Study On Metallogenesis And Prospecting Technology Of Saibo Copper Deposit,Xinjiang

The Saibo copper deposit in the western Tianshan Mountains of Xinjiang is a major prospecting achievement of the national"12th Five-Year Plan"scientific and technological support project"Strategic mineral resources prediction and target area evaluation of important metal ogenic belts in Xinjiang"?2011BAB06B0803?.The deposit and the Lamasu copper deposit are located in the Lamasu rock body,adjacent to each other in space,and should be the same deposit in geology.The two deposits and their adjacent areas have been identified as the Saibo ore cluster by the national"13th Five-Year Plan"deep-seated project.The discovery of the Saibo copper deposit fills in the blank of no large porphyry-skarn copper deposit in the western Tianshan Mountains.Therefore,a detailed study of the Saibo copper deposit is of great significance to the prospecting and exploration of the copper deposit in the western Tianshan Mountains.Based on previous studies and a large number of field geological surveys and prospecting,combined with petrology,geochemistry,chronology and ore-forming fluids,the diagenesis and mineralization process of the deposit are analyzed in detail in this paper.Through geophysical prospecting and exploration,the prospecting direction of the deposit is basically ascertained and the geological-geophysical prospecting and exploration model of the deposit is established.The occurrence location,mineralization and alteration zoning of ore bodies in the Saibo copper deposit are obviously controlled by granodiorite porphyry,granite porphyry and fault structure.Zircon U-Pb LA-ICP-MS ages of granodiorite porphyry and granite porphyry are 386.2±0.69 Ma and 386.9±0.71 Ma.Respectively,the Re-Os isotopic ages of Molybdenite in ore bodies are 379.2±7.7 Ma,which are basically the same for two years.This indicates that the Saibo copper deposit is closely related to magmatic activity in the early Hercynian of the Middle Devonian.Skarn alteration and porphyry alteration are the main alteration zones in the mining area.Skarn alteration occurs in the contact zone inside and outside porphyry body and its adjacent structural fracture zone.Garnet skarn,diopside skarn and wollastonite skarn are successively developed in the vicinity of porphyry body.Porphyry alteration mainly develops in some porphyry bodies,and occasionally occurs in the outer contact zone of porphyry bodies superimposed on the skarn alteration.Skarn alteration is accompanied by skarn mineralization,and tremolite,actinolite,chlorite,epidote and silicification are closely related to mineralization.Porphyry alteration is associated with porphyry mineralization.Mineralization often occurs in porphyry and contact zones within the rock mass,characterized by dense development of ore-bearing veins such as quartz veins,quartz calcite veins and chlorite?tremolite?quartz veins.Based on the study of mineralogy,ore-forming fluids and Hydrogen-Oxyge n isotopes,the sources of fluids and physicochemical characteristics in different ore-forming periods are summarized.The ore-forming fluids from Late magma-early hydrothermal stage are medium-high temperature?430-545??and high salinit y?13.4%?,the fluids are magmatic water.The ore-forming fluids in the early skarn stage are of medium temperature?475-510??and high salinity?16.94%?,while the temperature?383-485??and salinity?10.52%?of the ore-forming fluids in the late skarn stage decrease slightly,indicating that a small amount of atmospheric precipitation should be added.During the quartz-sulphide stage,atmospheric precipitation increased,and the ore-forming fluid was characterized by low temperature?195-270??and low salinity?3.3%?.The ore-forming fluid evolved into a mixture of magmatic water and atmospheric precipitation.The characteristics of H-O-S show that metal ogenic minerals have the characteristics of mixed magmatic and sedimentar y sulfur,the early hydrothermal fluid is mainly magmatic water,the advanced metal ogenic stage,hydrothermal evolutio n into magmatic water and atmospheric precipitation mixed hydrothermal.The ASI values of ore-forming porphyry is 0.76⁰.90,all less than 1.1,it is quasi-aluminous granite.The content of P2O5 and SiO2 is negatively correlated.Trace elements Th and Y are positively correlated with Rb,and the content of trace elements Zr+Y+Nb+Ce is 158.1ppm²63.7ppm,which is significantly lower than the lower limit value of A-type granite.Petrographic studies have found that the typical albite minera ls?sodium amphibole and sodium ferrite,etc.?of A-type granite and the typical mafic minerals?dolomite and garnet?of S-type granite are obviously absent in porphyry samples.At the same time,magnetite minerals appear in granitic intrusive rocks,indicating that the ore-forming porphyry is I-type granite.Geochemistry and Hf isotopes of I-type granites have the following characterist ics:high SiO₂ and CaO content,low TFe₂O₃,MgO,TiO₂,K₂O and Mg,low Co,Cr,Ni and other trace elements;high values of epsilon Hf?t?and ¹⁷⁶Hf/¹⁷⁷Hf,with epsilon Hf?t?ranging from-0.37 to 6.45,and average value of ¹⁷⁶Hf/¹⁷⁷Hf ranging from 0.283,?Rb/Sr?_N ratio from 0.077 to 0.285,and between the upper mantle?0.034?and upper mantle?0.034?.Between the crustal value?0.35?,the Nb/Ta ratio is 9.50-12.83,which is between the mantle value?17.5?and the crustal value?8.3?.In addition,the sample has a relatively rich set of incompatible elements?such as Th,U?and large ion lithophi le element?such as K,Sr?,high field strength elements?for example NB,Ta,P,Ti?can be characterized as relative depleted and obvious"TNT"negative abnormalities.The characteristics show that they are I-type granite,and which closely relate to the mineralized in Saibo,has the characteristics of a mixed source area of crust and mantle.Furthermore,its source rock may come from the basalt magma of depleted mantle,and during the process of rising,has the addition of some molten material from the new crust source subduction to the upper mantle.The zircon U-Pb age of I-type granite is 386.2±0.69 Ma and 386.9±0.71 Ma,and the Re-Os isotope age of ore body sulfide molybdenum ore is 379.2±7.7 Ma,which represents the diagenesis age respectively,which indicates that its diagenesis metal ogenic is Middle Devonian.During the Middle-Late Devonian and Early Carboniferous period,the northern Tianshan Ocean continued to dive to the southern Yili plate,which caused partial melting of the oceanic crust under subduction.Also accounted for the mantle wedge material,which led to the activation of the basement continental crust of the Sailimu microenvironment,and the mixing of the deep ore-bearing granitic magma in the crust and mantle.The deep ore-bearing granitic magma in the shell and mantle mixtur e invades along the fracture,the limestone copper ore body formed at the top of the rock mass.Then the Skarn type copper ore body formed near the contact zone between rocks mass and surrounding rock,thus the Saibo porphyry-skarn type copper deposit formed.We carried out a large number of geophysical prospecting and exploration work in the mining area,and it is found that the overlapping distribution areas around the rock mass in the mining area and the polarization rate above 2.21%should be considered as mineralization anomalies,which is an important prospecting clue.According to the results of magnetic method,IP and EH4 measurements,there is a great potential for prospecting in the northwest side of the mining area and deep around ZK08.There are 74 figures,15 tables and 240 references in this paper.