{"id":2349,"date":"2019-10-02T19:50:21","date_gmt":"2019-10-02T19:50:21","guid":{"rendered":"https:\/\/www.gsnv.org\/shop\/the-nicholson-gold-silver-deposit-an-intrusion-hosted-tombstone-like-system-in-southwestern-montana\/"},"modified":"2020-02-24T18:17:10","modified_gmt":"2020-02-24T18:17:10","slug":"the-nicholson-gold-silver-deposit-an-intrusion-hosted-tombstone-like-system-in-southwestern-montana","status":"publish","type":"product","link":"https:\/\/www.gsnv.org\/shop\/the-nicholson-gold-silver-deposit-an-intrusion-hosted-tombstone-like-system-in-southwestern-montana\/","title":{"rendered":"The Nicholson Gold-Silver Deposit, an Intrusion-Hosted, Tombstone-Like System in Southwestern Montana"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"<p>The Nicholson deposit is situated within the late Cretaceous,<br \/>\nigneous-cored precious metal-rich Tobacco Root Mountains, which<br \/>\nare located in a basement uplift of the Rocky Mountain foreland.<br \/>\nThe mostly felsic magmas that comprise the Tobacco Root batholith<br \/>\nintruded Archean age amphibolite and amphibolite-plagioclase<br \/>\nschist and gneiss of the Wyoming province.<br \/>\nThe deposit is hosted by a calc-alkalic, weakly metaluminous<br \/>\nto weakly peraluminous, mafic-poor, porphyritic and sheared granite<br \/>\npluton that was emplaced at shallow depth. Emplacement of the<br \/>\npluton was controlled by the steeply dipping Bismark fault, one of<br \/>\nnine major northwest-trending intrusion- and\/or deposit-controlling<br \/>\nstructures in the region, which have been intermittently active since<br \/>\nmiddle Proterozoic time.<br \/>\nThe deposit consists of at least five generations of quartz veins<br \/>\nand mineralized host rocks. The structurally oldest vein stages, one<br \/>\nand two, are one- to four-cm thick, of limited extent, barren of precious<br \/>\nmetals and lack alteration envelopes. The northwest striking<br \/>\nand steeply dipping stage three veins contain Au and Ag, anomously<br \/>\nhigh but variable amounts of Mo, W, Bi, and\/or Pb and low concentrations<br \/>\nof Cu, Zn, As and Sb. These tectonized veins do not have<br \/>\nwall rock alteration envelopes. Vein stage four consists of at least<br \/>\neight prominent east-trending and steeply dipping Au- and Ag-bearing,<br \/>\nsheeted quartz veins including the Nicholson vein, which alone<br \/>\nhas produced more than 10,000 ounces of gold. Anomalously high<br \/>\namounts of Pb, Bi, and Te are also present in the veins. Gold- and<br \/>\nAg-bearing sericite-quartz alteration envelopes halo both the stage<br \/>\nfour and the much smaller mineralized, northwest-striking, stage<br \/>\nfive veinlets.<br \/>\nThe deposit has characteristics of intrusion-related, Tombstonetype<br \/>\ndeposits found in magmatic belts in Alaska, Yukon and elsewhere<br \/>\nin the world. These characteristics include formation within a<br \/>\ntectonic and structural environment in-board of the proto North<br \/>\nAmerica continental margin containing old cratonic rocks. On a<br \/>\nsmaller scale, the district mineral deposit zoning, and the composition,<br \/>\ntexture and depth of emplacement of the host pluton, vein types<br \/>\nand structures, and vein metal assemblage of the Nicholson deposit<br \/>\nare also similar to other intrusion-related deposits.<\/p>\n","protected":false},"featured_media":4151,"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\/2349"}],"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=2349"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/media\/4151"}],"wp:attachment":[{"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/media?parent=2349"}],"wp:term":[{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product_cat?post=2349"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/www.gsnv.org\/wp-json\/wp\/v2\/product_tag?post=2349"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}