A fluid inclusion and stable isotope study of Au quartz veins in the Klondike District, Yukon Territory, Canada; a section through a mesothermal vein system

Abstract

Gold-bearing quartz veins in theKlondike district of Yukon Territory are of earliest Cretaceous age and are hosted by Permian, middle to upper greenschist facies, metasedimentary and meta-igneous lithologies belonging to the Yukon-Tanana terrane. The veins occur in brittle, extensional structures, which may have developed during extensional deformation during uplift of the Klondike region in the Late Jurassic to Early to middle Cretaceous, following thrust imbrication in the Early Jurassic. The quartz veins are massive and unbanded, with localized carbonate flooding and/or pyritization of the wall rocks.Fluid inclusion studies have delineated significant, regional P-T-X trends in primary inclusion fluids from the Au quartz veins. The fluids have low salinities (<6 wt % NaC1 equiv), but variable CO2 concentrations, decreasing from approximately 0.13 to 0.18 mole fraction CO2 in the southeastern Klondike, through variable concentrations in the central Klondike (Xco2 < 0.01 to •1.00), to dominantly aqueous fluids (Xco2 < 0.01) in veins from the northwest portion of the region. Estimated trapping pressures decrease from 2,300 +_ 700 bars to between 300 to 900 bars, from southeast to northwest. Estimated fluid temperatures range from 300 ø to 350øC in central and southern lodes, to 200 ø to 250øC in the northwest Klondike. The P-X trends are interpreted as evidence for (1) effervescence of CO• from the mineralizing fluid, most likely in response to regional uplift during the life of the hydrothermal system, and (2) that the Au quartz vein system represents a section through a mesothermal vein system with deeper structural levels exposed in the southeastern Klondike. Convection of the hydrothermal fluid may have been driven by an elevated geothermal gradient resulting from the rapid uplift.The calculated isotopic composition of the Au quartz vein fluids (b•aOauia 8.3 4-_ 1.2%oSMOW, bDauia • -150 +_ 18%oSMOW) indicates that the mineralizing fluid was meteoric in origin but underwent considerable isotopic evolution prior to mineralization. Additionally, the •Da•ia values of extracted inclusion fluids (-166 +_ 11%0) and from hydrothermal muscovites (-174 +_ 3%0) from the Sheba vein system are in good agreement and indicate that the deuterium signature reflects that of the primary mesothermal fluid.

Application of microchemical characterization of placer gold grains to exploration for epithermal gold mineralization in regions of poor exposure

“…Gold is hosted by discordant mesothermal quartz veins described by Mortensen et al (1992) and Rushton et al (1998). Two distinct compositional types have been identified: a low Ag gold alloy (10-20% Ag) with little or no Hg is prevalent in the south of the region at Hunker Dome, the Mitchell occurrence and the Aime occurrence (Fig.…”

Pure CO2 fluids in the Sarekoubu gold deposit at southern margin of Altai Mountains in Xinjiang, West China

“…Goldfarb et al have summarized tectonic, metallogenetic background of orogenic gold deposits in global [9] . Low salinities and CO 2 -rich are typical characteristics of fluid inclusions for orogenic gold deposits, including famous gold deposits in Abitibi greenstone belt of Canada [10][11][12] , and in Yilgar Block [13,14] in west Australia. CO 2 -rich fluid inclusions also occur in many vein gold deposits surrounding North China Craton [15][16][17] , but they often coexist with aqueous inclusions or occur as various fluids in different mineralizing stages.…”

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

“…Gold-bearing veins in the Klondike Schist are dominated by quartz, some of which is prismatic and has grown into open cavities (Rushton et al 1993). Vein formation occurred during uplift of the rock mass in the latter stages of the Bonanza event ( Fig.…”

“…However, there has been little or no enrichment of these metals during subsequent Au-bearing vein formation (Figs 10B and C). Minor chalcopyrite, sphalerite and galena occur in some Au-bearing veins, typically in central zones that apparently post-date the Au mineralization stage (Rushton et al 1993;MacKenzie et al 2008a). Scheelite is conspicuously absent from Klondike Au-bearing orogenic vein systems.…”