Pyrite

A review of previous studies of the world’s large hydrothermal gold deposits indicates that the largest deposits tend to show complicated parageneses where multiple gold enrichment events and processes have been involved in the deposit generation. These observations suggest that multistage processes may even be a requirement for the formation of large deposits. In some deposits (e.g. Witwatersrand, Boddington Cadia, Sukhoi Log or Carlin) the different enrichment processes occur millions of years apart. In others, such as many large porphyry deposits, the different stages are much closer in time. In many deposits, particularly sedimentary-hosted deposits, early diffuse enrichment occurs within a particular province that is then upgraded by more focused processes (e.g., Sukhoi Log; Kalgoorlie). The presence of this early diffuse enrichment could explain the tendency for gold deposits to cluster into camps.
This model has important implications, as the presence or absence of multiple gold events could be used to discriminate, at the exploration and feasibility stages, between small deposits with single stage ore genesis and more complicated deposits with multistage enrichment and the potential for larger gold endowment.

Shallow (<1500 mbsl) submarine arc-related hydrothermal systems can host base (Cu), precious (Au) and volatile elements (As, Se, Sb, Te, Tl) in significant quantities. Their wide application in the high-tech industry, but a potential eco-toxicological footprint gives them a strategic importance. However, the processes that concentrate these elements in submarine arc-related hydrothermal systems, compared to their mid-ocean ridge counterparts are still debated, and it is unclear whether boilingrelated processes and/or the contribution of magmatic volatiles are key for their enrichment. We present bulk sulfide-sulfate, isotope (S and Pb), and high-resolution microanalytical data of hydrothermal sulfides from the Niua South fore-arc volcano in north Tonga, where numerous black-smoker type sulfide-sulfate chimneys emit boiling fluids with temperatures (up to 325°C) near the seawater boiling curve at~1170 m water depth. Hence, this system represents an ideal natural laboratory to investigate the effect of fluid boiling on base, precious, and volatile element enrichment associated with hydrothermal seafloor mineralization. At Niua South, textural and chemical variations of multiple pyrite (framboidal, euhedral and massive), chalcopyrite (linings), and sphalerite (dendrites and linings) generations are indicative for sulfide precipitation from early low-temperature (~240°C) fluids that underwent abundant mixing with ambient seawater (low Se/Tl and Co/Ni ratios in pyrite) and from later high-temperature (up to 325°C) (high Se/Tl and Co/Ni ratios in pyrite). In addition, crustiform inclusion-rich pyrite that precipitated from high-temperature boiling fluids shows low Bi/Pb, Tl/Pb and Sb/Pb ratios due to volatile element loss (e.g., Tl and Sb) to the vapor phase compared to pyrite that formed during the low temperature stage. By contrast, late sphalerite (~280°C) is enriched in elements with an affinity to Cl-complexes like Mn, Co, Ni, Ga, Cd, In, and Sn, and therefore precipitated from the corresponding Cl-rich liquid phase. Gold occurs in solid-solution and as boiling-induced particles of native Au, electrum, and Au-rich Bi-tellurides in pyrite (up to 144 ppm Au), sphalerite (up to 60 ppm Au), and chalcopyrite (up to 37 ppm Au). These particles (<5-10 mm) probably formed during fluid boiling causing an extreme Au enrichment (>30 ppm) in the mature and late stage of chimney formation. Lead isotope data indicate that the hydrothermal fluids scavenged metals not only from the deeper basement in the reaction zone (20-40%), but also from young dacitic volcanic rocks near the seafloor in the upflow zone (60-80%). Sulfur isotope

The Tom and Jason sedimentary exhalative (SEDEX) Pb-Zn-Ag-(Ba) deposits in Yukon grade 7.4 weight % and 7.0 weight % Zn, and 6.5 weight % and 4.6 weight % Pb, with zinc and lead tonnages of 15.7 and 10.1 Mt, respectively. Pyrite is ubiquitous in SEDEX deposits and can potentially reveal much information about the environment and nature of deposition, hydrothermal fluid properties, genesis of mineralization, and may provide vectors toward mineralization. Pyrite-bearing samples from three drillholes situated 2 to 4 km from mineralization (but time-stratigraphically equivalent) were sampled, and four generations of pyrite were identified (Py1, Py2, Py3, Py4), each with distinct morphological characteristics and mineralogical associations. Synsedimentary (Py1), diagenetic (Py2), hydrothermal (Py3) and metamorphic (Py4) morphologies were identified. A representative subset of pyrite grains was analyzed for trace element contents by laser ablation-inductively coupled plasma mass spectrometry using raster grids to create quantitative trace element composition maps, in order to characterize the trace element composition of each pyrite generation.  A distal (2–4 km) expression of hydrothermal mineralization is recognized in Py3, which displays mineral associations and a trace element assemblage typical of hydrothermally precipitated pyrite. The trace element geochemistry of pyrite distal to SEDEX mineralization (and time-stratigraphically equivalent to it) displays enrichment in Zn, Mn, As  and Co, and these elements are generally more abundant in Py3 than other generations, indicating the presence of nearby concealed mineralization.

Pyrite-permineralized fruits and seeds from the London Clay Formation (Ypresian, England) in the NHMUK are stored in silicone oil to retard decay processes. X-ray micro-computed tomography (micro-CT) has revealed internal morphology for multiple holotypes (including severely cracked and encrusted specimens) scanned in the protective fluid. Silicone oil alone has a similar X-ray attenuation to parts of the specimens, causing minor uncertainty for digitally rendered surfaces, but key systematic characters are readily visualised. Further work is needed to optimise visualization of fine-scale cellular detail. Labelling and segmentation to visualise important structures is achievable with these micro-CT datasets. However, manual labelling of individual slices is required and defining boundaries between features can be difficult due to differential pyritization and silicone oil permeation. Digital sections through specimens can be made in any orientation and digital locule casts can be produced for studies in virtual taphonomy. These achievements have been accomplished with minimal risk to specimens, which remained in silicone oil and were studied within the museum. The datasets provide a potentially permanent record of at-risk specimens, can be made widely available to researchers unable to visit the collections and to other interested parties, and they enable monitoring for future conservation.

Well preserved pyritized radiolarian skeletons have been found within the grey-green Mid-Cretaceous
(Upper Cenomanian) shales in the Pieniny Klippen Belt (Carpathians, Poland). The skeletons contain numerous
pyrite framboids in different positions, in channels and inside the abdomen of cryptothoracic forms, but their
genetic context is not known. They were formed as a result of the reaction between dissolved iron and sulphide
originated from the bacterial sulphate reduction. Two sources of organic matter, “post mortem” in situ decaying
organic matter of radiolaria and disseminated organic matter from the surrounding sediment could be available for
this process. Pyrite found in the radiolarians probably originates from different processes. It is suggested that
pyritization of the radiolarian skeletons took place in the water column whereas pyrite framboids in the skeleton’s
free spaces could have been formed later during the diagenesis of the sediment. However, their simultaneous
formation in the water column or in the sediment cannot be excluded.

Fire use appears to have been relatively common among Neandertals in the Middle Palaeolithic. However, the means by which Neandertals procured their fire—either through the collection of natural fire, or by producing it themselves using tools—is still a matter of debate. We present here the first direct artefactual evidence for regular, systematic fire production by Neandertals. From archaeological layers attributed to late Mousterian industries at multiple sites throughout France, primarily to the Mousterian of Acheulean Tradition (MTA) technoculture (ca. 50,000 years BP), we identify using microwear analysis dozens of late Middle Palaeolithic bifacial tools that exhibit macroscopic and microscopic traces suggesting repeated percussion and/or forceful abrasion with a hard mineral material. Both the locations and nature of the polish and associated striations are comparable to those obtained experimentally by obliquely percussing fragments of pyrite (FeS 2) against the flat/convex sides of a biface to make fire. The striations within these discrete use zones are always oriented roughly parallel to the longitudinal axis of the tool, allowing us to rule out taphonomic origins for these traces. We therefore suggest that the occasional use of bifaces as 'strike-a-lights' was a technocultural feature shared among the late Neandertals in France.

Sulfide nodules composed of pyrite occur within black shales in the Lucky Bay area of the Bulong Domain,
Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia that correlate with the Neoarchean
Black Flag Group. Detailed petrography reveals a variety of shapes and textures, from spherical to ovoid
and zoned to uniform. Some nodules have recrystallized, resulting in a later generation of pyrite. All
have been affected by post-depositional metamorphism, as evidenced by pressure shadows containing
quartz
±
mica
±
carbonate assemblages. LA-ICP-MS analyses show that these nodules are enriched in a
range of trace elements, including Co, Ni, Cu, Ag, Sb, Te, Au, Tl, Pb, and Bi. Gold and Te concentrations range
from 0.3 to 1 ppm and 10 to 50 ppm, respectively. The Black Flag Group equivalents stratigraphically and
structurally underlie a younger basin east of Lucky Bay that contains turbidites, sandy debris flows and
BIF, the latter of which hosts several gold deposits at Randalls, 60 km SE of Kalgoorlie. It is likely that
the lateral equivalents of the nodular sulfide-bearing black shale originally occurred stratigraphically
beneath what is now the ore horizon at Randalls. Given its anomalous Au and Te content, this lithology is
a potential contributor of gold to the BIF-hosted gold deposits of the Randalls Goldfield, as well as other
similar gold resources elsewhere in the Eastern Goldfields Superterrane.