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Petrographic Study (petrographic + study)
Selected AbstractsMultiple Sources of Metals of Mineralization in Lower Cambrian Black Shales of South China: Evidence from Geochemical and Petrographic StudyRESOURCE GEOLOGY, Issue 1 2008Jan Pa Abstract Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni-Mo-platinum group elements (PGE)-Au phosphate- and sulfide-rich ores. These are confined to a ,0.2-m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate- and organic matter-rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100-fold), As (up to 97-fold), Mo (up to 95-fold), Sb (up to 67-fold), Rh (up to 49-fold), Cu (up to 37-fold), Pd (up to 33-fold), Ru (up to 24-fold), Zn (up to 23-fold), Pt (up to 21-fold), Ir (up to 15-fold), Co (up to 14-fold), and Pb (up to 13-fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21-fold) and Ni (12-fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (Corg) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni-, V-, Cr-, and Cu-enriched phosphate-rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal-rich hardground during weathering. The polymetallic Ni-Mo-PGE sulfide-rich ore bed is interpreted to represent a remnant of shallow-water hardground horizon rich in metals, which originated in a sediment-starved, semi-restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi-restricted basin, resulted in the formation of dense metalliferous brines; co-precipitation of metals together with phosphates and sulfides occurred at or above the oxic,anoxic sediment interface. Metal-enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni-Mo-PGE-Au sulfide ore bed, economic sedimentary exhalative (SEDEX)-type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX-type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni-Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals. [source] Reclassification and thermal history of Trenzano chondriteMETEORITICS & PLANETARY SCIENCE, Issue 12 2007A. M. FIORETTI The quenched intracrystalline Fe2+ -Mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature Tc, thus yielding useful constraints on the last thermal event undergone by the host rock. The orthopyroxene Tc of 522 ± 13 °C, calculated using a new calibration equation obtained by Stimpfl (2005b), is higher than in previously published H chondrite data. The orthopyroxene cooling rate at this Tc is about 100 °C/kyr. This fast rate is inconsistent with the much slower cooling rate expected for H6 in the onion shell structural and thermal model of chondrite parent bodies. A petrographic study carried out at the same time indicated that the Trenzano meteorite is an H5 chondrite and not an H6 chondrite, as it is officially classified. Furthermore, the two-pyroxene equilibrium temperature of Trenzano (824 ± 24 °C), calculated with QUILF95, is similar to the two-pyroxene temperature of 750,840 °C obtained for the Carcote (H5) chondrite (Kleinschrot and Okrusch 1999). [source] Gabbroic clay sources in Cornwall: a petrographic study of prehistoric pottery and clay samplesOXFORD JOURNAL OF ARCHAEOLOGY, Issue 3 2004Lucy Harrad Summary., This analysis of prehistoric pottery and clay samples from Cornwall demonstrates that the clay used to make Cornish gabbroic pottery in prehistory originated around the gabbro rock outcrop in a small area of the Lizard peninsula. The research uses petrographic and chemical analysis to subdivide the prehistoric pottery into six groups. Owing to the unusual geology of the Lizard these groups can be attributed to specific locations. The most abundant pottery fabric, Typical Gabbroic, was made using coarse clay which is mainly found in a 1 km2 area near Zoar. A finer version of this clay, found higher in the soil profile or slightly transported and redeposited, was used to make Fine Gabbroic pottery and an even finer variant called FNS (Fine Non-Sandy) Gabbroic. We identify for the first time here a Loessic/Gabbroic pottery fabric which can be matched exactly to clay found at Lowland Point. Serpentinitic/Gabbroic pottery was made using clay from the gabbro/serpentinite border zone. Pottery made from the Granitic/Gabbroic fabric did not match any clay from the Lizard, showing that gabbroic clay was sometimes removed and made into pottery elsewhere in Cornwall. The main clay source near Zoar was used for clay extraction throughout the Bronze Age and Iron Age for pottery which was traded all over Cornwall. Other gabbroic clay sources produced pottery only during certain periods and exclusively supplied particular settlements, such as the Loessic/Gabbroic fabric which was found only at Gear and Caer Vallack. The results suggest that pottery was produced by several small-scale cottage industries, which may have operated on a seasonal, part-time basis and probably formed only part of a wide range of activities located around the Lizard area. [source] ON THE WHITE AND COLOURED MARBLES OF THE ROMAN TOWN OF CUICUL (DJEMILA, ALGERIA)ARCHAEOMETRY, Issue 4 2010F. ANTONELLI This paper reports the results of an archaeometric study of the local and imported marbles found in the Roman town of Cuicul (now Djemila, Algeria), a research project funded by the Sixth Framework Programme of the European Union. Of the few imported coloured lithotypes that have been found, four are of Greek origin and one was imported from Asia Minor. In addition, two other classical Roman coloured stones found on the site are probably of local North African origin (most likely one from Numidia and one from Algeria). With regard to the grey and white marbles employed in the statuary and architecture, petrographic study in thin section and the ,13C and ,18O isotopic data emphasize the frequent use of the local fine-grained lithotype from Filfila (Skikda) together with imported Greek lithotypes (i.e., Pentelic marble, the dolomitic variety of Thasian marble, and Parian marble from Lakkoi) as well as different varieties of the so-called ,greco scritto', whose provenance in some cases still remains uncertain. In fact, the petrographic and geochemical features of the marbles do not always match those known for the classical ,greco scritto' from the quarry of Cap de Garde, near Annaba (Algeria). [source] TOWARDS A QUANTITATIVE PETROGRAPHIC DATABASE OF KHMER STONE MATERIALS,KOH KER STYLE SCULPTUREARCHAEOMETRY, Issue 2 2010F. CARÒ A comprehensive quantitative petrographic database of sandstones used by the Khmers for sculptural purposes would be a helpful tool for archaeologists, museum curators and others interested in pursuing research on early stone usage, geological source and provenance. Towards that end, this paper presents quantitative petrographic analysis of stone materials used in the production of some free-standing sculptures and architectural elements in the Koh Ker style of the 10th century from the collections of the National Museum of Cambodia and The Metropolitan Museum of Art. These materials are compared to samples from the quarry of Thmâ Anlong near the foothills of the Phnom Kulen, Sieam Reap province. Primary and secondary detrital modes and key grain-size parameters are used to identify three sandstone types. The free-standing sculptures are carved from feldspathic arenite and feldspato-lithic to litho-feldspathic arenite. Finely carved lintels are worked from a quartz arenite, which is significantly richer in quartz grains and of a finer grain size. The geological source of the two other lithotypes will have to await detailed geological survey of the Koh Ker area accompanied by petrographic study of selected samples from documented quarries. The significance and potentiality of quantitative petrographic study of Khmer stone materials are shown in supporting and integrating archaeological investigations in South-East Asia. [source] PHYSICOCHEMICAL COMPOSITIONAL ANALYSIS OF CERAMICS: A CASE STUDY IN KENTING, TAIWAN,ARCHAEOMETRY, Issue 4 2006MAA-LING CHEN The composition of ceramics does not just reflect the component of some specific, unprocessed, geological, raw material source, but also certain forms of human behaviour involved in its manufacture. The purpose of this research project is to apply the acid-extraction chemical method, complemented by a thin-section petrographic study, to the compositional analyses of certain local ceramic collections (mainly from several sites in the southern Taiwan area). The results present the raw materials that the ceramic manufacturers of the two cultural traditions (O-laun-pi Phase II and Phase III,IV), which overlapped temporally, used. These materials came from the same sources, but the ceramics were manufactured in different ways. Particularly, the people of O-laun-pi Phase III,IV also procured certain materials from either local sources or from somewhere in eastern Taiwan to make their pots. The results also indicate that there might have been a variation in terms of their manufacture among sites of the same cultural tradition. [source] THE ALPS,A BARRIER OR A PASSAGE FOR CERAMIC TRADE?*ARCHAEOMETRY, Issue 2 2005M. MAGGETTI The Alpsas a barrier: ceramic remnants of the so-called Laugen-Melaun culture (c. 11th to c. sixth centuries bc) can be found in the northern Italy (Trentino/Alto Adige),eastern Switzerland,Liechtenstein and western Austria region. A petrographic study of 454 sherds from this area covering a time span of 500 years reveals the following. (1) The pottery from the Trentino/Alto Adige contains a predominantly volcanic temper, which can be linked to the volcanic rocks of the Bolzano area,in other words, to the core region of this culture. This material is therefore of a local/regional production. (2) These ceramics were imported from the Bolzano region to southeastern Switzerland (the Inn Valley) and the amount of imported pottery decreases markedly from the 11th century bc (approximately 70% imported) to the seventh to sixth centuries bc (approximately 10% imported). (3) No imported pottery can be detected north of the Alpine crest in Switzerland, Liechtenstein and Austria, and in this region serpentinite temper was preferred by ancient potters. These results demonstrate that long-lasting contacts and ceramic trade existed between the populations of the Inn Valley and the Trentino/Alto Adige. Such contacts could have been motivated by intermarriages between the two populations and/or economic exchange. The potters north of the Alpine ridge adopted the Laugen-Melaun style and produced such pottery locally. The use of serpentinite temper is puzzling and not related to any technological advantage. (Could it be recycled material? Or does it have any sociocultural specificity?) The Alps as a passage: 59 fragments of a black gloss ware, the so-called Campana, unearthed at 11 Late Latene sites (second to first centuries bc) in Switzerland and neighbouring Germany were analysed chemically by X-ray fluorescence. The results revealed: (1) that all of them were produced either in Italy or Lyon and then exported to the north; (2) that two principal south,north exchange routes existed, (a) fluviatile, along the Rhône,Rhine corridor and (b) trans-Alpine, using the Alpine passes, such as the Simplon and the Grand St Bernard. [source] | ||||||||||