Magmatism And Mineralization In The Miaoershan-yuechengling Orefield Of NE Guangxi

Miaoershan-Yuechengling complex is located in the western of Nanling region. It mainly consists of Caledonian granites with Indosinian granites widely developed and some small Yanshannian stocks invaded. There are many deposits and ore occurances developed at the contact zone between Miaoershan-Yuechengling batholith and country rocks, such as Niutangjie W deposit, Jiepai W-Cu deposit, Changgangling Pb-Zn multi-metal deposit, Yuntoujie W-Mo deposit and so on. In recent years, some research was done about Miaoershan-Yuechengling area, such as time-space distribution, geochemisty characteristics, source of batholith, ore-forming age and so on. But there are little work done about ore forming process, geochemistry characteristics of mineralized-granite and difference between mineralized-granites and barren mineralized-granites. Deposits in Miaoershan-Yuechengling area have different metal association, however it is not clear about the factors controlling different metal association of deposits due to lack of study about magmatism and mineralization of typical deposits. Thus there still some important problems about Miaoershan-Yuechengling batholith:（1） What about the system of time-space distribution of Miaoershan-Yuechengling batholith and deposits? Do they happened at Caledonian, Indosinian or Yanshannian?（2） What are the geochemistry characteristics of mineralized-granite and the evolution process of ore-forming fluid?（3） What are the factors leading to deposits with different metal association.According to problems mentioned above, this paper conducts a research on Jiepai W-Cu deposit, Niutangjie W deposit and Shunhuangshan W deposits.（1） Collecting the background imformation of this area, making clear about the relationships between deposits and surrounding plutons and figuring out the mineralized-granite by field investigation and observation of alteration and mineralization stages under the microscope.（2） Testing Ar-Ar isotopic age of mica in gangues and LA-ICP-MS zircon U-Pb age of related pluton in order to analyze time-space evolution series of plutons and related deposits.（3） Testing major and trace elements, Sr-Nd-Hf isotope of related plutons around, especially mineralized-granite, to discuss their geochemistry and source characteristics and the factors for controlling the metal association of deposits.（4） Analyzing characteristics and evolution of ore-forming fluid in different deposits, combining with alteration characteristics, to find out the factors controlling metallic elements precipitation of different deposits. And main results are as follows:（1） Pluton closely associated with deposits mainly emplaced at Caledonian and Indosinian within Miaoershan-Yuechengling area, and deposits which were thought forming at Yanshannian are related with Caledonian and Indosinian magmatism.We analyze LA-ICP-MS zircon U-Pb ages of related plutons belonging to Jiepai, Niutangjie, Shunhuangshan deposits and so on. It reveals that two stages of granites in Shunhuangshan deposit formed at 219.6±2.4Ma and 220.3±3.6Ma, respectively, two stages of batholith and leucogranite of Jiepai deposit formed at 422±11Ma, 428.3±6.5Ma and 410±7.4Ma, respectively, Xianshuixiang diorite formed at 431.4±3.8Ma, Wuxingcun leucogranite formed at 412±14Ma, two stage batholith around Niutangjie deposit formed at 430±4.9Ma and 432±8.4Ma, respectively. Besides two stages of granites in Shunhuangshan deposit formed at Indosinian, all other plutons formed at Caledonian.The Jiepai W-Cu mineralization mainly develops in the skarn at the contact zone between porphyritic biotite granodiorite and limestone. Alteration mineral assemblages indicate that the forming temperature decreases from inner to outer contact zone, which suggesting that the porphyritic biotite granite is genetically related to W-Cu mineralization. Thus Jiepai deposit formed at Caledonian（at about 422±11Ma）. Shunhuangshan ore body developed as veins and were closely associated with widely greisenization within the granites, suggesting W mineralization was related to ore bearing granites and formed at Indosinian（at about 220Ma）. Previous research reveals Niutangjie W deposit formed at Caledonian and Yuntoujie W-Mo deposit, Gaoling W deposit formed at Indosinian. We conclude those W-Mo, W, W-Cu deposits in Miaoershan-Yuechengling area formed at Caledonian and Indosinian.（2） Miaoershan-Yuechengling batholith is mainly generated from partial remelting of mid-paleo Proterozoic crust, and most of them belong to peraluminous granite and have crust-drived characteristics.Acid rock is the main part of Miaoershan-Yuechengling batholith, which have minor intermediate rock. They reveal high Si, K, low Mg content and belong to high-potassium calc-alkaline to calc-alkaline series, and all samples are peraluminous. They enrich Rb, Th, U and deplete Sr, Ba, Ti, and they have Eu negative anomaly. What is more, late-stage pluton from Jiepai and Niutangjie mine have low REE content and “seagulls shape” REE pattern, which is similar to W-Sn mineralized-granite of Yanshannian in Nanling region.Plutons from Shunhuangshan deposit have low εNd（t）（-9.33 ^-10.58）, εHf（t）（-5.9 ^-10.5）. Correspondent two-stage model ages of Nd and Hf are 1907 2760 Ma and 1626 1918 Ma, respectively. Mineralized-granites of Niutangjie and Yuntoujie deposits have similar isotope characteristics. All of them remelted from paleo-crust. Pluton from Jiepai deposit also has low εNd（t）（-8.11 ^-9.40）, εHf（t）（-4.4 ^-10.7）, two-stage model ages of Nd and Hf are 1621 1963 Ma and 1690 2088 Ma, respectively, they have crust-dirived characteristics in all. But their εNd（t） exhibit relatively higher to Shunhuangshan granites and εHf（t）is scattered that indicate multiple source and mantle composition was likely add.（3） The source of mineralized-granites might be the key factor to explain different metal association of those deposits in Miaoershan-Yuechengling area.Mineralized-granite of Jiepai W-Cu, Shunhuangshan W, Niutangjie W and Yuntoujie W-Mo deposits have different geochemistry characteristics. Jiepai mineralized-granite has relatively higher Mg, Fe and εNd（t）, three other mineralized-granites are highly evolved and have relatively higher Si and lower εNd（t）, suggesting that highly evolved granite is in favor of forming W and W-Mo deposits and lowly evolved granites have intimate relationship to Cu-W mineralization. Mineralized-granites of W and W-Mo deposits are mainly from paleo-crust remelting but W-Cu mineralized-granite has minor injection of mantle or juvenile crust component. Different source of magma and difference of magmatism process are the main factor leading to deposits have different metal association.（4） The ore-forming fluid of Jiepai skarn deposit is mid-high temperature, low salinity NaCl-H2O-CO₂-CH4 liquid system, and fluid mixing leads to metallic elements precipitate for Jiepai deposit. The ore forming fluid of Shunhuangshan deposit are mid-low salinity NaCl-H2O-CO₂-CH4 liquid system, and cooling is the main factor for metal elements precipitation for Shunhuangshan deposit and immiscibility is possibly one of the factors.We have analyzed temperature of fluid inclusions in different mineralization stages from the Jiepai deposit. Results of microthermometric measurement show that fluid inclusions in pegmatite have a peak ranges of homogeneous temperature of 310°C to 330°C, salinity ranges of 0.18% NaCleqv to 5.71% NaCleqv. Moreover, Roman analysis reveals that the fluid inclusions of the pegmatite contain CO₂ and CH4, suggesting that the fluid of pegmatite belong to the mid-high temperature, low salinity NaCl-H2O-CO₂-CH4 liquid system. Fluid inclusions in scheelite-forming stage have two peak ranges of homogeneous temperature of 260°C to 280°C and 320°C to 340°C, respectively, salinity ranges of 0.35% NaCleqv to 5.56% NaCleqv, suggesting that the fluids of scheelite-forming stage belong to the mid-high temperature, low salinity liquid system. Fluid inclusions in quartz veins of late stage have a peak ranges of homogeneous temperature of 270°C to 300°C, salinity ranges of 0.18% NaCleqv to 3.17% NaCleqv. Smilar to the fluid inclusions in pegmatite, the fluid inclusions of the quartz veins also contain CO₂ and CH4, suggesting that the fluids of quartz veins belong to the mid-high temperature, low salinity NaCl-H2O-CO₂-CH4 liquid system. The relationship between homogeneous temperature and salinity of fluid inclusions in scheelite-forming stage indicates fluid mixing which lead to metal elements precipitation.Temperature and salinity of fluid inclusions in three mineralization stages of Shunhuangshan deposit were also analyzed. None of melt inclusions were found in quartz of pluton, and fluid inclusions from them have a peak ranges of homogeneous temperature of 210 240°C and salinity ranges of 0.18 3.55% NaCleqv. Homogeneous temperature ranges and salinity ranges of greisen liquid is similar to liquid in quartz of pluton. CO₂ and CH4 vapor were found in fluid inclusions of greisen, thus fluids of these two stages belong to mid-temperature, low salinity NaCl-H2O-CO₂-CH4 liquid system. The peak ranges of homogeneous temperature and salinity ranges of fluid in quartz veins of late stage are 190 220°C and 0.18 3.71% NaCleqv, respectively. They also contain CO₂ and CH4 vapor, thus they belong to mid-low temperature, low salinity NaCl-H2O-CO₂-CH4 liquid system. The big ranges of homogeneous temperature and small ranges of salinity indicate that Shunhuangshan ore-forming fluid underwent cooling, which lead to metal elements precipitate. Moreover coexist of vapor-rich inclusions and liquid-rich inclusions and the higher homogeneous temperature of vapor inclusions reveal fluid immiscibility, which is one possible factor for metal elements precipitation.