秦岭造山带栾川Mo-W矿集区和柞水-山阳Cu-Mo矿集区斑岩型矿床成矿差异性对比

Comparison on Metallogenic Differences of Porphyry Deposits between Luanchuan Mo-W and Zhashui-Shanyang Cu-Mo Ore-clusters in Qinling Orogenic Belt:Constraints of Magmatic Source and Metallogenic Conditions

栾川Mo-W矿集区和柞水–山阳Cu-Mo矿集区是秦岭造山带内152~140 Ma后碰撞造山环境下形成的两个典型斑岩型矿集区,其成矿差异显著,但控制因素尚不清楚。笔者收集两个矿集区的全岩地球化学、Sr-Nd-Hf同位素、锆石和磷灰石成分,从岩浆源区、岩浆水含量、氧逸度、挥发分和S含量等方面进行对比研究,揭示其成矿差异性的主控因素。柞水−山阳矿集区Cu-Mo矿的εHf(t)和εNd(t)值为−5~2和−6.6~−1.5,(^(87)Sr/^(86)Sr)_(i)值接近于上地幔(平均为0.7051),指示岩浆源区为增厚的新生下地壳部分熔融与幔源岩浆的混合。栾川矿集区具有相对较低的εHf(t)和εNd(t)值(平均值为−18.38和−14.63)以及较老的Hf二阶段模式年龄表明富Mo-W斑岩来源于古老的太华群基底和扬子板块俯冲陆壳沉积物部分熔融。柞水−山阳矿集区和栾川矿集区成矿斑岩具有高Sr低Y,全岩Eu/Eu*>0.6,锆石饱和温度较低(<750℃),锆石EuN/Eu_(N)^(*)>0.3,锆石Ce_(N)/Ce_(N)^(*)>100,Ce/Nd>10,全岩V/Sc>5,氧化还原状态>FMQ+3等,指示其成矿岩浆均具有高水含量和高氧逸度特征。此外,柞水−山阳矿集区斑岩Cu-Mo体系更富集Cl,而栾川矿集区斑岩Mo-W体系更富集F,二者的S含量相近。以上表明岩浆源区的不同是造成二者成矿差异的根本原因;Cl和F作为Cu和Mo在岩浆热液中迁移的主要配体,是造成两个矿集区成矿差异的另一关键因素;富水、高S和高氧逸度岩浆是两个矿集区斑岩型矿床形成的重要条件,但并不是造成矿化差异的直接原因。

The Luanchuan Mo-W ore district and the Zhashui-Shanyang Cu-Mo ore district are two typical porphyry ore districts formed in the post-collision setting during 152-140Ma in the Qinling Orogenic Belt.Despite significant differences in their mineralization,the controlling factors remain unclear.This study collected whole-rock geochemical data,Sr-Nd-Hf isotopes,and the compositions of zircon and apatite from both ore districts.A comparative analysis was conducted on aspects such as magmatic source,water content,oxygen fugacity,volatiles(F,Cl)and sulfur content to reveal the key controlling factors of their metallogenic differences.The Zhashui-Shanyang Cu-Mo ore district showsεHf(t)andεNd(t)variations ranging from−5 to 2 and−6.6 to−1.5,with(^(87)Sr/^(86)Sr)i value close to the upper mantle(averaging 0.7051),indicating a mixture of melting of thickened juvenile lower crustal components with mantle-derived magmas in the magma source.The Luanchuan Mo-W ore district exhibits relatively lowεHf(t)andεNd(t)values(averaging−18.38 and−14.63)and older Hf two-stage model ages,suggesting that the Mo-W-rich porphyries originated from the ancient Taihua Group basement and partial melting of the Yangtze Plate subducted continental crust sediment.Both ore districts'mineralized porphyries have high Sr and low Y,whole-rock Eu/Eu^(*)>0.6,low zircon saturation temperatures(<750℃),zircon Eu/Eu*>0.3,zircon Ce_(N)/Ce_(N)^(*)>100,Ce/Nd>10,whole-rock V/Sc>5,and oxidation state>FMQ+3,indicating characteristics of high water content and high oxygen fugacity in their mineralizing magmas.Furthermore,the Cu-Mo system in the Zhashui-Shanyang ore district is enriched in Cl,while the Mo-W system in the Luanchuan ore district is enriched in F,with similar S contents.These differences in the magma source are the fundamental reasons for the mineralization disparities between the two districts.Cl and F,as the main ligands for the migration of Cu and Mo in magmatic hydrothermal fluids,are another key factor causing the mineralization differences between the two ore districts.Enriched water,high S,and high oxygen fugacity magmas are important conditions for the formation of porphyry ore deposits in both districts,but they are not the direct causes of the mineralization differences.