{"id":2308,"date":"2019-10-02T19:49:19","date_gmt":"2019-10-02T19:49:19","guid":{"rendered":"https:\/\/www.gsnv.org\/shop\/summary-of-structural-setting-and-fluid-characteristics-of-low-sulfide-au-quartz-veins-in-northwestern-nevada\/"},"modified":"2020-02-24T18:16:57","modified_gmt":"2020-02-24T18:16:57","slug":"summary-of-structural-setting-and-fluid-characteristics-of-low-sulfide-au-quartz-veins-in-northwestern-nevada","status":"publish","type":"product","link":"https:\/\/www.gsnv.org\/shop\/summary-of-structural-setting-and-fluid-characteristics-of-low-sulfide-au-quartz-veins-in-northwestern-nevada\/","title":{"rendered":"Summary of Structural Setting and Fluid Characteristics of Low-Sulfide Au-Quartz Veins in Northwestern Nevada"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"<p>Low-sulfide Au\u00d0quartz veins in northwestern Nevada formed<br \/>\nduring both brittle and brittle-ductile shear deformation and were<br \/>\naccompanied by sparse base-metal minerals. The veins are concentrated<br \/>\nin 12 mining districts in a 60\u00d0 to 100\u00d0km-wide, 200\u00d0km-long,<br \/>\nlinear, north-trending corridor extending from the Humboldt Range<br \/>\nin the south to the Pueblo Mountains in the north. The veins show a<br \/>\nconsistent northeast strike in the central parts of the corridor,<br \/>\nwhich\u00d1on the basis of several kinematic indicators\u00d1strongly suggests<br \/>\nthat this broad zone acted as a regional-scale shear zone. The<br \/>\nmetamorphic grade of the host rocks ranges from sub-greenschist to<br \/>\namphibolite facies, but most host rocks have been metamorphosed<br \/>\nto greenschist facies. Dating, by both 40Ar\/39Ar and K\u00d0Ar methods,<br \/>\nand cross cutting relations indicate that age of veining and mineralization<br \/>\nis Late Cretaceous.<br \/>\nMost low-sulfide Au\u00d0quartz veins in northwestern Nevada may<br \/>\nbe classified into four main types of vein systems: (1) beddingand(<br \/>\nor) foliation-parallel veins; (2) shear-related and ladder veins;<br \/>\n(3) fault-related veins; and (4) fold-related and saddle reef veins.<br \/>\nBedding- or foliation-parallel and fault-related veins are present in 1<br \/>\nto 3 sets of planar veins, while shear-related and ladder veins are<br \/>\npresent in en echelon patterns characteristic of shear zones. Foldrelated<br \/>\nand saddle reef veins are restricted either to fold hinge zones<br \/>\nor along the fold limbs. The geometry of all these quartz veins is<br \/>\nrelated to host rock lithology, competency contrast, and degree of<br \/>\ndeformation. The vein systems may have developed in conjunction<br \/>\nwith shear or extensional fractures that accompanied emplacement<br \/>\nof veins in either brittle-ductile or ductile deformation regimes.<br \/>\nQuartz textures in most low-sulfide Au\u00d0quartz veins are syntectonic<br \/>\nvein growth and cavity-filled bull quartz with ribbon, stylolitic,<br \/>\nfibrous, and laminated textures. Calcite also is intergrown<br \/>\nwith quartz in some veins. The veins are composed predominantly<br \/>\nof irregular, anhedral, and recrystallized quartz crystals with local<br \/>\npyrite, galena, sphalerite, and other sulfide minerals. Alteration selvages<br \/>\nchiefly are composed of white mica. In addition to Au, local<br \/>\nareas have anomalous concentrations of Ag and base metals.<br \/>\nStructural styles and textures strongly suggest that the veins formed<br \/>\nat a deep crustal level during regional deformation accompanied by<br \/>\nfluid flow during syn- or post-metamorphic processes.<br \/>\nFluid-inclusions in vein quartz contain H2O\u00d0CO2\u00d0NaCl fluids<br \/>\nof relatively low salinity (<10.0 wt. % NaCl equiv., median 3 to 5\nwt. % NaCl equiv.) with no daughter minerals. The range of homogenization\ntemperatures (Th) in these inclusions is from 200 to 300\u00fbC.\nStable isotope data of muscovite-quartz pairs indicate oxygen isotope\nequilibrium temperatures between 280 and 470\u00fbC. The d18O,\ndD, and d13C data from vein materials suggest that metamorphic\ndehydration reactions are the most likely source of the mineralizing\nfluid. These low-sulfide Au\u00d0quartz veins are interpreted, on the\nbasis of these data, to have formed at temperatures of approximately\n300 to 450\u00fbC and at fluid pressures between 1.2 and 2.8 kb, which\nare consistent with temperature- and depth-estimates of the brittleductile\ntransition and greenschist facies metamorphism in this part\nof Nevada. Regional distribution of low-sulfide Au\u00d0quartz veins and\nthese data indicate that a regional-scale, deep crustal, thermo-tectonic\nevent with widespread fluid flow occurred during the late\nMesozoic throughout much of northwestern Nevada. The fluid that\nformed these veins was of metamorphic origin.\n<\/p>\n","protected":false},"featured_media":4131,"comment_status":"closed","ping_status":"closed","template":"","meta":{"pmpro_default_level":""},"product_cat":[154],"product_tag":[],"_links":{"self":[{"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product\/2308"}],"collection":[{"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product"}],"about":[{"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/types\/product"}],"replies":[{"embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/comments?post=2308"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/media\/4131"}],"wp:attachment":[{"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/media?parent=2308"}],"wp:term":[{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product_cat?post=2308"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product_tag?post=2308"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}