The Bulletin lode-gold deposit is within the northernmost part of the Norseman-Wiluna greenstone belt in me Archaean Yilgarn Block, Western Australia. It is located within a brittle-ductile shear zone and hosted by tholeiitic metavolcanic rocks. Syn-metamorphic wallrock alteration envelops the gold mineralisation and is pervasive throughout the entire shear zone and extends up to 150 m into the undeformed wallrocks. Alteration is characterised by the sequence of distal chlorite-calcite, intermediate calcite-dolomite, outer proximal sericite and inner proximal dolomite-sericite zones. The thickness of the alteration envelope, and the occurrence of dolomite in the alteration sequence, can be used as a rough guide to the width, extent and grade of gold mineralisation, because a positive correlation exists between these variables. Mass transfer evaluations indicate that chemical changes related to the wallrock alteration are similar in all host rocks: in general, Ag, As, Au, Ba, C02, K, Rb, S, Sb, Те and W are enriched, Na and Y are depleted, and Al, Cr, Cu, Fe, Mg, Mn, Nb, Ni, P, Se, V, Zn and Zr are immobile, while Ca, Si and Sr show only minor or negligible relative changes. The degree of mobility of each component increases with proximity to gold mineralisation. The largest potential exploration targets are possibly defined by regional As (>6 ppm) and Sb (>0.6 ppm) anomalies. These anomalies, if real, extend laterally for > 150 m from the mineralised shear zone into areas of apparently unaltered rocks. Anomalies defined by Те (> 10 ppb), W (>0.6 ppm), carbonation indices, local enrichment of Sb (>2.0 ppm) and As (>28 ppm), and potassic alteration indices also form significant exploration targets extending beyond the HJB shear zone and the Au anomaly (>6 ppb) and, locally, into apparently unaltered rock. Gold, itself, has a restricted dispersion, with an anomaly extending for 1-35 m from ore, and being restricted to within the shear zone itself. Amongst individual geochemical parameters, only As and Sb define significant, consistent and smooth trends (vectors) when laterally approaching the ore. However, the respective dimensions of individual geochenucal anomalies can be used as an extensive, though stepwise, vector towards ore

No single model satisfactorily accounts for the diverse characteristic of Fe-oxide-rich hydrothennal systems. Consideration of a spectrum of geologically reasonable models gives insight into the origins of variability among these deposits. Key features that need to be rationalized by any model are the abundance of hydrothermal magnetite and/or hematite, the chemically distinct suite of elements (REE-Cu-Co-Au-Ag-U), the variability of associated magmas, the distributions and volumes of associated hydrothennal alteration, and the broader geologic setting(s).

Geologic and geochemical evidence show that the ore-fonning fluids are brines, but the source of the brines is controversial. Multiple sources are possible, indeed likely. The identity and consequences of alternative sources - magmatic and non-magmatic are considered: First, by a review of plausible fluids and general consequences, second, by examination of the system characteristics, third, by specific consideration of the consequences of alternative models, and fourth, by consideration of selected systems where non-magmatic brines must play a major role.

We review some of the key characteristics of different types of hydrothermal Fe-oxide-rich(-Cu-Au) systems. Some are economic; many are only geochemically anomalous. Two end-members and several variants on these end members are proposed. One group is typified by relatively high-temperature mineralization, and relatively high K/Na and Si/Fe in the alteration. We suggest that these features (and others) are distinctive of magmatic fluid sources and that this group overlaps with porphyry Cu-Au and related deposit types. A second, broad group is typified by more oxide-rich, sulfide-poor mineralization, low Si/Fe ratios, and voluminous alkali-rich alteration where sodic types commonly exceed K-rich varieties. We suggest that the key features of this group reflect involvement of non-magmatic brines and that ore grades are less common as the metals are less easily trapped. Hybrid examples, where fluids of both types are involved, are expected (and known).

Conceptual and quantitative models of magmatic and non-magmatic fluid sources yield insight into the expected differences, the source and distribution of metals within these systems, and possible controls on ore deposition. These models highlight the difference between magma-sourced fluids and non-magmatic fluids. The former tend to be focused at the tops of magma chambers and have a built-in depositional mechanism -cooling. The latter require a different type of focusing mechanism - structural or stratigraphic, and different traps - mixing, specialized host rocks, and/or boiling. These models predict consistent differences in mineral assemblages, metal contents, alteration volumes, zoning, paragenesis, and geochemistry. For magmatic fluid sources, the models reproduce the key characteristics of that group, notably the porphyry-related systems. For non-magmatic brine sources, predicted characteristics match well with observations of Fe-oxide-rich systems in environments where these fluids are known to dominate, including mafic igneous systems and modem analogs such as the Salton Sea. These cases show that Fe-oxide (-Cu-Au-REE-Co) enrichments can result from non-magmatic sources. In other environments (e.g., with intermediate to felsic igneous rocks; settings deeper than ~5 km) the relative importance of various fluid sources and their consequences for mineralization remain to be fully explored. Young systems in the American Cordillera and elsewhere can help unravel the many threads that relate these enigmatic mineral deposits.

The Upper Cretaceous rocks of southeastern Vancouver Island contain important coal deposits, which have been known for more than a century and have long provided British Columbia with a major industry. Gradual depletion of the more accessible reserves has resulted in efforts both by company officials and, from time to time, by Government geologists, to acquire additional structural and stratigraphic information that might serve to prolong the life of these deposits <...>

This book focuses on the first vertebrates to conquer the land, and on their long journey to become fully independent from the water. It will trace the origin of tetrapod features and try to explain how and why they transformed into organs that permit life on land. The classic idea of early land vertebrates is that they were similar to modern amphibians. Right or wrong, the vast majority of early tetrapods are therefore classified as amphibians (or more precisely their stem taxa). Accordingly, this book is centered on early amphibian evolution, a topic that effectively includes all early tetrapods, and it will also analyze facts and opinions on the origins of modern amphibians. The major part of the story covers events that occurred over the past 370 million years, but it is far from restricted to paleontology.

My own motivation to study the amphibian fossil record derives in large part from a fascination with the development, ecology, and evolution of their modern representatives. Therefore I consider many topics that can only be covered by examination of extant animals: features of the soft body, functions of organs that mediate breathing, feeding, hearing, and locomotion, the morphogenesis of body parts, larval development, metamorphosis, and ecology.