Three of the world's largest Cu-Mo deposits, Los Pelambres, Rio Blanco-Los Bronces and El Teniente, formed in close temporal association with southward migration of the locus of subduction of the Juan Fernandez Ridge and the resultant decrease in subduction angle below central Chile during the Miocene and Pliocene. All three contain large Cu-mineralised magmatic-hydrothermal biotite itourmaline ±anhydrite breccia pipes generated by exsolution of saline, high-temperature fluids from crystallising magmas. Sr, Nd, Pb, S, Os, 0 and H isotopic data indicate that the metals these breccias contain, and aqueous fluids responsible for their emplacement, were derived from the same magmas that produced igneous rocks associated with each deposit. Isotopic data are consistent with derivation of these magmas from subduction-modified subarc mantle, and suggest that formation of these deposits did not involve either dehydration or melting of continental crust. Each deposit formed by multiple mineralising events occurring over a >2 m.y. period during which there is no evidence for coeval volcanic activity. Assuming an average Andean magma with 100 ppm Cu, the original lOOxlO6 tonnes of Cu in each deposit prior to erosion requires a parent body of magma with a batholith-size dimension of approximately >600 km3. We suggest that the multiple Cu-mineralised breccia pipes in each deposit were generated by exsolution of magmatic fluids from the roofs of large, long-lived, open-system magma chambers, crystallising at depths of >4 km below the palaeosurface as indicated by

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.

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.

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). <...>