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Происхождение высокосортной золотой руды, источник флюидных компонентов руды и генезис месторождений Мейкл и соседних месторождений Карлинского типа, Северный Карлин-Тренд, Невада
The Meikle mine exploits one of the world’s highest grade Carlin-type gold deposits with reserves of ca. 220 t gold at an average grade of 24.7 g/t. Locally, gold grades exceed 400 g/t. Several geologic events converged at Meikle to create these spectacular gold grades. Prior to mineralization, a Devonian hydrothermal system altered the Bootstrap limestone to Fe-rich dolomite. Subsequently the rocks were brecciated by faulting and Late Jurassic intrusive activity. The resulting permeability focused flow of late Eocene Carlin-type ore fluids and allowed them to react with the Fe-rich dolomite. Fluid inclusion data and mineral assemblages indicate that these fluids were hot (ca. 220°C),of moderate salinity (<6 wt % NaCl equiv), acidic, and H2S rich. Gold-rich pyrite formed by dissolution of dolomite and sulfidation of its contained Fe. Where dissolution and replacement were complete, ore-stage pyrite and other insoluble minerals were all that remained. Locally, these minerals accumulated as internal sediments in dissolution cavities to form ore with gold grades >400 g/t.
This book is intended for graduate students of the Earth Sciences who require a comprehensive examination of the origins of igneous rocks as recorded by the isotope compositions of the strontium, neodymium, lead, and oxygen they contain. Students who have not had a formal course in the systematics of radiogenic isotopes can acquire a basic understanding of this subject by a careful study of Chap. 1. Additional information is readily available in a textbook by Faure (1986). The primary purpose of this book is to demonstrate how the isotope composition of Sr, Nd, Pb, and 0 in igneous rocks has been used to shed light on the origin of igneous rocks and hence on the activity of the mantle and on its interactions with the continental and oceanic crust.
In this book the author attempts to provide up-to-date information about the geochemistry, exotic mineralogy, petrology, and experimental studies on ultrapotassic feldspathoid-bearing mafic and ultramafic rocks, which are quite distinct from the rocks of basalt family. The parental liquids for this intriguing group of rocks bear definite signature of their deep mantle source.
The stratiform deposits make up a special group of lead-zinc deposits possessing many common features in which they differ from the similar deposits of other industrial-genetic types. They are characterized by ores confined to strata of carbonate rocks, most frequently dolomites, by ore bodies of predominantly stratal form represented by impregnation ores of simple mineral composition, within which galena usually predominates over sphalerite (rarely the reverse), by the absence of magmatic rocks of similar age to the ore in the vicinity of the deposits,
Sometimes interest in the problem of the Moon’s genesis seems exaggerated. Why does this small celestial body, one of many in the solar system, attract so much attention?
First of all, the Moon genesis is part of the Earth genesis problem. Knowledge of our own planet, understanding of how and when its oceans and atmosphere came into existence, how and when the crust and the core of the Earth were formed, and how life originated on the Earth are not just academic issues; these are profound issues of human self-consciousness. Understanding the Earth’s genesis is impossible without solving simultaneously the Moon genesis problem.
The so-called ‘mesothermal’ gold deposits are associated with regionally metamorphosed terranes of all ages. Ores were formed during compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens. In both types of orogen, hydrated marine sedimentary and volcanic rocks have been added to continental margins during tens to some 100 million years of collision.
Franke, W., Haak, V., Oncken, O. & Tanner, D. Orogenic processes: quantification and modelling in the Variscan Belt McKerrow, W. S. & van Staal, C, R. The Palaeozoic time scale reviewed McKerrow, W. S., MacNiocaill, C., Ahlberg, P. E., Clayton, G., Cleal, C. J. & Eagar, R. M. C. The Late Palaeozoic relations between Gondwana and Laurussia Tait, J., Schatz, M., Bachtadse, V. & Soffel, H. Palaeomagnetism and Palaeozoic palaeogeography of Gondwana and European terranes Franke, W. The mid-European segment of the Variscides: tectonostratigraphic units, terrane boundaries and plate tectonic evolution Franke, W. & Zelazniewicz, A. The eastern termination of the Variscides: terrane correlation and kinematic evolution Belka, Z., Ahrendt, FI., Franke, W. & Wemmer, K. The Baltica-Gondwana suture in central Europe: evidence from K-Ar ages of detrital muscovites and biogeographical data Finger. F., Hanzl, P., Pin, C., von Quadt, A. & Steyrer. FI. P. The Brunovistulian: Avalonian Precambrian sequence at the eastern end of the Central European Variscides? Hegner, E. & Kroner. A. Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions
In Chapter 4 you looked at plate tectonics and its influence on the climate and habitability of the Earth. In this chapter you will look at a specific aspect of this relationship, namely mountain building. Mountain ranges attract their own microclimates, which tend to be cooler and often wetter than the lowland areas that surround them.
It may strike you as odd that temperatures drop as altitudes increase; after all, the higher the altitude, the closer the Earth’s surface is to the Sun. This is primarily because direct solar radiation causes very little heating of the air; most heating is due to radiation reflected back from the Earth’s surface. Furthermore, air forced to rise by the presence of a mountain will expand and cool in response to the decreasing atmospheric pressure. Eventually, any water vapour in the air will condense. forming clouds and precipitation, which at high altitudes may fall as snow. Even at low latitudes, high mountains may be capped with snow or ice (Figure 5.1). <...>
The term geophysical refers to the workings of the earth. This includes movements on the earth’s surface (crust) as well as beneath the surface. These movements can be hazardous for humans such as when earthquakes and volcanic eruptions occur. Earthquakes and volcanoes occur in the earth’s lithosphere. This is the solid zone of rock on the earth, including the crust and the upper part of the mantle, that extends downwards from the earth’s surface to a depth of about 70 kilometres.
