Gold, platinum and palladium enrichments in arcs: role of mantle wedge, arc crust and halogen-rich slab fluids

Abstract

Arc-related magmas are frequently enriched in Au, Pt and Pd in respect to MORB and OIB igneous suites. Magmatic arcs commonly host large-scale hydrothermal Au and Au-Cu and PGE mineralization related to young volcanic systems and zoned ultramafic complexes respectively. Island-arc mantle xenoliths show Au, Pt, Pd enrichments related to mantle wedge metasomatism by slab-derived fluids. Long-lived plumbing systems in arc crust (arc magma chambers) show further enhancement of Au, Pt and Pd enrichments through subduction-related metamorphic and metasomatic processes in the presence of halogen-rich, aqueous fluids. We propose that Au-Pt-Pd enrichments in arcs are caused by mantle wedge-slab interactions followed by differentiation and metamorphism of magmatic conduits in arc crust.

Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

“…The data presented above suggest an initially magmatic origin for gold-bearing alloys in iron-oxide ore and associated volcanic rocks from the LKR deposits and emphasizes role of liquid immiscibility processes in precious metal evolution in mineralized volcanic systems. However, possible trigger mechanisms and conditions necessary for separation of precious metal phases from silicate, sulfide and sulfide-silicate melts still remain quite enigmatic [16,35,38,39,44,48,49,52]. Previous studies suggest that gold crystallizes from silicate melt as native element or intermetallic compound (typically with copper and silver) [14][15][16][17]39,47,48,99], or as a minor component in base metal sulfides [100][101][102][103].…”

“…Under this scenario, Au, Ag, Pt and Pd partition into intermetallic compounds, when sulfides are replaced by metal alloys and native metals during serpentinization [125]. Co-existing base metal sulfides (chalcopyrite, bornite, pentlandite) and gold-bearing alloys (as well as native gold in some cases) have been reported from peridotites [28,126,127] and subduction-related ultramafic rocks [38,39,128]. These findings suggest that such serpentinization process accompanied by sulfide breakdown is operational in mantle-derived peridotites.…”

“…Volcanic processes also appear to play significant role in gold transformations at the upper crustal levels, as native gold and gold-bearing alloys occur in lava flows of basaltic to dacitic composition [13][14][15][16][17], gas vents and fumaroles [18][19][20][21][22][23] as well as volcanic ash plumes [19,[24][25][26][27]. The presence of native gold in ultramafic rocks [28][29][30] along with bulk-rock gold enrichments in some mantle peridotites [31][32][33][34] and crustal plutonic complexes [35][36][37], indicate that gold is transported from lithospheric mantle sources through magmatic plumbing conduits and finally concentrated at economic levels in epithermal environment [16,19,[38][39][40][41][42][43][44]. Although gold appears to behave as an incompatible element during magmatic differentiation under certain conditions [45][46][47][48], its geochemical behavior is strongly controlled by sulfur and oxygen fugacity in most magmatic-hydrothermal systems [49][50][51]…”

“…Although gold appears to behave as an incompatible element during magmatic differentiation under certain conditions [45][46][47][48], its geochemical behavior is strongly controlled by sulfur and oxygen fugacity in most magmatic-hydrothermal systems [49][50][51][52][53]. In general, gold is scavenged into sulfides in sulfur-rich, mafic to intermediate magmas [54][55][56][57][58] and is deposited as native metal or intermetallic compound in presence of reduced fluids [14,15,17,38,39,47]. The formation of native gold and gold-bearing alloys in magmas and volcanic systems is still a poorly documented and ambiguously understood phenomenon, which requires further constraints both from representative suites of natural samples as well as experimental studies.…”

Silicate, Iron Oxide and Copper-Gold-Silver Microspherules in Ores and Pyroclastics of the Kostenginskoye Iron Ore Deposit (Russian Far East)

“…Многие исследователи также предполагают многоступенчатую архитектуру долгоживущих коровых рудообразующих систем, в которых железо-фосфорные месторождения с магнетитом и апатитом (так называемый Кирунский тип) занимают наиболее глубинные их горизонты, а железооксидно-медно-золотое (собственно IOCG Андийского типа) оруденение ассоциируется с субвулканическими системами и тесно связано с медно-золотыми порфировыми и высокосульфидными эпитермальными месторождениями [15,77,88,89,92,94,100]. Основным связующим звеном в этих долгоживущих (до 100 млн лет [58,59]), многоуровневых коровых рудно-магматических системах являются обогащенные металлами субдукционные и постсубдукционные магмы, возникающие, согласно современным изотопно-геохимическим данным, из флюидов и расплавов, образовавшихся при дегидратации или плавлении погружающейся океанической плиты под перекрывающий ее перидотитовый мантийный клин [47,57,58,73,87].…”