Geochemical And Geological Characteristics Of The Concealed Granitic Batholith And Yuku Mo–W Deposit At The Luanchuan Ore Cluster

Integrated geophysical and geochemical prospecting in the Luanchuan ore cluster by the Henan Institute of Geological Survey led to the discovery of the Yuku concealed giant porphyry Mo–W deposit.This paper focuses on the geological,geochemical,and chronological features of the deposit with the goal of discussing the genesis of the deposit and the associated concealed granitic batholith.Skarn and/or hornfels occurred in the contact zone between the granitic batholith and the wall rocks.The main orebodies are hosted in porphyry granites instead of in the skarnand/orhornfels,unlikeinpreexistinglargeMo–Wdeposits?e.g.,the Nannihu–Sandaozhuang Mo–W deposit?.The ores are mainly porphyry-type,skarn-type,and hornfels-type ores.The laser ablation inductively coupled plasma mass spectrometry?LA–ICP–MS?zircon U–Pb dating constrains three episodes of magmatic emplacement:the main body of porphyraceous biotite monzogranite at 153.1±1.2 Ma,the ore-causative porphyraceous syenogranite at 147.1±1.3 to 148.0±1.6 Ma,and the last porphyraceous monzogranite at 130.0±1.3 Ma.The U–Pb ages of the ore-causative porphyraceous syenogranite was closely correlated to Mo mineralization and involved more intense potassium alteration and siliconization than the most outcropped plutons compared with the other stages.The age matches well with the ore-forming Re–Os ages of the Yuku Mo–W deposit?146.2±0.9Ma?along with the ore-forming ages of the Nannihu Mo–W deposit and the Shangfanggou Mo–Fe deposit within the range of error.As mentioned above,the granitic batholiths is connected to the outcropped plutons on the surface in the Luanchuan ore cluster,and the Mo–W mineralization in all the Mo–W deposits was closely correlated to the magmatic activity from 147.1±1.3 to 148.0±1.6 Ma.The granitic batholiths have high contents of SiO₂,Al₂O₃ and K₂O+Na₂O;obvious fractionation between light and heavy rare earth elements[?La/Yb?_N=17.3–37.3];a negative Eu anomaly??Eu=0.62–0.84?;enrichment in Rb,Th,U,and Sr;and depletion in P and Ti.These features indicate the fractionation of plagioclase,amphibole,garnet,and rutile from the primary magmas or as residues in the source.The?_Hf?t?values of the zircons are concentrated between-21 and-13,with corresponding two-stage model ages(t_DM2)between 2.1 and 1.7 Ga.The I_Srr of the ore-causative porphyraceous syenogranite are between 0.683471 to 0.709276,average 0.703600.The?_Nd?t?values are at-19.06 to-16.95,and the calculated T_DMM are between 1.81 to 2.21Ga.The T_DMM values are similar to the(t_DM2)of Hf isotope.The(²⁰⁶Pb/²⁰⁴Pb)t values of the ore-causative porphyraceous syenogranite are at 17.16637 to 17.49745,average 17.35471;the(²⁰⁷Pb/²⁰⁴Pb)t values are between15.45590 and 15.48114,average 15.46768;the(²⁰⁸Pb/²⁰⁴Pb)t values are between 38.12242 and38.57785,average 38.32162.The Hf,Sr,Nd and Pb isotopic characteristics show that,the ore-causative porphyraceous syenogranite were derived from the partial melting of the thickened lower crust.The above characteristics indicate that the granitic batholiths were derived from the partial melting of the thickened lower crust during the Mesozoic to Neozoic.The ore-forming magma was emplaced in the contact zone between the granitic batholith and the wall rocks,leading to metasomatic alteration and the deposition of Mo–W metallogenic material.