Diagenesis-Mineralization And Metallogenic Prognosis Of Skarn Fe Deposits In Pingshun Area, South Shanxi

Located in the south of Shanxi province, Pingshun deposit is an important locality for skarn iron deposits in the North China. With single type and obvious mineralization and alteration zones, the ore bodies in various forms are hosted along the contact belt between the intrusives and carbonate rocks. On the basis of petrology, geochronology, geochemical, ore deposit geology and exploration and prospecting geology studies, this study makes investigation on source, migration, precipitation of materials and ore-controlling factors, proposing the relationship between rocks and deposits, the metallogenic model, prospecting targets and directions.Located in the south Taihang mountains structural magmatic belt, Pingshun iron deposits have large of Yanshan epoch magmatic rocks. Zircon from olivine gabbro-diabase and diorite were first yield SHRIMP U-Pb ages of123.4±1.7Ma and125.5±2.3Ma respectively, formed in early cretaceous. Petrological and geochemical features of complex rocks show that:(1) complex rocks are mainly composed of olivine gabbro-diabase, hornblende diorite, diorite-monzodiorite, sinaite and dioritic porphyrite. Olive gabbro-diabas, hornblende diorite and diorite have olivine and pyroxene capture crystals and zonal structure plagioclase respectively, according to the dates by electron probe, the core of which indicates that they derived from mantle source, outside band from crust-mantle mixed source;(2) The complex rocks are of the similar geochemical features such as low slicon and high magnesium, enrichment of light REE with a weak positive anomaly of Eu, depletion of heavy REE, enrichment of LILE, especially Sr, Ba and K and depletion of HFSE, especially Nb, Ta and Ti, which indicate that the magma derived from earth mantle, mixing with the lower crustal matters.(3) The diagram of La/Sm-La shows that formations of complex rocks is closely related with magma mixing or degree of mantle partial melting, instead of fractional crystallization;(4) The research of Sr-Nd and Pb isotopic indicates that magma of complex rocks is originated from partial melting EMI, and mixed with the lower crustal matter. It is noticed that the B001sample is originated from EMII and resulted from subduction of the Paleo-Pacific plate. Considering that the diagenetic ages of complex rock body in Pingshun agrees with the the magmatic formation of other parts of the Taihang Mountains or other regions in north China (120Ma～135Ma) sharing the similar geochemical features, it shows that they have the same tectonic environment in Early Cretaceous. Based on this, this study puts forward the genetic model of complex body.The mineralized alteration zoning of iron ore deposit in Pingshun area are obvious. Through studying the composition of mineral elements in alteration zoning and the characteristics of fluid inclusions of alteration mineral, it proposes such features as follows: First, Fe migrates from rock mass to outward. To the contrary, Na migrates from the surrounding rock to inward. Second, the physicochemical characteristics of the fluid (diopside and garnet) before mineralization and the fluid characteristics of (epidote and calcite) after mineralization changed significantly, which may be the dominant factor that lead to Fe precipitation. Third, that Fe migrates from the center to wall rocks is due to Cl element functioning as a carrier and multiple magmatism resulting in power and fluid. The compositions of trace elements and REE indicated that orebody and rockmass have some of the inheritance, which can explain the phenomenon that they are closely related in the course of formation. In addition, the S-Pb isotope of rock (ore) indicated the following cases:S comes from the stratum, the source of Pb is more complex. Mantle, orogen and upper crust have a contribution to the source of Pb. Regarding the spatial distribution of rock, magma emplacement, and the interval of time and distribution of ore bodies as well as the material source, migration and precipitation etc. This study established the metallogenetic model.The deposits’Spatial location is mainly controled by magmatic intrusions, folds, faults and other factors. Intrusions:There are two magmatic belts in Pingshun area. Based on the comprehensive study of tectonic association, petrology, geochemistry and wallrock alteration, this study points that the first magmatic belt is a passive mechanism. The xenolithediron body bearing in the rock that has excellent ore potential. The second magmatic belt is an active mechanism, in which Xenolith is hardly found while the iron body mainly exists in the boundary between rock and surrounding rocks. Meanwhile,both of the two magmatic belt belong to the same geological event. The second magmatic belt was resulted from lateral emplacement of the first magmatic belt, two of which are very likely to be connected in the deep and have mineralization. Folds:It decide the general distribution of magmatic rocks. Usually, magmatic intrusions distribute in the kernel part of the anticlinal folds. It also effects the surrounding rock, forming interlayered fractured zone and slippage, during which magma injection, metasomatism and mineralization took place along with weak layer penetration. On the basis of this, iron ore bodies are shaped and the original anticlinal folds tectonic are retained. Faults:there are three main faults in the study region, east-west ancient faults, south-north faults, and north north east to subprime faults. New faults penetrated with old faults, resulting in fault’s intersections. Usually, in fault’s intersections magma emplacement and metallogenic broke out, leading to the existence of rocks with the characteristics of isometric distribution in space and distance ranging from4km to5km.Based on the comprehensive analyses and with geological settings mentioned above, the metallogenic regularity and the criteria for ore prospecting have been proposed. By applying the geologic and magnetic method, it points such8metallogenic prognosis as the third metallogenic belt, northern part of Lugou, Beiluoxia, concealed orebody, Long jianggou, Shuang jing, Luosai and Dongjiao...