Dynamics on the Formation of Quartz‐Vein Wolframite Deposits In the Dajishan Area, Jiangxi Province, China

tungsten ore deposit, which is widely distributed in the Nanling region, Southern China. The research on its dynamic genesis can supply the understanding of driving force and physical constraint on transportation of hydrothermal fluid in fracture channel, and has potential significance for acquisition of ore-forming pressure, identification of the type, magnitude and scale of hydrothermal activity, inversion of hydrothermal oreforming process, and metallogenic prognosis. Quartz-vein wolframite deposit in the Dajishan area, Jiangxi Province of China, is one of the most typical hightemperature hydrothermal deposits in the Nanling area of Southern China. All the veins are basically located between Chuandiwo Fault to the west and Peak Dajishan Fault to the east, which are divided into three groups, viz. Northern, Middle and Southern ones, of quasi-parallel and equidistance. Along the strike and down the inclination, the veins take root from medium-grained two-mica monzonitic granite and fine-grained muscovite granite, and display a series of bifurcation, recombination, thinout, reappearance, lateral appearance, swelling and shrinking. Away from the granitic rock body, the geometry of the veins change from thick veins through thin veins, fine veins and line veins to micro-veins in the external contact zone like a fractal tree (called “fivestoreyed” model). The mineral assembles across the thickness of a vein at different depths show obvious different characteristics. In the upper mineralized zone, the content of fluorite tend to increase, and the mineral assembles tend to change from muscovite at the edge of vein through quartz and fluorite to sulfide and wolframite in the center. In the middle one, the content of wolframite increases, and the assembles change from muscovite at the edge through wolframite to sulfide, fluorite and calcite. In the lower one, the content of albite increases, and the assembles are similar to the middle mineralized zone, but the sizes of albite, wolframite and fluorite become large. The change from fine-grained muscovite granite through feldspar-rich quartz veins to quartz-rich veins can be seen at the deep zone. In addition, there exists pegmatitic marginal zone at the contact zone with fine-grained muscovite granite. Acoustic emission experiments of wall rocks show that rock microcracks continually emerge with the gradual increase of load. Once the critical rupture is reached, amounts of acoustic emission events suddenly appear and then they rapidly decline. In general, acoustic emission events experience three processes of occurrence, quiescence and burst. Rupture processes have the characteristics of cascade of avalanches-punctuated equilibrium temporally. Microscopic examination, acoustic emission and dynamic analysis imply that the formation of multiple hydraulic fractures superposing on regional fractures is the dominant control on the distribution of veins. Periodic accumulation and release of pressures in the magma chamber result in the formation of self-organized critical fractures and fracture conduit oscillators. From lower to upper and from center to edge, the veins bifurcatedly grow along the pre-existing fractures and the new hydraulic (or fluid-driven) fractures by themselves and further show fractal characteristics macroscopically. The opening and closure of fractures is control by both the pressure changes of fluid injecting into the cracks and the average growth rates of mineral crystallization. Initial main conduit veins are emerged by the cooperation, enslavement and competition of amounts of oscillators, which results in the development of superior veins and the suppression of LIU Yongshun, PENG Nian and LIU Ningqiang, 2014. Dynamics on the Formation of Quartz-Vein Wolframite Deposits in the Dajishan Area, Jiangxi Province, China. Acta Geologica Sinica (English Edition), 88(supp. 2): 16-17.