粤北海西早期沉积盆地扩张与热水成矿

EARLY VARISCAN SEDIMENTARY BASIN SPREADING AND HYDROTHERMAL MINERALIZATION IN NORTHERN GUANGDONG

关键词:  盆地扩张  张裂  粤北  热水沉积  喷气岩

Key words:  basin spreading  extensional faulting  northern Guangdong  hydrothermal deposits  exhalite

摘要:

晚古生代期间,粤北半地堑式裂陷盆地受控于华南板块内的三叉张裂盆地系统。沉积演化阶段包括基底上隆、张裂、沉陷（三角洲充填）、下沉和封闭阶段。海西盆地演化史中的沉陷至稳定早期阶段对热水成矿有利。热水（喷气）矿床一般具有"三明治"式的矿石序列:底板蚀变（脉状矿石）一整合块状硫化物矿体→顶板蚀变和/或喷气盖层,以及底部爆发和沸腾特征。热水沉积（喷气）岩具有负的δ¹³C和δ¹⁸O和δ¹⁸O值以及低于正常海相硅岩的δ¹⁸O值,具有强烈的Eu正常REE模式。海西旋回可识别出4个与矿化层位有关的热事件:中泥盆统、上泥盆统、中—上石炭统和二叠统。区内绝大多数块状硫化物矿床是盆地扩张早期产物,而某些矿床（Au、Ag、Cu）则是盆地封闭阶段——印支运动（T₅—J₁）的产物。

Abstract:

The half graben-like rifted basin in northern Guangdong was controlled by a trifurcate spreading basin system within the South China plate during Late Palaeozoic time.The sedimentary evolution has undergone several stages of basement uplifting,extensional faulting,subsidence (delta infilling),submergence and closure,of which the subsidence and early stable stages are believed to be favourable for hydrothermal mineralization.The hydrothermal(exhalative)ore deposits are generally characterized by the "sandwich" ore sequence:footwall alteration (vein ores)→concordant massive sulfide ore bodies→roof alteration and/or exhalative cover,and explosing and boiling features at the bottom of the sequence.The hydrothermal sedimentary(exhalative)rocks have lower negative δ¹³C and δ¹⁸O values than those of the normal marine silicolites,and REE patterns with strong Euanomalies.
Four mineralization-related thermal events have been distinguished in the early Variscan cycles.They once occurred in the Middle Devonion,Upper Devonian,Middle and Upper Carboniferous and Lower Permian.The authors conclude that most of the massive sulfide deposits in the study area were generated in the early stage of basin spreading, whereas the other (e.g.Au,Ag and Cu)ore deposits were formed during the Indosinian-the closure stage of the basin.