The Analysis Of Metallogenic Geochemistry And Metallogenic Conditi Ons Of Matou Copper-molybdenum Deposit In Chizhou,Anhui

Matou Cu-Mo ore deposit,a medium-sized porphyry deposit,occurs on the northern margin of Yangtze paraplatform,and is located near Mei Village,Guichi District,Chizhou City,Anhui Province.In this paper,we focus on the research results of a new-round exploration.On the basis of detailed geological fieldwork,according to comprehensive studies,including anomalies of ore-forming elements in the ore area,petrochemistry and U-Pb isotopic dating of ore-bearing rock bodies,fluid inclusions in ore-bearing quartz,etc,metallogenic geochemistry and controlling factors of Matou Cu-Mo ore deposit are discussed in this paper.Matou Cu-Mo ore(mineralized)bodies mainly occur in the contact zones between granodiorites and Silurian wallrocks,and minor in the moyite and granodiorites nearby.Controlled by the ore-bearing joint-fracture zone,the stratiform or stratiform-like ore bodies generally strike along NNE and dip to NW with the dip angles which are gentle in the upper parts while steep in the lower.The ores are characterized by automorphic or semi-automorphic granular texture and metasomatic texture,veined,veinlet-stockwork or disseminated structures.The ore minerals are represented by molybdenite,chalcopyrite,jordisite,pyrite,etc,while gangue minerals are represented by quartz,feldspar,sericite,biotite,amphibole,epidote,chlorite and carbonate,etc.The wall rocks were mainly silicated,potashfeldspathizatized,sericitized,chloritized and carbonatized,etc.The element anomaly analysis indicated that ore-forming elements are mainly of Mo,Cu,Au,associated with W,Bi,Ag and As,while secondary indicator elements are Sn,Zn,Pb,Cd,Sb and Hg.Mo was enriched in the Silurian Fentou formation(S2f)and rock bodies,which could be reach the ore-level locally.The granodiorites occurred in the ore area are classified into calc-alkalic and metaluminous rocks,in which the content of Si02 is between 61.19%and 63.75%,A1203 is between 15.11%and 16.17%,and K20 is between 2.37%and 4.30%.The altered moyite occurred in the ore area are classified into peralkaline and metaluminous rocks,in which the content of Si02 is between 67.80%and 74.54%,and NKI is between 0.98 and 0.99.These rocks are characterized by the enrichment of LREEs,lithophile elements with large ions(LILEs,Rb,Th,U and La)and Pb,and the depletion of HREEs,HSFEs(Nb,Ta,Ti,P and Ce),Sr and Ba.The LA-ICP-MS zircon U-Pb dating indicated that the diagenetic age of granodiorite is 145.6±1.5Ma and of moyite is 141.5±1.4 Ma.Both of them are derived from magmatism in the late stage of Yanshan movement.The inherited zircons indicated that magmatism happened in Matou ore area and Chizhou many times.The metallogenic fluids of Matou Cu-Mo deposit at the late stage were dominated by fluid-rich and binary water solution inclusions.The fluid inclusions are characterized by relatively low homogeneous temperature between 153 and 381? in average,200-230? at peak,and medium-low salinity between 0.4%and 9.3wt%NaCl,between 8%and 10wt%at peak,1.2 km in depth approximately.We speculated that the ore area was influenced by late-stage ore-forming fluids which were hypabyssal,with low temperature and salinity.Migmatization was supposed to play an important role at the late metallogenic stage.At around 145Ma,the structural setting of South China had changed from compressional to extensional,which gave rise to diagenesis and mineralization at Chizhou.The ore-forming materials were mainly originated from granodiorites and moyites,and S2f possibly.The intersection part of the main NNE-trending shear fracture F1 and NW-trending F2 was the channel for magmatic emplacement,and also for ore-forming fluid transportation.The host fissures(micro-fissures)in wall rocks and the contact zones provided the advantageous spaces for ore-bearing hydrothermal solutions permeation and mineral precipitation.In the magmatic-hydrothermal system,K+-rich solutions diffused and percolated in various joint fissures,and formed easily-dissolved complexes with ore-forming elements,hence,prompted the remobilization and mineralization of these elements under favorable conditions.