凡口铅锌矿床地球化学特征及成矿作用分析

凡口铅锌矿床是发育于碳酸盐岩建造中的海底热泉喷溢沉积矿床,以“一大二富三集中”的特点和典型的地质地球化学特征吸引着中外矿床地质工作者。常量元素和矿化元素的分布、矿物包裹体特征、稀土元素组成和硫同位素组成反映出该矿床与外生作用有关。铅同位素组成具有壳源和下地壳来源铅的特征,矿物包裹体水氢、氧同位素组成表明,成矿溶液可能与深层建造水有关,后期与大气降水有关。矿区主要矿层经历海底热泉喷溢沉积-成岩的演化。

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF FANKOU Pb-Zn DEPOSIT AND ITS METALLOGENIC ANALYSIS

The Fankou Pb-Zn deposit, one of the most important strata-bound deposits in North Guang-dong, China, is a sedimentary-accumulative deposit from ore-bearing hot spring. The host rocks arethe Upper-Middle Devonian and Lower Carboniferous limestones. The ore-bearing hot water circulat-ing at depth was exhalated along contemporaneous faults onto the sea floor, followed by the precipita-tion of metallic sulfides to form orebodies on both sides of the contemporaneous faults. The mineraliza-tion and precipitation of carbonates were developed at the same time. There is no intersection betweenbedding orebodies and vein-like orebodies. Owing to the innuence of ore-bearing acidic hot spring wa-ter, the contents of S, Pb, Zn, Fe2+ and SiO2 in the limestones at the apical plate of the orebodiestend to increase obviously while the CaO content to decrease. Subrounded pyrite gravels are observedin the limestones at the apical plate.The mineralogical composition is simple, and the metallic sulfides are very fine in size (80% ofthem < 0. 1 ～0. 2 mm). The metallic minerals are mainly pyrite, sphalerite and galena, and thegangue minerals are quartz, calcite, clay and dolomite. The ΣREE of ores are lower than those of thelimestones, and the ΣREE of pyrite separated from ores is lower than that of sphalerite.The δ13CPDB and δ18OSMOW of carbonates from ores are- 5. 99‰ - 5. 25‰ and 16. 32‰- 17. 72‰, in-dicating an exogenic origin. The δ14S values of sulfides from the ores are 15‰ - 25‰, demonstratinga marine sulfate origin. The lead isotopic composition of ores is of simple crustal origin with μ= 9. 90- 9. 39 and the single-stage model age of 310 Ma is equivalent to the formation time of the Paleozoicsedimentary basin.It is suggested that the acidic ore-bearing hot spring water erupting along the contepsporaneousfaults prevented CaCO3 in the sea water around it from crystallo-precipitation, and a "V" -shapedtrongh was formed. This "V" -shaped trough not only made the ore-forming solution with a higherdensity stay in it for a long time, but also prevented the sulfides crystallo-precipitate on the sea floorfrom the large-scale washing of sea current. Therefore, this "V" -shaped trough is the key to the for-mation of massive sulfide deposits such as the Fankou Pb-Zn deposit.