Study on Mineralization Age of Xiaoban Gold Deposit, Fujian Province

The Xiaoban gold deposit is a large size deposit recently found in middle area of Fujian Province. It belongs to magmatic hydrothermal type occurred in Mayuan Group metamorphic rocks of Middle Proterozoic and is controlled by low angle fault (detachment) structures. The contents of Au in Mayuan Group metamorphic rocks, Caledonian Indosinian deformed granite and early Yanshanian granite are higher with Au enrichment coefficient of 2.06-5.68, 5.11 and 6.67 than those in other geological bodies. And the higher enrichment coefficients (> 2) of Ag, S, Sn and Te are similar to those of gold ore. Meanwhile, the distribution of Au in Mayuan Group metamorphic rocks and early Yanshanian granite with a low D-value (0.58 and 0.67) is favorable to gold mineralization. REE characteristics of gold ore, ratios of (LREE/HREE), (La/Sm)_n, (Yb/Lu)_n, (La/Tb)_n and (Sm/Nd)_n are similar to Mayuan Group metamorphic rocks, only non or little normal Eu abnormal of ore is dissimilar to metamorphic rocks. The δ(³⁴S) of the gold ore, with a high homogenization, is (-4.7×10^-3) - (-2.7×10^-3). The study of inclusion indicates 180-249 ℃ of mineralization temperature, 3.69 %-11.81 % of salinities and 0.869-0.991 g/cm 3 of densities of mineralization fluid. Based on hydrogen and oxygen isotope (δ(¹⁸O) =11.0×10^-3 -11.7×10^-3, δ (D) = (-48×10^-3) - (-62×10^-3)) and initial w(⁸⁷Sr)/w(⁸⁶Sr)=0.715, combining to the analysis of geological history, regional metamorphism and magamtic activity, the authors confirm that the source for the ore fluid was mainly from magmatic, partly from metamorphic water, and with a little influence of meteoric water. Isotopic dating made on Rb Sr isochron age of 182 Ma, by using alteration minerals of gold ores from the deposit, indicates that the mineralization occurs in early Yanshanian epoch. This is close to the age of 187 Ma of the Anchun magmatite with a similar alteration and gold mineralization to the Xiaoban gold deposit. The age of early Yanshanian epoch of the Xiaoban gold is indentical with the characteristics of southern China gold metallogenic belt and the geotectonic evolution of the transition from paleo Asian system and paleo Tethyan system to paleo Pacific active continental margin in eastern Asia.