| Liwu copper-zinc ore filed is a typical and unique one of the large number of Cu-ploymetallic ore filed in the western margin of Yangtze Plateform. It gradually meets with the crisis of exhausted resource due to mine’s crisis, since the Liwu copper ore deposit consitently developing and prospecting from the year 1958. In order to provide theoretical basis for guiding the implement of the deep and periphery prospecting in Liwu copper zinc ore field and making a breakthrough in the ore-search, we choose the Liwu copper-zinc orefiled as the research object, with the modern metallogenic theory and mineral field structure theory as a guide, make a comparison of several deposits within the ore filed to investigate the difference of mineralization, carried on the protolith restoration of host strata and talk about the tectonic environment. Through the study of ore fields of ore-controlling structure, we discuss the relationship between structures and mineralization. Through the redefinition of main metallogenic period and the study of the evolution of structural characteristics from time and space views, to discusse the tectonic evolution of ore deposit. Based on geochemical characteristics of the deposit and ore field on the study of fluid inclusion characteristics, determine the source of ore-forming materials. By the comprehensive summary and analysis of metallogenic geological background, ore-controlling geological conditions, rock metallogenic epoch and genesis and metallogenic regularity of ore fields, we constructed the metallogenic model of Liwu ore field, and has carried on the forecast concealed ore body.(1) In comparasson of the typical ore deposits which were found in the ore field,Liwu copper zinc ore controlling structure can be divided into three parts: primary ore-controlling tectonic Jianglang dome anticline structure and decoupling between the chronostratigraphic decollement, control the tectonic framework of the whole vault,second ore-controlling tectonic control of the secondary detachment fault distribution and indirect control of the main types of ore in the vault of the distribution of the position, the three-level ore-controlling structure of schistosity ore-controlling, direct control of ore body in the formation of output.The initial source bed(volcanic sedimentary structure)and ductile shear- into the decollement zone in the Liwu copper ore filed is the most important ore-controlling structures.(2) Through the study of assigning(Liwu Rock Group) discussed reconstruction of rock-forminng environment and tectonic environment, concluded in Liwu Rock Group formed in small stable continental margin rift environment is a set of rapid accumulation of terrigenous clastic mixed a small "bimodal type" Marine volcanic rock association.(3) The results of isotope geochemical study(such as silica, lead and other REE)have showed that the source of Liwu copper and zinic originated from the strata of ore-bearing series, which haven’t relationship with the granitic strata of Northeast of Wenjiaping dome. Isotope characteristics over time changes from small to big, it can reflect the early provenance is given priority to with the mantle source, advanced blending in the earth’s crust material, at the same time, the initial value of osmium isotopes were(3.65, 2.32, 0.69) and validation features the same origin. Of the result ofanalysis on trace elements from pyrite Co/Ni ratio(1.93~89.35) also showed that the ore depost belongs to endogenous ore deposit genesis. Hydrogen and oxygen isotope exchange mainly distributed in atmospheric precipitation and hydrothermal area showed early is given priority to with hydrothermal, a mixture of water and late in a mixture of atmospheric precipitation, so that the ore field inside the material is derived from the early volcanic activity(which may be derived from the proterozoic submarine volcano eruption of lava), and in the later superimposed by metamorphism and hydrothermal process synthesis.(4) After fully collecting predecessors dating data field large-scale mineralization time is determined to be 149.6~101 Ma. Comprehensive ore deposit geochemical characteristics and ore field is given priority to with hydrothermal filling metasomatic genesis ores and ore containing a small amount of shear and Liwu Rock Group metamorphism metallogenic material from the old base in fact, think the formation of the ore field is Marine sedimentary- metamorphic hydrothermal type, and establish the metallogenic model of ore fields "trinity" : volcanic sedimentary tectonic sources(original) + early ductile shearing plastic flow(mineral preliminary migration enrichment)+ late brittle ductile detachment(metallogenic systems) superposition of three main factors to form rich ore. Specific as follows:(1) proterozoic to early Paleozoic, the formation of early proterozoic "source bed", and in later times volcanic activity becomes further enrichment of minerals.(2) from the late indosinian to yanshanian early: in the late Permian, lean ore bodies formed by stretching environment, poor orebody inrelatively developed along the schistosity distribution of the shear ore by plastic deformation. At the same time, the activities of the Emei mantle plume heat rising mantle material deep source of Cu-polymetallic element to the earth’s crust accumulation, and the early formation of mineral bearing hydrothermal superimposition matrix further, may for the formation of Liwu copper zinc ore field in certain minerals; Songpan- Ganzi orogenic belt going through the ancient stage since Mesozoic period, the main tectonic deformation mainly occurred in late Triassic.In this period,Songpan- Ganzi granite magma activity(219-8~219 + 3 Ma) for about 30 Ma, these caused the late indosinian to yanshanian granite early(190-160 Ma) Songpan- Ganzi region metamorphic core complex events of the doming, such as Pike dome, Jianglang dome. The zircon age of granite rock mass(160.9~181.4 Ma) represents the dome first big power thermal metamorphism events, Jianglang dome early uplift events, and accompanied by a small amount of ore-forming materials(quartz veins containing ore deposit in the dating to get to 191 + 18 Ma in Liwu cpper oredeposit). At the same time the formation of rutile is spot(184-190 Ma).(3) yanshan period(the main metallogenic period) : Liwu ore fields in large-scale metallogenic events(149.6~101 Ma).Jiang dome continuously lift that early ductile shearing into brittle ductile fault, due to the temperature, pressure, physical and chemical environment mutation metallogenic matter precipitation gathered in ductile shear zone, and locate in gravitational decollement zone.In this period the most important ore-controlling structure is the gravitational decollement.(4) the Himalayan orogenic period: Himalayan too Songpan- Ganzi neo-tethys orogenic period, on the intracontinental orogenic belt of continuous extrusion uplift area, in the study area mainly form the thrust nappe, north east and north west Trust fault with large angle.Secondly, some surface layered and brittle deformation also were observed.at this stage.Although there are a variety of tectonic movement, but has formed rich orebody modification is not too big effect.But there are still a small amount of ore-forming material this period.(5) On the comprehensive research achievements of all points out that the search for "Liwu" in the field of the two most important factors are: the initial source bed(volcanic sedimentary structure) and ductile shear- from the slip bands. And principles prospecting prospect areas: Liwu Rock Group periphery Jiaba Rock Group because it is similar to the former background jianglang dome inside may have good metallogenic prospective,likely found in the strata with the similar Liwu Rock Group in rich copper deposit.Jianglang dome peripheral vision area: in the field of Liwu periphery prospectingprospect areas, Qiasi, Wachang, Tangyang, Changqiang, Taka, Sanya and a series of axial NNW- SN short axis dome body, therefore, from the source, ore-forming space, etc for the above every dome basic consistent with Jianglang dome, thus, may also be formed in the vault above similar to Liwu copper-zinc orefield. |
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