На своей тридцать четвертой сессии бывший Комитет по газу Европейской экономической комиссии Организации Объединенных Наций, рассмотрев вопрос о развитии газового сектора, постановил обновить прежний ’’Глосссарий по запасам природного газа и экономике их эксплуатации”, опубликованный голландской компанией Rijks Geologische Dienst. В основу нового варианта этого глоссария положены результаты работы Совещания экспертов по ресурсам природного газа, и в частности подготовленный правительством Нидерландов документ GAS/GE.4/R. 31/Add.7, а также проект сводного доклада ’’Классификация запасов и ресурсов природного газа” (ENERGY/WP.3/GE.l/R.l/Rev.l), подготовленный правительством бывшего Союза Советских Социалистических Республик, и окончательный вариант руководства ’’Составление классификации скважин” (GAS/GE.4/R. 26/Add.l/Rev.4), представленный правительством Австрии. Совещание экспертов по ресурсам природного газа постановило распространить настоящий глоссарий на своей восемнадцатой сессии в июне 1995 года. Глоссарий был подготовлен докладчиком от Германии.

I have been teaching Structural Geology and Tectonics for the past four decades and during this period, I always felt a need for a glossary or definitional dictionary devoted to this branch. I therefory, made an attempt in this direction. The editor for while doing the groundwork of the book made use of Glossary of Geology edited by R. Bates & J. Jackson (Am. Geo!. Inst., 1980); Glossary of Geology in Hindi edited by myself (CSTT Govt. of India 1996); Introduction to the structure of the earth by E. Spencer; Tectonic Geology by myself (2006); Geology: an Introduction by myself (2004).

Classifications of ore deposits provide essential frameworks for designing exploration strategies, evaluating prospects, and performing resource assessments of selected areas. A rational geological classification of the commonly recognized lode gold deposits is feasible if it is based on the geological settings of the deposits, host rocks, nature of mineralization and geochemical signature.

Newly recognized gold-rich sedimentary-exhalative (sedex) mineralization in Nevada, with an average gold grade of 14 g/tonne (t), and the occurrence of significant amounts of gold in classic sedex deposits like Rammelsberg, Germany (30 Mt at 1 g/t), Anvil, Canada (120 Mt at 0.7 g/t), and Triumph, Idaho (? at 2.2 g/t) demonstrate that basin brines can form gold ore. The sedex Au mineralization in Nevada represents a previously unrecognized end member in a spectrum of sedex deposits that also includes large Zn-Pb, intermediate Zn-Pb-Ba ± Au, and barite deposits. Study of ore deposits, modern brines, and chemical modeling indicates that variation in metal ratios and their abundance in sedex deposits are dominantly controlled by the concentration and redox state of sulfur in brines. For example, Au and Ba solubilities are highest in H2S-rich, SO4-poor fluids, whereas base metal solubilities are highest when H2S is not present. Chemical modeling indicates a typical reduced brine (15 wt % NaCl equiv, pH = 5.5, H2S = 0.01 m) at 200°C is capable of transporting as much as 1 ppm Au in solution.

The H2S content in brines is controlled by the rate of its production through thermochemical reduction of sulfate by organic matter and the rate of its removal from the fluid through the sulfidation of reactive Fe in the sediments. Thus, sedimentary basins with high organic carbon and sulfate in rocks low in reactive Fe, such as carbonates and shales, are most likely to produce H2S-rich brines that may form gold-rich sedex deposits. Because of the tremendous scale of sedex hydrothermal systems, evidence that basin fluids can transport gold identifies a new mechanism for concentrating gold in sedimentary basins and opens extensive areas to further gold exploration.