Diversity of Pyrite-Hosted Solid Inclusions and their Metallogenic Implications—A Case Study from the Myszków Mo–Cu–W Porphyry Deposit (the Kraków–Lubliniec Fault Zone, Poland)

Pyrite from the central part of the Myszków porphyry deposit in Poland was investigated using a combination of reflected and transmitted polarizing microscopy, back-scattered imaging with energy-dispersive X-ray spectroscopy, and Raman micro-spectroscopy. Five generations of pyrite (I–V) found in hydrothermal veins were distinguished, differing in morphology, microtexture, and the types and amounts of solid inclusions. In general, pyrite hosts a diversity of mineral inclusions, including both gangue and ore phases, i.e., chlorite, quartz, monazite, cerianite-(Ce), xenotime, K-feldspars, albite, sericite, barite, magnetite, chalcopyrite, galena, sphalerite, bastnaesite (Ce), bismuthinite, native silver, cassiterite, rutile, anatase, and aikinite-group species. The presence of inclusions is good evidence of various stages of the evolution of the hydrothermal lode system ranging from high- to low-temperature conditions. During the formation of stockworks, some fluctuations in the physicochemical conditions of mineralizing fluids were indicated by the occurrence of cassiterite formed from acidic, reducing solutions, and hematite hosted in xenotime or REE phases found in pyrite, which signal more oxidizing conditions. Periodically, some episodes of boiling in the hydrothermal, porphyry-related system were recorded. They were mainly evidenced by the presence of (1) lattice-bladed calcite found in the close vicinity of pyrite II, (2) irregular grain edges of pyrite I, (3) clustered micropores in pyrite I, and (4) the variety of mineral inclusions hosted in I and II generations of pyrite.

Olivine in komatiite records origin and travel from the deep upper mantle

The deep upper mantle is the main source of high-temperature magmatism, but the only known naturally occurring samples of high-pressure mantle constituents are mineral inclusions in diamonds. Trace elements in olivine crystals from the 3.33 Ga Commondale Greenstone Belt in South Africa reveal that these crystals formed in the deep upper mantle as high-pressure phenocrysts, and some perhaps even formed in the mantle transition zone (410–600 km) where they began as wadsleyite. The crystals were entrained within ascending komatiite magma and conveyed to the surface. The olivine crystals have the highest contents of Al2O3 (0.3 wt%) recorded in any terrestrial olivine, which is indicative of formation at high pressure. The deep mantle gave rise to Archean komatiites, extraordinarily hot magmas (up to 1700 °C), which provide insight into Earth’s early mantle evolution and the formation of most ancient continental and oceanic crust. In spite of extensive research since their discovery over 50 years ago, the origins of komatiites have remained contentious. Plumes—thermochemical instabilities originating at the core-mantle boundary—are the most likely source, but no direct evidence of a deep mantle origin of komatiite has yet been recognized.

Mineral inclusions in the late bronze age metal objects оf Southern Transurals

The paper is devoted to the determination of copper raw material types based on the analysis of mineral inclusions and the composition of metal objects from the Late Bronze Age settlements of the Southern Transurals (XIX–XIII centuries BC). The composition of alloys, inclusions of sulfdes, oxides and metals of objects was established by scanning electron microscopy. The composition of objects is dominated by copper and tin bronze, with a subordinate role of arsenic bronze. The presence of chalcocite and bornite inclusions in most objects indicates the use of rich ores from secondary sulfde enrichment zone. In comparison with analogs, the low total amount of sulfdes in the Southern Transuralian metal objects may indicate the use of mixed oxide and sulfde concentrates. The high Se and Te concentrations of sulfdes are indicative of using of ores of volcanic-hosted massive sulfde or skarn deposits. Keywords: metal objects, copper, bronze, sulfdes, Late Bronze Age, Southern Transurals

Hadean zircon formed due to hydrated ultramafic protocrust melting

Hadean zircons, from the Jack Hills (Western Australia) and other localities, are currently the only window into the earliest terrestrial felsic crust, the formation of which remains enigmatic. Based upon new experimental results, generation of such early crust has been hypothesized to involve the partial melting of hydrated peridotite interacting with basaltic melt at low pressure (<10 km), but it has yet to be demonstrated that such liquids can indeed crystallize zircons comparable to Jack Hills zircon. We used thermodynamic and geochemical modeling to test this hypothesis. The predicted zircon saturation temperatures of <750 °C, together with the model zircon Th, U, Nb, Hf, Y, and rare earth element (REE) contents at 700 °C, δ18OVSMOW (Vienna standard mean ocean water) signatures, and co-crystallizing mineral assemblage were compared to those of the Jack Hills zircon. This comparison was favorable with respect to crystallization temperature, most trace-element contents, and mineral inclusions in zircon. The discrepancy in δ18OVSMOW signatures may be explained by hotter conditions of Hadean protocrust hydration. Our work supports the idea that felsic magma generation at shallow depths involving a primordial weathered ultramafic protocrust and local basaltic intrusions is indeed a viable mechanism for the formation of felsic crust on early Earth.

Archaeological applications of natural gold analyses

Compositional studies of natural gold usually have a geological focus, but are also important in archaeological provenancing. Both methodologies rely on compositional comparison of two sets of samples, one of which is geographically constrained. Here we describe how experiences in gold characterization resulting from geological studies are relevant to archaeology. Microchemical characterization of polished sections of natural gold identifies alloy compositions, alloy heterogeneity and mineral inclusions. Gold from all deposit types shows Cu and Sn values much lower than those recorded during numerous studies of artefacts. Inclusions in artefact gold include various Cu- and Sn-bearing compounds which indicate specific high temperature reactions that could ultimately illuminate the conditions of (s)melting. The use of LA-ICP-MS to generate a wide range of elemental discriminants for provenance studies may be compromised by alloy adulteration and/or unrepresentative analysis of natural/artefact alloys, which are commonly highly heterogeneous at the micron scale. Geological studies normally characterize only the earliest-formed (hypogene) alloy, whereas archaeology-focussed studies should entail analyses of bulk alloy compositions and impurities that may be incorporated during (s)melting. Isotopic-based provenancing alleviates many of these problems but, to date, generates regional rather than locality specific targets. A dual isotopic-compositional approach is recommended.

Thermobarometry of Diamond Inclusions: Evidence Mantle Evolution beneath Siberian Craton and Archean Cratons Worldwide.

Thermobarometric calculations for mineral inclusions in diamonds provide a systematic comparison of PTXFO2 conditions for different cratons worldwide, using a database of 4440 mineral EPMA analyses. Beneath all cratons, the cold branch of the mantle geotherm (35-32 mWm−2) relates to the sub-Ca garnets and rarely omphacitic diamond inclusions, referring to major continental growth events in Archean. High-temperature plume-related geotherms are common in Proterozoic kimberlites such as Premier, Mesozoic – Roberts Victor etc. and are common in Slave and Siberian cratons. In mobile belts: Limpopo, Magondi, Ural Ural, Khapchan belts and in the marginal parts of cratons like Kimberly Australia pyroxenitic and eclogitic pyroxenes and garnets prevail. The pyropes in the mobile belts are more Fe- and Ca-rich, in central parts of cratons, the peridotitic associations with sub- Ca pyropes prevail. The accretionary complexes like Khapchan and Magondi belts a thick eclogite-pyroxenite lens is highly diamondiferous. Comparison by minerals shows that the PT estimates for clinopyroxenes and orthopyroxene from peridotites and eclogites are representing mainly the middle part of the sub-lithospheric mantle while garnets gives more high-pressure estimates. refer to eclogites and reflect the processes of the differentiation during migration of partial melts. This produces the trends of joint decreasing Mg’ and pressures. The PT for the chromites reflect conditions just above the lithosphere-asthenosphere boundary and mainly were formed due to interaction with the hydrous plume protokimberlite melts. Archean diamond inclusions from Wawa province Canada are represented by Ca-enrich pyropes giving low-temperature conditions. Inclusions from younger kimberlites in Superior and Slave (and Siberian and East European ) cratons show complex high-temperature geotherms due to plumes influence. Peridotite garnets beneath the Amazonian craton indicate complex layering in the lithosphere base and a pyroxene layer in the middle part of SCLM. Diamond inclusions from the Kimberley craton of Australia show the greatest variations in the temperatures and composition.

Spectroscopy and Microscopy of Corundum from Primary Deposits Found in Greece

Corundum primary deposits in Greece occur in four locations: Paranesti in Drama and Gorgona in Xanthi, both belonging to the wider Rhodope Massif, as well as, Ikaria island and Kinidaros in Naxos island, both belonging to Attic-Cycladic Massif. Eight samples were examined with spectroscopic methods (FTIR, UV-Vis, EDXRF) in order to better characterize these four primary deposits: two pink sapphires from Paranesti, a pink and a blue sapphire from Gorgona, two blue sapphires from Ikaria and three blue sapphires from Kinidaros. Under the microscope, all samples present characteristics linked to post-crystallization deformation, decreasing their gem quality. The FTIR absorption spectra of all samples present in different relative intensities, bands of boehmite, diaspore, goethite, mica and/or chlorite inclusions and CO2 in fluid inclusions. Boehmite and diaspore inclusions are most likely epigenetic. In the UV-Vis spectra, the pink color of the samples is linked with Cr3+ absorptions and the blue color with absorptions due to Fe2+-Ti4+ intervalence charge transfer. EDXRF analyses in the studied samples show relatively high titanium and iron concentrations that are related with mineral inclusions. Gallium is slightly variable in samples from different regions; also, different colored samples from Gorgona present diverse gallium content.

A pilot study on coarse ware ceramic fabrics from the Ayios Vasileios Survey Project (Greece)

In this article, we present the results of our pilot study on coarse ware ceramic fabrics from the Ayios Vasileios Survey Project (Laconia, Greece). The aim of this pilot was to explore the potential of optical fabric analysis on coarse wares on the basis of (mineral) inclusions detectable by eye or under modest magnification. We aimed to answer the following question: can we discern Bronze Age coarse wares from Byzantine/Early Modern coarse wares by means of this technique? We studied 177 ceramic fragments by eye and by means of a stereo microscope. This resulted in the description of 51 different provisional fabrics. Only a few of these fabrics could be assigned to a specific time period with certainty, based on a consistent dating of the sherds by the ceramic specialists, who looked at shape, decoration and fabric. Most of the fabrics seem to consist of sherds stemming from various time periods. A comparison between our provisional fabric groups and those published by other researchers in Laconia shows that possible connections or matches between fabrics made by us should be considered either as tentative or as unreliable beyond the level of argued assumptions. To arrive at more reliable ceramic fabric connections, or the identification of similar fabrics, it will be necessary to publish not only textual descriptions and images of thin sections—as seems to be the common approach—but also series of high-resolution pictures of sherds and their fresh sections, as has been done in this article, together with more detailed descriptions of these sherds.