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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.
Агатова А.Р., Непоп Р.К. Сейсмотектоническая активность как триггер солифлюкционно-оползневых процессов в высокогорной части Алтая в позднем плейстоцене – голоцене Алексеев Н.Л., Богомолов Е.С., Сергеев С.А., Каменев И.А., Егоров М.С. Тектоно-термальная эволюция метаморфического комплекса островов Реуер (Восточная Антарктида) в позднем докембрии – раннем палеозое Андреев Г.П. Вскрываемая «физика геологии». Резонансная природа цикличности седиментогенеза Артамонов А.В. Влияние разломообразования на формирование внутриплитных тектоно-магматических структур Артюшков Е.В., Чехович П.А. Ретроградный метаморфизм в докембрийской коре и его роль в плиоцен-четвертичных поднятиях Архипова Е.В., Жигалин А.Д., Гусева И.С., Гусева А.С. Системное сейсмотектоническое взаимодействие горизонтов литосферы Восточной Сибири и Дальнего Востока
Маринин А.В., Тверитинова Т.Ю. Строение и тектонические напряжения Туапсинской сдвиговой зоны Мелик-Адамян Г.У. Начальные стадии позднеорогенного тектогенеза Армении в свете современных биостратиграфических представлений Мельниченко Ю.И., Съедин В.Т., Обжиров А.И., Шакиров Р.Б., Лепешко В.В. Вулканотектоника и особенности геодинамики Японского и Охотского морей Минц М.В. Неоархей-протерозойский суперконтинент (2.75-0.9 млрд лет): альтернатива модели суперконтинентальных циклов 17 Михеев Е.И., Владимиров А.Г. Корреляция и геодинамическая интерпретация метаморфизма и гранитоидных комплексов Ольхонского региона (Прибайкалье) и п-ова Святой Нос (Забайкалье) Монастырев Б.В. Сейсморазведочная модель севера ЗападноСибирской геосинеклизы в аспекте теории рифтогенеза
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