A stand-alone Co mineral deposit in northeastern Hunan Province, South China: Its timing, origin of ore fluids and metal Co, and geodynamic setting

摘要

Graphical abstractDisplay OmittedHighlights?The Hengdong Co mineralization was formed at the early Cretaceous of ca. 125?Ma age.?The ore materials (e.g., Co) were most likely extracted by the ore fluids from the metamafic rocks of Lianyunshan Group.?The ore fluids were initially mesothermal and then evolved to lower temperatures in the later stages.?The early Cretaceous period of 130–120?Ma was also a potential mineralization age in South China.AbstractThe Hengdong cobalt (Co) deposit, located in northeastern Hunan Province of South China, is hosted by the low-grade metamorphic volcaniclastic sedimentary rocks of the early Neoproterozoic Lengjiaxi Group. The Co orebodies strictly controlled by the NE- to ENE-trending Changsha-Pingjiang deep fault zone (CPDFZ) and its secondary structures. Occurring in altered breccias and cataclasites with similar mineral assemblages, Co mineralization is characterized by zoned alteration with predominant silicification and chloritization proximal to the orebodies, and sericitization and carbonatization distal from the mineralization. The integrated field and microscope observations reveal three hydrothermal stages marked by quartz?+?pyrite?+?muscovite?±?chalcopyrite of the early-stage mineralization (E-stage), quartz?+?polymetallic sulfides?+?chlorite of the middle-stage mineralization (M?stage), and quartz?+?chlorite?+?carbonate of the late-stage mineralization (L-stage). Muscovite from both the E-stage Co-bearing altered breccia and the CPDFZ mylonite yield40Ar–39Ar plateau ages of 124.7?±?0.6?Ma (1σ) and 130.3?±?1.4?Ma (1σ), respectively, indicating an early Cretaceous mineralization likely associated with the last movement of CPDFZ strike-slip shearing. The δ34S values of pyrite and chalcopyrite ranging from ?1.5 to ?15.9% with a majority between ?7.5 and ?15.9%, and the lead isotope compositions of the pyrite (206Pb/204Pb?=?18.156–18.761,207Pb/204Pb?=?15.645–15.662 and208Pb/204Pb?=?38.469–39.172) overlapping with those of upper crust, indicate a main crust-derived source. The chemical compositions of pyrite further indicate the ore fluids and metal Co of the Hengdong deposit are most likely linked to the meta-mafic and volcanic rocks of the Neoarchean to Paleoproterozoic Lianyunshan Group, but with a contamination by the wall rocks of Lengjiaxi Group and Lianyunshan granitoids. Fluid inclusi