pH <1 liquid because of high concentrations of H2SO4 within the vadose zone and forming kaolinite, alunite, and Fe oxyhydroxides. This genetic framework of formation environments of advanced (and intermediate) argillic alteration provides the basis to interpret alteration mineralogy, in combination with alteration textures and morphology plus zonation, including the overprint of one alteration style on another. This framework can be used to help focus exploration for and assessment of hydrothermal ore deposits, including epithermal, porphyry, and volcanic-hosted massive sulfide.

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Sulfur-poor intense acid hydrothermal alteration: A distinctive hydrothermal environment

Cited by 17 publications

References 30 publications

Geology, Apatite Geochronology, and Geochemistry of the Ernest Henry Inter-lens: Implications for a Re-Examined Deposit Model

Geology, Apatite Geochronology, and Geochemistry of the Ernest Henry Inter-lens: Implications for a Re-Examined Deposit Model

Formation timing and genesis of Madiu fluorite deposit in East Qinling, China: Constraints from fluid inclusion, geochemistry, and H–O–Sr–Nd isotopes

Exploration Implications of Multiple Formation Environments of Advanced Argillic Minerals

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