海南抱伦金矿床成矿时代研究

Metallogenic age of Baolun gold deposit, Hainan Province

抱伦金矿床是海南省新近发现的大型金矿床之一,属于发育于下志留统陀烈组浅变质岩系中受断裂构造裂隙控制的岩浆热液型金矿床。成矿流体包裹体特征和氢氧同位素研究表明,成矿流体以岩浆水为主,有部分变质水的参与,大气降水影响比较小;成矿元素地球化学背景、硫同位素、稀土元素和初始锶比值等反映成矿物质来源虽然以变质岩为主,但有部分来源于岩浆岩;成矿物质和成矿流体来源反映出成矿作用与岩浆活动的密切关系。由热液蚀变矿物Rb-Sr等时线年龄234Ma和K-Ar年龄213Ma可知,金矿化年龄为210～230Ma,所以,抱伦金矿床的成矿时代为印支期。这一结果与粤西-海南成矿带的成矿时代特征及特提斯构造演化特点相吻合。

Baolun gold deposit, as a recently found large scale magmatic hydrothermal type one in Hainan Province, occurred in Tuolie Formation epimetamorphic rock (TFER) of lower Silurian and is controlled by fault structures. The contents of Au and Bi in Indosinian stage Jianfengling granite (JG) and lower memberepimetamorphic rock of Tuolie Formation, with Au and Bi enrichment coefficientsof 2.04 and 3.87 and 70 and 53, respectively, are higher than those in other geologic bodies. Meanwhile, the distribution of Au in JG and lower member epimetamorphic rock of Tuolie Formation with a low fractal dimension D is favorable to gold mineralization. REE characteristics of gold ore, low ΣLREE/ΣHREE ratio, non or little Eu abnormal and ratio of (La/Sm)N, (La/Tb)N and (Sm/Nd)N are similar to those of TFER, but dissimilar to JR, while the ratio of (Yb/Lu)N is between these of the TFER and JG. The δ34S of the gold ore, with a high homogenization temperature, is -2.3‰～+0.1‰,showing a closely relation to the magmatite. The study of inclusion indicates 230～309 ℃of metallogenic temperature, 2.68%～7.15%of salinities and 0.783～0.975 g/cm3 of densities of metallogenic fluid.Based on hydrogen and oxygen isotopes (δ18O=+11.0‰～11.7‰, δD=-61‰～-62‰) and (87Sr/86Sr)0=0.818～0.823, combining to the analysis of geological history, regional metamorphism and magmatic activity, it is confirmed that the ore fluid is mainly from magmatic water, partly from metamorphic one, and hardly meteoric one. The Rb Sr isochron ages of 234～236 Ma and K Ar isotopic age of 213 Ma, by using altered minerals of gold ores from the deposit, indicate that the mineralization occurred at 230～210 Ma. This is close to U Pb isotopic age 208Ma of the JG related to the mineralization. Therefore, Baolun gold deposit formed in Indosinian stage. This is identical with the characteristics of west Guangdong Hainan gold metallogenic belt and the evolution of Tethys tectonics.