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Characteristics and 40Ar/39Ar Geochronology of the Erdenet Cu-Mo Deposit, Mongolia

2017; Volume: 112; Issue: 5 Linguagem: Inglês

10.5382/econgeo.2017.4500

1554-0774

Imants Kavalieris, Bat‐Erdene Khashgerel, Leah E. Morgan, Alexander Undrakhtamir, Adiya Borohul,

Geology and Paleoclimatology Research

Research Article| August 01, 2017 Characteristics and 40Ar/39Ar Geochronology of the Erdenet Cu-Mo Deposit, Mongolia☼ Imants Kavalieris; Imants Kavalieris † 1Plus Minerals LLC, 309-302 River Garden, 15th Khoroo, Khan-Uul district, 17024, Ulaanbaatar, Mongolia †Corresponding author: e-mail, imantskgeo@gmail.com Search for other works by this author on: GSW Google Scholar Bat-Erdene Khashgerel; Bat-Erdene Khashgerel 1Plus Minerals LLC, 309-302 River Garden, 15th Khoroo, Khan-Uul district, 17024, Ulaanbaatar, Mongolia Search for other works by this author on: GSW Google Scholar Leah E. Morgan; Leah E. Morgan 2U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Alexander Undrakhtamir; Alexander Undrakhtamir 3Erdenet Mining Corporation, Friendship Square, Bayan-Undur soum, Orkhon province, 61027, Mongolia Search for other works by this author on: GSW Google Scholar Adiya Borohul Adiya Borohul 3Erdenet Mining Corporation, Friendship Square, Bayan-Undur soum, Orkhon province, 61027, Mongolia Search for other works by this author on: GSW Google Scholar Author and Article Information Imants Kavalieris † 1Plus Minerals LLC, 309-302 River Garden, 15th Khoroo, Khan-Uul district, 17024, Ulaanbaatar, Mongolia Bat-Erdene Khashgerel 1Plus Minerals LLC, 309-302 River Garden, 15th Khoroo, Khan-Uul district, 17024, Ulaanbaatar, Mongolia Leah E. Morgan 2U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225, USA Alexander Undrakhtamir 3Erdenet Mining Corporation, Friendship Square, Bayan-Undur soum, Orkhon province, 61027, Mongolia Adiya Borohul 3Erdenet Mining Corporation, Friendship Square, Bayan-Undur soum, Orkhon province, 61027, Mongolia †Corresponding author: e-mail, imantskgeo@gmail.com Publisher: Society of Economic Geologists First Online: 24 May 2017 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2017 Society of Economic Geologists.Society of Economic Geologists Economic Geology (2017) 112 (5): 1033–1053. https://doi.org/10.5382/econgeo.2017.4500 Article history First Online: 24 May 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Imants Kavalieris, Bat-Erdene Khashgerel, Leah E. Morgan, Alexander Undrakhtamir, Adiya Borohul; Characteristics and 40Ar/39Ar Geochronology of the Erdenet Cu-Mo Deposit, Mongolia. Economic Geology 2017;; 112 (5): 1033–1053. doi: https://doi.org/10.5382/econgeo.2017.4500 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The Early to Middle Triassic Erdenet porphyry Cu-Mo deposit, in northern Mongolia, developed in a continent-continent arc collision zone, within the Central Asian orogenic belt. The porphyry system is related to multiple intrusions of crystal-crowded biotite granodiorite porphyry, which formed a composite stock about 900 m in diameter, with multiple porphyritic microgranodiorite dikes. Wall rocks are Late Permian to Early Triassic, medium-grained granodiorite, with similar whole-rock geochemistry, mineralogy, and composition to the granodiorite porphyry. Whole-rock analysis of the granodiorite porphyry and wall rocks shows that these rocks cannot be discriminated, but both have depleted middle heavy rare earth elements and Y, typical of fertile porphyry magmatic suites.At the current pit level (1,250 m elev), early porphyry-style quartz veins (A and B type) are locally infilled by pyrite-chalcopyrite, with subordinate bornite, but most of the chalcopyrite occurs in D veins that constitute more than 50% of the Cu grade (~0.5 wt % Cu). The 0.3 wt % Cu shell resembles a molar tooth, enveloping the granodiorite porphyry, with deeper roots extending down the wal-rock contacts. Molybdenite occurs in monomineralic veins, and in finely laminated to massive quartz-molybdenite veins.The most important alteration is quartz-muscovite, which occurs as relatively coarse (100–500 µm) alteration selvages (1–5 cm) that envelop D veins. The D veins cut illite ± kaolinite-smectite (or intermediate argillic) alteration. Intermediate argillic alteration, together with abundant pink anhydrite (commonly hydrated to gypsum), extends from at least 1,300- to 900-m elevation in the deepest drill holes, and has overprinted early potassic alteration, or relatively unaltered red granodiorite. Meter-wide zones of kaolinite cut the anhydrite-gypsum at all levels. There is an abrupt transition outward from the intermediate argillic alteration to chlorite-epidote (propylitic) alteration, at 50 to 200 m from the granodiorite porphyry contact, although D veins (and chalcopyrite) extend outward to the propylitic zone.The Erdenet porphyry system, was overprinted by advanced argillic alteration, which outcrops 2 km northwest of the pit, and forms a lithocap that extends over 10 × 2.5 km. It is characterized by residual quartz, andalusite, Na-Ca and K-alunite, diaspore, pyrophyllite, zunyite, topaz, dickite, and kaolinite. The upper part of the porphyry Cu-Mo deposit (removed by mining), comprised a bornite-chalcocite enriched zone up to 300 m thick with an average grade of 0.7 wt % Cu and up to 5 wt % Cu locally. Based on hypogene bornite-chalcocite mineral textures and high-sulfidation state mineralogy, the enriched zone is inferred to be of hypogene origin, but modified by supergene processes. Consequently, it may be related to formation of the lithocap.Previous Re-Os dates of 240.4 and 240.7 ± 0.8 Ma for molybdenite in quartz veins are comparable to new 40Ar/39Ar dates of 239.7 ± 1.6 and 240 ± 2 Ma for muscovite that envelops D veins. One 40Ar/39Ar date on K-alunite from the lithocap of 223.5 ± 1.9 Ma suggests that it may be about 16 m.y. younger than Erdenet, but this result needs to be verified by further dating. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.