| 西华山花岗岩及其成矿作用 |
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| THE XIHUASHAN GRANITE AND ITS MINERALIZATION |
| The famous Xihuashan-Dangping tungsten deposit occurs in the Xihua-shan composite granite body. According to their contact relations, petrology, REE and trace element geochemistry, and isotopio age, the granites of the said body are assigned to two stages: early stage and the late.The porphyritic medium-grained biotite-granite intruded in the early stage has dated at a Rb-Sr age of 15lMa and U-Pb age of 152Ma, while the medium-grained biotite-granite intruded in the late stage gives a Rb-Sr age of 139Ma. The geological evidence shows that the latter intruded into the former Marginal pegmatoid crust is often found around the contact zone at the apex of the latter and contains micro-pinnate wolframite mineralization. Wolframite-(feldspar)-quartz veins or woiframite-beryl-quartz veins which are the major tungsten mineralization in the study area, all intersect the granites and pegmatoid crust and are in turn cut by ( wolframite) sulfidequ-artz veins and barren quartz veins formed in a later stage. From the pegmatoid to quartz vein, the ΣREE drastically decreases from 332.9-759.53 ppm to 4.24-6.45ppm. At the W-Sn-Be mineralization stage, REE wert-concentrated mainly in wolframite, and the enrichment of HREE was dominant.The evolutionary regularities ot the. formation temperature, salinity, characteristics and composition of fluid inclusions in quartz at different mineralization stages are as follows:The fluid inclusions in quartz at the pegmatoid stage are regular in form, high in gas/liquid ratio, with the gas phase being 40%-50% and include a few gas inclusions. Their formation temperatures range from 410 to 460t (corrected for pressure, the same below), the pressures are from 60 to 100 MPa, the oxygen fugacities are from 10-22 to 10-27 Pa and the salinity of their fluid is 10% (equiv wt% NaCl, the same below) . The fluid inclusions in quartz from the wolframite (feldspar)-quartz vein or wolfram-ite-beryl-quartz vein show an ellipsoidal, negative crystal form and a lower gas-liquid ratio, with the gas phase being 15% to 30%.The formation tempe- ratures range from 310 to 360℃, the pressures from 30 to 60 MPa, the oxygen fugacities from 10-28 to 10-32 Pa, and the salinity is 7 ± 1%. The fluid inclusions from the barren quartz vein of the later mineralization stage are characterized by an irregular form and a low gas/liquid ratio (with the liquid phase being up to 95%). The formation tempertures range from 180 to 230℃, the pressures, from 10 to 30 MPa, the oxygen fugacities, from 10-32 to 10-37 Pa, and the salinity is<5%.The chemical composition of the fluid inclusions from quartz formed at different stages varies regularly. The total of gas components (H2O, CO2, CO, CH4, H2 and N2) in the fluid inclusion from quartz in the late granite is 87.57ppm, that in the late pegmatoid, 803.09ppm, and that in the late wol-framite-(feldspar)-quartz vein or wolframite-beryl-quartz vein 1416.53ppm. The liquid phase in the fluid inclusions of this stage is rich in Na+,K+,Cl-and F-, but poor in Ca2+ and Mg2+.The total of gas components in the inclusions from the barren quartz vein is up to 3528.51ppm (98-99.5% H2O), about forty times higher than that in the fluid inclusions in the quartz from the granite. The, contents of Na+,K+,Cl" and F- in the liquid phase are evidently decreased.The oxygen, hydrogen and carbon isotope compositions of quartz, wolframite and their fluid inclusions of different mineralization stages also change regularly. The δ18O values of quartz of the early pegmatoid stage and the main W, Sn and Be mineralization stage are rather stable and range from +11.3 to + 12.3‰; the δ18O value of wolframite is +5.8‰; that of quartz in intermediate temperature hydrothermal sulfide-quartz vein and barren quartz vein decreases to +5.7%; that of wolframite is +4.4‰; and than of huebaerite in the miarolitic cavity of wolframite-quartz vein reduces to -6.5‰. |
| LIU Jia-qi.1989.THE XIHUASHAN GRANITE AND ITS MINERALIZATION[J].Acta Geoscientica Sinica,11(1):83-105. |
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