地质学报2026，Vol.100Issue(3)：938-960,23.DOI:10.19762/j.cnki.dizhixuebao.2024120
河北中关铁矿闪长岩体磷灰石和角闪石地球化学特征及对成岩成矿的记录
Geochemical characteristics of apatite and hornblende in diorite of the Zhongguan iron deposit in Hebei Province and their records of petrogenesis and mineralization
摘要
Abstract
Skarn-type iron deposits are an important component of iron ore resources in China.To understand their formation mechanism,it is necessary to investigate the source,genesis,and physicochemical evolution of the ore-forming magma.This study presents BSE images and corresponding major and trace element compositions of hornblende and apatite from the diorite of the Zhongguan iron deposit.These data are used to identify the magma source,magma mixing,and crustal contamination processes,as well as the resultant changes in magmatic physicochemical conditions.Finally,the requisite magmatic conditions for the formation of the Zhongguan skarn iron deposit are proposed.The results show that the ore-forming magma evolved within a dual magma chamber system.In a deep chamber,hornblende phenocrysts crystallized at an average temperature of 943 ℃,pressure of 315 MPa,oxygen fugacity of ΔNNO+0.34,and water content of 5.97％.In contrast,the hornblende matrix crystallized in a shallow magma chamber at a lower average temperature(773 ℃)and pressure(89 MPa),with higher oxygen fugacity(ΔNNO+1.5)and Cl content(0.15％),and a lower water content(average 4.87％).Variations in the Al2O3 content of hornblende,along with the initial 87Sr/86Sr values of apatite(ranging from 0.7053 to 0.7076),suggest the ore-forming magma was mainly mantle-derived but was subsequently mixed with a minor amount of crustal materials.BSE imaging of apatite reveals obvious core-rim structures,with cores generally appearing brighter than the rims.The cores are enriched in SiO2,MnO,Ga,and REEs,whereas the rims are enriched in SO3,Na2O,and Cl.Furthermore,the rims exhibit higher δEu values than the cores.The compositional differences between phenocrysts and matrix of hornblende,in conjunction with the core-to-rim variations in apatite,indicate that the ore-forming magma underwent contamination by gypsum-bearing strata,assimilation of crustal material,and fluid exsolution during its ascent and emplacement.These processes led to a significant increase in the oxygen fugacity of magma,which promoted the enrichment of volatiles and iron.In summary,the assimilation of gypsum-bearing country rock and/or mixing with crust-derived magma,coupled with hypabyssal emplacement,are necessary conditions for the formation of the high-grade Zhongguan skarn iron deposit.关键词
中关铁矿/岩浆成因/磷灰石与角闪石矿物化学/膏岩层混染/形成机理Key words
Zhongguan iron deposit/magma genesis/mineral chemistry of apatite and hornblende/contamination of gypsum rock strata/formation mechanism引用本文复制引用
曹冲,曹庆,张艳博,王玲,董博萧,张榕方..河北中关铁矿闪长岩体磷灰石和角闪石地球化学特征及对成岩成矿的记录[J].地质学报,2026,100(3):938-960,23.基金项目
本文为河北省创新能力提升计划项目(编号23564201D)、河北省自然科学基金项目(编号D2023219016)、河北省中央引导地方科技发展资金项目(编号236Z3804G)和国家自然科学基金项目(编号42002098)联合资助的成果. （编号23564201D）
