Metallogenesis Of The Taijiying Gold Deposit In Beipiao,Liaoning Province

Domestic scholars have different opininons on the genetic types of gold deposits in the northern margin of the North China Craton:?greenstone-type gold deposits;?orogenic gold deposits;?gold deposits associated with intrusive rocks.Discussing the constraints of greenstone formation,orogenic process and magmatic activity of gold mineralization can renew the meanings of gold mineralization.The resources of the Taijiying gold deposit in the Lingyuan-Beipiao gold metallogenic belt in the eastern part of the northern margin of the North China Craton has been greatly enhanced by the exploration.The magmatic intrusion is not developed in the goldfield with some exposed medium-acid intrusive vein,and the strata is the Xiaotazigou Greenstone Formation of the Jianping Group in the Archaic.Therefore the Taijiying gold deposit is an ideal place for researching the mineralization of hydrothermal gold deposits.The Taijiying gold deposit in Beipiao,Liaoning Province is a concealed deposit,controlled by secondary faults in the Lingyuan-Beipiao lithosphere fault.The altered rock type ore and quartz vein type ore are in a block-like,disseminated structure with grain structure and fine-grained gold.The surrounding rock alteration inlcude pyrite mineralization,silicification,sericitization,chlorite,and carbonation.The ore body alteration zone is not clear.Mineralization is divided into four stages.The Zircon U-Pb dating shows that the diorite and granite porphyry invade in?258.0±1.9?Ma and?241.5±2.2?Ma respectively,and the sericite K-Ar dating suggests metallogenic time is?236.6±2.7?Ma.The geochemical characteristics indicate that diorite is formed in the continental marginal environment of the Andean type,and the granite porphyry is formed in the extended environment after collisional orogeny,further confirming that the closure time of the ancient Asian Ocean is Early Triassic.The gneiss of the Xiaotazigou Formation is rich in Fe,Mg and Ca,and is poor in Si,Na and K.The light rare earth is slightly fractionated and has a right-wing shape,which is significantly depleted in Th,U and Nb,strongly enriched in K,and moderately depleted in P.The original rock is the basalt of the plaque produced in the island arc environment,which is from the depleted mantle and forms the initial gold enrichment layer.The sulfur isotope?1.87‰?,the lead isotope is consistent with the Xiaotazigou Formation,and the main trace,rare earth and the peaks of Co in the fluid components indicate that the Xiaotazigou Formation is the gold source layer.Studies on the fluid show that the ore-forming fluid belongs to medium-te mperature?241°C?,low salinity?2.04%¹3.10%?,low-density?0.536g/cm3⁰.731g/cm3?,CO₂-rich H₂O-CO₂-NaCl hydrothermal system.Combined with the hyd rogen and oxygen isotope?¹⁸O_H2O value?3.77‰?and?D water value?-96.5‰?,the fluid is mainly a source of metamorphism.The ore-forming depth is betw een 5.4km and 13.9km.The Taijiying Gold deposit is a mesozonal-hypozonal orogenic-type gold deposit.The Jianping Group Xiaotazigou Formation is the gold source layer.The gold deposits in the Lingyuan-Beipiaojin metallogenic belt are all derived from greenstone formation.Different from the gold deposits related to the intrusive rocks,the early Mesozoic intrusive rocks of the Taijiying Gold deposit have good spatial and temporal relationship with the ore body but are not closely related to the source of ore-forming materials.It is an important activation mechanism of gold mineralization and an effective indicator for prospecting.This paper summarizes the metallogenic regularity of the Lingyuan-Beipiao metallogenic belt and proposes a new understanding of the trinity mineralizati on system of“gold-bearing formation-fracture structure-magmatic activity”.On t his basis,the regional prospecting indicators are given and six gold ore fields are identified,namely Taijiying-Mahugou ore field,Shengjiagou-Baoguo Lao or-e field,Zhuhugou-Shajingou ore field,Huanggutun-Yangshulin ore field,Jincha-nggouliang-Erdaogou ore field,Dongwujiazi-Xiaotazigou ore field.