Parameters for the formation of orogenic gold deposits

Abstract

Orogenic gold deposits are the main source of gold for humanity. These deposits formed from the Archaean to Phanerozoic at crustal depths of more than 4 km. The key parameters accounting for their formation remain under discussion. I review these parameters in light of recent scientific advances using a systemic approach, where the relative pertinence of each component of a complex system in time and space is addressed. From the base to the top of the mineralising system, the following components and processes are reviewed: (1) the fluid sources; (2) the appropriate ligands and their sources; (3) the solubility of gold and its potential sources; (4) the function of faults as conduits; and (5) the mechanisms for precipitating gold. This review provides further support for the role of carbon-rich and pyritic sedimentary rocks in the formation of orogenic gold deposits throughout geological time.

Mineralogy and genesis of the Oleninskoe gold deposit (Kola Peninsula).

“…Отличает Оленинское месторождение от месторождений орогенического типа и состав рудообразующих флюидов. Согласно современным представлениям, в формировании орогенических месторождений золота определяющую роль играют растворы / флюиды метаморфогенного происхождения, эти флюиды характеризуются водно-углекислотным составом, близнейтральными значениями pH, низкой соленостью (Phillips, Powell, 2010;Gaboury, 2019;Zhu et al, 2011). Флюиды с указанными особенностями состава могут переносить золото в виде комплексов с HS -, такими как Au(HS) 0 и Au (HS)2 -, но они бедны цветными металлами и серебром.…”

“…Флюиды с указанными особенностями состава могут переносить золото в виде комплексов с HS -, такими как Au(HS) 0 и Au (HS)2 -, но они бедны цветными металлами и серебром. Поэтому под воздействием метаморфогенных флюидов формируются орогенические собственно золоторудные месторождения с низким содержанием минералов цветных металлов, типичная геохимическая ассоциация элементов в таких месторождениях включает Au, As, S, Sb, Te, W ± Ag, B, Bi, Co, Cu (Gaboury, 2019). Как показано выше в разделе 5.1, флюиды Оленинского месторождения характеризуются высокой и средней соленостью (до значений более 400 г/т) и высоким содержанием цветных металлов и серебра.…”

Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, North-central Nigeria, using airborne magnetic and gamma-ray spectrometry data

“…The mineral systems approach [48][49][50][51][52][53][54] can be employed to better understand hydrothermal alteration subsystem that is related to orogenic gold mineralization in the study area. Under dehydration and devolatilization metamorphic conditions, the presence of iron-rich mineral assemblage (pyrite, chalcopyrite, covellite, chalcocite, molybdenite, galena) and metapelitic minerals (chlorite, sericite, quartz, epidote, albite and calcite) present in phyllites and greenschists in the study area promoted the formation of metamorphic fluids and gold ligand (HS − ) [15,30,38,44,45,47,[55][56][57][58]. Due to melt/magma mixing, crystal segregation, adsorption, phase immiscibility and sulfur globulization during granitoid emplacement, the mixing of the oxidized magmatic fluids with the metamorphic fluids and gold ligands (HS − ) resulted to an increment in oxygen fugacity, thereby promoting the precipitation of orogenic gold minerals [15,30,40,47,52,53].…”

“…Under dehydration and devolatilization metamorphic conditions, the presence of iron-rich mineral assemblage (pyrite, chalcopyrite, covellite, chalcocite, molybdenite, galena) and metapelitic minerals (chlorite, sericite, quartz, epidote, albite and calcite) present in phyllites and greenschists in the study area promoted the formation of metamorphic fluids and gold ligand (HS − ) [15,30,38,44,45,47,[55][56][57][58]. Due to melt/magma mixing, crystal segregation, adsorption, phase immiscibility and sulfur globulization during granitoid emplacement, the mixing of the oxidized magmatic fluids with the metamorphic fluids and gold ligands (HS − ) resulted to an increment in oxygen fugacity, thereby promoting the precipitation of orogenic gold minerals [15,30,40,47,52,53]. Geologic structures such as faults, shear zones, fractures, and lithological contacts (where rheological contrast is significant) constitute migration pathways for the deepseated hydrothermal fluids comprising of gold thiosulfate complex [Au(S 2 O 3 ) 2 ] 3− to precipitate and localize gold minerals at higher crustal [30,53].…”

“…Even though geologic structures are critical to orogenic gold mineralization in the Kushaka schist belt and in other orogens in the world, it is not all geologic structures that exist in a geologically permissive field that are mineralized [15]. The manifestation of hydrothermal alteration haloes in a genetically endowed setting like the study area is an indication that auriferous mineralizing fluid has traversed through the geologic structures and deposited gold minerals [11,16].…”