Genesis Of Pyrite Research Articles

Determining the ore-forming processes of Dongshengmiao Zn-Pb-Cu deposit: Evidence from the linear discriminant analysis of pyrite geochemistry

The orogenic base metal deposits gain more and more attentions in recent years. The ore-forming fluids associated with these deposits are enriched in reduced sulfur and have low salinity. Since this kind of fluid has low affinity to transport base metals, pre-enrichment of sulfide should take place during the formation of orogenic base metal deposits. The Dongshengmiao Zn-Pb-Cu deposit, which is located in the northern margin of the North China Block, was considered as orogenic base metal deposit, and a two-stage mineralization process was proposed by previous researchers, but other researchers proposed that the Dongshengmiao is a typical sedimentary exhalative (SEDEX) deposit. Even though the tectonic environment, fluid inclusion, geochronology and isotopic geochemistry have been widely investigated in the Dongshengmiao, its genesis is still under debate, and new data or proof should be presented to decipher the genesis model of the Dongshengmiao deposit. In this study, linear discriminant analysis (LDA), one of the commonly used machine learning methods, was employed to discriminate the genesis of pyrite in the Dongshengmiao deposit based on the trace element concentrations analyzed by LA-ICP-MS. The LDA results demonstrate that nearly all the early-stage fine-grained pyrites (Py1) show the same geochemical features as the pyrites from volcanic hosted massive sulfide (VHMS), whereas most of the late-stage recrystallized pyrite (Py2) is of orogenic origin. The Mesoproterozoic submarine volcanic activities resulted in pre-enrichment of sulfide with VHMS geochemical signature in the rocks hosting Dongshengmiao deposit. The pre-enriched sulfides were subsequently remobilized during the subsequent metamorphism in the early Cretaceous, leading to the formation of giant an orogenic base metal deposit.

Genesis of Pyrite in Clastic Rocks of Deep Salt-Related Strata in the Simao Basin and Its Implication for Potash Mineralization: A Case Study of the Well MK-3

In depth of the Simao Basin (2390 to 2650 m depth interval), many gray mudstone or carbonate rocks are developed in the red salt-related strata, and pyrite crystals are found in the fissure and matrix. In this study, petrology, mineralogy, element geochemistry, and LA-MC-ICP-MS in situ sulfur isotope analysis were used to constrain the genesis of pyrite, and the influence of relevant geological activities on potash mineralization was discussed. The results show that: (1) In the upper part of the salt layer, particle size of the pyrite ranges from 50 to 300 μm. The crystal morphology is mainly pentagonal-dodecahedral and irregularly granular, with a small amount of cuboidal pyrite. In the interlayer between rock salt, particle size of the pyrite is from 50 to 100 μm, and the crystals are mainly octahedral. (2) The S/Fe value of pentagonal-dodecahedral pyrite is significantly greater than 2; the S/Fe value of octahedral and cubic pyrite is less than 2; and the S/Fe value of irregular granular pyrite is close to 2. (3) The δ34SV-CDT values of pyrite in the upper salt-related strata range from −15.65‰ to 11.81‰, and the average δ34SV-CDT values of all samples range from 0.79‰ to 8.20‰. The δ34SV-CDT values of pyrite interlayer between rock salt range from −15.02‰ to −6.36‰, with an average value of −10.66‰. The above results indicate that the pyrite in the upper part of the rock salt layer was formed in a medium-low temperature hydrothermal environment, and the ore-forming sulfur elements have hydrothermal sources, bacterial sulfate reduction (BSR) sources, and thermochemical sulfate reduction (TSR) contributions. The pyrite between the rock salt layers is of sedimentary origin, and the ore-forming sulfur element comes from BSR. At present, there is no evidence of the influence of hydrothermal activities on deep potash-rich salt bodies, and the influence on the Mengyejing potash deposit has continued since the metallogenic period.

The Genesis of Pyrite in the Fule Pb-Zn Deposit, Northeast Yunnan Province, China: Evidence from Mineral Chemistry and In Situ Sulfur Isotope

The Fule deposit is a typical Cd-, Ge- and Ga-enriched Pb-Zn deposit located in the southeast of the Sichuan–Yunnan–Guizhou Pb-Zn polymetallic ore province in China. Zoned, euhedral cubic and pentagonal dodecahedral and anhedral pyrites were observed, and they are thought to comprise two generations. First generation pyrite (Py1) is homogeneous and entirely confined to a crystal core, whereas second generation pyrite (Py2) forms bright and irregular rims around the former. Second generation pyrite also occurs as a cubic and pentagonal dodecahedral crystal in/near the ore body or as an anhedral crystal generally closed to the surrounding rock. The content of S, Fe, Co, and Ni in Py1 are from 52.49 to 53.40%, 41.91 to 44.85%, 0.19 to 0.50% and 0.76 to 1.55%, respectively. The values of Co/Ni, Cu/Ni and Zn/Ni are from 0.22 to 0.42, 0.02 to 0.08 and 0.43 to 1.49, respectively, showing that the Py1 was formed in the sedimentary diagenetic stage. However, the contents of S, Fe, Co, and Ni in Py2 are in the range from 51.67 to 54.60%, 45.01 to 46.52%, 0.03 to 0.07% and 0.01 to 0.16%, respectively. The Co/Ni, Cu/Ni and Zn/Ni values of Py2 are from 0.40 to 12.33, 0.14 to 13.70 and 0.04 to 74.75, respectively, which is characterized by hydrothermal pyrite (mineralization stage). The different δ34S values of the Py1 (−34.9 to −32.3‰) and the Py2 (9.7 to 20.5‰) indicate that there are at least two different sources of sulfur in the Fule deposit. The sulfur in Py1 was derived from the bacterial sulfate reduction (BSR), whereas the sulfur in the ore-forming fluids (Py2) was derived from the thermochemical sulfate reduction (TSR). The main reasons for the different morphologies of pyrite in the regular spatial distribution in the Fule deposit are temperature and sulfur fugacity.

Testing the global significance of the sulfur isotope record of the ca. 2.0 Ga Zaonega Formation: A micro-scale S isotope investigation

The Paleoproterozoic metasedimentary rocks of the Zaonega Formation (Onega Basin, NW Russia) are important archives of inferred global environmental change following the initial oxygenation of the Earth’s atmosphere and oceans. However, the geochemical signals preserved in these exceptionally organic-and pyrite-rich metasedimentary rocks and their environmental meaning remain contested. In particular, the Zaonega Formation’s unusually high pyrite sulfur isotope ratios (δ34S) have been explained by either global or local forcings acting on sulfur cycling processes. We tested former interpretations of the Zaonega Formation’s sedimentary pyrite record by integrating bulk and micro-scale δ34S analysis to discriminate the isotopic signatures of different generations of pyrite and determine the underlying mechanisms contributing to δ34S variability. We show that the prolonged genesis of pyrite occurred via multiple stages and included precipitation from early diagenetic fluids, organic matter pyritization, and late-stage alteration fluids. Our results demonstrate that early-stage pyrite typically carries more variable and lower δ34S values than late-stage pyrite. Although the early pyrite captures pore water S isotope signatures least evolved from the seawater, their contribution to the bulk δ34S results can be dwarfed by the greater volume of late-stage coarse pyrite. Consequently, determining the sequence of pyrite precipitation and δ34S characteristics of individual generations in any given sample are fundamental to interpreting bulk δ34S records. Our micro-scale results suggest that previous estimates based on bulk pyrite data (ca. 6 to 18‰) should not be related to the original seawater sulfate’s isotopic composition. These results demonstrate that a thorough understanding of the geological context and mechanisms associated with S-cycling, and pyrite formation is necessary to interpret bulk δ34S records accurately.

Trace element and fluid inclusion geochemistry constraint for genesis of gold-polymetallic mineralization in the Songhung deposit, DPR Korea

The Songhung deposit is located in the southwestern part of the Yangdok metamorphic core complex (YMCC) in the northern portion of the Pyongnam Basin, the eastern part of the Sino-Korean Craton. In this paper, we present a detailed study on the magma sources of the granitoids (Yangdok and Hoechang graintic intrusions), genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events, petrogenesis of the granitoids and mineralization in the study deposit. The Yangdok granite has lower Al2O3/TiO2 ratios (mean value of 60.58) than the Hoechang granite (mean value of 994.46), indicating the higher temperature magma source of the former. On the Rb/Ba vs. Rb/Sr and CaO/(TFeO + MgO + TiO2) vs. (CaO + TFeO + MgO + TiO2) discriminant diagrams, the magma source of the Yangdok granite belongs in the plagioclase-rich and clay-poor source rocks, while those of the Hoechang granite plots either in the plagioclase-rich and clay-poor source rocks (for granite and fine-grained granite) or in the plagioclase-poor and clay-rich source rocks (for granite porphyry and felsite). On the Nb vs. Y, Ta vs. Yb, Rb vs. Y + Nb and Rb vs. Yb + Ta tectonomagmatic discrimination diagrams, these two granites are connected with the volcanic arc-related setting and plot in post-collision setting. Moreover, some data of the Hoechang granite fall in WPG field, suggesting that the volcanic arc setting may be changed to an intraplate setting from Middle Cretaceous.The pyrite trace element geochemistry, showing the high Co/Ni ratio than one with an average of 8.2 and high Co content and low Ni content, suggests that its formation was closely linked with I-type granitic magma-derived hydrothermal fluid mixed with meteoric water. It could also be assumed by the Co and As contents in pyrite, indicating a certain degree of meteoric water in the ore forming fluid. It is consonant to the Pb, S, C and O isotope geochemistry in the previous study, suggesting that ore-forming fluids and metals could be derived from both the Yangdok granite and the Proterozoic and Paleozoic meta-sedimentary rocks exposed in the study area. All of the pyrite grains have not compositional zoning and the similar distribution patterns of Co and Ni are appeared in single pyrite grain (from core to rim), suggesting the stable crystallization environment of pyrites and same ore forming fluid source. In pyrite grains, the positive correlation between gold and arsenic is appeared. The Au exists either as a micro- and nano-size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice. Based on the petrological and microthermometric characteristics of the fluid inclusions in ore-bearing quartz, we suggest that the ore-forming fluid is represented as NaCl + H2O or NaCl + KCl + H2O systems with low salinity. The absence of CO2-enriched phase and vapor-only or liquid-only primary inclusions in quartz indicates the homogenous magma-derived ore forming fluids and a lack of boiling during ore-forming process. The formation temperature and pressure of this deposit approximately vary from 317 to 326 °C and from 105.46 to 111.69 × 105 Pa, respectively, exhibiting the hydrothermal deposit origin. In conclusion, the Songhung deposit is originated from I-type granitic magma source-derived hydrothermal fluid which was mixed with meteoric water.

Trace elements of pyrite and S, H, O isotopes from the Laowan gold deposit in Tongbai, Henan Province, China: implications for ore genesis

The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase. We present results from the occurrences of gold, trace elements and sulfur isotopes of pyrite, and hydrogen and oxygen isotopes of quartz and calcite to elucidate the sources of ore-forming fluid; the genesis of pyrite and the ore-forming process. From field observations, five generations of pyrite are identified; one formed in a metamorphic-diagenetic epoch (PyI), and the others during four mineralization stages: 1) the coarse-grained pyrite-quartz stage (PyII), 2) the quartz and medium- to fine-grained pyrite stage (PyIII), 3) the polymetallic sulfide stage (PyIV), and 4) the carbonate-quartz stage (PyV). Gold mainly occurs in PyIII and PyIV. We find that Au, Ag, Pb, and Cu are incorporated into pyrite as micro-/nano-inclusions and that Co, Ni, As, and Se enter the pyrite lattice via isomorphous replacement. The Co/Ni values and Se concentrations indicate that PyI formed from metamorphic hydrothermal fluids and that pyrites (PyII, PyIII, and PyIV) from the ore-forming stages typically reflect a hydrothermal genesis involving magmatic fluid. The δ34S values of PyI (1.45 ‰–2.09‰) are similar to that of plagioclase amphibole schist, indicating that S was primarily derived from wall rock, while those of PyII, PyIII, and PyIV (3.10‰–5.55‰) suggest that S was derived from the Guishanyan Formation and the Laowan granite. The four mineralization stages show a systematic decrease in δD (from −77.1‰ to −82.8‰, −84.7‰, and −102.7‰), while the $${{\rm{\delta }}^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values showed a gradual decrease from 5.7 to 2.7‰, 1.0‰, and −1.3‰. These data show that the ore-forming fluid was similar to a mixture of magmatic and meteoric waters. Thus, we conclude that the Laowan gold deposit is related to magmatic-hydrothermal fluid.

Trace element contents and in situ sulfur isotope analyses of pyrite in the Baiyun gold deposit, NE China: Implication for the genesis of intrusion-related gold deposits

Trace elements distribution in minerals and formation mechanism of visible gold are poorly understood in intrusion-related gold systems. Here, we choose the Baiyun gold deposit, which is hosted within the Paleoproterozoic metamorphic rocks in the Liaodong Peninsula, NE North China Craton (NCC), as a case study, to address these issues. The ore deposit geology characteristics and paragenesis are described in details; In situ geochemical and sulfur isotopic compositions of pyrite and bulk Pb isotopic ratios of pyrite were presented to define the genesis of pyrite that is closely associated with gold mineralization. Three generations of pyrite were recognized based on petrographic studies: metamorphic pyrite (Py0), hydrothermal pyrite (Py1) coexisting with milky quartz, and hydrothermal pyrite (Py2) coexisting with smoky quartz. In situ laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) spot analysis suggests that both Py0 and Py1 contain low contents of invisible gold (mean 0.19 ppm and 0.17 ppm, respectively). However, Py1 is low in most other trace element contents and contains Au-Ag-Cu-Pb-Bi micro-inclusions. In contrast, Py2 contains both invisible gold (mean 0.50 ppm) and Au-Ag-Cu-Pb-Bi micro-inclusions. Furthermore, LA-ICP-MS mapping reveals the distributions of Ag, Cu, Pb, Bi and Te closely mimic that of Au, indicating an episode of ore-forming fluid rich in Au, Ag, Cu, Pb, Bi and Te. In situ sulfur isotope analysis of pyrite shows that Py0 has significantly positive δ34S values (+11.74–17.33‰), suggesting that sulfur was derived from sedimentary sources. Py1 and Py2 have negative δ34S values (–8.53––6.19‰, –10.44––6.86‰, respectively), indicating that sulfur was derived from oxidized magmatic fluids. The magmatic fluids are concluded to be released from the early Cretaceous microdiorite magmas, providing most of the sulfur and ore-forming metals. Proofs include the close spatial association of the ore bodies and the dykes, as well the uniform Pb isotopic ratios of Py1 and the early Cretaceous microdiorite. Lines of geological, mineralogical, geochemical and isotopic evidence consistently suggest that the gold mineralization in the Baiyun deposit is intrusion-related, and was resulted from the ~126 Ma magmatic-hydrothermal activities in the region. Visible gold precipitating in pyrite and fractures was from metal-rich magmatic fluids rather than being remobilized from the metamorphic pyrite.

Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China

AbstractNorth China Craton experienced significant lithospheric destruction or delamination during the Late Mesozoic, accompanied with the emergence of numerous basins and intensive volcanic activities. Extensional basins also formed in eastern Shandong Province. Even though they have been researched for decades, the relation between basin development and deep tectonic processes still remains obscure. Recently, a set of Early Cretaceous strata, characterized by translating from turbidite deposits to terrestrial strata unit and ending up with a unique volcanicalstic formation within a pretty short time span, has been found on Lingshan Island. Previous Studies have reached an agreement that Lingshan Island strata was formed in a distinct sedimentary background compared with the coeval sedimentary units in Jiaolai Basin. Essential information about basin development and its tectonic setting in the region during Early Cretaceous are preserved in the Lingshan Island strata. In this article, we show the characteristic of heavy mineral assemblage from the bottom to the top, and the characteristic of detrital minerals’ chemical component in the two representative samples. Based on these new works, we indicate that the Lingshan Island basin was developed in transpressional tectonic setting with complex provenance materials mainly from Qianliyan‐Uplift during the period ca.123∼120Ma. Then, the basin evolved within a extensional region and filled with locally derived clastics during 120 to 105Ma. Additionally, the basin was evolved during the procedure of progressive lithospheric thinning and asthenosphere upwelling, which could be proven by stratigraphic characteristics and chemical component of detrital spinels.

Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China

AbstractAs a widely‐developed mineral in various types of rocks, pyrite features important geological information such as temperature and pressure during its formation and evolution (An et al., 2014; An et al., 2018). It is an important geological formation for studying the origins of rocks, mineralization, and deposits (Xue et al., 2014; An et al., 2016). The study of the genesis of gold deposits is a research hotspot in current geology and mineral deposits not only because of high economic value, but also because of important practical significance (An et al., 2017; Yang et al., 2014). Shandong Zhaoyuan, as the third largest gold production area in the world, has important research significance of the origin and generation of gold‐bearing minerals (Xue et al., 2014; Wen et al., 2014). In this study, pyrite from augen granite (figure 1a), syenite (figure 1b), basite (figure 1c) and gold ore (figure 1d) at Zhaoyuan gold deposit Shandong Province, was selected as the research object. The morphological and structural micro‐fabrics were analysed by polarized light microscopy (PLM) and Raman spectroscopy to reveal the source and process of gold further.

Ore-Forming Processes at the Xiajinbao Gold Deposit in Eastern Hebei Province: Constraints from EPMA and LA-ICPMS Analysis

The Xiajinbao gold deposit is located at the northern margin of the North China Craton. Hydrothermal pyrites belonging to three stages were identified: Py1; Py2; and Py3. Geochemical study of these pyrites was conducted using electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry to investigate the distributions of minor and trace elements, constrain pyrite genesis, and to obtain an improved understanding of the ore-forming processes. Py1 and Py2 contain high concentrations of Au and are interpreted to have been deposited from fluids from a dominantly magmatic source. Py3 grains have the lowest Co/Ni ratios. All generations of pyrite were deposited by mixing of meteoric waters with magmatic-hydrothermal fluids. Boiling of early ore-forming fluids led to the precipitation of Py1 and gold. Decreasing fO2 in the ore-forming system resulted in the formation of Py2 and gold. Fluid mixing was the dominant controlling factor for the precipitation of Py3 together with small amounts of gold.

Questioning the biogenicity of Neoproterozoic superheavy pyrite by SIMS

The Neoproterozoic sulfur isotope (δ34S) record is characterized by anomalously high δ34Spyrite values. Many δ34Spyrite values are higher than the contemporaneous δ34Ssulfate (i.e., δ34Spyrite > δ34Ssulfate), showing reversed fractionation. This phenomenon has been reported from the Neoproterozoic post-glacial strata globally and is called “Neoproterozoic superheavy pyrite.” The commonly assumed biogenic genesis of superheavy pyrite conflicts with current understanding of the marine sulfur cycle. Various models have been proposed to interpret this phenomenon, including extremely low concentrations of sulfate in seawaters or pore waters, or the existence of a geographically isolated and geochemically stratified ocean. Implicit and fundamental in all these published models is the assumption of a biogenic origin for pyrite genesis, which hypothesizes that the superheavy pyrite is syngenetic (in the water column) or early diagenetic (in shallow marine sediments) in origin and formed via microbial sulfate reduction (MSR). In this study, the Cryogenian Datangpo Formation in South China, which preserves some of the highest δ34Spyrite values up to +70‰, is studied by secondary ion mass spectrometry (SIMS) at unprecedented spatial resolutions (2 μm). Based on textures and the new sulfur isotope results, we propose that the Datangpo superheavy pyrite formed via thermochemical sulfate reduction (TSR) in hydrothermal fluids during late burial diagenesis and, therefore, lacks a biogeochemical connection to the Neoproterozoic sulfur cycle. Our study demonstrates that SEM-SIMS is an effective approach to assess the genesis of sedimentary pyrite using combined SEM petrography and micrometer-scale δ34S measurements by SIMS. The possibility that pervasive TSR has overprinted the primary δ34Spyrite signals during late diagenesis in other localities may necessitate the reappraisal of some of the δ34Spyrite profiles associated with superheavy pyrite throughout Earth’s history.

Multi-stage pyrite genesis and epigenetic selenium enrichment of Greenburn coals (East Ayrshire)

Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average UK and world compositions, substituting for sulphur in pyrite. Greenburn surface mine coals are characterized by syngenetic concretionary pyrite ( c. 15% total area), occurring as bedding-parallel banding, and later-formed (epigenetic) cross-cutting pyrite in cleats ( c. 9% total area). In these, sulphur isotope compositions for both syngenetic and epigenetic pyrite include isotopically light and heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se (up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm). Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide. Supplementary material: LA-ICP-MS maps for Fe, Se, Ag, As, Cu, Hg, Pb and Te for Greenburn coal samples from seams 9300 Lime and 6900 Burnfoot Bridge are available at https://doi.org/10.6084/m9.figshare.c.3967860

Geochemical Characteristics and Genesis of Pyrite from the Dongguashan Cu‐Au Deposit, Anhui Province, China

Acta Geologica Sinica - English EditionVolume 88, Issue s2 p. 60-61 Meeting Abstracts Geochemical Characteristics and Genesis of Pyrite from the Dongguashan Cu-Au Deposit, Anhui Province, China Jiandong ZHANG, Corresponding Author Jiandong ZHANG Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaCorresponding author. E-mail: csuzjd@sina.comSearch for more papers by this authorYongjun SHAO, Yongjun SHAO Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaSearch for more papers by this authorZhongfa LIU, Zhongfa LIU Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaSearch for more papers by this author Jiandong ZHANG, Corresponding Author Jiandong ZHANG Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaCorresponding author. E-mail: csuzjd@sina.comSearch for more papers by this authorYongjun SHAO, Yongjun SHAO Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaSearch for more papers by this authorZhongfa LIU, Zhongfa LIU Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Infophysics, Central South University, Changsha 410083 ChinaSearch for more papers by this author First published: 29 December 2014 https://doi.org/10.1111/1755-6724.12367_29Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume88, Issues2Special Issue: Meeting Abstracts: The 14th Quadrennial International Association on the Genesis of Ore Deposits Symposium. August 19–22, 2014, Kunming, ChinaDecember 2014Pages 60-61 RelatedInformation

Redox status and heavy metal risk in intertidal sediments in NW Spain as inferred from the degrees of pyritization of iron and trace elements

Mariculture is an important economic activity in shallow marine areas of the Rías Baixas (Galicia, NW Spain). The maintenance of high product quality requires surveillance of environmental quality, including the risk of metal toxicity. In this study the redox status of intertidal sediments in the Bay of San Simón, and the risk of toxicity posed by their As, Cd, Cr, Cu, Mn, Ni, Pb and Zn contents, were evaluated by determination of operationally defined reactive, silicate-bound, organic and pyrite-related fractions of these elements and of Fe. The large silicate-bound fractions of most of these metals indicate their lithogenic origin; the main exception is Pb, which in all respects exhibits singular behaviour associated with its predominantly anthropogenic origin in a ceramics factory. In sediments with larger fine-grained particle contents, which are oxic only in the top few centimetres, greater proportions of the trace elements are present as sulphides or associated with sulphide minerals: the degree of pyritization of Fe (DOP) is 46% overall, and the pyrite fraction of some elements doubtless increases at the expense of the reactive fraction, most overall degrees of trace metal pyritization (DTMPs) lying in the range 10–50%. A decline in pyrite genesis at depths below about 18 cm in these sediments is attributed to the exhaustion of organic matter susceptible to metabolization by sulphide-generating bacteria. In coarse-grained, oxic sediments the oxidation of sulphides makes pyrite-related fractions very small, and reactive and silicate-bound fractions are negatively correlated; reactive fractions associated with Fe–Mn oxyhydroxides are large, and DOP and DTMPs are low (generally much lower than in mud-rich sediments), except for Pb. Most of the elements studied are mainly present in forms that are neither bioavailable nor potentially bioavailable, and so do not constitute a significant environmental threat. However, the high DTMPs of Cu and Pb indicate significant potential bioavailability, which should be taken into account in evaluations of environmental quality and the risk to bivalve cultures.

Research on Genesis of Pyrite near the Permian-Triassic Boundary in Meishan, Zhejiang, China

Abstract The content and crystal forms of pyrite and sulfur isotope composition of pyrite sulfur as well as its vertical distribution near the Permian-Triassic (P/T) boundary in the Meishan section, Changxing county, Zhejiang province, China were studied using geological, petrological, mineralogical and geochemical methods (techniques). The result showed that the genesis of abundant pyrites in bed 24e2 at the uppermost part of the Changxing Formation in the Meishan section may be related to volcanic activity. In bed 24e2 of the Meishan section, pyrite has its highest content of 1.84% and the sulfur isotope composition has the highest δ 34 S value at +2.2‰ which is very similar to that of the average value of volcanic gas. There are some volcanic products such as β-quartz, siliceous cylinders and siliceous spherules which coexisted with pyrites in beds 24e2 and 24f. It can be concluded that a large quantity of volcanic ash fell into the South China Sea and was incorporated into marine sediments during the formation of limestone at the uppermost part of the Changxing Formation. The volcanic eruption with massive amounts of H 2 S and SO 2 gas at the end of the Permian period resulted in the enrichment of H 2 S in the South China Sea areas. The reaction of H 2 S with reactive iron minerals formed the mass of abundant pyrites.

Geochemical phases of Fe and degree of pyritization in sediments from Ría de Pontevedra (NW Spain): Implications of mussel raft culture

To assess the influence of mussel raft systems on several geochemical and sedimentological properties (carbonate and organic matter contents, fractions of Fe and degree of pyritization), six sediment cores were collected from the Ría de Pontevedra area. Four of those cores were collected in mussel raft areas (biodeposits) and the other two in adjacent areas where mussel rafts do not operate. The degree of pyritization (DOP) varied between 11.89% and 67.30%, with a mean value of 46.36 ± 13.15%. The maximum values of DOP were obtained in sediments from the mussel raft areas, which in turn showed higher values of pyrite Fe, organic matter and mud than the areas without mussel rafts. On the contrary, in the latter areas, coarser sediments with high carbonate content and Fe bound to silicates were the predominant phases. The results show a dominance of more reducing conditions in the biodeposit areas than in the adjacent areas. The DOP values indicate that reactive Fe was not totally converted to pyrite Fe. The significant correlation (r = 0.61) between DOP and organic matter confirmed that the latter is the limiting factor in pyrite genesis. These results allow us to conclude that mussel raft culture significantly changes the sediment texture and geochemical forms of Fe, with the consequent geochemical and environmental implications.

Quartz-Pebble Conglomerates of Chikmagalur Area, Karnataka, India: Implications on Uranium Concentration

The Quartz - Pebble Conglomerates (QPC) represent the angular unconformity prevailed between the older group of Sargur rocks and younger Dharwar volcano-sedimentary association in Chikmagalur area of Karnataka state. The older group of rocks consist of amphibolites, Peninsular gneisses, granites, quartzites and quartz-sericite schists whereas the younger group has amphibolites, quartzites, phyllites, chlorite schists, differentiated volcanic rocks and banded iron formations. The QPCs have rutile, ilmenite, pyrite, pyrrhotite, chalcopyrite and rarely uraninite as the major opaque phases. Gamma ray spectrometry, autoradiography and ore petrographic studies have shown that the concentration of uranium in the QPCs is due to solution redeposition of uranium by adsorption or absorption on rutile generated by the decomposition of ilmenite with hydrous iron as another product. The genesis of pyrite is described through a polyplylitic process . The oxidising environments prevailed in Pre-cambrian might have promoted the transportation of U +6, S +6 and Cr +6 and were concentrated in reducing pockets of Bababudan as U +4, S −2 and Cr +3. Cr +3 is represented by fuchsite mica abundant in pyrite rich zones. The scarcity of uraninite is due to the destruction of these grains by oxidation during transportation.

A sulfur isotope study of pyrite genesis: The mid-proterozoic Newland formation, belt supergroup, Montana

Different generations of sedimentary pyrite from the Mid-Proterozoic Newland Formation, USA, have been analysed for their sulfur isotopic compositions. The results indicate bacterial sulfate reduction as the pyrite forming process. The δ34S values for early diagenetic pyrite, around −14%., are in contrast to dominantly more positive values for many other Middle Proterozoic units. A progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34S content (Rayleigh Distillation) as well as through detailed petrographic observations. Contemporaneous seawater had a sulfur isotopic ratio between +14 and +18%. as measured from sedimentary barite within the unit.

Marine origin of pyritic sulfur in the Lower Bakerstown coal bed, Castleman coal field, Maryland (U.S.A.)

The amount, kind, distribution, and genesis of pyrite in the Lower Bakerstown coal bed in a 150 × 15 m area of the Bettinger mine, Castleman coal field, Maryland, were studied by various analytical techniques. The mined coal, which had a nonmarine roof rock, contained 1.4–2.8 wt.% total sulfur, generally much lower than the high-sulfur coal (> 3.0 wt.% total S) to the north, which is associated with marine roof rocks. Small-scale systematic and nonsystematic variations in total sulfur and pyrite distribution were found in the mined area. In the column sample, most of the pyrite was found in the upper 9 cm of the 69-cm-thick mined coal and occurred mainly as a pyrite lens containing cell fillings in seed-fern tissue (coal ball). As-bearing pyrite was detected by laser microprobe techniques in the cell walls of this tissue but not elsewhere in the column sample. This may indicate that the As was derived from decomposition of organic matter in the cell walls. The sulfur isotopic composition and distribution of pyrite in the coal are consistent with introduction of marine sulfate shortly after peat deposition, followed by bacterial reduction and pyrite precipitation. Epigenetic cleat pyrite in the coal is isotopically heavy, implying that later aqueous sulfate was 34S-enriched.

Microbial pyrite removal from hard coal

Thiobacilli may either attack coal-contained pyrite directly or contribute to its oxidation via catalysing the oxidation of ferrous salts by oxygen dissolved in water. The part played by either of the above mechanisms during pyrite removal from hard coals is discussed. This is followed by a review of experiments meant to identify the influence of coal rank, grain size, pyrite genesis and content, on pyrite removal efficiency over time. The paper reports on experiments to determine the seepage rate of the nutritive solution with bacteria, termed “biopulp”, in coal heaps. Investigations into the alteration of coal properties due to pyrite removal are dealt with. Concluding, plant dimensions and the costs of pyrite removal, as derived from two designs of relevant plants, are presented.