Premium
Geochronology and S Isotope Geochemistry of the Haoyaoerhudong Gold Deposit Hosted by Black Schist of Bayan Obo Group, Inner Mongolia, China: Implications for Ore Genesis
Author(s) -
LIU Yifei,
NIE Fengjun
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12370_8
Subject(s) - metallogeny , beijing , china , geochemistry , geology , inner mongolia , mineral resource classification , schist , mineral , library science , archaeology , geography , chemistry , metamorphic rock , pyrite , computer science , organic chemistry , sphalerite
Haoyaoerhudong gold deposit is hosted by black schists of the Mesoproterozoic Bilute formation, Bayan Obo group. The gold mineralization is associated with sulfide veinlets or sulfide-quartz veinlets mainly along the schistosity of the black schists, and locally also crosscutting the schistsosity and with disseminated sulfides occurring in black schists. The sulfide mineral assemblage is dominated by pyrrhotite and pyrite, with less common arsenopyrite, chalcopyrite and sphalerite. Gold mainly occurs as small inclusions in sulfides and quartz grains, or at the boundaries of sulfides and quartz grains. Hydrothermal alteration includes silicification, sericitization, biotitization and local carbonatization. There are multi-stage magmatic dykes intruding the Bilute formation, Bayan Obo, group that host the Haoyaoerhudong gold mineralization, including premineralization meta-diorite porphyry dykes, nonmetamorphosed pre-mineralization hornblende olivine gabbro dykes, and post-mineralization tourmaline pegmatite. In order to constrain the mineralization age and the genetic relationship between the gold mineralization and the black schists, zircons from meta-diorite porphyry, hornblende olivine gabbro and tourmaline pegmatite were dated by LA-ICP-MS analysis, and gold-bearing pyrite was analyzed for δ34S. A reliable weighted mean 206Pb/238U age of 287.7±2.5 Ma (MSWD = 2.4) was obtained for meta-diorite porphyry intruding along the schistosity of the mineralized host rock. The zircons from hornblende olivine gabbro yielded a weighted mean 206Pb/238U age of 281.9±1.1 Ma (MSWD = 0.58). The zircons from tourmaline pegmatite gave a weighted mean 206Pb/238U age of 181.8±1.0 Ma (MSWD=1.04). The ages indicate that the gold mineralization occurred between 281.9±1.1 Ma ~ 181.8±1.0 Ma, which is consistent with the 40Ar-39Ar ages obtained from hydrothermal biotite and muscovite. The ages also suggest that the Haoyaoerhudong gold mineralization formed after regional metamorphism of the Bayan Obo group, i.e. the formation of Haoyaoerhudong gold mineralization was not related to the regional metamorphism of the Bayan Obo group. The analysis of gold-bearing pyrite gave positive δ34SV-CDT data ranging from +6.8~+13.4‰, with an average of +11.6‰, these data are different to δ34S of typical black shale with a wide range. The narrow range of the δ34S data suggests that the sulfur was not derived from the black schists of Bayan Obo group, but derived from a relatively uniform reservoir. In consideration of abundant contemporaneous granitic intrusions in the Haoyaoerhudong district, we suggest that the sulfur of the gold-bearing sulfides was most probably derived from a 34S enriched degassed magmatic reservoir. Both the ages of dykes and the δ34S data of gold-bearing pyrite suggest that the Haoyaoerhudong gold deposit is not formed by sedimentary-metamorphic processes related to the black schists of the Bayan Obo group, but is probably associated with magmatic-hydrothermal activities. LIU Yifei and NIE Fengjun, 2014. Geochronology and S Isotope Geochemistry of the Haoyaoerhudong Gold Deposit Hosted by Black Schist of Bayan Obo Group, Inner Mongolia, China: Implications for Ore Genesis. Acta Geologica Sinica (English Edition), 88(supp. 2): 262.