Journal ArticleDOI
A Carbonaceous Sedimentary Source-Rock Model for Carlin-Type and Orogenic Gold Deposits
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In this paper, the authors present evidence and arguments that carbonaceous sedimentary rocks were a source for Au and As in sediment-hosted orogenic and Carlin-type gold deposits and develop a corresponding genetic model.Abstract:
This paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for Au and As in sediment-hosted orogenic and Carlin-type gold deposits and develops a corresponding genetic model. In this two-stage basin-scale model, gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis (stage 1) and concentrated to ore grades by later hydrothermal, structural, or magmatic processes (stage 2). In reduced continental margin basin settings, organic matter, sedimented under anoxic to euxinic conditions, immobilizes and concentrates gold, arsenic, and a range of trace elements (particularly V, Ni, Se, Ag, Zn, Mo, Cu, U) present in marine bottom waters, into fine-grained black mudstone and siltstone of slope and basin facies. During early diagenesis, gold and certain other trace elements (Ni, Se, Te, Ag, Mo, Cu, ±PGE) are preferentially partitioned into arsenian pyrite that grows in the muds. These processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic, commonly from 5 to 100 ppb Au and 10 to 200 ppm As. Rare organic- and sulfide-rich metalliferous black shales may contain up to 1 to 2 ppm Au and over 1,000 ppm As, present as refractory gold in arsenian pyrite and nanoparticles of free gold. During late diagenesis and early metamorphism (stage 2) the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations, and the organic matter is cooked to bitumen. Under higher grade metamorphism (lower greenschist facies and above) arsenian pyrite in carbonaceous shales is converted to pyrrhotite. These processes release gold, arsenic, sulfur and other elements (Sb, Te, Cu, Zn, Mo, Bi, Tl, and Pb) from the source rocks to become concentrated by hydrothermal processes, locally to produce gold ores, in structural sites such as fold hinge zones, shear or breccia zones within or above the black shale sequence. LA-ICP-MS analyses of diagenetic pyrite in carbonaceous sediments, both associated and not associated with gold deposits, suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite, are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits. Application of this sedimentary source-rock model enables a systematic exploration approach for sediment-hosted gold deposits, based on the distribution, composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite.read more
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Journal ArticleDOI
Orogenic gold: Common or evolving fluid and metal sources through time
TL;DR: In this paper, the authors show that gold deposits of all ages, from Paleo-archean to Tertiary, show consistency in chemical composition, with high concentrations of CH 4 and/or N 2, common estimates of 0.01-0.36% H 2 S, a near neutral pH of 5.5, and salinities of 3-7.5.
Journal ArticleDOI
Trace element content of sedimentary pyrite as a new proxy for deep-time ocean-atmosphere evolution
Ross R. Large,Jacqueline A. Halpin,Leonid V. Danyushevsky,Valeriy V. Maslennikov,Stuart W. Bull,John A. Long,John A. Long,Daniel D. Gregory,Elena Lounejeva,Timothy W. Lyons,Patrick J. Sack,Peter J. McGoldrick,Clive R. Calver +12 more
TL;DR: In this paper, a suite of trace elements in sedimentary pyrite from marine black shales were quantified to track the primary elemental abundances in coeval seawater.
Journal ArticleDOI
Trace Element Content of Sedimentary Pyrite in Black Shales
Daniel D. Gregory,Ross R. Large,Jacqueline A. Halpin,Elena Lounejeva Baturina,Timothy W. Lyons,Selina Wu,Leonid V. Danyushevsky,Patrick J. Sack,Anthony Chappaz,Valeriy V. Maslennikov,Stuart W. Bull +10 more
TL;DR: In this article, the authors performed laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of 1,407 sedimentary pyrites from 45 carbonaceous shale and unconsolidated sulfidic sediment samples, ranging in age from Paleo-archean to present day.
Journal ArticleDOI
Sunlight-Induced Reduction of Ionic Ag and Au to Metallic Nanoparticles by Dissolved Organic Matter
TL;DR: It is shown that dissolved organic matter (DOM) in environmental waters can mediate the reduction of ionic Ag and Au to their metallic nanoparticles under natural sunlight, suggesting that this process may be general for metals with high reduction potential.
Journal ArticleDOI
Tectonics and metallogeny of mainland Southeast Asia — A review and contribution
Khin Zaw,Sebastien Meffre,Chun-Kit Lai,Clive Burrett,M. Santosh,Ian T. Graham,T Manaka,Abhisit Salam,T Kamvong,Paul Cromie +9 more
TL;DR: In this article, the authors present a new tectonic and metallogenic model for Phanerozoic mainland SE Asia and conclude that incipient arc/backarc basin magmatism is the key to the formation of many important ore deposits in the Truong Son and Loei fold belts.
References
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