Exploring magmatic gas and subvolcanic hydrothermal system interactions: Mineralogy and sulfur isotope characteristics of the Holocene volcanic products at Mt. Tangkuban Parahu, Indonesia.

Abstract A subvolcanic-hydrothermal system involves complex interaction between magma, magmatic fluids, and hydrothermal system at stratovolcanoes in subduction setting. These interactions are responsible for magmatic-hydrothermal eruption associated with rapid injection of magmatic gas into hydrothermal system at a certain depth of volcanic edifice. However, capturing these interactions is challenging due to inaccessibility to the crater conduit within the edifice. Therefore, we selected a method to analyze the volcanic products from several episodic phreatic and phreatomagmatic eruptions during the Holocene at Tangkuban Parahu, Indonesia. In this context, Holocene volcanic products are one of the best examples to understand an interplay between magma, magmatic fluids, and hydrothermal system in producing violent eruptions. In this study, we carried out petrological and sulfur isotope analysis only for the hydrothermally altered lithic ash particles, a part of proximal volcanic products. Mineral assemblages mostly exhibit a typical acid-sulfate and advanced argillic alteration, consisting of alunite, kaolinite, and silica minerals. Acid-sulfate and advanced argillic alteration indicates that those mineral assemblages were formed under the formation temperature ranging from ~100 to ~260 . The calculated temperature from sulfur isotopic fractionation of sulfate-sulfide shows 230-240 , which is almost identical with assigned temperature from mineral assemblages. Sulfur isotope and jarosite occurrence indicate the supergene alteration associated with oxygen entrainment to the hydrothermal system that oxidize pyrite to jarosite. Sulfur isotopic variation throughout the studied stratigraphy represents influx of magmatic gas to the hydrothermal system. Moreover, zoned P-bearing alunite represents repetitive injection of magmatic gas to the active acidic hydrothermal system, which also indicates the magmatic-hydrothermal interaction below the crater. Occurrence of enargite and chalcopyrite represents the nature of upper-level high sulfidation system at shallow volcanic edifice of the Tangkuban Parahu volcano. Furthermore, we showed that coupled petrological and sulfur isotope analysis has paramount importance to evaluate the conditions of the subvolcanic hydrothermal system, magmatic-hydrothermal interaction, and the origin of steam-blast eruptions at volcanoes that contain subvolcanic-hydrothermal systems.

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Reconstruction of an Early Permian, Sublacustrine Magmatic-Hydrothermal System: Mount Carlton Epithermal Au-Ag-Cu Deposit, Northeastern Australia

Economic Geology ◽

10.5382/econgeo.4696 ◽

2020 ◽

Vol 115 (1) ◽

pp. 129-152

Author(s):

Fredrik Sahlström ◽

Zhaoshan Chang ◽

Antonio Arribas ◽

Paul Dirks ◽

Craig A. Johnson ◽

...

Keyword(s):

Hydrothermal System ◽

Meteoric Water ◽

Open Pit ◽

Early Permian ◽

High Sulfidation ◽

Isotope Data ◽

Epithermal Mineralization ◽

Argillic Alteration ◽

Advanced Argillic Alteration ◽

Mineralizing Fluids

Abstract The Mt. Carlton Au-Ag-Cu deposit, northern Bowen basin, northeastern Australia, is an uncommon example of a sublacustrine hydrothermal system containing economic high-sulfidation epithermal mineralization. The deposit formed in the early Permian and comprises vein- and hydrothermal breccia-hosted Au-Cu mineralization within a massive rhyodacite porphyry (V2 open pit) and stratabound Ag-barite mineralization within volcano-lacustrine sedimentary rocks (A39 open pit). These orebodies are all associated with extensive advanced argillic alteration of the volcanic host rocks. Stable isotope data for disseminated alunite (δ34S = 6.3–29.2‰; δ18OSO4 = –0.1 to 9.8‰; δ18OOH = –15.3 to –3.4‰; δD = –102 to –79‰) and pyrite (δ34S = –8.8 to –2.7‰), and void-filling anhydrite (δ34S = 17.2–19.2‰; δ18OSO4 = 1.8–5.7‰), suggest that early advanced argillic alteration formed within a magmatic-hydrothermal system. The ascending magmatic vapor (δ34SΣS ≈ –1.3‰) was absorbed by meteoric water (~50–60% meteoric component), producing an acidic (pH ≈ 1) condensate that formed a silicic → quartz-alunite → quartz-dickite-kaolinite zoned alteration halo with increasing distance from feeder structures. The oxygen and hydrogen isotope compositions of alunite-forming fluids at Mt. Carlton are lighter than those documented at similar deposits elsewhere, probably due to the high paleolatitude (~S60°) of northeastern Australia in the early Permian. Veins of coarse-grained, banded plumose alunite (δ34S = 0.4– 7.0‰; δ18OSO4 = 2.3–6.0‰; δ18OOH = –10.3 to –2.9‰; δD = –106 to –93‰) formed within feeder structures during the final stages of advanced argillic alteration. Epithermal mineralization was deposited subsequently, initially as fracture- and fissure-filling, Au-Cu–rich assemblages within feeder structures at depth. As the mineralizing fluids discharged into lakes, they produced syngenetic Ag-barite ore. Isotope data for ore-related sulfides and sulfosalts (δ34S = –15.0 to –3.0‰) and barite (δ34S = 22.3–23.8‰; δ18OSO4 = –0.2 to 1.3‰), and microthermometric data for primary fluid inclusions in barite (Th = 116°– 233°C; 0.0–1.7 wt % NaCl), are consistent with metal deposition at temperatures of ~200 ± 40°C (for Au-Cu mineralization in V2 pit) and ~150 ± 30°C (Ag mineralization in A39 pit) from a low-salinity, sulfur- and metal-rich magmatic-hydrothermal liquid that mixed with vapor-heated meteoric water. The mineralizing fluids initially had a high-sulfidation state, producing enargite-dominated ore with associated silicification of the early-altered wall rock. With time, the fluids evolved to an intermediate-sulfidation state, depositing sphalerite- and tennantite-dominated ore mineral assemblages. Void-filling massive dickite (δ18O = –1.1 to 2.1‰; δD = –121 to –103‰) with pyrite was deposited from an increasingly diluted magmatic-hydrothermal liquid (≥70% meteoric component) exsolved from a progressively degassed magma. Gypsum (δ34S = 11.4–19.2‰; δ18OSO4 = 0.5–3.4‰) occurs in veins within postmineralization faults and fracture networks, likely derived from early anhydrite that was dissolved by circulating meteoric water during extensional deformation. This process may explain the apparent scarcity of hypogene anhydrite in lithocaps elsewhere. While the Mt. Carlton system is similar to those that form subaerial high-sulfidation epithermal deposits, it also shares several key characteristics with magmatic-hydrothermal systems that form base and precious metal mineralization in shallow-submarine volcanic arc and back-arc settings. The lacustrine paleosurface features documented at Mt. Carlton may be useful as exploration indicators for concealed epithermal mineralization in similar extensional terranes elsewhere.

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Comparison of Different Algorithms to Map Hydrothermal Alteration Zones Using ASTER Remote Sensing Data for Polymetallic Vein-Type Ore Exploration: Toroud–Chahshirin Magmatic Belt (TCMB), North Iran

Remote Sensing ◽

10.3390/rs11050495 ◽

2019 ◽

Vol 11 (5) ◽

pp. 495 ◽

Cited By ~ 19

Author(s):

Lida Noori ◽

Amin Pour ◽

Ghasem Askari ◽

Nader Taghipour ◽

Biswajeet Pradhan ◽

...

Keyword(s):

Remote Sensing ◽

Hydrothermal Alteration ◽

Remote Sensing Data ◽

Base Metals ◽

Argillic Alteration ◽

Mineral Assemblages ◽

Vein Type ◽

North Of Iran ◽

Advanced Argillic Alteration ◽

Hydrothermal Alteration Zones

Polymetallic vein-type ores are important sources of precious metal and a principal type of orebody for various base-metals. In this research, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing data were used for mapping hydrothermal alteration zones associated with epithermal polymetallic vein-type mineralization in the Toroud–Chahshirin Magmatic Belt (TCMB), North of Iran. The TCMB is the largest known goldfield and base metals province in the central-north of Iran. Propylitic, phyllic, argillic, and advanced argillic alteration and silicification zones are typically associated with Au-Cu, Ag, and/or Pb-Zn mineralization in the TCMB. Specialized image processing techniques, namely Selective Principal Component Analysis (SPCA), Band Ratio Matrix Transformation (BRMT), Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) were implemented and compared to map hydrothermal alteration minerals at the pixel and sub-pixel levels. Subtle differences between altered and non-altered rocks and hydrothermal alteration mineral assemblages were detected and mapped in the study area. The SPCA and BRMT spectral transformation algorithms discriminated the propylitic, phyllic, argillic and advanced argillic alteration and silicification zones as well as lithological units. The SAM and MTMF spectral mapping algorithms detected spectrally dominated mineral groups such as muscovite/montmorillonite/illite, hematite/jarosite, and chlorite/epidote/calcite mineral assemblages, systematically. Comprehensive fieldwork and laboratory analysis, including X-ray diffraction (XRD), petrographic study, and spectroscopy were conducted in the study area for verifying the remote sensing outputs. Results indicate several high potential zones of epithermal polymetallic vein-type mineralization in the northeastern and southwestern parts of the study area, which can be considered for future systematic exploration programs. The approach used in this research has great implications for the exploration of epithermal polymetallic vein-type mineralization in other base metals provinces in Iran and semi-arid regions around the world.

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The sensitivity of Neotoma to climate change and biodiversity loss over the late Quaternary

Quaternary Research ◽

10.1017/qua.2021.29 ◽

2021 ◽

pp. 1-15

Author(s):

Catalina P. Tomé ◽

S. Kathleen Lyons ◽

Seth D. Newsome ◽

Felisa A. Smith

Keyword(s):

Body Size ◽

Late Quaternary ◽

Climatic Variability ◽

Isotope Analysis ◽

Biodiversity Loss ◽

Bone Collagen ◽

Cam Plants ◽

The Holocene ◽

Carbon And Nitrogen ◽

Terminal Pleistocene

Abstract The late Quaternary in North America was marked by highly variable climate and considerable biodiversity loss including a megafaunal extinction event at the terminal Pleistocene. Here, we focus on changes in body size and diet in Neotoma (woodrats) in response to these ecological perturbations using the fossil record from the Edwards Plateau (Texas) across the past 20,000 years. Body mass was estimated using measurements of fossil teeth and diet was quantified using stable isotope analysis of carbon and nitrogen from fossil bone collagen. Prior to ca. 7000 cal yr BP, maximum mass was positively correlated to precipitation and negatively correlated to temperature. Independently, mass was negatively correlated to community composition, becoming more similar to modern over time. Neotoma diet in the Pleistocene was primarily sourced from C3 plants, but became progressively more reliant on C4 (and potentially CAM) plants through the Holocene. Decreasing population mass and higher C4/CAM consumption was associated with a transition from a mesic to xeric landscape. Our results suggest that Neotoma responded to climatic variability during the terminal Pleistocene through changes in body size, while changes in resource availability during the Holocene likely led to shifts in the relative abundance of different Neotoma species in the community.

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Paragenesis of veins of the Duck Pond tin prospect, Meguma Group, East Kemptville, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e89-171 ◽

1989 ◽

Vol 26 (10) ◽

pp. 2032-2043 ◽

Cited By ~ 1

Author(s):

Christian V. Pitre ◽

Jean M. Richardson

Keyword(s):

Nova Scotia ◽

Manganese Oxides ◽

Open Pit ◽

Granitic Magma ◽

Sulphide Minerals ◽

Main Indicator ◽

Argillic Alteration ◽

Mineral Assemblages ◽

Indicator Mineral ◽

Host Rocks

The Duck Pond tin prospect is a vein- and strata-bound cassiterite prospect that is located 2 km west of the East Kemptville open-pit tin mine in southwestern Nova Scotia. The host rocks of the Duck Pond prospect are interbedded metawacke and meta-argillite that belong to the transition unit of the Meguma Group. These rocks contain quartz, sericite, chlorite, hematite, rutile, manganese oxides, feldspar, and porphyroblastic garnet, but not detrital cassiterite. The prospect is structurally controlled and contains several cross-cutting vein sets that have alkalic, chloritic, or argillic alteration assemblages. Muscovite is the main indicator mineral for alkalic alteration and occurs in veins that contain anorthoclase or quartz. Cassiterite is associated with chloritic alteration and occurs as subhedral to euhedral grains, acicular needles, and colloform layers in veins in meta-argillite and as strata-bound disseminations in metawacke. Most cassiterite precipitated under externally buffered conditions with respect to oxygen. Fe, Cu, Zn, and As sulphide minerals and quartz were deposited during argillic alteration. Late-stage processes such as recrystallization, sulphidation, and oxidation also occurred. Chalcopyrite is replaced by bornite and covellite; pyrite is replaced by marcasite.Unlike the F-rich East Kemptville deposit, fluorine-rich and tin-sulphide minerals are not present in the Duck Pond prospect. Trace tourmaline, absent at East Kemptville, is found at Duck Pond. However, the source of tin-mineralizing fluids at Duck Pond and East Kemptville was likely the granitic magma of the Davis Lake complex, which also hosts the East Kemptville deposit. From the mineral assemblages and textural relationships, it appears that as the temperature dropped from 425–405 °C to less than 200 °C at Duck Pond, the pH dropped from 5.2 to no lower than 3. Log [Formula: see text] dropped from at least −19 to −43. Log [Formula: see text] rose from < −15 to > −10. Cassiterite precipitated at the higher ends of the temperature and pH ranges and the lower end of the log [Formula: see text] range.

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