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Diversification of skeletal microstructures of organisms through the interval from the latest precambrian to the Early Cambrian

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Science China Earth Sciences 2003年第10期46卷 977-985页

作者：冯伟民陈哲孙卫国 Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences and State Key Laboratory of Palaeo-biology and Stratigraphy NIGPAS Nanjing 210008 China

Research on early skeletal fossils of southern Shaanxi Province and easternYunnan Province shows that the interval from the latest precambrian to the Early Cambrian was animportant period of significant changes in biomineralization of various organisms. The latestprecambrian skeletal fossils, represented by Cloudina, are characterized by cone-in-cone structures,relatively high content of organic matter, and various shell shapes with obvious plasticdeformation. In the Early Cambrian the skeletal organisms, consisting of phosphatic, carbonate andsiliceous minerals, began to appear in great abundance and to distribute widely. Moreover,microstructure of these skeletal organisms appeared to have been diversified, for example, maintypes of recent molluscan microstructures, such as prismatic, lamello-fibrillar and regular foliatedstructures, were already developed at that time; fibrous structures further diversified, such aslamello-fibrillas indicative of mollusks and fibre bundles of hyoliths; there were at least twolayers in a shell. This shows that biologically controlled biomineralization had played the mainrole in the Early Cambrian and it laid a key foundation for formation of the true shell of diverseinvertebrates, giving rise to the 'Cambrian explosion'.

关键词： precambrian, Early Cambrian, skeletal microstructure diversification, biomineralization.

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Gold-Platinoid Mineralization of Metasomatically Altered Ultramafites in precambrian Protrusions of Mamynsky Geoblok

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Global Geology 2003年第2期8卷 160-165页

作者： V.G.Khomich V.P.Molchanov N.G.Boriskina Geological Institute of the Far Eastern Branch Russian Academy of Sciences Vladivostok 690022 RussiaGeological Institute of the Far Eastern Branch Russian Academy of Sciences Vladivostok 690022 RussiaGeological Institute of the Far Eastern Branch Russian Academy of Sciences Vladivostok 690022 Russia

On the contiguous territories of Russia and China, along the left and right banks of the Amur River (Heilongjiang Province of China, and Amur Oblast’ of Russia), several precambrian protrusions (Gonzhinsk, Mamynsk, Amurkhe, and Khumakhe) are known. On the Russian territory, along the setting and on the area of the protrusions, lode manifestations, precious-metal deposits, and gold-platinoid placers are known having the industrial importance. Ultramafites are metasomatically altered more likely by the action of the Late Paleozoic intrusions and produced by them hydrothermae, and are transformed into listvenites. It can be concluded that as one of the sources of precious metals in the placers were the aureoles of listvenitization. This is evidenced by the presence of talc (typomorphic mineral of apoultrabasites) inclusions together with Pt-, Pd- and Ir-bearing gold in the corrosive coatings of the primary platinoids. This conclusion requires the revision of the work strategy of prospecting the lode gold and PGE manifestations within the ore-placer node because apoultrabasites before were considered non-promising for precious metals.

关键词： ultramafites, gold-platinoid, mineralization, precambrian, AmurRiver

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