Geochemical Characteristics And Metallogenic Model Of Lala Copper Deposit

Kangdian zone, which has a lot of noted deposits, is a famous polymetallic metallogenic belt located in southwest of china.The lala copper deposit is one of them in Huili area. It has been exploited for hundreds of years. Since prospecting and exploitation for nearly 60 years, the original proved reserves of the area has been insufficient, seriously restricts the sustainable development of Lala copper deposit. So the countries carried out the projects-old mine deep and periphery prospecting. This paper is carried out in this background.The Lala copper deposit is located in the mid-west of Kangdian copper belt, ore bodies are hosted by Paleoproterozoic greenschist metamorphosed volcanic-sedimentary sequences of Luodang Formation of Hekou Group, main ore bodies are bedded, layered, contacting with gradient integrated rock, and its strata-bound characteristic is significant. The main composition of mineral is copper sulfide, and accessory minerals are magnetite etc.On the basis of predecessors’ research work, a few times of field geological investigation and a large number of indoor test analysis have done respectively, the assignment of lala copper deposit ore rock and accessory mineral magnetite have been carried on the study of fluid inclusions and the main analysis of characteristics of trace elements. The results are as follows:1. The type of Fluid inclusions in Lala copper deposit is simple, and each stage of hydrothermal mineral inclusions has different types, The Basic characteristic is:the inclusions in the early quartz sulphide is the type Ⅰ. The type Ⅱ and Ⅲ are mainly in late calcite and quartz sulfide. the inclusion of type I contains mostly the salt crystal, which uniform temperature is relatively high, almost between 200℃ to 380℃, and salinity range of 30 to 45 wB%NaCleq.. The type Ⅱ and Ⅲinclusions are mainly gas and liquid inclusions, gas phase is CO2 and its proportion is lower, more between 5% to 10%.Size is relatively small, takes the directional arrangement in the host minerals, such as linear, planar. All the characteristics reflect what is late feature.Uniform temperature is relatively low, changes between 120℃ to 170 ℃, salinity tends to concentrate in the 10 to 25 wB%NaCleq.. Type Ⅱis higher than type Ⅲ in salinity; Lala copper deposit inclusions minimum pressure is between 15 to 20.0 MP. By conversion, metallogenic depth is between 600 to 800m, which close to the earth’s surface and shallow. Hydrogen and oxygen isotope results show that the sources of ore-forming is complicated.In different causes water delta δD-δ18O diagram, the date of lala copper deposit show that the ore-forming fluid include metamorphic water and magmatic water and close to the atmospheric precipitation line at the same time, which reflects that late ore-forming characteristics of atmospheric precipitation participate in mineralization.2. The contents of titanium in magnetite of Lala copper deposit change large, Some samples of Titanium dioxide have a higher score, these date structure suggest the earth’s crust and mantle material heterogeneous. Magnetite origin point display for magma deposits, And affected by the late magmata. Fe2O3/FeO points reflect the ore environment in highly oxidation conditions. This characteristic showing lala copper deposit and the IOCG deposit have the same characteristic under the condition of high oxygen fugacity. The Relationship between FeO/MgO and TiO2 pitch points display this deposit metallogenic in oceanic island and basalt environment. The oxide content in the ore between SiO2 has a certain relationship, For example:the content of TiO2, Fe2O3, MnO, MgO, CaO and P2O5, with the increase of SiO2 content, has a tendency to reduce. But Na2O and K2O content is positive, showing a obvious later hydrothermal transformed characteristics. Result showed that there is obvious difference of trace element content. Which Lost of element Sr, Hf, Y.The characteristics of Eu conform with the feldspar alteration.Ta and Nb elements reflects the channel characteristics. The standard curve of chondrite of rare earth element reveals a deficit of heavy rare earth enriched the light one. The average delta of Eu is 2.25, which shows that the digenetic mineralization process occurs under the condition of oxidation. The isotope characteristic of S and Pb shows that the deposit magma comes from the mantle and with high radioactive lead during the time of jinning period.3. According to the different Timing results of lala copper deposit analyzed by predecessor, which demonstrated the particularity of multi minerogenetic stages of lala copper deposite.the process can be summarized as follows:(1) In the early Proterozoic (about 1600ma～1700 ma) volcanic exhalative sedimentation mineralization.(2) In the late Proterozoic (about 1000 ma～1200 ma) metamorphic hydrothermal mineralization.(3) In the early neoproterozoic (about 800 ma～1000 ma) metamorphic hydrothermal alteration.4. After Combined with the predecessors’ achievements, this paper derived lala copper metallogenic process as follow:In the early Proterozoic (1600ma～1800ma), after the action of submarine volcano plume in the region. Mantle magma intruded and formed the spilite-keratophyre to sediment ate in shallow sea facies.In the late proterozoic (1000 ma～1200 ma),with strong regional metamorphism occurred in Kangdian area, The mineral of hekou group reactivated and enrich during this time, The surrounding rock fractured by the proceed of the tectonic activity, which provides the space for ore accumulation once more.In the early neoproterozoic (about 800 ma～1000 ma), Magmatic promote early metallogenic material form ore-body in tectonic fractures. Deposit uplift by tectonic plate extrusion.