Formation of late-stage hydrothermal mineralization in the Mesoarchean Boula-Nuasahi ultramafic complex, Odisha, India: Constraints from arsenopyrite geothermometry and trace element data
Graphical abstract
Introduction
There are only very few common sulphide minerals such as sphalerite and arsenopyrite that are suitable as geothermometers or geobarometers. This is because these phases exhibit appreciable solid-solution, the chemical variations are sensitive to pressure or temperature and they have a refractory nature and are not easily modified by post-depositional processes. Experiments on the stability fields of arsenopyrite in the system Fe-As-S have been conducted by several researchers (Clark, 1960a, Clark, 1960b, Barton, 1970, Scott, 1976). Because of the refractory nature of arsenopyrite, these experiments were limited by extremely slow rates of reaction. Sharp et al. (1985) reviewed and re-evaluated the arsenopyrite geothermometer by analysing natural assemblages whose P-T conditions were independently measured or approximated by fluid-inclusion trapping temperatures, silicate phase-equilibria and stable isotope fractionation data. They concluded that application of the arsenopyrite geothermometer may be valid for deposits metamorphosed to greenschist and lower amphibolite facies, but yields too low temperatures for deposits metamorphosed to upper amphibolite and granulite facies and inconsistent temperatures for low-temperature hydrothermal deposits. The As/S atomic ratio of the arsenopyrite that may coexist with other phases buffering the S activity in the system As-S-Fe has been experimentally verified and calibrated as a geothermometer (Kretschmar and Scott, 1976, Sharp et al., 1985). However, application of the arsenopyrite geothermometer has not been straightforward because of the widespread presence of other minor and trace elements in arsenopyrite and because in many instances, arsenopyrite is found to be zoned with respect to the arsenic content (Vesselinov and Kerestedjian, 1995, Kerestedjian, 1997, Choi and Youm, 2000, Mikulski, 2005). Additional complications may arise from post-depositional modification of the arsenopyrite.
In this paper, we report the textural features, paragenesis and mineral chemistry of arsenopyrites that occur as late-stage vein minerals in the mafic–ultramafic rocks of the Bangur area in Boula-Nuasahi ultramafic complex (BNUC) situated in the south eastern flank of the Singhbhum Craton, India. Although a detailed account of various sulphide minerals in the BNUC has been previously reported (Mondal et al., 2001; Mohanty et al., 2002; Augé et al., 2002, Jena et al., 2016), the arsenopyrite mineralization has not been investigated. These arsenopyrites are found to be a surprisingly pure variety with almost close to stoichiometric compositions. We have therefore used the composition of the arsenopyrite for geothermometric applications, yielding inferred formation temperatures of the last phase of hydrothermal sulphide mineralization in the area.
Section snippets
Geological setting
The Boula-Nuasahi ultramafic complex is situated on the southeastern flanks of the Singhbhum Craton and has been emplaced into the regionally metamorphosed greenschist facies metasedimentary rocks of the Precambrian Iron-Ore Group of India (>3.1–3.3 Ga; Mukhopadhyay, 2001, Augé et al., 2003). It forms an elongate body (∼3 km long and 0.5 km wide) trending NW-SE in its northern part and N-S in the southern part (Fig. 1).
The BNUC consists primarily of four major lithostructural units: 1) an
Methods of investigation
Polished thin-sections (2 cm by 3 cm) of the samples were prepared by conventional techniques by mounting on glass-slides in araldite, followed by grinding and polishing with diamond paste. The samples were petrographically studied using a Leica DM 4000 P transmitted- and reflected-light microscope. On the same polished sections, electron probe micro-analysis (EPMA), QEMSCAN mineral mappings and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses were carried out at
Petrography and textures of arsenopyrite
Well-crystallized and euhedral arsenopyrite crystals, which are not associated with any other sulphide minerals, have been found as vein minerals in a partially altered fine-grained anorthositic rock of the hanging-wall side gabbro-anorthosite suite in the Bangur area. The arsenopyrite crystals vary in size from <1 mm to ∼1 cm and occur along the foliation planes/fractures (Fig. 5a and b). Most of the crystals are fractured. Under plane polarized light, arsenopyrite is pleochroic and shows
Mineral chemistry of arsenpoyrite
Electron probe micro-analysis of 45 points in different arsenopyrite grains reveals that their chemical composition varies only within narrow limits (Table 2). The concentrations of As are 44.62–46.84 wt% (average: 45.41 wt%), of Fe are 34.17–34.97 wt% (average: 34.47 wt%) and of S are 19.78–20.72 wt% (average: 20.22 wt%). From the atomic percentages, it can be inferred that these crystals are among the purest forms of arsenopyrite found in natural occurrences with very uniform and
Conclusion
Despite many potential issues related to the application of arsenopyrite geothermometry for low-temperature hydrothermal mineralizations, the chemically pure and unzoned arsenopyrite crystals in the BNUC provide a good opportunity to use them for estimating their temperature of formation. The calculated temperatures of 335–425 °C thus constrain the temperature of formation of the last stage of hydrothermal mineralization in the area that is likely related to the late-stage cross faulting.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, India is thanked for supporting the initial work on this project. Dr. M.S. Jena had helped during the sample collection. The visit of B. Nayak to RWTH was financially supported by the Alexander von Humboldt Foundation, Bonn, Germany. Roman Klinghardt and Lars Gronen assisted in operating the analytical equipment. Thomas Derichs prepared the polished thin sections. Prof. S. Basu, Director, CSIR-IMMT is thanked for encouraging
References (29)
- et al.
Age of the Baula PGE mineralization (Orissa, India) and its implications concerning the Singhbhum Archaean nucleus
Precamb. Res.
(2003) Thermochemical study of the system Fe-As-S
Geochim. Cosmochim. Acta
(1969)- et al.
Characterization of low grade PGE ores of Boula-Nuasahi Area, Odisha, India and implication on beneficiation
Ore Geol. Rev.
(2016) The Archaean Nucleus of Singhbhum: the present state of knowledge
Gond. Res.
(2001)Calculation of oxygen isotope fractionation in hydroxyl-bearing silicates
Earth Planet. Sci. Lett.
(1993)- et al.
Magmatic and hydrothermal platinum-group minerals and base-metal sulphides in the Baula Complex, India
Can. Mineral.
(2002) - et al.
Mineral-chemistry and stable-isotope constraints on the magmatism, hydrothermal alteration, and related PGE - (base-metal sulphide) mineralisation of the Mesoarchaean Baula-Nuasahi Complex, India
Min. Deposita
(2004) - Barton, P.B., Jr., 1970. Sulfide petrology. Mineral Soc. Amer. Spec. Pap.3,...
The gabbro rocks found near Gorumahisani Pahar
Proc. Natl. Inst. Sci. India
(1945)- et al.
Compositional variation of arsenopyrite and fluid evolution at the Ulsan deposit, Southeastern Korea: a low sulfidation porphyry system
Can. Mineral.
(2000)
The Fe-As-S system: phase relations and applications
Econ. Geol.
The Fe-As-S system. Variations of arsenopyrite compositions as a function of T and P
Carnegie Inst. Wash. Year Book
The composition of Co-Ni-Fe sulfarsenides, diarsenides and triarsenides from the San Juan De Plan deposit, Central Pyrenees, Spain
Can. Mineral.
SILLS: a matlab based program for the reduction of laser ablation ICP-MS data of homogeneous materials and inclusions
Mineral. Assoc. Canada Short Courses Series
Cited by (2)
Evaluation of groundwater heavy metal pollution index through analytical hierarchy process and its health risk assessment via Monte Carlo simulation
2023, Process Safety and Environmental ProtectionCitation Excerpt :Ahmed et al., (2022) in his study reported that sewage and agricultural runoff, dumping of municipal waste into streams and river were the major source of Ni, Cu and Cr contamination in groundwater. Moreover, Cr concentration in the groundwater is due to highly weathered soils depleted in isotopically heavy Cr and chromite mineralisation in the ophiolitic rocks (Lone et al., 2020; Nayak et al., 2021). With 15.69% of the total variance, the PC3 was comprised of Cr, Cd and Ni.