Оценка геохимических методов исследования почв для обнаружения медно-золотой порфировой минерализации в четвертичных ледниково-флювиальных отложениях в зонах WBX-MBX и 66, гора Миллиган, северо-центральная часть Британской Колумбии.

This study is the second and final part of a Geoscience BC funded project (Project 2009-19) carried out by the author to test the effectiveness of a variety of commonly used chemical extractions at detecting mineralization through thick Quaternary glaciofluvial cover. In the first part carried out at the Kwanika Central Zone (Heberlein and Samson, 2010), results showed that conventional soil sampling (an aqua regia digestion of -80 mesh screened, upper B horizon) is ineffective at detecting the buried mineralization. Furthermore, laboratory specific extractions like MMI-M (SGS) and Ionic Leach (ALS-Chemex), Enzyme Leach and Bioleach (Actlabs) also performed poorly.

Age-frequency data are used to determine amounts of vertical tectonic displacement experienced by the global population of orogenic gold deposits following their emplacement at a crustal depth of 10 ± 1 km. Knowledge of this tectonic dispersion allows for an estimate of the total crustal endowment of gold in orogenic gold deposits. This estimate is based on a compilation of data on 365 orogenic gold deposits, of which gold contents are available for 314 deposits and good age control is available for 126 deposits. Ages of well-dated
 deposits form three clusters that range in age from 47 to 850 Ma (primarily Phanerozoic; 69 deposits), 1730 to 2090 Ma (Proterozoic; 13 deposits), and 2540 to 3107 Ma (Archean; 44 deposits).

Магматические гидротермальные флюиды в осадочных вмещающих породах, связанное с интрузиями золо-медное месторождение Телфер, Ороген Патерсон, Западная Австралия: Ограничения давления, температуры и состава рудообразующих флюидов

The Neoproterozoic Telfer deposit, one of Australia’s largest gold-copper deposits, is located in the Paterson orogen. Several highly differentiated calc-alkaline to alkali-calcic peraluminous granites intruded the metasedimentary rocks near (5–20 km) Telfer contemporaneously with structurally controlled gold-copper mineralization. Fluid inclusion assemblages with different fluid inclusion types were identified in samples from a range of different vein types.

A metamorphic devolatilization model can explain the enrichment, segregation, timing, distribution and character of many goldfields such as those found in Archean greenstone belts, slate-belts and other goldonly provinces. In this genetic model, hydrated and carbonated greenschist facies rocks, particularly metabasic rocks, are devolatilized primarily across the greenschist–amphibolite facies boundary in an orogenic setting. Devolatilization operates on the scale of individual mineral grains, extracting not just H2O and CO2 but also S and, in turn, Au.

The continuum model has been one of the more widely advocated genetic models for ‘gold-only’ deposits such as those found in Archaean greenstone belts. It postulates that hydrothermal gold deposits were formed throughout a 20–25 km vertical crustal profile, from temperatures above 700 °C to below 180 °C, and that the deposition occurred synchronous with the peak of metamorphism. The continuum model is reviewed at this stage because we believe that it does not successfully account for many aspects of gold deposit formation.

The Hattu schist belt is an emerging gold-producing ore district in the western part of the Archean Karelian Province of the Fennoscandian Shield. The belt consists of 2.76 to 2.70 Ga tonalite, granodiorite, and leucogranite intruded into a mafic-felsic epiclastic-volcanic sequence of an only slightly older age. Complex and successive folding, shearing, and hydrothermal processes affected these rocks prior to the lower amphibolites facies peak metamorphism (550° ± 50°C; 3–5 kbar) at ca. 2.70 Ga. Orogenic gold deposits are hosted by the highly strained zones that developed during the Archean deformation of the belt. However, previous K-Ar and Rb-Sr geochronological studies indicated that a second tectonothermal overprint affected the Hattu schist belt between 1.7 and 1.8 Ga during the Svecofennian orogeny.

Accretionary orogens are the sites of long-lived convergent margin tectonics, both compressional and extensional. They are also the hosts to the majority of the world’s important gold deposits. A very diverse range of deposit types occurs within accretionary orogens, commonly in close proximity in space and time to each other. These include porphyry and associated high-sulphidation Au–Cu–Ag deposits, classic low-sulphidation Au–Ag deposits, low-sulphidation Au deposits centred on alkalic intrusive complexes, Carlin-type Au deposits, Au-rich volcanichosted massive sulphide deposits, orogenic Au deposits, intrusion-related Au deposits and iron oxide Cu–Au deposits. Empirical patterns of spatial distribution of these deposits suggest there must be fundamental generic controls on gold metallogeny.

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.

This book will address three primary metals and their associated metals. The primary metals are Platinum Group of Elements or Metals (PGE or PGM), nickel, and chromium. The associated metals include copper, gold, silver, and cobalt. The platinum group consists of six metals and occurs naturally in close association with one another as well as with nickel, chromium, copper, and cobalt. The group of metals represents a unique geological process having a common source of metal supply and a genetic model. The PGM is among the least abundant group of elements of the Earth’s element family.

History and Genesis of Deposits is the product of an effort by the Society of Economic Geologists to publish materials that will expand knowledge concerning timely, specific topics important to the study of economic geology and to economic geologists. A volume on gold was selected for a general review-type publication because of the importance of the gold mining industry in the 1980s. The officers and council of the Society of Economic Geologists authorized the preparation of this book on gold in 1981, and Dr. Robert W. Boyle was selected as its author.