T319 Mineral Resources for Society: Honoring the Career and Contributions to Economic Geology of Jean S. Cline (Posters)

Wednesday, 28 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

OROGENIC-TYPE GOLD MINERALIZATION AND GENETIC CONDITIONS: EXAMPLES FROM THE BOROO, GATSUURT AND ULAANBULAG GOLD DEPOSITS IN THE NORTH KHENTEI GOLD BELT, CENTRAL NORTHERN MONGOLIA

Paper number: T319-12
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Gold mineralization and crystallization processes of ore-forming minerals in representative deposits of the North Khentei gold belt of Mongolia were investigated to characterize the ore genesis and its evolution. The gold mineralization in representative deposits occurs as two ore types: I) disseminated and stockwork ores; and II) auriferous quartz-vein ores. Type-I mineralization in the 1Boroo, 2Gatsuurt and 3Ulaanbulag deposits is composed of four distinct stages: (i) 1,2,3pyrite-I + 1,2,3arsenopyrite-I, (ii) 1,2,3pyrite-II + 1,2,3arsenopyrite-II, (iii) 1,2,3sphalerite + 1,2,3galena + 1,2,3chalcopyrite + 1,2tetrahedrite + 1,2bournonite + 1,2boulangerite + 2jamesonite + 2scheelite + 1alloclasite + 1native gold and (iv) 1,2,3native gold. In Type-II mineralization, five, four and four crystallization stages are also recognized in these deposits, respectively: (i) 1,2,3pyrite-I + 1,3arsenopyrite, (ii) 1,2,3pyrite-II + 1,2,3arsenopyrite + 2galena + 2tetrahedrite-tennantite, + 2sphalerite + 2chalcopyrite + 2,3bournonite, (iii) 1,3sphalerite + 1,3galena + 1,3chalcopyrite + 2geocronite + 2geerite + 2native gold, (iv) 1tetrahedrite-tennantite + 1bournonite + 1geerite + 1,2,3native gold, and (v) 1electrum. Both ore types are associated with sericitic and siliceous alterations. At Boroo and Gatsuurt both ore types contain coexisting CO2-rich and aqueous fluid inclusions. The inclusions in the Type-I ores homogenized between 254–362ºC, whereas Boroo Type-II ore inclusions homogenized between 237–305ºC. Fluid salinities in bothore types range from 3–6 wt% (NaCl equiv.). The U-Pb age of zircons from Boroohost granites of 472.5 ± 6.9 Ma is much older than previously defined alteration minerals ages. By applying arsenopyrite geothermometer to arsenopyrite-II in the Type-II ores, crystallization temperature and logfs2 are estimated to be 300-365ºC and -7.5 to -10.1, respectively. The results indicate that these gold deposits formed from the same source of the hydrothermal activity in this region. Thus, gold deposits can be classified as contiguous orogenic-type gold mineralization that developed in two stages. Type-I ores are early stage, formed by hydrothermal metasomatic alteration, and Type-II ores are later stage, deposited due to rapidly cooling temperature of the hydrothermal fluids

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-280474

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.