The processes of ultra-enrichment and mineralization of the Ni-Co in the Shansonggang Co-Ni-Cu deposit from the Liao-Ji Paleoproterozoic orogenic belt
The nickel and cobalt are critical scarce metal minerals with strategic significance on the national economy and social development in China,however,these two resources are very limited in China and are highly depended on import.In this case,it is necessary to strengthen the study on the metallogenetic regularity of the nickel and cobalt and ore prospection strategic action interiorly.The Shansonggang Co-Ni-Cu Deposit(SCNCD)from Linjiang City,Jilin Province is located at the northeastern part of the Liao-Ji Paleoproterozoic orogenic belt,and it is a typical metasedimentary rock-hosted stratabound-controlled Co-Ni-Cu deposit.However,the occurrence of Ni-Co,the enrichment and metallogenic sequences and regularity of Ni-Co in this deposit are poorly studied.Here,the Ni-Co ores and host rocks from the deposit were selected for an integrated study involving microstructure observations,scanning electron microscope(SEM)-energy spectrum analysis,in-situ S isotopic analysis and electron probe microanalysis of minerals.We proposed that the SCNCD underwent multiple stages of metamorphism and hydrothermal alterations.The metamorphic stage is characterized by the occurrence of cobaltite and chalcopyrite that formed as inclusions within metamorphic minerals.The hydrothermal stage can be divided into two phases:(1)The precipitation of abundant Ni-Co minerals(cobaltite,polydymite and pentlandite)along with tallitization,dolomitization and silicification marks the early-stage hydrotherm,which represents the main metallogenic epoch of the Ni-Co.The Ni-Co minerals exhibit homogeneous S isotope values(10.92‰～13.67‰)that are in line with those of sedimentary strata from the Zhenzhumen Formation.Ni and Co were suggested to be extracted from the deep magmatic hydrotherm.The S from the Zhenzhumen Formation was largely extracted by the upmigrating ore-bearing fluid,which finally resulted to the precipitation and enrichment of Ni-Co minerals in the Dalizi Formation.(2)The late-stage hydrotherm is marked by the precipitation of Cu-Fe sulfides(chalcopyrite,pyrrhotite and pyrite)and a few cobalt pentlandite,siegenite and pentlandite accompanied with calcitization,silicification and chloritization.The δ34S values(6.53‰～8.59‰)of sulfides are consistent with the ones of Jurassic granitic plutons and associated gold and polymetallic sulfide deposits.The late-stage hydrotherm was most likely related to the intermediate-acid magmatic hydrotherm that was derived from the Paleo-Pacific subduction event.The nickel from the SCNCD exists mainly in the form of polydymite and pentlandite,and secondly cobalt pentlandite and siegenite.Cobalt occurs mainly in cobaltite,secondly polydymite,pentlandite,cobalt pentlandite and siegenite.The tallitization and dolomitization are considered as the recommended prospecting criteria.Combined with previous studies,we proposed that the SCNCD can be regarded as a poly-orogenic Co-Ni-Cu deposit that documented complex evolution processes of sedimentation,metamorphism-deformation and multiple hydrothermal overprinting.The pristine sedimentation and diagenesis provided important ore-forming conditions for the Co mineralization.The Paleoproterozoic collision orogeny and regional metamorphism-deformation controlled the original Co mobilization and migration.The early-stage Ni-Co-enriched deep magmatic hydrotherm dominated the ultra-enrichment and mineralization of the Ni-Co.The Yanshanian intermediate-acid magmatic hydrotherm dismembered the Ni-Co-enriched ore block,and as a result,it is unfavorable to the Ni-Co mineralization.
Shansonggang Co-Ni-Cu depositOccurrence states of Ni and CoMetamorphism and hydrothermAlteration typesProspecting indicator
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