This book is a photographic introduction to metamorphic rocks. It is meant to be a survey of mostly typical metamorphic rocks, minerals, and structures as they appear in the field, and the metamorphic processes that make them. Its purpose is to help guide the eye of any student of geology to better see the geologic features in metamorphic rocks that might otherwise remain invisible or obscure. This book is a training tool, one of many, to help budding geologists of metamorphic rocks, young and old. <...>

A rapid field method for gold analysis in geochemical exploration has been developed. Cold extraction of Au, at room temperature, using a mixture of sodium bromide, sulphuric acid, hydrogen peroxide is performed; the technique has the advantage of avoiding the irritating odour of commonly used aqua regia digestion. Polyurethane foam is used to concentrate gold from solution. After desorption of Au using mixed reagents (0.5% Na2S03-NaCl solution at pH 8), two sequential procedures, depending on the concentration, are followed for the determination of gold. (1) A 1 mL portion of desorbed solution is used to form Au-TMK-DBS (Thio Micher's Ketone and dodecyl benzene sodium sulphonate) ternary complex. Concentrations below 20 ng/g Au are determined by visual colour comparison of the organic layer with a series of standards. (2) If the concentration is greater than 20 ng/g Au, a complexation reaction using the same reagents is followed by fibre-optic colorimetry. The method is rapid and simple, and the tiresome operation of ashing the foam is avoided. The limit of detection is 0.5 ng/g Au and eighty determinations can be made in one working day. The method could be used for rapid follow-up of rock sample or in situ drill core analyses. About 600 samples from 5 gold districts were tested by this method. The results are very satisfactory.

The Urals orogen represents the site of Palaeozoic oceanic crust creation and subsequently a zone of arc development, arc-continent collision, continent-continent collision and post-orogenic collapse. The orogen is host to a number of world-class VMS deposits in the Silurian to Devonian arc sequences but in addition is host to highly significant iron oxide deposits of both hydrothermal and orthomagmatic origin. The hydrothermal ores are developed in Palaeozoic belts associated with rift-related, dominantly mafic, largely subaerial, alkaline volcanism intruded by comagmatic stocks of varying ages, from the Late Silurian to Early Carboniferous. Volcanism, sedimentation and mineralisation all seem to be controlled by major N to NNE trending structures. Much of the mafic volcanic sequence shows hematisation, which is evidence of early oxidation of the lava-tuff packages. Mineralisation comprises massive and disseminated magnetite bodies with elevated REE and ubiquitous accessory apatite. The deposits can be huge, as for example the giant Carboniferous Kachar deposit in Kazakhstan with reserves of over a billion tonnes of >45% Fe are defined. Some of the bodies are true contact skarns developed at the interface between intrusive bodies and volcano-sediments which include limestones. Other bodies, including Kachar, are distal to any possible related intrusions and are developed within regionally extensive scapolite alteration zones. A regionally consistent pattern of early feldspar ± biotite alteration followed by ore-stage pyroxene-garnet-scapolite followed by late hydrous silicate-carbonate alteration is repeated throughout the Urals. Regionally extensive scapolitisation is common in most of the belts. Base metals are generally present in the deposits, often appearing late in the paragenetic sequence, with some bodies having near economic copper grades (0.6% Cu) and significant precious metals.

Two Himalayan porphyry copper-molybdenum-gold belts have been developed in the eastern part of the Himalayan-Tibet orogenic zone related to the collision between the Indian and Asian Plates. Both were accompanied by the emplacement of high-level intracontinental, alkali-rich, potassic felsic magmas which produced a huge Cenozoic belt of potassic igneous rock. The emplacement of these magmas was controlled by large-scale strike-slip fault systems, orientated roughly orthogonal to the of the Indo-Asian continental convergence, which adjusted the collisional strain. The Jomda-Markam-Xiangyun copper-molybdenum belt is the western of the two, developed along a narrow zone following the Nanqian thrust, the Jinshajiang fault system, and the Red River shear zone, whereas the eastern, the Zhongdian-Yanyuan-Yao'an porphyry copper-gold-silver belt, was developed along the western margin of the Yangtze Craton. The ore-bearing porphyries have compositions which include granite, monzogranite, and monzonite, with a small amount of quartz-syenite porphyry. They are distinguished from barren porphyries by their higher Si02 (>63 wt %), lower Y (<20 ppm) and their adakitic magma affinity. All alkali-rich porphyries are relatively enriched in large-ion lithophile elements (K, Rb and Ba) and depleted in high-field strength elements (Nb, Ta, Ti and P) with a wide range of Nb/Y ratios.